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rfc:rfc3108

Network Working Group R. Kumar Request for Comments: 3108 M. Mostafa Category: Standards Track Cisco Systems

                                                              May 2001
 Conventions for the use of the Session Description Protocol (SDP)
                     for ATM Bearer Connections

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 This document describes conventions for using the Session Description
 Protocol (SDP) described in RFC 2327 for controlling ATM Bearer
 Connections, and any associated ATM Adaptation Layer (AAL).  The AALs
 addressed are Type 1, Type 2 and Type 5.  This list of conventions is
 meant to be exhaustive.  Individual applications can use subsets of
 these conventions.  Further, these conventions are meant to comply
 strictly with the SDP syntax as defined in RFC 2327.

Table of Contents

 1. Introduction...................................................  3
 1.1  Key words to indicate Requirement Levels.....................  5
 2. Representation of Certain Fields within SDP description lines..  5
 2.1  Representation of Extension Attributes.......................  5
 2.2  Representation of Parameter Values...........................  5
 2.3  Directionality Convention....................................  6
 2.4 Case convention...............................................  7
 2.5 Use of special characters in SDP parameter values.............  8
 3. Capabilities Provided by SDP conventions.......................  8
 4. Format of the ATM Session Description..........................  9
 5.  Structure of the Session Description Lines.................... 11
 5.1  The Origin Line.............................................. 11
 5.2  The Session Name Line........................................ 12
 5.3  The Connection Information Line.............................. 13
 5.4  The Timestamp Line........................................... 15

Kumar & Mostafa Standards Track [Page 1] RFC 3108 ATM SDP May 2001

 5.5  Media Information Line for ATM connections................... 16
 5.5.1  The Virtual Connection ID.................................. 16
 5.5.2  The Transport Parameter.................................... 19
 5.5.3  The Format List for AAL1 and AAL5 applications............. 21
 5.5.4  The Format List for AAL2 applications...................... 21
 5.5.5  Media information line construction........................ 22
 5.6  The Media Attribute Lines.................................... 27
 5.6.1  ATM bearer connection attributes........................... 28
 5.6.1.1  The 'eecid' attribute.................................... 30
 5.6.1.2  The 'aalType' attribute.................................. 31
 5.6.1.3  The 'capability' attribute............................... 32
 5.6.1.4  The 'qosClass' attribute................................. 33
 5.6.1.5  The 'bcob' attribute..................................... 34
 5.6.1.6  The 'stc' attribute...................................... 34
 5.6.1.7  The 'upcc' attribute..................................... 35
 5.6.1.8  The 'atmQOSparms' attribute.............................. 35
 5.6.1.9  The 'atmTrfcDesc'  attribute............................. 37
 5.6.1.10 The 'abrParms' attribute................................. 39
 5.6.1.11 The 'abrSetup' attribute................................. 40
 5.6.1.12 The 'bearerType' attribute............................... 41
 5.6.1.13 The 'lij' attribute...................................... 42
 5.6.1.14 The 'anycast' attribute.................................. 43
 5.6.1.15 The 'cache' attribute.................................... 43
 5.6.1.16 The 'bearerSigIE' attribute.............................. 44
 5.6.2  ATM Adaptation Layer (AAL) attributes...................... 45
 5.6.2.1  The 'aalApp' attribute................................... 46
 5.6.2.2  The 'cbrRate' attribute.................................. 48
 5.6.2.3  The 'sbc' attribute...................................... 49
 5.6.2.4  The 'clkrec' attribute................................... 51
 5.6.2.5  The 'fec' attribute...................................... 51
 5.6.2.6  The 'prtfl' attribute.................................... 51
 5.6.2.7  The 'structure' attribute................................ 52
 5.6.2.8  The 'cpsSDUsize' attribute............................... 53
 5.6.2.9  The 'aal2CPS' attribute.................................. 53
 5.6.2.10 The 'aal2CPSSDUrate' attribute........................... 54
 5.6.2.11 The 'aal2sscs3661unassured' attribute.................... 54
 5.6.2.12 The 'aal2sscs3661assured' attribute...................... 55
 5.6.2.13 The 'aal2sscs3662' attribute............................. 56
 5.6.2.14 The 'aal5sscop' attribute................................ 58
 5.6.3  Service attributes......................................... 58
 5.6.3.1  The 'atmmap' attribute................................... 60
 5.6.3.2  The 'silenceSupp' attribute.............................. 63
 5.6.3.3  The 'ecan' attribute..................................... 65
 5.6.3.4  The 'gc' attributes...................................... 66
 5.6.3.5  The 'profileDesc' attribute.............................. 67
 5.6.3.6  The 'vsel' attribute..................................... 68
 5.6.3.7  The 'dsel' attribute..................................... 70
 5.6.3.8  The 'fsel' attribute..................................... 72

Kumar & Mostafa Standards Track [Page 2] RFC 3108 ATM SDP May 2001

 5.6.3.9  The 'onewaySel' attribute................................ 73
 5.6.3.10 The 'codecconfig' attribute.............................. 75
 5.6.3.11 The 'isup_usi' attribute................................. 76
 5.6.3.12 The 'uiLayer1_Prot' attribute............................ 76
 5.6.4  Miscellaneous media attributes............................. 77
 5.6.4.1 The 'chain' attribute..................................... 77
 5.6.5  Use of the second media-level part in H.323 Annex C
        applications............................................... 78
 5.6.6  Use of the eecid media attribute in call establishment
        procedures................................................. 78
 6. List of Parameters with  Representations....................... 83
 7. Examples of ATM session descriptions using SDP................. 93
 8. Security Considerations........................................ 94
 8.1  Bearer Security.............................................. 94
 8.2  Security of the SDP description.............................. 95
 9. ATM SDP Grammar................................................ 95
 References........................................................104
 Acknowledgements..................................................109
 Authors' Addresses................................................109
 Full Copyright Statement..........................................110

1. Introduction

 SDP will be used in conjunction with a connection handling /device
 control protocol such as Megaco (H.248) [26], SIP [18] or MGCP [25]
 to communicate the information needed to set up ATM and AAL2 bearer
 connections.  These connections include voice connections, voiceband
 data connections, clear channel circuit emulation connections, video
 connections and baseband data connections (such as fax relay, modem
 relay, SSCOP, frame relay etc.).
 These conventions use standard SDP syntax as defined in RFC 2327 [1]
 to describe the ATM-level and AAL-level connections, addresses and
 other parameters.  In general, parameters associated with layers
 higher than the ATM adaptation layer are included only if they are
 tightly coupled to the ATM or AAL layers.  Since the syntax conforms
 to RFC 2327, standard SDP parsers should react in a well-defined and
 safe manner on receiving session descriptions based on the SDP
 conventions in this document.  This is done by extending the values
 of fields defined in RFC 2327 rather than by defining new fields.
 This is true for all SDP lines except the of the media attribute
 lines, in which case new attributes are defined.  The SDP protocol
 allows the definition of new attributes in the media attribute lines
 which are free-form.  For the remaining lines, the fact that the
 <networkType> field in an SDP descriptor is set to "ATM" should
 preclude the misinterpretation of extended parameter values by RFC
 2327-compliant SDP parsers.

Kumar & Mostafa Standards Track [Page 3] RFC 3108 ATM SDP May 2001

 These conventions are meant to address the following ATM
 applications:
    1. Applications in which a new SVC is set-up for each service
       connection.  These SVCs could be AAL1 or AAL5 SVCs or single-
       CID AAL2 SVCs.
    2. Applications in which existing path resources are assigned to
       service connections.  These resources could be:
  • AAL1/AAL5 PVCs, SPVCs or cached SVCs,
  • AAL2 single-CID PVCs, SPVCs or cached SVCs,
  • CIDs within AAL2 SVCs/PVCs/SPVCs that multiplex multiple

CIDs.

  • Subchannels (identified by CIDs) within AAL1 [8] or AAL2

[11] SVCs/PVCs/SPVCs.

 Note that the difference between PVCs and SPVCs is in the way the
 bearer virtual circuit connection is set up.  SPVCs are a class of
 PVCs that use bearer signaling, as opposed to node-by-node
 provisioning, for connection establishment.
 This document is limited to the case when the network type is ATM.
 This includes raw RTP encapsulation [45] or voice sample
 encapsulation [46] over AAL5 with no intervening IP layer.  It does
 not address SDP usage for IP, with or without ATM as a lower layer.
 In some cases, IP connection set-up is independent of lower layers,
 which are configured prior to it.  For example, AAL5 PVCs that
 connect IP routers can be used for VoIP calls.  In other cases, VoIP
 call set-up is closely tied to ATM-level connection set-up.  This
 might require a chaining of IP and ATM descriptors, as described in
 section 5.6.4.1.
 This document makes no assumptions on who constructs the session
 descriptions (media gateway, intermediate ATM/AAL2 switch, media
 gateway controller etc.).  This will be different in different
 applications.  Further, it allows the use of one session description
 for both directions of a connection (as in SIP and MGCP applications)
 or the use of separate session descriptions for different directions.
 It also addresses the ATM multicast and anycast capabilities.
 This document makes no assumptions about how the SDP description will
 be coded.  Although the descriptions shown here are encoded as text,
 alternate codings are possible:
  1. Binary encoding such as ASN.1. This is an option (in addition to

text encoding) in the Megaco context.

Kumar & Mostafa Standards Track [Page 4] RFC 3108 ATM SDP May 2001

  1. Use of extended ISUP parameters [36] to encode the information in

SDP descriptors, with conversion to/from binary/text-based SDP

    encoding when needed.

1.1 Key words to indicate Requirement Levels

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [62].

2. Representation of Certain Fields within SDP description lines

 This document conforms to the syntactic conventions of standard SDP
 as defined in RFC 2327 [1].

2.1 Representation of Extension Attributes

 The SDP protocol [1] requires that non-standard attributes and codec
 names use an "X-" prefix.
 In this internet document, the "X-" prefix is used consistently for
 codec names (Table 2) that have not been registered with the IANA.
 The IANA-registered codec names listed in [31] do not use this
 prefix, regardless of  whether they are statically or dynamically
 assigned payload types.
 However, this prefix is not used for the extension SDP attributes
 defined in this document.  This has been done to enhance legibility.
 This document suggests that parsers be flexible in the use of the
 "X-" prefix convention.  They should accept codec names and attribute
 names with or without the "X-" prefix.

2.2 Representation of Parameter Values

 Depending on the format of their representation in SDP, the
 parameters defined in this document fall into the following classes:
 (1) Parameters always represented in a decimal format.
 (2) Parameters always represented in a hexadecimal format.
 (3) Parameters always represented as character strings.
 (4) Parameters that can be represented in either decimal or
     hexadecimal format.
 No prefixes are needed for classes 1 - 3, since the format is fixed.
 For class 4, a "0x" prefix shall always be used to differentiate the
 hexadecimal from the decimal format.

Kumar & Mostafa Standards Track [Page 5] RFC 3108 ATM SDP May 2001

 For both decimal and hex representations, if the underlying bit field
 is smaller or larger than the binary equivalent of the SDP
 representation, then leading 0 bits should be added or removed as
 needed.  Thus, 3 and 0x3 translate into the following five-bit
 pattern: 0 0011.  The SDP representations 0x12 and 18 translate into
 the following five-bit pattern: 1 0010.
 Leading 0 digits shall not be used in decimal representations.
 Generally, these are also not used in hexadecimal representations.
 Exceptions are when an exact number of hex digits is expected, as in
 the case of NSAP addresses.  Parsers shall not reject leading zeros
 in hex values.
 Both single-character and multi-character string values are enclosed
 in double quotes (i.e., ").  By contrast, single quotes (i.e., ') are
 used for emphasizing keywords rather than to refer to characters or
 strings.
 In the text representation of decimal and hex numbers, digits to the
 left are more significant than digits to the right.

2.3 Directionality Convention

 This section defined the meaning of the terms 'forward' and
 'backward' as used in this document.  This is specially applicable to
 parameters that have a specific direction associated with them.
 In this document, 'forward' refers to the direction away from the ATM
 node under consideration, while 'backward' refers to the direction
 towards the ATM node.  This convention must be used in all SDP-based
 session descriptions regardless of whether underlying bearer is an
 SVC, a dynamically allocated PVC/SPVC or a dynamically allocated CID.
 This is regardless of which side originates the service connection.
 If ATM SVC or AAL2 Q.2630.1 signaling is used, the directionality
 convention is independent of which side originates the SVC or AAL2
 connection.
 This provides a simple way of identifying the direction in which a
 parameter is applicable, in a manner that is independent of the
 underlying ATM or AAL2 bearer.  This simplicity comes at a price,
 described below.
 The convention used by all ATM/AAL2 signaling specifications (e.g.,
 Q.2931 Section 1.3.3 and Q.2630.1) mandates that forward direction is
 from the end initiating setup/establishment via bearer signaling
 towards the end receiving the setup/establishment request.  The
 backward direction is in the opposite direction.  In some cases, the
 'forward' and 'backward' directions of the ATM signaling convention

Kumar & Mostafa Standards Track [Page 6] RFC 3108 ATM SDP May 2001

 might be the exact opposite of the SDP convention described above,
 requiring the media gateway to perform the necessary translation.  An
 example case in which this is needed is described below.
 Consider an SDP description sent by a media gateway controller to the
 gateway originating a service-level call.  In the backward SVC call
 set-up model, this gateway terminates (rather than originates) an SVC
 call.  The media gateway refers to the traffic descriptor (and hence
 the PCR) in the direction away from this gateway as the forward
 traffic descriptor and forward PCR.  Clearly, this is at odds with
 ATM SVC signaling which refers to this very PCR as the backward PCR.
 The gateway needs to be able to perform the required swap of
 directions.  In this example, the media gateway terminating the
 service level call (and hence originating the SVC call) does not need
 to perform this swap.
 Certain parameters within attributes are defined exclusively for the
 forward or  backward directions.  Examples for the forward direction
 are the <fsssar> subparameter within the 'aal2sscs3661unassured'
 media attribute line, the <fsssar>, <fsscopsdu> and <fsscopuu>
 subparameters within the 'aal2sscs3661assured' media attribute line,
 the <fsscopsdu> and <fsscopuu> subparameters within the 'aal5sscop'
 media attribute line, and the <fmaxFrame> parameter within the
 'aal2sscs3662' media attribute line.  Examples for the backward
 direction are the <bsssar> subparameter within the
 'aal2sscs3661unassured' media attribute line, the <bsssar>,
 <bsscopsdu> and <bsscopuu> subparameters within the
 'aal2sscs3661assured' media attribute line, the <bsscopsdu> and
 <bsscopuu> subparameters within the 'aal5sscop' media attribute line,
 and the <bmaxFrame> parameter within the 'aal2sscs3662' media
 attribute line.

2.4 Case convention

 As defined in RFC 2327 [1], SDP syntax is case-sensitive.  Since
 these ATM conventions conform strictly with SDP syntax, they are
 case-sensitive.  SDP line types (e.g., "c", "m", "o", "a") and fields
 in the SDP lines should be built according to the case conventions in
 [1] and in this document.  It is suggested, but not required, that
 SDP parsers for ATM applications be case-tolerant where ignoring case
 does not result in ambiguity.  Encoding names, which are defined
 outside the SDP protocol, are case-insensitive.

Kumar & Mostafa Standards Track [Page 7] RFC 3108 ATM SDP May 2001

2.5 Use of special characters in SDP parameter values

 In general, RFC 2327-conformant string values of SDP parameters [1]
 do not include special characters that are neither alphabets nor
 digits.  An exception is the "/" character used in the value
 "RTP/AVP" of transport sub-field of the 'm' line.
 String values used in SDP descriptions of ATM connections retain this
 convention, while allowing the use of the special character "/" in a
 manner commensurate with [1].  In addition, the special characters
 "$" and "-" are used in the following manner.  A "$" value is a
 wildcard that allows the recipient of the SDP description to select
 any permitted value of the parameter.  A "-" value indicates that it
 is not necessary to specify the value of the parameter in the SDP
 description because this parameter is irrelevant for this
 application, or because its value can be known from another source
 such as provisioning, defaults, another protocol, another SDP
 descriptor or another part of the same SDP descriptor.  If the use of
 these special characters is construed as a violation of RFC 2327 [1]
 syntax, then reserved string values can be used.  The string "CHOOSE"
 can be used in lieu of "$".  The string "OMIT" can be used in lieu of
 "-" for an omitted parameter.

3. Capabilities Provided by SDP conventions

 To support the applications listed in section 1, the SDP conventions
 in this document provide the following session control capabilities:
  • Identification of the underlying bearer network type as ATM.
  • Identification by an ATM network element of its own address, in

one of several possible formats. A connection peer can

       initiate SVC set-up to this address.  A call agent or
       connection peer can select an pre-established bearer path to
       this address.
  • Identification of the ATM bearer connection that is to be bound

to the service-level connection. Depending on the application,

       this is either a VCC or a subchannel (identified by a CID)
       within a VCC.
  • Identification of media type: audio, video, data.
  • In AAL1/AAL5 applications, declaration of a set of payload

types that can be bound to the ATM bearer connection. The

       encoding names and payload types defined for use in the RTP
       context [31] are re-used for AAL1 and AAL5, if applicable.

Kumar & Mostafa Standards Track [Page 8] RFC 3108 ATM SDP May 2001

  • In AAL2 applications, declaration of a set of profiles that can

be bound to the ATM bearer connection. A mechanism for

       dynamically defining custom profiles within the SDP session
       description is included.  This allows the use of custom
       profiles for connections that span multi-network interfaces.
  • A means of correlating service-level connections with

underlying ATM bearer connections. The backbone network

       connection identifier or bnc-id specified in ITU Q.1901 [36]
       standardization work is used for this purpose.  In order to
       provide a common SDP base for applications based on Q.1901 and
       SIP/SIP+, the neutral term 'eecid' is used in lieu of 'bnc-id'
       in the SDP session descriptor.
  • A means of mapping codec types and packetization periods into

service types (voice, voiceband data and facsimile). This is

       useful in determining the encoding to use when the connection
       is upspeeded in response to modem or facsimile tones.
  • A means of describing the adaptation type, QoS class, ATM

transfer capability/service category, broadband bearer class,

       traffic parameters, CPS parameters and SSCS parameters related
       the underlying bearer connection.
  • Means for enabling or describing special functions such as

leaf- initiated-join, anycast and SVC caching.

  • For H.323 Annex C applications, a means of specifying the IP

address and port number on which the node will receive RTCP

       messages.
  • A means of chaining consecutive SDP descriptors so that they

refer to different layers of the same connection.

4. Format of the ATM Session Description

 The sequence of lines in the session descriptions in this document
 conforms to RFC 2327 [1].  In general, a session description consists
 of a  session-level part followed by zero or more media-level parts.
 ATM session descriptions consist of a session-level part followed by
 one or two media-level parts.  The only two media applicable are the
 ATM bearer medium and RTCP control (where applicable).
 The session level part consists of the following lines:
 v=  (protocol version, zero or one line)
 o=  (origin, zero or one line)
 s=  (session name, zero or one line)

Kumar & Mostafa Standards Track [Page 9] RFC 3108 ATM SDP May 2001

 c=  (connection information, one line)
 b=  (bandwidth, zero or more lines)
 t=  (timestamp, zero or one line)
 k=  (encryption key, zero or one line)
 In ATM session descriptions, there are no media attribute lines in
 the session level part.  These are present in the media-level parts.
 The media-level part for the ATM bearer consists of the following
 lines:
 m=  (media information and transport address, one line)
 b=  (bandwidth, zero or more lines)
 k=  (encryption key, zero or more lines)
 a=  (media attribute, zero or more lines)
 The media-level part for RTCP control consists of the following
 lines:
 m=  (media information and transport address, one line)
 c=  (connection information for control only, one line)
 In general, the 'v', 'o', 's', and 't' lines are mandatory.  However,
 in the Megaco [26] context, these lines have been made optional.  The
 'o', 's', and 't' lines are omitted in most MGCP [25] applications.
 Note that SDP session descriptors for ATM can contain bandwidth (b=)
 and encryption key (k=) lines.  Like all other lines, these lines
 should strictly conform to the SDP standard [1].
 The bandwidth (b=) line is not necessarily redundant in the ATM
 context since, in some applications, it can be used to convey
 application-level information which does not map directly into the
 atmTrfcDesc media attribute line.  For instance, the 'b' line can be
 used in SDP descriptors in RTSP commands to describe content
 bandwidth.
 The encryption key line (k=) can be used to indicate an encryption
 key for the bearer, and a method to obtain the key.  At present, the
 encryption of ATM and AAL2 bearers has not been conventionalized,
 unlike the encryption of RTP payloads.  Nor has the authentication or
 encryption of ATM or AAL2 bearer signaling.  In the ATM and AAL2
 contexts, the term 'bearer' can include 'bearer signaling' as well as
 'bearer payloads'.
 The order of lines in an ATM session description is exactly in the
 RFC 2327-conformant order depicted above.  However, there is no order
 of the media attribute ('a') lines with respect to other 'a' lines.

Kumar & Mostafa Standards Track [Page 10] RFC 3108 ATM SDP May 2001

 The SDP protocol version for session descriptions using these
 conventions is 0.  In conformance with standard SDP, it  is strongly
 recommended that the 'v' line be included at the beginning of each
 SDP session description.  In some contexts such as Megaco, the
 'v' line is optional and may be omitted unless several session
 descriptions are provided in sequence, in which case the 'v' line
 serves as a delimiter.  Depending on the application, sequences of
 session descriptions might refer to:
  1. Different connections or sessions.
  2. Alternate ways of realizing the same connection or session.
  3. Different layers of the same session (section 5.6.4.1).
 The 'o', 's' and 't' lines are included for strict conformance with
 RFC 2327.  It is possible that these lines might not carry useful
 information in some ATM-based applications.  Therefore, some
 applications might omit these lines, although it is recommended that
 they not do so.  For maximum interoperability, it is preferable that
 SDP parsers not reject session descriptions that do not contain these
 lines.

5. Structure of the Session Description Lines

5.1 The Origin Line

 The origin line for an ATM-based session is structured as follows:
       o=<username> <sessionID> <version> <networkType>
         <addressType> <address>
 The <username> is set to "-".
 The <sessionID> can be  set to one of the following:
  • an NTP timestamp referring to the moment when the SDP session

descriptor was created.

  • a Call ID, connection ID or context ID that uniquely identifies

the session within the scope of the ATM node. Since calls can

       comprise multiple connections (sessions), call IDs are
       generally not suitable for this purpose.
 NTP time stamps can be represented as decimal or hex integers.  The
 part of the NTP timestamp that refers to an integer number of seconds
 is sufficient.  This is a 32-bit field
 On the other hand, call IDs, connection IDs and context IDs can be
 can be 32 hex digits long.

Kumar & Mostafa Standards Track [Page 11] RFC 3108 ATM SDP May 2001

 The <sessionID> field is represented as a decimal or hex number of up
 to 32 digits.  A "0x" prefix is used before the hex representation.
 The <version> refers to the version of the SDP session descriptor
 (not that of the SDP protocol).  This is can be set to one of the
 following:
  • 0.
  • an NTP timestamp referring to the moment when the SDP session

descriptor was modified. If the SDP session descriptor has not

       been modified by an intermediate entity (such as an MGC), then
       the <version> timestamp will be the same as the <sessionId>
       timestamp, if any.  As with the <sessionId>, only the integer
       part of the NTP timestamp is used.
 When equated to the integer part of an NTP timestamp, the <version>
 field is 10 digits wide.  This is more restricted than [1], which
 allows unlimited size.  As in [1], the most significant digit is
 non-zero when an NTP timestamp is used.
 The <networkType> in SDP session descriptions for ATM applications
 should be assigned the string value "ATM" or wildcarded to a "$" or
 "-".
 The <addressType> and <address>  parameters are identical to those
 for the connection information ('c') line (Section 5.3).  Each of
 these parameters can be wildcarded per the conventions described for
 the 'c' line in Section 5.3.  These parameters should not me omitted
 since this would violate SDP syntax [1].
 As with the 'c' line, SDP parsers are not expected to check the
 consistency of <networkType> with <addressType>, <address> pairs.
 The <addressType> and <address> need to be consistent with each
 other.

5.2 The Session Name Line

 In general, the session name line is structured as follows:
      s=<sessionName>
 For ATM-based sessions, the <sessionName> parameter is set to a "-".
 The resulting line is:
      s=-

Kumar & Mostafa Standards Track [Page 12] RFC 3108 ATM SDP May 2001

5.3 The Connection Information Line

 In general, the connection information line [1] is structured as
 follows:
      c=<networkType> <addressType> <address>
 For ATM networks, additional values of <networkType>, <addressType>
 and <address> are defined, over and above those listed in [1].  The
 ABNF syntax (Section 9) for ATM SDP does not limit the ways in which
 <networkType> can be combined with <addressType>, <address> pairs.
 However, some combinations will not be valid in certain applications,
 while others will never be valid.  Invalid combinations should be
 rejected by application-specific functions, and not by generic
 parsers.  The ABNF syntax does limit the ways in which <addressType>
 and <address> can be paired.
 For ATM networks, the value of <networkType> should be set to "ATM".
 Further, this may be wildcarded to "$" or "-".  If this is done, an
 node using ATM as the basic transport mechanism will select a value
 of "ATM".  A node that interfaces with multiple network types ("IN",
 "ATM" etc.) that include ATM can also choose a value of "ATM".
 When the SDP description is built by a node such as a media gateway,
 the <address> refers to the address of the node building the SDP
 description.  When this description is forwarded to another node, it
 still contains the original node's address.  When the media gateway
 controller builds part or all of the SDP description, the local
 descriptor contains the address of the local node, while the remote
 descriptor contains the address of the remote node.  If the <address>
 and/or <addressType> are irrelevant or are known by other means, they
 can be set to a "$" or a "-", as described below.
 Additionally, in all contexts, the 'm' line can have an ATM address
 in the <virtualConnectionId> subparameter which, if present, is the
 remote address if the 'c' line address is local, and vice versa.
 For ATM networks, the <addressType> can be NSAP, E164 or GWID
 (ALIAS).  For ATM networks, the <address> syntax depends on the
 syntax of the <addressType>.  SDP parsers should check the
 consistency of <addressType> with <address>.
 NSAP: If the addressType is NSAP, the address is expressed in the
 standard dotted hex form.  This is a string of 40 hex digits, with
 dots after the 2nd, 6th, 10th, 14th, 18th, 22nd, 26th, 30th, 34th and
 38th digits.  The last octet of the NSAP address is the 'selector'
 field that is available for non-standard use.  An example of a line
 with an NSAP address is:

Kumar & Mostafa Standards Track [Page 13] RFC 3108 ATM SDP May 2001

     c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
 A "0x" prefix shall not be used in this case since this is always in
 hexadecimal format.
 E164: If the addressType is E164, the address is expressed as a
 decimal number  with up to 15 digits.  For example:
      c=ATM E164 9738294382
 The use of E.164 numbers in the B-ISDN context is defined in ITU
 E.191.  There is a disparity between the ATM forum and the ITU in the
 use of E.164 numbers for ATM addressing.  The ATM forum (e.g., UNI
 Signaling 4.0) allows only International Format E.164 numbers, while
 the ITU (e.g., Q.2931) allows private numbering plans.  Since the
 goal of this SDP specification is to interoperate with all bearer
 signaling protocols, it allows the use of numbers that do not conform
 to the E.164 International Format.  However, to maximize overall
 consistency, network administrators can restrict the provisioning of
 numbers to the E.164 International Format.
 GWID (ALIAS): If the addressType is GWID, it means that the address
 is a Gateway Identifier or Node Alias.  This may or may not be
 globally unique.  In this format, the address is expressed as an
 alphanumeric string ("A"-"Z", "a"-"z", "0" - "9",".","-","_").  For
 example:
     c=ATM GWID officeABCmgx101vism12
 Since these SDP conventions can be used for more than gateways, the
 string "ALIAS" can be used instead of "GWID" in the 'c' line.  Thus,
 the example above is equivalent to:
     c=ATM ALIAS officeABCmgx101vism12
 An example of a GWID (ALIAS)is the CLLI code used for telecom
 equipment.  For all practical purposes, it should be adequate for the
 GWID (ALIAS) to be a variable length string with a maximum size of 32
 characters.
 The connection information line is always present in an SDP session
 descriptor.  However, each of the parameters on this line can be
 wildcarded to a "$" or a "-", independently of whether other
 parameters on this line are wildcarded or not.  Not all syntactically
 legal wildcard combinations are meaningful in a particular
 application.

Kumar & Mostafa Standards Track [Page 14] RFC 3108 ATM SDP May 2001

 Examples of meaningful wildcard combinations in the ATM context are:
       c=- - -
       c=$ $ $
       c=ATM - -
       c=ATM $ $
       c=ATM <addressType> -
       c=ATM <addressType> $
 Specifying the ATM address type without specifying the ATM address is
 useful when the recipient is asked to select an ATM address of a
 certain type (NSAP, E.164 etc.).
 Examples of syntactically legal wildcard combinations of dubious
 utility are:
       c=- $ -
       c=- $ $
       c=- <addressType> -
       c=$ <addressType> $
       c=- <addressType> <address>
       c=$ <addressType> <address>
 Note that <addressType> and/or <address> should not omitted without
 being set to a "-" or "$" since this would violate basic SDP syntax
 [1].

5.4 The Timestamp Line

 The timestamp line for an SDP session descriptor is structured as
 follows:
       t= <startTime> <stopTime>
 Per Ref. [49], NTP time stamps use a 32 bit unsigned representation
 of seconds, and a 32 bit unsigned representation of fractional
 seconds.  For ATM-based sessions, the <startTime>parameter can be
 made equal to the NTP timestamp referring to the moment when the SDP
 session descriptor was created.  It can also be set to 0 indicating
 its irrelevance.  If it made equal to the NTP timestamp in seconds,
 the fractional part of the NTP timestamp is omitted.  When equated to
 the integer part of an NTP timestamp, the <startTime> field is 10
 digits wide.  This is more restricted than [1], which allows
 unlimited size.  As in [1], the most significant digit is non-zero
 when an NTP timestamp is used.
 The <stopTime> parameter is set to 0 for ATM-based SDP descriptors.

Kumar & Mostafa Standards Track [Page 15] RFC 3108 ATM SDP May 2001

5.5 Media Information Line for ATM connections

 The general format of the media information line adapted for AAL1 and
 AAL5 applications is:
 m=<media> <virtualConnectionId> <transport> <format list>
 The general format of the media information line adapted for AAL2
 applications is:

m=<media> <virtualConnectionId> <transport#1> <format list#1>

       <transport#2> <format list#2> ... <transport#M> <format list#M>
 Note that <virtualConnectionId> is equivalent to <port> in [1].
 The subparameter <media> can take on all the values defined in [1].
 These are: "audio", "video", "application", "data" and "control".
 When the <transport> parameter has more than one value in the 'm'
 line, the <transport> <format list> pairs can be arranged in
 preferential order.

5.5.1 The Virtual Connection ID

 In applications in which the media-level part of a session descriptor
 is bound to an ATM virtual circuit, the <virtualConnectionId> can be
 in one of the following formats:
  • <ex_vcci>
  • <addressType>-<address>/<ex_vcci>
  • <address>/<ex_vcci>
  • <ex_bcg>/<ex_vcci>
  • <ex_portId>/<ex_vpi>/<ex_vci>
  • <ex_bcg>/<ex_vpi>/<ex_vci>
  • <ex_vpci>/<ex_vci>
  • <addressType>-<address>/<ex_vpci>/<ex_vci>
  • <address>/<ex_vpci>/<ex_vci>
 In applications in which the media-level part of a session descriptor
 is bound to a subchannel within an ATM virtual circuit, the
 <virtualConnectionId> can be in one of the following formats:
  • <ex_vcci>/<ex_cid>
  • <addressType>-<address>/<ex_vcci>/<ex_cid>
  • <address>/<ex_vcci>/<ex_cid>
  • <ex_bcg>/<ex_vcci>/<ex_cid>
  • <ex_portId>/<ex_vpi>/<ex_vci>/<ex_cid>
  • <ex_bcg>/<ex_vpi>/<ex_vci>/<ex_cid>

Kumar & Mostafa Standards Track [Page 16] RFC 3108 ATM SDP May 2001

  • <ex_vpci>/<ex_vci>/<ex_cid>
  • <addressType>-<address>/<ex_vpci>/<ex_vci>/<ex_cid>
  • <address>/<ex_vpci>/<ex_vci>/<ex_cid>
 Here,
        <ex_vcci> = VCCI-<vcci>
        <ex_vpci> = VPCI-<vpci>
        <ex_bcg> = BCG-<bcg>
        <ex_portId> = PORT-<portId>
        <ex_vpi> = VPI-<vpi>
        <ex_vci> = VCI-<vci>
        <ex_cid> = CID-<cid>
 The <vcci>, <vpi>, <vci>, <vpci> and <cid> are decimal numbers or
 hexadecimal numbers.  An "0x" prefix is used before their values when
 they are in the hex format.
 The <portId> is always a hexadecimal number.  An "0x" prefix is not
 used with it.
 The <addressType> and <address> are identical to their definitions
 above for the connection information line with the difference that
 this address refers to the remote peer in the media information line.
 Since the <virtualConnectionId>, as defined here, is meant for use in
 ATM networks, the values of <addressType> and <address> in the
 <virtualConnectionId> are limited to ATM-specific values.
 The <vpi>, <vci> and <cid> are the Virtual Path Identifier, Virtual
 Circuit Identifier and Channel Identifier respectively. The <vpi> is
 an 8 or 12 bit field. The <vci> is a 16-bit field. The <cid> is an
 8-bit field ([8] and [11]). For AAL1 applications, it corresponds to
 the channel number defined in Annex C of [8].
 The <vpci> is a 16-bit field defined in Section 4.5.16 of ITU Q.2931
 [Ref. 15].  The <vpci> is similar to the <vpi>, except for its width
 and the fact that it retains its value across VP crossconnects.  In
 some applications, the size of the <vpci> is the same as the size of
 the <vpi> (8 or 12 bits).  In this case, the most significant 8 or 4
 bits are ignored.
 The <vcci> is a 16-bit field defined in ITU Recommendation Q.2941.2
 [32].  The <vcci> is similar to the <vci>, except for the fact that
 it retains its value across VC crossconnects.
 In general, <vpci> and <vcci> values are unique between a pair of
 nodes.  When they are unique between a pair of nodes but not unique
 within a network, they need to be qualified, at any node, by the ATM

Kumar & Mostafa Standards Track [Page 17] RFC 3108 ATM SDP May 2001

 address of the remote node.  These parameters can be pre-provisioned
 or signaled.  When signaled, the <vpci> is encapsulated in the
 connection identifier information element of SVC signaling messages.
 The <vcci> is encapsulated in the Generic Information Transport (GIT)
 information element of SVC signaling messages.  In an ATM node pair,
 either node can assign <vcci> values and signal it to the other end
 via SVC signaling.  A glare avoidance scheme is defined in [32] and
 [44].  This mechanism works in SVC applications.  A different glare
 avoidance technique is needed when a pool of existing PVCs/SPVCs is
 dynamically assigned to calls.  One such scheme for glare reduction
 is the assignment of <vcci> values from different ends of the <vcci>
 range, using the lowest or highest available value as applicable.
 When <vpci> and <vcci> values are pre-provisioned, administrations
 have the option of provisioning them uniquely in a network.  In this
 case, the ATM address of the far end is not needed to qualify these
 parameters.
 In the AAL2 context, the definition of a VCC implies that there is no
 CID-level switching between its ends.  If either end can assign <cid>
 values, then a glare reduction mechanism is needed.  One such scheme
 for glare reduction is the assignment of <cid> values from different
 ends of the <cid> range, using the lowest or highest available value
 as applicable.
 The <portId> parameter is used to identify the physical trunk port on
 an ATM module.  It can be represented as a hexadecimal number of up
 to 32 hex digits.
 In some applications, it is meaningful to bundle a set of connections
 between a pair of ATM nodes into a bearer connection group.  The
 <bcg> subparameter is an eight bit field that allows the bundling of
 up to 255 VPCs or VCCs.
 In some applications, it is necessary to wildcard the
 <virtualConnectionId> parameter, or some elements of this parameter.
 The "$" wildcard character can be substituted for the entire
 <virtualConnectionId> parameter, or some of its terms.  In the latter
 case, the constant strings that qualify the terms in the
 <virtualConnectionId> are retained.  The concatenation
 <addressType>-<address> can be wildcarded in the following ways:
  • The entire concatenation, <addressType>-<address>, is replaced

with a "$".

  • <address> is replaced with a "$", but <addressType> is not.

Kumar & Mostafa Standards Track [Page 18] RFC 3108 ATM SDP May 2001

 Examples of wildcarding the <virtualConnectionId> in the AAL1 and
 AAL5 contexts are: $, VCCI-$, BCG-100/VPI-20/VCI-$.  Examples of
 wildcarding the <virtualConnectionId> in the AAL2 context are: $,
 VCCI-40/CID-$, BCG-100/VPI-20/VCI-120/CID-$, NSAP-$/VCCI-$/CID-$,
 $/VCCI-$/CID-$.
 It is also permissible to set the entire <virtualConnectionId>
 parameter to a "-" indicating its irrelevance.

5.5.2 The Transport Parameter

 The <transport> parameter indicates the method used to encapsulate
 the service payload.  These methods are not defined in this document,
 which refers to existing ATMF and ITU-T standards, which, in turn,
 might refer to other standards.  For ATM applications, the following
 <transport> values are defined:

Kumar & Mostafa Standards Track [Page 19] RFC 3108 ATM SDP May 2001

 Table 1: List of Transport Parameter values used in SDP in the ATM
          context

+———————————————————————+

Controlling Document for
Transport Encapsulation of Service Payload

+————————+——————————————–+

AAL1/ATMF af-vtoa-0078.000 [7]

+————————+——————————————–+

AAL1/ITU ITU-T H.222.1 [51]

+————————+——————————————–+

AAL5/ATMF af-vtoa-0083.000 [46]

+————————+——————————————–+

AAL5/ITU ITU-T H.222.1 [51]

+————————+——————————————–+

AAL2/ATMF af-vtoa-0113.000 [44] and
af-vmoa-0145.000 [52]

+————————+——————————————–+

AAL2/ITU ITU-T I.366.2 [13]

+————————+——————————————–+

AAL1/custom Corporate document or
AAL2/custom application-specific interoperability
AAL5/custom statement.

+————————+——————————————–+

AAL1/<corporateName>
AAL2/<corporateName>
AAL5/<corporateName>
AAL1/IEEE:<oui> Corporate document
AAL2/IEEE:<oui>
AAL5/IEEE:<oui>

+————————+——————————————–+

RTP/AVP Annex C of H.323 [45]

+————————+——————————————–+

 In H.323 Annex C applications [45], the <transport> parameter has a
 value of "RTP/AVP".  This is because these applications use the RTP
 protocol [2] and audio/video profile [3].  The fact that RTP is
 carried directly over AAL5 per [45] can be indicated explicitly via
 the aalApp media attribute.
 A value of "AAL1/custom", "AAL2/custom" or "AAL5/custom" for the
 <transport> parameter can indicate non-standard or semi-standard
 encapsulation schemes defined by a corporation or a multi-vendor
 agreement.  Since there is no standard administration of this
 convention, care should be taken to preclude inconsistencies within
 the scope of a deployment.

Kumar & Mostafa Standards Track [Page 20] RFC 3108 ATM SDP May 2001

 The use of <transport> values "AAL1/<corporateName>",
 "AAL2/<corporateName>", "AAL5/<corporateName>", "AAL1/IEEE:<oui>",
 "AAL2/IEEE:<oui>" and "AAL5/IEEE:<oui>" is similar.  These indicate
 non-standard transport mechanisms or AAL2 profiles which should be
 used consistently within the scope of an application or deployment.
 The parameter <corporateName> is the registered, globally unique name
 of a corporation (e.g., Cisco, Telcordia etc.).  The parameter <oui>
 is the hex representation of a three-octet field identical to the OUI
 maintained by the IEEE.  Since this is always represented in hex, the
 "0x" prefix shall not be used.  Leading zeros can be omitted.  For
 example, "IEEE:00000C" and "IEEE:C" both refer to Cisco Systems, Inc.

5.5.3 The Format List for AAL1 and AAL5 applications

 In the AAL1 and AAL5 contexts, the <format list> is a list of payload
 types:
    <payloadType#1> <payloadType#2>...<payloadType#n>
 In most AAL1 and AAL5 applications, the ordering of payload types
 implies a preference (preferred payload types before less favored
 ones).  The payload type can be statically assigned or dynamically
 mapped.  Although the transport is not the same, SDP in the ATM
 context leverages the encoding names and payload types registered
 with IANA [31] for RTP.  Encoding names not listed in [31] use a "X-"
 prefix.  Encodings that are not statically mapped to payload types in
 [31] are to be dynamically mapped at the time of connection
 establishment to payload types in the decimal range 96-127.  The SDP
 'atmmap' attribute (similar to 'rtpmap') is used for this purpose.
 In addition to listing the IANA-registered encoding names and payload
 types found in [31], Table 2 defines a few non-standard encoding
 names(with "X-" prefixes).

5.5.4 The Format List for AAL2 applications

 In the AAL2 context, the <format list> is a list of AAL2 profile
 types:
    <profile#1> <profile#2>...<profile#n>
 In most applications, the ordering of profiles implies a preference
 (preferred profiles before less favored ones).  The <profile>
 parameter is expressed as a decimal number in the range 1-255.

Kumar & Mostafa Standards Track [Page 21] RFC 3108 ATM SDP May 2001

5.5.5 Media information line construction

 Using the parameter definitions above, the 'm' for AAL1-based audio
 media can be constructed as follows:
    m=audio <virtualConnectionId> AAL1/ATMF  <payloadType#1>
              <payloadType#2>...<payloadType #n>
 Note that only those payload types, whether statically mapped or
 dynamically assigned, that are consistent with af-vtoa-78 [7] can be
 used in this construction.
 Backwards compatibility note: The transport value "AAL1/AVP" used in
 previous versions of this document should be considered equivalent to
 the value "AAL1/ATMF" defined above.  "AAL1/AVP" is unsuitable
 because the AVP profile is closely tied to RTP.
 An example 'm' line use for audio media over AAL1 is:
    m=audio VCCI-27 AAL1/ATMF 0
 This indicates the use of an AAL1 VCC with VCCI=24 to carry PCMU
 audio that is encapsulated according to ATMF's af-vtoa-78 [7].
 Another example of the use of the 'm' line use for audio media over
 AAL1 is:
    m=audio $  AAL1/ATMF 0 8
 This indicates that any AAL1 VCC may be used.  If it exists already,
 then its selection is subject to glare rules.  The audio media on
 this VCC is encapsulated according to ATMF's af-vtoa-78 [7].  The
 encodings to be used are either PCMU or PCMA, in preferential order.
 The 'm' for AAL5-based audio media can be constructed as follows:
    m=audio <virtualConnectionId> AAL5/ATMF  <payloadType#1>
              <payloadType#2>...<payloadType #n>
 An example 'm' line use for audio media over AAL5 is:
    m=audio PORT-2/VPI-6/$  AAL5/ITU  9  15
 implies that any VCI on VPI= 6 of trunk port #2 may be used.  The
 identities of the terms in the virtual connection ID are implicit in
 the application context.  The audio media on this VCC is encapsulated
 according to ITU-T H.222.1 [51].  The encodings to be used are either
 ITU-T G.722 or ITU-T G.728 (LD-CELP), in preferential order.

Kumar & Mostafa Standards Track [Page 22] RFC 3108 ATM SDP May 2001

 The 'm' for AAL5-based H.323 Annex C audio [45] can be constructed as
 follows:
    m=audio <virtualConnectionId> RTP/AVP <payloadType#1>
                  <payloadType#2>...<payloadType #n>
 For example:
       m=audio PORT-9/VPI-3/VCI-$  RTP/AVP 2 96
       a=rtpmap:96 X-G727-32
       a=aalType:AAL5
       a=aalApp:itu_h323c - -
 implies that any VCI on VPI= 3 of trunk port #9 may be used.  This VC
 encapsulates RTP packets directly on AAL5 per [45].  The 'rtpmap'
 (rather than the 'atmmap') attribute is used to dynamically map the
 payload type of 96 into the codec name X-G727-32 (Table 2).  This
 name represents 32 kbps EADPCM.
 The 'm' line for AAL5-based video media can be constructed as
 follows:
    m=video <virtualConnectionId> AAL5/ITU  <payloadType#1>
              <payloadType#2>...<payloadType #n>
 In this case, the use of AAL5/ITU as the transport points to H.222.1
 as the controlling standard [51].  An example 'm' line use for video
 media is:
    m=video PORT-9/VPI-3/VCI-$  AAL5/ITU  33
 This indicates that any VCI on VPI= 3 of trunk port #9 may be used.
 The video media on this VCC is encapsulated according to ITU-T
 H.222.1 [51].  The encoding scheme is an MPEG 2 transport stream
 ("MP2T" in Table 1).  This is statically mapped per [31] to a payload
 type of 33.
 Using the parameter definitions in the previous subsections, the
 media information line for AAL2-based audio media can be constructed
 as follows:

m=<media> <virtualConnectionId> <transport#1> <format list#1>

      <transport#2> <format list#2> ... <transport#M> <format list#M>
 where <format list#i> has the form <profile#i_1>...<profile#i_N>
 Unlike the 'm' line for AAL1 or AAL5 applications, the 'm' line for
 AAL2 applications can have multiple <transport> parameters, each
 followed by a <format list>.  This is because it is possible to

Kumar & Mostafa Standards Track [Page 23] RFC 3108 ATM SDP May 2001

 consider definitions from multiple sources (ATMF, ITU and non-
 standard documents) when selecting AAL2 profile to be bound to a
 connection.
 In most applications, the ordering of profiles implies a preference
 (preferred profiles before less favored ones).  Therefore, there can
 be multiple instances of the same <transport> value in the same 'm'
 line.
 An example 'm' line use for audio media over AAL2 is:
    m=audio VCCI-27/CID-19 AAL2/ITU 7 AAL2/custom 100 AAL2/ITU 1
 This indicates the use of CID #19 on VCCI #27 to carry audio.  It
 provides a preferential list of profiles for this connection: profile
 AAL2/ITU 7 defined in [13], AAL2/custom 100 defined in an
 application-specific or interoperability document and profile
 AAL2/ITU 1 defined in [13].
 Another example of the use of the 'm' line use for audio media over
 AAL2 is:
    m=audio VCCI-$/CID-$  AAL2/ATMF 6 8
 This indicates that any AAL2 CID may be used, subject to any
 applicable glare avoidance/reduction rules.  The profiles that can be
 bound to this connection are AAL2/ATMF 6 defined in af-vtoa-0113.000
 [44] and AAL2/ATMF 8 defined in af-vmoa-0145.000 [52].  These sources
 use non-overlapping profile number ranges.  The profiles they define
 fall under the <transport> category "AAL2/ATMF".  This application
 does not order profiles preferentially.  This rule is known a priori.
 It is not embedded in the 'm' line.
 Another example of the use of the 'm' line use for audio media over
 AAL2 is:
    m=audio VCCI-20/CID-$  AAL2/xyzCorporation 11
 AAL2 VCCs in this application are single-CID VCCs.  Therefore, it is
 possible to wildcard the CID.  The single-CID VCC with VCCI=20 is
 selected.  The AAL2 profile to be used is AAL2/xyzCorporation 11
 defined by xyzCorporation.
 In some applications, an "-" can be used in lieu of:
  1. <format list>
  2. <transport> and <format list>

Kumar & Mostafa Standards Track [Page 24] RFC 3108 ATM SDP May 2001

 This implies that these parameters are irrelevant or are known by
 other means (such as defaults).  For example:
       m=audio VCCI-234 - -
       a=aalType:AAL1
 indicates the use of VCCI=234 with AAL1 adaptation and unspecified
 encoding.
 In another example application, the 'aal2sscs3662' attribute can
 indicate <faxDemod> = "on" and any other competing options as "off",
 and the <aalType> attribute can indicate AAL2.  Thus:
    m=audio VCCI-123/CID-5 - -
    a=aalType:AAL2
    a=aal2sscs3662:audio off off on off on off off off - - -
 Besides indicating an audio medium, a VCCI of 123 and a CID of 5, the
 'm' line indicates an unspecified profile.  The media attribute lines
 indicate an adaptation layer of AAL2, and the use of the audio SAP
 [13] to carry demodulated facsimile.
 The media information line for "data" media has one of the following
 the following formats:
    m=data <virtualConnectionId> - -
    m=data - - -
 The data could be circuit emulation data carried over AAL1 or AAL2,
 or packet data carried over AAL5.  Media attribute lines, rather than
 the 'm' line, are used to indicate the adaptation type for the data
 media.  Examples of the representation of data media are listed
 below.
       m=data  PORT-7/VPI-6/VCI-$  - -
       a=aalApp:AAL5_SSCOP-                             -
 implies that any VCI on VPI= 6 of trunk port #7 may be used.  This VC
 uses SSCOP on AAL5 to transport data.
       m=data  PORT-7/VPI-6/VCI-50  - -
       a=aalType:AAL1_SDT
       a=sbc:6
 implies that VCI 50 on VPI 6 on port 7 uses structured AAL1 to
 transfer 6 x 64 kbps circuit emulation data.  This may be alternately
 represented as:

Kumar & Mostafa Standards Track [Page 25] RFC 3108 ATM SDP May 2001

       m=data  PORT-7/VPI-6/VCI-50  - -
       b=AS:384
       a=aalType:AAL1_SDT
 The following lines:
       m=data VCCI-123/CID-5 - -
       a=aalType:AAL2
       a=sbc:2
 imply that CID 5 of VCCI 123 is used to transfer 2 x 64 kbps circuit
 emulation data.
 In the AAL1 context, it is also permissible to represent circuit mode
 data as an "audio" codec.  If this is done, the codec types used are
 X-CCD or X-CCD-CAS.  These encoding names are dynamically mapped into
 payload types through the 'atmmap' attribute.  For example:
       m=audio VCCI-27 AAL1/AVP 98
       a=atmmap:98 X-CCD
       a=sbc:6
 implies that AAL1 VCCI=27 is used for 6 x 64 transmission.
 In the AAL2 context, the X-CCD codec can be assigned a profile type
 and number.  Even though it is not possible to construct a profile
 table as described in ITU I.366.2 for this "codec", it is preferable
 to adopt the common AAL2 profile convention in its case.  An example
 AAL2 profile mapping for the X-CCD codec could be as follows:
    PROFILE TYPE         PROFILE NUMBER        "CODEC" (ONLY ONE)
      "custom"                200                     X-CCD
 The profile does not identify the number of subchannels ('n' in
 nx64).  This is known by other means such as the 'sbc' media
 attribute line.
 For example, the media information line:
       m=audio $ AAL2/custom 200
       a=sbc:6
 implies 384 kbps circuit emulation using AAL2 adaptation.
 It is not necessary to define a profile with the X-CCD-CAS codec,
 since this method of CAS transport [7] is not used in AAL2
 applications.

Kumar & Mostafa Standards Track [Page 26] RFC 3108 ATM SDP May 2001

5.6 The Media Attribute Lines

 In an SDP line sequence, the media information line 'm' is followed
 by one or more media attribute or 'a' lines.  Media attribute lines
 are per the format below:
    a=<attribute>:<value>
 or
    a=<value>
 In general, media attribute lines are optional except when needed to
 qualify the media information line.  This qualification is necessary
 when the "m" line for an AAL1 or AAL5 session specifies a payload
 type that needs to be dynamically mapped.  The 'atmmap' media
 attribute line defined below is used for this purpose.
 In attribute lines, subparameters that are meant to be left
 unspecified are set to a "-".  These are generally inapplicable or,
 if applicable, are known by other means such as provisioning.  In
 some cases, a media attribute line with all parameters set to "-"
 carries no information and should be preferably omitted.  In other
 cases, such as the 'lij' media attribute line, the very presence of
 the media attribute line conveys meaning.
 There are no restrictions placed by RFC 2327 [1] regarding the order
 of 'a' lines with respect to other 'a' lines.  However, these lines
 must not contradict each other or the other SDP lines.
 Inconsistencies are not to be ignored and should be flagged as
 errors.  Repeated media attribute lines can carry additional
 information.  These should not be inconsistent with each other.
 Applications will selectively use the optional media attribute lines
 listed below.  This is meant to be an exhaustive list for describing
 the general attributes of ATM bearer networks.
 The base specification for SDP, RFC 2327 [1], allows the definition f
 new attributes.  In keeping with this spirit, some of the attributes
 defined in this document can also be used in SDP descriptions of IP
 nd other non-ATM sessions.  For example, the 'vsel', 'dsel' and
 'fsel' attributes defined below refer generically to codec-s.  These
 can be bed for service-specific codec negotiation and assignment in
 non-ATM s well as ATM applications.
 SDP media attributes defined in this document for use in the ATM
 context are classified as:

Kumar & Mostafa Standards Track [Page 27] RFC 3108 ATM SDP May 2001

  • ATM bearer connection attributes (Section 5.6.1)
  • AAL attributes (Section 5.6.2)
  • Service attributes (Section 5.6.3).
  • Miscellaneous media attributes, that cannot be classified as

ATM, AAL or service attributes (Section 5.6.4).

 In addition to these, the SDP attributes defined in [1] can also be
 used in the ATM context.  Examples are:
  • The attributes defined in RFC 2327 which allow indication of

the direction in which a session is active. These are

       a=sendonly, a=recvonly, a=sendrecv, a=inactive.
  • The 'Ptime' attribute defined in RFC 2327. It indicates the

packet period. It is not recommended that this attribute be

       used in ATM applications since packet period information is
       provided with other parameters (e.g., the profile type and
       number in the 'm' line, and the 'vsel', 'dsel' and 'fsel'
       attributes).  Also, for AAL1 applications, 'ptime' is not
       applicable and should be flagged as an error.  If used in AAL2
       and AAL5 applications, 'ptime' should be consistent with the
       rest of the SDP description.
  • The 'fmtp' attribute used to designate format-specific

parameters.

5.6.1 ATM bearer connection attributes

 The following is a summary list of the SDP media attributes that can
 be used to describe ATM bearer connections.  These are detailed in
 subsequent subsections.
  • The 'eecid' attribute. This stands for 'end-to-end connection

identifier'. It provides a means of correlating service-level

       connections with underlying ATM bearer connections.  In the
       Q.1901 [36] context, the eecid is synonymous with the bnc-id
       (backbone network connection identifier).
  • The 'aalType' attribute. This is used to indicate the nature

of the ATM adaptation layer (AAL).

  • The 'capability' attribute, which indicates the ATM transfer

capability (ITU nomenclature), synonymous with the ATM Service

       Category (ATMF nomenclature).
  • The 'qosClass' attribute, which indicates the QoS class of the

ATM bearer connection.

Kumar & Mostafa Standards Track [Page 28] RFC 3108 ATM SDP May 2001

  • The 'bcob' attribute, which indicates the broadband connection

oriented bearer class, and whether end-to-end timing is

       required.
  • The 'stc' attribute, which indicates susceptibility to

clipping.

  • The 'upcc' attribute, which indicates the user plane connection

configuration.

  • The 'atmQOSparms' attribute, which is used to describe certain

key ATM QoS parameters.

  • The 'atmTrfcDesc' attribute, which is used to describe ATM

traffic descriptor parameters.

  • The 'abrParms' attribute, which is used to describe ABR-

specific parameters. These parameters are per the UNI 4.0

       signaling  specification [5].
  • The 'abrSetup' attribute, which is used to indicate the ABR

parameters needed during call/connection establishment.

  • The 'bearerType' attribute, which is used to indicate whether

the underlying bearer is an ATM PVC/SPVC, an ATM SVC, or a

       subchannel within an existing ATM SVC/PVC/SPVC.
  • The 'lij' attribute, which is used to indicate the presence of

a connection that uses the Leaf-initiated-join capability

       described in UNI 4.0 [5], and to optionally describe parameters
       associated with this capability.
  • The 'anycast' attribute, which is used to indicate the

applicability of the anycast function described in UNI 4.0 [5],

       and to optionally qualify it with certain parameters.
  • The 'cache' attribute, which is used to enable SVC caching and

to specify an inactivity timer for SVC release.

  • The 'bearerSigIE' attribute, which can be used to represent ITU

Q-series information elements in bit-map form. This is useful

       in describing parameters that are not closely coupled to the
       ATM and AAL layers.  Examples are the B-HLI and B-LLI IEs
       specified in ITU Q.2931 [15], and the user-to-user information
       element described in ITU Q.2957 [48].

Kumar & Mostafa Standards Track [Page 29] RFC 3108 ATM SDP May 2001

5.6.1.1 The 'eecid' attribute

 The 'eecid' attribute is synonymous with the 4-byte 'bnc-id'
 parameter used by T1SI, the ATM forum and the ITU (Q.1901)
 standardization effort.  The term 'eecid' stands for 'end-to-end
 connection identifier', while 'bnc-id' stands for 'backbone network
 connection identifier'.  The name "backbone" is slightly misleading
 since it refers to the entire ATM network including the ATM edge and
 ATM core networks.  In Q.1901 terminology, an ATM "backbone" connects
 TDM or analog edges.
 While the term 'bnc-id' might be used in the bearer signaling plane
 and in an ISUP (Q.1901) call control plane, SDP session descriptors
 use the neutral term 'eecid'.  This provides a common SDP baseline
 for applications that use ISUP (Q.1901) and applications that use
 SIP/SIP+.
 Section 5.6.6 depicts the use of the eecid in call establishment
 procedures.  In these procedures, the eecid is used to correlate
 service-level calls with SVC set-up requests.
 In the forward SVC establishment model, the call-terminating gateway
 selects an eecid and transmits it via SDP to the call-originating
 gateway.  The call originating gateway transmits this eecid to the
 call terminating gateway via the bearer set-up message (SVC set-up or
 Q.2630.1 establish request).
 In the backward SVC establishment model, the call-originating gateway
 selects an eecid and transmits it via SDP to the call-terminating
 gateway.  The call terminating gateway transmits this eecid to the
 call originating gateway via the bearer set-up message (SVC set-up or
 Q.2630.1 establish request).
 The value of the eecid attribute values needs to be unique within the
 node terminating the SVC set-up but not across multiple nodes.
 Hence, the SVC-terminating gateway has complete control over using
 and releasing values of this parameter.  The eecid attribute is used
 to correlate, one-to-one, received bearer set-up requests with
 service-level call control signaling.
 Within an SDP session description, the eecid attribute is used as
 follows:
       a=eecid:<eecid>
 where <eecid> consists of up to 8 hex digits (equivalent to 4
 octets).  Since this is always represented in hex, the "0x" prefix
 shall not be used.

Kumar & Mostafa Standards Track [Page 30] RFC 3108 ATM SDP May 2001

 Within the text representation of the <eecid> parameter, hex digits
 to the left are more significant than hex digits to the right
 (Section 2.2).
 This SDP document does not specify how the eecid (synonymous with
 bnc-id) is to be communicated through bearer signaling (Q.931, UNI,
 PNNI, AINI, IISP, proprietary signaling equivalent, Q.2630.1).  This
 is a task of these bearer signaling protocols.  However, the
 following informative statements are made to convey a sense of the
 interoperability that is a goal of current standardization efforts:
  1. ITU Q.2941.3 and the ATMF each recommend the use of the GIT IE for

carrying the eecid (synonymous with bnc-id) in the set-up message

    of ATM signaling protocols (Q.2931, UNI 4.0, PNNI, AINI, IISP).
    The coding for carrying the eecid (bnc-id) in the GIT IE is
    defined in ITU Q.2941.3 and accepted by the ATM forum.
  1. Another alternate method is to use the called party subaddress IE.

In some networks, this might be considered a protocol violation

    and is not the recommended means of carrying the eecid (bnc-id).
    The GIT IE is the preferred method of transporting the eecid
    (bnc-id) in ATM signaling messages.
  1. The establish request (ERQ) message of the Q.2630.1 [37] signaling

protocol can use the SUGR (Served User Generated Reference) IE to

    transport the eecid (bnc-id).
 The node assigning the eecid can release and re-use it when it
 receives a Q.2931 [15] set-up message or a Q.2630.1 [37] establish
 request message containing the eecid.
 However, in both cases (backward and forward models), it is
 recommended that this eecid be retained until the connection
 terminates.  Since the eecid space is large enough, it is not
 necessary to release it as soon as possible.

5.6.1.2 The 'aalType' attribute

 When present, the 'aalType' attribute is used to indicate the ATM
 adaptation layer.  If this information is redundant with the 'm'
 line, it can be omitted.  The format of the 'aalType' media attribute
 line is as follows:
    a=aalType: <aalType>

Kumar & Mostafa Standards Track [Page 31] RFC 3108 ATM SDP May 2001

 Here, <aalType> can take on the following string values: "AAL1",
 "AAL1_SDT", "AAL1_UDT", "AAL2", "AAL3/4", "AAL5" and
 "USER_DEFINED_AAL".  Note that "AAL3/4" and "USER DEFINED AAL" are
 not addressed in this document.

5.6.1.3 The 'capability' attribute

 When present, the 'capability' attribute indicates the ATM Transfer
 Capability described in ITU I.371 [28], equivalent to the ATM Service
 Category described in the UNI 4.1 Traffic Management specification
 [6].
 The 'capability' media attribute line is structured in one of the
 following ways:
    a=capability:<asc> <subtype>
    a=capability:<atc> <subtype>
 Possible values of the <asc> are enumerated below:
    "CBR", "nrt-VBR", "rt-VBR", "UBR", "ABR", "GFR"
 Possible values of the <atc> are enumerated below:
    "DBR","SBR","ABT/IT","ABT/DT","ABR"
 Some applications might use non-standard <atc> and <asc> values not
 listed above.  Equipment designers will need to agree on the meaning
 and implications of non-standard transfer capabilities / service
 capabilities.
 The <subtype> field essentially serves as a subscript to the <asc>
 and <atc> fields.  In general, it can take on any integer value, or
 the "-" value indicating that it does not apply or that the
 underlying data is to be known by other means, such as provisioning.
 For an <asc> value of CBR and an <atc> value of DBR, the <subtype>
 field can be assigned values from Table 4-6 of ITU Q.2931 [15].
 These are:

Kumar & Mostafa Standards Track [Page 32] RFC 3108 ATM SDP May 2001

    <asc>/<atc>    <subtype>   Meaning
     "CBR"/"DBR"      1        Voiceband signal transport
                               (ITU G.711, G.722, I.363)
     "CBR"/"DBR"      2        Circuit transport (ITU I.363)
     "CBR"/"DBR"      4        High-quality audio signal transport
                               (ITU I.363)
     "CBR"/"DBR"      5        Video signal transport (ITU I.363)
 Note that [15] does not define a <subtype> value of 3.
 For other values of the <asc> and <atc> parameters, the following
 values can be assigned to the <subtype> field, based on [6] and [28].
       <asc>/<atc>              <subtype>     Meaning
         nrt-VBR                   1          nrt-VBR.1
         nrt-VBR                   2          nrt-VBR.2
         nrt-VBR                   3          nrt-VBR.3
         rt-VBR                    1          rt-VBR.1
         rt-VBR                    2          rt-VBR.2
         rt-VBR                    3          rt-VBR.3
         UBR                       1          UBR.1
         UBR                       2          UBR.2
         GFR                       1          GFR.1
         GFR                       2          GRR.2
         SBR                       1          SBR1
         SBR                       2          SBR2
         SBR                       3          SBR3
 It is beyond the scope of this specification to examine the
 equivalence of some of the ATMF and ITU definitions.  These need to
 be recognized from the ATMF and ITU source specifications and
 exploited, as much as possible, to simplify ATM node design.
 When the bearer connection is a single AAL2 CID connection within a
 multiplexed AAL2 VC, the 'capability' attribute does not apply.

5.6.1.4 The 'qosClass' attribute

 When present, the 'qosClass' attribute indicates the QoS class
 specified in ITU I.2965.1 [34].
 The 'qosClass' media attribute line is structured as follows:
    a=qosClass:<qosClass>
 Here, <qosClass> is an integer in the range 0 - 5.

Kumar & Mostafa Standards Track [Page 33] RFC 3108 ATM SDP May 2001

    <qosClass>      Meaning
         0            Default QoS
         1            Stringent
         2            Tolerant
         3            Bi-level
         4            Unbounded
         5            Stringent bi-level

5.6.1.5 The 'bcob' attribute

 When present, the 'bcob' attribute represents the broadband
 connection oriented bearer class defined in [5], [15] and [33].  It
 can also be used to indicate whether end-to-end timing is required.
 The 'bcob' media attribute line is structured as follows:
    a=bcob:<bcob> <eetim>
 Here, <bcob> is the decimal or hex representation of a 5-bit field.
 The following values are currently defined:
       <bcob>          Meaning
       0x01             BCOB-A
       0x03             BCOB-C
       0x05             Frame relaying bearer service
       0x10             BCOB-X
       0x18             BCOB-VP (transparent VP service)
 The <eetim> parameter can be assigned a value of "on" or "off"
 depending on whether end-to-end timing is required or not (Table 4-8
 of [15]).
 Either of these parameters can be left unspecified by setting it to a
 "-".  A 'bcob' media attribute line with all parameters set to "-"
 carries no information and should be omitted.

5.6.1.6 The 'stc' attribute

 When present, the 'stc' attribute represents susceptibility to
 clipping.  The 'stc' media attribute line is structured as follows:
    a=stc:<stc>
 Here, <stc> is the decimal equivalent of a 2-bit field.  Currently,
 all values are unused and reserved with the following exceptions:

Kumar & Mostafa Standards Track [Page 34] RFC 3108 ATM SDP May 2001

    <stc> value      Binary Equivalent     Meaning
         0                   00            Not susceptible to clipping
         1                   01            Susceptible to clipping

5.6.1.7 The 'upcc' attribute

 When present, the 'upcc' attribute represents the user plane
 connection configuration.  The 'upcc' media attribute line is
 structured as follows:
    a=upcc:<upcc>
 Here, <upcc> is the decimal equivalent of a 2-bit field.  Currently,
 all values are unused and reserved with the following exceptions:
    <upcc> value     Binary Equivalent    Meaning
         0                 00             Point to point
         1                 01             Point to multipoint

5.6.1.8 The 'atmQOSparms' attribute

 When present, the 'atmQOSparms' attribute is used to describe certain
 key ATM QoS parameters.
 The 'atmQOSparms' media attribute line is structured as follows:
 a=atmQOSparms:<directionFlag><cdvType><acdv><ccdv><eetd><cmtd><aclr>
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and
 backward).  Conventions for the forward and backward directions are
 per section 2.3.
 The <cdvType> parameter can take on the string values of "PP" and
 "2P".  These refer to the peak-to-peak and two-point CDV as defined
 in UNI 4.0 [5] and ITU Q.2965.2 [35] respectively.
 The CDV parameters, <acdv> and <ccdv>, refer to the acceptable and
 cumulative CDVs respectively.  These are expressed in units of
 microseconds and represented as the decimal equivalent of a 24-bit
 field.  These use the cell loss ratio, <aclr>, as the "alpha"
 quantiles defined in the ATMF TM 4.1 specification [6] and in ITU
 I.356 [47].

Kumar & Mostafa Standards Track [Page 35] RFC 3108 ATM SDP May 2001

 The transit delay parameters, <eetd> and <cmtd>, refer to the end-
 to-end and cumulative transit delays respectively in milliseconds.
 These are represented as the decimal equivalents of 16-bit fields.
 These parameters are defined in Q.2965.2 [35], UNI 4.0 [5] and Q.2931
 [15].
 The <aclr> parameter refers to forward and backward acceptable cell
 loss ratios.  This is the ratio between the number of cells lost and
 the number of cells transmitted.  It is expressed as the decimal
 equivalent of an 8-bit field.  This field expresses an order of
 magnitude n, where n is an integer in the range 1-15.  The Cell Loss
 Ratio takes on the value 10 raised to the power of minus n.
 The <directionFlag> is always specified.  Except for the
 <directionFlag>, the remaining parameters can be set to "-" to
 indicate that they are not specified, inapplicable or implied.
 However, there must be some specified parameters for the line to be
 useful in an SDP description.
 There can be several 'atmQOSparms' lines in an SDP description.
 An example use of these attributes for an rt-VBR, single-CID AAL2
 voice VC is:
    a=atmQOSparms:f PP  8125 3455 32000 -  11
    a=atmQOSparms:b PP  4675 2155 18000 -  12
 This implies a forward acceptable peak-to-peak CDV of 8.125 ms, a
 backward acceptable peak-to-peak CDV of 4.675 ms, forward cumulative
 peak-to-peak CDV of 3.455 ms, a backward cumulative peak-to-peak CDV
 of 2.155 ms, a forward end-to-end transit delay of 32 ms, a backward
 end-to-end transit delay of 18 ms, an unspecified forward cumulative
 transit delay, an unspecified backward cumulative transit delay, a
 forward cell loss ratio of 10 raised to minus 11 and a backward cell
 loss ratio of 10 to the minus 12.
 An example of specifying the same parameters for the forward and
 backward directions is:
    a=atmQOSparms:fb PP  8125 3455 32000 -  11
 This implies a forward and backward acceptable peak-to-peak CDV of
 8.125 ms, a forward and backward cumulative peak-to-peak CDV of 3.455
 ms, a forward and backward end-to-end transit delay of 32 ms, an
 unspecified cumulative transit delay in the forward and backward
 directions, and a cell loss ratio of 10 raised to minus 11 in the
 forward and backward directions.

Kumar & Mostafa Standards Track [Page 36] RFC 3108 ATM SDP May 2001

5.6.1.9 The 'atmTrfcDesc' attribute

 When present, the 'atmTrfcDesc' attribute is used to indicate ATM
 traffic descriptor parameters.  There can be several 'atmTrfcDesc'
 lines in an SDP description.
 The 'atmTrfcDesc' media attribute line is structured as follows:
    a=atmTrfcDesc:<directionFlag><clpLvl>
              <pcr><scr><mbs><cdvt><mcr><mfs><fd><te>
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and
 backward).  Conventions for the forward and backward directions are
 per section 2.3.
 The <directionFlag> is always specified.  Except for the
 <directionFlag>, the remaining parameters can be set to "-" to
 indicate that they are not specified, inapplicable or implied.
 However, there must be some specified parameters for the line to be
 useful in an SDP description.
 The <clpLvl> (CLP level) parameter indicates whether the rates and
 bursts described in these media attribute lines apply to CLP values
 of 0 or (0+1).  It can take on the following string values: "0",
 "0+1" and "-".  If rates and bursts for both <clpLvl> values are to
 be described, then it is necessary to use two separate media
 attribute lines for each direction in the same session descriptor.
 If the <clpLvl> parameter is set to "-", then it implies that the CLP
 parameter is known by other means such as default, MIB provisioning
 etc.
 The meaning, units and applicability of the remaining parameters are
 per [6] and [28]:
 PARAMETER      MEANING       UNITS         APPLICABILITY
 <pcr>          PCR           Cells/        CBR, rt-VBR, nrt-VBR,
                              second        ABR, UBR, GFR;
                                            CLP=0,0+1
 <scr>          SCR           Cells/        rt-VBR, nrt-VBR;
                              second        CLP=0,0+1
 <mbs>          MBS           Cells         rt-VBR, nrt-VBR,
                                            GFR;
                                            CLP=0,0+1

Kumar & Mostafa Standards Track [Page 37] RFC 3108 ATM SDP May 2001

 <cdvt>        CDVT           Microsec.     CBR, rt-VBR, nrt-VBR,
                                            ABR, UBR, GFR;
                                            CLP=0,0+1
 <mcr>         MCR            Cells/        ABR,GFR;
                              second        CLP=0+1
 <mfs>         MFS            Cells         GFR;
                                            CLP=0,0+1
 <fd>         Frame          "on"/"off"     CBR, rt-VBR, nrt-VBR,
              Discard                       ABR, UBR, GFR;
              Allowed                       CLP=0+1
 <te>         CLP            "on"/"off"     CBR, rt-VBR, nrt-VBR,
              tagging                       ABR, UBR, GFR;
              Enabled                       CLP=0
 <fd> indicates that frame discard is permitted.  It can take on the
 string values of "on" or "off".  Note that, in the GFR case, frame
 discard is always enabled.  Hence, this subparameter can be set to
 "-" in the case of GFR.  Since the <fd> parameter is independent of
 CLP, it is meaningful in the case when <clpLvl> = "0+1".  It should
 be set to "-" for the case when <clpLvl> = "0".
 <te> (tag enable) indicates that CLP tagging is allowed.  These can
 take on the string values of "on" or "off".  Since the <te> parameter
 applies only to cells with a CLP of 0, it is meaningful in the case
 when <clpLvl> = "0".  It should be set to "-" for the case when
 <clpLvl> = "0+1".
 An example use of these media attribute lines for an rt-VBR, single-
 CID AAL2 voice VC is:
    a=atmTrfcDesc:f 0+1 200   100  20   - - - on  -
    a=atmTrfcDesc:f 0   200   80   15   - - - -  off
    a=atmTrfcDesc:b 0+1 200   100  20   - - - on -
    a=atmTrfcDesc:b 0   200   80   15   - - - -  off
 This implies a forward and backward PCR of 200 cells per second all
 cells regardless of CLP, forward and backward PCR of 200 cells per
 second for cells with CLP=0, a forward and backward SCR of 100 cells
 per second for all cells regardless of CLP, a forward and backward
 SCR of 80 cells per second for cells with CLP=0, a forward and
 backward MBS of 20 cells for all cells regardless of CLP, a forward

Kumar & Mostafa Standards Track [Page 38] RFC 3108 ATM SDP May 2001

 and backward MBS of 15 cells for cells with CLP=0, an unspecified
 CDVT which can be known by other means, and an MCR and MFS which are
 unspecified because they are inapplicable.  Frame discard is enabled
 in both the forward and backward directions.  Tagging is not enabled
 in either direction.
 The <pcr>, <scr>, <mbs>, <cdvt>, <mcr> and <mfs> are represented as
 decimal integers, with range as defined in Section 6.  See section
 2.2 regarding the omission of leading zeros in decimal
 representations.

5.6.1.10 The 'abrParms' attribute

 When present, the 'abrParms' attribute is used to indicate the '
 additional' ABR parameters specified in the UNI 4.0 signaling
 specification [5].  There can be several 'abrParms' lines in an SDP
 description.
 The 'abrParms' media attribute line is structured as follows:
    a=abrParms:<directionFlag><nrm><trm><cdf><adtf>
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and
 backward).  Conventions for the forward and backward directions are
 per section 2.3.
 The <directionFlag> is always specified.  Except for the
 <directionFlag>, the remaining parameters can be set to "-" to
 indicate that they are not specified, inapplicable or implied.
 However, there must be some specified parameters for the line to be
 useful in an SDP description.
 These parameters are mapped into the ABR service parameters in [6] in
 the manner described below.  These parameters can be represented in
 SDP as decimal integers, with fractions permitted for some.  Details
 of the meaning, units and applicability of these parameters are in
 [5] and [6].
 In SDP, these parameters are represented as the decimal or hex
 equivalent of the binary fields mentioned below.

Kumar & Mostafa Standards Track [Page 39] RFC 3108 ATM SDP May 2001

+———–+———————————-+———————–+

PARAMETER MEANING FIELD SIZE

+———–+———————————-+———————–+

<nrm> Maximum number of cells per 3 bits
forward Resource Management cell

+———–+———————————-+———————–+

<trm> Maximum time between 3 bits
forward Resource Management cells

+———–+———————————-+———————–+

<cdf> Cutoff Decrease Factor 3 bits

+———–+———————————-+———————–+

<adtf> Allowed Cell Rate Decrease 10 bits
Time Factor

+———–+———————————-+———————–+

5.6.1.11 The 'abrSetup' attribute

 When present, the 'abrSetup' attribute is used to indicate the ABR
 parameters needed during call/connection establishment (Section
 10.1.2.2 of the UNI 4.0 signaling specification [5]).  This line is
 structured as follows:
 a=abrSetup:<ficr><bicr><ftbe><btbe><crmrtt><frif><brif><frdf><brdf>
 These parameters are defined as follows:

Kumar & Mostafa Standards Track [Page 40] RFC 3108 ATM SDP May 2001

+———–+———————————-+———————–+

PARAMETER MEANING REPRESENTATION

+———–+———————————-+———————–+

<ficr> Forward Initial Cell Rate Decimal equivalent
(Cells per second) of 24-bit field

+———–+———————————-+———————–+

<bicr> Backward Initial Cell Rate Decimal equivalent
(Cells per second) of 24-bit field

+———–+———————————-+———————–+

<ftbe> Forward transient buffer Decimal equivalent
exposure (Cells) of 24-bit field

+———–+———————————-+———————–+

<btbe> Backward transient buffer Decimal equivalent
exposure (Cells) of 24-bit field

+———–+———————————-+———————–+

<crmrtt> Cumulative RM round-trip time Decimal equivalent
(Microseconds) of 24-bit field

+———–+———————————-+———————–+

<frif> Forward rate increase factor Decimal integer
(used to derive cell count) 0 -15

+———–+———————————-+———————–+

<brif> Backward rate increase factor Decimal integer
(used to derive cell count) 0 -15

+———–+———————————-+———————–+

<frdf> Forward rate decrease factor Decimal integer
(used to derive cell count) 0 -15

+———–+———————————-+———————–+

<brdf> Backward rate decrease factor Decimal integer
(used to derive cell count) 0 -15

+———–+———————————-+———————–+

 See Section 2.3 for a definition of the terms 'forward' and
 'backward'.
 If any of these parameters in the 'abrSetup' media attribute line is
 not specified, is inapplicable or is implied, then it is set to h "-
 ".

5.6.1.12 The 'bearerType' attribute

 When present, the 'bearerType' attribute is used to indicate whether
 the underlying bearer is an ATM PVC/SPVC, an ATM SVC, or a subchannel
 within an existing ATM SVC/PVC/SPVC.  Additionally, for ATM SVCs and
 AAL2 CID connections, the 'bearerType' attribute can be used to
 indicate whether the media gateway initiates connection set-up via
 bearer signaling (Q.2931-based or Q.2630.1 based).  The format of the
 'bearerType' media attribute line is as follows:

Kumar & Mostafa Standards Track [Page 41] RFC 3108 ATM SDP May 2001

    a=bearerType: <bearerType> <localInitiation>
 The <bearerType> field can take on the following string values:
 "PVC", "SVC", "CID", with semantics as defined above.  Here, "PVC"
 includes both the PVC and SPVC cases.
 In the case when the underlying bearer is a PVC/SPVC, or a CID
 assigned by the MGC rather than through bearer signaling, the
 <localInitiation> flag can be omitted or set to "-".  In the case
 when bearer signaling is used, this flag can be omitted when it is
 known by default or by other means whether the media gateway
 initiates the connection set-up via bearer signaling.  Only when this
 is to be indicated explicitly that the <localInitiation> flag takes
 on the values of "on" or "off".  An "on" value indicates that the
 media gateway is responsible for initiating connection set-up via
 bearer signaling (SVC signaling or Q.2630.1 signaling), an "off"
 value indicates otherwise.

5.6.1.13 The 'lij' attribute

 When present, the 'lij' attribute is used to indicate the presence of
 a connection that uses the Leaf-initiated-join capability described
 in UNI 4.0 [5], and to optionally describe parameters associated with
 this capability.  The format of the 'lij' media attribute line is as
 follows:
    a=lij: <sci><lsn>
 The <sci> (screening indication) is a 4-bit field expressed as a
 decimal or hex integer.  It is defined in the UNI 4.0 signaling
 specification [5].  It is possible that the values of this field will
 be defined later by the ATMF and/or ITU.  Currently, all values are
 reserved with the exception of 0, which indicates a 'Network Join
 without Root Notification'.
 The <lsn> (leaf sequence number) is a 32-bit field expressed as a
 decimal or hex integer.  Per the UNI 4.0 signaling specification [5],
 it is used by a joining leaf to associate messages and responses
 during LIJ (leaf initiated join) procedures.
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.

Kumar & Mostafa Standards Track [Page 42] RFC 3108 ATM SDP May 2001

5.6.1.14 The 'anycast' attribute

 When present, the 'anycast' attribute line is used to indicate the
 applicability of the anycast function described in UNI 4.0 [5].
 Optional parameters to qualify this function are provided. The format
 of the 'anycast' attribute is:
    a=anycast: <atmGroupAddress> <cdStd> <conScpTyp> <conScpSel>
 The <atmGroupAddress> is per Annex 5 of UNI 4.0 [5].  Within an SDP
 descriptor, it can be represented in one of the formats (NSAP, E.164,
 GWID/ALIAS) described elsewhere in this document.
 The remaining subparameters mirror the connection scope selection
 information element in UNI 4.0 [5].  Their meaning and representation
 is as shown below:
 PARAMETER      MEANING                                 REPRESENTATION
 <cdStd>        Coding standard for the                 Decimal or hex
                connection scope selection IE           equivalent of
                Definition: UNI 4.0 [5]                 2 bits
 <conScpTyp>    Type of connection scope                Decimal or hex
                Definition: UNI 4.0 [5]                 equivalent of
                                                        4 bits
 <conScpSel>    Connection scope selection              Decimal or hex
                Definition: UNI 4.0 [5]                 equivalent of
                                                        8 bits
 Currently, all values of <cdStd> and <conScpTyp> are reserved with
 the exception of <cdStd> = 3 (ATMF coding standard) and <conScpTyp> =
 1 (connection scope type of 'organizational').
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.

5.6.1.15 The 'cache' attribute

 This attribute is used to enable SVC caching.  This attribute has the
 following format:
    a=cache:<cacheEnable><cacheTimer>

Kumar & Mostafa Standards Track [Page 43] RFC 3108 ATM SDP May 2001

 The <cacheEnable> flag indicates whether caching is enabled or not,
 corresponding to the string values of "on" and "off" respectively.
 The <cacheTimer> indicates the period of inactivity following which
 the SVC is to be released by sending an SVC release message into the
 network.  This is specified as the decimal or hex equivalent of a
 32-bit field, indicating the timeout in seconds.  As usual, leading
 zeros can be omitted.  For instance,
    a=cache:on 7200
 implies that the cached SVC is to be deleted if it is idle for 2
 hours.
 The <cacheTimer> can be set to "-" if it is inapplicable or implied.

5.6.1.16 The 'bearerSigIE' attribute

 ATM signaling standards provide 'escape mechanisms' to represent,
 signal and negotiate higher-layer parameters.  Examples are the B-HLI
 and B-LLI IEs specified in ITU Q.2931 [15], and the user-to-user
 information element described in ITU Q.2957 [48].
 The 'bearerSigIE'(bearer signaling information element) attribute is
 defined to allow a similar escape mechanism that can be used with
 these ATM SDP conventions.  The format of this media attribute line
 is as follows:
    a=bearerSigIE: <bearerSigIEType> <bearerSigIELng> <bearerSigIEVal>
 When an 'bearerSigIE' media attribute line is present, all its
 subparameters are mandatory.  The "0x" prefix is not used since these
 are always represented in hex.
 The <bearerSigIEType> is represented as exactly 2 hex digits.  It is
 the unique IE identifier as defined in the ITU Q-series standards.
 Leading zeros are not omitted.  Some pertinent values are 7E (User-
 user IE per ITU Q.2957 [48]), 5F (B-LLI IE) and 5D (B-HLI IE).  B-LLI
 and B-HLI, which stand for Broadband Low-layer Information and
 Broadband High-layer Information respectively, are defined in ITU
 Q.2931 [15].  Both of these refer to layers above the ATM adaptation
 layer.
 The <bearerSigIELng> consists of 1-4 hex digits.  It is the length of
 the information element in octets.  Leading zeros may be omitted.

Kumar & Mostafa Standards Track [Page 44] RFC 3108 ATM SDP May 2001

 The <bearerSigIEVal> is the value of the information element,
 represented as a hexadecimal bit map.  Although the size of this bit
 map is network/ service dependent, setting an upper bound of 256
 octets (512 hex digits) is adequate.  Since this a bit map, leading
 zeros should not be omitted. The number of hex digits in this bit map
 is even.

5.6.2 ATM Adaptation Layer (AAL) attributes

 The following is a summary list of the SDP media attributes that can
 be used to describe the ATM Adaptation Layer (AAL).  These are
 detailed in subsequent subsections.
  • The 'aalApp' attribute, which is used to point to the

controlling standard for an application layer above the ATM

       adaptation layer.
  • The 'cbrRate' attribute, which represents the CBR rate octet

defined in Table 4-6 of ITU Q.2931 [15].

  • The 'sbc' attribute, which denotes the subchannel count in the

case of n x 64 clear channel communication.

  • The 'clkrec' attribute, which indicates the clock recovery

method for AAL1 unstructured data transfer (UDT).

  • The 'fec' attribute, which indicates the use of forward error

correction.

  • The 'prtfl' attribute, which indicates indicate the fill level

of partially filled cells.

  • The 'structure' attribute, which is used to indicate the

presence or absence of AAL1 structured data transfer (SDT), and

       the size of the SDT blocks.
  • The 'cpsSDUsize' attribute, which is used to indicate the

maximum size of the CPCS SDU payload.

  • The 'aal2CPS' attribute, which is used to indicate that an AAL2

CPS sublayer as defined in ITU I.363.2 [13] is associated with

       the VCC referred to in the 'm' line.  Optionally, it can be
       used to indicate selected CPS options and parameter values for
       this VCC.
  • The 'aal2CPSSDUrate' attribute, which is used to place an upper

bound on the SDU bit rate for an AAL2 CID.

Kumar & Mostafa Standards Track [Page 45] RFC 3108 ATM SDP May 2001

  • The 'aal2sscs3661unassured' attribute, which is used to

indicate the presence of an AAL2 SSCS sublayer with unassured

       transmission as defined in ITU I.366.1 [12].  Optionally, it
       can be used to indicate selected options and parameter values
       for this SSCS.
  • The 'aal2sscs3661assured' attribute, which is used to indicate

the presence of an AAL2 SSCS sublayer with assured transmission

       as defined in ITU I.366.1 [12].  Optionally, it can be used to
       indicate selected options and parameter values for this SSCS.
  • The 'aal2sscs3662' attribute, which is used to indicate the

presence of an AAL2 SSCS sublayer as defined in ITU I.366.2.

       Optionally, it can be used to indicate selected options and
       parameter values for this SSCS.
  • The 'aal5sscop' attribute, which is used to indicate the

existence of an SSCOP protocol layer over an AAL5 CPS layer,

       and the parameters which pertain to this SSCOP layer.

5.6.2.1 The 'aalApp' attribute

 When present, the 'aalApp' attribute is used to  point to the
 controlling standard for an application layer above the ATM
 adaptation layer.  The format of the 'aalApp' media attribute line is
 as follows:
    a=aalApp: <appClass> <oui> <appId>
 If any of the subparameters, <appClass>, <oui> or <appId>, is meant
 to be left, unspecified, it is set to "-".  However, an 'aalApp'
 attribute line with all subparameters set to "-" carries no
 information and should be omitted.
 The <appClass>, or application class, field can take on the string
 values listed below.
 This list is not exhaustive.  An "X-" prefix should be used with
 <appClass> values not listed here.
   <appClass>            Meaning
   "itu_h323c"           Annex C of H.323 which specifies direct
                         RTP on AAL5 [45].
    "af83"               af-vtoa-0083.001, which specifies
                         variable size AAL5 PDUs with PCM voice
                         and a null SSCS [46].

Kumar & Mostafa Standards Track [Page 46] RFC 3108 ATM SDP May 2001

   "AAL5_SSCOP"          SSCOP as defined in ITU Q.2110 [43]
                         running over an AAL5 CPS [21].
                         No information is provided regarding
                         any layers above SSCOP such as Service
                         Specific Coordination Function  (SSCF)
                         layers.
 "itu_i3661_unassured"   SSCS with unassured transmission,
                         per ITU I.366.1 [12].
 "itu_i3661_assured"     SSCS with assured transmission,
                         per ITU I.366.1 [12].  This uses SSCOP [43].
    "itu_i3662"          SSCS per ITU I.366.2 [13].
    "itu_i3651"          Frame relay SSCS per ITU I.365.1 [39].
    "itu_i3652"          Service-specific coordination function,
                         as defined in ITU I.365.2, for Connection
                         Oriented Network Service (SSCF-CONS) [40].
                         This uses SSCOP [43].
    "itu_i3653"          Service-specific coordination function,
                         as defined in ITU I.365.3, for Connection
                         Oriented Transport Service (SSCF-COTS) [41].
                         This uses SSCOP [43].
    "itu_i3654"          HDLC Service-specific coordination function,
                         as defined in ITU I.365.4 [42].
    "FRF5"               Use of the FRF.5 frame relay standard [53],
                         which references ITU I.365.1 [39].
    "FRF8"               Use of the FRF.8.1 frame relay standard [54].
                         This implies a null SSCS and the mapping of
                         the frame relay header into the ATM header.
    "FRF11"              Use of the FRF.11 frame relay standard [55].
    "itu_h2221"          Use of the ITU standard H.222.1 for
                         audiovisual communication over AAL5 [51].
 The <oui>, or Organizationally Unique Identifier, refers to the
 organization responsible for defining the <appId>, or Application
 Identifier.  The <oui> is maintained by the IEEE.  One of its uses is
 in 802 MAC addresses.  It is a three-octet field represented as one
 to six hex digits.  Since this is always represented in hex, the "0x"
 prefix is not used.  Leading zeros may be omitted.

Kumar & Mostafa Standards Track [Page 47] RFC 3108 ATM SDP May 2001

 The <appId> subparameter refers to the application ID, a hex number
 consisting of up to 8 digits.  Leading zeros may be omitted.  The
 "0x" prefix is not used, since the representation is always
 hexadecimal.  Currently, the only organization that has defined
 application identifiers is the ATM forum.  These have been defined in
 the context of AAL2 ([44], [52], Section 5 of [61]).  Within SDP,
 these can be used with <appClass> = itu_i3662.  The <oui> value for
 the ATM forum is 0x00A03E.
 In the following example, the aalApp media attribute line is used to
 indicate 'Loop Emulation Service using CAS (POTS only) without the
 Emulated Loop Control Protocol (ELCP) [52].  The Application ID is
 defined by the ATM forum [61].  The SSCS used is per ITU I.366.2
 [13].
    a=aalApp:itu_i3662 A03E A
 If leading zeros are not dropped, this can be represented as:
    a=aalApp:itu_i3662 00A03E 0000000A
 Since application identifiers have been specified only in the context
 of the AAL2 SSCS defined in ITU I.366.2 [13],the <appClass> can be
 set to '-' without ambiguity.  The aalApp media attribute line can be
 reduced to:
    a=aalApp:- A03E A
 or
    a=aalApp:- 00A03E 0000000A

5.6.2.2 The 'cbrRate' attribute

 When present, the 'cbrRate' attribute is used to represent the CBR
 rate octet defined in Table 4-6 of ITU Q.2931 [15].  The format of
 this media attribute line is:
    a=cbrRate: <cbrRate>
 Here, <cbrRate> is represented as exactly two hex digits.  The "0x"
 prefix is omitted since this parameter is always represented in hex.
 Values currently defined by the ITU are:

Kumar & Mostafa Standards Track [Page 48] RFC 3108 ATM SDP May 2001

       +------------+-----------------------------------------------+
       |  VALUE     |             MEANING                           |
       |  (hex)     |                                               |
       +------------+-----------------------------------------------+
       |     01     |  64 kbps                                      |
       +------------+-----------------------------------------------+
       |     04     |  1544 kbps                                    |
       +------------+-----------------------------------------------+
       |     05     |  6312 kbps                                    |
       +------------+-----------------------------------------------+
       |     06     |  32064 kbps                                   |
       +------------+-----------------------------------------------+
       |     07     |  44736 kbps                                   |
       +------------+-----------------------------------------------+
       |     08     |  97728 kbps                                   |
       +------------+-----------------------------------------------+
       |     10     |  2048 kbps                                    |
       +------------+-----------------------------------------------+
       |     11     |  8448 kbps                                    |
       +------------+-----------------------------------------------+
       |     12     |  34368 kbps                                   |
       +------------+-----------------------------------------------+
       |     13     |  139264 kbps                                  |
       +------------+-----------------------------------------------+
       |     40     |  n x 64  kbps                                 |
       +------------+-----------------------------------------------+
       |     41     |  n x 8 kbps                                   |
       +------------+-----------------------------------------------+
 It is preferable that the cbrRate attribute be omitted rather than
 set to an unspecified value of "-", since it conveys no information
 in the latter case.

5.6.2.3 The 'sbc' attribute

 The 'sbc' media attribute line denotes the subchannel count and is
 meaningful only in the case of n x 64 clear channel communication.  A
 clear n x 64 channel can use AAL1 (ATM forum af-vtoa-78) or AAL2
 adaptation (ITU I.366.2).  Although no such standard definition
 exists, it is also possible to use AAL5 for this purpose.  An n x 64
 clear channel is represented by the encoding names of "X-CCD" and
 "X-CCD-CAS" in Table 2.
 The format of the 'sbc' media attribute line is as follows:
    a=sbc:<sbc>

Kumar & Mostafa Standards Track [Page 49] RFC 3108 ATM SDP May 2001

 Here, <sbc> can be expressed as a decimal or hex integer.  This
 attribute indicates the number of DS0s in a T1 or E1 frame that are
 aggregated for transmitting clear channel data.  For T1-based
 applications, it can take on integral values in the inclusive range
 [1...24].  For E1-based applications, it can take on integral values
 in the inclusive range [1...31].  When omitted, other means are to be
 used to determine the subchannel count.
 Use of the 'sbc' attribute provides a direct way to indicate the
 number of 64 kbps subchannels bundled into an n x 64 clear channel.
 An alternate mechanism to indicate this exists within the SDP
 bandwidth information, or 'b', line [1].  In this case, instead of
 specifying the number of subchannels, the aggregate bandwidth in kbps
 is specified.  The syntax of the 'b' line, copied verbatim from [1],
 is as follows:
    b=<modifier>:<bandwidth-value>
 In the case of n x 64 clear channels, the <modifier> is assigned a
 text string value of "AS", indicating that the 'b' line is
 application-specific.  The <bandwidth-value> parameter, which is a
 decimal number indicating the bandwidth in kbps, is limited to one of
 the following values in the n x 64 clear channel application context:
    64, 128, 192, 256, 320, 384, 448, 512, 576, 640, 704, 768, 832,
    896, 960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1600,
    1664, 1728, 1792, 1856, 1920, 1984
 Thus, for n x 64 circuit mode data service,
    a=sbc:6
 is equivalent to
    b=AS:384
 The media attribute line
    a=sbc:2
 is equivalent to
    b=AS:128

Kumar & Mostafa Standards Track [Page 50] RFC 3108 ATM SDP May 2001

5.6.2.4 The 'clkrec' attribute

 When present, the 'clkrec' attribute is used to indicate the clock
 recovery method.  This attribute is meaningful in the case of AAL1
 unstructured data transfer (UDT).  The format of the 'clkrec' media
 attribute line is as follows:
    a=clkrec:<clkrec>
 The <clkrec> field can take on the following string values: "NULL",
 "SRTS" or "ADAPTIVE".  SRTS and adaptive clock recovery are defined
 in ITU I.363.1 [10].  "NULL" indicates that the stream (e.g., T1/E1)
 encapsulated in ATM is synchronous to the ATM network or is retimed,
 before AAL1 encapsulation, via slip buffers.

5.6.2.5 The 'fec' attribute

 When present, the 'fec' attribute is used to indicate the use of
 forward error correction.  Currently, there exists a forward error
 correction method defined for AAL1 in ITU I.363.1 [10].  The format
 of the 'fec' media attribute line is as follows:
    a=fec:<fecEnable>
 The <fecEnable> flag indicates the presence of absence of Forward
 Error Correction.  It can take on the string values of "NULL",
 "LOSS_SENSITIVE" and "DELAY_SENSITIVE".  An "NULL" value implies
 disabling this capability.  FEC can be enabled differently for
 delay-sensitive and loss-sensitive connections.

5.6.2.6 The 'prtfl' attribute

 When present, the 'prtfl' attribute is used to indicate the fill
 level of cells.  When this attribute is absent, then other means
 (such as provisionable defaults) are used to determine the presence
 and level of partial fill.
 This attribute indicates the number of non-pad payload octets, not
 including any AAL SAR or convergence sublayer octets.  For example,
 in some AAL1 applications that use partially filled cells with
 padding at the end, this attribute indicates the number of leading
 payload octets not including any AAL overhead.
 The format of the 'prtfl' media attribute line is as follows:
    a=prtfl:<partialFill>
 Here, <partialFill> can be expressed as a decimal or a hex integer.

Kumar & Mostafa Standards Track [Page 51] RFC 3108 ATM SDP May 2001

 In general, permitted values are integers in the range 1 - 48
 inclusive.  However, this upper bound is different for different
 adaptations since the AAL overhead, if any, is different.  If the
 specified partial fill is greater than or equal to the maximum fill,
 then complete fill is used.  Using a 'partial' fill of 48 always
 disables partial fill.
 In the AAL1 context, this media attribute line applies uniformly to
 both P and non-P cells.  In AAL1 applications that do not distinguish
 between P and non-P cells, a value of 47 indicates complete fill
 (i.e., the absence of partial fill).  In AAL1 applications that
 distinguish between P and non-P cells, a value of 46 indicates no
 padding in P-cells and a padding of one in non-P cells.
 If partial fill is enabled (i.e there is padding in at least some
 cells), then AAL1 structures must not be split across cell
 boundaries.  These shall fit in any cell.  Hence, their size shall be
 less than or equal to the partial fill size.  Further, the partial
 fill size is preferably an integer multiple of the structure size.
 If not, then the partial fill size stated in the SDP description
 shall be truncated to an integer multiple (e.g., a partial fill size
 of 40 is truncated to 36 to support six 6 x 64 channels).

5.6.2.7 The 'structure' attribute

 This attribute applies to AAL1 connections only.  When present, the '
 structure' attribute is used to indicate the presence or absence of
 structured data transfer (SDT), and the size in octets of the SDT
 blocks.  The format of the 'structure' media attribute line is as
 follows:
    a=structure: <structureEnable> <blksz>
 where the <structureEnable> flag indicates the presence of absence of
 SDT.  It can take on the values of "on" or "off".  An "on" value
 implies AAL1 structured data transfer (SDT), while an "off" value
 implies AAL1 unstructured data transfer (UDT).
 The block size field, <blksz>, is an optional 16-bit field [15] that
 can be represented in decimal or hex.  It is set to a "-" when not
 applicable, as in the case of unstructured data transfer (UDT).  For
 SDT, it can be set to a "-" when <blksz> is known by other means.
 For instance, af-vtoa-78 [7] fixes the structure size for n x 64
 service, with or without CAS.  The theoretical maximum value of
 <blksz> is 65,535, although most services use much less.

Kumar & Mostafa Standards Track [Page 52] RFC 3108 ATM SDP May 2001

5.6.2.8 The 'cpsSDUsize' attribute

 When present, the 'cpsSDUsize' attribute is used to indicate the
 maximum size of the CPCS SDU payload.  There can be several '
 cpsSDUsize' lines in an SDP description.
 The format of this media attribute line is as follows:
    a=cpsSDUsize:<directionFlag><cpcs>
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and
 backward).  Conventions for the forward and backward directions are
 per section 2.3.
 The <cpcs> fields is a 16-bit integer that can be represented in
 decimal or in hex.  The meaning and values of these fields are as
 follows:
 Application    Field      Meaning                         Values
 AAL5           <cpcs>    Maximum CPCS-SDU size           1- 65,535
 AAL2           <cpcs>    Maximum CPCS-SDU size           45 or 64

5.6.2.9 The 'aal2CPS' attribute

 When present, the 'aal2CPS' attribute is used to describe parameters
 associated with the AAL2 CPS layer.
 The format of the 'aal2CPS' media attribute line is as follows:
 a=aal2CPS:<cidLowerLimit><cidUpperLimit><timerCU> <simplifiedCPS>
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.
 The <cidLowerLimit> and <cidUpperLimit> can be assigned integer
 values between 8 and 255 [11], with the limitation that
 <cidUpperLimit> be greater than or equal to <cidLowerLimit>.  For
 instance, for POTS applications based on [52], <cidLowerLimit> and
 <cidUpperLimit> can have values of 16 and 223 respectively.
 The <timerCU> integer represents the "combined use" timerCU defined
 in ITU I.363.2.  This timer is represented as an integer number of
 microseconds.  It is represented as the decimal integer equivalent of
 32 bits.

Kumar & Mostafa Standards Track [Page 53] RFC 3108 ATM SDP May 2001

 The <simplifiedCPS> parameter can be assigned the values "on" or
 "off".  When it is "on", the AAL2 CPS simplification described in
 [52] is adopted.  Under this simplification, each ATM cell contains
 exactly on AAL2 packet.  If necessary, octets at the end of the cell
 are padded with zeros.  Since the <timerCU> value in this context is
 always 0, it can be set to "-".

5.6.2.10 The 'aal2CPSSDUrate' attribute

 When present, the 'aal2CPSSDUrate' attribute is used to place an
 upper bound on the SDU bit rate for an AAL2 CID.  This is useful for
 limiting the bandwidth used by a CID, specially if the CID is used
 for frame mode data defined in [13], or with the SSSAR defined in
 [12].  The format of this media attribute line is as follows:
    a=aal2CPSSDUrate: <fSDUrate><bSDUrate>
 The fSDUrate and bSDUrate are the maximum forward and backward SDU
 rates in bits/second.  These are represented as decimal integers,
 with range as defined in Section 6.  If any of these parameters in
 these media attribute lines is not specified, is inapplicable or is
 implied, then it is set to "-".

5.6.2.11 The 'aal2sscs3661unassured' attribute

 When present, the 'aal2sscs3661unassured' attribute is used to
 indicate the options that pertain to the unassured transmission SSCS
 defined in ITU I.366.1 [12].  This SSCS can be selected via the
 aalApp attribute defined below, or by virtue of the presence of the '
 aal2sscs3661unassured' attribute.  The format of this media attribute
 line is as follows:
    a=aal2sscs3661unassured: <ted> <rastimer> <fsssar> <bsssar>
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.
 The <ted> flag indicates the presence or absence of transmission
 error detection as defined in I.366.1.  It can be assigned the values
 of "on" or "off".  An "on" value indicates presence of the
 capability.
 The <rastimer> subparameter indicates the SSSAR reassembly timer in
 microseconds.  It is represented as the decimal equivalent of 32
 bits.

Kumar & Mostafa Standards Track [Page 54] RFC 3108 ATM SDP May 2001

 The <fsssar> and <bsssar> fields are 24-bit integers that can be
 represented in decimal or in hex.  The meaning and values of the
 <fsssar> and <bsssar> fields are as follows:
 Field      Meaning                         Values
 <fsssar>   Maximum SSSAR-SDU size           1- 65,568
            forward direction
 <bsssar>   Maximum SSSAR-SDU size           1- 65,568
            backward direction
 If present, the SSTED (Service-Specific Transmission Error Detection)
 sublayer is above the SSSAR (Service-Specific Segmentation and
 Reassembly) sublayer [12].  Since the maximum size of the SSTED-SDUs
 can be derived from the maximum SSSAR-SDU size, it need not be
 specified separately.

5.6.2.12 The 'aal2sscs3661assured' attribute

 When present, the 'aal2sscs3661assured' attribute is used to indicate
 the options that pertain to the assured transmission SSCS defined in
 ITU I.366.1 [12] on the basis of ITU Q.2110 [43].  This SSCS can be
 selected via the aalApp attribute defined below, or by virtue of the
 presence of the 'aal2sscs3661assured' attribute.  The format of this
 media attribute line is as follows:
    a=aal2sscs3661assured: <rastimer> <fsssar> <bsssar> <fsscopsdu>
                           <bsscopsdu><fsscopuu> <bsscopuu>
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.
 The <rastimer> subparameter indicates the SSSAR reassembly timer in
 microseconds.  It is represented as the decimal equivalent of 32
 bits.
 The <fsssar> and <bsssar> fields are 24-bit integers that can be
 represented in decimal or in hex.  The <fsscopsdu>, <bsscopsdu>,
 <fsscopuu> and <bsscopuu> fields are 16-bit integers that can be
 represented in decimal or in hex.  The meaning and values of these
 fields is as follows:
 Field       Meaning                          Values
 <fsssar>    Maximum SSSAR-SDU size           1- 65,568
             forward direction

Kumar & Mostafa Standards Track [Page 55] RFC 3108 ATM SDP May 2001

 <bsssar>    Maximum SSSAR-SDU size           1- 65,568
             backward direction
 <fsscopsdu> Maximum SSCOP-SDU size           1- 65,528
             forward direction
 <bsscopsdu> Maximum SSCOP-SDU size           1- 65,528
             backward direction
 <fsscopuu>  Maximum SSCOP-UU field           1- 65,524
             size, forward direction
 <bsscopuu>  Maximum SSCOP-UU field           1- 65,524
             size, backward direction
 The SSTED (Service-Specific Transmission Error Detection) sublayer is
 above the SSSAR (Service-Specific Segmentation and Reassembly)
 sublayer [12].  The SSADT (Service-Specific Assured Data Transfer)
 sublayer is above the SSTED sublayer.  Since the maximum size of the
 SSTED-SDUs and SSADT-SDUs can be derived from the maximum SSSAR-SDU
 size, they need not be specified separately.
 The SSCOP protocol defined in [43] is used by the Assured Data
 Transfer service defined in [12].  In the context of the ITU I.366.1
 SSCS, it is possible to use the 'aal2sscs3661assured' attribute to
 limit the maximum sizes of the SSCOP SDUs and UU (user-to-user)
 fields in either direction.  Note that it is necessary for the
 parameters on the 'aal2sscs3661assured' media attribute line to be
 consistent with each other.

5.6.2.13 The 'aal2sscs3662' attribute

 When present, the 'aal2sscs3662' attribute is used to indicate the
 options that pertain to the SSCS defined in ITU I.366.2 [13].  This
 SSCS can be selected via the aalApp attribute defined below, or by
 the presence of the 'aal2sscs3662' attribute.
 The format of this media attribute line is as follows:
    a=aal2sscs3662: <sap> <circuitMode> <frameMode> <faxDemod>
                    <cas> <dtmf> <mfall> <mfr1> <mfr2>
                    <PCMencoding> <fmaxFrame> <bmaxFrame>
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.  Additionally, the values of these
 fields need to be consistent with each other.  Inconsistencies should
 be flagged as errors.

Kumar & Mostafa Standards Track [Page 56] RFC 3108 ATM SDP May 2001

 The <sap> field can take on the following string values: "AUDIO" and
 "MULTIRATE".  These correspond to the audio and multirate Service
 Access Points (SAPs) defined in ITU I.366.2.
 For the multirate SAP, the following parameters on the aal2sscs3662
 attribute line do not apply: <faxDemod>,<cas>, <dtmf>, <mfall>,
 <mfr1>,  <mfr2> and <PCMencoding>.  These are set to "-" for the
 multirate SAP.
 The <circuitMode> flag indicates whether the transport of circuit
 mode data is enabled or disabled, corresponding to the string values
 of "on" and "off" respectively.  For the multirate SAP, it cannot
 have a value of "off".  For the audio SAP, it can be assigned a value
 of "on", "off" or "-".  Note that the <sbc> attribute, defined
 elsewhere in this document, can be used to specify the number of 64
 kbps subchannels bundled into a circuit mode data channel.
 The <frameMode> flag indicates whether the transport of frame mode
 data is enabled or disabled, corresponding to the string values of
 "on" and "off" respectively.
 The <faxDemod> flag indicates whether facsimile demodulation and
 remodulation are enabled or disabled, corresponding to the string
 values of "on" and "off" respectively.
 The <cas> flag indicates whether the transport of Channel Associated
 Signaling (CAS) bits in AAL2 type 3 packets is enabled or disabled,
 corresponding to the string values of "on" and "off" respectively.
 The <dtmf> flag indicates whether the transport of DTMF dialled
 digits in AAL2 type 3 packets is enabled or disabled, corresponding
 to the string values of "on" and "off" respectively.
 The <mfall> flag indicates whether the transport of MF dialled digits
 in AAL2 type 3 packets is enabled or disabled, corresponding to the
 string values of "on" and "off" respectively.  This flag enables MF
 dialled digits in a generic manner, without specifying type (e.g.,
 R1, R2 etc.).
 The <mfr1> flag indicates whether the transport, in AAL2 type 3
 packets, of MF dialled digits for signaling system R1 is enabled or
 disabled, corresponding to the string values of "on" and "off"
 respectively.
 The <mfr2> flag indicates whether the transport, in AAL2 type 3
 packets, of MF dialled digits for signaling system R2 is enabled or
 disabled, corresponding to the string values of "on" and "off"
 respectively.

Kumar & Mostafa Standards Track [Page 57] RFC 3108 ATM SDP May 2001

 The <PCMencoding> field indicates whether PCM encoding, if used, is
 based on the A-law or the Mu-law.  This can be used to qualify the '
 generic PCM' codec stated in some of the AAL2 profiles.  The
 <PCMencoding> field can take on the string values of "PCMA" and
 "PCMU".
 The <fmaxFrame> and <bmaxFrame> fields are 16-bit integers that can
 be represented in decimal or in hex.  The meaning and values of the
 <fmaxFrame> and <bmaxFrame> fields are as follows:
 Field         Meaning                         Values
 <fmaxFrame>   Maximum length of a             1- 65,535
               frame mode data unit,
               forward direction
 <bmaxFrame>   Maximum length of a             1- 65,535
               frame mode data unit,
               backward direction

5.6.2.14 The 'aal5sscop' attribute

 When present, the 'aal5sscop' attribute is used to indicate the
 existence of an SSCOP [43] protocol layer over an AAL5 CPS layer
 [21], and the parameters which pertain to this SSCOP layer.  SSCOP
 over AAL5 can also be selected via the aalApp attribute defined
 below.  The format of the 'aal5sscop' media attribute line is as
 follows:
    a=aal5sscop: <fsscopsdu> <bsscopsdu> <fsscopuu> <bsscopuu>
 Each of these fields can be set to a "-" when the intention is to not
 specify them in an SDP descriptor.
 The representation, meaning and values of the <fsscopsdu>,
 <bsscopsdu>, <fsscopuu> and <bsscopuu> fields are identical to those
 for the 'aal2sscs3661assured' media attribute line (Section
 5.6.2.12).  Note that it is necessary for the parameters on the '
 aal5sscop' media attribute line to be consistent with each other.

5.6.3 Service attributes

 The following is a summary list of the SDP media attributes that can
 be used to describe the services that use the ATM Adaptation Layer
 (AAL).  These attributes are detailed in subsequent subsections.
  • The 'atmmap' attribute. In the AAL1 and AAL5 contexts, this is

used to dynamically map payload types into codec strings.

Kumar & Mostafa Standards Track [Page 58] RFC 3108 ATM SDP May 2001

  • The 'silenceSupp' attribute, used to indicate the use of of

voice activity detection for silence suppression, and to

       optionally parameterize the silence suppression function.
  • The 'ecan' attribute, used to indicate the use of of echo

cancellation, and to parameterize the this function.

  • The 'gc' attribute, used to indicate the use of of gain

control, and to parameterize the this function.

  • The 'profileDesc' attribute, which can be used to describe AAL2

profiles. Although any AAL2 profile can be so described, this

       attribute is useful for describing, at connection establishment
       time, custom profiles that might not be known to the far end.
       This attribute applies in the AAL2 context only.
  • The 'vsel' attribute, which indicates a prioritized list of 3-

tuples for voice service. Each 3-tuple indicates a codec, an

       optional packet length and an optional packetization period.
       This complements the 'm' line information and should be
       consistent with it.
  • The 'dsel' attribute, which indicates a prioritized list of 3-

tuples for voiceband data service. Each 3-tuple indicates a

       codec, an optional packet length and an optional packetization
       period.  This complements the 'm' line information and should
       be consistent with it.
  • The 'fsel' attribute, which indicates a prioritized list of 3-

tuples for facsimile service. Each 3-tuple indicates a codec,

       an optional packet length and an optional packetization period.
       This complements the 'm' line information and should be
       consistent with it.
  • The 'onewaySel' attribute, which indicates a prioritized list

of 3-tuples for one direction of an asymmetric connection.

       Each 3-tuple indicates a codec, an optional packet length and
       an optional packetization period.  This complements the 'm'
       line information and should be consistent with it.
  • The 'codecconfig' attribute, which is used to represent the

contents of the single codec information element (IE) defined

       in ITU Q.765.5 [57].
  • The 'isup_usi' attribute which is used to represent the bearer

capability information element defined in Section 4.5.5 of ITU

       Q.931 [59], and reiterated as the user service information
       element (IE) in Section 3.57  of ITU Q.763 [60].

Kumar & Mostafa Standards Track [Page 59] RFC 3108 ATM SDP May 2001

  • The 'uiLayer1_Prot' attribute, which is used to represent the '

User Information Layer 1 protocol' field within the bearer

       capability information element defined in Section 4.5.5 of ITU
       Q.931 [59].

5.6.3.1 The 'atmmap' attribute

 The 'atmmap' attribute is defined on the basis of the 'rtpmap'
 attribute used in RFC 2327.
    a=atmmap:<payloadType> <encodingName>
 The 'atmmap' attribute is used to dynamically map encoding names into
 payload types.  This is necessary for those encoding names which have
 not been assigned a static payload type through IANA [31].  Payload
 types and encoding techniques that have been registered with IANA for
 RTP are retained for AAL1 and AAL5.
 The range of statically defined payload types is in the range 0-95.
 All static assignments of payload types to codecs are listed in [31].
 The range of payload types defined dynamically via the 'atmmap'
 attribute is 96-127.
 In addition to reiterating the payload types and encoding names in
 [31], Table 2 defines non-standard encoding names (with "X-"
 prefixes).  Note that [31], rather than Table 2, is the authoritative
 list of standard codec names and payload types in the ATM context.
             Table 2: Encoding Names and Payload Types
    |---------------------|--------------|---------------------------|
    | Encoding Technique  | Encoding Name|    Payload type           |
    |---------------------|--------------|---------------------------|
    | PCM - Mu law        | "PCMU"       |    0 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | 32 kbps ADPCM       | "G726-32"    |    2 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    |Dual rate 5.3/6.3kbps| "G723"       |    4 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | PCM- A law          | "PCMA"       |    8 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | 7 KHz audio coding  | "G722"       |    9 (Statically Mapped)  |
    | within 64 kbps      |              |                           |
    |---------------------|--------------|---------------------------|
    | LD-CELP             | "G728"       |    15 (Statically Mapped) |
    |---------------------|--------------|---------------------------|
    | CS-ACELP            | "G729"       |    18 (Statically Mapped) |
    |(normal/low-complexity)             |                           |

Kumar & Mostafa Standards Track [Page 60] RFC 3108 ATM SDP May 2001

    |---------------------|--------------|---------------------------|
    | Low-complexity      | "X-G729a"    |    None, map dynamically  |
    | CS-ACELP            |              |                           |
    |---------------------|--------------|---------------------------|
    |Normal               | "X-G729b"    |    None, map dynamically  |
    |CS-ACELP w/ ITU      |              |                           |
    |defined silence      |              |                           |
    |suppression          |              |                           |
    +---------------------+--------------+---------------------------+
    |Low-complexity       | "X-G729ab"   |    None, map dynamically  |
    |CS-ACELP w/ ITU      |              |                           |
    |defined silence      |              |                           |
    |suppression          |              |                           |
    |---------------------|--------------|---------------------------|
    | 16 kbps ADPCM       | "X-G726-16"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    | 24 kbps ADPCM       | "X-G726-24"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    | 40 kbps ADPCM       | "X-G726-40"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    | Dual rate 5.3/6.3   |"X-G7231-H"   |    None, map dynamically  |
    | kbps - high rate    |              |                           |
    |---------------------|--------------|---------------------------|
    | Dual rate 5.3/6.3   |"X-G7231-L"   |   None, map dynamically   |
    | kbps - low rate     |              |                           |
    |---------------------|--------------|---------------------------|
    | Dual rate 5.3/6.3   |"X-G7231a-H"  |   None, map dynamically   |
    | kbps - high rate w/ |              |                           |
    | ITU-defined silence |              |                           |
    | suppression         |              |                           |
    |----------------------------------------------------------------|
    +---------------------+--------------+---------------------------+
    | Dual rate 5.3/6.3   |"X-G7231a-L"  |   None, map dynamically   |
    | kbps - high rate w/ |              |                           |
    | ITU-defined silence |              |                           |
    | suppression         |              |                           |
    |---------------------|--------------|---------------------------|
    | 16 kbps EADPCM      | "X-G727-16"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    | 24 kbps EADPCM      | "X-G727-24"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    | 32 kbps EADPCM      | "X-G727-32"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    |n x 64 kbps Clear    | "X-CCD"      |    None, map dynamically  |
    |Channel without CAS  |              |                           |
    |per af-vtoa-78 [7]   |              |                           |
    |---------------------|--------------|---------------------------|

Kumar & Mostafa Standards Track [Page 61] RFC 3108 ATM SDP May 2001

    |n x 64 kbps Clear    | "X-CCD-CAS"  |    None, map dynamically  |
    |Channel with CAS     |              |                           |
    |per af-vtoa-78 [7]   |              |                           |
    |---------------------|--------------|---------------------------|
    |GSM Full Rate        | "GSM"        |    3 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    |GSM Half Rate        |    "GSM-HR"  |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    |GSM-Enhanced Full Rate    "GSM-EFR" |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    |GSM-Enhanced Half Rate  "GSM-EHR"   |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    |Group 3 fax demod.   | "X-FXDMOD-3" |    None, map dynamically  |
    |---------------------|--------------|---------------------------|
    | Federal Standard    |    "1016"    |   1 (Statically Mapped)   |
    | FED-STD 1016 CELP   |              |                           |
    |---------------------|--------------|---------------------------|
    | DVI4, 8 KHz [3]     |    "DVI4"    |   5 (Statically Mapped)   |
    |---------------------|--------------|---------------------------|
    | DVI4, 16 KHz [3]    |    "DVI4"    |   6 (Statically Mapped)   |
    |---------------------|--------------|---------------------------|
    | LPC [3], Linear     |    "LPC"     |   7 (Statically Mapped)   |
    | Predictive Coding   |              |                           |
    |---------------------|--------------|---------------------------|
    | L16 [3], Sixteen    |    "L16"     |   10 (Statically Mapped)  |
    | Bit Linear PCM,     |              |                           |
    | Double channel      |              |                           |
    |---------------------|--------------|---------------------------|
    | L16 [3], Sixteen    |    "L16"     |   11 (Statically Mapped)  |
    | Bit Linear PCM,     |              |                           |
    | Single channel      |              |                           |
    |---------------------|--------------|---------------------------|
    | QCELP [3]           |    "QCELP"   |   12 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | MPEG1/MPEG2 audio   |    "MPA"     |   14 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    +---------------------+--------------+---------------------------+
    | DVI4, 11.025 KHz[3] |    "DVI4"    |   16 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | DVI4, 22.05 KHz [3] |    "DVI4"    |   17 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | MPEG1/MPEG2 video   |    "MPV"     |   32 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | MPEG 2 audio/video  |    "MP2T"    |   33 (Statically Mapped)  |
    | transport stream    |              |                           |
    |---------------------|--------------|---------------------------|
    | ITU H.261 video     |    "H261"    |   31 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|

Kumar & Mostafa Standards Track [Page 62] RFC 3108 ATM SDP May 2001

    | ITU H.263 video     |    "H263"    |   33 (Statically Mapped)  |
    |---------------------|--------------|---------------------------|
    | ITU H.263 video     |"H263-1998"   | None, map dynamically     |
    | 1998 version        |              |                           |
    |---------------------|--------------|---------------------------|
    |MPEG 1 system stream |    "MP1S"    | None, map dynamically     |
    |---------------------|--------------|---------------------------|
    |MPEG 2 program stream|    "MP2P"    | None, map dynamically     |
    |---------------------|--------------|---------------------------|
    |Redundancy           |    "RED"     | None, map dynamically     |
    |---------------------|--------------|---------------------------|
    |Variable rate DVI4   |    "VDVI"    | None, map dynamically     |
    |---------------------|--------------|---------------------------|
    |Cell-B               |    "CelB"    | 25                        |
    |---------------------|--------------|---------------------------|
    |JPEG                 |    "JPEG"    | 26                        |
    |---------------------|--------------|---------------------------|
    |nv                   |    "nv"      | 28                        |
    |---------------------|--------------|---------------------------|
    |L8, Eight Bit Linear |    "L8"      | None, map dynamically     |
    |PCM                  |              |                           |
    |---------------------|--------------|---------------------------|
    | ITU-R Recommendation|   "BT656"    | None, map dynamically     |
    | BT.656-3 for        |              |                           |
    | digital video       |              |                           |
    |---------------------|--------------|---------------------------|
    | Adaptive Multirate  |   "FR-AMR"   | None, map dynamically     |
    |-Full Rate (3GPP)[58]|              |                           |
    |---------------------|--------------|---------------------------|
    | Adaptive Multirate  |   "HR-AMR"   | None, map dynamically     |
    |-Half Rate (3GPP)[58]|              |                           |
    |---------------------|--------------|---------------------------|
    | Adaptive Multirate  |   "UMTS-AMR" | None, map dynamically     |
    |- UMTS(3GPP)  [58]   |              |                           |
    |---------------------|--------------|---------------------------|
    | Adaptive Multirate  |   "AMR"      | None, map dynamically     |
    |- Generic     [58]   |              |                           |
    |---------------------|--------------|---------------------------|

5.6.3.2 The 'silenceSupp' attribute

 When present, the 'silenceSupp' attribute is used to indicate the use
 or non-use of silence suppression.  The format of the 'silenceSupp'
 media attribute line is as follows:
 a=silenceSupp: <silenceSuppEnable> <silenceTimer> <suppPref> <sidUse>
                 <fxnslevel>

Kumar & Mostafa Standards Track [Page 63] RFC 3108 ATM SDP May 2001

 If any of the parameters in the silenceSupp media attribute line is
 not specified, is inapplicable or is implied, then it is set to "-".
 The <silenceSuppEnable> can take on values of "on" or "off".  If it
 is "on", then silence suppression is enabled.
 The <silenceTimer> is a 16-bit field which can be represented in
 decimal or hex.  Each increment (tick) of this timer represents a
 millisecond.  The maximum value of this timer is between 1 and 3
 minutes.  This timer represents the time-lag before silence
 suppression kicks in.  Even though this can, theoretically, be as low
 as 1 ms, most DSP algorithms take more than that to detect silence.
 Setting <silenceTimer> to a large value (say 1 minute> is equivalent
 to disabling silence suppression within a call.  However, idle
 channel suppression between calls on the basis of silence suppression
 is still operative in non-switched, trunking applications if
 <silenceSuppEnable> = "on" and <silenceTimer> is a large value.
 The <suppPref> specifies the preferred silence suppression method
 that is preferred or already selected.  It can take on the string
 values of "standard" and "custom".  If its value is "standard", then
 a standard method (e.g., ITU-defined) is preferred to custom methods
 if such a standard is defined.  Otherwise, a custom method may be
 used.  If <suppPref> is set to "custom", then a custom method, if
 available, is preferred to the standard method.
 The <sidUse> indicates whether SIDs (Silence Insertion Descriptors)
 are to be used, and whether they use fixed comfort noise or sampled
 background noise.  It can take on the string values of "No SID",
 "Fixed Noise", "Sampled Noise".
 If the value of <sidUse> is "Fixed Noise", then <fxnslevel> provides
 its level.  It can take on integer values in the range 0-127, as
 follows:
       +-----------------------+---------------------+
       | <fxnslevel> value     |         Meaning     |
       +-----------------------+---------------------+
       |  0-29                 |          Reserved   |
       |   30                  |          -30 dBm0   |
       |   31                  |          -31 dBm0   |
       |   . . .               |           . . .     |
       |   77                  |          -77 dBm0   |
       |   78                  |          -78 dBm0   |
       |  79-126               |          reserved   |
       |   127                 | Idle Code (no noise)|
       +-----------------------+---------------------+

Kumar & Mostafa Standards Track [Page 64] RFC 3108 ATM SDP May 2001

 In addition to the decimal representation of <fxnslevel>, a hex
 representation, preceded by a "0x" prefix, is also allowed.

5.6.3.3 The 'ecan' attribute

 When present, the 'ecan' attribute s is used to indicate the use or
 non-use of echo cancellation.  There can be several 'ecan' lines in
 an SDP description.
 The format of the 'ecan' media attribute line is as follows:
    a=ecan:<directionFlag><ecanEnable><ecanType>
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and
 backward).  Conventions for the forward and backward directions are
 per section 2.3.
 The <directionFlag> is always specified.  Except for the
 <directionFlag>, the remaining parameters can be set to "-" to
 indicate that they are not specified, inapplicable or implied.
 However, there must be some specified parameters for the line to be
 useful in an SDP description.
 If the 'ecan' media attribute lines is not present, then means other
 than the SDP descriptor must be used to determine the applicability
 and nature of echo cancellation for a connection direction.  Examples
 of such means are MIB provisioning, the local connection options
 structure in MGCP etc.
 The <ecanEnable> parameter can take on values of "on" or "off".  If
 it is "on", then echo cancellation is enabled.  If it is "off", then
 echo cancellation is disabled.
 The <ecanType> parameter can take on the string values "G165" and
 "G168" respectively.
 When SDP is used with some media gateway control protocols such as
 MGCP and Megaco [26], there exist means outside SDP descriptions to
 specify the echo cancellation properties of a connection.
 Nevertheless, this media attribute line is included for completeness.
 As a result, the SDP can be used for describing echo cancellation in
 applications where alternate means for this are unavailable.

Kumar & Mostafa Standards Track [Page 65] RFC 3108 ATM SDP May 2001

5.6.3.4 The 'gc' attributes

 When present, the 'gc' attribute is used to indicate the use or non-
 use of gain control.  There can be several 'gc' lines in an SDP
 description.
 The format of the 'gc' media attribute line is as follows:
    a=gc:<directionFlag><gcEnable><gcLvl>
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and
 backward).  Conventions for the forward and backward directions are
 per section 2.3.
 The <directionFlag> is always specified.  Except for the
 <directionFlag>, the remaining parameters can be set to "-" to
 indicate that they are not specified, inapplicable or implied.
 However, there must be some specified parameters for the line to be
 useful in an SDP description.
 If the 'gc' media attribute lines is not present, then means other
 than the SDP descriptor must be used to determine the applicability
 and nature of gain control for a connection direction.  Examples of
 such means are MIB provisioning, the local connection options
 structure in MGCP etc.
 The <gcEnable> parameter can take on values of "on" or "off".  If it
 is "on", then gain control is enabled.  If it is "off", then gain
 control is disabled.
 The <gcLvl> parameter is represented as the decimal or hex equivalent
 of a 16-bit binary field.  A value of 0xFFFF implies automatic gain
 control.  Otherwise, this number indicates the number of decibels of
 inserted loss.  The upper bound, 65,535 dB (0xFFFE) of inserted loss,
 is a large number and is a carryover from Megaco [26].  In practical
 applications, the inserted loss is much lower.
 When SDP is used with some media gateway control protocols such as
 MGCP and Megaco [26], there exist means outside SDP descriptions to
 specify the gain control properties of a connection.  Nevertheless,
 this media attribute line is included for completeness.  As a result,
 the SDP can be used for describing gain control in applications where
 alternate means for this are unavailable.

Kumar & Mostafa Standards Track [Page 66] RFC 3108 ATM SDP May 2001

5.6.3.5 The 'profileDesc' attribute

 There is one 'profileDesc' media attribute line for each AAL2 profile
 that is intended to be described.  The 'profileDesc' media attribute
 line is structured as follows:
    a=profileDesc: <aal2transport> <profile>  <uuiCodeRange#1>
      <encodingName#1> <packetLength#1> <packetTime#1>
      <uuiCodeRange#2> <encodingName#2> <packetLength#2>
      <packetTime#2>... <uuiCodeRange#N> <encodingName#N>
      <packetLength#N> <packetTime#N>
 Here, <aal2transport> can have those values of <transport> (Table 1)
 that pertain to AAL2.  These are:
          AAL2/ATMF
          AAL2/ITU
          AAL2/custom
          AAL2/<corporateName>
          AAL2/IEEE:<oui>
 The parameter <profile> is identical to its definition for the 'm'
 line (Section 5.5.4).
 The profile elements (rows in the profile tables of ITU I.366.2 or
 AF-VTOA-0113) are represented as four-tuples following the <profile>
 parameter in the 'profileDesc' media attribute line.  If a member of
 one of these four-tuples is not specified or is implied, then it is
 set to "-".
 The <uuiCodeRange> parameter is represented by D1-D2, where D1 and D2
 are decimal integers in the range 0 through 15.
 The <encodingName> parameter can take one of the values in column 2
 of Table 2.  Additionally, it can take on the following descriptor
 strings: "PCMG", "SIDG" and "SID729".  These stand for generic PCM,
 generic SID and G.729 SID respectively.
 The <packetLength> is a decimal integer representation of the AAL2
 packet length in octets.
 The <packetTime> is a decimal integer representation of the AAL2
 packetization interval in microseconds.
 For instance, the 'profileDesc' media attribute line below defines
 the AAL2/custom 100 profile.  This profile is reproduced in the Table
 3 below.  For a description of the parameters in this profile such as
 M and the sequence number interval, see ITU I.366.2 [13].

Kumar & Mostafa Standards Track [Page 67] RFC 3108 ATM SDP May 2001

 a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1 5000 8-15
     G726-32 40 10000 8-15 SIDG 1 5000
 If the <packetTime> parameter is to be omitted or implied, then the
 same profile can be represented as follows:
 a=profileDesc:AAL2/custom 100 0-7 PCMG 40 - 0-7 SIDG 1 - 8-15
      G726-32 40 - 8-15 SIDG 1 -
 If a gateway has a provisioned or hard coded definition of a profile,
 then any definition provided via the 'profileDesc' line overrides it.
 The exception to this rule is with regard to standard profiles such
 as ITU-defined profiles and ATMF-defined profiles.  In general, these
 should not be defined via a 'profileDesc' media attribute line.  If
 they are, then the definition needs to be consistent with the
 standard definition else the SDP session descriptor should be
 rejected with an appropriate error code.
           Table 3: Example of a  custom AAL2 profile
 |---------------------------------------------------------------|
 | UUI  | Packet |Encoding |               |     |Packet|Seq.No. |
 | Code | Length |per ITU  |Description of |  M  |Time  |Interval|
 |point |(octets)|I.366.2  |  Algorithm    |     |(ms)  |(ms)    |
 |Range |        |  2/99   |               |     |      |        |
 |      |        | version |               |     |      |        |
 |---------------------------------------------------------------|
 | 0-7  |    40  |  Figure | PCM, G.711-64,|   1 |    5 |    5   |
 |      |        |  B-1    |  generic      |     |      |        |
 |------|--------|---------|---------------|-----|------|--------|
 | 0-7  |    1   |  Figure | Generic SID   |   1 |    5 |    5   |
 |      |        |  I-1    |               |     |      |        |
 |------|--------|---------|---------------|-----|------|--------|
 | 8-15 |    40  |  Figure | ADPCM,        |   2 |   10 |    5   |
 |      |        |  E-2    | G.726-32      |     |      |        |
 |------|--------|---------|---------------|-----|------|--------|
 | 8-15 |    1   |  Figure | Generic SID   |   1 |    5 |    5   |
 |      |        |  I-1    |               |     |      |        |
 |------|--------|---------|---------------|-----|------|--------|

5.6.3.6 The 'vsel' attribute

 The 'vsel' attribute indicates a prioritized list of one or more 3-
 tuples for voice service.  Each 3-tuple indicates a codec, an
 optional packet length and an optional packetization period.  This
 complements the 'm' line information and should be consistent with
 it.

Kumar & Mostafa Standards Track [Page 68] RFC 3108 ATM SDP May 2001

 The 'vsel' attribute refers to all directions of a connection.  For a
 bidirectional connection, these are the forward and backward
 directions.  For a unidirectional connection, this can be either the
 backward or forward direction.
 The 'vsel' attribute is not meant to be used with bidirectional
 connections that have asymmetric codec configurations described in a
 single SDP descriptor.  For these, the 'onewaySel' attribute (section
 5.6.3.9) should be used.  See section 5.6.3.9 for the requirement to
 not use the 'vsel' and 'onewaySel' attributes in the same SDP
 descriptor.
 The 'vsel' line is structured as follows:
    a=vsel:<encodingName #1> <packetLength #1><packetTime #1>
              <encodingName #2> <packetLength #2><packetTime #2>
              ...
             <encodingName #N> <packetLength #N><packetTime #N>
 where the <encodingName> parameter can take one of the values in
 column 2 of Table 2.  The <packetLength> is a decimal integer
 representation of the packet length in octets.  The <packetTime> is a
 decimal integer representation of the packetization interval in
 microseconds.  The parameters <packetLength> and <packetTime> can be
 set to "-" when not needed.  Also, the entire 'vsel' media attribute
 line can be omitted when not needed.
 For example,
    a=vsel:G729 10 10000 G726-32 40 10000
 indicates first preference of G.729 or G.729a (both are
 interoperable) as the voice encoding scheme.  A packet length of 10
 octets and a packetization interval of 10 ms are associated with this
 codec.  G726-32 is the second preference stated in this line, with an
 associated packet length of 40 octets and a packetization interval of
 10 ms.  If the packet length and packetization interval are intended
 to be omitted, then this media attribute line becomes
    a=vsel:G729 - - G726-32 - -
 The media attribute line
    a=vsel:G726-32 40 10000
 indicates preference for or selection of 32 kbps ADPCM with a packet
 length of 40 octets and a packetization interval of 10 ms.

Kumar & Mostafa Standards Track [Page 69] RFC 3108 ATM SDP May 2001

 This media attribute line can be used in ATM as well as non-ATM
 contexts.  Within the ATM context, it can be applied to the AAL1,
 AAL2 and AAL5 adaptations.  The <packetLength> and <packetTime> are
 not meaningful in the AAL1 case and should be set to "-".  In the
 AAL2 case, this line determines the use of some or all of the rows in
 a given profile table.  If multiple 3-tuples are present, they can
 indicate a hierarchical assignment of some rows in that profile to
 voice service (e.g., row A preferred to row B etc.).  If multiple
 profiles are present on the 'm' line, the profile qualified by this
 attribute is the first profile.  If a single profile that has been
 selected for a connection is indicated in the 'm' line, the 'vsel'
 attribute qualifies the use, for voice service, of codecs within that
 profile.
 With most of the encoding names in Figure 2, the packet length and
 packetization period can be derived from each other.  One of them can
 be set to "-" without a loss of information.  There are some
 exceptions such as the IANA-registered encoding names G723, DVI4 and
 L16 for which this is not true.  Therefore, there is a need to retain
 both the packet length and packetization period in the definition of
 the 'vsel' line.

5.6.3.7 The 'dsel' attribute

 The 'dsel' attribute indicates a prioritized list of one or more 3-
 tuples for voiceband data service.  The <fxIncl> flag indicates
 whether this definition of voiceband data includes fax ("on" value)
 or not ("off" value).  If <fxIncl> is "on", then the 'dsel' line must
 be consistent with any 'fsel' line in the session description.  In
 this case, an error event is generated in the case of inconsistency.
 Each 3-tuple indicates a codec, an optional packet length and an
 optional packetization period.  This complements the 'm' line
 information and should be consistent with it.
 The 'dsel' attribute refers to all directions of a connection.  For a
 bidirectional connection, these are the forward and backward
 directions.  For a unidirectional connection, this can be either the
 backward or forward direction.
 The 'dsel' attribute is not meant to be used with bidirectional
 connections that have asymmetric codec configurations described in a
 single SDP descriptor.  For these, the 'onewaySel' attribute (section
 5.6.3.9) should be used.  See section 5.6.3.9 for the requirement to
 not use the 'dsel' and 'onewaySel' attributes in the same SDP
 descriptor.

Kumar & Mostafa Standards Track [Page 70] RFC 3108 ATM SDP May 2001

 The 'dsel' line is structured as follows:
    a=dsel:<fxIncl> <encodingName #1> <packetLength #1><packetTime #1>
              <encodingName #2> <packetLength #2><packetTime #2>
              ...
             <encodingName #N> <packetLength #N><packetTime #N>
 where the <encodingName> parameter can take one of the values in
 column 2 of Table 2. The <packetLength> and <packetTime> parameters
 are per their definition, above, for the 'vsel' media attribute line.
 The parameters <packetLength> and <packetTime>) can be set to "-"
 when not needed.  The <fxIncl> flag is presumed to be "off" if it is
 set to "-".  Also, the entire 'dsel' media attribute line can be
 omitted when not needed.
 For example,
    a=dsel:-  G726-32 20 5000 PCMU 40 5000
 indicates that this line does not address facsimile, and that the
 first preference for the voiceband data codes is 32 kbps ADPCM, while
 the second preference is PCMU.  The packet length and the
 packetization interval associated with G726-32 are 20 octets and 5 ms
 respectively.  For PCMU, they are 40 octets and 5 ms respectively.
 This media attribute line can be used in ATM as well as non-ATM
 contexts.  Within the ATM context, it can be applied to the AAL1,
 AAL2 and AAL5 adaptations.  The <packetLength> and <packetTime> are
 not meaningful in the AAL1 case and should be set to "-".  In the
 AAL2 case, this line determines the use of some or all of the rows in
 a given profile table.  If multiple 3-tuples are present, they can
 indicate a hierarchical assignment of some rows in that profile to
 voiceband data service (e.g., row A preferred to row B etc.)  If
 multiple profiles are present on the 'm' line, the profile qualified
 by this attribute is the first profile.  If a single profile that has
 been selected for a connection is indicated in the 'm' line, the '
 dsel' attribute qualifies the use, for voiceband data service, of
 codecs within that profile.
 With most of the encoding names in Figure 2, the packet length and
 packetization period can be derived from each other.  One of them can
 be set to "-" without a loss of information.  There are some
 exceptions such as the IANA-registered encoding names G723, DVI4 and
 L16 for which this is not true.  Therefore, there is a need to retain
 both the packet length and packetization period in the definition of
 the 'dsel' line.

Kumar & Mostafa Standards Track [Page 71] RFC 3108 ATM SDP May 2001

5.6.3.8 The 'fsel' attribute

 The 'fsel' attribute indicates a prioritized list of one or more 3-
 tuples for facsimile service.  If an 'fsel' line is present, any '
 dsel' line with <fxIncl> set to "on" in the session description must
 be consistent with it.  In this case, an error event is generated in
 the case of inconsistency.  Each 3-tuple indicates a codec, an
 optional packet length and an optional packetization period.  This
 complements the 'm' line information and should be consistent with
 it.
 The 'fsel' attribute refers to all directions of a connection.  For a
 bidirectional connection, these are the forward and backward
 directions.  For a unidirectional connection, this can be either the
 backward or forward direction.
 The 'fsel' attribute is not meant to be used with bidirectional
 connections that have asymmetric codec configurations described in a
 --single SDP descriptor.  For these, the 'onewaySel' attribute
 (section 5.6.3.9) should be used.  See section 5.6.3.9 for the
 requirement to not use the 'fsel' and 'onewaySel' attributes in the
 same SDP descriptor.
 The 'fsel' line is structured as follows:
    a=fsel:<encodingName #1> <packetLength #1><packetTime #1>
              <encodingName #2> <packetLength #2><packetTime #2>
              ...
             <encodingName #N> <packetLength #N><packetTime #N>
 where the <encodingName> parameter can take one of the values in
 column 2 of Table 2.  The <packetLength> and <packetTime> parameters
 are per their definition, above, for the 'vsel' media attribute line.
 The parameters <packetLength> and <packetTime> can be set to "-" when
 not needed.  Also, the entire 'fsel' media attribute line can be
 omitted when not needed.
 For example,
    a=fsel:FXDMOD-3 - -
 indicates demodulation and remodulation of ITU-T group 3 fax at the
 gateway.
    a=fsel:PCMU 40 5000 G726-32 20 5000

Kumar & Mostafa Standards Track [Page 72] RFC 3108 ATM SDP May 2001

 indicates a first and second preference of Mu-law PCM and 32 kbps
 ADPCM as the facsimile encoding scheme.  The packet length and the
 packetization interval associated with G726-32 are 20 octets and 5 ms
 respectively.  For PCMU, they are 40 octets and 5 ms respectively.
 This media attribute line can be used in ATM as well as non-ATM
 contexts.  Within the ATM context, it can be applied to the AAL1,
 AAL2 and AAL5 adaptations.  The <packetLength> and <packetTime> are
 not meaningful in the AAL1 case and should be set to "-".  In the
 AAL2 case, this line determines the use of some or all of the rows in
 a given profile table.  If multiple 3-tuples are present, they can
 indicate a hierarchical assignment of some rows in that profile to
 facsimile service (e.g., row A preferred to row B etc.).  If multiple
 profiles are present on the 'm' line, the profile qualified by this
 attribute is the first profile.  If a single profile that has been
 selected for a connection is indicated in the 'm' line, the 'fsel'
 attribute qualifies the use, for facsimile service, of codecs within
 that profile.
 With most of the encoding names in Figure 2, the packet length and
 packetization period can be derived from each other.  One of them can
 be set to "-" without a loss of information.  There are some
 exceptions such as the IANA-registered encoding names G723, DVI4 and
 L16 for which this is not true.  Therefore, there is a need to retain
 both the packet length and packetization period in the definition of
 the 'fsel' line.

5.6.3.9 The 'onewaySel' attribute

 The 'onewaySel' (one way select) attribute can be used with
 connections that have asymmetric codec configurations.  There can be
 several 'onewaySel' lines in an SDP description.  The 'onewaySel'
 line is structured as follows:
    a=onewaySel:<serviceType> <directionFlag>
              <encodingName #1> <packetLength #1><packetTime #1>
              <encodingName #2> <packetLength #2><packetTime #2>
              ...
              <encodingName #N> <packetLength #N><packetTime #N>
 The <serviceType> parameter can be assigned the following string
 values: "v", "d", "f", "df" and "all".  These indicate voice,
 voiceband data (fax not included), fax, voiceband data (fax included)
 and all services respectively.
 The <directionFlag> can be assigned the following string values: "f",
 "b" and "fb".  "f" and "b" indicate the forward and backward
 directions respectively.  "fb" refers to both directions (forward and

Kumar & Mostafa Standards Track [Page 73] RFC 3108 ATM SDP May 2001

 backward) and shall not be used with the 'onewaySel' line.
 Conventions for the forward and backward directions are per section
 2.3.
 Following <directionFlag>, there is a prioritized list of one or more
 3-tuples.  Each 3-tuple indicates a codec, an optional packet length
 and an optional packetization period.  This complements the 'm' line
 information and should be consistent with it.
 Within each 3-tuple, the <encodingName> parameter can take one of the
 values in column 2 of Table 2.  The <packetLength> is a decimal
 integer representation of the packet length in octets.  The
 <packetTime> is a decimal integer representation of the packetization
 interval in microseconds.
 The 'onewaySel' attribute must not be used in SDP descriptors that
 have one or more of the following attributes: 'vsel', 'dsel', 'fsel'.
 If it is present, then command containing the SDP description may be
 rejected.  An alternate response to such an ill-formed SDP descriptor
 might the selective ignoring of some attributes, which must be
 coordinated via an application-wide policy.
 The <serviceType>, <directionFlag> and <encodingName> parameters may
 not be set to "-".  However, the parameters <packetLength> and
 <packetTime> can be set to "-" when not needed.
 For example,
    a=onewaySel:v f G729 10 10000
    a=onewaySel:v b G726-32 40 10000
 indicates that for voice service, the codec to be used in the forward
 direction is G.729 or G.729a (both are interoperable), and the codec
 to be used in the backward direction is G726-32.  A packet length of
 10 octets and a packetization interval of 10 ms are associated with
 the G.729/G.729a codec.  A packet length of 40 octets and a
 packetization interval of 10 ms are associated with the G726-32
 codec.
 For example,
    a=onewaySel:d f G726-32 20 5000
    a=onewaySel:d b PCMU 40 5000
 indicates that for voiceband service (fax not included), the codec to
 be used in the forward direction is G726-32), and the codec to be
 used in the backward direction is PCMU.  A packet length of 20 octets

Kumar & Mostafa Standards Track [Page 74] RFC 3108 ATM SDP May 2001

 and a packetization interval of 5 ms are associated with the G726-32
 codec.  A packet length of 40 octets and a packetization interval of
 5 ms are associated with the PCMU codec.
 This media attribute line can be used in ATM as well as non-ATM
 contexts.  Within the ATM context, it can be applied to the AAL1,
 AAL2 and AAL5 adaptations.  The <packetLength> and <packetTime> are
 not meaningful in the AAL1 case and should be set to "-".  In the
 AAL2 case, these lines determine the use of some or all of the rows
 in a given profile table.  If multiple 3-tuples are present, they can
 indicate a hierarchical assignment of some rows in that profile to
 voice service (e.g., row A preferred to row B etc.).  If multiple
 profiles are present on the 'm' line, the profile qualified by this
 attribute is the first profile.
 With most of the encoding names in Figure 2, the packet length and
 packetization period can be derived from each other.  One of them can
 be set to "-" without a loss of information.  There are some
 exceptions such as the IANA-registered encoding names G723, DVI4 and
 L16 for which this is not true.  Therefore, there is a need to retain
 both the packet length and packetization period in the definition of
 the 'onewaySel' line.

5.6.3.10 The 'codecconfig' attribute

 When present, the 'codecconfig' attribute is used to represent the
 contents of the single codec information element (IE) defined in
 [57].  The contents of this IE are: a single-octet Organizational
 Identifier (OID) field, followed by a single-octet Codec Type field,
 followed by zero or more octets of a codec configuration bit-map.
 The semantics of the codec configuration bit-map are specific to the
 organization [57, 58].  The 'codecconfig' attribute is represented as
 follows:
    a=codecconfig:<q7655scc>
 The <q7655scc> (Q.765.5 single codec IE contents) parameter is
 represented as a string of hex digits.  The number of hex digits is
 even (range 4 -32).  The "0x" prefix shall be omitted since this
 value is always hexadecimal.  As with other hex values [Section 2.2],
 digits to the left are more significant than digits to the right.
 Leading zeros shall not be omitted.
 An example of the use of this media attribute is:
    a=codecconfig:01080C

Kumar & Mostafa Standards Track [Page 75] RFC 3108 ATM SDP May 2001

 The first octet indicates an Organizational Identifier of 0x01 (the
 ITU-T).  Using ITU Q.765.5 [57], the second octet (0x08) indicates a
 codec type of G.726 (ADPCM).  The last octet, 0x0C indicates that 16
 kbps and 24 kbps rates are NOT supported, while the 32 kbps and 40
 kbps rates ARE supported.

5.6.3.11 The 'isup_usi' attribute

 When present, the 'isup_usi' attribute is used to represent the
 bearer capability information element defined in Section 4.5.5 of ITU
 Q.931 [59] (excluding the information element identifier and length).
 This information element is reiterated as the user service
 information element (IE) in Section 3.57 of ITU Q.763 [60].  The '
 isup_usi' attribute is represented as follows:
    a=isup_usi:<isupUsi>
 The <isupUsi> parameter is represented as a string of hex digits.
 The number of hex digits is even (allowed range 4 -24).  The "0x"
 prefix shall be omitted since this value is always hexadecimal.  As
 with other hex values [Section 2.2], digits to the left are more
 significant than digits to the right.  Leading zeros shall not be
 omitted.

5.6.3.12 The 'uiLayer1_Prot' attribute

 When present, the 'uiLayer1_Prot' attribute is used to represent the
 'User Information Layer 1 protocol' field within the bearer
 capability information element defined in Section 4.5.5 of [59], and
 reiterated as the user service information element (IE) in Section
 3.57 of [60].  The 'User Information Layer 1 protocol' field consists
 of the five least significant bits of Octet 5 of this information
 element.
 Within SDP, the 'uiLayer1_Prot' attribute is represented as follows:
    a='uiLayer1_Prot':<uiLayer1Prot>
 The <uiLayer1Prot> parameter is represented as a string of two hex
 digits.  The "0x" prefix shall be omitted since this value is always
 hexadecimal.  As with other hex values [Section 2.2], digits to the
 left are more significant than digits to the right.  These hex digits
 are constructed from an octet with three leading '0' bits and last
 five bits equal to the 'User Information Layer 1 protocol' field
 described above.  As specified in [59] and [26], bit 5 of this field
 is the most significant bit.  The resulting values of the
 <uiLayer1Prot> parameter are as follows:

Kumar & Mostafa Standards Track [Page 76] RFC 3108 ATM SDP May 2001

 VALUE   MEANING
 0x01    CCITT standardized rate adaption V.110 and X.30
 0x02    Recommendation G.711 Mu-law
 0x03    Recommendation G.711 A-law
 0x04    Recommendation G.721 32 kbps ADPCM and Recommendation I.460
 0x05    Recommendations H.221 and H.242
 0x06    Recommendation  H.223 and H.245
 0x07    Non-ITU-T standardized rate adaption
 0x08    ITU-T standardized rate adaption V.120
 0x09    CCITT standardized rate adaption X.31 HDLC flag stuffing

5.6.4 Miscellaneous media attributes

 The 'chain' media attribute line, which is used to chain consecutive
 SDP descriptions, cannot be classified as an ATM, AAL or service
 attribute.  It is detailed in the following subsection.

5.6.4.1 The 'chain' attribute

 The start of an SDP descriptor is marked by a 'v' line.  In some
 applications, consecutive SDP descriptions are alternative
 descriptions of the same session.  In others, these describe
 different layers of the same connection (e.g., IP, ATM, frame relay).
 This is useful when these connectivity at these layers are
 established at the same time (e.g., an IP-based session over an ATM
 SVC).  To distinguish between the alternation and concatenation of
 SDP descriptions, a 'chain' attribute can be used in the case of
 concatenation.
 When present, the 'chain' attribute binds an SDP description to the
 next or previous SDP description.  The next or previous description
 is separated from the current one by a 'v' line.  It is not necessary
 that this description also have a 'chain' media attribute line.
 Chaining averts the need to set up a single SDP description for a
 session that is simultaneously created at multiple layers.  It allows
 the SDP descriptors for different layers to remain simple and clean.
 Chaining is not needed in the Megaco context, where it is possible to
 create separate terminations for the different layers of a
 connection.
 The 'chain' media attribute line has the following format:
    a=chain:<chainPointer>
 The <chainPointer> field can take on the following string values:
 "NEXT", "PREVIOUS" and "NULL".  The value "NULL" is not equivalent to
 omitting the chain attribute from a description since it expressly

Kumar & Mostafa Standards Track [Page 77] RFC 3108 ATM SDP May 2001

 precludes the possibility of chaining.  If the 'chain' attribute is
 absent in an SDP description, chaining can still be realized by the
 presence of a chain media attribute line in the previous or next
 description.

5.6.5 Use of the second media-level part in H.323 Annex C applications

 Section 4 mentions that H.323 annex C applications have a second
 media level part for the ATM session description.  This is used to
 convey information about the RTCP stream.  Although the RTP stream is
 encapsulated in AAL5 with no intervening IP layer, the RTCP stream is
 sent to an IP address and RTCP port.  This media-level part has the
 following format:
    m= control <rtcpPortNum> H323c -
    c= IN IP4 <rtcpIPaddr>
 Consistency with RFC 2327 is maintained in the location and format of
 these lines.  The <fmt list> in the 'm' line is set to "-".  The 'c'
 line in the second media-level part pertains to RTCP only.
 The <rtcpPortNum> and <rtcpIPaddr> subparameters indicate the port
 number and IP address on which the media gateway is prepared to
 receive RTCP packets.
 Any of the subparameters on these lines can be set to "-" if they are
 known by other means.
 The range and format of the <rtcpPortNum> and <rtcpIPaddr>
 subparameters is per [1].  The <rtcpPortNum> is a decimal number
 between 1024 and 65535.  It is an odd number.  If an even number in
 this range is specified, the next odd number is used.  The
 <rtcpIPaddr> is expressed in the usual dotted decimal IP address
 representation, from 0.0.0.0 to 255.255.255.255.

5.6.6 Use of the eecid media attribute in call establishment

   procedures
 This informative section supplements the definition of the eecid
 attribute (Section 5.6.1.1) by describing example procedures for its
 use.  These procedures assume a bearer-signaling mechanism for
 connection set-up that is independent of service-level call control.
 These procedures are independent of the media gateway control
 protocol (MGCP, Megaco, SIP etc.), the protocol used between media
 gateway controllers (ITU Q.1901, SIP etc.) and the protocol used for
 bearer connection set-up (Q.2931, UNI, PNNI, AINI, IISP, Q.2630.1
 etc.).

Kumar & Mostafa Standards Track [Page 78] RFC 3108 ATM SDP May 2001

                          Inter-MGC
             +---------+  Protocol        +---------+
             |   MGC   |------------------|   MGC   |
             +---------+                  +---------+
                  |                            |
                  |Media Gateway               |Media Gateway
                  |Control Protocol            |Control Protocol
                  |                            |
              +------------+  (ATM Network)   +------------+
              |Originating |------------------|Terminating |
              |Media       |  Bearer Setup    |Media       |
              |Gateway     |  Protocol        |Gateway     |
              +------------+                  +------------+
 In the diagram above, the originating media gateway originates the
 service-level call.  The terminating media gateway terminates it.  In
 the forward bearer connection set-up model, the originating media
 gateway initiates bearer connection set-up.  In the backward bearer
 connection set-up model, the terminating gateway initiates bearer
 connection set-up.
 Example use of the Backward Bearer Connection Set-up Model:
 (1)  The originating media gateway controller (OMGC) initiates
      service-level call establishment by sending the appropriate
      control message to the originating media gateway (OMG).
 (2)  The originating media gateway (OMG) provides its NSAP address
      and an eecid value to the OMGC, using the following SDP
      description:
 v=0
 o=- 2873397496 0 ATM NSAP
    47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
 s=-
 c=ATM NSAP
   47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
 t=0 0
 m=audio $ AAL2/ITU 8
 a=eecid:B3D58E32
 (3)  The originating media gateway controller (OMGC) signals the
      terminating media gateway controller (TMGC) through the
      appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.).
      It provides the TMGC with the NSAP address and the eecid
      provided by the OMG.

Kumar & Mostafa Standards Track [Page 79] RFC 3108 ATM SDP May 2001

 (4)  The TMGC sends the appropriate control message to the TMG.  This
      includes the session descriptor received from the OMG.  This
      descriptor contains the NSAP address of the OMG and the EECID
      assigned by the OMG.  Additionally, the TMGC instructs the TMG
      to set up an SVC to the OMG.  It also requests the TMG to notify
      the TMGC when SVC set-up is complete.  Depending on the control
      protocol used, this can be done through a variety of means.  In
      the Megaco context, the request to set-up an SVC (not the
      notification request for the SVC set-up event) can be made
      through the following local descriptor:
 v=0
 o=- 2873397497 0 ATM - -
 s=-
 c=ATM - -
 t=0 0
 m=audio $ - -
 a=bearerType:SVC on
 The 'bearerType' attribute indicates that an SVC is to be used and
 that the <localInitiation> flag is on i.e., the SVC is to be set up
 by the TMG.
 (5)  The TMG acknowledges the control message from the TMGC.  It
      returns the following SDP descriptor with the acknowledge:
 v=0
 o=- 2873397498 0 ATM NSAP
    47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
 s=-
 c=ATM NSAP
   47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
 t=0 0
 m=audio $ AAL2/ITU 8
 The NSAP address information provided in this descriptor is not
 needed.  It can be omitted (by setting it to "- -").
 (6)  The TMG sends an SVC set-up message to the OMG.  Within the GIT
      information element, it includes eecid (B3D58E32) received from
      the OMG.
 (7)  The OMG uses the eecid to correlate the SVC set-up request with
      service-level control message received before from the OMGC.
 (8)  The OMG returns an SVC connect message to the TMG.  On receiving
      this message, the TMG sends an event notification to the TMGC
      indicating successful SVC set-up.

Kumar & Mostafa Standards Track [Page 80] RFC 3108 ATM SDP May 2001

      Note that, for this example, the "v=", "o=", "s=" and "t=" lines
      can be omitted in the Megaco context.
 Example use of the Forward Bearer Connection Set-up Model:
 (1)  The originating media gateway controller (OMGC) initiates
      service-level call establishment by sending the appropriate
      controlsmessage to the originating media gateway (OMG).
 (2)  The originating media gateway (OMG) provides its NSAP address to
      the OMGC, using the following SDP description:
 v=0
 o=- 2873397496 0 ATM NSAP
    47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
 s=-
 c=ATM NSAP
   47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
 t=0 0
 m=audio $ AAL2/ITU 8
 The NSAP address information provided in this descriptor is not
 needed.  It can be omitted (by setting it to "- -").
 (3)  The originating media gateway controller (OMGC) signals the
      terminating media gateway controller (TMGC) through the
      appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.).
      Although this is not necessary, it can provide the TMGC with the
      NSAP address provided by the OMG.
 (4)  The TMGC sends the appropriate control message to the TMG.  This
      includes the session descriptor received from the OMG.  This
      descriptor contains the NSAP address of the OMG.
 (5)  The TMG acknowledges the control message from the TMGC.  Along
      with the acknowledgement, it provides an SDP descriptor with a
      locally assigned eecid.
 v=0
 o=- 2873397714 0 ATM NSAP
    47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
 s=-
 c=ATM NSAP
   47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
 t=0 0
 m=audio $ AAL2/ITU 8
 a=eecid:B3D58E32

Kumar & Mostafa Standards Track [Page 81] RFC 3108 ATM SDP May 2001

 (6)  The terminating media gateway controller (TMGC) signals the
      originating media gateway controller (OMGC) through the
      appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.).
      It provides the OMGC with the NSAP address and the eecid
      provided by the TMG.
 (7)  The OMGC sends the appropriate control message to the OMG.  This
      includes the session descriptor received from the TMG.  This
      descriptor contains the NSAP address of the TMG and the EECID
      assigned by the TMG.  Additionally, the OMGC instructs the OMG
      to set up an SVC to the TMG.  It also requests the OMG to notify
      the OMGC when SVC set-up is complete.  Depending on the control
      protocol used, this can be done through a variety of means.  In
      the Megaco context, the request to set-up an SVC (not the
      notification request for the SVC set-up event) can be made
      through the following local descriptor:
 v=0
 o=- 2873397874 0 ATM - -
 s=-
 c=ATM - -
 t=0 0
 m=audio $ - -
 a=bearerType:SVC on
 The 'bearerType' attribute indicates that an SVC is to be used and
 that the <localInitiation> flag is on i.e., the SVC is to be set up
 by the TMG.
 (8)  The OMG acknowledges the control message from the OMGC.
 (9)  The OMG sends an SVC set-up message to the TMG.  Within the GIT
      information element, it includes eecid (B3D58E32) received from
      the TMG.
 (10) The TMG uses the eecid to correlate the SVC set-up request with
      the service-level control message received before from the TMGC.
 (11) The TMG returns an SVC connect message to the OMG.  On receiving
      this message, the OMG sends an event notification to the OMGC
      indicating successful SVC set-up.
      Note that, for this example,  the "v=", "o=", "s=" and "t="
      lines can be omitted in the Megaco context.

Kumar & Mostafa Standards Track [Page 82] RFC 3108 ATM SDP May 2001

6. List of Parameters with Representations

 This section provides a list of the parameters used in this document,
 and the formats used to represent them in SDP descriptions.  In
 general, a "-" value can be used for any field that is not specified,
 is inapplicable or is implied.

PARAMETER MEANING REPRESENTATION

<username> User name Constant "-"

<sessionID> Session ID Up to 32 decimal or

                                       hex digits

<version> Version of "0" or 10 decimal digits

                  SDP descriptor

<networkType> Network type Constant "ATM" for ATM transport

<addressType> Address type String values:

                                       "NSAP", "E164", "GWID",
                                       "ALIAS"

<address> Address "NSAP": 40 hex digits, dotted

                                      "E164":  up to 15 decimal digits
                                      "GWID":  up to 32 characters
                                      "ALIAS": up to 32 characters

<sessionName> Session name Constant "-"

<startTime> Session start "0" or 10 decimal digits

                  time

<stopTime> Session stop Constant "0"

                  time

<vcci> Virtual Circuit Decimal or hex equivalent

                  Connection           of 16 bits
                  Identifier

<ex_vcci> Explicit "VCCI-" prefixed to <vcci>

                  representation
                  of <vcci>

<bcg> Bearer Connection Decimal or hex equivalent

                  Group                of 8 bits

Kumar & Mostafa Standards Track [Page 83] RFC 3108 ATM SDP May 2001

<ex_bcg> Explicit "BCG-" prefixed to <bcg>

                  representation
                  of <bcg>

<portId> Port ID Hex number of up to 32 digits

<ex_portId> Explicit "PORT-" prefixed to <portId>

                  representation
                  of <portId>

<vpi> Virtual Path Decimal or hex equivalent

                  Identifier           of 8 or 12 bits

<ex_vpi> Explicit "VPI-" prefixed to <vpi>

                  representation
                  of <vpi>

<vci> Virtual Circui t Decimal or hex equivalent

                   Identifier          of 16 bits

<ex_vci> Explicit "VCI-" prefixed to <vci>

                   representation
                   of <vci>

<vpci> Virtual Path Decimal or hex equivalent

                   Connection          of 16 bits
                   Identifier

<ex_vpci> Explicit "VPCI-" prefixed to <vpci>

                   representation
                   of <vpci>

<cid> Channel Decimal or hex equivalent

                   Identifier          of 8 bits

<ex_cid> Explicit "CID-" prefixed to <cid>

                   representation
                   of <cid>

<payloadType> Payload Decimal integer 0-127

                   Type

<transport> Transport Values listed in

                                        Table 1.

<profile> Profile Decimal integer 1-255

Kumar & Mostafa Standards Track [Page 84] RFC 3108 ATM SDP May 2001

<eecid> End-to-end Up to 8 hex digits

                   Connection
                   Identifier

<aalType> AAL type String values:

                                        "AAL1","AAL1_SDT","AAL1_UDT",
                                        "AAL2", "AAL3/4",
                                        "AAL5", "USER_DEFINED_AAL"

<asc> ATM service String values:

                  category defined      "CBR", "nrt-VBR", "rt-VBR",
                  by the ATMF           "UBR", "ABR", "GFR"

<atc> ATM transfer String values:

                  capability            "DBR","SBR","ABT/IT","ABT/DT",
                  defined by the        "ABR"
                  ITU

<subtype> <asc>/<atc> Decimal integer 1-10

                   subtype

<qosClass> QoS Class Decimal integer 0-5

<bcob> Broadband Bearer Decimal or hex representation

                   Class                of 5-bit field

<eetim> End-to-end timing String values: "on",

                   required             "off".

<stc> Susceptibility Decimal equivalent of

                   to clipping          a 2-bit field

<upcc> User plane Decimal equivalent of

                   connection           a 2-bit field
                   configuration

<directionFlag> Direction Flag String values: "f", "b",

                                        "fb"

<cdvType> CDV type String values:

                                        "PP", "2P"

<acdv> Acceptable CDV Decimal equivalent

                                        of 24-bit field

<ccdv> Cumulative CDV Decimal equivalent

                                        of 24-bit field

Kumar & Mostafa Standards Track [Page 85] RFC 3108 ATM SDP May 2001

<eetd> End-to-end transit Decimal equivalent

                   delay                of 16-bit field

<cmtd> Cumulative transit Decimal equivalent

                   delay                of 16-bit field

<aclr> Acceptable Decimal equivalent

                   Cell Loss Ratio      of 8-bit field

<clpLvl> CLP level String values:

                                        "0", "0+1"

<pcr> Peak Decimal

                   Cell Rate            equivalent of a 24-bit field.

<scr> Sustained Decimal

                   Cell Rate            equivalent of a 24-bit field

<mbs> Maximum Decimal

                   Burst Size           equivalent of 16-bit field

<cdvt> CDVT Decimal equivalent of 24-bit

                                        field.

<mcr> Minimum Decimal

                   Cell Rate            equivalent of a 24-bit field

<mfs> Maximum Decimal

                   Frame Size           equivalent of a 16-bit field

<fd> Frame Discard String Values:

                   Allowed              "on", "off"

<te> CLP tagging String Values:

                                        "on", "off"

<nrm> NRM Decimal/hex equivalent

                                        of 3 bit field

<trm> TRM -ditto-

<cdf> CDF -ditto-

<adtf> ADTF Decimal/Hex equivalent

                                        of 10 bit field

Kumar & Mostafa Standards Track [Page 86] RFC 3108 ATM SDP May 2001

<ficr> Forward Initial Decimal equivalent of

                   Cell Rate            24-bit field

<bicr> Backward Initial Decimal equivalent of

                   Cell Rate            24-bit field

<ftbe> Forward Transient Decimal equivalent of

                   Buffer Exposure      24-bit field

<btbe> Backward Transient Decimal equivalent of

                   Buffer Exposure      24-bit field

<crmrtt> Cumulative RM Decimal equivalent of

                   round-trip time      24-bit field
                   (Microseconds)

<frif> Forward rate Decimal integer

                   increase factor      0 -15

<brif> Backward rate Decimal integer

                   increase factor      0 -15

<frdf> Forward rate Decimal integer

                   decrease factor      0 -15

<brdf> Backward rate Decimal integer

                   decrease factor      0 -15

<bearerType> Bearer Type String Values:

                                        "PVC", "SVC", "CID"

<localInitiation> Local Initiation String values:

                                         "on", "off"

<sci> Screening Indication Decimal or hex

                                         equivalent of 4  bits.

<lsn> Leaf Sequence Number Decimal or hex

                                         equivalent of 32 bits.

<cdStd> Coding standard for Decimal or hex

                   connection scope             equivalent of 2 bits.
                   selection IE
                   Definition: UNI 4.0 [5]

<conScpTyp> Type of connection scope Decimal or hex

                   Definition: UNI 4.0 [5]      equivalent of 4 bits

Kumar & Mostafa Standards Track [Page 87] RFC 3108 ATM SDP May 2001

<conScpSel> Connection scope selection Decimal or hex

                   Definition: UNI 4.0 [5]      equivalent of 8 bits

<cacheEnable> Enable SVC caching String values: "on",

                                                "off"

<cacheTimer> Timer for cached SVC Decimal or hex equivalent

                  deletion                   of 32-bit field

<bearerSigIEType> Bearer Signaling IE Type 2 hex digits

<bearerSigIELng> Bearer Signaling IE Length 1-4 hex digits

<bearerSigIEVal> Bearer Signaling IE Value Even number of hex

                                                digits, 2-512

<appClass> Application String values:

                  specification              "itu_h323c","af83",
                                             "AAL5_SSCOP",
                                             "itu_i3661_unassured",
                                             "itu_i3661_assured",
                                             "itu_i3662",
                                             "itu_i3651", "itu_i3652",
                                             "itu_i3653", "itu_i3654",
                                             "FRF5", "FRF8","FRF11",
                                             "itu_h2221"

<oui> Organizationally 1 to 6 hex digits

                  Unique Identifier

<appId> Application Identifier 1 to 8 digits

<cbrRate> CBR Rate Two hex digits.

<sbc> Subchannel Count T1: Decimal integer 1-24

                                           or hex equivalent
                                           E1: Decimal integer 1-31
                                           or hex equivalent

<clkrec> Clock Recovery String values:

                   Method                  "NULL", "SRTS",
                                           "ADAPTIVE"

<fecEnable> Forward Error String values:

                   Correction Enable       "NULL", "LOSS_SENSITIVE"
                                           "DELAY_SENSITIVE"

Kumar & Mostafa Standards Track [Page 88] RFC 3108 ATM SDP May 2001

<partialFill> Partial Fill Decimal integer 1-48

                                           or hex equivalent

<structureEnable> Structure Present String values:

                                           "on", "off"

<blksz> Block Size Decimal or hexadecimal

                                           equivalent of 16 bits

<cpcs> Maximum AAL5: Decimal or hex

                  CPCS SDU size            equivalent of 16 bits
                                           AAL2: 45 or 64, decimal
                                           or hex representation

<cidLowerLimit> AAL2 CID lower limit Decimal integer 8-255

                                           or hex equivalent

<cidUpperLimit> AAL2 CID upper limit Decimal integer 8-255

                                           or hex equivalent

<timerCU> Timer, combined use Integer decimal; range

                  (microseconds)           determined by application.
                                           Use decimal equivalent of
                                           32 bits.

<simplifiedCPS> Simplified CPS [52] String values:

                                           "on", "off"

<fSDUrate> Forward SDU rate Decimal equivalent of

                  (bits per second)        24-bit field

<bSDUrate> Backward SDU rate Decimal equivalent of

                  (bits per second)        24-bit field

<ted> Transmission Error String values:

                  Detection Enable         "on", "off"

<rastimer> SSSAR reassembly Integer decimal,

                  (microseconds)           Range determined by
                                           application.  Use decimal
                                           equivalent of 32 bits.

<fsssar> Maximum SSSAR-SDU Decimal 1- 65568

                  size, forward            or hex equivalent
                  direction

Kumar & Mostafa Standards Track [Page 89] RFC 3108 ATM SDP May 2001

<bsssar> Maximum SSSAR-SDU Decimal 1- 65568

                  size, backward           or hex equivalent
                  direction

<fsscopsdu> Maximum SSCOP-SDU Decimal 1- 65528

                  size, forward            or hex equivalent
                  direction

<bsscopsdu> Maximum SSCOP-SDU Decimal 1- 65528

                  size, backward           or hex equivalent
                  direction

<fsscopuu> Maximum SSCOP-UU Decimal 1- 65524

                  field size, forward      or hex equivalent
                  direction

<bsscopuu> Maximum SSCOP-UU Decimal 1- 65524

                  field size, backward     or hex equivalent
                  direction

<sap> Service Access String values:

                  Point                    "AUDIO", "MULTIRATE"

<circuitMode> Circuit Mode String values:

                  Enable                   "on", "off"

<frameMode> Frame Mode String values:

                  Enable                   "on", "off"

<faxDemod> Fax Demodulation String values:

                  Enable                   "on", "off"

<cas> Enable CAS transport String values:

                  via Type 3 packets       "on", "off"

<dtmf> Enable DTMF transport String values:

                  via Type 3 packets       "on", "off"

<mfall> Enable MF transport String values:

                  via Type 3 packets       "on", "off"

<mfr1> Enable MF (R1) String values:

                  transport via             "on", "off"
                  Type 3 packets

<mfr2> Enable MF (R2) String values:

                  transport via             "on", "off"
                  Type 3 packets

Kumar & Mostafa Standards Track [Page 90] RFC 3108 ATM SDP May 2001

<PCMencoding> PCM encoding String values:

                                           "PCMA", "PCMU"

<fmaxFrame> Maximum length of a Decimal or hex

                  frame mode data unit,    equivalent of
                  forward direction        16-bit field

<bmaxFrame> Maximum length of a -ditto-

                  frame mode data unit,
                  backward direction

<silenceSuppEnable> Silence suppression String values:

                   Enable               "on", "off"

<silenceTimer> Kick-in timer Decimal or hex representation

                   for silence          of 16-bit field
                   suppression

<suppPref> Preferred Silence String values:

                  Suppression Method    "standard", "custom"

<sidUse> SID Use String values:

                  Method                "No SID", "Fixed Noise",
                                        "Sampled Noise"

<fxnslevel> Fixed Noise Decimal or hex representation

                  Level                 of a 7-bit field

<ecanEnable> Enable Echo String values:

                  Cancellation          "on", "off"

<ecanType> Type of Echo String values:

                   Cancellation         "G165", "G168"

<gcEnable> Enable Gain String values:

                   Control              "on", "off"

<gcLvl> Level of inserted Decimal or hex equivalent

                   Loss                 of 16-bit field

<aal2transport> AAL2 transport Values listed in Table 1

                                        that begin with the string
                                        "AAL2"

<uuiCodeRange> UUI code range Decimal integer 0-15

Kumar & Mostafa Standards Track [Page 91] RFC 3108 ATM SDP May 2001

<encodingName> Encoding name String values:

                                        "PCMG", "SIDG", "SID729",
                                        any value from column 2
                                        of Table 2

<packetLength> Packet length Decimal integer 0-45

<packetTime> Packetization Decimal integer 1-65,536

                  Interval in microsec.

<fxIncl> Facsimile included String values: "on", "off"

<serviceType> Service type String values: "v", "d", "f",

                                        "df", "all"

<q7655scc> Contents of the Even number of hex

                  Q.765.5 Single        digits (4-32)
                  Codec IE

<isupUsi> ISUP User Service Even number of hex digits

                  Information           (4-24)

<uiLayer1Prot> User Information Two hex digits

                  Layer 1 Protocol

<chainPointer> Chain pointer String values: "NEXT",

                                        "PREVIOUS", "NULL"

<rtcpPortNum> RTCP port number for Odd decimal in range 1,024 to

                 H.323 Annex C           65,535.
                 applications            Preferred: Odd number in
                                         the range 49,152 to 65,535

<rtcpIPaddr> IP address for receipt Dotted decimal, 7-15 chars

                of RTCP packets

Kumar & Mostafa Standards Track [Page 92] RFC 3108 ATM SDP May 2001

7. Examples of ATM session descriptions using SDP

 An example of a complete AAL1 session description in SDP is:
    v=0
    o=- A3C47F21456789F0 0 ATM NSAP
       47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    s=-
    c=ATM NSAP
        47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    t=0 0
    m=audio $ AAL1/AVP 18 0 96
    a=atmmap:96 X-G727-32
    a=eecid:B3D58E32
 An example of a complete AAL2 session description in SDP is:
    v=0
    o=- A3C47F21456789F0 0 ATM NSAP
    47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    s=-
    c=ATM NSAP
         47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    t=0 0
    m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
    a=eecid:B3E32
 The AAL2 session descriptor below is the same as the one above except
 that it states an explicit preference for a voice codec, a voiceband
 data codec and a voiceband fax codec.  Further, it defines the
 profile AAL2/custom 100 rather than assume that the far-end is
 cognizant of the elements of this profile.
    v=0
    o=- A3C47F21456789F0 0 ATM NSAP
    47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    s=-
    c=ATM NSAP
    47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    t=0 0
    m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
    a=eecid:B3E32
    a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1
    5000 8-15 G726-32 40 10000 8-15 SIDG 1 5000
    a=vsel:G726-32 40 10000
    a=dsel:off PCMU - -
    a=fsel:G726-32 40 10000

Kumar & Mostafa Standards Track [Page 93] RFC 3108 ATM SDP May 2001

 An example of an SDP session descriptor for an AAL5 switched virtual
 circuit for delivering MPEG-2 video:
    v=0
    o=- A3C47F21456789F0 0 ATM NSAP
    47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    s=-
    c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    t=0 0
    m=video $ AAL5/ITU 33
    a=eecid:B3E32
    a=aalType:AAL5
    a=bearerType:SVC on
    a=atmTrfcDesc:f 0+1 7816 - - - - - off -
    a=atmTrfcDesc:b 0+1 0 - - - - - on -
    a=cpsSDUsize:f 20680
    a=aalApp:itu_h2221 - -
 An example of an SDP session descriptor for an AAL5 permanent virtual
 circuit for delivering MPEG-2 video:
    v=0
    o=- A3C47F21456789F0 0 ATM - -
    s=-
    c=ATM - -
    t=0 0
    m=video PORT-$/VPI-0/VCI-$ AAL5/ITU 33
    a=bearerType:PVC -
    a=atmTrfcDesc:f 0+1 7816 - - - - - off -
    a=atmTrfcDesc:b 0+1 0 - - - - - on -
    a=cpsSDUsize:f 20680
    a=aalApp:itu_h2221 - -

8. Security Considerations

8.1 Bearer Security

 At present, standard means of encrypting ATM and AAL2 bearers are not
 conventionalized in the same manner as means of encrypting RTP
 payloads.  Nor has the authentication of ATM or AAL2 bearer
 signaling.
 The SDP encryption key line (k=) defined in RFC 2327 can be used to
 represent the encryption key and the method of obtaining the key.  In
 the ATM and AAL2 contexts, the term 'bearer' can include 'bearer
 signaling' as well as 'bearer payloads'.

Kumar & Mostafa Standards Track [Page 94] RFC 3108 ATM SDP May 2001

8.2 Security of the SDP description

 The SDP session descriptions might originate in untrusted areas such
 as equipment owned by end-subscribers or located at end-subscriber
 premises.  SDP relies on the security mechanisms of the encapsulating
 protocol or layers below the encapsulating protocol.  Examples of
 encapsulating protocols are the Session Initiation Protocol (SIP),
 MGCP and Multimedia Gateway Control Protocol (MEGACO).  No additional
 security mechanisms are needed.  SIP, MGCP and MEGACO can use IPSec
 authentication as described in RFC 1826 [Ref.  27].  IPSec encryption
 can be optionally used with authentication to provide an additional,
 potentially more expensive level of security.  IPSec security
 associations can be made between equipment located in untrusted areas
 and equipment located in trusted areas through configured shared
 secrets or the use of a certificate authority.

9. ATM SDP Grammar

 This appendix provides an Augmented BNF (ABNF) grammar for the ATM
 conventions for SDP. ABNF is defined in rfc2234. This is not a
 complete ABNF description of SDP. Readers are referred to [1] for an
 ABNF description of the SDP base line protocol, and to rfc2848,
 rfc2543, rfc2045 and rfc2326 for application-specific conventions for
 SDP use. For case conventions, see section 2.4.

; Constant definitions

safe = alpha-numeric / "'" / "-" / "." / "/" / ":" / "?" / DQUOTE /

 "#" / "$" / "&" / "*" / ";" / "=" / "@" / "[" / "]" / "^" / "_" /
 "`" / "{" / "|" / "}" / "+" / "~"

DQUOTE = %x22 ; double quote alpha-numeric = ALPHA / DIGIT ALPHA = "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" / "i" / "j" /

      "k" / "l" / "m" / "n" / "o" / "p" / "q" / "r" / "s" / "t" /
      "u" / "v" / "w" / "x" / "y" / "z" /
      "A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" / "I" / "J" /
      "K" / "L" / "M" / "N" / "O" / "P" / "Q" / "R" / "S" / "T" /
      "U" / "V" / "W" / "X" / "Y" / "Z"

DIGIT = "0" / POS-DIGIT POS-DIGIT = "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9" hex-prefix = "0" ("x" / "X") HEXDIG = DIGIT / "a" / "b" / "c" / "d" / "e" / "f" /

                    "A" / "B" / "C" / "D" / "E" / "F"

space = %d32 EOL = (CR / LF / CRLF) ; as per Megaco RFC CR = %d13 LF = %d10

Kumar & Mostafa Standards Track [Page 95] RFC 3108 ATM SDP May 2001

decimal-uchar = DIGIT

                       / POS-DIGIT DIGIT
                       / ("1" 2*(DIGIT))
                       / ("2" ("0"/"1"/"2"/"3"/"4") DIGIT)
                       / ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5"))

generic-U8 = (hex-prefix hex-U8) / decimal-uchar generic-U12 = (hex-prefix hex-U12) / 1*4 (DIGIT) generic-U16 = (hex-prefix hex-U16) / 1*5(DIGIT) generic-U24 = (hex-prefix hex-U24) / 1*8(DIGIT) generic-U32 = (hex-prefix hex-U32) / 1*10(DIGIT) hex-U8 = 1*2(HEXDIG) hex-U12 = 1*3(HEXDIG) hex-U16 = 1*4(HEXDIG) hex-U24 = 1*6(HEXDIG) hex-U32 = 1*8(HEXDIG) generic-U8-or-null = generic-U8 / "-" generic-U12-or-null = generic-U12 / "-" generic-U16-or-null = generic-U16 / "-" generic-U24-or-null = generic-U24 / "-" generic-U32-or-null = generic-U32 / "-" decimal-U8-or-null = decimal-uchar / "-" decimal-U12-or-null = 1*4(DIGIT) / "-" decimal-U16-or-null = 1*5(DIGIT) / "-" decimal-U24-or-null = 1*8 (DIGIT) / "-" decimal-U32-or-null = 1*10(DIGIT) / "-" on-off-or-null = "on" / "off" / "-"

; ABNF definition of SDP with ATM conventions

SDP-infoset = 1*(announcement)announcement = proto-version origin-field session-name-field information-field uri-field email-fields phone-fields connection-field bandwidth-fields time-fields key-field attribute-fields media-descriptions

proto-version = ["v=" 1*4(DIGIT) EOL] ; use "v=0" for ATM SDP

origin-field = ["o=" username space sess-id space sess-version space

 net-type-addr EOL]

username = 1* safe ; for ATM use "-"

sess-id = (1*32 DIGIT) / (hex-prefix 1*32 HEXDIG) sess-version = (1*10 DIGIT) / (hex-prefix 1*8 HEXDIG)

net-type-addr= nettype space addrtype-addr

netttype = "ATM" / "IN" / "TN" / "-" / "$"

Kumar & Mostafa Standards Track [Page 96] RFC 3108 ATM SDP May 2001

; Other nettype values may be defined in the future in other documents ; Validity of nettype and addrtype-addr combination to be checked at ; application level, not protocol syntax level

addrtype-addr = atm-addrtype-addr / ip-addrtype-addr / tn-addrtype-addr

 ; ip-addrtype-addr per rfc2327
 ; tn-addrtype-addr per rfc2848

; ATM address definition

atm-addrtype-addr = atm-nsap-addr / atm-e164-addr / atm-alias-addr

atm-nsap-addr = ("NSAP" / "-" / "$") space (nsap-addr / "-" / "$") atm-e164-addr = ("E164" / "-" / "$") space (e164-addr / "-" / "$") atm-alias-addr = ("GWID" / "ALIAS" / "-" / "$") space (alias-addr /

                "-" / "$")

nsap-addr = 2(HEXDIG) "." 9(4(HEXDIG) ".") 2(HEXDIG)

e164-addr = 1*15 (DIGIT) alias-addr = 1*32(alpha-numeric / "-" / "." / "_")

session-name-field = ["s=" text EOL] ; for ATM use "s=-" text = byte-string byte-string = 1*(byte-string-char) ; definition per rfc2327 byte-string-char = %x01-09/ %x0B/ %x0C/ %x0E-FF ; all ASCII except

                 NUL, CR & LF

; Definitions of information-field, uri-field, email-fields, ; phone-fields per rfc2327. These fields are omitted in ; ATM SDP descriptions. If received, they are ignored in the ATM ; context

connection-field = ["c=" c-net-type-addr]

       ; connection-field required, not optional, in ATM

c-net-type-addr = nettype space c-addrtype-addr c-addrtype-addr = atm-addrtype-addr / c-ip-addrtype-addr /

                tn-addrtype-addr
 ; atm-addrtype-addr defined above
 ; c-ip-addrtype-addr per rfc2327
 ; difference in address usage between 'o' and 'c' lines per rfc2327
 ; tn-addrtype-addr per rfc2848

bandwidth-fields = *("b=" bwtype ":" bandwidth EOL)

Kumar & Mostafa Standards Track [Page 97] RFC 3108 ATM SDP May 2001

bwtype = 1*(alpha-numeric) bandwidth = 1*(DIGIT)

time-fields = *( "t=" start-time space stop-time

  • (EOL repeat-fields) EOL)

[zone-adjustments EOL] start-time = time / "0" stop-time = time / "0" ; always "0" in ATM time = POS-DIGIT 9*(DIGIT) ; same as rfc2327 ; repeat-fields and zone-adjustments per rfc2327, not used in ATM

; Definition of optional key-field per rfc2327 ;

attribute-fields = *("a=" attribute EOL)

; SDP descriptors for ATM do not have session-level media attribute ; lines. If these are provided, they should be ignored.

media-descriptions = *(media-description) media-description = media-field information-field *(connection-field)

                   bandwidth-fields key-field attribute-fields

; Definitions of information-field per RFC 2327. These fields are ; omitted in ATM SDP descriptions. If received, they are ignored in ; the ATM context ; ; In ATM, the connection-field is used in media-description to indicate ; the IP address associated with the RTCP control protocol in H.323.C ; applications. In this case, the connection field is per the RFC 2327 ; definition for IP v4-based connections. Otherwise, it is not used in ; media-description. If received as part of media-description, ; it is ignored. ; ; Definition of optional bandwidth-fields as above. : Definition of optional key-field as in RFC 2327

media-field = rfc2327-media-field / rfc2848-media-field /

            atm-media-field
  ; rfc2327-media-field and rfc2848-media-field defined in those rfc's

atm-media-field = "m=" media space vcId space transport-fmts EOL

 ; superset of rfc2327 definition

media = "audio" / "video" / "data" / "application" / "control" /

      1*(alpha-numeric)

vcId = "$" / "-" / ex-vcci / (ex-vcci "/" ex-cid) /

   (atm-type-addr-m  "/" ex-vcci) /

Kumar & Mostafa Standards Track [Page 98] RFC 3108 ATM SDP May 2001

   (atm-type-addr-m "/" ex-vcci "/" ex-cid) /
   (ex-bcg "/" ex-vcci) / (ex-bcg "/" ex-vcci "/" ex-cid)
   (ex-portid "/" ex-vpi "/" ex-vci) /
   (ex-portid "/" ex-vpi "/" ex-vci "/" ex-cid) /
   (ex-bcg "/" ex-vpi "/" ex-vci) /
   (ex-bcg "/" ex-vpi "/" ex-vci "/" ex-cid) /
   (ex-vpci "/" ex-vci) /
   (ex-vpci "/" ex-vci "/" ex-cid) /
   (atm-type-addr-m  "/" ex-vpci "/" ex-vci) /
   (atm-type-addr-m  "/" ex-vpci "/" ex-vci "/" ex-cid)

atm-type-addr-m = atm-nsap-addr-m / atm-e164-addr-m / atm-alias-addr-m atm-nsap-addr-m = ["NSAP-"] (nsap-addr / "$") atm-e164-addr-m = ["E164-"] (e164-addr / "$") atm-alias-addr-m = ["GWID-" / "ALIAS-"] (alias-addr / "$") ; The -m at the end indicates use in the media field ; Wildcarding rules different from ATM address on 'o' and 'c' lines

ex-vcci = "VCCI-" vcci ex-cid = "CID-" cid ex-bcg = "BCG-" bcg ex-portid = "PORT-" portid ex-vpi = "VPI-" vpi ex-vci = "VCI-" vci ex-vpci = "VPCI-" vpci

vcci = generic-U16 cid = generic-U8 bcg = generic-U8 portid = 1*32 (HEXDIG) vpi = generic-U12 vci = generic-U16 vpci = generic-U16

transport-fmts = generic-transport-fmts / known-transport-fmts / "- -" generic-transport-fmts = generic-transport 1*(space fmt) generic-transport = 1*(alpha-numeric / "/") fmt = 1*(alpha-numeric)

known-transport-fmts = aal1-transport space aal1-fmt-list /

                     aal2-transport space aal2-fmt-list
                     *(space aal2-transport space aal2-fmt-list) /
                     aal5-transport space aal5-fmt-list /
                     rtp-transport space rtp-fmt-list /
                     tn-proto space tn-fmt-list /
                     h323c-proto "-"

h323c-proto = "H323c"

Kumar & Mostafa Standards Track [Page 99] RFC 3108 ATM SDP May 2001

  ; h323c-proto used for RTCP control ports in H.323 annex C
  ; applications.  tn-proto and tn-fmt-list per rfc2848

aal1-transport = "AAL1" "/" aal1-transport-list aal1-transport-list = "ATMF" / "ITU" / "custom" / "IEEE:" oui /

                    corporate-name

corporate-name = 1*(safe) aal2-transport = "AAL2" "/" aal2-transport-list aal2-transport-list = aal1-transport-list aal5-transport = "AAL5" "/" aal5-transport-list aal5-transport-list = aal1-transport-list rtp-transport = "RTP" "/" rtp-transport-list rtp-transport-list = "AVP"

aal1-fmt-list = (payload-type *(space payload-type)) / "-" payload-type = decimal-uchar aal5-fmt-list = aal1-fmt-list rtp-fmt-list = aal1-fmt-list aal2-fmt-list = (profile *(space profile)) / "-" profile = decimal-uchar attribute-fields = *("a=" attribute EOL) attribute = known-attribute / (generic-att-field ":" att-value) /

          generic-att-field

generic-att-field = 1*(alpha-numeric) att-value = byte-string known-attribute = atm-attribute / PINT-attribute / rfc2327-attribute

       ; PINT-attribute as defined in rfc2848
       ; rfc2327 attribute as defined in that rfc

atm-attribute =

    "eecid" ":" eecid /
    "aalType" ":" aalType /
    "capability" ":" (asc / atc) space subtype /
    "qosclass" ":" qosclass /
    "bcob" ":" bcob space eetim /
    "stc" ":" stc /
    "upcc" ":" upcc /
    "atmQOSparms" ":" directionFlag space cdvType
                    space acdv space ccdv space eetd space cmtd
                    space aclr /
    "atmTrfcDesc" ":" directionFlag space clpLvl
                    space pcr space scr space mbs space cdvt space
                    mcr space mfs space fd space te /
    "abrParms" ":" directionFlag  space nrm space trm space cdf
                  space adtf /
    "abrSetup" ":" ficr space bicr space ftbe space btbe space
           crmrtt space frif space brif space frdf space brdf /
    "bearertype" ":" bearerType space localInitiation  /

Kumar & Mostafa Standards Track [Page 100] RFC 3108 ATM SDP May 2001

    "lij" ":" sci space lsn /
    "anycast" ":" atmGroupAddress space cdStd space
               conScpTyp space conScpSel /
    "cache" ":" cacheEnable space cacheTimer /
    "bearerSigIE" ":" bearerSigIEType space
             bearerSigIELng space bearerSigIEVal /
    "aalApp" ":" appClass space oui space appId /
    "cbrRate" ":" cbrRate /
    "sbc" ":" sbc /
    "clkrec" ":" clkrec /
    "fec" ":" fecEnable /
    "prtfl" ":" partialFill /
    "structure" ":" structureEnable space blksz /
    "cpsSDUsize" ":" directionFlag space cpcs /
    "aal2CPS" ":" cidLowerLimit space cidUpperLimit space
             timerCU space simplifiedCPS /
    "aal2CPSSDUrate" ":" fSDUrate space bSDUrate /
    "aal2sscs3661unassured" ":" ted space rastimer space fsssar
              space bsssar /
    "aal2sscs3661assured" ":" rastimer space fsssar space bsssar
         space fsscopsdu space bsscopsdu space fsscopuu
         space bsscopuu  /
    "aal2sscs3662" ":" sap space circuitMode space frameMode
         space faxDemod space cas space dtmf space mfall space mfr1
         space mfr2 space PCMencoding space fmaxFrame
         space bmaxFrame /
    "aal5sscop" ":" fsscopsdu space bsscopsdu space fsscopuu
           space bsscopuu  /
    "atmmap" ":" payload-type space encoding-name /
    "silenceSupp" ":" silenceSuppEnable space silenceTimer
             space suppPref space sidUse space fxnslevel /
    "ecan" ":" directionFlag space ecanEnable space ecanType /
    "gc" ":" directionFlag space gcEnable space gcLvl /
    "profileDesc" ":" aal2-transport space profile space
       1*(profile-row) /
    "vsel" ":" 1*(encoding-name space packet-length space
                                packet-time space) /
    "dsel" ":" fxIncl space
               1*(encoding-name space packet-length space
                                packet-time space) /
    "fsel" ":" 1*(encoding-name space packet-length space
                                packet-time space) /
    "onewaySel" ":" serviceType space directionFlag space
               1*(encoding-name space packet-length space
                                packet-time space) /
    "codecconfig" ":" q7655scc /
    "isup_usi" ":" isupUsi /

Kumar & Mostafa Standards Track [Page 101] RFC 3108 ATM SDP May 2001

    "uiLayer1_Prot" ":" uiLayer1Prot /
    "chain" ":" chainPointer

eecid = 8 (HEXDIG) aalType = "AAL1" / "AAL2" / "AAL3/4" / "AAL5" / "USER_DEFINED_AAL" asc = "CBR" / "nrt-VBR" / "rt-VBR" / "UBR" / "ABR" / "GFR" atc = "DBR" / "SBR" / "ABT/IT" / "ABT/DT" / "ABR" subtype = decimal-U8-or-null qosclass = decimal-U8-or-null bcob = generic-U8 eetim = on-off-or-null stc = decimal-uchar upcc = decimal-uchar directionFlag = "f" / "b" / "fb" cdvType = "PP" / "2P" / "-" acdv = decimal-U32-or-null ccdv = decimal-U32-or-null eetd = decimal-U16-or-null cmtd = decimal-U16-or-null aclr = decimal-U8-or-null clpLvl = "0" / "0+1" / "-" pcr = decimal-U24-or-null scr = decimal-U24-or-null mbs = decimal-U16-or-null cdvt = decimal-U24-or-null mcr = decimal-U24-or-null mfs = decimal-U16-or-null fd = on-off-or-null te = on-off-or-null nrm = generic-U8-or-null trm = generic-U8-or-null cdf = generic-U8-or-null adtf = generic-U16-or-null ficr = decimal-U24-or-null bicr = decimal-U24-or-null ftbe = decimal-U24-or-null btbe = decimal-U24-or-null crmrtt = decimal-U24-or-null frif = 1*2 (DIGIT) brif = 1*2 (DIGIT) frdf = 1*2 (DIGIT) brdf = 1*2 (DIGIT) bearerType = "PVC" / "SVC" / "CID" localInitiation = on-off-or-null sci = generic-U8-or-null lsn = generic-U32-or-null atmGroupAddress = atm-type-addr cdStd = generic-U8-or-null

Kumar & Mostafa Standards Track [Page 102] RFC 3108 ATM SDP May 2001

conScpTyp = generic-U8-or-null conScpSel = generic-U8-or-null cacheEnable = on-off-or-null cacheTimer = generic-U32-or-null bearerSigIEType = 2 * (HEXDIG) bearerSigIELng = 1*4 (HEXDIG) bearerSigIEVal = 2*512 (HEXDIG) appClass = "-" /

        "itu_h323c" / "af83" / "AAL5_SSCOP" / "itu_i3661_unassured" /
        "itu_ i3661_assured"/ "itu_i3662"/ "itu_i3651" /
        "itu_i3652" / "itu_i3653" / "itu_i3654" / "FRF11" / "FRF5" /
        "FRF8" / "itu_h2221"

oui = "-" / 1*6 (HEXDIG) appId = "-" / 1*8 (HEXDIG) cbrRate = 2 (HEXDIG) sbc = generic-U8 clkrec = "NULL" / "SRTS" / "ADAPTIVE" fecEnable = "NULL" / "LOSS_SENSITIVE" / "DELAY_SENSITIVE" partialFill = generic-U8 structureEnable = on-off-or-null blksz = generic-U16-or-null cpcs = generic-U16 cidLowerLimit = generic-U8-or-null cidUpperLimit = generic-U8-or-null timerCU = decimal-U32-or-null simplifiedCPS = on-off-or-null fSDUrate = decimal-U24-or-null bSDUrate = decimal-U24-or-null ted = on-off-or-null rastimer = decimal-U32-or-null fsssar = generic-U24-or-null bsssar = generic-U24-or-null fsscopsdu = generic-U16-or-null bsscopsdu = generic-U16-or-null fsscopuu = generic-U16-or-null bsscopuu = generic-U16-or-null sap = "AUDIO" / "MULTIRATE" / "-" circuitMode = on-off-or-null frameMode = on-off-or-null faxDemod = on-off-or-null cas = on-off-or-null dtmf = on-off-or-null mfall = on-off-or-null mfr1 = on-off-or-null mfr2 = on-off-or-null PCMencoding = "PCMA" / "PCMU" / "-" fmaxframe = generic-U16-or-null bmaxframe = generic-U16-or-null

Kumar & Mostafa Standards Track [Page 103] RFC 3108 ATM SDP May 2001

silenceSuppEnable = on-off-or-null silenceTimer = generic-U16-or-null suppPref = "standard" / "custom" / "-" sidUse = "No SID" / "Fixed Noise" / "Sampled Noise" / "-" fxnslevel = generic-U8-or-null ecanEnable = on-off-or-null ecanType = "G165" / "G168" / "-" gcEnable = on-off-or-null gcLvl = generic-U16-or-null

profile-row = uuiCodeRange space encoding-name space packet-length

                 space packet-time space

uuiCodeRange = decimal-uchar "-" decimal-uchar / "-" encoding-name = "-" /

              "PCMG" / "SIDG" / "SID729" /
              "PCMU" / "G726-32" / "G723" / "PCMA" / "G722" / "G728" /
              "G729" / "X-G729a" / "X-G729b" / "X-G729ab" /
              "X-G726-16" / "X-G726-24" / "X-G726-40" / "X-G7231-H" /
              "X-G7231-L" / "X-G7231a-H" / "X-G7231a-L" /
              "X-G727-16" / "X-G727-24" / "X-G727-32" /
              "X-CCD" / "X-CCD-CAS" / "GSM" / "GSM-HR" / "GSM-EFR" /
              "GSM-EHR" / "X-FXDMOD-3" / "1016" / "DVI4" / "L16" /
              "LPC" / "MPA" / "QCELP" / "H263" / "H263-1998" /
              "JPEG" / "H261" / "MPV" / "MP2T" / "nv" / "RED" /
              "CelB" / "L8" / "VDVI" / "MP1S" / "MP2P" / "BT656" /
              "FR-AMR" / "HR-AMR" / "UMTS-AMR" / "AMR"

packet-length = decimal-U8-or-null packet-time = decimal-U16-or-null fxIncl = on-off-or-null serviceType = "v" / "d" / "f" / "df" / "all" q7655scc = 4*32 (HEXDIG) isupUsi = 4*24 (HEXDIG) uiLayer1Prot = 2 (HEXDIG)

chainPointer = "NEXT" / "PREVIOUS" / "NULL"

References

 [1]  Handley, M. and V. Jacobson, "SDP: Session Description
      Protocol", RFC 2327, April 1998.
 [2]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
      "RTP:  A Transport Protocol for Real-Time Applications", RFC
      1889, January 1996.
      RFC 1889 will be obsoleted, in a substantially backwards
      compatible manner, by a work in progress that will become an
      RFC.

Kumar & Mostafa Standards Track [Page 104] RFC 3108 ATM SDP May 2001

 [3]  Schulzrinne, H., "RTP Profile for Audio and Video Conferences
      with Minimal Control", RFC 1890, January 1996.
      RFC 1890 will be obsoleted, in a fully backwards compatible
      manner, by a work in progress that will become an RFC.
 [4]  ATMF UNI 3.1 Specification,  af-uni-0010.002. Of special
      interest for this document is  Section 5.4.5.5,  ATM Adaptation
      Layer Parameters.
 [5]  ATMF UNI 4.0 Signaling Specification, af-sig-0061.000.
 [6]  ATMF Traffic Management Specification, Version 4.1, af-tm-
      0121.000.
 [7]  ATMF Circuit Emulation Service (CES) Interoperability
      Specification, version 2.0, af-vtoa-0078.000, Jan. 97.
 [8]  ATMF Voice and Telephony over ATM - ATM Trunking using AAL1 for
      Narrowband Services, version 1.0, af-vtoa-0089.000, July 1997.
 [9]  ATMF Specifications of (DBCES) Dynamic Bandwidth Utilization -
      in 64kbps Timeslot Trunking over ATM  - using CES, af-vtoa-
      0085.000, July 1997.
 [10] ITU-T I.363.1, B-ISDN ATM Adaptation Layer Specification: Type 1
      AAL, August 1996.
 [11] ITU-T I.363.2, B-ISDN ATM Adaptation Layer Specification: Type 2
      AAL, Sept. 1997.
 [12] ITU-T I.366.1, Segmentation and Reassembly Service Specific
      Convergence Sublayer  for AAL Type 2, June 1998.
 [13] ITU-T I.366.2, AAL Type 2 Reassembly Service Specific
      Convergence Sublayer  for Trunking, Feb. 99.
 [14] Petrack, S., "RTP payloads for Telephone Signal Events", Work in
      Progress.
 [15] ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling.
 [16] Amendment 1, 2, 3 and 4 to ITU-T Q.2931, B-ISDN Application
      Protocol for Access Signaling.
 [17] Handley, M., Perkins C. and E. Whelan, "Session Announcement
      Protocol", RFC 2974, October 2000.

Kumar & Mostafa Standards Track [Page 105] RFC 3108 ATM SDP May 2001

 [18] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,
      "Session Initiation Protocol (SIP)", RFC 2543, March 1999.
 [19] Almquist, P., "Type of Service in the Internet Protocol Suite",
      July 1992.
 [20] Nichols, K., Blake, S., Baker, F. and D. Black, "Definition of
      the Differentiated Services Field (DS Field) in the IPv4 and
      IPv6 Headers", December 1998.
 [21] ITU-T I.363.5, B-ISDN ATM Adaptation Layer Specification: Type 5
      AAL, Aug. 1996.
 [22] ATMF PNNI 1.0, af-pnni-0055.000, March 1996.
 [23] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
      "RTP: A Transport Protocol for Real-Time Applications", Work in
      Progress.
 [24] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
      Conferences with Minimal Control", Work in Progress.
 [25] Arango, M., Dugan, A., Elliott, I., Huitema, C. and S. Pickett,
      "Media Gateway Control Protocol (MGCP)", RFC 2705, October 1999.
 [26] Cuervo, F., Greene, N., Rayhan, A., Huitema, C., Rosen, B. and
      J.  Segers, "Megaco Protocol Version 1.0", RFC 3015, November
      2000.
 [27] Atkinson, R., "IP Authentication Header", RFC 1826, August 1995.
 [28] ITU I.371, Traffic Control and Congestion Control in the BISDN.
 [29] ITU E.191, BISDN Numbering and Addressing.
 [30] ATM Forum Addressing: Reference Guide, af-ra-0106.000.
 [31] http://www.iana.org/assignments/rtp-parameters for a list of
      codecs with static payload types.
 [32] ITU Q.2941-2, Digital Subscriber Signalling System No. 2 (DSS
      2): Generic identifier transport extensions.
 [33] ITU Q.2961, Digital subscriber signalling system no.2 (DSS 2) -
      additional traffic parameters. Also, Amendment 2 to Q.2961.
 [34] ITU Q. 2965.1, Digital subscriber signalling system no.2 (DSS 2)
      - Support of Quality of Service classes.

Kumar & Mostafa Standards Track [Page 106] RFC 3108 ATM SDP May 2001

 [35] ITU Q. 2965.2, Digital subscriber signalling system no.2 (DSS 2)
      - Signalling of individual Quality of Service parameters.
 [36] ITU Q.1901, Bearer Independent Call Control Protocol.
 [37] ITU Q.2630.1, AAL type 2 signaling protocol - capability set 1.
 [38] ITU I.363.5, B-ISDN ATM Adaptation Layer specification: Type 5
      AAL.
 [39] I.365.1,Frame relaying service specific convergence sublayer
      (FR-SSCS).
 [40] I.365.2, B-ISDN ATM adaptation layer sublayers: service specific
      coordination function to provide the connection oriented network
      service.
 [41] I.365.3, B-ISDN ATM adaptation layer sublayers: service specific
      coordination function to provide the connection-oriented
      transport service.
 [42] I.365.4, B-ISDN ATM adaptation layer sublayers: Service specific
      convergence sublayer for HDLC applications.
 [43] Q.2110, B-ISDN ATM adaptation layer - service specific
      connection oriented  protocol (SSCOP).
 [44] af-vtoa-0113.000, ATM trunking using AAL2 for narrowband
      services.
 [45] H.323-2, Packet-based multimedia communications systems.
 [46] af-vtoa-0083.000, Voice and Telephony Over ATM to the Desktop.
 [47] I.356, BISDN ATM layer cell transfer performance.
 [48] ITU Q.2957, Digital Subscriber Signaling System No. 2, User to
      user signaling.
 [49] Mills, D., "Network Time Protocol (Version 3) Specification,
      Implementation and Analysis", RFC 1305, March 1992.
 [50] TIA/EIA/IS-J-STD-025-A, Lawfully Authorized Electronic
      Surveillance, May 2000.
 [51] ITU-T H.222.1, Multimedia multiplex and synchronization for
      audiovisual communication in ATM environments.

Kumar & Mostafa Standards Track [Page 107] RFC 3108 ATM SDP May 2001

 [52] af-vmoa-0145.000, Voice and Multimedia over ATM, Loop Emulation
      Service using AAL2.
 [53] FRF.5, Frame Relay/ATM PVC Network Interworking Implementation
      Agreement.
 [54] FRF.8.1, Frame Relay/ATM PVC Service Interworking Implementation
      Agreement.
 [55] FRF.11, Voice over Frame Relay Implementation Agreement.
 [56] Crocker, D. and P. Overell, "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, November 1997.
 [57] ITU Q.765.5, Application Transport Mechanism - Bearer
      Independent Call Control.
 [58] http://www.3gpp.org/ftp/Specs for specifications related to
      3GPP, including AMR codecs.
 [59] ITU Q.931, Digital Subscriber Signaling System No. 1: Network
      Layer.
 [60] ITU Q.763, SS7 - ISUP formats and codes.
 [61] http://www.atmforum.com/atmforum/specs/specs.html, ATM Forum,
      Well-known addresses and assigned codes.
 [62] Bradner, S., "Keywords for use in RFCs to indicate requirement
      levels", BCP 14, RFC 2119, March 1997.

Kumar & Mostafa Standards Track [Page 108] RFC 3108 ATM SDP May 2001

Acknowledgements

 The authors wish to thank several colleagues at Cisco and in the
 industry who have contributed towards the development of these SDP
 conventions, and who have reviewed, implemented and tested these
 constructs.  Valuable technical ideas that have been incorporated
 into this internet document have been provided by Hisham Abdelhamid,
 Flemming Andreasen, David Auerbach, Robert Biskner, Bruce Buffam,
 Steve Casner, Alex Clemm, Bill Foster, Snehal Karia, Raghu Thirumalai
 Rajan, Joe Stone, Bruce Thompson, Dan Wing and Ken Young of Cisco,
 Michael Brown, Rade Gvozdanovic, Graeme Gibbs, Tom-PT Taylor, Mark
 Watson and Sophia Scoggins of Nortel Networks, Brian Rosen, Tim
 Dwight and Michael Mackey of Marconi, Ed Guy and Petros Mouchtaris of
 Telcordia, Christian Groves of Ericsson, Charles Eckel of Vovida
 Networks, Tom Jepsen, Dal Chohan, Sagar Gordhan and Chris Gallon of
 Fujitsu, Mahamood Hussain of Hughes Software Systems and Sean Sheedy
 of nCUBE Corporation, Narendra Tulpule of Intel, Albrecht Schwarz of
 Alcatel, and Jonathan Rosenberg of Dynamicsoft.  The authors also
 wish to thank the ISC device control group, and the MMUSIC and MEGACO
 subgroups of the IETF, especially Bill Foster, Joerg Ott, Sean Sheedy
 and Brian Rosen for their help in the preparation of this document.
 Finally, thanks are due to Narendra Tulpule of Intel whose ABNF
 grammar was adapted for this document.

Authors' Addresses

 Rajesh Kumar
 Cisco Systems, Inc.
 M/S SJC01/3
 170 West Tasman Drive
 San Jose, CA 95134-1706
 Phone: 1-800-250-4800
 EMail: rkumar@cisco.com
 Mohamed Mostafa
 Cisco Systems, Inc.
 M/S SJC01/3
 170 West Tasman Drive
 San Jose, CA 95134-1706
 Phone: 1-800-250-4800
 EMail: mmostafa@cisco.com

Kumar & Mostafa Standards Track [Page 109] RFC 3108 ATM SDP May 2001

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Kumar & Mostafa Standards Track [Page 110]

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