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rfc:rfc5762

Internet Engineering Task Force (IETF) C. Perkins Request for Comments: 5762 University of Glasgow Category: Standards Track April 2010 ISSN: 2070-1721

      RTP and the Datagram Congestion Control Protocol (DCCP)

Abstract

 The Real-time Transport Protocol (RTP) is a widely used transport for
 real-time multimedia on IP networks.  The Datagram Congestion Control
 Protocol (DCCP) is a transport protocol that provides desirable
 services for real-time applications.  This memo specifies a mapping
 of RTP onto DCCP, along with associated signalling, such that real-
 time applications can make use of the services provided by DCCP.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5762.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Perkins Standards Track [Page 1] RFC 5762 RTP over DCCP April 2010

 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1. Introduction ....................................................3
 2. Rationale .......................................................3
 3. Conventions Used in This Memo ...................................4
 4. RTP over DCCP: Framing ..........................................4
    4.1. RTP Data Packets ...........................................4
    4.2. RTP Control Packets ........................................5
    4.3. Multiplexing Data and Control ..............................7
    4.4. RTP Sessions and DCCP Connections ..........................7
    4.5. RTP Profiles ...............................................8
 5. RTP over DCCP: Signalling using SDP .............................8
    5.1. Protocol Identification ....................................8
    5.2. Service Codes .............................................10
    5.3. Connection Management .....................................11
    5.4. Multiplexing Data and Control .............................11
    5.5. Example ...................................................11
 6. Security Considerations ........................................12
 7. IANA Considerations ............................................13
 8. Acknowledgements ...............................................14
 9. References .....................................................14
    9.1. Normative References ......................................14
    9.2. Informative References ....................................15

Perkins Standards Track [Page 2] RFC 5762 RTP over DCCP April 2010

1. Introduction

 The Real-time Transport Protocol (RTP) [1] is widely used in video
 streaming, telephony, and other real-time networked applications.
 RTP can run over a range of lower-layer transport protocols, and the
 performance of an application using RTP is heavily influenced by the
 choice of lower-layer transport.  The Datagram Congestion Control
 Protocol (DCCP) [2] is a transport protocol that provides desirable
 properties for real-time applications running on unmanaged best-
 effort IP networks.  This memo describes how RTP can be framed for
 transport using DCCP, and discusses some of the implications of such
 a framing.  It also describes how the Session Description Protocol
 (SDP) [3] can be used to signal such sessions.
 The remainder of this memo is structured as follows: it begins with a
 rationale for the work in Section 2, describing why a mapping of RTP
 onto DCCP is needed.  Following a description of the conventions used
 in this memo in Section 3, the specification begins in Section 4 with
 the definition of how RTP packets are framed within DCCP.  Associated
 signalling is described in Section 5.  Security considerations are
 discussed in Section 6, and IANA considerations in Section 7.

2. Rationale

 With the widespread adoption of RTP have come concerns that many
 real-time applications do not implement congestion control, leading
 to the potential for congestion collapse of the network [15].  The
 designers of RTP recognised this issue, stating in RFC 3551 that [4]:
    If best-effort service is being used, RTP receivers SHOULD monitor
    packet loss to ensure that the packet loss rate is within
    acceptable parameters.  Packet loss is considered acceptable if a
    TCP flow across the same network path and experiencing the same
    network conditions would achieve an average throughput, measured
    on a reasonable timescale, that is not less than the RTP flow is
    achieving.  This condition can be satisfied by implementing
    congestion control mechanisms to adapt the transmission rate (or
    the number of layers subscribed for a layered multicast session),
    or by arranging for a receiver to leave the session if the loss
    rate is unacceptably high.
 While the goals are clear, the development of TCP friendly congestion
 control that can be used with RTP and real-time media applications is
 an open research question with many proposals for new algorithms, but
 little deployment experience.

Perkins Standards Track [Page 3] RFC 5762 RTP over DCCP April 2010

 Two approaches have been used to provide congestion control for RTP:
 1) develop RTP extensions that incorporate congestion control; and 2)
 provide mechanisms for running RTP over congestion-controlled
 transport protocols.  An example of the first approach can be found
 in [16], extending RTP to incorporate feedback information such that
 TCP Friendly Rate Control (TFRC) [17] can be implemented at the
 application level.  This will allow congestion control to be added to
 existing applications without operating system or network support,
 and it offers the flexibility to experiment with new congestion
 control algorithms as they are developed.  Unfortunately, it also
 passes the complexity of implementing congestion control onto
 application authors, a burden which many would prefer to avoid.
 The second approach is to run RTP on a lower-layer transport protocol
 that provides congestion control.  One possibility is to run RTP over
 TCP, as defined in [5], but the reliable nature of TCP and the
 dynamics of its congestion control algorithm make this inappropriate
 for most interactive real-time applications (the Stream Control
 Transmission Protocol (SCTP) is inappropriate for similar reasons).
 A better fit for such applications may be to run RTP over DCCP, since
 DCCP offers unreliable packet delivery and a choice of congestion
 control.  This gives applications the ability to tailor the transport
 to their needs, taking advantage of better congestion control
 algorithms as they come available, while passing the complexity of
 implementation to the operating system.  If DCCP should come to be
 widely available, it is believed these will be compelling advantages.
 Accordingly, this memo defines a mapping of RTP onto DCCP.

3. Conventions Used in This Memo

 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 [6].

4. RTP over DCCP: Framing

 The following section defines how RTP and RTP Control Protocol (RTCP)
 packets can be framed for transport using DCCP.  It also describes
 the differences between RTP sessions and DCCP connections, and the
 impact these have on the design of applications.

4.1. RTP Data Packets

 Each RTP data packet MUST be conveyed in a single DCCP datagram.
 Fields in the RTP header MUST be interpreted according to the RTP
 specification, and any applicable RTP Profile and Payload Format.
 Header processing is not affected by DCCP framing (in particular,

Perkins Standards Track [Page 4] RFC 5762 RTP over DCCP April 2010

 note that the semantics of the RTP sequence number and the DCCP
 sequence number are not compatible, and the value of one cannot be
 inferred from the other).
 A DCCP connection is opened when an end system joins an RTP session,
 and it remains open for the duration of the session.  To ensure NAT
 bindings are kept open, an end system SHOULD send a zero-length DCCP-
 Data packet once every 15 seconds during periods when it has no other
 data to send.  This removes the need for RTP no-op packets [18], and
 similar application-level keepalives, when using RTP over DCCP.  This
 application-level keepalive does not need to be sent if it is known
 that the DCCP CCID in use provides a transport-level keepalive, or if
 the application can determine that there are no NAT devices on the
 path.
 RTP data packets MUST obey the dictates of DCCP congestion control.
 In some cases, the congestion control will require a sender to send
 at a rate below that which the payload format would otherwise use.
 To support this, an application could use either a rate-adaptive
 payload format, or a range of payload formats (allowing it to switch
 to a lower rate format if necessary).  Details of the rate adaptation
 policy for particular payload formats are outside the scope of this
 memo (but see [19] and [20] for guidance).
 RTP extensions that provide application-level congestion control
 (e.g., [16]) will conflict with DCCP congestion control, and MUST NOT
 be used.
 DCCP allows an application to choose the checksum coverage, using a
 partial checksum to allow an application to receive packets with
 corrupt payloads.  Some RTP Payload Formats (e.g., [21]) can make use
 of this feature in conjunction with payload-specific mechanisms to
 improve performance when operating in environments with frequent non-
 congestive packet corruption.  If such a payload format is used, an
 RTP end system MAY enable partial checksums at the DCCP layer, in
 which case the checksum MUST cover at least the DCCP and RTP headers
 to ensure packets are correctly delivered.  Partial checksums MUST
 NOT be used unless supported by mechanisms in the RTP payload format.

4.2. RTP Control Packets

 The RTP Control Protocol (RTCP) is used in the standard manner with
 DCCP.  RTCP packets are grouped into compound packets, as described
 in Section 6.1 of [1], and each compound RTCP packet is transported
 in a single DCCP datagram.

Perkins Standards Track [Page 5] RFC 5762 RTP over DCCP April 2010

 The usual RTCP timing rules apply, with the additional constraint
 that RTCP packets MUST obey the DCCP congestion control algorithm
 negotiated for the connection.  This can prevent a participant from
 sending an RTCP packet at the expiration of the RTCP transmission
 timer if there is insufficient network capacity available.  In such
 cases the RTCP packet is delayed and sent at the earliest possible
 instant when capacity becomes available.  The actual time the RTCP
 packet was sent is then used as the basis for calculating the next
 RTCP transmission time.
 RTCP packets comprise only a small fraction of the total traffic in
 an RTP session.  Accordingly, it is expected that delays in their
 transmission due to congestion control will not be common, provided
 the configured nominal "session bandwidth" (see Section 6.2 of [1])
 is in line with the bandwidth achievable on the DCCP connection.  If,
 however, the capacity of the DCCP connection is significantly below
 the nominal session bandwidth, RTCP packets may be delayed enough for
 participants to time out due to apparent inactivity.  In such cases,
 the session parameters SHOULD be re-negotiated to more closely match
 the available capacity, for example by performing a re-invite with an
 updated "b=" line when using the Session Initiation Protocol [22] for
 signalling.
    Note: Since the nominal session bandwidth is chosen based on media
    codec capabilities, a session where the nominal bandwidth is much
    larger than the available bandwidth will likely become unusable
    due to constraints on the media channel, and so require
    negotiation of a lower bandwidth codec, before it becomes unusable
    due to constraints on the RTCP channel.
 As noted in Section 17.1 of [2], there is the potential for overlap
 between information conveyed in RTCP packets and that conveyed in
 DCCP acknowledgement options.  In general this is not an issue since
 RTCP packets contain media-specific data that is not present in DCCP
 acknowledgement options, and DCCP options contain network-level data
 that is not present in RTCP.  Indeed, there is no overlap between the
 five RTCP packet types defined in the RTP specification [1] and the
 standard DCCP options [2].  There are, however, cases where overlap
 does occur: most clearly between the Loss RLE Report Blocks defined
 as part of the RTCP Extended Reports [23] and the DCCP Ack Vector
 option.  If there is overlap between RTCP report packets and DCCP
 acknowledgements, an application SHOULD use either RTCP feedback or
 DCCP acknowledgements, but not both (use of both types of feedback
 will waste available network capacity, but is not otherwise harmful).

Perkins Standards Track [Page 6] RFC 5762 RTP over DCCP April 2010

4.3. Multiplexing Data and Control

 The obvious mapping of RTP onto DCCP creates two DCCP connections for
 each RTP flow: one for RTP data packets and one for RTP control
 packets.  A frequent criticism of RTP relates to the number of ports
 it uses, since large telephony gateways can support more than 32768
 RTP flows between pairs of gateways, and so run out of UDP ports.  In
 addition, use of multiple ports complicates NAT traversal.  For these
 reasons, it is RECOMMENDED that the RTP and RTCP traffic for a single
 RTP session is multiplexed onto a single DCCP connection following
 the guidelines in [7], where possible (it may not be possible in all
 circumstances, for example when translating from an RTP stream over a
 non-DCCP transport that uses conflicting RTP payload types and RTCP
 packet types).

4.4. RTP Sessions and DCCP Connections

 An end system SHOULD NOT assume that it will observe only a single
 RTP synchronisation source (SSRC) because it is using DCCP framing.
 An RTP session can span any number of transport connections, and can
 include RTP mixers or translators bringing other participants into
 the session.  The use of a unicast DCCP connection does not imply
 that the RTP session will have only two participants, and RTP end
 systems SHOULD assume that multiple synchronisation sources may be
 observed when using RTP over DCCP, unless otherwise signalled.
 An RTP translator bridging multiple DCCP connections to form a single
 RTP session needs to be aware of the congestion state of each DCCP
 connection, and must adapt the media to the available capacity of
 each.  The Codec Control Messages defined in [24] may be used to
 signal congestion state to the media senders, allowing them to adapt
 their transmission.  Alternatively, media transcoding may be used to
 perform adaptation: this is computationally expensive, induces delay,
 and generally gives poor-quality results.  Depending on the payload,
 it might also be possible to use some form of scalable coding.
 A single RTP session may also span a DCCP connection and some other
 type of transport connection.  An example might be an RTP over DCCP
 connection from an RTP end system to an RTP translator, with an RTP
 over UDP/IP multicast group on the other side of the translator.  A
 second example might be an RTP over DCCP connection that links Public
 Switched Telephone Network (PSTN) gateways.  The issues for such an
 RTP translator are similar to those when linking two DCCP
 connections, except that the congestion control algorithms on either
 side of the translator may not be compatible.  Implementation of
 effective translators for such an environment is non-trivial.

Perkins Standards Track [Page 7] RFC 5762 RTP over DCCP April 2010

4.5. RTP Profiles

 In general, there is no conflict between new RTP profiles and DCCP
 framing, and most RTP profiles can be negotiated for use over DCCP
 with the following exceptions:
 o  An RTP profile that is intolerant of packet corruption may
    conflict with the DCCP partial checksum feature.  An example of
    this is the integrity protection provided by the RTP/SAVP profile,
    which cannot be used in conjunction with DCCP partial checksums.
 o  An RTP profile that mandates a particular non-DCCP lower-layer
    transport will conflict with DCCP.
 RTP profiles that fall under these exceptions SHOULD NOT be used with
 DCCP unless the conflicting features can be disabled.
 Of the profiles currently defined, the RTP Profile for Audio and
 Video Conferences with Minimal Control [4], the Secure Real-time
 Transport Protocol [8], the Extended RTP Profile for RTCP-based
 Feedback [9], and the Extended Secure RTP Profile for RTCP-based
 Feedback [10] MAY be used with DCCP (noting the potential conflict
 between DCCP partial checksums and the integrity protection provided
 by the secure RTP variants -- see Section 6).

5. RTP over DCCP: Signalling using SDP

 The Session Description Protocol (SDP) [3] and the offer/answer model
 [11] are widely used to negotiate RTP sessions (for example, using
 the Session Initiation Protocol [22]).  This section describes how
 SDP is used to signal RTP sessions running over DCCP.

5.1. Protocol Identification

 SDP uses a media ("m=") line to convey details of the media format
 and transport protocol used.  The ABNF syntax of a media line is as
 follows (from [3]):
     media-field = %x6d "=" media SP port ["/" integer] SP proto
                   1*(SP fmt) CRLF
 The proto field denotes the transport protocol used for the media,
 while the port indicates the transport port to which the media is
 sent.  Following [5] and [12], this memo defines these five values of
 the proto field to indicate media transported using DCCP:

Perkins Standards Track [Page 8] RFC 5762 RTP over DCCP April 2010

     DCCP
     DCCP/RTP/AVP
     DCCP/RTP/SAVP
     DCCP/RTP/AVPF
     DCCP/RTP/SAVPF
 The "DCCP" protocol identifier is similar to the "UDP" and "TCP"
 protocol identifiers and denotes the DCCP transport protocol [2], but
 not its upper-layer protocol.  An SDP "m=" line that specifies the
 "DCCP" protocol MUST further qualify the application-layer protocol
 using a "fmt" identifier (the "fmt" namespace is managed in the same
 manner as for the "UDP" protocol identifier).  A single DCCP port is
 used, as denoted by the port field in the media line.  The "DCCP"
 protocol identifier MUST NOT be used to signal RTP sessions running
 over DCCP; those sessions MUST use a protocol identifier of the form
 "DCCP/RTP/..." as described below.
 The "DCCP/RTP/AVP" protocol identifier refers to RTP using the RTP
 Profile for Audio and Video Conferences with Minimal Control [4]
 running over DCCP.
 The "DCCP/RTP/SAVP" protocol identifier refers to RTP using the
 Secure Real-time Transport Protocol [8] running over DCCP.
 The "DCCP/RTP/AVPF" protocol identifier refers to RTP using the
 Extended RTP Profile for RTCP-based Feedback [9] running over DCCP.
 The "DCCP/RTP/SAVPF" protocol identifier refers to RTP using the
 Extended Secure RTP Profile for RTCP-based Feedback [10] running over
 DCCP.
 RTP payload formats used with the "DCCP/RTP/AVP", "DCCP/RTP/SAVP",
 "DCCP/RTP/AVPF", and "DCCP/RTP/SAVPF" protocol identifiers MUST use
 the payload type number as their "fmt" value.  If the payload type
 number is dynamically assigned, an additional "rtpmap" attribute MUST
 be included to specify the format name and parameters as defined by
 the media type registration for the payload format.
 DCCP port 5004 is registered for use by the RTP profiles listed
 above, and SHOULD be the default port chosen by applications using
 those profiles.  If multiple RTP sessions are active from a host,
 even-numbered ports in the dynamic range SHOULD be used for the other
 sessions.  If RTCP is to be sent on a separate DCCP connection to
 RTP, the RTCP connection SHOULD use the next higher destination port
 number, unless an alternative DCCP port is signalled using the
 "a=rtcp:" attribute [13].  For improved interoperability, "a=rtcp:"
 SHOULD be used whenever an alternate DCCP port is used.

Perkins Standards Track [Page 9] RFC 5762 RTP over DCCP April 2010

5.2. Service Codes

 In addition to the port number, specified on the SDP "m=" line, a
 DCCP connection has an associated service code.  A single new SDP
 attribute ("dccp-service-code") is defined to signal the DCCP service
 code according to the following ABNF [14]:
     dccp-service-attr = %x61 "=dccp-service-code:" service-code
     service-code      = hex-sc / decimal-sc / ascii-sc
     hex-sc            = %x53 %x43 "=" %x78 *HEXDIG
     decimal-sc        = %x53 %x43 "="  *DIGIT
     ascii-sc          = %x53 %x43 ":"  *sc-char
     sc-char           = %d42-43 / %d45-47 / %d63-90 / %d95 / %d97-122
 where DIGIT and HEXDIG are as defined in [14].  The service code is
 interpreted as defined in Section 8.1.2 of [2] and may be specified
 using either the hexadecimal, decimal, or ASCII formats.  A parser
 MUST interpret service codes according to their numeric value,
 independent of the format used to represent them in SDP.
 The following DCCP service codes are registered for use with RTP:
 o  SC:RTPA (equivalently SC=1381257281 or SC=x52545041): an RTP
    session conveying audio data (and OPTIONAL multiplexed RTCP)
 o  SC:RTPV (equivalently SC=1381257302 or SC=x52545056): an RTP
    session conveying video data (and OPTIONAL multiplexed RTCP)
 o  SC:RTPT (equivalently SC=1381257300 or SC=x52545054): an RTP
    session conveying text media (and OPTIONAL multiplexed RTCP)
 o  SC:RTPO (equivalently SC=1381257295 or SC=x5254504f): an RTP
    session conveying any other type of media (and OPTIONAL
    multiplexed RTCP)
 o  SC:RTCP (equivalently SC=1381253968 or SC=x52544350): an RTCP
    connection, separate from the corresponding RTP
 To ease the job of middleboxes, applications SHOULD use these service
 codes to identify RTP sessions running within DCCP.  The service code
 SHOULD match the top-level media type signalled for the session

Perkins Standards Track [Page 10] RFC 5762 RTP over DCCP April 2010

 (i.e., the SDP "m=" line), with the exception connections using media
 types other than audio, video, or text, which use SC:RTPO, and
 connections that transport only RTCP packets, which use SC:RTCP.
 The "a=dccp-service-code:" attribute is a media-level attribute that
 is not subject to the charset attribute.

5.3. Connection Management

 The "a=setup:" attribute indicates which of the endpoints should
 initiate the DCCP connection establishment (i.e., send the initial
 DCCP-Request packet).  The "a=setup:" attribute MUST be used in a
 manner comparable with [12], except that DCCP connections are being
 initiated rather than TCP connections.
 After the initial offer/answer exchange, the endpoints may decide to
 re-negotiate various parameters.  The "a=connection:" attribute MUST
 be used in a manner compatible with [12] to decide whether a new DCCP
 connection needs to be established as a result of subsequent offer/
 answer exchanges, or if the existing connection should still be used.

5.4. Multiplexing Data and Control

 A single DCCP connection can be used to transport multiplexed RTP and
 RTCP packets.  Such multiplexing MUST be signalled using an "a=rtcp-
 mux" attribute according to [7].  If multiplexed RTP and RTCP are not
 to be used, then the "a=rtcp-mux" attribute MUST NOT be present in
 the SDP offer, and a separate DCCP connection MUST be opened to
 transport the RTCP data on a different DCCP port.

5.5. Example

 An offerer at 192.0.2.47 signals its availability for an H.261 video
 session, using RTP/AVP over DCCP with service code "RTPV" (using the
 hexadecimal encoding of the service code in the SDP).  RTP and RTCP
 packets are multiplexed onto a single DCCP connection:
     v=0
     o=alice 1129377363 1 IN IP4 192.0.2.47
     s=-
     c=IN IP4 192.0.2.47
     t=0 0
     m=video 5004 DCCP/RTP/AVP 99
     a=rtcp-mux
     a=rtpmap:99 h261/90000
     a=dccp-service-code:SC=x52545056
     a=setup:passive
     a=connection:new

Perkins Standards Track [Page 11] RFC 5762 RTP over DCCP April 2010

 An answerer at 192.0.2.128 receives this offer and responds with the
 following answer:
     v=0
     o=bob 1129377364 1 IN IP4 192.0.2.128
     s=-
     c=IN IP4 192.0.2.128
     t=0 0
     m=video 9 DCCP/RTP/AVP 99
     a=rtcp-mux
     a=rtpmap:99 h261/90000
     a=dccp-service-code:SC:RTPV
     a=setup:active
     a=connection:new
 The end point at 192.0.2.128 then initiates a DCCP connection to port
 5004 at 192.0.2.47.  DCCP port 5004 is used for both the RTP and RTCP
 data, and port 5005 is unused.  The textual encoding of the service
 code is used in the answer, and represents the same service code as
 in the offer.

6. Security Considerations

 The security considerations in the RTP specification [1] and any
 applicable RTP profile (e.g., [4], [8], [9], or [10]) or payload
 format apply when transporting RTP over DCCP.
 The security considerations in the DCCP specification [2] apply.
 The SDP signalling described in Section 5 is subject to the security
 considerations of [3], [11], [12], [5], and [7].
 The provision of effective congestion control for RTP through use of
 DCCP is expected to help reduce the potential for denial of service
 present when RTP flows ignore the advice in [1] to monitor packet
 loss and reduce their sending rate in the face of persistent
 congestion.
 There is a potential conflict between the Secure RTP profiles ([8],
 [10]) and the DCCP partial checksum option, since these profiles
 introduce, and recommend the use of, message authentication for RTP
 and RTCP packets.  Message authentication codes of the type used by
 these profiles cannot be used with partial checksums, since any bit
 error in the DCCP packet payload will cause the authentication check
 to fail.  Accordingly, DCCP partial checksums SHOULD NOT be used in
 conjunction with Secure Real-time Transport Protocol (SRTP)
 authentication.  The confidentiality features of the basic RTP
 specification cannot be used with DCCP partial checksums, since bit

Perkins Standards Track [Page 12] RFC 5762 RTP over DCCP April 2010

 errors propagate.  Also, despite the fact that bit errors do not
 propagate when using AES in counter mode, the Secure RTP profiles
 SHOULD NOT be used with DCCP partial checksums, since the profiles
 require authentication for security, and authentication is
 incompatible with partial checksums.

7. IANA Considerations

 The following SDP "proto" field identifiers have been registered (see
 Section 5.1):
    Type          SDP Name                                Reference
    ----          --------                                ---------
    proto         DCCP                                    [RFC5762]
                  DCCP/RTP/AVP                            [RFC5762]
                  DCCP/RTP/SAVP                           [RFC5762]
                  DCCP/RTP/AVPF                           [RFC5762]
                  DCCP/RTP/SAVPF                          [RFC5762]
 The following new SDP attribute ("att-field") has been registered:
    Contact name: Colin Perkins <csp@csperkins.org>
    Attribute name: dccp-service-code
    Long-form attribute name in English: DCCP service code
    Type of attribute: Media level.
    Subject to the charset attribute?  No.
    Purpose of the attribute: see RFC 5762, Section 5.2
    Allowed attribute values: see RFC 5762, Section 5.2
 The following DCCP service code values have been registered (see
 Section 5.2):
    1381257281    RTPA    RTP session conveying audio     [RFC5762]
                           data (and associated RTCP)
    1381257302    RTPV    RTP session conveying video     [RFC5762]
                           data (and associated RTCP)
    1381257300    RTPT    RTP session conveying text      [RFC5762]
                           media (and associated RTCP)
    1381257295    RTPO    RTP session conveying other     [RFC5762]
                           media (and associated RTCP)
    1381253968    RTCP    RTCP connection, separate from  [RFC5762]
                           the corresponding RTP

Perkins Standards Track [Page 13] RFC 5762 RTP over DCCP April 2010

 The following DCCP ports have been registered (see Section 5.1):
    avt-profile-1 5004/dccp  RTP media data       [RFC3551, RFC5762]
    avt-profile-2 5005/dccp  RTP control protocol [RFC3551, RFC5762]
 Note: ports 5004/tcp, 5004/udp, 5005/tcp, and 5005/udp have existing
 registrations, but incorrect descriptions and references.  The IANA
 has updated the existing registrations as follows:
    avt-profile-1 5004/tcp   RTP media data       [RFC3551, RFC4571]
    avt-profile-1 5004/udp   RTP media data       [RFC3551]
    avt-profile-2 5005/tcp   RTP control protocol [RFC3551, RFC4571]
    avt-profile-2 5005/udp   RTP control protocol [RFC3551]

8. Acknowledgements

 This work was supported in part by the UK Engineering and Physical
 Sciences Research Council.  Thanks are due to Philippe Gentric,
 Magnus Westerlund, Sally Floyd, Dan Wing, Gorry Fairhurst, Stephane
 Bortzmeyer, Arjuna Sathiaseelan, Tom Phelan, Lars Eggert, Eddie
 Kohler, Miguel Garcia, and the other members of the DCCP working
 group for their comments.

9. References

9.1. Normative References

 [1]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
       "RTP: A Transport Protocol for Real-Time Applications", STD 64,
       RFC 3550, July 2003.
 [2]   Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion
       Control Protocol (DCCP)", RFC 4340, March 2006.
 [3]   Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
       Description Protocol", RFC 4566, July 2006.
 [4]   Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
       Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
 [5]   Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and
       RTP Control Protocol (RTCP) Packets over Connection-Oriented
       Transport", RFC 4571, July 2006.
 [6]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.

Perkins Standards Track [Page 14] RFC 5762 RTP over DCCP April 2010

 [7]   Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
       Control Packets on a Single Port", RFC 5761, April 2010.
 [8]   Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
       Norrman, "The Secure Real-time Transport Protocol (SRTP)",
       RFC 3711, March 2004.
 [9]   Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
       "Extended RTP Profile for Real-time Transport Control Protocol
       (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006.
 [10]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-
       time Transport Control Protocol (RTCP)-Based Feedback (RTP/
       SAVPF)", RFC 5124, February 2008.
 [11]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
       Session Description Protocol (SDP)", RFC 3264, June 2002.
 [12]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
       Session Description Protocol (SDP)", RFC 4145, September 2005.
 [13]  Huitema, C., "Real Time Control Protocol (RTCP) attribute in
       Session Description Protocol (SDP)", RFC 3605, October 2003.
 [14]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
       Specifications: ABNF", STD 68, RFC 5234, January 2008.

9.2. Informative References

 [15]  Floyd, S. and J. Kempf, "IAB Concerns Regarding Congestion
       Control for Voice Traffic in the Internet", RFC 3714,
       March 2004.
 [16]  Gharai, L., "RTP with TCP Friendly Rate Control", Work
       in Progress, July 2007.
 [17]  Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
       Friendly Rate Control (TFRC): Protocol Specification",
       RFC 5348, September 2008.
 [18]  Andreasen, F., Oran, D., and D. Wing, "A No-Op Payload Format
       for RTP", Work in Progress, May 2005.
 [19]  Phelan, T., "Strategies for Streaming Media Applications Using
       TCP-Friendly Rate  Control", Work in Progress, July 2007.
 [20]  Phelan, T., "Datagram Congestion Control Protocol (DCCP) User
       Guide", Work in Progress, April 2005.

Perkins Standards Track [Page 15] RFC 5762 RTP over DCCP April 2010

 [21]  Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie, "RTP
       Payload Format and File Storage Format for the Adaptive Multi-
       Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio
       Codecs", RFC 4867, April 2007.
 [22]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
       Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
       Session Initiation Protocol", RFC 3261, June 2002.
 [23]  Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol
       Extended Reports (RTCP XR)", RFC 3611, November 2003.
 [24]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman, "Codec
       Control Messages in the RTP Audio-Visual Profile with Feedback
       (AVPF)", Work in Progress, October 2007.

Author's Address

 Colin Perkins
 University of Glasgow
 Department of Computing Science
 Glasgow  G12 8QQ
 UK
 EMail: csp@csperkins.org

Perkins Standards Track [Page 16]

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