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rfc:rfc5938

Internet Engineering Task Force (IETF) A. Morton Request for Comments: 5938 AT&T Labs Updates: 5357 M. Chiba Category: Standards Track Cisco Systems ISSN: 2070-1721 August 2010

                 Individual Session Control Feature
        for the Two-Way Active Measurement Protocol (TWAMP)

Abstract

 The IETF has completed its work on the core specification of TWAMP --
 the Two-Way Active Measurement Protocol.  This memo describes an
 OPTIONAL feature for TWAMP, that gives the controlling host the
 ability to start and stop one or more individual test sessions using
 Session Identifiers.  The base capability of the TWAMP protocol
 requires all test sessions that were previously requested and
 accepted to start and stop at the same time.

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/rfc5938.

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.

Morton & Chiba Standards Track [Page 1] RFC 5938 TWAMP Session Control August 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
   1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
 2.  Purpose and Scope  . . . . . . . . . . . . . . . . . . . . . .  4
 3.  TWAMP Control Extensions . . . . . . . . . . . . . . . . . . .  4
   3.1.  Connection Setup with Individual Session Control . . . . .  5
   3.2.  Start-N-Sessions Command with Individual Session
         Control  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.3.  Start-N-Ack Command with Individual Session Control  . . .  7
   3.4.  Stop-N-Sessions Command with Individual Session Control  .  9
   3.5.  Stop-N-Ack Command with Individual Session Control . . . . 10
   3.6.  SERVWAIT Timeout Operation . . . . . . . . . . . . . . . . 12
   3.7.  Additional Considerations  . . . . . . . . . . . . . . . . 12
 4.  TWAMP Test with Individual Session Control . . . . . . . . . . 13
   4.1.  Sender Behavior  . . . . . . . . . . . . . . . . . . . . . 13
   4.2.  Reflector Behavior . . . . . . . . . . . . . . . . . . . . 13
 5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
 6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   6.1.  Registry Specification . . . . . . . . . . . . . . . . . . 14
   6.2.  Registry Management  . . . . . . . . . . . . . . . . . . . 14
   6.3.  Experimental Numbers . . . . . . . . . . . . . . . . . . . 15
   6.4.  Registry Contents  . . . . . . . . . . . . . . . . . . . . 15
 7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
 8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   8.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
   8.2.  Informative References . . . . . . . . . . . . . . . . . . 16

Morton & Chiba Standards Track [Page 2] RFC 5938 TWAMP Session Control August 2010

1. Introduction

 The IETF has completed its work on the core specification of TWAMP --
 the Two-Way Active Measurement Protocol [RFC5357].  TWAMP is an
 extension of the One-way Active Measurement Protocol, OWAMP
 [RFC4656].  The TWAMP specification gathered wide review as it
 approached completion, and the by-products were several
 recommendations for new features in TWAMP.  There are a growing
 number of TWAMP implementations at present, and widespread usage is
 expected.  There are even devices that are designed to test
 implementations for protocol compliance.
 This memo describes an OPTIONAL feature for TWAMP.  [RFC5357] TWAMP
 (and OWAMP) start all previously requested and accepted test sessions
 at once.  This feature allows the Control-Client to control
 individual test sessions on the basis of their Session Identifier
 (SID).  This feature permits a short-duration TWAMP test to start
 (and/or stop) during a longer test.  This feature permits a specific
 diagnostic test to begin if intermediate results indicate that the
 test is warranted, for example.
 This feature requires a Modes field bit position assignment and the
 use of two new TWAMP command numbers (for the augmented Start and
 Stop commands).  This feature also specifies the use of a new Stop-N-
 ACK Server response, to complete the symmetry of the session-stopping
 process in the same way as the Start-ACK (Start-N-ACK when used with
 this feature) response.
 The Individual Session Control feature gives the Control-Client new
 flexibility to manage any number of test sessions once they are
 established.  However, [RFC5357] test sessions are established in
 serial order and the total establishment time grows with the number
 of sessions and the round-trip time.  Therefore, implementers of this
 feature may also wish to implement the "Reflect Octets" feature,
 described in [REFLECT].  This feature allows a Control-Client to
 distinguish between parallel Request-TW-Session commands because a
 participating Server can return octets (e.g., the Control-Client's
 local index) in its reply to the request.  Thus, the Reflect Octets
 feature supports the efficient establishment of many simultaneous
 test sessions that the Individual Session Control feature can then
 manage (start/stop).
 This memo is an update to the TWAMP core protocol specified in
 [RFC5357].  Measurement systems are not required to implement the
 feature described in this memo to claim compliance with [RFC5357].

Morton & Chiba Standards Track [Page 3] RFC 5938 TWAMP Session Control August 2010

 Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set
 to zero by senders and MUST be ignored by receivers.  Also, the HMAC
 (Hashed Message Authentication Code) MUST be calculated as defined in
 Section 3.2 of [RFC4656].

1.1. Requirements Language

 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 [RFC2119].

2. Purpose and Scope

 The purpose of this memo is to describe an additional OPTIONAL
 function and feature for TWAMP [RFC5357].
 The scope of the memo is limited to specifications of the following
 features:
 1.  extension of the modes of operation through assignment of a new
     value in the Modes field to communicate feature capability and
     use,
 2.  the definitions of augmented start session and stop session
     commands (with corresponding acknowledgements), and
 3.  the definition of related procedures for TWAMP entities.
 The motivation for this feature is the ability to start and stop
 individual test sessions at will, using a single TWAMP-Control
 connection.
 When the Server and Control-Client have agreed to use the Individual
 Session Control mode during control connection setup, then the
 Control-Client, the Server, the Session-Sender, and the Session-
 Reflector MUST all conform to the requirements of that mode, as
 identified below.  The original TWAMP-Control Start and Stop commands
 MUST NOT be used.

3. TWAMP Control Extensions

 The TWAMP-Control protocol is a derivative of the OWAMP-Control
 protocol, and provides two-way measurement capability.  TWAMP
 [RFC5357] uses the Modes field to identify and select specific
 communication capabilities, and this field is a recognized extension
 mechanism.  The following sections describe one such extension.

Morton & Chiba Standards Track [Page 4] RFC 5938 TWAMP Session Control August 2010

3.1. Connection Setup with Individual Session Control

 TWAMP-Control connection establishment follows the procedure defined
 in Section 3.1 of [RFC4656] OWAMP.  The Individual Session Control
 mode requires one new bit position (and value) to identify the
 ability of the Server/Session-Reflector to start and stop specific
 sessions (according to their Session Identifier, or SID).  This new
 feature requires an additional TWAMP mode bit assignment as follows:
 Value  Description             Reference/Explanation
 0      Reserved
 1      Unauthenticated         RFC 4656, Section 3.1
 2      Authenticated           RFC 4656, Section 3.1
 4      Encrypted               RFC 4656, Section 3.1
 8      Unauth. TEST protocol,  RFC 5618, Section 3.1
        Encrypted CONTROL
 --------------------------------------------------------
 16     Individual Session      RFC 5938, bit position 4
        Control
 In the original OWAMP Modes field, setting bit positions 0, 1, or 2
 indicated the security mode of the Control protocol, and the Test
 protocol inherited the same mode (see Section 4 of [RFC4656]).  In
 the [RFC5618] memo, bit position (3) allows a different security mode
 in the Test protocol and uses the unauthenticated test packet format.
 If the Server sets the new bit position (bit position 4) in the
 Server Greeting message to indicate its capabilities, then the Server
 and Session-Reflector MUST comply with the requirements of this memo
 to control sessions on an individual basis if desired.
 If the Control-Client intends to control sessions on an individual
 basis (according to the requirements in this memo), it MUST set the
 mode bit (4, corresponding to the new mode) in the Setup Response
 message.  This means that:
 1.  The Control-Client and the Server MUST use the start and stop
     commands intended for individual session control and the
     corresponding acknowledgements, as defined in the sections that
     follow.
 2.  The Control-Client and the Server MUST NOT use the start and stop
     commands (2 and 3) and the acknowledgement defined in [RFC5357].
 The Control-Client MUST also set one mode bit to indicate the chosen
 security mode (currently bits 0, 1, 2, or 3), consistent with the
 modes offered by the Server.  The Control-Client MAY also set Modes

Morton & Chiba Standards Track [Page 5] RFC 5938 TWAMP Session Control August 2010

 field bit 4 with other features and bit positions (such as the
 reflect octets feature).

3.2. Start-N-Sessions Command with Individual Session Control

 Having
 o  initiated Individual Session Control mode in the Setup Response,
 o  requested one or more test sessions, and
 o  received affirmative Accept-Session response(s),
 a TWAMP Client MAY start the execution of one or more test sessions
 by sending a Start-N-Sessions message to the Server (note that "N"
 indicates that this command is applicable to one or more sessions,
 and does not change with the number of sessions identified in the
 command).
 The format of the Start-N-Sessions message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |      7        |                                               |
 +-+-+-+-+-+-+-+-+                                               +
 |                        MBZ (11 octets)                        |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Number of Sessions                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                    First SID (16 octets)                      |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 .                 remaining SIDs (16 octets each)               .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                       HMAC (16 octets)                        |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 Note: In figures, "B" indicates the boundary of a 16-octet word.

Morton & Chiba Standards Track [Page 6] RFC 5938 TWAMP Session Control August 2010

 The Command Number value of 7 indicates that this is a Start-N-
 Sessions command.  The Control-Client MUST compose this command, and
 the Server MUST interpret this command, according to the field
 descriptions below.
 The Number of Sessions field indicates the count of sessions that
 this Start command applies to, and MUST be one or greater.  The
 number of SID fields that follow MUST be equal to the value in the
 Number of Sessions field (otherwise, the command MUST NOT be affirmed
 with a zero Accept field in the Start-N-Ack response).
 All SID fields are constructed as defined in the last paragraph of
 Section 3.5 of OWAMP [RFC4656] (and referenced in TWAMP).  Note that
 the SID is assigned by the Server during the session request
 exchange.
 The message is terminated with a single block HMAC, as illustrated
 above.
 The Server MUST respond with one or more Start-N-Ack messages (which
 SHOULD be sent as quickly as possible).  Start-N-Ack messages SHALL
 have the format defined in the next session.
 When using Individual Session Control mode and its Start-N-Ack
 command as described in the next section, multiple Start-N-Sessions
 commands MAY be sent without waiting for acknowledgement, and the
 Start-N-sessions commands MAY arrive in any order.

3.3. Start-N-Ack Command with Individual Session Control

 The Server responds to the Start-N-Sessions command (for one or more
 specific sessions referenced by their SIDs) with one or more Start-N-
 Ack commands with Accept fields corresponding to one or more of the
 SIDs.  This allows for the possibility that a Server cannot
 immediately start one or more of the sessions referenced in a
 particular Start-N-Sessions command, but can start one or more of the
 sessions.

Morton & Chiba Standards Track [Page 7] RFC 5938 TWAMP Session Control August 2010

 The format of the message is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |      8        |     Accept    |            MBZ                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        MBZ (8 octets)                         |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Number of Sessions                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                    First SID (16 octets)                      |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 .                remaining SIDs (16 octets each)                .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                       HMAC (16 octets)                        |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Command Number value of 8 indicates that this is a Start-N-Ack
 message.  The Server MUST compose this command, and the Control-
 Client MUST interpret this command, according to the field
 descriptions below.
 The Accept field values are defined in Section 3.3 of OWAMP
 [RFC4656].
 The Number of Sessions field indicates the count of sessions that
 this Start-N-Ack command applies to, and MUST be one or greater.  The
 number of SID fields that follow MUST be equal to the value in the
 Number of Sessions field.
 All SID fields are constructed as defined in the last paragraph of
 Section 3.5 of OWAMP [RFC4656] (and referenced in TWAMP).  Note that
 the SID is assigned by the Server during the session request
 exchange.
 The message is terminated with a single block HMAC, as illustrated
 above.

Morton & Chiba Standards Track [Page 8] RFC 5938 TWAMP Session Control August 2010

 Note that the SIDs for all Sessions with the same 'Accept' code can
 be acknowledged using the same Start-N-Ack message.
 For example, say that the Server receives a Start-N-Sessions command
 for SIDs 1, 2, 3, and 4.  The Server determines that the resources
 for SID=3 are temporarily unavailable.  The Server responds with two
 Start-N-Ack commands with fields as follows:
    Accept = 0   Number of Sessions = 3    SIDs 1, 2, 4
    Accept = 5   Number of Sessions = 1    SID 3

3.4. Stop-N-Sessions Command with Individual Session Control

 The Stop-N-Sessions command can only be issued by the Control-Client.
 The command MUST contain at least one SID.
 The TWAMP Stop-N-Sessions command for use in Individual Session
 Control mode is formatted as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |      9        |                                               |
 +-+-+-+-+-+-+-+-+                                               +
 |                        MBZ (11 octets)                        |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Number of Sessions                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                    First SID (16 octets)                      |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 .                remaining SIDs (16 octets each)                .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                       HMAC (16 octets)                        |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B

Morton & Chiba Standards Track [Page 9] RFC 5938 TWAMP Session Control August 2010

 The Command Number value of 9 indicates that this is a Stop-N-
 Sessions command.  The Control-Client MUST compose this command, and
 the Server MUST interpret this command, according to the field
 descriptions below.
 The Number of Sessions field indicates the count of sessions to which
 this Stop-N-Sessions command applies.  The SID is as defined in
 Section 3.5 of OWAMP [RFC4656] (and TWAMP), and the value MUST be one
 or greater.  The number of SID fields that follow MUST be equal to
 the value in the Number of Sessions field.
 The message is terminated with a single block HMAC, as illustrated
 above.
 The Server MUST respond with one or more Stop-N-Ack messages (which
 SHOULD be sent as quickly as possible).  Stop-N-Ack messages SHALL
 have the format defined in the next session.

3.5. Stop-N-Ack Command with Individual Session Control

 In response to the Stop-N-Sessions command (for one or more specific
 sessions referenced by their SIDs), the Server MUST reply with one or
 more Stop-N-Ack commands with Accept fields corresponding to one or
 more of the SIDs.  This allows for the possibility that a Server
 cannot immediately stop one or more of the sessions referenced in a
 particular Stop-N-Sessions command, but can stop one or more of the
 sessions.

Morton & Chiba Standards Track [Page 10] RFC 5938 TWAMP Session Control August 2010

 The format for the Stop-N-Ack command is as follows:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |      10       |     Accept    |            MBZ                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        MBZ (8 octets)                         |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Number of Sessions                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                    First SID (16 octets)                      |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 .                 remaining SIDs (16 octets each)               .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
 |                                                               |
 |                       HMAC (16 octets)                        |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Command Number value of 10 indicates that this is a Stop-N-Ack
 message.  The Server MUST compose this command, and the Control-
 Client MUST interpret this command, according to the field
 descriptions below.
 The Accept Field values are defined in Section 3.3 of OWAMP
 [RFC4656].
 The Number of Sessions field indicates the count of sessions that
 this Stop-N-Ack command applies to, and MUST be one or greater.  The
 number of SID fields that follow MUST be equal to the value in the
 Number of Sessions field.
 All SID fields are constructed as defined in the last paragraph of
 Section 3.5 of OWAMP [RFC4656] (and referenced in TWAMP).  Note that
 the SID is assigned by the Server during the session request
 exchange.
 The message is terminated with a single block HMAC, as illustrated
 above.

Morton & Chiba Standards Track [Page 11] RFC 5938 TWAMP Session Control August 2010

 Note that the SIDs for all Sessions with the same 'Accept' code can
 be acknowledged using the same Stop-N-Ack message.

3.6. SERVWAIT Timeout Operation

 Section 3.1 of [RFC5357] describes the operation of the optional
 SERVWAIT timer.  In normal TWAMP operation, the Server suspends
 monitoring the SERVWAIT timer while test sessions are in progress.
 When the Individual Session Control feature is utilized, this
 suspension is extended to cover the time when ANY test session is in
 progress.
 Thus, the Server SHALL suspend monitoring control connection activity
 after receiving any Start-N-Sessions command, and after receiving a
 Stop-N-Sessions command for all corresponding SIDs (and no test
 sessions are in progress), OR when REFWAIT expires on ALL test
 sessions initiated by a TWAMP-Control connection, then the SERVWAIT
 monitoring SHALL resume (as though a Stop-N-Sessions command had been
 received).  An implementation that supports the SERVWAIT timeout
 option SHOULD also implement the REFWAIT timeout option.
 The diagram below illustrates the operation of timers SERVWAIT and
 REFWAIT.
   SERVWAIT                   REFWAIT                  SERVWAIT
 +-+-+-+-+-+-+-+-+                                   +-+-+-+-+-+-+
 (no sessions
  in progress)
                  +-+-+-+-+-+-+-+-+-+-+-+
                          SID="1"
                                 +-+-+-+-+
                                  SID="2"
                                   +-+-+-+-+-+-+-+-+
                                         SID="3"
 >>>>>>>>>> Time >>>>>>>>>>>>>>>>>>> Time >>>>>>>>>>>>>>>> Time >>>>>

3.7. Additional Considerations

 The value of the Modes field sent by the Server (in the Server
 Greeting message) is the bit-wise OR of the mode values that it is
 willing to support during this session.
 With the publication of this feature, bit positions 0 through 4 of
 the 32-bit Modes field are used.  A Control-Client MAY ignore bit
 positions greater than 2 in the Modes field, or it MAY support

Morton & Chiba Standards Track [Page 12] RFC 5938 TWAMP Session Control August 2010

 OPTIONAL features that are communicated in bit positions 3 and
 higher.  (The unassigned bits are available for future protocol
 extensions.)
 Other ways in which TWAMP extends OWAMP are described in [RFC5357].

4. TWAMP Test with Individual Session Control

 The TWAMP test protocol is similar to the OWAMP [RFC4656] test
 protocol with the exception that the Session-Reflector transmits test
 packets to the Session-Sender in response to each test packet it
 receives.  TWAMP [RFC5357] defines two different test packet formats,
 one for packets transmitted by the Session-Sender and one for packets
 transmitted by the Session-Reflector.  As with the OWAMP-Test
 protocol, there are three security modes: unauthenticated,
 authenticated, and encrypted.  The unauthenticated mode has one test
 packet format, while the authenticated and encrypted modes use
 another (common) format.

4.1. Sender Behavior

 The individual session control feature requires that the sender MUST
 manage test sessions according to their SID.  Otherwise, the sender
 behavior is as described in Section 4.1 of [RFC5357].

4.2. Reflector Behavior

 The TWAMP Reflector follows the procedures and guidelines in Section
 4.2 of [RFC5357], with the following additional functions required by
 this feature:
 o  The Session-Reflector MUST manage all test sessions accepted
    according to their SID.
 o  Upon receipt of a TWAMP-Control Stop-N-Sessions command
    referencing a specific session/SID, the Session-Reflector MUST
    ignore TWAMP-Test packets (in the same session/SID) that arrive at
    the current time plus the Timeout (in the Request-TW-Session
    command and assuming subsequent acknowledgement).  The Session-
    Reflector MUST NOT generate a test packet to the Session-Sender
    for packets that are ignored.  (Note: The Request-TW-Session
    command includes sender address + port and receiver address +
    port, and this is usually sufficient to distinguish sessions.)
 o  If the REFWAIT timer is implemented, it SHOULD be enforced when
    any test session is in progress (started and not stopped).

Morton & Chiba Standards Track [Page 13] RFC 5938 TWAMP Session Control August 2010

5. Security Considerations

 The security considerations that apply to any active measurement of
 live networks are relevant here as well.  See the security
 considerations in [RFC4656] and [RFC5357].

6. IANA Considerations

 As a result of this document, IANA has assigned one mode bit
 position/value for a mode in the IANA registry for the TWAMP Modes
 field, and this memo describes the behavior when the new mode is
 used.  This field is a recognized extension mechanism for TWAMP.
 As a result of this document, IANA has assigned four command numbers
 in the "TWAMP-Control Command Numbers" registry, and this memo
 describes the use of the new commands.  The command number field is a
 recognized extension mechanism for TWAMP.

6.1. Registry Specification

 IANA has created a "TWAMP-Modes" registry (as requested in
 [RFC5618]).  TWAMP-Modes are specified in TWAMP Server Greeting
 messages and Set-Up-Response messages, as described in Section 3.1 of
 [RFC5357], consistent with Section 3.1 of [RFC4656], and extended by
 this memo.  Modes are indicated by setting bits in the 32-bit Modes
 field that correspond to values in the "TWAMP-Modes" registry.  For
 the "TWAMP-Modes" registry, we expect that new features will be
 assigned increasing registry values that correspond to single bit
 positions, unless there is a good reason to do otherwise (more
 complex encoding than single bit positions may be used in the future
 to access the 2^32 value space).
 IANA has also created the "TWAMP-Control Command Numbers" registry.
 TWAMP-Control commands are specified by the first octet in TWAMP-
 Control messages as specified in Section 3.5 of [RFC5357], and
 augmented by this memo.  This registry may contain 256 possible
 values.

6.2. Registry Management

 Because the "TWAMP-Control Command Numbers" registry can contain only
 256 values and "TWAMP-Modes" are based on only 32 bit positions with
 a maximum of 2^32 values, and because TWAMP is an IETF protocol,
 these registries must be updated only by "IETF Consensus" as
 specified in [RFC5226] (an RFC that documents registry use and is
 approved by the IESG).  Management of these registries is described
 in Section 8.2 of [RFC5357] and [RFC5618].

Morton & Chiba Standards Track [Page 14] RFC 5938 TWAMP Session Control August 2010

 The values 7, 8, 9, and 10 have been assigned in the "TWAMP-Control
 Command Numbers" Registry.  The value 16 corresponding to the next
 available bit position (4) (as described in Sections 3.1 and 3.7) has
 been assigned in the "TWAMP-Modes" registry.

6.3. Experimental Numbers

 One experimental value has been assigned in the "TWAMP-Control
 Command Numbers" registry.
 No additional experimental values are assigned in the TWAMP-Modes
 registry.

6.4. Registry Contents

 TWAMP-Control Command Numbers Registry
 Value  Description             Semantics Definition
  0      Reserved
  1      Forbidden
  2      Start-Sessions          RFC 4656, Section 3.7
  3      Stop-Sessions           RFC 4656, Section 3.8
  4      Reserved
  5      Request-TW-Session      RFC 5357, Section 3.5
  6      Experimentation         RFC 5357, Section 8.3
 ------------------------------------------------------------------
  7      Start-N-Sessions        RFC 5938, Section 3.2
  8      Start-N-Ack             RFC 5938, Section 3.3
  9      Stop-N-Sessions         RFC 5938, Section 3.4
 10      Stop-N-Ack              RFC 5938, Section 3.5
 TWAMP-Modes Registry
 Value  Description             Reference/Explanation
 0      Reserved
 1      Unauthenticated         RFC 4656, Section 3.1
 2      Authenticated           RFC 4656, Section 3.1
 4      Encrypted               RFC 4656, Section 3.1
 8      Unauth. TEST protocol,  RFC 5618, Section 3.1
        Encrypted CONTROL
 --------------------------------------------------------
 16     Individual Session       RFC 5938, Section 3.1
        Control                  bit position 4

Morton & Chiba Standards Track [Page 15] RFC 5938 TWAMP Session Control August 2010

7. Acknowledgements

 The authors thank everyone who provided comments on this feature,
 especially Lars Eggert, Adrian Farrel, and Alexey Melnikov.

8. References

8.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
            Zekauskas, "A One-way Active Measurement Protocol
            (OWAMP)", RFC 4656, September 2006.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
            Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
            RFC 5357, October 2008.
 [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
            Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
            August 2009.

8.2. Informative References

 [REFLECT]  Morton, A. and L. Ciavattone, "TWAMP Reflect Octets and
            Symmetrical Size Features", Work in Progress, June 2010.

Morton & Chiba Standards Track [Page 16] RFC 5938 TWAMP Session Control August 2010

Authors' Addresses

 Al Morton
 AT&T Labs
 200 Laurel Avenue South
 Middletown, NJ  07748
 USA
 Phone: +1 732 420 1571
 Fax:   +1 732 368 1192
 EMail: acmorton@att.com
 URI:   http://home.comcast.net/~acmacm/
 Murtaza Chiba
 Cisco Systems
 170 W. Tasman Drive
 San Jose, CA  95134
 USA
 Phone: +1 800 553 NETS
 EMail: mchiba@cisco.com

Morton & Chiba Standards Track [Page 17]

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