Network Working Group                                          A. Morton
Internet-Draft                                                 AT&T Labs
Intended status: Standards Track                                M. Chiba
Expires: April 29, September 7, 2009                                 Cisco Systems
                                                        October 26, 2008
                                                           March 6, 2009

              Individual Session Control Feature for TWAMP
                 draft-ietf-ippm-twamp-session-cntrl-00
                 draft-ietf-ippm-twamp-session-cntrl-01

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of which he BCP 78 and BCP 79.  This document may contain material
   from IETF Documents or she is aware
   have been IETF Contributions published or will 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 disclosed, modified outside the IETF Standards Process, and any
   derivative works of which he or she becomes
   aware will it may not be disclosed, in accordance with Section 6 of BCP 79. created outside the IETF Standards
   Process, except to format it for publication as an RFC or to
   translate it into languages other than English.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 29, September 7, 2009.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

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

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].

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
   2.  Purpose and Scope  . . . . . . . . . . . . . . . . . . . . . .  3  4
   3.  TWAMP Control Extensions . . . . . . . . . . . . . . . . . . .  4  5
     3.1.  Connection Setup with Individual Session Control . . . . .  4  5
     3.2.  Start-Sessions  Start-N-Sessions Command with Individual Session
           Control  . . . . . . .  5 . . . . . . . . . . . . . . . . . .  6
     3.3.  Stop-Sessions  Start-N-Ack Command with Individual Session Control  . . .  8
     3.4.  Stop-N-Sessions Command with Individual Session Control  . 10
     3.5.  Stop-N-Ack Command with Individual Session Control . . . .  6
     3.4. 11
     3.6.  SERVWAIT Timeout Operation . . . . . . . . . . . . . . . .  7
     3.5. 13
     3.7.  Additional considerations  . . . . . . . . . . . . . . . .  8 13
   4.  TWAMP Test with Individual Session Control . . . . . . . . . .  8 14
     4.1.  Sender Behavior  . . . . . . . . . . . . . . . . . . . . .  9 14
     4.2.  Reflector Behavior . . . . . . . . . . . . . . . . . . . .  9 14
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9 15
     6.1.  Registry Specification . . . . . . . . . . . . . . . . . .  9 15
     6.2.  Registry Management  . . . . . . . . . . . . . . . . . . . 10 15
     6.3.  Experimental Numbers . . . . . . . . . . . . . . . . . . . 10 15
     6.4.  Registry Contents  . . . . . . . . . . . . . . . . . . . . 10 16
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 16
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 16
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11 16
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13 17

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 wide-spread usage is
   expected.  There are even devices that are designed to test
   implementations for protocol compliance.

   This memo describes a new feature for TWAMP.  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).  The  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 Mode bit position assignment and the
   assignment of two new TWAMP command numbers (for the augmented Start
   and Stop commands).  This feature also specifies a new Stop-ACK
   Server response, to complete the symmetry of the session stopping
   process in the same way as the Start-ACK response.

   Implementers of this feature may also wish to implement the "Reflect
   Octets" feature, described in [draft-ietf-ippm-twamp-reflect-octets,
   work in progress]. [I-D.ietf-ippm-twamp-reflect-octets].
   This feature allows a Control-Client to insert a locally-specified
   request number into the Request-TW-Session command (in octets
   originally designated MBZ=Must Be Zero), and a compliant Server will
   return the request number in its reply (Accept message).

   This memo is intended to be an update to the TWAMP RFC.

   Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set
   to zero by senders and MUST be ignored by receivers.

2.  Purpose and Scope

   The purpose of this memo is to describe an additional function and
   feature for TWAMP [RFC5357].  The feature needs a clear description
   so it can be discussed and (hopefully) adopted in the IP Performance
   Metrics Charter.

   The scope of the memo is currently limited to specifications of the
   following features:

   1.  Extension of the modes of operation through assignment of a new
       value in the Mode field to communicate feature capability and
       use,

   2.  the definition definitions of augmented Start Session start session and Stop Session
       commands, stop session
       commands (with corresponding acknowledgements), and

   3.  the definition of related procedures for TWAMP entities.

   The motivation for this added feature is the ability to start and stop
   individual test sessions at will, using a single TWAMP-control
   connection.

3.  TWAMP Control Extensions

   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.

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         RFC4656, Section 3.1
   2      Authenticated           RFC4656, Section 3.1
   4      Encrypted               RFC4656, Section 3.1
   8      Unauth. TEST protocol,  draft-...-more-twamp (3)
          Auth. CONTROL
   --------------------------------------------------------
   zzz    Individual Session      this memo, bit position (Z)
          Control

   In the original OWAMP mode 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 [I-D.ietf-ippm-more-twamp] 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 Z) 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 (Z, corresponding to the new mode) in the Setup Response
   message.

   IF  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
   bit Z with other features and bit positions (such as the reflect
   octets feature).

   If the Control-Client has selected the Reflect Octets feature
   [draft-ietf-ippm-twamp-reflect-octets, work in progress]
   [I-D.ietf-ippm-twamp-reflect-octets] in combination with the
   Individual Session Control feature (after the Server identified its
   capability), AND utilizes the feature to insert a locally-specified
   request number in the Request-TW-Session command, THEN the Control
   Client MAY send more than one Request-TW-Session command to a given
   Server without waiting for the corresponding Accept-Session message.
   In such a case the Access-Session response reflects the locally-
   specified request number.  Note that when the Reflect Octets feature
   is being used all Request-TW-Session command and Accept-Session
   responses MUST include the locally-specified request number.

3.2.  Start-Sessions  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 sessions, and
   o  received affirmative Accept-Session responses, response(s),

   a TWAMP Client MAY start the execution of
   the requested one or more test sessions
   by sending a Start-Sessions Start-N-Sessions message to the server. 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 this 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

   The Command Number value of sessions 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. to, and must be one or greater.  The
   number of SID is as defined in OWAMP (and
   TWAMP) section 3.5 [RFC4656].

   The Server fields that follow MUST respond with a Start-Ack message (which SHOULD be
   sent as quickly as possible).  Start-Ack messages have equal to the format
   defined value in section 3.7 the
   Number of [RFC4656].

   The Control Client Sessions field (otherwise, the command MUST NOT send be affirmed
   with a subsequent Start Sessions command zero Accept field in the Start-N-Ack response).

   All SID fields are constructed as defined in the last paragraph of
   OWAMP section 3.5 [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.

   <<<<< Comment: Al thinks we don't need the limitation below now,
   unless it refers to the EXISTING Start-Sessions command.  The real
   question is, Do we require (MUST) the use of the -N- commands in
   Indiv.Sess.Cntrl mode, or allow both types???  I'm leaning toward -N-
   commands ONLY. >>>> The Control Client MUST NOT send a subsequent
   Start Sessions command until an outstanding message is acknowledged
   with a Start-Ack message.

   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.  Stop-Sessions  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 the sessions referenced in a particular
   Start-N-Sessions command, but can start one or more of the sessions.

   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 OWAMP section 3.3 [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
   OWAMP section 3.5 [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.

   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

   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 that
   this Stop-N-Sessions command applies to.  The SID is as defined in
   OWAMP (and TWAMP) section 3.5 [RFC4656] 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

   The Stop-Sessions

   In response to the Stop-N-Sessions command can only be issued (for one or more specific
   sessions referenced by their SIDs), the Control-Client.
   The message Server MUST contain at least reply with one SID.  The message is terminated or
   more Stop-N-Ack commands with a single block HMAC, Accept fields corresponding to complete one or
   more of the Stop-Sessions Command.

   Thus, SIDs.  This allows for the TWAMP Stop-Sessions command possibility that a Server
   cannot immediately stop one or more the sessions referenced in a
   particular Stop-N-Sessions command, but can stop one or more of the
   sessions.

   The format for individual session control the Stop-N-Ack command is constructed 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      10       |     Accept    |            MBZ                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Number of Sessions                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        MBZ (8 octets)                         |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Number of Sessions                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
   |                                                               |
   |                   First  SID (16 octets)                      |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
   |                                                               |
   .                remaining  SIDs (16 octets each)               .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
   |                                                               |
   |                       HMAC (16 octets)                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Command Number value of sessions 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 OWAMP section 3.3 [RFC4656].

   The Number of Sessions field indicates the count of sessions that
   this Stop Stop-N-Ack command applies to. to, and must be one or greater.  The
   number of SID is 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
   OWAMP (and
   TWAMP) section 3.5 [RFC4656].

3.4. [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.

   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-Sessions Start-N-Sessions command, and after receiving a
   Stop-Sessions
   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-Sessions Stop-N-Sessions command had been
   received).  An implementation which 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 >>>>>

3.5.

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.

   If this feature is adopted, the last ???? bits of the Modes 32-bit
   field are used.  A Control-Client MAY ignore other bit positions
   greater than 2 in the Modes Field, or it MAY support other features
   that are communicated in these bit positions.  (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 OWAMP-Test protocol
   there are three security modes: unauthenticated, authenticated, and
   encrypted.  Unauthenticated mode has one test packet format, while
   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 describe 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  Packets for  Upon receipt of a TWAMP-Control Stop-N-Sessions command
      referencing a specific session/SID not received within session/SID, the Session-Reflector MUST
      ignore TWAMP-Test packets (in the Timeout
      (following same session/SID) that arrive at
      the Stop-Session command) MUST be ignored by current time plus the
      Session-Reflector. Timeout (in the Request-TW-Session
      command and assuming subsequent acknowledgement).  The Session-Reflector Session-
      Reflector MUST NOT generate a test packet to the Session-Sender
      for packets that are ignored.

   o  If the RECOMMENDED REFWAIT timer is implemented, it SHOULD be
      enforced when any test session is in-progress (started and not
      stopped).

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

   This memo requests assignment of one mode bit position/value to the
   IANA registry for the TWAMP Mode field, and describes behavior when
   the new mode is used.  This field is a recognized extension mechanism
   for TWAMP.

   This memo also requests assignment of two four command numbers in the
   TWAMP-Control Command Number registry, and 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
   [I-D.ietf-ippm-more-twamp]).  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.  Thus, this registry can contain a
   total of 32 possible values.

   IANA has also created a TWAMP-Control Command Number 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 sixteen 256 possible
   values.

6.2.  Registry Management

   Because the TWAMP-Control Command Number registry can contain only
   sixteen values,
   256 values and TWAMP-Modes can only contain thirty-two values, and
   because TWAMP is an IETF protocol, these registries must be updated
   only by "IETF Consensus" as specified in [RFC2434](an RFC documenting
   registry use that is approved by the IESG).  Management of these
   registries is described in section 8.2 of [RFC5357] and
   [I-D.ietf-ippm-more-twamp].

   This memo proposes assignment of values 7 7, 8, 9 and 8. 10 in the Command
   number Registry, and the next available bit position (indicated by
   "Z") and corresponding value (indicated by "zzz") in section 3.1
   above.  Note that these values should be replaced by IANA or the RFC
   Editor when assigned.

6.3.  Experimental Numbers

   One experimental value has been assigned in the TWAMP-Control Command
   Number registry.

   No additional experimental values are assigned in the TWAMP-Modes
   registry.

6.4.  Registry Contents

   TWAMP-Control Command Number Registry

   Value  Description             Semantics Definition
    0      Reserved
    1      Forbidden
    2      Start-Sessions          RFC4656, Section 3.7
    3      Stop-Sessions           RFC4656, Section 3.8
    4      Reserved
    5      Request-TW-Session      draft-ietf-ippm-twamp,      RFC5357, Section 3.5
    6      Experimentation         draft-ietf-ippm-twamp,         RFC5357, Section 8.3
   ------------------------------------------------------------------
    7      Start-Sessions with      Start-N-Sessions        this memo, Section 3.2
           Individ. Session Cntrl.
    8      Stop-Sessions with      Start-N-Ack             this memo, Section 3.3
           Individ. Session Cntrl.
    9      Stop-N-Sessions         this memo, Section 3.4
   10      Stop-N-Ack              this memo, Section 3.5

   TWAMP-Modes Registry

   Value  Description             Reference/Explanation
   0      Reserved
   1      Unauthenticated         RFC4656, Section 3.1
   2      Authenticated           RFC4656, Section 3.1
   4      Encrypted               RFC4656, Section 3.1
   8      Unauth. TEST protocol,  draft-...-more-twamp (3)
          Auth. CONTROL
   --------------------------------------------------------
   zzz    Individual Session       this memo, Section 3.1
          Control                  bit position (Z)

7.  Acknowledgements

   The author would like to thank anyone who provides valuable comments
   on this feature.

8.  References

8.1.  Normative References

   [I-D.ietf-ippm-more-twamp]
              Morton, A. and K. Hedayat, "More Features for TWAMP",
              draft-ietf-ippm-more-twamp-00 (work in progress),
              October 2008.

   [I-D.ietf-ippm-twamp-reflect-octets]
              Morton, A. and L. Ciavattone, "TWAMP Reflect Octets
              Feature", draft-ietf-ippm-twamp-reflect-octets-00 (work in
              progress), October 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

8.2.  Informative References

   [x]        "".

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,   95134
   USA

   Phone: +1 800 553 NETS
   Fax:   +1
   Email: mchiba@cisco.com
   URI:

Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.