K. Hedayat
  Internet Draft                                          Brix Networks
  Expires: May June 2008                                      R. Krzanowski
                                                                 K. Yum
                                                       Juniper Networks
                                                              A. Morton
                                                              AT&T Labs
                                                             J. Babiarz
                                                        Nortel Networks
                                                          December 2007

                A Two-way Active Measurement Protocol (TWAMP)

 Status of this Memo

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 Copyright Notice

    Copyright (C) The IETF Trust (2007).


    The IPPM IP Performance Metrics (IPPM) working group's One-way Active
    Measurement Protocol [RFC4656] (OWAMP) provides a common protocol
    for measuring one-way metrics between network devices.  OWAMP can
    be used bi-directionally to measure one-way metrics in both
    directions between two network elements.  However, it does not
    accommodate round-trip or two-way measurements.  This memo
    specifies a Two-way Active Measurement Protocol (TWAMP), based on
    the OWAMP, that adds two-way or round-trip measurement
    capabilities.  The TWAMP measurement architecture is usually
    comprised of two hosts with specific roles, and this allows for
    some protocol simplifications, making it an attractive alternative
    in some circumstances.

 Table of Contents

    1. Introduction..................................................3
       1.1 Relationship of Test and Control Protocols................3
       1.2 Logical Model.............................................3
    2. Protocol Overview.............................................5
    3. TWAMP Control.................................................5
       3.1 Connection Setup..........................................5 Setup..........................................6
       3.2 Integrity Protection......................................6
       3.3 Value of the Accept Fields................................6
       3.4 TWAMP Control Commands....................................6
       3.5 Creating Test Sessions....................................6
       3.6 Send Schedules............................................8 Schedules............................................9
       3.7 Starting Test Sessions....................................8 Sessions....................................9
       3.8 Stop-Sessions.............................................9
       3.9 Fetch-Session.............................................9
    4. TWAMP Test....................................................9
       4.1 Sender Behavior...........................................9 Behavior..........................................10
       4.2 Reflector Behavior.......................................10
    5. Implementers Guide...........................................16
       5.1 Complete TWAMP...........................................17
       5.2 TWAMP Light..............................................17
    6. Security Considerations......................................18
    7. Acknowledgements.............................................18
    8. IANA Considerations..........................................19
       8.1 Registry Specification...................................19
       8.2 Registry Management......................................19
       8.3 Experimental Numbers.....................................20
       8.4 Initial Registry Contents................................20
    9. Internationalization Considerations..........................20
    10. References..................................................21
       10.1 Normative References....................................21
       10.2 Informative References..................................21

 1. Introduction

    The IETF IP Performance Metrics (IPPM) working group has completed
    a draft standard for the round-trip delay [RFC2681] metric.  IPPM
    has also completed a protocol for the control and collection of
    one-way measurements, the One-way Active Measurement Protocol
    (OWAMP) [RFC4656].  However, OWAMP does not accommodate round-trip
    or two-way measurements.

    Two-way measurements are common in IP networks, primarily because
    time accuracy is less demanding for round-trip delay, and
    measurement support at the remote end may be limited to a simple
    echo function.  This memo specifies the Two-way Active Measurement
    Protocol, or TWAMP.  TWAMP uses the methodology and architecture of
    OWAMP [RFC4656] to define an open protocol for measurement of
    two-way or round-trip metrics (henceforth in this document the term
    two-way also signifies round-trip).  The TWAMP measurement
    architecture is usually comprised of only two hosts with specific
    roles, and this allows for some protocol simplifications, making it
    an attractive alternative to OWAMP in some circumstances.

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
    "OPTIONAL" in this document are to be interpreted as described in
    RFC 2119 [RFC2119].

 1.1 Relationship of Test and Control Protocols

    Similar to OWAMP [RFC4656], TWAMP consists of two inter-related
    protocols: TWAMP-Control and TWAMP-Test.  The relationship of these
    protocols is as defined in section 1.1 of OWAMP [RFC4656].
    TWAMP-Control is used to initiate, start, and stop test sessions,
    whereas TWAMP-Test is used to exchange test packets between two
    TWAMP entities.

 1.2 Logical Model
    The role and definition of the logical entities are as defined in
    section 1.2 of OWAMP [RFC4656] with the following exceptions:

    -  The Session-Receiver is called the Session-Reflector in the
        TWAMP architecture.  The Session-Reflector has the capability
        to create and send a measurement packet when it receives a
        measurement packet.  Unlike the Session-Receiver, the
        Session-Reflector does not collect any packet information.

    -  The Server is an end system that manages one or more TWAMP
        sessions, and is capable of configuring per-session state in
        the end-points.  However, a Server associated with a
        Session-Reflector would not have the capability to return the
        results of a test session, and this is a difference from OWAMP.

    -  The Fetch-Client entity does not exist in the TWAMP
        architecture, as the Session-Reflector does not collect any
        packet information to be fetched.  Consequently there is no
        need for the Fetch-Client.

    An example of possible relationship scenarios between these roles
    are presented below.  In this example different logical roles are
    played on different hosts.  Unlabeled links in the figure are
    unspecified by this document and may be proprietary protocols.

           +----------------+               +-------------------+
           | Session-Sender |<-TWAMP-Test-->| Session-Reflector |
           +----------------+               +-------------------+
             ^                                     ^
             |                                     |
             |                                     |
             |                                     |
             |  +----------------+<----------------+
             |  |     Server     |
             |  +----------------+
             |    ^
             |    |
             | TWAMP-Control
             |    |
             v    v
           | Control-Client |

    As in OWAMP [RFC4656], different logical roles can be played by the
    same host.  For example, in the figure above, there could be
    actually two hosts: one playing the roles of Control-Client and
    Session-Sender, and the other playing the roles of  Server and
    Session-Reflector.  This example is shown below.

           +-----------------+                   +-------------------+
           | Control-Client  |<--TWAMP Control-->|      Server       |
           |                 |                   |                   |
           | Session-Sender  |<--TWAMP-Test----->| Session-Reflector |
           +-----------------+                   +-------------------+

    Additionally, following the guidelines of OWAMP [RFC4656], TWAMP
    has been defined to allow for small test packets that would fit
    inside the payload of a single ATM cell (only in unauthenticated

 2. Protocol Overview

    The Two-way Active Measurement Protocol is an open protocol for
    measurement of two-way metrics.  It is based on OWAMP [RFC4656] and
    adheres to its overall architecture and design.  The protocol
    defined in this document extends and changes OWAMP [RFC4656] as

    -  Define a new logical entity, Session-Reflector, in place of the

    -  Define the Session-Reflector behavior in place of the
        Session-Receiver behavior of OWAMP [RFC4656].

    -  Define a new test packet format for packets transmitted from the
        Session-Reflector to Session-Sender.

    -  Fetch client does not exist in the TWAMP architecture.

    All multi-octet quantities defined in this document are represented
    as unsigned integers in network byte order unless specified

 3. TWAMP Control

    TWAMP-Control is a derivative of the OWAMP-Control for two-way
    measurements.  All TWAMP Control messages are similar in format and
    follow similar guidelines to those defined in section 3 of OWAMP
    [RFC4656] with the exceptions outlined in the following sections.

    All OWAMP [RFC4656] Control messages except for the Fetch-Session
    command apply to TWAMP.

 3.1 Connection Setup

    Connection establishment of TWAMP follows the same procedure
    defined in section 3.1 of OWAMP [RFC4656].  The mode values are
    identical to OWAMP. The only exception is the well-known port
    number for TWAMP-control. A client opens a TCP connection to the
    server on well-known port N (Refer to the IANA Considerations
    section below for the TWAMP-control port number assignment). The
    host that initiates the TCP connection takes the roles of Control-
    Control-Client and (in the two-host implementation) the
    Session-Sender.  The host that acknowledges the TCP connection
    accepts the roles of Server and (in the two-host implementation)
    the Session Reflector.

 3.2 Integrity Protection

    Integrity protection of TWAMP follows the same procedure defined in
    section 3.2 of OWAMP [RFC4656].

 3.3 Value of the Accept Fields

    Accept values used in TWAMP are the same as the values defined in
    section 3.3 of OWAMP [RFC4656].

 3.4 TWAMP Control Commands

    TWAMP control commands are as defined in section 3.4 of OWAMP
    [RFC4656] except that the Fetch-Session command does not apply to

 3.5 Creating Test Sessions

    Test sessions creation follows the same procedure as defined in
    section 3.5 of OWAMP [RFC4656].

    In order to distinguish the session as a two-way versus a one-way
    measurement session the first octet of the Request-Session command
    MUST be set to 5.  Value of 5 indicates that this is a
    Request-Session for a two-way metrics measurement session.

    In TWAMP, the first octet is referred to as the Command Number, and
    the Command Number is a recognized extension mechanism. Readers are
    encouraged to consult the TWAMP Command Number Registry to
    determine if there have been additional values assigned.

    If a TWAMP server receives an unexpected command number, it MUST SHOULD
    respond with the Accept field set to 3 (meaning "Some aspect of
    request is not supported") in the Server-Start message.

    In OWAMP, the Conf-Sender field is set to 1 when the
    Request-Session message describes a task where the Server will
    configure a one-way test packet sender.  Likewise, the
    Conf-Receiver field is set to 1 when the message describes the
    configuration for a Session-Receiver.  In TWAMP, both endpoints
    perform in these roles, with the Session-Sender first sending and
    then receiving test packets.  The Session-Reflector first receives
    the test packets, and returns each test packet to the
    Session-Sender as fast as possible.

    Both Conf-Sender field and Conf-Receiver field MUST be set to 0
    since the Session-Reflector will both receive and send packets, and
    the roles are established according to which host initiates the TCP
    connection for control.  The server MUST interpret any non-zero
    value as zero.

    The Session-Reflector in TWAMP does not process incoming test
    packets for performance metrics and consequently does not need to
    know the number of incoming packets and their timing schedule.
    Consequently the Number of Scheduled Slots and Number of Packets
    MUST be set to 0.

    The Sender Port is the UDP port from which TWAMP-Test packets will
    be sent and the port to which TWAMP-Test packets will be sent by
    the Session-Reflector (Session-Sender will use the same UDP port to
    send and receive packets).  Receiver Port is the desired UDP port
    to which TWAMP test packets will be sent by the Session-Sender (the
    port where the Session-Reflector is asked to receive test packets).
    Receiver Port is also the UDP port from which TWAMP test packets
    will be sent by the Session-Reflector (Session-Reflector will use
    the same UDP port to send and receive packets).

    The Sender Address and Receiver Address fields contain,
    respectively, the sender and receiver addresses of the endpoints of
    the Internet path over which a TWAMP test session is requested.

    They MAY be set to 0, in which case the IP addresses used for the
    Session-Sender to Session-Reflector Control Message exchange MUST
    be used in the test packets.

    The SID Session Identifier (SID) is as defined in OWAMP [RFC4656].
    Since the SID is always generated by the receiving side, the
    Session-Reflector determines the SID, and the SID in the
    Request-Session message MUST be set to 0.

    The Start Time is as as defined in OWAMP [RFC4656].

    The Timeout is interpreted differently from the definition in OWAMP
    [RFC4656].  In TWAMP, Timeout is the interval that the
    Session-Reflector MUST wait after receiving a Stop-Sessions
    message.  In case there are test packets still in transit, the
    Session Reflector MUST reflect them if they arrive within the
    timeout interval following the reception of the Stop-Sessions
    message.  The Session-Reflector MUST NOT reflect packets that are
    received beyond the timeout.

    Type-P descriptor is as defined in OWAMP [RFC4656].  The only
    capability of this field is to set the Differentiated Services Code
    Point (DSCP) as defined in [RFC2474].  The same value of DCSP MUST
    be used in test packets reflected by the Session-Reflector.

    Since there are no Schedule Slot Descriptions, the Request-Session
    Message is completed by MBZ (Must Be Zero) and HMAC (Hash Message
    Authentication Code) fields.  This completes one logical message,
    referred to as the Request-Session Command.

    The Session-Reflector MUST respond to each Request-Session Command
    with an Accept-Message as defined in OWAMP [RFC4656].  When the
    Accept Field = 0, the Port field confirms (repeats) the port to
    which TWAMP test packets are sent by the Session-Sender toward the
    Session-Reflector.  In other words, the Port field indicates the
    port number where the Session-Reflector expects to receive packets
    from the Session-Sender.

    When the requested Receiver Port is not available (e.g., port in
    use), the Server at the Session-Reflector MAY suggest an alternate
    and available port for this session in the Port Field.  The
    Session-Sender either accepts the alternate port, or composes a new
    Session-Request message with suitable parameters. Otherwise, the
    Server at the Session-Reflector uses the Accept Field to convey
    other forms of session rejection or failure and MUST NOT suggest an
    alternate port.  In this case the Port Field MUST be set to zero.

 3.6 Send Schedules

    The Send Schedule for test packets defined in section 3.6 of OWAMP
    [RFC4656] is not used in TWAMP.  The Control-Client and
    Session-Sender MAY autonomously decide the Send Schedule.  The
    Session-Reflector SHOULD return each test packet to the
    Session-Sender as quickly as possible.

 3.7 Starting Test Sessions

    The procedure and guidelines for Starting test sessions is the same
    as defined in section 3.7 of OWAMP [RFC4656].

 3.8 Stop-Sessions

    The procedure and guidelines for Stopping test sessions is the same
    as defined in section 3.8 of OWAMP [RFC4656].  The Stop-Session
    command can only be issued by the Session-Sender.  The Next SeqNo
    and Number of Skip Ranges MUST be set to 0 and the message MUST NOT
    contain any session description records or skip ranges.  The
    message is terminated with a single block HMAC, to complete the
    Stop-Sessions Command.

 3.9 Fetch-Session

    The purpose of TWAMP is measurement of two-way metrics.  Two-way
    measurements do not rely on packet level data collected by the
    Session-Reflector such as sequence number, timestamp, and TTL.  As
    such the protocol does not require the retrieval of packet level
    data from the Server and the Fetch-Session command is not defined
    in TWAMP.

 4. TWAMP Test

    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 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 [RFC4656] test
    protocol there are three modes: unauthenticated, authenticated, and

 4.1 Sender Behavior

    The sender behavior is determined by the configuration of the
    Session-Sender and is not defined in this standard.  Further, the
    Session-Reflector does not need to know the Session-Sender
    behaviour to the degree of detail as needed in OWAMP [RFC4656].
    Additionally the Session-Sender collects and records the necessary
    information provided from the packets transmitted by the
    Session-Reflector for measuring two-way metrics.  The information
    recording based on the received packet by the Session-Sender is
    implementation dependent.

 4.1.1 Packet Timings

    Since the Send Schedule is not communicated to the
    Session-Reflector, there is no need for a standardized computation
    of packet timing.

    Regardless of any scheduling delays, each packet that is actually
    sent MUST have the best possible approximation of its real time of
    departure as its timestamp (in the packet).

 4.1.2 Packet Format and Content

    The Session-Sender packet format and content follow the same
    procedure and guidelines as defined in section 4.1.2 of OWAMP
    [RFC4656] (with the exception of the reference to the Send

 4.2 Reflector Behavior

    TWAMP requires the Session-Reflector to transmit a packet to the
    Session-Sender in response to each packet it receives.

    As packets are received the Session-Reflector will,
    -  Timestamp the received packet.  Each packet that is actually
        received MUST have the best possible approximation of its real
        time of arrival entered as its timestamp (in the packet).

    -  In authenticated or encrypted mode, decrypt the first block (16
        octets) of the packet body.

    -  Copy the packet sequence number into the corresponding reflected
        packet to the Session-Sender.

    -  Sender TTL value is extracted from the TTL/Hop Limit value of
        received packets. Session-Reflector Implementations SHOULD
        fetch the TTL/Hop Limit value from the IP header of the packet,
        replacing the value of 255 set by the Session-Sender.  If an
        implementation does not fetch the actual TTL value (the only
        good reason not to do so is an inability to access the TTL
        field of arriving packets), it MUST set the Sender TTL value as

    -  Transmit a test packet to the Session-Sender in response to
        every received packet.  The response MUST be generated as
        immediately as possible.  The format and content of the test
        packet is defined in section 5.2.1.  Prior to the transmission
        of the test packet, the Session-Reflector MUST enter the best
        possible approximation of its actual sending time of as its
        Timestamp (in the packet). This permits the determination of
        the elapsed time between the reception of the packet and its

    -  Packets not received within the Timeout are ignored by the
       Reflector.  The Session-Reflector MUST NOT generate a test
       packet to the Session-Sender for packets that are ignored.

 4.2.1 TWAMP-Test Packet Format and Content

    The Session-Reflector MUST transmit a packet to the Session-Sender
    in response to each packet received.  The Session-Reflector SHOULD
    transmit the packets as immediately as possible.  The
    Session-Reflector SHOULD set the TTL in IPV4 (or Hop Limit in IPv6)
    in the UDP packet to 255.

    The test packet will have the necessary information for calculating
    two-way metrics by the Session-Sender.  The format of the test
    packet depends on the mode being used.  The various formats of the
    packet are presented below.

    For unauthenticated mode:

    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
    |                        Sequence Number                        |
    |                          Timestamp                            |
    |                                                               |
    |         Error Estimate        |           MBZ                 |
    |                          Receive Timestamp                    |
    |                                                               |
    |                        Sender Sequence Number                 |
    |                      Sender Timestamp                         |
    |                                                               |
    |      Sender Error Estimate    |           MBZ                 |
    |  Sender TTL   |                                               |
    +++++++++++++++++                                               |
    |                                                               |
    .                                                               .
    .                         Packet Padding                        .
    .                                                               .
    |                                                               |
    For authenticated and encrypted modes:

    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
    |                        Sequence Number                        |
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    |                          Timestamp                            |
    |                                                               |
    |         Error Estimate        |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                        MBZ (6 octets)                         |
    |                        Receive Timestamp                      |
    |                                                               |
    |                        MBZ (8 octets)                         |
    |                                                               |
    |                        Sender Sequence Number                 |
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    |                      Sender Timestamp                         |
    |                                                               |
    |      Sender Error Estimate    |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                        MBZ (6 octets)                         |
    |  Sender TTL   |                                               |
    +++++++++++++++++                                               |
    |                                                               |
    |                                                               |
    |                        MBZ (15 octets)                        |
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    |                                                               |
    .                                                               .
    .                         Packet Padding                        .
    .                                                               .
    |                                                               |

    Sequence Number is the sequence number of the test packet according
    to its transmit order.It starts with zero and is incremented by one
    for each subsequent packet.  The Sequence Number generated by the
    Session-Reflector is independent from the sequence number of the
    arriving packets.

    Timestamp and Error Estimate are the Session-Reflector's transmit
    timestamp and error estimate for the reflected test packet,
    respectively.  The format of all timestamp and error estimate
    fields follow the definition and formats defined by OWAMP[RFC4656].

    Sender Timestamp and Sender Error Estimate are exact copies of the
    timestamp and error estimate from the Session-Sender test packet
    that corresponds to this test packet.

    Sender TTL is 255 when transmitted by the Session Sender.  Sender
    TTL is set to the Time To Live (or Hop Count) value of the received
    packet from the IP packet header when transmitted by the Session

    Receive Timestamp is the time the test packet was received by the
    reflector.  The difference between Timestamp and Receive Timestamp
    is the amount of time the packet was in transition in the
    Session-Reflector.  The Error Estimate associated with the
    Timestamp field also applies to the Receive Timestamp.

    Sender Sequence Number is a copy of the Sequence Number of the
    packet transmitted by the Session-Sender that caused the
    Session-Reflector to generate and send this test packet.

    Similar to OWAMP [RFC4656] the TWAMP packet layout is the same in
    authenticated and encrypted modes.  The encryption operation of
    Session-Sender packet follow the same rules of Session-Sender
    packets as defined in OWAMP [RFC4656].

    The minimum data segment length is, therefore, 41 octets in
    unauthenticated mode, and 104 octets in both authenticated mode and
    encrypted modes (with the implication that the later two modes will
    not fit in a single ATM cell).

    The Session-Reflector TWAMP-Test packet layout is the same in
    authenticated and encrypted modes.  The encryption operations are,
    however, different.  The difference is that in encrypted mode both
    the sequence numbers and timestamps are encrypted to provide
    maximum data integrity protection while in authenticated mode the
    sequence numbers are encrypted and the timestamps are sent in clear
    text.  Sending the timestamp in clear text in authenticated mode
    allows one to reduce the time between when a timestamp is obtained
    by a reflector and when the packet is reflected out.  In encrypted
    mode, both the sender and reflector have to fetch the timestamp,
    encrypt it, and send it; in authenticated mode, the middle step is
    removed, potentially improving accuracy (the sequence number can be
    encrypted before the timestamp is fetched).

    In authenticated mode, the first block (16 octets) of each packet
    is encrypted using AES Electronic Cookbook (ECB) mode.

    Obtaining the key, encryption method, and packet padding follows
    the same procedure as OWAMP as described below.
    Similarly to each TWAMP-Control session, each TWAMP-Test session
    has two keys: an AES Session-key and an HMAC Session-key.  However,
    there is a difference in how the keys are obtained: in the case of
    TWAMP-Control, the keys are generated by the client and
    communicated (as part of the Token) during connection setup as part
    of Set-Up-Response message; in the case of TWAMP-Test, described
    here, the keys are derived from the TWAMP-Control keys and the SID.

    The TWAMP-Test AES Session-key is obtained as follows: the
    TWAMP-Control AES Session-key (the same AES Session-key as is used
    for the corresponding TWAMP-Control session, where it is used in a
    different chaining mode) is encrypted, using AES, with the 16-octet
    session identifier (SID) as the key; this is a single-block ECB
    encryption; its result is the TWAMP-Test AES Session-key to use in
    encrypting (and decrypting) the packets of the particular
    TWAMP-Test session.  Note that all of TWAMP-Test AES Session-key,
    TWAMP-Control AES Session-key, and the SID are comprised of 16

    The TWAMP-Test HMAC Session-key is obtained as follows: the
    TWAMP-Control HMAC Session-key (the same HMAC Session-key as is
    used for the corresponding TWAMP-Control session) is encrypted,
    using AES, with the 16-octet session identifier (SID) as the key;
    this is a two-block CBC encryption, always performed with IV=0; its
    result is the TWAMP-Test HMAC Session-key to use in authenticating
    the packets of the particular TWAMP-Test session.  Note that all of
    TWAMP-Test HMAC Session-key and TWAMP-Control HMAC Session-key are
    comprised of 32 octets, while the SID is 16 octets.

    ECB mode used for encrypting the first block of TWAMP-Test packets
    in authenticated mode does not involve any actual chaining; this
    way, lost, duplicated, or reordered packets do not cause problems
    with deciphering any packet in an TWAMP-Test session.

    In encrypted mode, the first six blocks (96octets) are encrypted
    using AES CBC mode.  The AES Session-key to use is obtained in the
    same way as the key for authenticated mode.  Each TWAMP-Test packet
    is encrypted as a separate stream, with just one chaining
    operation; chaining does not span multiple packets so that lost,
    duplicated, or reordered packets do not cause problems.  The
    initialization vector for the CBC encryption is a value with all
    bits equal to zero.

    Implementation note: Naturally, the key schedule for each
    TWAMP-Test session MAY be set up only once per session, not once
    per packet.

    HMAC in TWAMP-Test only covers the part of the packet that is also
    encrypted.  So, in authenticated mode, HMAC covers the first block
    (16 octets); in encrypted mode, HMAC covers two first blocks (32
    octets).  In TWAMP-Test HMAC is not encrypted (note that this is
    different from TWAMP-Control, where encryption in stream mode is
    used, so everything including the HMAC blocks ends up being

    In unauthenticated mode, no encryption or authentication is

    Packet Padding in TWAMP-Test SHOULD be pseudo-random (it MUST be
    generated independently of any other pseudo-random numbers
    mentioned in this document).  However, implementations MUST provide
    a configuration parameter, an option, or a different means of
    making Packet Padding consist of all zeros.

 5. Implementers Guide

    This section serves as guidance to implementers of TWAMP.  Two
    architectures are presented in this section for implementations
    where two hosts play the subsystem roles of TWAMP.  Although only
    two architectures are presented here the protocol does not require
    their use.  Similar to OWAMP [RFC4656] TWAMP is designed with
    complete flexibility to allow different architectures that suite
    multiple system requirements.

 5.1 Complete TWAMP

    In this example the roles of Control-Client and Session-Sender are
    implemented in one host referred to as the controller and the roles
    of Server and Session-Reflector are implemented in another host
    referred to as the responder.

               controller                              responder
           +-----------------+                   +-------------------+
           | Control-Client  |<--TWAMP-Control-->| Server            |
           |                 |                   |                   |
           | Session-Sender  |<--TWAMP-Test----->| Session-Reflector |
           +-----------------+                   +-------------------+

    This example provides an architecture that supports the full TWAMP
    standard.  The controller establishes the test session with the
    responder through the TWAMP-Control protocol.  After the session is
    established the controller transmits test packets to the responder.
    The responder follows the Session-Reflctor behavior of TWAMP as
    described in section 4.2.

 5.2 TWAMP Light

    In this example the roles of Control-Client, Server, and
    Session-Sender are implemented in one host referred to as the
    controller and the role of Session-Reflector is implemented in
    another host referred to as the responder.

               controller                              responder
           +-----------------+                   +-------------------+
           |     Server      |<----------------->|                   |
           | Control-Client  |                   | Session-Reflector |
           | Session-Sender  |<--TWAMP-Test----->|                   |
           +-----------------+                   +-------------------+

    This example provides a simple architecture for responders where
    their role will be to simply act as light test points in the
    network.  The controller establishes the test session with the
    Server through non-standard means.  After the session is
    established the controller transmits test packets to the responder.
    The responder follows the Session-Reflector behavior of TWAMP as
    described in section 4.2 with the following exceptions.

    In the case of TWAMP Light,  the Session-Reflector does not
    necessarily have knowledge of the session state. IF the
    Session-Reflector does not have knowledge of the session state,
    THEN the Session-Reflector MUST copy the Sequence Number of the
    received packet to the Sequence Number field of the reflected
    packet.  The controller receives the reflected test packets and
    collects two-way metrics. This architecture allows for collection
    of two-way metrics.

    This example eliminates the need for the TWAMP-Control protocol and
    assumes that the Session-Reflector is configured and communicates
    its configuration with the Server through non-standard means.  The
    Session-Reflector simply reflects the incoming packets back to the
    controller while copying the necessary information and generating
    sequence number and timestamp values per section 4.2.1.

 6. Security Considerations

    Fundamentally TWAMP and OWAMP use the same protocol for
    establishment of Control and Test procedures. The main difference
    between TWAMP and OWAMP is the Session-Reflector behavior in TWAMP
    vs. the Session-Receiver behavior in OWAMP.  This difference in
    behavior does not introduce any known security vulnerabilities that
    are not already addressed by the security features of OWAMP.  The
    entire security considerations of OWAMP [RFC4656] applies to TWAMP.

    The only area where TWAMP may introduce new security considerations
    is the TWAMP Light version described above. The non-standard means
    to control the responder and establish test sessions SHOULD offer
    the features listed below.

    The non-standard responder control protocol SHOULD have an
    authenticated mode of operation.  The responder SHOULD be
    configurable to accept only authenticated control sessions.

    The non-standard responder control protocol SHOULD have a means to
    activate the authenticated and encrypted modes of the TWAMP-Test

 7. Acknowledgements

    We would like to thank Nagarjuna Venna, Sharee McNab, Nick Kinraid,
    Stanislav Shalunov, Matt Zekauskas, Walt Steverson and Jeff Boote
    for their comments, suggestions, reviews, helpful discussion and

 8. IANA Considerations

    IANA has allocated a well-known TCP port number (861) for the
    OWAMP-Control part of the OWAMP [RFC4656] protocol.
    owamp-control   861/tcp    OWAMP-Control
    owamp-control   861/udp    OWAMP-Control
    #                          [RFC4656]
    #               862-872    Unassigned

    IANA is requested to allocate a well-known TCP/UDP port number for
    the TWAMP-Control protocol. It would be ideal if the port number
    assignment was adjacent to the OWAMP assignment. The recommended
    Keyword for this entry is "twamp-control" and the Description is
    "Two-way Active Measurement Protocol (TWAMP) Control".

    During final editing, port N in section 3.1 should be replaced with
    the assigned port number.

    Since TWAMP adds an additional Control command to the OWAMP-Control
    specification, and describes behavior when this control command is
    used, this memo requests creation an IANA registry for the TWAMP
    Command Number field.  The field is not explicitly named in
    [RFC4656] but is called out for each command. This field is a
    recognized extension mechanism for TWAMP.

 8.1 Registry Specification

    IANA will create an TWAMP-Control Command registry.  TWAMP-Control
    commands are specified by the first octet in OWAMP-Control messages
    as shown in section 3.4 of [RFC4656], and modified by this
    document. Thus this registry may contain sixteen possible values.

 8.2 Registry Management

    Because the registry may only contain sixteen values, and because
    OWAMP and TWAMP are IETF protocols, this registry must only be
    updated by "IETF Consensus" as specified in [RFC2434] -- an RFC
    documenting the use that is approved by the IESG.  We expect that
    new values will be assigned as monotonically increasing integers in
    the range [0-15], unless there is a good reason to do otherwise.

 8.3 Experimental Numbers

    [RFC3692] recommends allocating an appropriate number of values for
    experimentation and testing.  It is not clear to the authors
    exactly how many might be useful in this space, nor if it would be
    useful that they were easily distinguishable or at the "high end"
    of the number range.  Two might be useful, say one for session
    control, and one for session fetch.  On the other hand, a single
    number would allow for unlimited extension, because the format of
    the rest of the message could be tailored, with allocation of other
    numbers done once usefulness has been proven.  Thus, this document
    will allocate one number, the next sequential number 6, as
    designated for experimentation and testing.

 8.4 Initial Registry Contents

    TWAMP-Control Command Registry

    Value  Description             Semantics Definition
    0      Reserved
    1      Forbidden
    2      Start-Sessions          RFC4656, Section 3.7
    3      Stop-Sessions           RFC4656, Section 3.8
    4      Fetch-Session           RFC4656, Section 3.9
    5      Request-TW-Session      this document, Section 3.5
    6      Experimentation         undefined, see Section 8.3.

 9. Internationalization Considerations

    The protocol does not carry any information in a natural language,
    with the possible exception of the KeyID in TWAMP-Control, which is
    encoded in UTF-8.

 10. References

 10.1 Normative References

       [RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J.,
                  Zekauskas, M., "A One-way Active Measurement Protocol
                  (OWAMP)", draft-ietf-ippm-owdp-11.txt, October 2004.

       [RFC2681] Almes, G., Kalidindi, S., Zekauskas, M., "A
                  Round-Trip Delay Metric for IPPM". RFC 2681, STD 1,
                  September 1999.

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

       [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
                 Definition of the Differentiated Services Field (DS
                 Field) in the IPv4 and IPv6 Headers", RFC 2474,
                 December 1998.

       [RFC2434] Narten, T., Alvestrand, H., Guidelines for Writing
                 an IANA Considerations Section in RFCs, RFC 2474,
                 October 1998.

 10.2 Informative References

       [RFC3692] Narten, T., Assigning Experimental and Testing Numbers
                 Considered Useful, RFC 3692, January 2004.

    Authors' Addresses

       Kaynam Hedayat
       Brix Networks
       285 Mill Road
       Chelmsford, MA  01824

       EMail: khedayat@brixnet.com
       URI:   http://www.brixnet.com/
       Roman M. Krzanowski, Ph.D.
       500 Westchester Ave.
       White Plains, NY

       EMail: roman.krzanowski@verizon.com
       URI:   http://www.verizon.com/

       Al Morton
       AT&T Labs
       Room D3 - 3C06
       200 Laurel Ave. South
       Middletown, NJ 07748

       Phone  +1 732 420 1571
       EMail: acmorton@att.com
       URI:   http://home.comcast.net/~acmacm/

       Kiho Yum
       Juniper Networks
       1194 Mathilda Ave.
       Sunnyvale, CA

       EMail: kyum@juniper.net
       URI:   http://www.juniper.com/

       Jozef Z. Babiarz
       Nortel Networks
       3500 Carling Avenue
       Ottawa, Ont  K2H 8E9

       Email: babiarz@nortel.com
       URI:   http://www.nortel.com/

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