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rfc:rfc6802

Internet Engineering Task Force (IETF) S. Baillargeon Request for Comments: 6802 C. Flinta Category: Informational A. Johnsson ISSN: 2070-1721 Ericsson

                                                         November 2012

Ericsson Two-Way Active Measurement Protocol (TWAMP) Value-Added Octets

Abstract

 This memo describes an extension to the Two-Way Active Measurement
 Protocol (TWAMP).  Specifically, it extends the TWAMP-Test protocol,
 which identifies and manages packet trains, in order to measure
 capacity metrics like the available path capacity, tight section
 capacity, and UDP delivery rate in the forward and reverse path
 directions.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It has been approved for publication by the Internet
 Engineering Steering Group (IESG).  Not all documents approved by the
 IESG are a candidate for any level of Internet Standard; see 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/rfc6802.

Copyright Notice

 Copyright (c) 2012 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.

Baillargeon, et al. Informational [Page 1] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

Table of Contents

 1. Introduction ....................................................2
    1.1. Requirements Language ......................................3
 2. Purpose and Scope ...............................................3
 3. Capacity Measurement Principles .................................4
 4. TWAMP-Control Extensions ........................................5
    4.1. Additional Considerations ..................................6
 5. Extended TWAMP-Test .............................................6
    5.1. Sender Behavior ............................................6
         5.1.1. Packet Timings ......................................7
         5.1.2. Session-Sender Packet Format ........................7
    5.2. Reflector Behavior ........................................12
         5.2.1. Session-Reflector Packet Format ....................13
    5.3. Additional Considerations .................................13
 6. Experiments ....................................................14
 7. Security Considerations ........................................14
 8. Acknowledgements ...............................................14
 9. References .....................................................15
    9.1. Normative References ......................................15
    9.2. Informative References ....................................15

1. Introduction

 The notion of embedding a number of meaningful fields in the padding
 octets has been established as a viable methodology for carrying
 additional information within the TWAMP-Test protocol running between
 a Session-Sender and a Session-Reflector [RFC5357] [RFC6038].
 This memo describes an optional extension to the Two-Way Active
 Measurement Protocol (TWAMP) [RFC5357].  It is called the Ericsson
 TWAMP Value-Added Octets feature.  This memo defines version 1.
 This feature enables the controller host to measure capacity metrics
 like the IP-type-P available path capacity (APC) [RFC5136], IP-layer
 tight section capacity (TSC) [Y1540], and UDP delivery rate on both
 forward and reverse paths using a single TWAMP test session.  The
 actual method to calculate the APC, TSC, or the UDP delivery rate
 from packet-level performance data is not discussed in this memo.
 The Valued-Added Octets feature consists of new behaviors for the
 Session-Sender and Session-Reflector and a set of value-added octets
 of information that are placed at the beginning of the Packet Padding
 [RFC5357] or immediately after the Server Octets in the Packet
 Padding (to be reflected) [RFC6038] by the Session-Sender and are
 reflected or returned by the Session-Reflector.  The length of the
 value-added octets in version 1 is 10 octets.  The Valued-Added

Baillargeon, et al. Informational [Page 2] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 Octets feature does not change the basic roles and functions of the
 TWAMP hosts, which are still responsible to include timestamp(s) and
 sequence number(s) in the test packets.

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 the Ericsson TWAMP Valued-
 Added Octets feature (version 1) for TWAMP [RFC5357].
 The scope of the memo is limited to specifications of the following
 enhancements:
 o  The definition of a structure for embedding a sequence of value-
    added fields at the beginning of the Packet Padding [RFC5357] or
    Packet Padding (to be reflected) [RFC6038] in the TWAMP-Test
    packets
 o  The definition of new Session-Sender and Session-Reflector
    behaviors
 The motivation for this feature is to enable the measurement of
 capacity metrics on both the forward and reverse paths using a single
 TWAMP test session.  Multiple TWAMP test sessions between a
 controller and a responder with different Diffserv Code Points
 (DSCPs) may also be used to evaluate the QoS impacts on the capacity
 metrics.
 This memo captures the prototype presented and demonstrated at IETF
 80.  It may be used as a reference for future work or may be used
 during benchmark analysis to compare the accuracy or performance of
 the available path capacity estimates under various condition or use
 cases.
 This memo does not extend the standard modes of operation through
 assignment of a new value in the Modes field (see Section 3.1 of
 [RFC4656] for the format of the Server Greeting message).  This memo
 does not define a vendor-specific or experimental mode since the
 Modes field as currently defined does not explicitly reserve a value
 or range of values for this purpose.

Baillargeon, et al. Informational [Page 3] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 This memo assumes the TWAMP controller is capable to send test
 packets with value-added padding octets and the TWAMP responder is
 configured to interpret the value-added padding octets embedded in
 each TWAMP-Test packet.  Bootstrapping such behavior at the TWAMP
 responder is implementation specific.  By default, the feature MUST
 be disabled on the TWAMP host.  The Value-Added Octets feature MUST
 be deployed in an environment where both controller and responder are
 managed by the same administrative entity and such entity has
 established an agreement to operate the Value-Added Octets feature
 between the pair of hosts or between specific UDP endpoints between
 the pair of hosts.  See Sections 4 and 5.3 for additional
 considerations.
 The Value-Added Octets Version 1 feature is intended to work in
 conjunction with any TWAMP modes.  When the Server and Control-Client
 are configured or have agreed to use the Value-Added Octets Version 1
 feature, then the Control-Client, the Server, the Session-Sender, and
 the Session-Reflector must all conform to the requirements of that
 feature, as identified below.

3. Capacity Measurement Principles

 Most capacity estimation methods for APC [RRBNC] [PDM] [ENHJMMB]
 [SBW] and for UDP delivery rate need to send and receive packets in
 groups, called "packet trains" or simply "trains".  Each train is
 sent at a specific transmission rate in a given direction.  These
 trains must be identified within each bidirectional test session
 stream.
 The first measurement principle is to send multiple trains within a
 test session stream from one IP node to another IP node in order to
 estimate the APC, TSC, or UDP delivery rate in the forward direction.
 Each train consists of a group of test packets that are separated
 from each other by a packet interval, as shown in the figure below.
 The packet interval is measured using either the first bit or the
 last bit of two consecutive packets.
       tt                      tt                      tt
 |<---------->|          |<---------->|          |<---------->|
 |            |          |            |          |            |
 +------------+          +------------+          +------------+
 |  Packet 1  |          |  Packet 2  |          |  Packet 3  |
 +------------+          +------------+          +------------+
 |                       |                       |
 |<--------------------->|<--------------------->|
     packet interval 1       packet interval 2

Baillargeon, et al. Informational [Page 4] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 The test packet size and interval between consecutive packets for
 each train sent by the Session-Sender and reflected by the Session-
 Reflector MUST be calculated and determined by the controller or an
 application or entity communicating with the controller.  The packet
 size and interval MAY vary within a train and/or between trains.
 Determination of the packet size and interval is implementation
 specific.
 The transmission time tt to send one packet (i.e., determined by the
 interface speed and the IP packet size) is also shown in the figure
 above.  Observe that the packet interval MUST be larger than or equal
 to tt.
 At the Session-Reflector, each received test packet within a forward
 train is time stamped.  This provides a second set of packet interval
 values.  Methods for measuring the APC, TSC, and UDP delivery rate
 use the packet intervals obtained from both endpoints in the
 estimation process.  The method of measuring the UDP delivery rate
 may also require the rate of packet loss.  The estimation process
 itself, as well as any requirements on software or hardware, is
 implementation specific.
 The second measurement principle is referred to as "self-induced
 congestion".  According to this principle, in order to measure APC,
 TSC, and UDP delivery rates, some trains MUST cause momentary
 congestion on the network path.  In essence, this means that some
 trains MUST be sent at a higher rate than what is available on the
 network path.
 In order to fulfill the above measurement principles and to measure
 the APC, TSC, and UDP delivery rates in the reverse direction, the
 test packets at the Session-Reflector MUST be regrouped into trains
 and then transmitted back to the Session-Sender with a provided
 packet interval.

4. TWAMP-Control Extensions

 TWAMP connection establishment follows the procedure defined in
 Section 3.1 of [RFC4656] and Section 3.1 of [RFC5357].  The TWAMP-
 Control protocol [RFC5357] uses the Modes field to identify and
 select specific communication capabilities.  According to the
 standard specifications, the Value-Added Octets feature requires one
 new bit position (and value) to identify the ability of the
 Server/Session-Reflector to read and act upon the new fields in the
 value-added octets.  Such bit position (and value) is not defined in
 this memo.  Bootstrapping the TWAMP Value-Added Octets Version 1
 feature is implementation specific.

Baillargeon, et al. Informational [Page 5] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 Both the Reflect Octets mode and Symmetrical Size mode MAY be
 selected to ensure the reflection of the value-added padding octets
 by the Session-Reflector and symmetrical size TWAMP-Test packets in
 the forward and reverse directions of transmission.

4.1. Additional Considerations

 In the TWAMP control architecture, the TWAMP reflector (server)
 signals the modes it wishes to operate and the TWAMP controller
 (control-client) selects the mode or modes supported by the
 responder.  This feature is designed to retain backward compatibility
 with the original TWAMP-Control and TWAMP-Test protocols.  As an
 alternative, the user may opt for TWAMP Light architecture, which
 does not require the TWAMP-Control protocol.
 The methods to determine if the Value-Added Octets feature is
 supported on a TWAMP reflector is implementation specific.  When the
 Value-Added Octets feature is not supported on a TWAMP reflector, the
 TWAMP controller MUST NOT select the Value-Added Octets feature and
 MUST NOT include any value-added octets in the test packets.  If the
 TWAMP controller inadvertently sends value-added octets in the test
 packets to a TWAMP responder that does not support such feature, the
 TWAMP responder shall treat the value-added octets as regular padding
 octets and return the test packets as quickly as possible to the
 Session-Sender as defined in [RFC5357].

5. Extended TWAMP-Test

 The forward and reverse APC, TSC, and UDP delivery rate measurement
 characteristics depend on the size and packet intervals of the test
 packets.  This memo allows variable packet sizes and packet intervals
 between trains and even between packets in the same train.  The
 functionality is described below.
 The TWAMP-Test protocol carrying the value-added padding octets is
 identical to TWAMP [RFC5357] except for the definition of the first
 10 octets in the Packet Padding that the Session-Sender expects to be
 reflected.  The new octets define fields for Value-Added Octets
 Version, Flags, Last Sequence Number in Train, and Desired Reverse
 Packet Interval.  Each of these fields are described in detail below.
 The Session-Sender and Session-Reflector behaviors are also modified.

5.1. Sender Behavior

 This section describes the extensions to the behavior of the TWAMP
 Session-Sender.

Baillargeon, et al. Informational [Page 6] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

5.1.1. Packet Timings

 The Send Schedule is not utilized in TWAMP, and this is unchanged in
 this memo.

5.1.2. Session-Sender Packet Format

 The Session-Sender packet format follows the same procedure and
 guidelines as defined in TWAMP [RFC5357] and TWAMP Reflect Octets and
 Symmetrical Size Features [RFC6038].
 This feature allows the Session-Sender to set the first few octets in
 the TWAMP-Test Packet Padding with information to communicate value-
 added padding version number, flag bits, sequence number of the last
 packet in a train, and desired reverse packet interval (or per-packet
 waiting time) for the reverse path direction of transmission.
 The Valued-Added Octets feature must be placed immediately after the
 TWAMP header or immediately after any new field that could be added
 to the TWAMP header or added to the beginning of the padding octets
 in the future.  Therefore, the placement of the first bit from the
 valued-added octets depends on the mode(s) being selected.
 A version number and a sequence of flag bits are defined at the very
 beginning of the value-added padding octets.  The version number
 identifies the version of the value-added padding octets and meaning
 of the flag bits and corresponding fields.  Each flag bit indicates
 if a specific field is used in the valued-added padding octets.  The
 version number and flag bits provide an effective method for
 extracting information at Session-Reflector and Session-Sender.  This
 document defines version 1 with two flag bits: L and I.
 The format of the test packet depends on the TWAMP modes.  The Value-
 Added Octets Version 1 feature is intended to work with any TWAMP
 modes.
 The Session-Sender SHALL use the following TWAMP-Test packet format
 when the Value-Added Octets Version 1 feature is selected in
 conjunction with the Unauthenticated mode:

Baillargeon, et al. Informational [Page 7] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

   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        |  Ver  |L|I|     Reserved      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Last Seqno In Train                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                Desired Reverse Packet Interval                |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Additional Packet Padding                   |
  .                                                               .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Baillargeon, et al. Informational [Page 8] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 The Session-Sender SHALL use the following TWAMP-Test packet format
 when the Value-Added Octets Version 1 feature is selected in
 conjunction with the Unauthenticated mode, Symmetrical Size mode, and
 Reflect Octets 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 (27 octets)                       |
  |                                                               |
  |                                                               |
  |                                                               |
  |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               |  Ver  |L|I|      Reserved     |    Last...    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               Seqno in Train                  |   Desired...  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Reverse Packet Interval               | Additional... |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Packet Padding                          |
  .                                                               .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Baillargeon, et al. Informational [Page 9] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 The Session-Sender SHALL use the following TWAMP-Test packet format
 when the Value-Added Octets Version 1 feature is selected in
 conjunction with the Unauthenticated mode, Symmetrical Size mode, and
 Reflect Octets mode with a non-zero value in the Server Octets field:
   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 (27 octets)                       |
  |                                                               |
  |                                                               |
  |                                                               |
  |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               |         Server Octets         |  Ver  |L|I|...|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Reserved    |               Last Seqno in...                |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Train       |             Desired Reverse Packet...         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Interval    |         Additional Packet Padding             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  .                                                               .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 In the mode using Reflect Octets illustrated above, the value-added
 padding octets are embedded in the Packet Padding (to be reflected).
 The Version (Ver) field MUST be encoded in the first 4 bits.  It
 identifies the version number of the value-added padding octets and
 meaning of the flag bits and the corresponding fields.  This memo
 defines version 1 with two flag bits: L and I.  When the Value-Added
 Octets Version 1 feature is selected, the Session-Sender MUST set the
 Ver field to 1.
 The 2 bits after the Version field are used for flags: L and I.

Baillargeon, et al. Informational [Page 10] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

 The Last Seqno in Train bit (L) is the first flag.  When the Value-
 Added Octets Version 1 feature is selected, the Session-Sender MAY
 set the Last Seqno in Train bit L to 1.
 The Desired Reverse Packet Interval bit (I) is the second flag.  When
 the Value-Added Octets Version 1 feature is selected, the Session-
 Sender MAY set the Desired Reverse Packet Interval bit I to 1.
 The Reserved field is reserved for future use.  All 10 bits of the
 Reserved field MUST be transmitted as zero by the Session-Sender.
 If the Last Seqno in Train bit is set to 1, then the Last Seqno in
 Train field MUST contain an unsigned 32-bit integer generated by the
 Session-Sender.  It MUST indicate the expected sequence number of the
 last packet in the train.  It SHOULD be used by the Session-Sender
 and Session-Reflector to identify the train to which a test packet
 belongs.  The packets belonging to a train are determined by
 observing the test packet Sequence Number in relation to the Last
 Seqno in Train. The Last Seqno in Train MUST be higher or equal to
 Sequence Number of the packet.  It must also be higher than the Last
 Seqno in Train for the previous train.  If the L bit is set to 0, the
 Session-Sender shall set all the bits in the Last Seqno in Train
 field to zero.
 If the Desired Reverse Packet Interval bit is set to 1, then the
 Desired Reverse Packet Interval field MUST contain an unsigned 32 bit
 integer generated by the Session-Sender.  It MUST indicate the
 desired packet interval (or the waiting time) that the Session-
 Reflector SHOULD use when transmitting the reflected test packets
 towards the Session-Sender.  The value 0 means the Session-Reflector
 SHOULD return the test packet to the Session-Sender as quickly as
 possible.  The format of this field MUST be a fractional part of a
 second as defined in the One-Way Active Measurement Protocol (OWAMP)
 [RFC4656].  If the I bit is set to 0, the Session-Sender shall set
 all the bits in the Desired Reverse Packet Interval field to zero.
 The values of the above fields are usually provided by a measurement
 method, tool, or algorithm.  This measurement algorithm is outside
 the scope of this specification.

Baillargeon, et al. Informational [Page 11] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

5.2. Reflector Behavior

 The TWAMP Session-Reflector follows the procedures and guidelines in
 Section 4.2 of [RFC5357], with some changes and additional functions.
 When the Value-Added Octets Version 1 feature is selected, the
 behavior of the Session-Reflector SHALL be as follows:
 o  The Session-Reflector MUST read the Version field.  If Ver = 1,
    the Session-Reflector MUST read the L and I flag bits.
 o  If L=1 and I=1, the Session-Reflector MUST read and extract the
    information from the Last Seqno in Train field and the Desired
    Reverse Packet Interval field in the value-added padding octets.
  1. The Last Seqno in Train MUST be compared to Sequence Number in

the same packet in order to determine when a complete train has

       been collected.  The Session-Reflector SHOULD buffer the
       packets belonging to the current train (or store the packet-
       level performance data).  After the last packet of the train
       has been received, the Session-Reflector SHOULD transmit the
       packets belonging to a reverse train with a waiting time
       (packet interval) for each packet indicated in the Desired
       Reverse Packet Interval field.  If the Desired Reverse Packet
       Interval field is set to zero, then the Session-Reflector
       SHOULD transmit the packet as quickly as possible.  The last
       packet within a train has Sender Sequence Number = Last Seqno
       in Train.
  1. The Last Seqno in Train of a packet MUST also be compared to

the Last Seqno in Train of the previous packet in order to

       determine if a new train needs to be collected.  In case of
       packet loss, the Session-Reflector MUST transmit the incomplete
       train when it receives a packet with a Last Seqno in Train
       belonging to another train (e.g., next train) of the test
       session or after a timeout.  The timeout MAY be the REFWAIT
       timer specified in section 4.2 of [RFC5357].
  1. Packets arriving out-of-order within a train MUST be buffered

at the Session-Reflector if the train is not yet transmitted to

       the Session-Sender.  If the train is already transmitted, the
       test packet SHOULD be returned to the Session-Sender as quickly
       as possible.  The Session-Reflector MUST NOT reorder the test
       packets if they happen to arrive out-of-sequence.
  1. Duplicate packets within a train MUST be buffered at the

Session-Reflector if the train is not yet transmitted to the

       Session-Sender.  If the train is already transmitted, the

Baillargeon, et al. Informational [Page 12] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

       duplicate test packet SHOULD be returned to the Session-Sender
       as quickly as possible.  The Session-Reflector MUST NOT discard
       duplicate test packets.
 For any other combinations of the Version field and the L and I
 flags, the Session-Reflector SHOULD return the test packet to the
 Session-Sender as quickly as possible.
 The Session-Reflector MUST implement the changes described above when
 the Value-Added Octets Version 1 feature is selected.

5.2.1 Session-Reflector Packet Format

 The Session-Reflector packet format follows the same procedure and
 guidelines as defined in TWAMP [RFC5357] and TWAMP Reflect Octets and
 Symmetrical Size Features [RFC6038], with the following changes:
 o  The Session-Reflector MUST reuse (reflect) the value-added padding
    octets (10 octets) provided in the Sender's Packet Padding.
 o  The Session-Reflector MAY reuse the rest of the padding octets in
    the Sender's Packet Padding.
 The truncation process [RFC5357] is recommended when the Symmetrical
 mode is not used.  The Session-Reflector MUST truncate exactly 27
 octets of padding in Unauthenticated mode and exactly 56 octets in
 Authenticated and Encrypted modes.

5.3. Additional Considerations

 The Session-Reflector supporting the Value-Added Octets feature
 should revert back to the standard Session-Reflector behavior if it
 cannot interpret the value-added padding octets in a given test
 packet.  Section 5.2 also describes such behavior.  For instance, the
 test packet is returned as quickly as possible to the Session-Sender
 when the Last Seqno in the Train is not what is expected.
 Capacity measurements introduce an additional consideration when the
 test sessions operate in TWAMP Light.  When the Session-Reflector
 does not have knowledge of the session state, the measurement system
 may be restricted to estimating or calculating the capacity metrics
 in the forward path direction of transmission only.  Capacity
 measurements in the reverse path direction is best handled with a
 Session-Reflector supporting knowledge of the session state and being
 capable of identifying the test packets belonging to a specific test
 session.  A method for creating a session state from the initial test
 packet may be implemented on the TWAMP Light Session-Reflector.  This
 is outside the scope of this specification.

Baillargeon, et al. Informational [Page 13] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

6. Experiments

 This memo describes the protocol used in the current working
 prototype implementation of the Value-Added Octets feature in the
 Ericsson lab.  The prototype has been tested in real network
 environments.  The conclusion from these tests is that the Value-
 Added Octets feature is able to enable estimation of capacity metrics
 such as available path capacity in both the forward and reverse
 directions of the network path.
 During the experiments with the protocol described in this memo, we
 have identified a need for the controller and responder to use the
 same maximum train length.  The reflector must be able to buffer the
 whole train received from the controller.  In order to reduce the
 risk for buffer overrun, the maximum train length should be
 negotiated.  This can be resolved through configuration, introduction
 of a new field in the value-added octets, or a new maximum train
 length field in the Request-TW-Session message.
 The Sender Discriminator (SD) field, which was proposed in an early
 draft of this document, was removed because of complications with
 different Session-Reflector implementations.  A Session-Reflector may
 not be able to easily identify the SD field or associate it with a
 specific Session-Sender, which may skew the test results.
 The flags defined in the value-added octets now indicate the usage of
 fields and not the presence of fields.  This modification was needed
 to simplify the responder implementation in the working prototype.

7. Security Considerations

 The value-added padding octets permit DoS attacks on the responder
 host communicating with core TWAMP [RFC5357].  For instance, a DoS
 condition could arise when the Last Seqno in Train is too large to
 handle, potentially causing undesirable processing delay or discard
 of the TWAMP-Test packets.  The responder host MUST provide a
 mechanism to protect or limit the use of its local memory, buffer
 space, or maximum transmission time for a train.
 The security considerations that apply to any active measurement of
 live networks are relevant here as well.  See [RFC4656] and
 [RFC5357].

8. Acknowledgements

 The authors thank Svante Ekelin for providing direction and comments
 on this document.

Baillargeon, et al. Informational [Page 14] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

9. References

9.1. 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.
 [RFC5136]   Chimento, P. and J. Ishac, "Defining Network Capacity",
             RFC 5136, February 2008.
 [RFC5357]   Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
             Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
             RFC 5357, October 2008.
 [RFC6038]   Morton, A. and L. Ciavattone, "Two-Way Active Measurement
             Protocol (TWAMP) Reflect Octets and Symmetrical Size
             Features", RFC 6038, October 2010.

9.2. Informative References

 [ENHJMMB]   Ekelin, S., Nilsson, M., Hartikainen, E., Johnsson, A.,
             Mangs, J., Melander, B., and M. Bjorkman, "Real-Time
             Measurement of End-to-End Available Bandwidth Using
             Kalman Filtering", Proceedings to the IEEE/IFIP Network
             Operations and Management Symposium, 2006.
 [PDM]       Dovrolis, C., Ramanathan, P., and D. Moore, "Packet-
             Dispersion Techniques and a Capacity-Estimation
             Methodology", IEEE/ACM Transactions on Networking,
             December 2004.
 [RRBNC]     Ribeiro, V., Riedi, R., Baraniuk, R., Navratil, J., and
             L. Cottrel, "pathChirp: Efficient Available Bandwidth
             Estimation for Network Paths", Passive and Active
             Monitoring Workshop, 2003.
 [SBW]       Sommers, J., Barford, P., and W. Willinger, "Laboratory-
             based Calibration of Available Bandwidth Estimation
             Tools", Microprocessors and Microsystems, 2007.
 [Y1540]     International Telecommunications Union, "Internet
             protocol data communication service - IP packet transfer
             and availability performance parameters", ITU-T
             Recommendation Y.1540, 2011.

Baillargeon, et al. Informational [Page 15] RFC 6802 Ericsson TWAMP Value-Added Octets November 2012

Authors' Addresses

 Steve Baillargeon
 Ericsson
 3500 Carling Avenue
 Ottawa, Ontario K2H 8E9
 Canada
 EMail: steve.baillargeon@ericsson.com
 Christofer Flinta
 Ericsson
 Farogatan 6
 Stockholm, 164 80
 Sweden
 EMail: christofer.flinta@ericsson.com
 Andreas Johnsson
 Ericsson
 Farogatan 6
 Stockholm, 164 80
 Sweden
 EMail: andreas.a.johnsson@ericsson.com

Baillargeon, et al. Informational [Page 16]

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