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Versions: (draft-baillargeon-ippm-twamp-value-added-octets) 00 01 02 03 04 05 06 07 09 RFC 6802

Network Working Group                                     S. Baillargeon
INTERNET-DRAFT                                                 C. Flinta
Intended Status: Informational                               A. Johnsson
Expires: March 30, 2013                                         Ericsson
                                                      September 26, 2012


                   Ericsson TWAMP Value-Added Octets
            draft-ietf-ippm-twamp-value-added-octets-09.txt


Abstract

   This memo describes an extension to the TWAMP test protocol for
   identifying and managing packet trains, which enables measuring
   capacity metrics like the available path capacity, tight section
   capacity and UDP delivery rate in the forward and reverse path
   directions.

   This memo contains the description of a working prototype. It does
   not represent a consensus of the IETF community. The IETF community
   is currently working on the problem statement and has not reached
   consensus on the preferred method for measuring capacity metrics.


Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on March 30, 2013.






Copyright and License Notice



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   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.







































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Table of Contents

   1  Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
      1.1  Requirements Language . . . . . . . . . . . . . . . . . . . 4
   2  Purpose and scope  . . . . . . . . . . . . . . . . . . . . . . . 4
   3  Capacity Measurement Principles  . . . . . . . . . . . . . . . . 6
   4  TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . . 7
      4.1  Additional Considerations . . . . . . . . . . . . . . . . . 7
   5  Extended TWAMP Test  . . . . . . . . . . . . . . . . . . . . . . 8
      5.1  Sender Behavior . . . . . . . . . . . . . . . . . . . . . . 8
         5.1.1  Packet Timings . . . . . . . . . . . . . . . . . . . . 8
         5.1.2  Session-Sender Packet Format . . . . . . . . . . . . . 8
      5.2  Reflector behavior  . . . . . . . . . . . . . . . . . . .  13
         5.2.1  Session-Reflector Packet Format  . . . . . . . . . .  15
      5.3  Additional Considerations . . . . . . . . . . . . . . . .  15
   6  Experiments  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   7  Security Considerations  . . . . . . . . . . . . . . . . . . .  16
   8  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  16
   9  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  17
   10  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
      10.1  Normative References . . . . . . . . . . . . . . . . . .  17
      10.2  Informative References . . . . . . . . . . . . . . . . .  17
   Author's Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18




























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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 [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 data 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
   field [RFC5357] or immediately after the Server Octets in the Packet
   Padding (to be reflected) field [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 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.

   This memo contains the description of a working prototype. It does
   not represent a consensus of the IETF community. The IETF community
   is currently working on the problem statement and has not reached
   consensus on the preferred method for measuring capacity metrics.


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].





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   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 field
         [RFC5357] or Packet Padding (to be reflected) field [RFC6038]
         in the TWAMP test packets and,

      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 DSCPs may also be used to evaluate the
   QoS impacts on the capacity metrics.

   The motivation for this document is to capture the prototype
   presented and demonstrated at the 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.

   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 section 4 and section 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



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   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 bi-directional 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 which are separated
   from each other by a packet interval, as shown in the picture 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


   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 picture.
   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 end points in the estimation
   process. The method to measuring the UDP delivery rate may also



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   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 re-grouped 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.

   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-cient) selects the mode or modes supported by the responder.
   This feature is designed to retain backward compatibility with the
   original TWAMP control and 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



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   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 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.

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 field 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.



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   The Valued-Added Octets feature must be immediately placed 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.

































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   The Session-Sender SHALL use the following TWAMP test packet format
   when the Value-Added Octets version 1 is selected in conjunction with
   the 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        |  Ver  |L|I|     Reserved      |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                      Last Seqno In Train                      |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                Desired Reverse Packet Interval                |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                   Additional Packet Padding                   |
         .                                                               .
         .                                                               .
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





























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   The Session-Sender SHALL use the following TWAMP test packet format
   when the Value-Added Octets Version 1 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                          |
         .                                                               .
         .                                                               .
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


















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   The Session-Sender SHALL use the following TWAMP test packet format
   when the Value-Added Octets Version 1 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)field.

   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.




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   The 2 bits after the Version field are used for flags: L and I.

   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 a test packet belongs to. The
   packets belonging to a train are determined by observing the test
   packet sequence number in relation to the Last Seqno for a train. The
   Last Seqno in Train MUST be higher or equal to the 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 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 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.


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 is selected, the behavior of



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   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.

         -  The Last Seqno in Train field 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.

         -  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].

         -  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.

         -  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
            duplicate test packet SHOULD be returned to the Session-
            Sender as quickly as possible. The Session-Reflector MUST
            NOT discard duplicate test packets.




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   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 re-use (reflect) the value-added
         padding octets (10 octets) provided in the Sender's Packet
         Padding.

      o  The Session-Reflector MAY re-use 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.




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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 with a new maximum train length
   field in the Request-TW-Session message.

   The Sender Discriminator (SD) field that is defined in the first
   draft has been 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  IANA Considerations

   This document has no actions for IANA.




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9  Acknowledgements

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


10  References

10.1  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 Ishac,J., "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., Ciavattone, L., TWAMP Reflect Octets and
               Symmetrical Size Features, RFC6038 , October 2010.


10.2  Informative References

   [RRBNC]     Ribeiro, V., Riedi, R., Baraniuk, R., Navratil, J.,
               Cottrel, L., Pathchirp: Efficient available bandwidth
               estimation for network paths, Passive and Active
               Measurement Workshop, 2003.

   [PDM]       Dovrolis, C., Ramanathan, P., and Moore D., Packet
               Dispersion Techniques and a Capacity Estimation
               Methodology, IEEE/ACM Transactions on Networking,
               December 2004.

   [ENHJMMB]   Ekelin, S., Nilsson, M., Hartikainen, E., Johnsson, A.,
               Mangs, J., Melander, B., Bjorkman, M., Real-time
               measurement of end-to-end available bandwidth using
               kalman filtering, Proceedings to the IEEE IFIP Network
               Operations and Management Symposium, 2006.

   [SBW]       Sommers, J., Barford, P., Willinger, W., Laboratory-based
               calibration of available bandwidth estimation tools,



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               Microprocess Microsyst., 2007.

   [Y1540]   ITU-T Y.1540, Internet protocol data communication service
               - IP packet transfer and availability performance
               parameters, 2011.


Author's 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




















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