Movatterモバイル変換

Internet Engineering Task Force (IETF)                    S. BaillargeonRequest for Comments: 6802                                     C. FlintaCategory: Informational                                      A. JohnssonISSN: 2070-1721                                                 Ericsson                                                           November 2012Ericsson Two-Way Active Measurement Protocol (TWAMP) Value-Added OctetsAbstract   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; seeSection2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 2012Table of Contents1. Introduction ....................................................21.1. Requirements Language ......................................32. Purpose and Scope ...............................................33. Capacity Measurement Principles .................................44. TWAMP-Control Extensions ........................................54.1. Additional Considerations ..................................65. Extended TWAMP-Test .............................................65.1. Sender Behavior ............................................65.1.1. Packet Timings ......................................75.1.2. Session-Sender Packet Format ........................75.2. Reflector Behavior ........................................125.2.1. Session-Reflector Packet Format ....................135.3. Additional Considerations .................................136. Experiments ....................................................147. Security Considerations ........................................148. Acknowledgements ...............................................149. References .....................................................159.1. Normative References ......................................159.2. Informative References ....................................151.  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-AddedBaillargeon, 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 inRFC 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 (seeSection 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 Sections4 and5.3 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 2Baillargeon, 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 inSection 3.1 of [RFC4656] andSection 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 20125.1.1.  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 20125.2.  Reflector Behavior   The TWAMP Session-Reflector follows the procedures and guidelines inSection 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.      -  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.      -  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 insection 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, theBaillargeon, 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 20126.  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 20129.  References9.1.  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 2012Authors' 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.comBaillargeon, et al.           Informational                    [Page 16]