IPPM WG                                                         R. Civil
Internet-Draft                                         Ciena Corporation
Intended status: Standards Track                               A. Morton
Expires: September 22, 2016 January 9, 2017                                       AT&T Labs
                                                                L. Zheng
                                                     Huawei Technologies
                                                               R. Rahman
                                                         M. Jethanandani
                                                           Cisco Systems
                                                     K. Pentikousis, Ed.
                                                                    EICT
                                                          March 21,
                                                              Travelping
                                                                L. Zheng
                                                     Huawei Technologies
                                                            July 8, 2016

         Two-Way Active Measurement Protocol (TWAMP) Data Model
                     draft-ietf-ippm-twamp-yang-00
                     draft-ietf-ippm-twamp-yang-01

Abstract

   This document specifies a data model for client and server
   implementations of the Two-Way Active Measurement Protocol (TWAMP).
   We define the TWAMP data model through Unified Modeling Language
   (UML) class diagrams and formally specify it using YANG.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Document Organization . . . . . . . . . . . . . . . . . .   3
   2.  Scope, Model, and Applicability . . . . . . . . . . . . . . .   4
   3.  Data Model Overview . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .   5   6
     3.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .   6   7
     3.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .   7
   4.  Data Model Parameters . . . . . . . . . . . . . . . . . . . .   7   8
     4.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .   7   8
     4.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .  14  11
     4.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .  19  12
     4.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .  22  13
   5.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .  26  15
     5.1.  YANG Tree Diagram . . . . . . . . . . . . . . . . . . . .  26  15
     5.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  28  18
   6.  Data Model Examples . . . . . . . . . . . . . . . . . . . . .  44
     6.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .  44
     6.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .  45  46
     6.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .  46  47
     6.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .  47  48
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  48  51
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  49  51
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  49  52
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  49  52
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  49  52
     10.2.  Informative References . . . . . . . . . . . . . . . . .  50  53
   Appendix A.  Detailed Data Model Examples . . . . . . . . . . . .  52  54
     A.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .  52  54
     A.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .  53  57
     A.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .  54  58
     A.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .  55  59
   Appendix B.  TWAMP Operational Commands . . . . . . . . . . . . .  57  62
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  57  62

1.  Introduction

   The Two-Way Active Measurement Protocol (TWAMP) [RFC5357] is used to
   measure network performance parameters such as latency, bandwidth,
   and packet loss by sending probe packets and measuring their
   experience in the network.  To date, TWAMP implementations do not
   come with a standard management framework and, as such, configuration
   depends on the various proprietary mechanisms developed by the corresponding
   TWAMP vendor.  This document addresses this gap by formally
   specifying the TWAMP data model using YANG.

1.1.  Motivation

   In current TWAMP deployments, deployments the lack of a standardized data model
   limits the flexibility to dynamically instantiate TWAMP-based
   measurements across equipment from different vendors.  In large,
   virtualized, and dynamically instantiated infrastructures where
   network functions are placed according to orchestration algorithms as
   discussed in [I-D.unify-nfvrg-challenges][I-D.unify-nfvrg-devops],
   proprietary mechanisms for managing TWAMP measurements pose severe
   limitations with respect to programmability.

   Two major trends call for revisiting the standardization on TWAMP
   management aspects.  First, we expect that in the coming years large-
   scale and multi-vendor TWAMP deployments will become the norm.  From
   an operations perspective, dealing with several vendor-specific TWAMP
   configuration mechanisms is simply unsustainable in this context.
   Second, the increasingly software-defined and virtualized nature of
   network infrastructures, based on dynamic service chains [NSC] and
   programmable control and management planes [RFC7426] requires a well-
   defined data model for TWAMP implementations.  This document defines
   such a TWAMP data model and specifies it formally using the YANG data
   modeling language [RFC6020].

1.2.  Terminology

   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 [RFC2119].

1.3.  Document Organization

   The rest of this document is organized as follows.  Section 2
   presents the scope and applicability of this document.  Section 3
   provides a high-level overview of the TWAMP data model.  Section 4
   details the configuration parameters of the data model and Section 5
   specifies in YANG the TWAMP data model.  Section 6 lists illustrative
   examples which conform to the YANG data model specified in this
   document.  Appendix A elaborates these examples further.

2.  Scope, Model, and Applicability

   The purpose of this document is the specification of a vendor-
   independent data model for TWAMP implementations.

   Figure 1 illustrates a redrawn version of the TWAMP logical model
   found in Section 1.2 of [RFC5357].  The figure is annotated with
   pointers to the UML diagrams provided in this document and associated
   with the data model of the four logical entities in a TWAMP
   deployment, namely the TWAMP Control-Client, Server, Session-Sender
   and Session-Reflector.

   As per [RFC5357], unlabeled links in Figure 1 are left unspecified
   and may be proprietary protocols.

       [Fig. 3]                                 [Fig. 4]
   +----------------+                          +--------+
   | Control-Client |  <-- TWAMP-Control -->   | Server |
   +----------------+                          +--------+
           ^                                        ^
           |                                        |
           V                                        V
   +----------------+                     +-------------------+
   | Session-Sender |  <-- TWAMP-Test --> | Session-Reflector |
   +----------------+                     +-------------------+
       [Fig. 5]                                 [Fig. 6]

                  Figure 1: Annotated TWAMP logical model

   As per [RFC5357], a TWAMP implementation may follow a simplified
   logical model, in which the same node acts both as the Control-Client and
   Session-Sender, while another node acts at the same time as the TWAMP
   Server and Session-Reflector.  Figure 2 illustrates this simplified
   logical model and indicates the interaction between the TWAMP
   configuration client and server using, for instance, NETCONF
   [RFC6241] or RESTCONF [I-D.ietf-netconf-restconf].  Note, however,
   that the specific protocol used to communicate the TWAMP
   configuration parameters specified herein is outside the scope of
   this document.  Appendix B considers TWAMP operational commands,
   which are also outside the scope of this document.

   o-------------------o                       o-------------------o
   |   Config client   |                       |   Config client   |
   o-------------------o                       o-------------------o
            ||                                          ||
    NETCONF || RESTCONF                         NETCONF || RESTCONF
            ||                                          ||
   o-------------------o                       o-------------------o
   |   Config server   |                       |   Config server   |
   |    [Fig. 3, 5]    |                       |    [Fig. 4, 6]    |
   +-------------------+                       +-------------------+
   |   Control-Client  | <-- TWAMP-Control --> |      Server       |
   |                   |                       |                   |
   |   Session-Sender  |  <-- TWAMP-Test -->   | Session-Reflector |
   +-------------------+                       +-------------------+

              Figure 2: Simplified TWAMP model and protocols

   We note that the data model defined in this document is orthogonal to
   the specific protocol used between the Config client and Config
   server to communicate the TWAMP configuration parameters.

   Operational actions such as how TWAMP-Test sessions are started and
   stopped, how perfmormance measurement results are retrieved, or how
   stored results are cleared, and so on, are not addressed by the
   configuration model defined in this docuemnt.  As noted above, such
   operational actions are not part of the TWAMP specification [RFC5357]
   and hence are out of scope of this document.  See also Appendix B.

3.  Data Model Overview

   A

   The TWAMP data model includes four categories of configuration items.

   Global configuration items relate to parameters that are set on a per
   device level.  For example, the administrative status of the device
   with respect to whether it allows TWAMP sessions and, if so, in what
   capacity (e.g.  Control-Client, Server or both), are typical
   instances of global configuration items.

   A second category includes attributes that can be configured on a per control
   TWAMP-Control connection basis, such as the Server IP address.

   A third category includes attributes related to per test TWAMP-Test
   session attributes, for instance setting different values in the
   Differentiated Services Code Point (DSCP) field.

   Finally, the data model could include includes attributes that relate to the
   operational state of the TWAMP implementation.

   As we describe the TWAMP data model in the remaining sections of this
   document, readers should keep in mind the functional entity grouping
   illustrated in Figure 1.

3.1.  Control-Client

   A TWAMP Control-Client has an administrative status field set at the
   device level that indicates whether the node is enabled to function
   as such.

   Each TWAMP Control-Client is associated with zero or more TWAMP
   control TWAMP-
   Control connections.  The main configuration parameters of each
   control connection are:

   o  A name which can be used to uniquely identify at the Control-
      Client a particular control connection.  This name is necessary
      for programmability reasons because at the time of creation of a
      TWAMP control
      TWAMP-Control connection not all IP and TCP port number
      information needed to uniquely identify the connection is
      available.

   o  The IP address of the interface the Control-Client will use for
      connections
      connections.

   o  The IP address of the remote Server TWAMP Server.

   o  Authentication and Encryption attributes such as KeyID, Token and
      the Client Initialization Vector (Client-IV) [RFC4656]. (Client-IV); see also the last
      paragraph of Section 6 in [RFC4656] and [RFC4086].

   Each TWAMP control TWAMP-Control connection, in turn, is associated with zero or
   more test TWAMP-Test sessions.  For each test session we note the
   following configuration items:

   o  The test session name that uniquely identifies a particular test
      session at the Control-Client and Session-Sender.  Similarly to
      the control connections above, this unique test session name is
      needed because at the time of creation of a test TWAMP-Test session,
      for example, the source UDP port number is not known to uniquely
      identify the test session.

   o  The IP address and UDP port number of the Session-Sender of on the
      path under test by TWAMP TWAMP.

   o  The IP address and UDP port number of the Session-Reflector of on
      said path path.

   o  Information pertaining to the test packet stream, such as the test
      starting time time, which performance metric is to be used
      [I-D.ietf-ippm-metric-registry], or whether the test should be
      repeated.

3.2.  Server

   Each TWAMP Server has an administrative status field set at the
   device level to indicate whether the node is enabled to function as a
   TWAMP Server.

   Each TWAMP Server is associated with zero or more control TWAMP-Control
   connections.  Each control connection is uniquely identified by the
   4-tuple {Control-Client IP address, Control-Client TCP port number,
   Server IP address, Server TCP port}. Control connection configuration
   items on a TWAMP Server are read-only.

3.3.  Session-Sender

   There is one TWAMP Session-Sender instance for each test TWAMP-Test session that
   is initiated from the sending device.  Primary configuration fields
   include:

   o  The test session name that MUST be identical with the
      corresponding test session name on the TWAMP Control-Client
      (Section 3.1)

   o  The control connection name, which along with the test session
      name uniquely identify the TWAMP Session-Sender instance

   o  Information pertaining to the test packet stream, such as, for
      example, the number of test packets and the packet distribution to
      be employed. employed; see also [RFC3432].

3.4.  Session-Reflector

   Each TWAMP Session-Reflector is associated with zero or more test TWAMP-Test
   sessions.  For each test session, the REFWAIT parameter (Section 4.2
   of [RFC5357] can be configured.

   Read-only access to other data model parameters, such as the Sender
   IP address is foreseen.  Each test session can be uniquely identified
   by the 4-tuple mentioned in Section 3.2.

4.  Data Model Parameters

   This section defines the TWAMP data model using UML and describes all introduces
   selected parameters associated parameters.

4.1.  Control-Client

   The twamp-client container (see Figure 3) holds items that are
   related to the configuration of with the four TWAMP Control-Client logical
   entity.  These are divided up into entities.
   The complete TWAMP data model specification is provided in the YANG
   module presented in Section 5.2.

4.1.  Control-Client

   The client container (see Figure 3) holds items that are associated with related to
   the configuration of the TWAMP Control-Client as a whole (e.g. client-admin-
   state) and items logical entity (recall
   Figure 1).

   The client container includes an administrative configuration
   parameter (client/admin-state) that are associated with individual control
   connections initiated by indicates whether the Control-Client entity (twamp-client-
   ctrl-connection).

 +--------------------+ device is
   allowed to initiate TWAMP-Control connections.

   +-------------+
   | twamp-client client      |
 +--------------------+
   +-------------+                   1..* +-----------------------+
   | client-admin-state admin-state |<>----------------------| mode-preference-chain |
   |             |                        +-----------------------+
   |             |  1..* +------------+   | priority              |
   |             |<>-----| key-chain  |   | mode                  |
 +--------------------+
   +-------------+       +------------+   +-----------------------+
          ^              | key-id     |
          V              | secret-key |
          |              +------------+
          | 0..*
 +------------------------------+
   +------------------------+
   | twamp-client-ctrl-connection ctrl-connection        |
 +------------------------------+
   +------------------------+
   | ctrl-connection-name name                   |
   | client-ip              |
   | server-ip              |
   | server-tcp-port        |    0..* +-------------------------+ +----------------------+
   | dscp control-packet-dscp    |<>-------| twamp-session-request test-session-request |
   | key-id                 |         +-------------------------+         +----------------------+
   | max-count              |         | test-session-name name                 |
   | client-tcp-port   {ro} |         | sender-ip            |
   | server-start-time {ro} |         | sender-udp-port      |
   | ctrl-connection-state state             {ro} |         | reflector-ip         |
   | selected-mode     {ro} |         | reflector-udp-port   |
   | token             {ro} |         | timeout              |
   | client-iv         {ro} |         | padding-length       |
 +------------------------------+
   +------------------------+         | dscp test-packet-dscp     |
                                      | start-time           |
               +-------------+ 1      | repeat               |
               | pm-reg-list |------<>| repeat-interval      |
               +-------------+        | test-session-state state           {ro} |
               | pm-index    |        | sid             {ro} |
               +-------------+        +-------------------------+        +----------------------+

             Figure 3: TWAMP Control-Client UML class diagram

   The twamp-client container includes an administrative parameter
   (client-admin-state) that controls whether the device is allowed to
   initiate TWAMP control sessions.

   The twamp-client client container holds a list (mode-preference-chain) which
   specifies the preferred Mode values according to their preferred order of use, use
   by the operator of this Control-Client, including the authentication
   and encryption Modes.  Specifically, mode-preference-chain lists each
   priority (expressed as a 16-bit unsigned integer, where zero is the
   highest priority and subsequent values monotonically increasing) with
   their corresponding mode (expressed as a 32-bit Hexadecimal value).

   Depending on the Modes available in the Server Greeting, the Control-Client Control-
   Client MUST choose the highest priority Mode from the configured mode-preference-
   chain
   mode-preference-chain list.

   Note that the list of preferred Modes may set bit position
   combinations when necessary, such as when referring to the extended
   TWAMP features in [RFC5618], [RFC5938], [RFC6038], and [RFC6038]. [RFC7717].  If
   the Control-Client cannot determine an acceptable Mode, it MUST
   respond with zero Mode bits set in the Set-up Response message,
   indicating it will not continue with the control connection.

   In addition, the twamp-client client container holds a list named key-chain which
   relates KeyIDs with the respective secret keys.  Both the Server and
   the Control-Client use the same mappings from KeyIDs to shared
   secrets (key-id and secret-key in Figure 3, respectively).  The
   Server, being prepared to conduct sessions with more than one
   Control-Client, uses KeyIDs to choose the appropriate secret-key; a
   Control-Client would typically have different secret keys for
   different Servers.  The secret-key is the shared secret, an octet
   string of arbitrary length whose interpretation as a text string is
   unspecified.  The key-id and secret-key encoding should follow
   Section 9.4 of [RFC6020].  The derived key length (dkLen in
   [RFC2898]) MUST be 128-bits for the AES Session-key used for
   encryption and a 256-bit HMAC-SHA1 Session-key used for
   authentication (see Section 6.10 of [RFC4656]).

   Each twamp-client client container also holds a list of twamp-client-ctrl-
   connection, ctrl-connections, where
   each item in the list describes a TWAMP control connection that will
   be initiated by this Control-Client.  There SHALL be one instance of twamp-client-ctrl-connection
   ctrl-connection per TWAMP-
   Control TWAMP-Control (TCP) connection that is to be
   initiated from this device.

   The configuration items for twamp-client-ctrl-connection are:

   ctrl-connection-name
           A unique name used as

   Each ctrl-connection holds a key to identify this individual TWAMP
           control connection on the Control-Client device.

   client-ip
           The IP address list of test-session-request.  test-
   session-request holds information associated with the local Control-Client device, to be
           placed in the source IP address field of the IP header in
           TWAMP-Control (TCP) packets belonging to
   for this control
           connection.  If not configured, the device SHALL choose its
           own source IP address.

   server-ip
           The IP address belonging to the remote Server device, which
           the TWAMP-Control connection will be initiated to. test session.  This item includes information that is mandatory.

   server-tcp-port
           This parameter defines associated
   with the TCP port number Request-TW-Session/Accept-Session message exchange (see
   Section 3.5 of [RFC5357]).

   There SHALL be one instance of test-session-request for each TWAMP-
   Test session that is to be used negotiated by this outgoing TWAMP-Control connection.  Typically, this
           is the well-known TWAMP port number (862) as per [RFC5357].
           However, there are known realizations of TWAMP in the field
           that were implemented before this well-known port number was
           allocated.  These early implementations allowed the port
           number to be configured.  This parameter is therefore
           provided for backward compatibility reasons.
   connection via a Request-TW-Session/Accept-Session exchange.

   The default
           value Control-Client is 862.

   dscp also responsible for scheduling and results
   collection for TWAMP-Test sessions, so test-session-request will also
   hold information related to these actions (e.g. pm-index, repeat-
   interval).

4.2.  Server

   The DSCP value server container (see Figure 4) holds items that are related to be placed in
   the TCP header configuration of TWAMP-
           Control packets generated by this Control-Client.  The
           default value is 0.

   key-id the TWAMP Server logical entity (recall
   Figure 1).

   The key-id value server container includes an administrative configuration
   parameter (server/admin-state) that indicates whether the device is selected for this
   allowed to receive TWAMP-Control
           connection.

   max-count
           If an attacking system sets the maximum value connections.

   A device operating in Count
           (2**32), then the system under attack would stall for Server role cannot configure attributes on
   a
           significant period of time while per TWAMP-Control connection basis, as it attempts to generate
           keys.  Therefore, TWAMP-compliant systems SHOULD have a
           configuration control to limit has no foreknowledge of
   the maximum Count value.  The
           default max-count value SHOULD incoming TWAMP-Control connections to be 32768.

   The following twamp-client-ctrl-connection parameters are read-only:

   client-tcp-port
           The source TCP port number used in received.  As such, any
   parameter that the TWAMP-Control packets
           belonging Server might want to this apply to an incoming control connection.

   server-start-time
           The Start-Time advertized by
   connection must be configured at the overall Server in the Server-Start
           message ([RFC4656], Section 3.1).  This is a timestamp
           representing the time when the current instantiation of the
           Server started operating.

   ctrl-connection-state
           The level, and will
   then be applied to all incoming TWAMP-Control connection connections.

   +---------------------+
   | server              |
   +---------------------+
   | admin-state         |   1..* +------------+
   | server-tcp-port     |<>------| key-chain  |
   | servwait            |        +------------+
   | control-packet-dscp |        | key-id     |
   | count               |        | secret-key |
   | max-count           |        +------------+
   | modes               |
   |                     |   0..* +--------------------------+
   |                     |<>------| ctrl-connection          |
   +---------------------+        +--------------------------+
                                  | client-ip           {ro} |
                                  | client-tcp-port     {ro} |
                                  | server-ip           {ro} |
                                  | server-tcp-port     {ro} |
                                  | state can be either active or
           idle.               {ro} |
                                  | control-packet-dscp {ro} |
                                  | selected-mode
           The       {ro} |
                                  | key-id              {ro} |
                                  | count               {ro} |
                                  | max-count           {ro} |
                                  | salt                {ro} |
                                  | server-iv           {ro} |
                                  | challenge           {ro} |
                                  +--------------------------+

                 Figure 4: TWAMP Mode that Server UML class diagram

   Each server container holds a list named key-chain which relates
   KeyIDs with the Control-Client has chosen for this
           control connection as set respective secret keys.  As mentioned in the Mode field of the Set-Up-
           Response message ([RFC4656], Section 3.1).

   token   This parameter holds the 64 octets containing 4.1,
   both the
           concatenation of a 16-octet challenge, a 16-octet AES
           Session-key used for encryption, and a 32-octet HMAC-SHA1
           Session-key used for authentication.  AES Session-key Server and
           HMAC Session-key are generated randomly by the Control-
           Client.  AES Session-key and HMAC Session-key MUST be
           generated Control-Client use the same mappings from
   KeyIDs to shared secrets.  The Server, being prepared to conduct
   sessions with sufficient entropy not more than one Control-Client, uses KeyIDs to reduce choose the security
           of
   appropriate secret-key; a Control-Client would typically have
   different secret keys for different Servers. key-id tells the underlying cipher [RFC4086].  The token itself Server
   which shared-secret the Control-Client wishes to use for
   authentication or encryption.

   Each incoming control connection that is
           encrypted using active on the AES (Advanced Encryption Standard) in
           Cipher Block Chaining (CBC).  Encryption MUST Server will be performed
           using
   represented by an Initialization Vector (IV) instance of zero and a key derived
           from the shared secret associated with KeyID.  Challenge ctrl-connection object.  There SHALL
   be one instance of ctrl-connection per incoming TWAMP-Control (TCP)
   connection that is
           the same as transmitted by received and active on the Server (Section 4.2) device.

   All items in the
           clear; see also the last paragraph ctrl-connection object are read-only.  Each instance
   of Section 6 in [RFC4656].

   client-iv
           The Control-Client Initialization Vector (Client-IV) is
           generated randomly by the Control-Client.  Client-IV merely
           needs to be unique (i.e., it MUST never ctrl-connection can be repeated for
           different sessions using uniquely identified by the same secret key; a simple way to
           achieve 4-tuple {client-
   ip, client-tcp-port, server-ip, server-tcp-port}.

4.3.  Session-Sender

   The session-sender container, illustrated in Figure 5, holds items
   that without the use of cumbersome state is are related to
           generate the Client-IV values using a cryptographically
           secure pseudo-random number source.

   Each twamp-client-ctrl-connection holds a list configuration of twamp-session-
   request. twamp-session-request holds information associated with the
   Control-Client for this test session.  This TWAMP Session-Sender
   logical entity.

   The session-sender container includes information an administrative parameter
   (session-sender/admin-state) that
   is associated with controls whether the Request-TW-Session/Accept-Session message
   exchange (see Section 3.5 of [RFC5357]).  The Control-Client is also
   responsible for scheduling and results collection for TWAMP-Test
   sessions, so twamp-session-request will also hold information related
   these actions (e.g. pm-index, repeat-interval).

   There SHALL be one instance of twamp-session-request for each TWAMP-
   Test session that device is
   allowed to be negotiated by this TWAMP-Control
   connection via a Request-TW-Session/Accept-Session exchange.

   The configuration items for twamp-session-request are:

   test-session-name
           A unique initiate TWAMP-Test sessions.

   +----------------+
   | session-sender |
   +----------------+  0..* +---------------------------+
   | admin-state    |<>-----| test-session              |
   +----------------+       +---------------------------+
                            | name for this test session to be used for
           identification of this                      |
                            | ctrl-connection-name {ro} |
                            | fill-mode                 |
                            | number-of-packets         |
                            | state {ro}                |
                            | sent-packets         {ro} |
                            | rcv-packets          {ro} |
                            | last-sent-seq        {ro} |
                            | last-rcv-seq         {ro} |
                            +---------------------------+
                                         ^
                                         V
                                         | 1
                             +---------------------+
                             | packet-distribution |
                             +---------------------+
                             | periodic /  poisson |
                             +---------------------+
                                 |           |
                +-------------------------+  |
                | periodic-interval       |  |
                | periodic-interval-units |  |
                +-------------------------+  |
                                             |
                                 +------------------------+
                                 | lambda                 |
                                 | lambda-units           |
                                 | max-interval           |
                                 | truncation-point-units |
                                 +------------------------+

             Figure 5: TWAMP Session-Sender UML class diagram

   Each TWAMP-Test session on the Control-
           Client.

   sender-ip
           The IP address of initiated by the Session-Sender device, which is to will be
           placed in the source IP address field
   represented by an instance of the IP header in a test-session object.  There SHALL be
   one instance of test-session for each TWAMP-Test (UDP) session for which
   packets belonging to this test session.

           This value will be used are being sent.

4.4.  Session-Reflector

   The session-reflector container, illustrated in Figure 6, holds items
   that are related to populate the sender address field configuration of the Request-TW-Session message.  If not configured, the
           device SHALL choose its own source IP address.

   sender-udp-port TWAMP Session-Reflector
   logical entity.

   The UDP port number session-reflector container includes an administrative parameter
   (session-reflector/admin-state) that is to be used by controls whether the Session-Sender
           for this TWAMP-Test session.  The number device is restricted
   allowed to the
           dynamic port range (49152 .. 65535). respond to incoming TWAMP test sessions.

   A value of zero
           indicates that the Control-Client SHALL auto-allocate a UDP
           port number for this TWAMP-Test session.  The configured (or
           auto-allocated) value is advertized in the Sender Port field
           of the Request-TW-session message (see also Section 3.5 of
           [RFC5357]).  Note that in the scenario where a device auto-
           allocates a UDP port number for a session, and the repeat
           parameter for that session indicates that it should be
           repeated, operating in the device is free to auto-allocate Session-Reflector role cannot configure
   attributes on a different UDP
           port number when per-session basis, as it negotiates the next (repeated) iteration has no foreknowledge of this session.

   reflector-ip
           The IP address belonging to what
   incoming sessions it will receive.  As such, any parameter that the remote
   Session-Reflector
           device might want to which the apply to an incoming TWAMP-Test
   session will must be initiated.
           This value configured at the overall Session-Reflector level,
   and will then be used applied to populate the receiver address
           field of the Request-TW-Session message.  This item is
           mandatory. all incoming sessions.

   +----=--------------+
   | session-reflector |
   +-------------------+
   | admin-state       |
   | refwait           |
   +-------------------+
            ^
            V
            |
            | 0..*
   +----------------------------------------+
   | test-session                           |
   +----------------------------------------+
   | sid                               {ro} |
   | sender-ip                         {ro} |
   | sender-udp-port                   {ro} |
   | reflector-ip                      {ro} |
   | reflector-udp-port
           This parameter defines the UDP port number that will be used
           by the                {ro} |
   | parent-connection-client-ip       {ro} |
   | parent-connection-client-tcp-port {ro} |
   | parent-connection-server-ip       {ro} |
   | parent-connection-server-tcp-port {ro} |
   | test-packet-dscp                  {ro} |
   | sent-packets                      {ro} |
   | rcv-packets                       {ro} |
   | last-sent-seq                     {ro} |
   | last-rcv-seq                      {ro} |
   +----------------------------------------+

            Figure 6: TWAMP Session-Reflector for this UML class diagram

   Each incoming TWAMP-Test session.  The
           number session that is restricted to the dynamic port range (49152 ..
           65535).  This value will be placed in the Receiver Port field
           of the Request-TW-Session message.  If this value is not set, active on the device Session-
   Reflector SHALL use the same port number as defined in the
           server-tcp-port parameter of this twamp-session-request's
           parent twamp-client-ctrl-connection.

   timeout The length of time (in seconds) that the Session-Reflector
           should continue to respond to packets belonging to this
           TWAMP-Test session after a Stop-Sessions TWAMP-Control
           message has been received ([RFC5357], Section 3.8).  This
           value will be placed in the Timeout field of the Request-TW-
           Session message.  The default value is 2 seconds.

   padding-length
           The number of bytes of padding that will be added to the
           TWAMP-Test (UDP) packets generated represented by the Session-Sender.
           This value will be placed in the Padding Length field of the
           Request-TW-Session message ([RFC4656], Section 3.5).

   dscp    The DSCP value to be placed in the UDP header an instance of TWAMP-Test
           packets generated by the Session-Sender, and a test-session
   object.  All items in the UDP
           header test-session object are read-only.

   Instances of the TWAMP-Test response packets generated test-session are indexed by the
           Session-Reflector for this test session.  This value will be
           placed in the Type-P Descriptor field of the Request-TW-
           Session message ([RFC5357]).

   start-time
           Time when the a session is to be started (but not before the
           Start-Sessions command is issued). identifier (sid).
   This value is placed in
           the Start Time field of the Request-TW-Session message.  The
           default value of 0 indicates that auto-allocated by the session will be started
           as soon TWAMP Server as the Start-Sessions message is received.

   repeat
           This value determines if the TWAMP-Test session must be
           repeated.  When a test session has completed, the repeat
           parameter is checked.  The value of 0 indicates that the
           session MUST NOT be repeated.  If the value is 1 through
           4,294,967,294 then the test session SHALL be repeated using
           the information in repeat-interval parameter, and the parent
           TWAMP-Control connection for this test session is restarted
           to negotiate a new instance of this TWAMP-Test session.  The
           implementation MUST decrement the value of repeat after
           determining a repeated session is expected.  The value of
           4,294,967,295 indicates that the test session SHALL be
           repeated *forever* using the information in repeat-interval
           parameter, and SHALL NOT decrement the value.  The default
           value of repeat is 0, indicating that once the session has
           completed, it will not be renegotiated and restarted.

   repeat-interval
           This parameter determines the timing of repeated test
           sessions when repeat > 0.  When the value of repeat-interval
           is 0, the negotiation of a new test session SHALL begin
           immediately after the previous test session completes.
           Otherwise, the Control-Client will wait for the number of
           minutes specified in the repeat-interval parameter before
           negotiating the new instance of this TWAMP-Test session.  The
           default value of repeat-interval is 0, indicating immediate
           re-start.

   pm-reg-list
           A list of one or more Performance Metric Registry Index
           values (see [I-D.ietf-ippm-metric-registry], which
           communicate packet stream characteristics and one or more
           metrics to be measured.  All members of the pm-reg-list MUST
           have the same stream characteristics, such that they combine
           to specify all metrics that shall be measured on a single
           stream.

   pm-index
           One or more Numerical index values of a Registered Metric in
           the Performance Metric Registry
           [I-D.ietf-ippm-metric-registry] comprise the pm-reg-list.
           Output statistics are specified in the corresponding Registry
           entry.

   The following twamp-session-request parameters are read-only:

   test-session-state
           The TWAMP-Test session state can be either accepted or
           indicate the respective error code.

   sid     The SID allocated by the Server for this TWAMP-Test session,
           and communicated back to the Control-Client in the SID field
           of the Accept-Session message; see Section 4.3 of [RFC6038].

4.2.  Server

   The twamp-server container (see Figure 4) holds items that are
   related to the configuration of the TWAMP Server logical entity
   (recall Figure 1).

   +------------------ -+
   | twamp-server       |
   +--------------------+
   | server-admin-state |   1..* +------------+
   | server-tcp-port    |<>------| key-chain  |
   | servwait           |        +------------+
   | dscp               |        | key-id     |
   | count              |        | secret-key |
   | max-count          |        +------------+
   | modes              |
   |                    |   0..* +-----------------------------------+
   |                    |<>------| twamp-server-ctrl-connection      |
   +--------------------+        +-----------------------------------+
                                 | client-ip                    {ro} |
                                 | client-tcp-port              {ro} |
                                 | server-ip                    {ro} |
                                 | server-tcp-port              {ro} |
                                 | server-ctrl-connection-state {ro} |
                                 | dscp                         {ro} |
                                 | selected-mode                {ro} |
                                 | key-id                       {ro} |
                                 | count                        {ro} |
                                 | max-count                    {ro} |
                                 | salt                         {ro} |
                                 | server-iv                    {ro} |
                                 | challenge                    {ro} |
                                 +-----------------------------------+

                 Figure 4: TWAMP Server UML class diagram

   A device operating in the Server role cannot configure attributes on
   a per TWAMP-Control connection basis, as it has no foreknowledge of
   what incoming TWAMP-Control connections it will receive.  As such,
   any parameter that the Server might want to apply to an incoming
   control connection must be configured at the overall Server level,
   and will then be applied to all incoming TWAMP-Control connections.

   Each twamp-server container holds a list named key-chain which
   relates KeyIDs with the respective secret keys.  As mentioned in
   Section 4.1, both the Server and the Control-Client use the same
   mappings from KeyIDs to shared secrets.  The Server, being prepared
   to conduct sessions with more than one Control-Client, uses KeyIDs to
   choose the appropriate secret-key; a Control-Client would typically
   have different secret keys for different Servers. key-id tells the
   Server which shared-secret the Control-Client wishes to use for
   authentication or encryption.

   Each incoming control connection that is active on the Server will be
   represented by an instance of a twamp-server-ctrl-connection object.
   All items in the twamp-server-ctrl-connection object are read-only,
   as we explain later in this section.

   The twamp-server container items are as follows:

   server-admin-state
           This administrative parameter controls whether the device is
           allowed to operate as a TWAMP Server.  As defined in
           [RFC5357] the roles of Server and Session-Reflector can be
           played by the same host; recall Figure 2.  For a host
           operating in this manner, this parameter controls whether the
           device is allowed to respond to TWAMP control sessions.

   server-tcp-port
           This parameter defines the well known TCP port number that is
           used by TWAMP-Control.  The Server will listen on this port
           number for incoming TWAMP-Control connections.  Although this
           is defined as a fixed value (862) in [RFC5357], there are
           several realizations of TWAMP in the field that were
           implemented before this well-known port number was allocated.
           These early implementations allowed the port number to be
           configured.  This parameter is therefore provided for
           backward compatibility reasons.  The default value is 862.

   servwait
           TWAMP-Control (TCP) session timeout, in seconds (([RFC5357],
           Section 3.1)).

   dscp    The DSCP value to be placed in the IP header of TWAMP-Control
           (TCP) packets generated by the Server.  Section 3.1 of
           [RFC5357] specifies that the server SHOULD use the DSCP value
           from the Control-Client's TCP SYN.  However, for practical
           purposes TWAMP will typically be implemented using a general
           purpose TCP stack provided by the underlying operating
           system, and such a stack may not provide this information to
           the user.  Consequently, it is not always possible to
           implement the behavior described in [RFC5357] in an OS-
           portable version of TWAMP.  The default behavior if this item
           is not set is to use the DSCP value from the Control-Client's
           TCP SYN, as per Section 3.1 of [RFC5357].

   count   Parameter used in deriving a key from a shared secret as
           described in Section 3.1 of [RFC4656], and are communicated
           to the Control-Client as part of the Server Greeting message.
           count MUST be a power of 2. count MUST be at least 1024.

           count SHOULD be increased as more computing power becomes
           common.

   max-count
           If an attacking system sets the maximum value in count
           (2**32), then the system under attack would stall for a
           significant period of time while it attempts to generate
           keys.  Therefore, TWAMP-compliant systems SHOULD have a
           configuration control to limit the maximum count value.  The
           default max-count value SHOULD be 32768.

   modes
           The bit mask of TWAMP Modes this Server instance is willing
           to support; see IANA TWAMP Modes Registry.  Each bit position
           set represents a mode; see TWAMP-Modes at
           http://www.iana.org/assignments/twamp-parameters/twamp-
           parameters.xhtml.  Note: Modes requiring Authentication or
           Encryption MUST include the related attributes.

   There SHALL be one instance of twamp-server-ctrl-connection per
   incoming TWAMP-Control (TCP) connection that is received and active
   on the Server device.  All items in the twamp-server-ctrl-connection
   are read-only.  Each instance of twamp-server-ctrl-connection uses
   the following 4-tuple as its unique key: client-ip, client-tcp-port,
   server-ip, server-tcp-port.

   The twamp-server-ctrl-connection container items are all read-only:

   client-ip
           The IP address on the remote Control-Client device, which is
           the source IP address used in the TWAMP-Control (TCP) packets
           belonging to this control connection.

   client-tcp-port
           The source TCP port number used in the TWAMP-Control (TCP)
           packets belonging to this control connection.

   server-ip
           The IP address of the local Server device, which is the
           destination IP address used in the TWAMP-Control (TCP)
           packets belonging to this control connection.

   server-tcp-port
           The destination TCP port number used in the TWAMP-Control
           (TCP) packets belonging to this control connection.  This
           will usually be the same value as the server-tcp-port
           configured under twamp-server.  However, in the event that
           the user re-configured twamp-server:server-tcp-port after
           this control connection was initiated, this value will
           indicate the server-tcp-port that is actually in use for this
           control connection.

   server-ctrl-connection-state
           The Server TWAMP-Control connection state can be active or
           SERVWAIT.

   dscp
           The DSCP value used in the IP header of the TWAMP-Control
           (TCP) packets sent by the Server for this control connection.
           This will usually be the same value as is configured in the
           dscp parameter under the twamp-server container.  However, in
           the event that the user re-configures twamp-server:dscp after
           this control connection is already in progress, this read-
           only value will show the actual dscp value in use by this
           TWAMP-Control connection.

   selected-mode
           The Mode that was chosen for this TWAMP-Control connection as
           set in the Mode field of the Set-Up-Response message.

   key-id
           The KeyID value that is in use by this TWAMP-Control
           connection.  The Control-Client selects the key-id for the
           control connection.

   count
           The count value that is in use by this TWAMP-Control
           connection.  This will usually be the same value as is
           configured under twamp-server.  However, in the event that
           the user re-configured twamp-server:count after this control
           connection is already in progress, this read-only value will
           show the actual count that is in use for this TWAMP-Control
           connection.

   max-count
           The max-count value that is in use by this TWAMP-Control
           connection.  This will usually be the same value as is
           configured under twamp-server.  However, in the event that
           the user re-configured twamp-server:max-count after this
           control connection is already in progress, this read-only
           value will show the actual max-count that is in use for this
           control connection.

   salt    A parameter used in deriving a key from a shared secret as
           described in Section 3.1 of [RFC4656].  Salt MUST be
           generated pseudo-randomly (independently of anything else in
           the RFC) and is communicated to the Control-Client as part of
           the Server Greeting message.

   server-iv
           The Server Initialization Vector (IV) is generated randomly
           by the Server.

   challenge
           A random sequence of octets generated by the Server.  As
           described in Section 4.1 challenge is used by the Control-
           Client to prove possession of a shared secret.

4.3.  Session-Sender

   The twamp-session-sender container, illustrated in Figure 5, holds
   items that are related to the configuration of the TWAMP Session-
   Sender logical entity.

   The twamp-session-sender container includes an administrative
   parameter (session-sender-admin-state) that controls whether the
   device is allowed to initiate TWAMP test sessions.

   There is one instance of twamp-sender-test-session for each TWAMP-
   Test session for which packets are being sent.

   +----------------------------+
   | twamp-session-sender       |
   +----------------------------+  0..* +---------------------------+
   | session-sender-admin-state |<>-----| twamp-sender-test-session |
   +----------------------------+       +---------------------------+
                                        | test-session-name         |
                                        | ctrl-connection-name {ro} |
                                        | fill-mode                 |
                                        | number-of-packets         |
                                        | sender-session-state {ro} |
                                        | sent-packets         {ro} |
                                        | rcv-packets          {ro} |
                                        | last-sent-seq        {ro} |
                                        | last-rcv-seq         {ro} |
                                        +---------------------------+
                                                   ^
                                                   V
                                                   | 1
                                         +---------------------+
                                         | packet-distribution |
                                         +---------------------+
                                         | periodic /  poisson |
                                         +---------------------+
                                             |           |
                            +-------------------------+  |
                            | periodic-interval       |  |
                            | periodic-interval-units |  |
                            +-------------------------+  |
                                             +------------------------+
                                             | lambda                 |
                                             | lambda-units           |
                                             | max-interval           |
                                             | truncation-point-units |
                                             +------------------------+

             Figure 5: TWAMP Session-Sender UML class diagram

   The twamp-sender-test-session container items are:

   test-session-name
           A unique name for this TWAMP-Test session to be used for
           identifying this test session by the Session-Sender logical
           entity.

   ctrl-connection-name
           The name of the parent TWAMP-Control connection that is
           responsible for negotiating this TWAMP-Test session.

   fill-mode
           Indicates whether the padding added to the TWAMP-Test (UDP)
           packets will contain pseudo-random numbers, or whether it
           should consist of all zeroes, as per Section 4.2.1 of
           [RFC5357].

   number-of-packets
           The overall number of TWAMP-Test (UDP) packets to be
           transmitted by the Session-Sender for this test session.

   packet-distribution
           Defines whether TWAMP-Test (UDP) packets are to be
           transmitted with a fixed interval between them, or whether a
           Poisson distribution is to be used.

   periodic-interval and periodic-interval-units
           If packet-distribution is set to periodic, these two values
           are used together to determine the period to wait between the
           first bits of TWAMP-Test (UDP) packet transmissions for this
           test session.  periodic-interval-units is one of seconds,
           milliseconds, microseconds, nanoseconds; see [RFC3432].

   lambda and lambda-units
           If packet-distribution is Poisson, the lambda parameter
           determines the corresponding average rate of packet
           transmission.  lambda-units defines the units of lambda in
           reciprocal seconds; see [RFC3432].

   max-interval
           If packet-distribution is Poisson, then this parameter keeps
           a stream active by setting a maximum time between packet
           transmissions.

   truncation-point-units
           One of seconds, milliseconds, microseconds, nanoseconds.

   The following twamp-sender-test-session parameters are read-only:

   sender-session-state
           This read-only item can be either Active or Idle.

   sent-packets
           The number of TWAMP-Test (UDP) packets belonging to this
           session that have been transmitted by the Session-Sender.

   rcv-packets
           The number of TWAMP-Test (UDP) packets belonging to this
           session that have been received from the Session-Reflector.

           The round trip loss for a test session can be calculated as
           sent-packets - rcv-packets.

   last-sent-seq
           The value in the sequence number field of the last TWAMP-Test
           (UDP) packet transmitted for this test session.  Sequence
           numbers start from zero, so this should always be one less
           than the sent-packets value.

   last-rcv-seq
           The value in the sequence number field of the last TWAMP-Test
           (UDP) packet received for this test session.  In the case of
           packet loss in the Session-Sender to Session-Reflector
           direction, this value minus the last-sent-seq will quantify
           the number of packets that were lost in the Session-Sender to
           Session-Reflector direction.

4.4.  Session-Reflector

   The twamp-session-reflector container, illustrated in Figure 6, holds
   items that are related to the configuration of the TWAMP Session-
   Reflector logical entity.

   A device operating in the Session-Reflector role cannot configure
   attributes on a per-session basis, as it has no foreknowledge of what
   incoming sessions it will receive.  As such, any parameter that the
   Session-Reflector might want to apply to an incoming TWAMP-Test
   session must be configured at the overall Session-Reflector level,
   and will then be applied to all incoming sessions.

   The twamp-session-sender container includes an administrative
   parameter (session-reflector-admin-state) that controls whether the
   device is allowed to respond to incoming TWAMP test sessions.  Each
   incoming TWAMP-Test session that is active on the Session-Reflector
   will be represented by an instance of a twamp-reflector-test-session
   object.  All items in the twamp-reflector-test-session object are
   read-only.

   +----=--------------------------+
   | twamp-session-reflector       |
   +-------------------------------+
   | session-reflector-admin-state |
   | refwait                       |
   +-------------------------------+
                    ^
                    V
                    |
                    | 0..*
   +----------------------------------------+
   | twamp-reflector-test-session           |
   +----------------------------------------+
   | sid                               {ro} |
   | sender-ip                         {ro} |
   | sender-udp-port                   {ro} |
   | reflector-ip                      {ro} |
   | reflector-udp-port                {ro} |
   | parent-connection-client-ip       {ro} |
   | parent-connection-client-tcp-port {ro} |
   | parent-connection-server-ip       {ro} |
   | parent-connection-server-tcp-port {ro} |
   | dscp                              {ro} |
   | sent-packets                      {ro} |
   | rcv-packets                       {ro} |
   | last-sent-seq                     {ro} |
   | last-rcv-seq                      {ro} |
   +----------------------------------------+

            Figure 6: TWAMP Session-Reflector UML class diagram

   The twamp-session-reflector configuration items are:

   refwait
           The Session-Reflector MAY discontinue any session that has
           been started when no packet associated with that session has
           been received for REFWAIT seconds.  The default value of
           REFWAIT SHALL be 900 seconds, and this waiting time MAY be
           configurable.  This timeout allows a Session-Reflector to
           free up resources in case of failure.

   Instances of twamp-reflector-test-session are indexed by a session
   identifier (sid).  This value is auto-allocated by the Server as test
   session requests are received, and communicated back to the Control-
   Client in the SID field of the Accept-Session message; see
   Section 4.3 of [RFC6038].

   When attempting to retrieve operational data for active test sessions
   from a Session-Reflector device, the user will not know what sessions
   are currently active on that device, or what SIDs have been auto-
   allocated for these test sessions.  If the user has network access to
   the Control-Client device, then it is possible to read the data for
   this session under twamp-client:twamp-client-ctrl-connection:twamp-
   session-request:sid and obtain the SID (see Figure 3).  The user may
   then use this SID value as an index to retrieve an individual twamp-
   session-reflector:twamp-reflector-test-session instance on the
   Session-Reflector device.

   If the user has no network access to the Control-Client device, then
   the only option is to retrieve all twamp-reflector-test-session
   instances from the Session-Reflector device.  This could be
   problematic if a large number of test sessions are currently active
   on that device.

   Each Session-Reflector TWAMP-Test session contains the following
   4-tuple: {parent-connection-client-ip, parent-connection-client-tcp-
   port, parent-connection-server-ip, parent-connection-server-tcp-
   port}. This 4-tuple corresponds to the equivalent 4-tuple {client-ip,
   client-tcp-port, server-ip, server-tcp-port} in the twamp-server-
   ctrl-connection object.  This 4-tuple allows the user to trace back
   from the TWAMP-Test session to the (parent) TWAMP-Control connection
   that negotiated this test session.

   All data under twamp-reflector-test-session is read-only:

   sid     An auto-allocated identifier for this TWAMP-Test session,
           that is unique within the context of this Server/Session-
           Reflector device only.  This value will be
   requests are received, and communicated to
           the Control-Client that requested the test session in the SID
           field of the Accept-Session message.

   sender-ip
           The IP address on the remote device, which is the source IP
           address used in the TWAMP-Test (UDP) packets belonging to
           this test session.

   sender-udp-port
           The source UDP port used in the TWAMP-Test packets belonging
           to this test session.  The number is restricted to the
           dynamic port range (49152 .. 65535).

   reflector-ip
           The IP address of the local Session-Reflector device, which
           is the destination IP address used in the TWAMP-Test (UDP)
           packets belonging to this test session.

   reflector-udp-port
           The destination UDP port number used in the TWAMP-Test (UDP)
           test packets belonging to this test session.  The number is
           restricted to the dynamic port range (49152 .. 65535).

   parent-connection-client-ip
           The IP address on the Control-Client device, which is the
           source IP address used in the TWAMP-Control (TCP) packets
           belonging to the parent control connection that negotiated
           this test session.

   parent-connection-client-tcp-port
           The source TCP port number used in the TWAMP TCP control
           packets belonging to the parent control connection that
           negotiated this test session.

   parent-connection-server-ip
           The IP address of the Server device, which is the destination
           IP address used in the TWAMP-Control (TCP) packets belonging
           to the parent control connection that negotiated this test
           session.

   parent-connection-server-tcp-port
           The destination TCP port number used in the TWAMP-Control
           (TCP) packets belonging to the parent control connection that
           negotiated this test session.

   dscp    The DSCP value present back to the Control-Client in
   the IP header of TWAMP-Test (UDP)
           packets belonging to this test session.

   sent-packets
           The number SID field of TWAMP-Test (UDP) response packets that have
           been sent by the Session-Reflector Accept-Session message; see Section 4.3 of
   [RFC6038].

   When attempting to retrieve operational data for this active test session.

   rcv-packets
           The number of TWAMP-Test (UDP) packets sessions
   from a Session-Reflector device, the user will not know what sessions
   are currently active on that device, or what SIDs have been
           received by the Session-Reflector auto-
   allocated for this these test session.
           Since sessions.  If the Session-Reflector should respond user has network access to every test
           packet
   the Control-Client device, then it receives, is possible to read the sent-packets data for
   this session under client/ctrl-connection/test-session-request/sid
   and rcv-packets values
           should always be identical.

   last-sent-seq obtain the SID (see Figure 3).  The user may then use this SID
   value in as an index to retrieve an individual session-reflector/test-
   session instance on the sequence Session-Reflector device.

   If the user has no network access to the Control-Client device, then
   the only option is to retrieve all test-session instances from the
   Session-Reflector device.  This could be problematic if a large
   number field of the last TWAMP-Test
           (UDP) response packet transmitted for this test session.

   last-rcv-seq
           The value sessions are currently active on that device.

   Each Session-Reflector TWAMP-Test session contains the following
   4-tuple: {parent-connection-client-ip, parent-connection-client-tcp-
   port, parent-connection-server-ip, parent-connection-server-tcp-
   port}.  This 4-tuple MUST correspond to the equivalent 4-tuple
   {client-ip, client-tcp-port, server-ip, server-tcp-port} in the sequence number field of
   server/ctrl-connection object.  This 4-tuple allows the user to trace
   back from the last TWAMP-Test
           (UDP) packet received for session to the (parent) TWAMP-Control
   connection that negotiated this test session.

5.  Data Model

   This section formally specifies the TWAMP data model using YANG.

5.1.  YANG Tree Diagram

   This section presents a simplified graphical representation of the
   TWAMP data model using a YANG tree diagram.  Readers should keep in
   mind that the limit of 72 characters per line forces us to introduce
   artificial line breaks in some tree diagram nodes.

  module: ietf-twamp
     +--rw twamp
        +--rw twamp-client! client! {control-client}?
        |  +--rw client-admin-state admin-state              boolean
        |  +--rw mode-preference-chain* [priority]
        |  |  +--rw priority    uint16
        |  |  +--rw mode?       mode       twamp-modes
        |  +--rw key-chain* [key-id]
        |  |  +--rw key-id        string
        |  |  +--rw secret-key?   string
        |  +--rw twamp-client-ctrl-connection* [ctrl-connection-name] ctrl-connection* [name]
        |     +--rw ctrl-connection-name name                    string
        |     +--rw client-ip?              inet:ip-address
        |     +--rw server-ip               inet:ip-address
        |     +--rw server-tcp-port?        inet:port-number
        |     +--rw dscp? control-packet-dscp?    inet:dscp
        |     +--rw key-id?                 string
        |     +--rw max-count?              uint32
        |     +--ro client-tcp-port?        inet:port-number
        |     +--ro server-start-time?      uint64
        |     +--ro ctrl-connection-state?   ctrl-connection-state state? \
                            control-client-connection-state
        |     +--ro selected-mode?           mode          twamp-modes
        |     +--ro token?                  binary
        |     +--ro client-iv?              binary
        |     +--rw twamp-session-request* [test-session-name] test-session-request* [name]
        |        +--rw test-session-name name                  string
        |        +--rw sender-ip?            inet:ip-address
        |        +--rw sender-udp-port?      inet:port-number      dynamic-port-number
        |        +--rw reflector-ip          inet:ip-address
        |        +--rw reflector-udp-port?   inet:port-number   dynamic-port-number
        |        +--rw timeout?              uint64
        |        +--rw padding-length?       uint32
        |        +--rw dscp? test-packet-dscp?     inet:dscp
        |        +--rw start-time?           uint64
        |        +--rw repeat?               uint32
        |        +--rw repeat-interval?      uint32
        |        +--rw pm-reg-list* [pm-index]
        |        |  +--rw pm-index    uint16
        |        +--ro test-session-state? state?                test-session-state
        |        +--ro sid?                  string
        +--rw twamp-server! server! {server}?
        |  +--rw server-admin-state admin-state            boolean
        |  +--rw server-tcp-port?       inet:port-number
        |  +--rw servwait?              uint32
        |  +--rw dscp? control-packet-dscp?   inet:dscp
        |  +--rw count?                 uint32
        |  +--rw max-count?             uint32
        |  +--rw modes?                          mode                 twamp-modes
        |  +--rw key-chain* [key-id]
        |  |  +--rw key-id        string
        |  |  +--rw secret-key?   string
        |  +--ro twamp-server-ctrl-connection* ctrl-connection* \
                  [client-ip client-tcp-port server-ip server-tcp-port]
        |     +--ro client-ip              inet:ip-address
        |     +--ro client-tcp-port        inet:port-number
        |     +--ro server-ip              inet:ip-address
        |     +--ro server-tcp-port        inet:port-number
        |     +--ro server-ctrl-connection-state? state?                 server-ctrl-connection-state
        |     +--ro dscp? control-packet-dscp?   inet:dscp
        |     +--ro selected-mode?                  mode         twamp-modes
        |     +--ro key-id?                string
        |     +--ro count?                 uint32
        |     +--ro max-count?             uint32
        |     +--ro salt?                  binary
        |     +--ro server-iv?             binary
        |     +--ro challenge?             binary
        +--rw twamp-session-sender! session-sender! {session-sender}?
        |  +--rw session-sender-admin-state admin-state     boolean
        |  +--rw twamp-sender-test-session* [test-session-name] test-session* [name]
        |     +--rw test-session-name name                       string
        |     +--ro ctrl-connection-name?      string
        |     +--rw fill-mode?                 fill-mode                 padding-fill-mode
        |     +--rw number-of-packets?         uint32
        |     +--rw (packet-distribution)?
        |     |  +--:(periodic)
        |     |  |  +--rw periodic-interval?         uint32
        |     |  |  +--rw periodic-interval-units?   units   time-units
        |     |  +--:(poisson)
        |     |     +--rw lambda?                    uint32
        |     |     +--rw lambda-units?              uint32
        |     |     +--rw max-interval?              uint32
        |     |     +--rw truncation-point-units?    units    time-units
        |     +--ro sender-session-state? state?                     sender-session-state
        |     +--ro sent-packets?              uint32
        |     +--ro rcv-packets?               uint32
        |     +--ro last-sent-seq?             uint32
        |     +--ro last-rcv-seq?              uint32
        +--rw twamp-session-reflector! session-reflector! {session-reflector}?
           +--rw session-reflector-admin-state admin-state     boolean
           +--rw refwait?        uint32
           +--ro twamp-reflector-test-session* test-session* \
                          [sender-ip sender-udp-port \
                          reflector-ip reflector-udp-port]
              +--ro sid?                                 string
              +--ro sender-ip                   \
                                                  inet:ip-address
              +--ro sender-udp-port                      inet:port-number             \
                                                  dynamic-port-number
              +--ro reflector-ip                         inet:ip-address
              +--ro reflector-udp-port                   inet:port-number          \
                                                  dynamic-port-number
              +--ro parent-connection-client-ip? parent-connection-client-ip?\
                                                  inet:ip-address
              +--ro parent-connection-client-tcp-port? \
                                                  inet:port-number
              +--ro parent-connection-server-ip? \
                                                  inet:ip-address
              +--ro parent-connection-server-tcp-port? \
                                                  inet:port-number
              +--ro dscp? test-packet-dscp?                    inet:dscp
              +--ro sent-packets?                        uint32
              +--ro rcv-packets?                         uint32
              +--ro last-sent-seq?                       uint32
              +--ro last-rcv-seq?                        uint32

5.2.  YANG Module

   This section presents the YANG module for the TWAMP data model
   defined in this document.

  <CODE BEGINS> file "ietf-twamp@2016-03-21.yang" "ietf-twamp@2016-07-07.yang"

  module ietf-twamp {
  namespace "urn:ietf:params:xml:ns:yang:ietf-twamp";
   //namespace need
    //namespace need to be assigned by IANA
    namespace
      urn:ietf:params:xml:ns:yang:ietf-twamp;
    prefix
      ietf-twamp;

    import ietf-inet-types {
      prefix inet;
    }

    organization
      "IETF IPPM (IP Performance Metrics) Working Group";

    contact
      draft-ietf-ippm-twamp-yang@tools.ietf.org;

    description
      "This YANG module specifies a vendor-independent data
      model for the Two-Way Active Measurement Protocol (TWAMP).

      The data model covers four TWAMP logical entities:
      Control-Client, Server, Session-Sender, and Session-Reflector.
      See Fig. 1 of draft-ietf-ippm-twamp-yang for an illustration
      of the annotated TWAMP logical model.

      The YANG module uses features to indicate which of the four
      logical entities are supported by an implementation.";

    revision 2016-07-07 {
      description
          "Revision appearing in draft-ietf-ippm-twamp-yang-01.
          Covers RFC 5357, RFC 5618, RFC 5938, RFC 6038, RFC 7717,
          and draft-ietf-ippm-metric-registry";
      reference
          draft-ietf-ippm-twamp-yang;
    }

    /*
     * Typedefs
     */

    typedef twamp-modes {
      type bits {
        bit unauthenticated {
          position 0;
          description
              "Unauthenticated mode. See RFC 7717 Section 7.";
        }
        bit authenticated {
          position 1;
          description
              "Authenticated mode. See RFC 7717 Section 7.";
        }
        bit encrypted {
          position 2;
          description
              "Encrypted mode. See RFC 7717 Section 7.";
        }
        bit unauth-test-encrpyt-control {
          position 3;
          description
              "Mixed Security Mode: TWAMP-Test protocol security
              mode in Unauthenticated mode, TWAMP-Control protocol
              in Encrypted mode.";
          reference
              "RFC 5618: Mixed Security Mode for the Two-Way Active
              Measurement Protocol (TWAMP)";
        }
        bit individual-session-control {
          position 4;
          description
              "Individual Session Control.";
          reference
              "RFC 5938: Individual Session Control Feature
              for the Two-Way Active Measurement Protocol (TWAMP)";

        }
        bit reflect-octets {
          position 5;
          description
              "Reflect Octets Capability.";
          reference
              "RFC 6038: Two-Way Active Measurement Protocol (TWAMP)
              Reflect Octets and Symmetrical Size Features";
        }
        bit symmetrical-size {
          position 6;
          description
              "Symmetrical Size Sender Test Packet Format.";
          reference
              "RFC 6038: Two-Way Active Measurement Protocol (TWAMP)
              Reflect Octets and Symmetrical Size Features";
        }
        bit IKEv2Derived {
          position 7;
          description
              "IKEv2Derived Mode Capability.";
          reference
              "RFC 7717: IKEv2-Derived Shared Secret Key for
              the One-Way Active Measurement Protocol (OWAMP)
              and Two-Way Active Measurement Protocol (TWAMP)";
        }
      }
      description
          "Specifies the configurable TWAMP-Modes used during a
          TWAMP-Control Connection setup between a Control-Client
          and a Server. RFC 7717 Section 7 summarizes the
          TWAMP-Modes registry.";
    }

    typedef control-client-connection-state {
      type enumeration {
        enum active {
          description
              "Indicates an active TWAMP-Control connection to be assigned by IANA
  prefix "ietf-twamp";

  import ietf-inet-types Server.";
        }
        enum idle {
    prefix inet;
          description
              "Indicates an idle TWAMP-Control connection to Server.";
        }
      }

  organization "IETF IPPM (IP Performance Metrics) Working Group";

  contact "draft-ietf-ippm-twamp-yang@tools.ietf.org";
      description "TWAMP Data Model";

  revision "2016-03-21" "Control-Client control connection state";
    }
    typedef test-session-state {
      type enumeration {
        enum accepted {
          value 0;
          description "01 version. RFC5357, RFC5618, RFC5938 and RFC6038
    is covered. draft-ietf-ippm-metric-registry
              "Indicates that the TWAMP-Test session request
              is also considered";

  reference "draft-ietf-ippm-twamp-yang"; accepted.";
        }
  feature control-client
        enum failed {
          value 1;
          description "This feature relates
              "Indicates a TWAMP-Test session failure due to the device functions as
    the TWAMP Control-Client.";
              some unspecified reason (catch-all).";
        }

  feature server
        enum internal-error {
          value 2;
          description "This feature relates
              "Indicates a TWAMP-Test session failure due to
              an internal error.";
        }
        enum not-supported {
          value 3;
          description
              "Indicates a TWAMP-Test session failure because
              some aspect of the device functions as
    the TWAMP Server."; TWAMP-Test session request
              is not supported.";
        }

  feature session-sender
        enum permanent-resource-limit {
          value 4;
          description "This feature relates
              "Indicates a TWAMP-Test session failure due to the device functions as
    the TWAMP Session-Sender.";
              permanent resource limitations.";
        }

  feature session-reflector
        enum temp-resource-limit {
          value 5;
          description "This feature relates
              "Indicates a TWAMP-Test session failure due to
              temporary resource limitations.";
        }
      }
      description "TWAMP-Test session state";
    }

    typedef server-ctrl-connection-state {
      type enumeration {
        enum active {
          description "Indicates an active TWAMP-Control connection
          to the device functions as Control-Client.";

        }
        enum servwait {
          description "Indicates that the TWAMP Session-Reflector."; TWAMP-Control connection
          to the Control-Client is in SERVWAIT according to RFC 5357
          (Section 3.1): [a] Server MAY discontinue any established
          control connection when no packet associated with that
          connection has been received within SERVWAIT seconds.";
        }
      }
      description "Server control connection state";
    }

    typedef ctrl-connection-state sender-session-state {
      type enumeration {
        enum active {
          description "Control
              "Indicates that the TWAMP-Test session is active.";
        }
        enum idle failure {
          description "Control
              "Indicates that the TWAMP-Test session is idle."; has failed.";
        }
      }
      description "Control connection state"; "Session-Sender session state.";
    }

    typedef mode padding-fill-mode {
      type bits enumeration {
      bit unauthenticated
        enum zero {
        position "0";
          description "Unauthenticated"; "Packets will be padded with
          all zeros";
        }
      bit authenticated
        enum random {
        position "1";
          description "Authenticated"; "Packets will be padded with
          pseudo-random numbers";
        }
      }
      bit encrypted {
        position "2";
      description "Encrypted"; "Indicates what type of packet padding is
      to be used for the UDP TWAMP-Test packets.";
    }
      bit unauth-test-encrpyt-control

    typedef time-units  {
      type enumeration {
        enum s {
        position "3";
          description "Mixed Security Mode per RFC 5618. Test
        protocol security mode in Unauthenticated mode,
        Control protocol in Encrypted mode."; "Seconds.";
        }
      bit individual-session-control
        enum ms {
        position "4";
          description "Individual session control per RFC5938."; "Milliseconds.";

        }
      bit reflect-octets
        enum us {
        position "5";
          description "Reflect octets capability per RFC6038."; "Microseconds.";
        }
      bit symmetrical-size
        enum ns {
        position "6";
          description "Symmetrical size per RFC6038."; "Nanoseconds.";
        }
      }
      description "Authentication mode bit mask"; "TWAMP configuration parameters time units.";
    }

    typedef test-session-state dynamic-port-number {
    type enumeration inet:port-number {
      enum ok
      range 49152..65535;
    }
    description "Dynamic range for port numbers";
    }

    /*
     * Features
     */

    feature control-client {
        value 0;
      description "Test session is accepted.";
          "Indicates that the device supports configuration
          of the TWAMP Control-Client.";
    }
      enum failed

    feature server {
        value 1;
      description "Failure, reason unspecified (catch-all).";
          "Indicates that the device supports configuration
          of the TWAMP Server.";
    }
      enum internal-error

    feature session-sender {
        value 2;
      description "Internal error.";
          "Indicates that the device supports configuration
          of the TWAMP Session-Sender.";
    }
      enum not-supported

    feature session-reflector {
        value 3;
      description "Some aspect
          "Indicates that the device supports configuration
          of request is not supported."; the TWAMP Session-Reflector.";
    }
      enum permanent-resource-limit

    /*
     * Reusable node groups
     */

    grouping key-management {
        value 4;

      list key-chain {
          key key-id;
          leaf key-id {
            type string {
              length 1..80;
            }
            description "Cannot perform request due
              "KeyID to
        permanent resource limitations."; be used for a TWAMP-Control connection.";
          }
      enum temp-resource-limit

          leaf secret-key {
        value 5;
            type string;
            description "Cannot perform request due to
        temporary resource limitations.";
              "The corresponding secret key for the
              TWAMP-Control connection.";
          }
          description
              "Relates KeyIDs with the respective secret keys
              for a TWAMP-Control connection.";
      }
      description "Test session state"; "TWAMP-Control key management.";
    }

  typedef server-ctrl-connection-state {
    type enumeration

    grouping maintenance-statistics {
      enum "active"

      leaf sent-packets {
        type uint32;
        config false;
        description "Active"; "Packets sent";
      }
      enum "servwait"

      leaf rcv-packets {
        type uint32;
        config false;
        description "Servwait";
      }
    }
    description "Server control connection state"; "Packets received";
      }

  typedef fill-mode

      leaf last-sent-seq {
        type enumeration {
      enum zero { uint32;
        config false;
        description "Zero"; "Last sent sequence number";
      }
      enum random
      leaf last-rcv-seq {
        type uint32;
        config false;
        description "Random"; "Last received sequence number";
      }
      description "TWAMP-Test maintenance statistics";
    }

    /*
     * Configuration data nodes
     */

    container twamp {
      description
          "TWAMP logical entity configuration grouping.";

      container client {
        if-feature control-client;
        presence client;
        description
          "Configuration of the TWAMP Control-Client logical entity.";

        leaf admin-state {
          type boolean;
          mandatory true;
          description
              "Indicates whether the padding added device is allowed to the
    UDP test packets will contain pseudo-random numbers, or
    whether it should consist of all zeroes."; operate
              as a TWAMP Control-Client.";
        }

  typedef units  {
    type enumeration

        list mode-preference-chain {
      enum seconds
          key priority;
          unique mode;
          leaf priority {
            type uint16;
            description "Seconds"; "Priority.";
          }
      enum milliseconds
          leaf mode {
            type twamp-modes;
            description "Milliseconds"; "Supported TWAMP Mode.";

          }
      enum microseconds {
          description "Microseconds";
              "Indicates the preferred order of use for the
              corresponding supported TWAMP Modes";
        }
      enum nanoseconds
        uses key-management;

        list ctrl-connection {
          key name;
          description "Nanoseconds";
      }
    }
              "List of TWAMP Control-Client control connections.
              Each item in the list describes a control connection
              that will be initiated by this Control-Client";

          leaf name {
            type string;
            description "Time units";
              "A unique name used as a key to identify this individual
              TWAMP control connection on the Control-Client device.";
          }
  typedef sender-session-state
          leaf client-ip {
            type enumeration {
      enum setup { inet:ip-address;
            description "Test session is active.";
              "The IP address of the local Control-Client device,
              to be placed in the source IP address field of the
              IP header in TWAMP-Control (TCP) packets belonging
              to this control connection. If not configured, the
              device SHALL choose its own source IP address.";
          }
      enum failure
          leaf server-ip {
            type inet:ip-address;
            mandatory true;
            description "Test session is idle.";
      }
    }
    description "Sender session state.";
              "The IP address belonging to the remote Server device,
              which the TWAMP-Control connection will be
              initiated to.";
          }

  typedef dynamic-port-number

          leaf server-tcp-port {
            type inet:port-number {
    range "49152 .. 65535";
  } inet:port-number;
            default 862;
            description "Dynamic range for
              "This parameter defines the TCP port numbers"; number that is
              to be used by this outgoing TWAMP-Control connection.
              Typically, this is the well-known TWAMP port number (862)
              as per RFC 5357 However, there are known
              realizations of TWAMP in the field that were implemented
              before this well-known port number was allocated. These
              early implementations allowed the port number to be
              configured. This parameter is therefore provided for
              backward compatibility reasons.";
          }

  grouping maintenance-statistics {
    description "Maintenance statistics grouping";
          leaf sent-packets control-packet-dscp {
            type uint32;
      config "false"; inet:dscp;
            default 0;
            description "Packets sent";
              "The DSCP value to be placed in the IP header of
              TWAMP-Control (TCP) packets generated by this
              Control-Client.";
          }

          leaf rcv-packets key-id {
            type uint32;
      config "false"; string {
              length 1..80;
            }
            description "Packets received";
             "The KeyID value that is selected
              for this TWAMP-Control connection.";

          }

          leaf last-sent-seq max-count {
            type uint32;
      config "false"; uint32 {
              range 1024..4294967295;
            }
            default 32768;
            description "Last sent sequence number";
              "This parameter limits the maximum Count value.

              If an attacking system sets the maximum value in
              Count (2**32), then the system under attack would stall
              for a significant period of time while it attempts to
              generate keys.";
          }

          leaf last-rcv-seq client-tcp-port {
            type uint32; inet:port-number;
            config "false";
      description "Last received sequence number";
    }
  }

  container twamp {
    description "Top level container";
    container twamp-client {
      if-feature control-client;
      presence "twamp-client"; false;
            description "Twamp client container";
              "The source TCP port number used in the TWAMP-Control
              packets belonging to this control connection.";
          }

          leaf client-admin-state server-start-time {
            type boolean;
        mandatory "true"; uint64;
            config false;
            description "Indicates whether this device
              "The Start-Time advertized by the Server in the
              Server-Start message (RFC 4656, Section 3.1). This is allowed to run
        TWAMP to initiate control sessions";
              a timestamp representing the time when the current
              instantiation of the Server started operating.";
          }

      list mode-preference-chain {
        key "priority";
        unique "mode";

          leaf priority state {
            type uint16; control-client-connection-state;
            config false;
            description "priority";
              "Indicates the currest state of the TWAMP-Control
              connection state.";
          }

          leaf mode selected-mode {
            type mode;
          description "Authentication mode bit mask";
        } twamp-modes;
            config false;
            description "Authentication mode preference";
              "The TWAMP Mode that the Control-Client has chosen for
              this control connection as set in the Mode field of the
              Set-Up-Response message (RFC 4656, Section 3.1).";
          }

      list key-chain {
        key "key-id";

          leaf key-id token {
              type string binary {
              length "1..80"; 64;
            }
            config false;
            description "Key ID";
              "This parameter holds the 64 octets containing the
              concatenation of a 16-octet Challenge, a 16-octet AES
              Session-key used for encryption, and a 32-octet
              HMAC-SHA1 Session-key used for authentication.

              AES Session-key and HMAC Session-key are generated
              randomly by the Control-Client. AES Session-key and
              HMAC Session-key MUST be generated with sufficient
              entropy not to reduce the security of the underlying
              cipher. The token itself is encrypted
              using the AES (Advanced Encryption Standard) in
              Cipher Block Chaining (CBC). Encryption MUST be
              performed using an Initialization Vector (IV)
              of zero and a key derived from the shared secret
              associated with KeyID. Challenge is the same as
              transmitted by the Server in the clear; see also the
              last paragraph of Section 6 in RFC 4656.";
            reference
              "RFC 4086: Randomness Requirements for Security";
          }

          leaf secret-key client-iv {
            type string;
          description "Secret key"; binary {
              length 16;
            }
            config false;
            description "Key chain";
              "The Control-Client Initialization Vector (Client-IV)
              is generated randomly by the Control-Client.

              Client-IV merely needs to be unique (i.e., it MUST
              never be repeated for different sessions using the
              same secret key; a simple way to achieve that without
              the use of cumbersome state is to generate the
              Client-IV values using a cryptographically secure
              pseudo-random number source.";
          }

          list twamp-client-ctrl-connection test-session-request {
            key "ctrl-connection-name"; name;
            description "Twamp client control connections";
              "Information associated with the Control-Client
              for this test session";

            leaf ctrl-connection-name name {
              type string;
              description
                  "A unique name used as a key to identify be used for identification of
                  this
            individual TWAMP control connection TWAMP-Test session on the
            Control-Client device.";
        }
        leaf client-ip {
          type inet:ip-address;
          description "Client IP address"; Control-Client.";
            }

            leaf server-ip sender-ip {
              type inet:ip-address;
          mandatory "true";
          description "Server IP address";
        }
        leaf server-tcp-port {
          type inet:port-number;
          default "862";
          description "Server tcp port";
        }
        leaf dscp{
          type inet:dscp;
          default "0";
              description
                  "The DSCP value IP address of the Session-Sender device,
                  which is to be placed in the source IP header address
                  field of the TWAMP TCP Control IP header in TWAMP-Test (UDP) packets generated
            by
                  belonging to this test session. This value will be
                  used to populate the Control-Client";
        }
        leaf key-id {
          type string {
            length "1..80";
          }
          description "Key ID";
        }
        leaf max-count {
          type uint32 {
            range 1024..4294967295;
          }
          default 32768;
          description "Max count value.";
        }
        leaf client-tcp-port {
          type inet:port-number;
          config "false";
          description "Client TCP port"; sender address field of the
                  Request-TW-Session message. If not configured,
                  the device SHALL choose its own source IP address.";
            }

            leaf server-start-time sender-udp-port {
              type uint64;
          config "false"; dynamic-port-number;
              description
                  "The Start-Time advertized UDP port number that is to be used by
                  the Server in Session-Sender for this TWAMP-Test session.
                  The number is restricted to the Server-Start message";
        }
        leaf ctrl-connection-state {
          type ctrl-connection-state;
          config "false";
          description "Control connection state";
        }
        leaf selected-mode {
          type mode;
          config "false";
          description "The TWAMP mode dynamic port range.
                  A value of zero indicates that the Control-Client has
          chosen
                  SHALL auto-allocate a UDP port number for this control connection as set
                  TWAMP-Test session. The configured
                  (or auto-allocated) value is advertized in the Mode
                  Sender Port field of the Set-Up-Response message";
        }
        leaf token {
            type binary {
            length "64";
          }
          config "false";
          description "64 octets, containing the concatenation Request-TW-session message
                  (see also Section 3.5 of RFC 5357. Note that in the
                  scenario where a
            16-octet challenge, device auto-allocates a 16-octet AES Session-key used UDP port
                  number for encryption, and a 32-octet HMAC-SHA1 Session-key
            used for authentication";
        }
        leaf client-iv{
          type binary {
            length "16";
          }
          config "false";
          description "16 octets, Client-IV is generated randomly
            by session, and the Control-Client.";
        }

        list twamp-session-request {
          key "test-session-name";
          description "Twamp session requests";
          leaf test-session-name {
            type string;
            description "A unique name repeat parameter
                  for this test that session to indicates that it should be
            used as a key for this test session on
                  repeated, the
            Control-Client.";
          }
          leaf sender-ip {
            type inet:ip-address;
            description "Sender IP address";
          }
          leaf sender-udp-port {
            type dynamic-port-number;
            description "Sender device is free to auto-allocate a
                  different UDP port"; port number when it negotiates the
                  next (repeated) iteration of this session.";
            }

            leaf reflector-ip {
              type inet:ip-address;
              mandatory "true"; true;
              description "Reflector
                  "The IP address."; address belonging to the remote
                  Session-Reflector device to which the TWAMP-Test
                  session will be initiated. This value will be
                  used to populate the receiver address field of
                  the Request-TW-Session message.";
            }

            leaf reflector-udp-port {
              type dynamic-port-number;
              description "Reflector
                  "This parameter defines the UDP port. port number that
                  will be used by the Session-Reflector for
                  this TWAMP-Test session. The number is restricted
                  to the dynamic port range and is to be placed in
                  the Receiver Port field of the Request-TW-Session
                  message. If this value is not set, the device shall SHALL
                  use the same port number as defined in the server-tcp-port parameter
                  server-tcp-port parameter of this
                  test-session-request's parent
                  twamp/client/ctrl-connection.";
            }

            leaf timeout {
              type uint64;
              default 2;
              description
                  "The length of time (in seconds) that the
                  Session-Reflector should continue to respond to
                  packets belonging to this TWAMP-Test session after
                  a Stop-Sessions TWAMP-Control message has been
                  received (RFC 5357, Section 3.8).

                  This value will be placed in the Timeout field of this
            twamp-session-request's
            parent client-control-connection.";
          }
          leaf timeout {
            type uint64;
            default "2";
            description "The time (in seconds)Session-Reflector MUST
            wait after receiving a Stop-Session
                  the Request-TW-Session message.";
            }

            leaf padding-length {
              type uint32{ uint32 {
                range "64..4096"; 64..4096;
              }
              description
                  "The number of bytes of padding that should bytes to be added to the UDP test
                  TWAMP-Test (UDP) packets generated by the
                sender. Jumbo sized packets supported.";
                  Session-Sender.

                  This value will be placed in the Padding Length
                  field of the Request-TW-Session message
                  (RFC 4656, Section 3.5).";
            }

            leaf dscp test-packet-dscp {
              type inet:dscp;
              description
                  "The DSCP value to be placed in the UDP IP header
                  of TWAMP-Test packets generated by the
                  Session-Sender, and in the UDP header of the
                  TWAMP-Test response packets generated by the
                  Session-Reflector for this test session."; session.

                  This value will be placed in the Type-P Descriptor
                  field of the Request-TW-Session message (RFC 5357).";
            }

            leaf start-time {
              type uint64;
              default "0"; 0;
              description
                  "Time when the session is to be started
                  (but not before the TWAMP Start-Sessions command
                  is issued).
            This issued; see RFC 5357, Section 3.4).

                  The start-time value is placed in the Start Time
                  field of the Request-TW-Session message.

                  The default value of 0 indicates that the session
                  will be started as soon as the Start-Sessions message
                  is received.";
            }

            leaf repeat {
              type uint32;
              default "0"; 0;
              description "Determines
                  "This value determines if the TWAMP-Test session must
                  be repeated. When a test session has completed, the
                  repeat parameter is to be
            run repeatedly. checked.

                  The default value of repeat is 0,
            indicating 0 indicates that once the session has completed, it
            will not MUST NOT be renegotiated and restarted.
                  repeated.

                  If the value is 1 thru through 4,294,967,294
            indicate then the number of repetitions, test
                  session SHALL be repeated using the information in
                  repeat-interval parameter, and the max parent
                  TWAMP-Control connection for this test session is
                  restarted to negotiate a new instance of this
                  TWAMP-Test session. The implementation MUST decrement
                  the value of repeat after determining a repeated
                  session is expected.

                  The value of 4,294,967,295 indicates repeat forever."; that the test
                  session SHALL be repeated *forever* using the
                  information in repeat-interval parameter, and
                  SHALL NOT decrement the value.";
            }

            leaf repeat-interval  {
              when "../repeat!='0'" {
                description "When
                  "This parameter determines the timing of repeated
                  test sessions when repeat is not more than 0.

                  When the value of repeat-interval is 0, the
                  negotiation of a new test is to be
              repeated"; session SHALL begin
                  immediately after the previous test session
                  completes. Otherwise, the Control-Client will
                  wait for the number of minutes specified in the
                  repeat-interval parameter before negotiating the
                  new instance of this TWAMP-Test session.";
              }
              type uint32;
              default 0;
              description "Repeat interval (in minutes)";
            }

            list pm-reg-list {
              key "pm-index"; pm-index;
              leaf pm-index {
                type uint16;
                description "One or more Numerical
                  "Numerical index values value of a Registered Metric
                  in the Performance Metric Registry"; Registry
                  (see ietf-ippm-metric-registry). Output statistics
                  are specified in the corresponding Registry entry.";
              }
              description
                  "A list of one or more pm-index Performance Metric Registry
                  Index values, which communicate packet stream
                  characteristics and along with one or more metrics
                  to be measured."; measured.

                  All members of the pm-reg-list MUST have the same
                  stream characteristics, such that they combine
                  to specify all metrics that shall be measured on
                  a single stream.";
              reference
              "ietf-ippm-metric-registry:
                  Registry for Performance Metrics";
            }
            leaf test-session-state state {
              type test-session-state;
              config "false"; false;
              description "Test
                  "Indicates the TWAMP-Test session state"; state (accepted or
                  indication of an error); see Section 3.5 of
                  RFC 5357.";
            }
            leaf sid{ sid {
              type string;
              config "false"; false;
              description
                  "The SID allocated by the Server for this test session"; TWAMP-Test
                  session, and communicated back to the Control-Client
                  in the SID field of the Accept-Session message;
                  see Section 4.3 of RFC 6038.";
            }
          }
        }
      }

      container twamp-server{ server {
        if-feature server;
        presence "twamp-server"; server;
        description "Twamp sever container";
          "Configuration of the TWAMP Server logical entity.";

        leaf server-admin-state{ admin-state {
          type boolean;
          mandatory "true"; true;
          description
              "Indicates whether this the device is allowed to run operate
              as a TWAMP to respond to control sessions"; Server.";
        }

        leaf server-tcp-port {
          type inet:port-number;
          default "862"; 862;
          description
              "This parameter defines the well known TCP port number
              that is used by TWAMP."; TWAMP-Control. The Server will listen
              on this port number for incoming TWAMP-Control
              connections. Although this is defined as a fixed value
              (862) in RFC 5357, there are several realizations of
              TWAMP in the field that were implemented before this
              well-known port number was allocated. These early
              implementations allowed the port number to be
              configured. This parameter is therefore provided for
              backward compatibility reasons.";
        }

        leaf servwait {
          type uint32 {
            range 1..604800;
          }
          default 900;
          description "SERVWAIT (TWAMP Control
              "TWAMP-Control (TCP) session timeout), timeout, in seconds
              (RFC 5357, Section 3.1)).";
        }

        leaf control-packet-dscp {
          type inet:dscp;
          description
              "The DSCP value to be placed in the IP header of
              TWAMP-Control (TCP) packets generated by the Server.

              Section 3.1 of  RFC 5357 specifies that the server
              SHOULD use the DSCP value from the Control-Client's
              TCP SYN. However, for practical purposes TWAMP will
              typically be implemented using a general purpose TCP
              stack provided by the underlying operating system,
              and such a stack may not provide this information to the
              user. Consequently, it is not always possible to
              implement the behavior described in RFC 5357 in an
              OS-portable version of TWAMP. The default value behavior if
              this item is 900";
      }
      leaf dscp {
        type inet:dscp;
        description "The not set is to use the DSCP value to be placed in from
              the IP header of Control-Client's TCP TWAMP-Control packets generated by the Server"; SYN, as per Section 3.1
              of RFC 5357.";
        }

        leaf count {
          type uint32 {
            range 1024..4294967295;
          }
          description
              "Parameter used in deriving a key from a shared
              secret "; as described in Section 3.1 of  RFC 4656,
              and are communicated to the Control-Client as part
              of the Server Greeting message.

              count MUST be a power of 2.

              count MUST be at least 1024.

              count SHOULD be increased as more computing power
              becomes common.";
        }
        leaf max-count {
          type uint32 {
            range 1024..4294967295;
          }
          default 32768;
          description "Max
              "This parameter limits the maximum Count value.

              If an attacking system sets the maximum value in
              Count (2**32), then the system under attack would stall
              for a significant period of time while it attempts to
              generate keys.

              TWAMP-compliant systems SHOULD have a configuration
              control to limit the maximum count value."; value. The
              default max-count value SHOULD be 32768.";
        }

        leaf modes {
          type mode; twamp-modes;
          description
              "The bit mask of TWAMP Modes this Server instance
              is willing to support.";
      }

      list key-chain {
        key "key-id";
        leaf key-id {
          type string {
            length "1..80";
          }
          description "Key IDs.";
        }
        leaf secret-key {
          type string;
          description "Secret keys.";
        }
        description "KeyIDs with the respective secret keys."; support; see IANA TWAMP Modes Registry.";
        }

        uses key-management;
        list twamp-server-ctrl-connection ctrl-connection {
          key
              "client-ip client-tcp-port server-ip server-tcp-port";
          config "false"; false;
          description "Twamp server control
              "List of all incoming TWAMP-Control (TCP) connections";

          leaf client-ip {
            type inet:ip-address;
            description "Client
              "The IP address on the remote Control-Client device,
              which is the source IP address"; address used in the
              TWAMP-Control (TCP) packets belonging to this control
              connection.";
          }

          leaf client-tcp-port {
            type inet:port-number;
            description "Client
              "The source TCP port"; port number used in the TWAMP-Control
              (TCP) packets belonging to this control connection.";
          }

          leaf server-ip {
            type inet:ip-address;
            description "Server
              "The IP address of the local Server device, which is
              the destination IP address"; address used in the
              TWAMP-Control (TCP) packets belonging to this control
              connection.";
          }

          leaf server-tcp-port {
            type inet:port-number;
            description "Server
              "The destination TCP port"; port number used in the
              TWAMP-Control (TCP) packets belonging to this
              control connection. This will usually be the
              same value as the server-tcp-port configured
              under twamp/server. However, in the event that
              the user re-configured server/server-tcp-port
              after this control connection was initiated, this
              value will indicate the server-tcp-port that is
              actually in use for this control connection.";
          }

          leaf server-ctrl-connection-state state {
            type server-ctrl-connection-state;
            description "Server control
              "Indicates the Server TWAMP-Control connection state"; state.";
          }

          leaf dscp control-packet-dscp {
            type inet:dscp;
            description
              "The DSCP value used in the IP header of the
          TCP control
              TWAMP-Control (TCP) packets sent by the Server
              for this control connection. This will usually
              be the same value as is configured for twamp-server:dscp in the
              control-packet-dscp parameter under the twamp-server. twamp/server
              container.  However, in the event that the user
              re-configures
          twamp-server:dscp server/dscp after this control
              connection is already in progress, this read-only
              value will show the actual dscp value in use by this control
              TWAMP-Control connection.";
          }

          leaf selected-mode {
            type mode; twamp-modes;
            description
              "The mode Mode that was chosen for this control TWAMP-Control
              connection as set in the Mode field of the
              Set-Up-Response message.";
          }

          leaf key-id {
            type string {
              length "1..80"; 1..80;
            }
            description
              "The key-id KeyID value that is in use by this
                  control connection."; TWAMP-Control
              connection as selected by Control-Client.";
          }

          leaf count {
            type uint32 {
              range 1024..4294967295;
            }
            description
              "The count value that is in use by this control TWAMP-Control
              connection. This will usually be the same value
              as is configured under twamp-server. twamp/server. However, in the
              event that the user re-configured twamp-server:count server/count
              after this control connection is already in progress,
              this read-only value will show the different actual count that
              is in use for this control TWAMP-Control connection.";

          }

          leaf max-count {
            type uint32 {
              range 1024..4294967295;
            }
            description
              "The max-count value that is in use by this
          control
              TWAMP-Control connection. This will usually be the
              same value as is configured under twamp-server. twamp/server. However,
              in the event that the user re-configured twamp-server:max-count
              server/max-count after this control connection is
              already in progress, this read-only value will show the different
              actual max-count that is in use for this
              control connection.";
          }

          leaf salt{ salt {
            type binary {
              length "16"; 16;
            }
            description "Salt
              "A parameter used in deriving a key from a
              shared secret as described in Section 3.1 of RFC 4656.
              Salt MUST be generated pseudo-randomly"; pseudo-randomly (independently
              of anything else in the RFC) and is communicated to
              the Control-Client as part of the Server Greeting
              message.";
          }

          leaf server-iv {
            type binary {
              length "16"; 16;
            }
            description "16 octets, Server-IV
              "The Server Initialization Vector
              (IV) is generated randomly by the Control-Client."; Server.";
          }

          leaf challenge {
            type binary {
              length "16"; 16;
            }
            description "Challenge is a
              "A random sequence of octets generated by the Server"; Server.
              As described in client/token, Challenge is used
              by the Control-Client to prove possession of a
              shared secret.";

          }
        }
      }

      container twamp-session-sender{ session-sender {
        if-feature session-sender;
        presence "twamp-session-sender"; session-sender;
        description "Twamp session sender container";
          "Configuration of the TWAMP Session-Sender
          logical entity";
        leaf session-sender-admin-state admin-state {
          type boolean;
          mandatory "true"; true;
          description
              "Indicates whether this the device is allowed to run operate
              as a TWAMP to initiate test sessions"; Session-Sender.";
        }

        list twamp-sender-test-session{ test-session{
          key "test-session-name"; name;
          description "Twamp sender
              "TWAMP Session-Sender test sessions"; sessions.";

          leaf test-session-name name {
            type string;
            description
              "A unique name for this test TWAMP-Test session to be used as a key
              for identifying this test session by the Session-Sender
              logical entity.";
          }

          leaf ctrl-connection-name {
            type string;
            config "false"; false;
            description
              "The name of the parent control TWAMP-Control connection that
              is responsible for negotiating this test TWAMP-Test session.";
          }

          leaf fill-mode {
            type fill-mode; padding-fill-mode;
            default zero;
            description
              "Indicates whether the padding added to the
          UDP test
              TWAMP-Test (UDP) packets will contain pseudo-random
              numbers, or whether it should consist of all zeroes."; zeroes,
              as per Section 4.2.1 of RFC 5357.";
          }
          leaf number-of-packets {
            type uint32;
            description
              "The overall number of UDP test TWAMP-Test (UDP) packets to
              be transmitted by the sender Session-Sender
              for this test session.";
          }

          choice packet-distribution {
            description "Packet distributions, poisson or periodic";
              "Indicates the distribution to be used for transmitting
              the TWAMP-Test (UDP) packets.";
            case periodic {
              leaf periodic-interval {
                type uint32;
                description "Periodic interval";
                  "Indicates the period to wait between the first bits
                  of TWAMP-Test (UDP) packet transmissions for
                  this test session";
              }
              leaf periodic-interval-units  {
                type units; time-units;
                description "Periodic interval units"; time unit.";
                reference
                "RFC 3432: Network performance measurement
                           with periodic streams";
              }
            }
            case poisson {
              leaf lambda{ lambda {
                type uint32;
                description "The
                  "Indicates the average rate of packet transmission."; transmission rate.";
              }
              leaf lambda-units{ lambda-units {
                type uint32;
                description "Lambda units.";
                  "Indicates the units of lambda in
                  reciprocal seconds.";
               reference
                "RFC 3432: Network performance measurement
                           with periodic streams";
              }
              leaf max-interval{ max-interval {
                type uint32;
                description "maximum
                  "Indicates the maximum time between packet
                  transmissions.";

              }
              leaf truncation-point-units{ truncation-point-units {
                type units; time-units;
                description "Truncation point units"; "Time units to truncate.";
              }
            }
          }

          leaf sender-session-state state {
            type sender-session-state;
            config "false"; false;
            description "Sender
              "Indicates the Session-Sender test session state.";
          }

          uses maintenance-statistics;
        }
      }

      container twamp-session-reflector session-reflector {
        if-feature session-reflector;
        presence "twamp-session-reflector"; session-reflector;
        description "Twamp session reflector container";
          "Configuration of the TWAMP Session-Reflector
          logical entity";

        leaf session-reflector-admin-state admin-state {
          type boolean;
          mandatory "true"; true;
          description
              "Indicates whether this the device is allowed to run operate
              as a TWAMP to respond to test sessions"; Session-Reflector.";
        }

        leaf refwait {
          type uint32 {
            range 1..604800;
          }
          default 900;
          description "REFWAIT (TWAMP test
              "The Session-Reflector MAY discontinue any session timeout),
          the
              that has been started when no packet associated with
              that session has been received for REFWAIT seconds.

              The default value is 900"; of REFWAIT SHALL be 900 seconds, and
              this waiting time MAY be configurable. This timeout
              allows a Session-Reflector to free up resources in
              case of failure.";

        }

        list twamp-reflector-test-session test-session {
          key
              "sender-ip sender-udp-port
              reflector-ip reflector-udp-port";
          config "false"; false;
          description "Twamp reflector test sessions";
              "TWAMP Session-Reflectortest sessions.";

          leaf sid{ sid {
            type string;
            description
              "An auto-allocated identifier for this test TWAMP-Test
              session, that is unique within the context of this
              Server/Session-Reflector device only. "; This value
              will be communicated to the Control-Client that
              requested the test session in the SID field of the
              Accept-Session message.";
          }

          leaf sender-ip {
            type inet:ip-address;
            description "Sender
              "The IP address."; address on the remote device, which is the
              source IP address used in the TWAMP-Test
              (UDP) packets belonging to this test session.";
          }

          leaf sender-udp-port {
            type dynamic-port-number;
            description "Sender
              "The source UDP port."; port used in the TWAMP-Test packets
              belonging to this test session.";
          }

          leaf reflector-ip {
            type inet:ip-address;
            description "Reflector
              "The IP address."; address of the local Session-Reflector
              device, which is the destination IP address used
              in the TWAMP-Test (UDP) packets belonging to this test
              session.";
          }

          leaf reflector-udp-port {
            type dynamic-port-number;
            description "Reflector
              "The destination UDP port."; port number used in the
              TWAMP-Test (UDP) test packets belonging to this
              test session.";
          }

          leaf parent-connection-client-ip {
            type inet:ip-address;
            description "Parent connction client
              "The IP address."; address on the Control-Client device, which
              is the source IP address used in the TWAMP-Control
              (TCP) packets belonging to the parent control
              connection that negotiated this test session.";
          }

          leaf parent-connection-client-tcp-port {
            type inet:port-number;
            description "Parent connection client
              "The source TCP port."; port number used in the TWAMP-Control
              (TCP) packets belonging to the parent control connection
              that negotiated this test session.";
          }

          leaf parent-connection-server-ip {
            type inet:ip-address;
            description "Parent connection server
              "The IP address."; address of the Server device, which is the
              destination IP address used in the TWAMP-Control
              (TCP) packets belonging to the parent control
              connection that negotiated this test session.";
          }

          leaf parent-connection-server-tcp-port {
            type inet:port-number;
            description "Parent connection server
              "The destination TCP port"; port number used in the TWAMP-Control
              (TCP) packets belonging to the parent control connection
              that negotiated this test session.";
          }

          leaf dscp test-packet-dscp {
            type inet:dscp;
            description
              "The DSCP value present in the IP header of
          TWAMP UDP test
              TWAMP-Test (UDP) packets belonging to this test
              session.";
          }

          uses maintenance-statistics;

        }
      }
    }
  }

  <CODE ENDS>

6.  Data Model Examples

   This section presents a simple but complete example of configuring
   all four entities in Figure 1, based on the YANG module specified in
   Section 5.  The example is illustrative in nature, but aims to be
   self-contained, i.e. were it to be executed in a real TWAMP
   implementation it would lead to a correctly configured test session.
   For completeness, examples are provided for both IPv4 and IPv6.

   A more elaborated example, which also includes authentication
   parameters, is provided in Appendix A.

6.1.  Control-Client

   The following configuration example shows a Control-Client with
   client-admin-state
   client/admin-state enabled.  In a real implementation following
   Figure 2 this would permit the initiation of TWAMP-Control
   connections and TWAMP-Test sessions.

   <?xml version="1.0" encoding="utf-8"?>
   <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-client>
            <client-admin-state>true</client-admin-state>
         </twamp-client>
         <client>
            <admin-state>true</admin-state>
         </client>
      </twamp>
   </config>

   The following configuration example shows a Control-Client with two
   instances of twamp-client-ctrl-connection, client/ctrl-connection, one called "RouterA" and another
   called "RouterB".

   Each TWAMP-Control connection is to a different Server.  The control
   connection named "RouterA" has two test session requests.  The TWAMP-Control TWAMP-
   Control connection named "RouterB" has no TWAMP-Test session
   requests.

   <?xml version="1.0" encoding="utf-8"?>
   <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-client>
            <client-admin-state>true</client-admin-state>
            <twamp-client-ctrl-connection>
               <ctrl-connection-name>RouterA</ctrl-connection-name>
         <client>
            <admin-state>true</admin-state>
            <ctrl-connection>
               <name>RouterA</name>
               <client-ip>203.0.113.1</client-ip>
               <server-ip>203.0.113.2</server-ip>
               <twamp-session-request>
                  <test-session-name>Test1</test-session-name>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>10.1.1.1</sender-ip>
                  <sender-udp-port>50000</sender-udp-port>
                  <reflector-ip>10.1.1.2</reflector-ip>
                  <reflector-udp-port>500001</reflector-udp-port>
                  <start-time>0</start-time>
               </twamp-session-request>
               <twamp-session-request>
                  <test-session-name>Test2</test-session-name>
               </test-session-request>
               <test-session-request>
                  <name>Test2</name>
                  <sender-ip>203.0.113.1</sender-ip>
                  <sender-udp-port>4001</sender-udp-port>
                  <reflector-ip>203.0.113.2</reflector-ip>
                  <reflector-udp-port>50001</reflector-udp-port>
                  <start-time>0</start-time>
               </twamp-session-request>
            </twamp-client-ctrl-connection>
            <twamp-client-ctrl-connection>
               <ctrl-connection-name>RouterB</ctrl-connection-name>
               </test-session-request>
            </ctrl-connection>
            <ctrl-connection>
               <name>RouterB</name>
               <client-ip>203.0.113.1</client-ip>
               <server-ip>203.0.113.3</server-ip>
            </twamp-client-ctrl-connection>
         </twamp-client>
            </ctrl-connection>
         </client>
      </twamp>
   </config>

   <?xml version="1.0" encoding="utf-8"?>
   <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <client>
            <admin-state>true</admin-state>
            <ctrl-connection>
               <name>RouterA</name>
               <client-ip>2001:DB8:203:0:113::1</client-ip>
               <server-ip>2001:DB8:203:0:113::2</server-ip>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>2001:DB8:10:1:1::1</sender-ip>
                  <sender-udp-port>4000</sender-udp-port>
                  <reflector-ip>2001:DB8:10:1:1::2</reflector-ip>
                  <reflector-udp-port>5000</reflector-udp-port>
                  <start-time>0</start-time>

               </test-session-request>
               <test-session-request>
                  <name>Test2</name>
                  <sender-ip>2001:DB8:203:0:113::1</sender-ip>
                  <sender-udp-port>4001</sender-udp-port>
                  <reflector-ip>2001:DB8:203:0:113::2</reflector-ip>
                  <reflector-udp-port>5001</reflector-udp-port>
                  <start-time>0</start-time>
               </test-session-request>
            </ctrl-connection>
            <ctrl-connection>
               <name>RouterB</name>
               <client-ip>2001:DB8:203:0:113::1</client-ip>
               <server-ip>2001:DB8:203:0:113::3</server-ip>
            </ctrl-connection>
         </client>
      </twamp>
   </config>

6.2.  Server

   This configuration example shows a Server with server-admin-state server/admin-state
   enabled, which permits a device following Figure 2 to respond to
   TWAMP-Control connections and TWAMP-Test sessions.

   <?xml version="1.0" encoding="utf-8"?>
   <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-server>
            <server-admin-state>true</server-admin-state>
         </twamp-server>
         <server>
            <admin-state>true</admin-state>
         </server>
      </twamp>
   </config>

   The following example presents a Server with the TWAMP-Control
   connection corresponding to the control connection name (ctrl-
   connection-name) (client/ctrl-
   connection/name) "RouterA" presented in Section 6.1.

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-server>
            <server-admin-state>true</server-admin-state>
            <twamp-server-ctrl-connection>
         <server>
            <admin-state>true</admin-state>
            <ctrl-connection>
               <client-ip>203.0.113.1</client-ip>
               <client-tcp-port>16341</client-tcp-port>
               <server-ip>203.0.113.2</server-ip>
               <server-tcp-port>862</server-tcp-port>
               <server-ctrl-connection-state>
               <state>
                  active
               </state>
            </ctrl-connection>
         </server>
      </twamp>
   </data>

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <server>
            <admin-state>true</admin-state>
            <ctrl-connection>
               <client-ip>2001:DB8:203:0:113::1</client-ip>
               <client-tcp-port>16341</client-tcp-port>
               <server-ip>2001:DB8:203:0:113::2</server-ip>
               <server-tcp-port>862</server-tcp-port>
               <state>
                  active
               </server-ctrl-connection-state>
            </twamp-server-ctrl-connection>
         </twamp-server>
               </state>
            </ctrl-connection>
         </server>
      </twamp>
   </data>

6.3.  Session-Sender

   The following configuration example shows a Session-Sender with the
   two TWAMP-Test sessions presented in Section 6.1.

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
        <twamp-session-sender>
           <session-sender-admin-state>true</session-sender-admin-state>
           <twamp-sender-test-session>
              <test-session-name>Test1</test-session-name>
        <session-sender>
           <admin-state>true</admin-state>
           <test-session>
              <name>Test1</name>
              <ctrl-connection-name>RouterA</ctrl-connection-name>
              <number-of-packets>900</number-of-packets>
              <periodic-interval>1</periodic-interval>
              <periodic-interval-units>seconds</periodic-interval-units>
              <sender-session-state>setup</sender-session-state>
           </twamp-sender-test-session>
           <twamp-sender-test-session>
              <test-session-name>Test2</test-session-name>
              <state>setup</state>
           </test-session>
           <test-session>
              <name>Test2</name>
              <ctrl-connection-name>
                RouterA
              </ctrl-connection-name>
              <number-of-packets>900</number-of-packets>
              <lambda>1</lambda>
              <lambda-units>1</lambda-units>
              <max-interval>2</max-interval>
              <truncation-point-units>seconds</truncation-point-units>
              <sender-session-state>setup</sender-session-state>
           </twamp-sender-test-session>
        </twamp-session-sender>
              <state>setup</state>
           </test-session>
        </session-sender>
     </twamp>
   </data>

6.4.  Session-Reflector

   The following example shows the two Session-Reflector TWAMP-Test
   sessions corresponding to the test sessions presented in Section 6.3.

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-session-reflector>
             <session-reflector-admin-state>
         <session-reflector>
             <admin-state>
                true
             </session-reflector-admin-state>
             <twamp-reflector-test-session>
             </admin-state>
             <test-session>
               <sender-ip>10.1.1.1</sender-ip>
               <sender-udp-port>4000</sender-udp-port>
               <reflector-ip>10.1.1.2</reflector-ip>
               <reflector-udp-port>50001</reflector-udp-port>
               <sid>1232</sid>
               <parent-connection-client-ip>
                  203.0.113.1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
               </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                  203.0.113.2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                  862
                </parent-connection-server-tcp-port>
               <sent-packets>2</sent-packets>
               <rcv-packets>2</rcv-packets>
               <last-sent-seq>1</last-sent-seq>
               <last-rcv-seq>1</last-rcv-seq>
            </twamp-reflector-test-session>
            <twamp-reflector-test-session>
            </test-session>
            <test-session>
               <sender-ip>203.0.113.1</sender-ip>
               <sender-udp-port>50000</sender-udp-port>
               <reflector-ip>192.68.0.2</reflector-ip>
               <reflector-udp-port>50001</reflector-udp-port>
               <sid>178943</sid>
               <parent-connection-client-ip>
                  203.0.113.1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
                </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                  203.0.113.2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                 862
               </parent-connection-server-tcp-port>
               <sent-packets>21</sent-packets>
               <rcv-packets>21</rcv-packets>
               <last-sent-seq>20</last-sent-seq>
               <last-rcv-seq>20</last-rcv-seq>
            </twamp-reflector-test-session>
         </twamp-session-reflector>
            </test-session>
         </session-reflector>
      </twamp>
   </data>

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <session-reflector>
             <admin-state>true</admin-state>
             <test-session>
               <sender-ip>10.1.1.1</sender-ip>
               <sender-udp-port>4000</sender-udp-port>
               <reflector-ip>10.1.1.2</reflector-ip>
               <reflector-udp-port>5000</reflector-udp-port>
               <sid>1232</sid>
               <parent-connection-client-ip>
                   203.0.113.1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
               </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                   203.0.113.2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                  862
                </parent-connection-server-tcp-port>
               <sent-packets>2</sent-packets>
               <rcv-packets>2</rcv-packets>
               <last-sent-seq>1</last-sent-seq>
               <last-rcv-seq>1</last-rcv-seq>
            </test-session>
            <test-session>
               <sender-ip>203.0.113.1</sender-ip>
               <sender-udp-port>4001</sender-udp-port>
               <reflector-ip>192.68.0.2</reflector-ip>
               <reflector-udp-port>5001</reflector-udp-port>
               <sid>178943</sid>
               <parent-connection-client-ip>
                   203.0.113.1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
                </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                   203.0.113.2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                 862
               </parent-connection-server-tcp-port>
               <sent-packets>21</sent-packets>
               <rcv-packets>21</rcv-packets>
               <last-sent-seq>20</last-sent-seq>
               <last-rcv-seq>20</last-rcv-seq>
            </test-session>
         </session-reflector>
      </twamp>

   </data>

7.  Security Considerations

   TBD

   The YANG module defined in Section 5 is designed to be accessed,
   among other protocols, via NETCONF [RFC6241].  Protocols like NETCONF
   use a secure transport layer like SSH that is mandatory to implement.
   The NETCONF Access Control Module (NACM) [RFC6536] provides the means
   to restrict access for particular users to a pre-configured set of
   NETCONF protocol operations and attributes.

   There are a number of nodes defined in this YANG module which are
   writeable.  These data nodes may be considered sensitive and
   vulnerable to attacks in some network environments.  Ability to write
   into these nodes without proper protection can have a negative effect
   on the devices that support this feature.

   Examples of nodes that are particularly vulnerable include several
   timeout values put in the protocol to protect against sessions that
   are not active but are consuming resources.

8.  IANA Considerations

   This document registers a URI in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registration is
   requested to be made.

   URI: urn:ietf:params:xml:ns:yang:ietf-twamp

   Registrant Contact: The IPPM WG of the IETF.

   XML: N/A, the requested URI is an XML namespace.

   This document registers a YANG module in the YANG Module Names
   registry [RFC6020].

   name: ietf-twamp

   namespace: urn:ietf:params:xml:ns:yang:ietf-twamp

   prefix: twamp

   reference: RFC XXXX

9.  Acknowledgements

   We thank Gregory Mirsky, Fred Baker, Kevin D'Souza, Gregory Mirsky, Brian Trammell
   and Robert Sherman for their thorough and constructive reviews,
   comments and text suggestions.

   Haoxing Shen contributed to the definition of the YANG module in
   Section 5.

   Jan Lindblad and Ladislav Lhokta did thorough review reviews of the YANG
   module and the
   examples. examples in Appendix A.

   Kostas Pentikousis is partially supported by FP7 UNIFY
   (http://fp7-unify.eu), a research project partially funded by the
   European Community under the Seventh Framework Program (grant
   agreement no. 619609).  The views expressed here are those of the
   authors only.  The European Commission is not liable for any use that
   may be made of the information in 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,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3432]  Raisanen, V., Grotefeld, G., and A. Morton, "Network
              performance measurement with periodic streams", RFC 3432,
              DOI 10.17487/RFC3432, November 2002,
              <http://www.rfc-editor.org/info/rfc3432>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
              <http://www.rfc-editor.org/info/rfc4656>.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, DOI 10.17487/RFC5357, October 2008,
              <http://www.rfc-editor.org/info/rfc5357>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <http://www.rfc-editor.org/info/rfc6020>.

   [RFC6038]  Morton, A. and L. Ciavattone, "Two-Way Active Measurement
              Protocol (TWAMP) Reflect Octets and Symmetrical Size
              Features", RFC 6038, DOI 10.17487/RFC6038, October 2010,
              <http://www.rfc-editor.org/info/rfc6038>.

   [RFC7717]  Pentikousis, K., Ed., Zhang, E., and Y. Cui,
              "IKEv2-Derived Shared Secret Key for the One-Way Active
              Measurement Protocol (OWAMP) and Two-Way Active
              Measurement Protocol (TWAMP)", RFC 7717,
              DOI 10.17487/RFC7717, December 2015,
              <http://www.rfc-editor.org/info/rfc7717>.

10.2.  Informative References

   [I-D.ietf-ippm-metric-registry]
              Bagnulo, M., Claise, B., Eardley, P., Morton, A., and A.
              Akhter, "Registry for Performance Metrics", draft-ietf-
              ippm-metric-registry-06 (work in progress), March 2016.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-10 draft-ietf-netconf-restconf-15 (work in
              progress), March July 2016.

   [I-D.unify-nfvrg-challenges]
              Szabo, R., Csaszar, A., Pentikousis, K., Kind, M., Daino,
              D., Qiang, Z., and H. Woesner, "Unifying Carrier and Cloud
              Networks: Problem Statement and Challenges", draft-unify-
              nfvrg-challenges-03 (work in progress), January 2016.

   [I-D.unify-nfvrg-devops]
              Meirosu, C., Manzalini, A., Steinert, R., Marchetto, G.,
              Papafili, I., Pentikousis, K., and S. Wright, "DevOps for
              Software-Defined Telecom Infrastructures", draft-unify-
              nfvrg-devops-04 (work in progress), March 2016.

   [NSC]      John, W., Pentikousis, K., et al., "Research directions in
              network service chaining", Proc. SDN for Future Networks
              and Services (SDN4FNS), Trento, Italy IEEE, November 2013.

   [RFC2898]  Kaliski, B., "PKCS #5: Password-Based Cryptography
              Specification Version 2.0", RFC 2898,
              DOI 10.17487/RFC2898, September 2000,
              <http://www.rfc-editor.org/info/rfc2898>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <http://www.rfc-editor.org/info/rfc4086>.

   [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
              Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
              DOI 10.17487/RFC5618, August 2009,
              <http://www.rfc-editor.org/info/rfc5618>.

   [RFC5938]  Morton, A. and M. Chiba, "Individual Session Control
              Feature for the Two-Way Active Measurement Protocol
              (TWAMP)", RFC 5938, DOI 10.17487/RFC5938, August 2010,
              <http://www.rfc-editor.org/info/rfc5938>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <http://www.rfc-editor.org/info/rfc6536>.

   [RFC7426]  Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
              Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
              Defined Networking (SDN): Layers and Architecture
              Terminology", RFC 7426, DOI 10.17487/RFC7426, January
              2015, <http://www.rfc-editor.org/info/rfc7426>.

Appendix A.  Detailed Data Model Examples

   This appendix extends the example presented in Section 6 by
   configuring more fields such as authentication parameters, dscp DSCP
   values and so on.

A.1.  Control-Client

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-client>
            <client-admin-state>true</client-admin-state>
         <client>
            <admin-state>true</admin-state>
            <mode-preference-chain>
               <priority>0</priority>
               <mode>authenticated</mode>
            </mode-preference-chain>
            <mode-preference-chain>
               <priority>1</priority>
               <mode>unauthenticated</mode>
            </mode-preference-chain>
            <key-chain>
               <key-id>KeyClient1ToRouterA</key-id>
               <secret-key>secret1</secret-key>
            </key-chain>
            <key-chain>
               <key-id>KeyForRouterB</key-id>
               <secret-key>secret2</secret-key>
            </key-chain>
            <twamp-client-ctrl-connection>
               <ctrl-connection-name>RouterA</ctrl-connection-name>
            <ctrl-connection>
               <name>RouterA</name>
               <client-ip>203.0.113.1</client-ip>
               <server-ip>203.0.113.2</server-ip>
               <dscp>32</dscp>
               <key-id>KeyClient1ToRouterA</key-id>
               <twamp-session-request>
                  <test-session-name>Test1</test-session-name>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>10.1.1.1</sender-ip>
                  <sender-udp-port>4000</sender-udp-port>
                  <reflector-ip>10.1.1.2</reflector-ip>
                  <reflector-udp-port>5000</reflector-udp-port>
                  <padding-length>64</padding-length>
                  <start-time>0</start-time>
                  <test-session-state>ok</test-session-state>
                  <state>ok</state>
                  <sid>1232</sid>
               </twamp-session-request>
               <twamp-session-request>
                  <test-session-name>Test2</test-session-name>
               </test-session-request>
               <test-session-request>
                  <name>Test2</name>
                  <sender-ip>203.0.113.1</sender-ip>
                  <sender-udp-port>4001</sender-udp-port>
                  <reflector-ip>203.0.113.2</reflector-ip>
                  <reflector-udp-port>5001</reflector-udp-port>
                  <padding-length>128</padding-length>
                  <start-time>0</start-time>
                  <test-session-state>ok</test-session-state>
                  <state>ok</state>
                  <sid>178943</sid>
               </test-session-request>
            </ctrl-connection>
         </client>
      </twamp>

   </data>

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <client>
            <admin-state>true</admin-state>
            <mode-preference-chain>
               <priority>0</priority>
               <mode>authenticated</mode>
            </mode-preference-chain>
            <mode-preference-chain>
               <priority>1</priority>
               <mode>unauthenticated</mode>
            </mode-preference-chain>
            <key-chain>
               <key-id>KeyClient1ToRouterA</key-id>
               <secret-key>secret1</secret-key>
            </key-chain>
            <key-chain>
               <key-id>KeyForRouterB</key-id>
               <secret-key>secret2</secret-key>
            </key-chain>
            <ctrl-connection>
               <name>RouterA</name>
               <client-ip>2001:DB8:203:0:113::1</client-ip>
               <server-ip>2001:DB8:203:0:113::2</server-ip>
               <dscp>32</dscp>
               <key-id>KeyClient1ToRouterA</key-id>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>2001:DB8:10:1:1::1</sender-ip>
                  <sender-udp-port>4000</sender-udp-port>
                  <reflector-ip>2001:DB8:10:1:1::2</reflector-ip>
                  <reflector-udp-port>5000</reflector-udp-port>
                  <padding-length>64</padding-length>
                  <start-time>0</start-time>
                  <state>ok</state>
                  <sid>1232</sid>
               </test-session-request>
               <test-session-request>
                  <name>Test2</name>
                  <sender-ip>2001:DB8:203:0:113::1</sender-ip>
                  <sender-udp-port>4001</sender-udp-port>
                  <reflector-ip>2001:DB8:203:0:113::2</reflector-ip>
                  <reflector-udp-port>5001</reflector-udp-port>
                  <padding-length>128</padding-length>
                  <start-time>0</start-time>
                  <state>ok</state>
                  <sid>178943</sid>
               </twamp-session-request>
            </twamp-client-ctrl-connection>
         </twamp-client>
               </test-session-request>
            </ctrl-connection>
         </client>
      </twamp>
   </data>

A.2.  Server

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-server>
            <server-admin-state>true</server-admin-state>
         <server>
            <admin-state>true</admin-state>
            <servwait>1800</servwait>
            <dscp>32</dscp>
            <modes>authenticated unauthenticated</modes>
            <count>1024</count>
            <key-chain>
               <key-id>KeyClient1ToRouterA</key-id>
               <secret-key>secret1</secret-key>
            </key-chain>
            <key-chain>
               <key-id>KeyClient10ToRouterA</key-id>
               <secret-key>secret10</secret-key>
            </key-chain>
            <twamp-server-ctrl-connection>
            <ctrl-connection>
               <client-ip>203.0.113.1</client-ip>
               <client-tcp-port>16341</client-tcp-port>
               <server-ip>203.0.113.2</server-ip>
               <server-tcp-port>862</server-tcp-port>
               <server-ctrl-connection-state>
               <state>
                  active
                </state>
               <dscp>32</dscp>
               <selected-mode>unauthenticated</selected-mode>
               <key-id>KeyClient1ToRouterA</key-id>
               <count>1024</count>
            </ctrl-connection>
         </server>
      </twamp>
   </data>

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <server>
            <admin-state>true</admin-state>
            <servwait>1800</servwait>
            <dscp>32</dscp>
            <modes>authenticated unauthenticated</modes>
            <count>1024</count>
            <key-chain>
               <key-id>KeyClient1ToRouterA</key-id>
               <secret-key>secret1</secret-key>
            </key-chain>
            <key-chain>
               <key-id>KeyClient10ToRouterA</key-id>
               <secret-key>secret10</secret-key>
            </key-chain>
            <ctrl-connection>
               <client-ip>2001:DB8:203:0:113::1</client-ip>
               <client-tcp-port>16341</client-tcp-port>
               <server-ip>2001:DB8:203:0:113::2</server-ip>
               <server-tcp-port>862</server-tcp-port>
               <state>
                  active
                </server-ctrl-connection-state>
                </state>
               <dscp>32</dscp>
               <selected-mode>unauthenticated</selected-mode>
               <key-id>KeyClient1ToRouterA</key-id>
               <count>1024</count>
            </twamp-server-ctrl-connection>
         </twamp-server>
            </ctrl-connection>
         </server>
      </twamp>
   </data>

A.3.  Session-Sender
   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
        <twamp-session-sender>
           <session-sender-admin-state>true</session-sender-admin-state>
           <twamp-sender-test-session>
              <test-session-name>Test1</test-session-name>
        <session-sender>
           <admin-state>true</admin-state>
           <test-session>
              <name>Test1</name>
              <ctrl-connection-name>RouterA</ctrl-connection-name>
              <fill-mode>zero</fill-mode>
              <number-of-packets>900</number-of-packets>
              <periodic-interval>1</periodic-interval>
              <periodic-interval-units>seconds</periodic-interval-units>
              <sender-session-state>setup</sender-session-state>
              <periodic-interval-units>
                   seconds
              </periodic-interval-units>
              <state>setup</state>
              <sent-packets>2</sent-packets>
              <rcv-packets>2</rcv-packets>
              <last-sent-seq>1</last-sent-seq>
              <last-rcv-seq>1</last-rcv-seq>
           </twamp-sender-test-session>
           <twamp-sender-test-session>
              <test-session-name>Test2</test-session-name>
           </test-session>
           <test-session>
              <name>Test2</name>
              <ctrl-connection-name>
                RouterA
              </ctrl-connection-name>
              <fill-mode>random</fill-mode>
              <number-of-packets>900</number-of-packets>
              <lambda>1</lambda>
              <lambda-units>1</lambda-units>
              <max-interval>2</max-interval>
              <truncation-point-units>seconds</truncation-point-units>
              <sender-session-state>setup</sender-session-state>
              <state>setup</state>
              <sent-packets>21</sent-packets>
              <rcv-packets>21</rcv-packets>
              <last-sent-seq>20</last-sent-seq>
              <last-rcv-seq>20</last-rcv-seq>
           </twamp-sender-test-session>
        </twamp-session-sender>
           </test-session>
        </session-sender>
     </twamp>
   </data>

A.4.  Session-Reflector

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <twamp-session-reflector>
            <session-reflector-admin-state>
         <session-reflector>
            <admin-state>
               true
            </session-reflector-admin-state>
            <twamp-reflector-test-session>
            </admin-state>
            <test-session>
               <sender-ip>10.1.1.1</sender-ip>
               <sender-udp-port>4000</sender-udp-port>
               <reflector-ip>10.1.1.2</reflector-ip>
               <reflector-udp-port>5000</reflector-udp-port>
               <sid>1232</sid>
               <parent-connection-client-ip>
                  203.0.113.1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
               </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                  203.0.113.2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                  862
               </parent-connection-server-tcp-port>
               <dscp>32</dscp>
               <sent-packets>2</sent-packets>
               <rcv-packets>2</rcv-packets>
               <last-sent-seq>1</last-sent-seq>
               <last-rcv-seq>1</last-rcv-seq>
            </twamp-reflector-test-session>
            <twamp-reflector-test-session>
            </test-session>
            <test-session>
               <sender-ip>203.0.113.1</sender-ip>
               <sender-udp-port>4001</sender-udp-port>
               <reflector-ip>192.68.0.2</reflector-ip>
               <reflector-udp-port>5001</reflector-udp-port>
               <sid>178943</sid>
               <parent-connection-client-ip>
                  203.0.113.1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
               </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                  203.0.113.2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                  862
               </parent-connection-server-tcp-port>
               <dscp>32</dscp>
               <sent-packets>21</sent-packets>
               <rcv-packets>21</rcv-packets>
               <last-sent-seq>20</last-sent-seq>
               <last-rcv-seq>20</last-rcv-seq>
            </twamp-reflector-test-session>

         </twamp-session-reflector>
            </test-session>
         </session-reflector>
      </twamp>
   </data>

   <?xml version="1.0" encoding="utf-8"?>
   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <twamp xmlns="urn:ietf:params:xml:ns:yang:ietf-twamp">
         <session-reflector>
            <admin-state>true</admin-state>
            <test-session>
               <sender-ip>2001:DB8:10:1:1::1</sender-ip>
               <sender-udp-port>4000</sender-udp-port>
               <reflector-ip>2001:DB8:10:1:1::2</reflector-ip>
               <reflector-udp-port>5000</reflector-udp-port>
               <sid>1232</sid>
               <parent-connection-client-ip>
                   2001:DB8:203:0:113::1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
               </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                   2001:DB8:203:0:113::2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                  862
               </parent-connection-server-tcp-port>
               <dscp>32</dscp>
               <sent-packets>2</sent-packets>
               <rcv-packets>2</rcv-packets>
               <last-sent-seq>1</last-sent-seq>
               <last-rcv-seq>1</last-rcv-seq>
            </test-session>
            <test-session>
               <sender-ip>2001:DB8:203:0:113::1</sender-ip>
               <sender-udp-port>4001</sender-udp-port>
               <reflector-ip>2001:DB8:192:68::2</reflector-ip>
               <reflector-udp-port>5001</reflector-udp-port>
               <sid>178943</sid>
               <parent-connection-client-ip>
                   2001:DB8:203:0:113::1
               </parent-connection-client-ip>
               <parent-connection-client-tcp-port>
                  16341
               </parent-connection-client-tcp-port>
               <parent-connection-server-ip>
                   2001:DB8:203:0:113::2
               </parent-connection-server-ip>
               <parent-connection-server-tcp-port>
                  862
               </parent-connection-server-tcp-port>
               <dscp>32</dscp>
               <sent-packets>21</sent-packets>
               <rcv-packets>21</rcv-packets>
               <last-sent-seq>20</last-sent-seq>
               <last-rcv-seq>20</last-rcv-seq>
            </test-session>
         </session-reflector>
      </twamp>
   </data>

Appendix B.  TWAMP Operational Commands

   This document is targeted at configuration details for TWAMP.
   Operational actions such as how TWAMP sessions are started/stopped,
   how results are retrieved, or stored results are cleared, and so on,
   are not addressed by this configuration model and are out of scope of
   this document.

   TWAMP operational commands could be performed programmatically or
   manually, e.g. using a command-line interface (CLI).

   With respect to programmability, YANG can be used to define NETCONF
   Remote Procedure Calls (RPC), therefore it would be be, in principle,
   possible to define TWAMP RPC operations for actions such as starting
   or stopping control connections or test sessions or groups of
   sessions; retrieving results; clearing stored results, and so on.

   However, [RFC5357] does not attempt to describe such operational
   actions,
   actions.  Refer also to Section 2 and it is likely that the unlabeled links in
   Figure 1.  In actual deployments different TWAMP implementations could may
   support different sets of operational commands, with different
   restrictions.  Therefore, this document considers it the
   responsibility of the individual implementation to define its
   corresponding TWAMP operational commands data model.

Authors' Addresses

   Ruth Civil
   Ciena Corporation
   307 Legget Drive
   Kanata, ON  K2K 3C8
   Canada

   Email: gcivil@ciena.com
   URI:   www.ciena.com
   Al Morton
   AT&T Labs
   200 Laurel Avenue South
   Middletown,, NJ  07748
   USA

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   Email: acmorton@att.com
   URI:   http://home.comcast.net/~acmacm/

   Lianshu Zheng
   Huawei Technologies
   China

   Email: vero.zheng@huawei.com

   Reshad Rahman
   Cisco Systems
   2000 Innovation Drive
   Kanata, ON  K2K 3E8
   Canada

   Email: rrahman@cisco.com

   Mahesh Jethanandani
   Cisco Systems
   3700 Cisco Way
   San Jose, CA  95134
   USA

   Email: mjethanandani@gmail.com

   Kostas Pentikousis (editor)
   Travelping
   Koernerstr. 7-10
   Berlin  10785
   Germany

   Email: pentikousis@gmail.com k.pentikousis@travelping.com

   Lianshu Zheng
   Huawei Technologies
   China

   Email: vero.zheng@huawei.com