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Versions: (draft-cmzrjp-ippm-twamp-yang) 00 01 02 03 04

IPPM WG                                                         R. Civil
Internet-Draft                                         Ciena Corporation
Intended status: Standards Track                               A. Morton
Expires: February 23, 2018                                     AT&T Labs
                                                               R. Rahman
                                                         M. Jethanandani
                                                           Cisco Systems
                                                     K. Pentikousis, Ed.
                                                              Travelping
                                                         August 22, 2017


         Two-Way Active Measurement Protocol (TWAMP) Data Model
                     draft-ietf-ippm-twamp-yang-04

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.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 23, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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  . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .   7
   4.  Data Model Parameters . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .  13
   5.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  YANG Tree Diagram . . . . . . . . . . . . . . . . . . . .  15
     5.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  18
   6.  Data Model Examples . . . . . . . . . . . . . . . . . . . . .  45
     6.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .  45
     6.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .  47
     6.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .  48
     6.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .  49
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  52
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  53
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  53
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  53
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  54
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  54
     11.2.  Informative References . . . . . . . . . . . . . . . . .  55
   Appendix A.  Detailed Data Model Examples . . . . . . . . . . . .  56
     A.1.  Control-Client  . . . . . . . . . . . . . . . . . . . . .  56
     A.2.  Server  . . . . . . . . . . . . . . . . . . . . . . . . .  58
     A.3.  Session-Sender  . . . . . . . . . . . . . . . . . . . . .  60
     A.4.  Session-Reflector . . . . . . . . . . . . . . . . . . . .  61
   Appendix B.  TWAMP Operational Commands . . . . . . . . . . . . .  63
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  63






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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 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 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 standardizing 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




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   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 Control-Client and
   Session-Sender, while another node acts at the same time as 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].












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   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

   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 performance measurement results are retrieved, or how
   stored results are cleared, and so on, are not addressed by the
   configuration model defined in this document.  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

   The TWAMP data model includes four categories of configuration items.

   First, 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), is a typical
   instance of a global configuration item.

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

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

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




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   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 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 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.

   o  The IP address of the remote TWAMP Server.

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

   Each TWAMP-Control connection, in turn, is associated with zero or
   more 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 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 on the
      path under test by TWAMP.

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





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   o  Information pertaining to the test packet stream, such as the test
      starting 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 Server is associated with zero or more 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

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

   There is one Session-Sender instance for each 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; see also [RFC3432].

3.4.  Session-Reflector

   Each TWAMP Session-Reflector has an administrative status field set
   at the device level to indicate whether the node is enabled to
   function as such.

   Each Session-Reflector is associated with zero or more TWAMP-Test
   sessions.  For each test session, the REFWAIT timeout parameter which
   determines whether to discontinue the session if no packets have been
   received ([RFC5357], Section 4.2) can be configured.



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   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 introduces
   selected parameters associated with the four TWAMP logical 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 related to
   the configuration of the TWAMP Control-Client logical entity (recall
   Figure 1).

   The client container includes an administrative configuration
   parameter (client/admin-state) that indicates whether the device is
   allowed to initiate TWAMP-Control connections.































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

             Figure 3: TWAMP Control-Client UML class diagram

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






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   Depending on the Modes available in the Server Greeting, the Control-
   Client MUST choose the highest priority Mode from the configured
   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 [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 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 16 octets for the AES Session-key used for
   encryption and 32 octets for the HMAC-SHA1 Session-key used for
   authentication; see also Section 6.10 of [RFC4656].

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

   In turn, each ctrl-connection holds a list of test-session-request.
   test-session-request holds information associated with the Control-
   Client for this test session.  This includes information associated
   with the 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 negotiated by this TWAMP-Control
   connection via a Request-TW-Session/Accept-Session exchange.

   The Control-Client is also responsible for scheduling TWAMP-Test
   sessions so test-session-request holds information related to these
   actions (e.g. pm-index, repeat-interval).






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4.2.  Server

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

   The server container includes an administrative configuration
   parameter (server/admin-state) that indicates whether the device is
   allowed to receive TWAMP-Control connections.

   A device operating in the Server role cannot configure attributes on
   a per TWAMP-Control connection basis, as it has no foreknowledge of
   the incoming TWAMP-Control connections to be received.  Consequently,
   any parameter that the Server might want to apply to an incoming
   control connection must be configured at the overall Server level and
   applied to all incoming TWAMP-Control 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               {ro} |
                                  | control-packet-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





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   Each 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 active on the Server is represented
   by a ctrl-connection.  There SHALL be one ctrl-connection per
   incoming TWAMP-Control (TCP) connection that is received and active
   on the Server.  Each ctrl-connection can be uniquely identified by
   the 4-tuple {client-ip, client-tcp-port, server-ip, server-tcp-port}.
   All items in the ctrl-connection list are read-only.

4.3.  Session-Sender

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

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

























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   +----------------+
   | session-sender |
   +----------------+  0..* +---------------------------+
   | admin-state    |<>-----| test-session              |
   +----------------+       +---------------------------+
                            | name                      |
                            | 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 |  |
                      +-------------------+  |
                                             |
                                     +--------------+
                                     | lambda       |
                                     | max-interval |
                                     +--------------+

             Figure 5: TWAMP Session-Sender UML class diagram

   Each TWAMP-Test session initiated by the Session-Sender will be
   represented by an instance of a test-session object.  There SHALL be
   one instance of test-session for each TWAMP-Test session for which
   packets are being sent.

4.4.  Session-Reflector

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






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   The session-reflector container includes an administrative parameter
   (session-reflector/admin-state) that controls whether the device is
   allowed to respond to incoming TWAMP-Test sessions.

   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
   are applied to 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                {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 UML class diagram

   Each incoming TWAMP-Test session that is active on the Session-
   Reflector SHALL be represented by an instance of a test-session
   object.  All items in the test-session object are read-only.

   Instances of test-session are indexed by a session identifier (sid).
   This value is auto-allocated by the TWAMP Server as test session



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   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 client/ctrl-connection/test-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 session-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 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 MUST correspond to the equivalent 4-tuple
   {client-ip, client-tcp-port, server-ip, server-tcp-port} in server/
   ctrl-connection.  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.

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 client! {control-client}?
        |  +--rw admin-state              boolean
        |  +--rw mode-preference-chain* [priority]
        |  |  +--rw priority    uint16
        |  |  +--rw mode?       twamp-modes
        |  +--rw key-chain* [key-id]
        |  |  +--rw key-id        binary



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        |  |  +--rw secret-key?   binary
        |  +--rw ctrl-connection* [name]
        |     +--rw name                    string
        |     +--rw client-ip?              inet:ip-address
        |     +--rw server-ip               inet:ip-address
        |     +--rw server-tcp-port?        inet:port-number
        |     +--rw control-packet-dscp?    inet:dscp
        |     +--rw key-id?                 string
        |     +--rw max-count?              uint8
        |     +--ro client-tcp-port?        inet:port-number
        |     +--ro server-start-time?      uint64
        |     +--ro state? \
                 control-client-connection-state
        |     +--ro selected-mode?          twamp-modes
        |     +--ro token?                  binary
        |     +--ro client-iv?              binary
        |     +--rw test-session-request* [name]
        |        +--rw name                  string
        |        +--rw sender-ip?            inet:ip-address
        |        +--rw sender-udp-port?      union
        |        +--rw reflector-ip          inet:ip-address
        |        +--rw reflector-udp-port?   dynamic-port-number
        |        +--rw timeout?              uint64
        |        +--rw padding-length?       uint32
        |        +--rw test-packet-dscp?     inet:dscp
        |        +--rw start-time?           uint64
        |        +--rw repeat?               union
        |        +--rw repeat-interval?      uint32
        |        +--rw pm-reg-list* [pm-index]
        |        |  +--rw pm-index    uint16
        |        +--ro state?                test-session-state
        |        +--ro sid?                  string
        +--rw server! {server}?
        |  +--rw admin-state            boolean
        |  +--rw server-tcp-port?       inet:port-number
        |  +--rw servwait?              uint32
        |  +--rw control-packet-dscp?   inet:dscp
        |  +--rw count?                 uint8
        |  +--rw max-count?             uint8
        |  +--rw modes?                 twamp-modes
        |  +--rw key-chain* [key-id]
        |  |  +--rw key-id        binary
        |  |  +--rw secret-key?   binary
        |  +--ro 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



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        |     +--ro server-tcp-port        inet:port-number
        |     +--ro state?                 server-ctrl-connection-state
        |     +--ro control-packet-dscp?   inet:dscp
        |     +--ro selected-mode?         twamp-modes
        |     +--ro key-id?                string
        |     +--ro count?                 uint8
        |     +--ro max-count?             uint8
        |     +--ro salt?                  binary
        |     +--ro server-iv?             binary
        |     +--ro challenge?             binary
        +--rw session-sender! {session-sender}?
        |  +--rw admin-state     boolean
        |  +--rw test-session* [name]
        |     +--rw name                    string
        |     +--ro ctrl-connection-name?   string
        |     +--rw fill-mode?              padding-fill-mode
        |     +--rw number-of-packets       uint32
        |     +--rw (packet-distribution)?
        |     |  +--:(periodic)
        |     |  |  +--rw periodic-interval       decimal64
        |     |  +--:(poisson)
        |     |     +--rw lambda                  decimal64
        |     |     +--rw max-interval?           decimal64
        |     +--ro state?                  sender-session-state
        |     +--ro sent-packets?           uint32
        |     +--ro rcv-packets?            uint32
        |     +--ro last-sent-seq?          uint32
        |     +--ro last-rcv-seq?           uint32
        +--rw session-reflector! {session-reflector}?
           +--rw admin-state     boolean
           +--rw refwait?        uint32
           +--ro 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 \
                 dynamic-port-number
              +--ro reflector-ip                         inet:ip-address
              +--ro reflector-udp-port \
                 dynamic-port-number
              +--ro 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 test-packet-dscp?                    inet:dscp



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              +--ro sent-packets?                        uint32
              +--ro rcv-packets?                         uint32
              +--ro last-sent-seq?                       uint32
              +--ro last-rcv-seq?                        uint32

                       Figure 7: YANG Tree Diagram.

5.2.  YANG Module

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

<CODE BEGINS> file "ietf-twamp@2017-02-22.yang"
module ietf-twamp {
  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, namely,
    Control-Client, Server, Session-Sender, and Session-Reflector,
    as illustrated in the annotated TWAMP logical model (Fig. 1
    of draft-ietf-ippm-twamp-yang).

    This YANG module uses features to indicate which of the four
    logical entities are supported by a TWAMP implementation.";

  revision 2017-02-22 {
    description
      "Revision appearing in draft-ietf-ippm-twamp-yang-03.

      Covers RFC 5357, RFC 5618, RFC 5938, RFC 6038, RFC 7717, and
      draft-ietf-ippm-metric-registry";



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    reference
      draft-ietf-ippm-twamp-yang;
  }


  /*
   * Typedefs
   */

  typedef twamp-modes {
    type bits {
      bit unauthenticated {
        position 0;
        description
          "Unauthenticated mode, in which no encryption or
          authentication is applied in TWAMP-Control and TWAMP-Test.
          KeyID, Token, and Client-IV are not used in the
          Set-Up-Response message. See Section 3.1 of RFC 4656.";
        reference
          "RFC 4656: A One-way Active Measurement Protocol (OWAMP)";
      }
      bit authenticated {
        position 1;
        description
          "Authenticated mode, in which the Control-Client and Server
          possess a shared secret thus prohibiting 'theft of service'.
          As per Section 6 of RFC 4656, in 'authenticated mode, the
          timestamp is in the clear and is not protected
          cryptographically in any way, while the rest of the message
          has the same protection as in encrypted mode. This mode
          allows one to trade off cryptographic protection against
          accuracy of timestamps.'";
        reference
          "RFC 4656: A One-way Active Measurement Protocol (OWAMP)";
      }
      bit encrypted {
        position 2;
        description
          "Encrypted mode 'makes it impossible to alter
          timestamps undetectably.' See also Section 4 of RFC 7717
          and Section 6 of RFC 4656.";
        reference
          "RFC 4656: A One-way Active Measurement Protocol (OWAMP)";
      }
      bit unauth-test-encrpyt-control {
        position 3;
        description
          "When using the Mixed Security Mode, the TWAMP-Test



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          protocol follows the Unauthenticated mode and the
          TWAMP-Control protocol the Encrypted mode.";
        reference
          "RFC 5618: Mixed Security Mode for the Two-Way Active
          Measurement Protocol (TWAMP)";
      }
      bit individual-session-control {
        position 4;
        description
          "This mode enables individual test sessions using
          Session Identifiers.";
        reference
          "RFC 5938: Individual Session Control Feature
          for the Two-Way Active Measurement Protocol (TWAMP)";
      }
      bit reflect-octets {
        position 5;
        description
          "This mode indicates the reflect octets capability.";
        reference
          "RFC 6038: Two-Way Active Measurement Protocol (TWAMP)
          Reflect Octets and Symmetrical Size Features";
      }
      bit symmetrical-size {
        position 6;
        description
          "This mode indicates support for the 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
          "In this mode the the shared key is derived
          from an IKEv2 security association (SA).";
        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 supported during a
      TWAMP-Control Connection setup between a Control-Client
      and a Server. Section 7 of RFC 7717 summarizes the
      TWAMP-Modes registry and points to their formal



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      specification.";
  }

  typedef control-client-connection-state {
    type enumeration {
      enum active {
        description
          "Indicates an active TWAMP-Control connection to Server.";
      }
      enum idle {
        description
          "Indicates an idle TWAMP-Control connection to Server.";
      }
    }
    description
      "Indicates the Control-Client TWAMP-Control connection state.";
  }

  typedef test-session-state {
    type enumeration {
      enum accepted {
        value 0;
        description
          "Indicates that accepted TWAMP-Test session request.";
      }
      enum failed {
        value 1;
        description
          "Indicates a TWAMP-Test session failure due to
          some unspecified reason (catch-all).";
      }
      enum internal-error {
        value 2;
        description
          "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 TWAMP-Test session request
          is not supported.";
      }
      enum permanent-resource-limit {
        value 4;
        description
          "Indicates a TWAMP-Test session failure due to



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          permanent resource limitations.";
      }
      enum temp-resource-limit {
        value 5;
        description
          "Indicates a TWAMP-Test session failure due to
          temporary resource limitations.";
      }
    }
    description
      "Indicates the Control-Client TWAMP-Test session state.";
  }

  typedef server-ctrl-connection-state {
    type enumeration {
      enum active {
        description
          "Indicates an active TWAMP-Control connection
          to the Control-Client.";
      }
      enum servwait {
        description
          "Indicates that the TWAMP-Control connection to the
          Control-Client is in SERVWAIT as per the definition of
          Section 3.1 of RFC 5357.";
      }
    }
    description
      "Indicates the Server TWAMP-Control connection state.";
  }

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

  typedef padding-fill-mode {
    type enumeration {



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      enum zero {
        description
          "TWAMP-Test packets are padded with all zeros.";
      }
      enum random {
        description
          "TWAMP-Test packets are padded with pseudo-random
          numbers.";
      }
    }
    description
      "Indicates what type of packet padding is used in the
      TWAMP-Test packets.";
  }

  typedef dynamic-port-number {
    type inet:port-number {
      range 49152..65535;
    }
    description "Dynamic range for port numbers.";
  }

  /*
   * Features
   */

  feature control-client {
    description
      "Indicates that the device supports configuration of the
      TWAMP Control-Client logical entity.";
  }

  feature server {
    description
      "Indicates that the device supports configuration of the
      TWAMP Server logical entity.";
  }

  feature session-sender {
    description
      "Indicates that the device supports configuration of the
      TWAMP Session-Sender logical entity.";
  }

  feature session-reflector {
    description
      "Indicates that the device supports configuration of the
      TWAMP Session-Reflector logical entity.";



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  }


  /*
   * Reusable node groups
   */

  grouping key-management {
    list key-chain {
      key key-id;
      leaf key-id {
        type binary {
          length 1..80;
        }
        description
          "KeyID used for a TWAMP-Control connection. As per
          Section 3.1 of RFC 4656, KeyID is 'a UTF-8 string, up to
          80 octets in length' and is used to select which 'shared
          shared secret the [Control-Client] wishes to use to
          authenticate or encrypt'.";
        }
        leaf secret-key {
          type binary;
          description
            "The secret key corresponding to the KeyID for this
            TWAMP-Control connection.";
        }
        description
          "Relates KeyIDs with their respective secret keys
          in a TWAMP-Control connection.";
    }
    description
        "Used by the Control-Client and Server for TWAMP-Control
        key management.";
  }

  grouping maintenance-statistics {
    leaf sent-packets {
      type uint32;
      config false;
      description "Indicates the number of packets sent.";
    }

    leaf rcv-packets {
      type uint32;
      config false;
      description "Indicates the number of packets received.";
    }



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    leaf last-sent-seq {
      type uint32;
      config false;
      description "Indicates the last sent sequence number.";
    }

    leaf last-rcv-seq {
      type uint32;
      config false;
      description "Indicates the last received sequence number.";
    }
    description "Used for TWAMP-Test maintenance statistics.";
  }

  grouping count {
    leaf count {
      type uint8 {
        range "10..31";
      }
      default 10;
      description
        "Parameter communicated to the Control-Client as part of the
        Server Greeting message and used for deriving a key from a
        shared secret as per Section 3.1 of  RFC 4656:  MUST be a
        power of 2 and at least 1024; SHOULD be increased as more
        computing power becomes common.";
      }
   description
     "Reusable data structure for count which is used both in the
     Server container.";
  }

  grouping max-count {
    leaf max-count {
      type uint8 {
        range "10..31";
      }
      default 15;
      description
        "This parameter limits the maximum Count value, which MUST
        be a power of 2 and at least 1024 as per RFC 5357. It is
        configured by providing said power. For example,
        configuring 10 here means max count 2^10 = 1024.
        The default is 15, meaning 2^15 = 32768.

        A TWAMP Server uses this configured value in the
        Server-Greeting message sent to the Control-Client.




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        A TWAMP Control-Client uses this configured value to prevent
        denial-of-service (DOS) attacks by closing the control
        connection to the Server if it 'receives a Server-Greeting
        message with Count greater that its maximum configured value',
        as per Section 6 of RFC 5357.

        Further, note that according to Section 6 of RFC 5357:

          '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. The default
          max-count value SHOULD be 32768.'

        RFC 5357 does not qualify 'significant period' in terms of
        time, but it is clear that this depends on the processing
        capacity available and operators need to pay attention to
        this security consideration.";
      }
    description
      "Reusable data structure for max-count which is used both at
      the Control-Client and the Server containers.";
  }


  /*
   * Configuration data nodes
   */

  container twamp {
    description
        "TWAMP logical entity configuration grouping of four models
        which correspond to the four TWAMP logical entities
        Control-Client, Server, Session-Sender, and Session-Reflector
        as illustrated in Fig. 1 of draft-ietf-ippm-twamp-yang.";

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

      leaf admin-state {
        type boolean;
        mandatory true;



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        description
          "Indicates whether the device is allowed to operate as a
          TWAMP Control-Client.";
      }

      list mode-preference-chain {
        key priority;
        unique mode;
        leaf priority {
          type uint16;
          description
            "Indicates the Control-Client Mode preference priority
            expressed as a 16-bit unsigned integer, where zero is the
            highest priority and subsequent values monotonically
            increasing.";
        }
        leaf mode {
          type twamp-modes;
          description
            "The supported TWAMP Mode matching the corresponding
            priority.";

        }
        description
            "Indicates the Control-Client preferred order of use of
            the supported TWAMP Modes.

            Depending on the Modes available in the TWAMP Server
            Greeting message (see Fig. 2 of RFC 7717), the
            this Control-Client MUST choose the highest priority Mode
            from the configured mode-preference-chain list.";
      }

      uses key-management;

      list ctrl-connection {
        key name;
        description
          "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
            "A unique name used as a key to identify this individual
            TWAMP-Control connection on the Control-Client device.";
        }



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        leaf client-ip {
          type inet:ip-address;
          description
            "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.";
        }
        leaf server-ip {
          type inet:ip-address;
          mandatory true;
          description
            "The IP address of the remote Server device, which the
            TWAMP-Control connection will be initiated to.";
        }

        leaf server-tcp-port {
          type inet:port-number;
          default 862;
          description
            "This parameter defines the TCP port number that is
            to be used by this outgoing TWAMP-Control connection.
            Typically, this is the well-known TWAMP-Control
            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.";
        }

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

        leaf key-id {
          type string {
            length 1..80;
          }
          description
           "Indicates the KeyID value selected for this
           TWAMP-Control connection.";



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        }

        uses max-count;

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

        leaf server-start-time {
          type uint64;
          config false;
          description
            "Indicates the Start-Time advertized by the Server in the
            Server-Start message (RFC 4656, Section 3.1),
            representing the time when the current
            instantiation of the Server started operating.
            The timestamp format follows RFC 1305
            according to Section 4.1.2 of RFC 4656.";
        }

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

        leaf selected-mode {
          type twamp-modes;
          config false;
          description
            "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).";
        }

        leaf token {
            type binary {
            length 64;
          }
          config false;
          description



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            "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; see also
            the last paragraph of Section 6 in RFC 4656.

            If the Mode defined in RFC 7717 is selected (selected-mode),
            Token is limited to 16 octets.";
          reference
            "RFC 4086: Randomness Requirements for Security

             RFC 7717: IKEv2-Derived Shared Secret Key for the One-Way
             Active Measurement Protocol (OWAMP) and Two-Way Active
             Measurement Protocol (TWAMP)";
        }

        leaf client-iv {
          type binary {
            length 16;
          }
          config false;
          description
            "Indicates the Control-Client Initialization Vector
            (Client-IV), that is generated randomly by the
            Control-Client. As per RFC 4656:

              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.

            If the Mode defined in RFC 7717 is selected (selected-mode),
            Client-IV is limited to 12 octets.";
          reference
            "RFC 4656: A One-way Active Measurement Protocol (OWAMP)

             RFC 7717: IKEv2-Derived Shared Secret Key for the One-Way
             Active Measurement Protocol (OWAMP) and Two-Way Active
             Measurement Protocol (TWAMP)";        }

        list test-session-request {
          key name;
          description
            "Information associated with the Control-Client
            for this test session";




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          leaf name {
            type string;
            description
              "A unique name to be used for identification of
              this TWAMP-Test session on the Control-Client.";
          }

          leaf sender-ip {
            type inet:ip-address;
            description
              "The IP address of the Session-Sender device,
              which is to be placed in the source IP address
              field of the IP header in TWAMP-Test (UDP) packets
              belonging to this test session. This value will be
              used to populate the sender address field of the
              Request-TW-Session message.

              If not configured, the device SHALL choose its own
              source IP address.";
          }

          leaf sender-udp-port {
            type union {
              type dynamic-port-number;
              type enumeration {
                enum autoallocate {
                  description
                    "Indicates that the Contol-Client will
                    auto-allocate the TWAMP-Test (UDP) port number
                    from the dynamic port range.";
                }
              }
            }
            default autoallocate;
            description
              "The UDP port number that is to be used by
              the Session-Sender for this TWAMP-Test session.
              The number is restricted to the dynamic port range.

              By default 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 Section 3.5 of RFC 5357). 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



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              repeated, the device is free to auto-allocate a
              different UDP port number when it negotiates the
              next (repeated) iteration of this session.";
          }

          leaf reflector-ip {
            type inet:ip-address;
            mandatory true;
            description
              "The IP 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
              "This parameter defines the UDP 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.";
          }

          leaf timeout {
            type uint64;
            units seconds;
            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
                the Request-TW-Session message.";
          }

          leaf padding-length {
            type uint32 {
              range 64..4096;
            }
            description
                "The number of padding bytes to be added to the



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                TWAMP-Test (UDP) packets generated by the
                Session-Sender.

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

          leaf test-packet-dscp {
            type inet:dscp;
            default 0;
            description
                "The DSCP value to be placed in the 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.

                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;
            description
                "Time when the session is to be started
                (but not before the TWAMP Start-Sessions command
                is issued; see Section 3.4 of RFC 5357).

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

                The timestamp format follows RFC 1305 as per
                Section 3.5 of RFC 4656.

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

          leaf repeat {
            type union {
              type uint32 {
                range 0..4294967294;
              }
              type enumeration {
                enum forever {



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                  description
                    "Indicates that the test session SHALL be
                    repeated *forever* using the information in
                    repeat-interval parameter, and SHALL NOT
                    decrement the value.";
                }
              }
            }
            default 0;
            description
                "This value determines if the TWAMP-Test session must
                be repeated. When a test session has completed, the
                repeat parameter is checked.

                The default value of 0 indicates that the session
                MUST NOT be repeated.

                If the repeat 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.";
          }

          leaf repeat-interval  {
            when "../repeat!='0'" {
              description
                "This parameter determines the timing of repeated
                TWAMP-Test sessions when repeat is more than 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 seconds specified in the
                repeat-interval parameter before negotiating the
                new instance of this TWAMP-Test session.";
            }
            type uint32;
            units seconds;
            default 0;
            description "Repeat interval (in seconds).";
          }

          list pm-reg-list {



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            key pm-index;
            leaf pm-index {
              type uint16;
              description
                "Numerical index value of a Registered Metric
                in the Performance Metric Registry
                (see ietf-ippm-metric-registry). Output statistics
                are specified in the corresponding Registry entry.";
            }
            description
                "A list of one or more Performance Metric Registry
                Index values, which communicate packet stream
                characteristics along with 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.";
            reference
              "ietf-ippm-metric-registry:
                Registry for Performance Metrics";
          }
          leaf state {
            type test-session-state;
            config false;
            description
                "Indicates the TWAMP-Test session state (accepted or
                indication of an error); see Section 3.5 of
                RFC 5357.";
          }
          leaf sid {
            type string;
            config false;
            description
                "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 RFC 6038.";
          }
        }
      }
    }

    container server {
      if-feature server;
      presence "Enables TWAMP Server functionality.";
      description "Configuration of the TWAMP Server logical entity.";



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

      leaf server-tcp-port {
        type inet:port-number;
        default 862;
        description
            "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 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;
        }
        units seconds;
        default 900;
        description
          "TWAMP-Control (TCP) session timeout, in seconds.
          According to Section 3.1 of RFC 5357,

            Server MAY discontinue any established control
            connection when no packet associated with that
            connection has been received within SERVWAIT seconds.";
      }

      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



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            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 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 RFC 5357.";
      }

      uses count;

      uses max-count;

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

      uses key-management;

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

        leaf client-ip {
          type inet:ip-address;
          description
            "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.";
        }

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

        leaf server-ip {



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          type inet:ip-address;
          description
            "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.";
        }

        leaf server-tcp-port {
          type inet:port-number;
          description
            "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 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 state {
          type server-ctrl-connection-state;
          description
            "Indicates the Server TWAMP-Control connection state.";
        }

        leaf control-packet-dscp {
          type inet:dscp;
          description
            "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
            control-packet-dscp parameter under the twamp/server
            container.  However, in the event that the user
            re-configures 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.";
        }

        leaf selected-mode {
          type twamp-modes;
          description
            "The Mode that was chosen for this TWAMP-Control
            connection as set in the Mode field of the



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            Set-Up-Response message.";
        }

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

        uses count {
          description
            "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 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.";
        }

        uses max-count {
          description
            "This read-only value indicates the actual max-count in use
            for this control connection. Usually this would be the
            same value as configured under twamp/server.";
        }

        leaf salt {
          type binary {
            length 16;
          }
          description
            "A parameter used in deriving a key from a
            shared secret as described in Section 3.1 of RFC 4656.
            It is communicated to the Control-Client as part of
            the Server Greeting message.";
        }

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



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        }

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

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

      list test-session{
        key name;
        description "List of TWAMP Session-Sender test sessions.";

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

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




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        leaf fill-mode {
          type padding-fill-mode;
          default zero;
          description
            "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 RFC 5357.";
        }

        leaf number-of-packets {
          type uint32;
          mandatory true;
          description
            "The overall number of TWAMP-Test (UDP) packets to be
            transmitted by the Session-Sender for this test session.";
        }

        choice packet-distribution {
          description
            "Indicates the distribution to be used for transmitting
            the TWAMP-Test (UDP) packets.";
          case periodic {
            leaf periodic-interval {
              type decimal64 {
                fraction-digits 5;
              }
              units seconds;
              mandatory true;
              description
                "Indicates the time to wait (in seconds) between the
                first bits of TWAMP-Test (UDP) packet transmissions for
                this test session";
              reference
                "RFC 3432: Network performance measurement
                           with periodic streams";
            }
          }
          case poisson {
            leaf lambda {
              type decimal64 {
                fraction-digits 5;
              }
              units seconds;
              mandatory true;
              description
                "Indicates the average time interval (in seconds)
                between packets in the Poisson distribution.



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                The packet is calculated using the reciprocal of lambda
                and the TWAMP-Test packet size (which depends on the
                selected Mode and the packet padding).";
             reference
               "RFC 2330: Framework for IP Performance Metrics";
            }
            leaf max-interval {
              type decimal64 {
                fraction-digits 5;
              }
              units seconds;
              description
                "Indicates the maximum time (in seconds)
                between packet transmissions.";
              reference
                "RFC 7312: Advanced Stream and Sampling Framework
                           for IP Performance Metrics (IPPM)";
            }
          }
        }

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

        uses maintenance-statistics;
      }
    }

    container session-reflector {
      if-feature session-reflector;
      presence "Enables TWAMP Session-Reflector functionality.";
      description
        "Configuration of the TWAMP Session-Reflector logical entity";

      leaf admin-state {
        type boolean;
        mandatory true;
        description
          "Indicates whether the device is allowed to operate
          as a TWAMP Session-Reflector.";
      }

      leaf refwait {
        type uint32 {



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          range 1..604800;
        }
        units seconds;
        default 900;
        description
          "The Session-Reflector MAY discontinue any session that has
          been started when no packet associated with that session has
          been received for REFWAIT seconds. As per Section 3.1 of
          RFC 5357, this timeout allows a Session-Reflector to free up
          resources in case of failure.";
      }

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

        leaf sid {
          type string;
          description
            "An auto-allocated identifier for this TWAMP-Test
            session that is unique within the context of this
            Server/Session-Reflector device only. This value
            is 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
            "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.";
        }

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

        leaf reflector-ip {
          type inet:ip-address;
          description



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            "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.";
        }

        leaf reflector-udp-port {
          type dynamic-port-number;
          description
            "The destination UDP 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
            "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.";
        }

        leaf parent-connection-client-tcp-port {
          type inet:port-number;
          description
            "The source TCP 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
            "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.";
        }

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




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

   Figure 8 shows a configuration example for a Control-Client with
   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">
         <client>
            <admin-state>true</admin-state>
         </client>
      </twamp>
   </config>

         Figure 8: XML instance enabling Control-Client operation.

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



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   "RouterB".  Each TWAMP-Control connection is to a different Server.
   The control connection named "RouterA" has two test session requests.
   The 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">
         <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>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>203.0.113.3</sender-ip>
                  <sender-udp-port>54001</sender-udp-port>
                  <reflector-ip>203.0.113.4</reflector-ip>
                  <reflector-udp-port>50001</reflector-udp-port>
                  <start-time>0</start-time>
               </test-session-request>
               <test-session-request>
                  <name>Test2</name>
                  <sender-ip>203.0.113.1</sender-ip>
                  <sender-udp-port>54001</sender-udp-port>
                  <reflector-ip>203.0.113.2</reflector-ip>
                  <reflector-udp-port>50001</reflector-udp-port>
                  <start-time>0</start-time>
               </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>
            </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>



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               <server-ip>2001:DB8:203:0:113::2</server-ip>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>2001:DB8:203:1:113::3</sender-ip>
                  <sender-udp-port>54000</sender-udp-port>
                  <reflector-ip>2001:DB8:203:1:113::4</reflector-ip>
                  <reflector-udp-port>55000</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>54001</sender-udp-port>
                  <reflector-ip>2001:DB8:203:0:113::2</reflector-ip>
                  <reflector-udp-port>55001</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

   Figure 9 shows a configuration example for a Server with 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">
         <server>
            <admin-state>true</admin-state>
         </server>
      </twamp>
   </config>

             Figure 9: XML instance enabling Server operation.

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




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   <?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>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>
               <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
               </state>
            </ctrl-connection>
         </server>
      </twamp>
   </data>

6.3.  Session-Sender

   Figure 10 shows a configuration example for a Session-Sender with
   session-sender/admin-state enabled, which permits a device following
   Figure 2 to initiate TWAMP-Test sessions.










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   <?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">
         <session-sender>
            <admin-state>true</admin-state>
         </session-sender>
      </twamp>
   </config>

        Figure 10: XML instance enabling Session-Sender operation.

   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">
        <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>
              <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>
              <max-interval>2</max-interval>
              <state>setup</state>
           </test-session>
        </session-sender>
     </twamp>
   </data>

6.4.  Session-Reflector

   This configuration example shows a Session-Reflector with session-
   reflector/admin-state enabled, which permits a device following
   Figure 2 to respond to TWAMP-Test sessions.






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   <?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">
         <session-reflector>
            <admin-state>true</admin-state>
         </session-reflector>
      </twamp>
   </config>

       Figure 11: XML instance enabling Session-Reflector operation.

   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">
         <session-reflector>
             <admin-state>true</admin-state>
             <test-session>
               <sender-ip>203.0.113.3</sender-ip>
               <sender-udp-port>54000</sender-udp-port>
               <reflector-ip>203.0.113.4</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>
            </test-session>
            <test-session>
               <sender-ip>203.0.113.1</sender-ip>
               <sender-udp-port>54001</sender-udp-port>
               <reflector-ip>192.68.0.2</reflector-ip>
               <reflector-udp-port>50001</reflector-udp-port>
               <sid>178943</sid>



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               <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>

   <?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>203.0.113.3</sender-ip>
               <sender-udp-port>54000</sender-udp-port>
               <reflector-ip>203.0.113.4</reflector-ip>
               <reflector-udp-port>54001</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>



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            </test-session>
            <test-session>
               <sender-ip>203.0.113.1</sender-ip>
               <sender-udp-port>54001</sender-udp-port>
               <reflector-ip>192.68.0.2</reflector-ip>
               <reflector-udp-port>55001</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

   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.





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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 Fred Baker, Kevin D'Souza, Gregory Mirsky, Brian Trammell,
   Robert Sherman, and Marius Georgescu 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 reviews of the YANG
   module and the examples in Appendix A.

   Kostas Pentikousis was 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.  Contributors

   Lianshu Zheng, Huawei Technologies, China

   Email: vero.zheng@huawei.com




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11.  References

11.1.  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, <https://www.rfc-
              editor.org/info/rfc3432>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004, <https://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,
              <https://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,
              <https://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,
              <https://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, <https://www.rfc-
              editor.org/info/rfc7717>.







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11.2.  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-12 (work in progress), June 2017.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-18 (work in
              progress), October 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-04 (work in progress), July 2016.

   [I-D.unify-nfvrg-devops]
              Meirosu, C., Manzalini, A., Steinert, R., Marchetto, G.,
              Pentikousis, K., Wright, S., Lynch, P., and W. John,
              "DevOps for Software-Defined Telecom Infrastructures",
              draft-unify-nfvrg-devops-06 (work in progress), July 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, <https://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, <https://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, <https://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,
              <https://www.rfc-editor.org/info/rfc5938>.




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   [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, <https://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, <https://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
   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">
         <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>203.0.113.1</client-ip>



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               <server-ip>203.0.113.2</server-ip>
               <dscp>32</dscp>
               <key-id>KeyClient1ToRouterA</key-id>
               <test-session-request>
                  <name>Test1</name>
                  <sender-ip>203.0.113.3</sender-ip>
                  <sender-udp-port>54000</sender-udp-port>
                  <reflector-ip>203.0.113.4</reflector-ip>
                  <reflector-udp-port>55000</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>203.0.113.1</sender-ip>
                  <sender-udp-port>54001</sender-udp-port>
                  <reflector-ip>203.0.113.2</reflector-ip>
                  <reflector-udp-port>55001</reflector-udp-port>
                  <padding-length>128</padding-length>
                  <start-time>0</start-time>
                  <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>



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               <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>54000</sender-udp-port>
                  <reflector-ip>2001:DB8:10:1:1::2</reflector-ip>
                  <reflector-udp-port>55000</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>54001</sender-udp-port>
                  <reflector-ip>2001:DB8:203:0:113::2</reflector-ip>
                  <reflector-udp-port>55001</reflector-udp-port>
                  <padding-length>128</padding-length>
                  <start-time>0</start-time>
                  <state>ok</state>
                  <sid>178943</sid>
               </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">
         <server>
            <admin-state>true</admin-state>
            <servwait>1800</servwait>
            <dscp>32</dscp>
            <modes>authenticated unauthenticated</modes>
            <count>1024</count>
            <key-chain>



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               <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>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>
               <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



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                </state>
               <dscp>32</dscp>
               <selected-mode>unauthenticated</selected-mode>
               <key-id>KeyClient1ToRouterA</key-id>
               <count>1024</count>
            </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">
        <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>
              <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>
           </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>
              <max-interval>2</max-interval>
              <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>
           </test-session>
        </session-sender>
     </twamp>
   </data>




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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">
         <session-reflector>
            <admin-state>
               true
            </admin-state>
            <test-session>
               <sender-ip>203.0.113.3</sender-ip>
               <sender-udp-port>54000</sender-udp-port>
               <reflector-ip>203.0.113.4</reflector-ip>
               <reflector-udp-port>55000</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>
            </test-session>
            <test-session>
               <sender-ip>203.0.113.1</sender-ip>
               <sender-udp-port>54001</sender-udp-port>
               <reflector-ip>192.68.0.2</reflector-ip>
               <reflector-udp-port>55001</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>



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               <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>

   <?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>54000</sender-udp-port>
               <reflector-ip>2001:DB8:10:1:1::2</reflector-ip>
               <reflector-udp-port>55000</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>54001</sender-udp-port>
               <reflector-ip>2001:DB8:192:68::2</reflector-ip>
               <reflector-udp-port>55001</reflector-udp-port>
               <sid>178943</sid>



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               <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

   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, 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.  Refer also to Section 2 and the unlabeled links in
   Figure 1.  In actual deployments different TWAMP implementations 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









Civil, et al.           Expires February 23, 2018              [Page 63]


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   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


   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
   Siemensdamm 50
   Berlin  13629
   Germany

   Email: k.pentikousis@travelping.com





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