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Versions: 00 01

I2RS Working Group                                           Xian Zhang
Internet-Draft                                              Baoquan Rao
Intended status: Standards Track                                 Huawei
                                                             Xufeng Liu
                                                               Ericsson


Expires: September 9, 2015                                March 9, 2015




             A YANG Data Model for Layer 1 Network Topology

                draft-zhang-i2rs-l1-topo-yang-model-01.txt


Abstract

   This draft describes a YANG data model to manipulate the topologies
   of a layer 1 network. It is independent of data plan technologies
   and control plane protocols. It can be augmented to include
   technology-specific data, such as for Optical Transport Networks
   (OTN).

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 9, 2015.

   Copyright Notice

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   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction ................................................ 2
   2. Conventions used in this document............................ 3
   3. Terminology and Notations.................................... 3
   4. YANG Data Model for Layer 1 Topology......................... 4
      4.1. YANG Tree .............................................  4
         4.1.1. The node and link list............................. 5
         4.1.2. Notification....................................... 5
      4.2. YANG Code .............................................. 5
   5. Security Considerations .....................................21
   6. Manageability Considerations ................................21
   7. IANA Considerations ........................................ 21
   8. Acknowledgements ........................................... 21
   9. References ................................................. 22
      9.1. Normative References .................................. 22
      9.2. Informative References ................................ 22
   10. Contributors' Addresses ....................................22
   11. Authors' Addresses .........................................22



1. Introduction

   This document defines a data model of a layer one network topology,
   using YANG [RFC6020]. The model can be used by an application via
   the I2RS interface [draft-ietf-i2rs-architecture], in the following
   ways (but not limited to):

     o to obtain a whole view of the network topology information of
   its interest;

      o to receive notifications with regard to the information of the
   change of the network topology of its interest;


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      o to enforce the establishment/update of a network topology with
   the characteristic specified in the data model;

   This model is confined to describe layer 1 networks, but it is data
   plane technology independent and can be augmented to specify the
   topology for networks such as Optical Transport networks (OTN),
   Synchronous Digital Network/ (SDH/SONET)  DWDM (Dense Wavelength
   Division Multiplexing).

   [Editor's Note: The authors are aware that there are other drafts
   closely relating to this draft. Coordination works have been
   undergoing to get these drafts aligned. The authors are working on
   obtaining layer one topology by augmenting the data model proposed
   in draft-clemm-i2rs-yang-network-topo in the next version of this
   draft.]

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

3. Terminology and Notations

   A simplified graphical representation of the data model is used in
   this document. The meaning of the symbols in the YANG data tree
   presented later in this draft is defined in [ietf-netmod-rfc6087bis].
   They are provided below for reference.

     o  Brackets "[" and "]" enclose list keys.

      o  Abbreviations before data node names: "rw" means configuration
   (read-write) and "ro" state data (read-only).

      o  Symbols after data node names: "?" means an optional node, "!"
   means a presence container, and "*" denotes a list and leaf-list.

      o  Parentheses enclose choice and case nodes, and case nodes are
   also marked with a colon (":").

      o  Ellipsis ("...") stands for contents of subtrees that are not
   shown.







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4. YANG Data Model for Layer 1 Topology

4.1. YANG Tree

module: ietf-layer1topology
   +--rw layer-one-topology
      +--rw topology* [topology-id]
         +--rw topology-id            topology-id
         +--rw name?                  string
         +--rw supporting-topology* [topo-ref]
         |  +--rw topo-ref    leafref
         +--rw node* [node-id]
         |  +--rw node-id                node-id
         |  +--rw interface* [interface-id]
         |  |  +--rw interface-id             interface-id
         |  |  +--rw interface-name?          if:interface-state-ref
         |  |  +--rw adaptation-capability
         |  +--rw connectivity-matrix* [id]
         |     +--rw id               uint32
         |     +--rw type?            enumeration
         |     +--rw in-interface* [interface-ref]
         |     |  +--rw interface-ref    leafref
         |     +--rw out-interface* [interface-ref]
         |     |  +--rw interface-ref    leafref
         |     +--rw dir?             enumeration
         +--rw link* [link-id]
            +--rw link-id            link-id
            +--rw local
            |  +--rw local-node         leafref
            |  +--rw local-interface    leafref
            +--rw remote
            |  +--rw remote-node         leafref
            |  +--rw remote-interface    leafref
            +--rw supporting-path* [supporting-path-index]
            |  +--rw supporting-path-index     uint32
            |  +--rw topo-ref?                 leafref
            |  +--rw server-path-identifier
            |  +--rw server-path-srlg
            |     +--rw srlg-values* [srlg-value]
            |        +--rw srlg-value    uint32
            +--rw attributes
               +--ro information-source?              enumeration
               +--ro credibility-preference?          uint16
               +--rw admin-status?                    enumeration
               +--ro oper-status?                     enumeration
               +--rw area-id?                         binary
               +--rw max-link-bandwidth?              decimal64


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               +--rw unreserved-bandwidth* [priority]
               |  +--rw priority     uint8
               |  +--rw bandwidth?   decimal64
               +--ro distance?                        uint32
               +--rw te-metric?                       uint32
               +--rw link-protection-type?            enumeration
               +--rw switching-capability?            switching-
capabilities
               +--rw encoding?                        encoding-types
               +--rw switching-capability-specific
               +--rw srlg
                  +--rw srlg-values* [srlg-value]
                     +--rw srlg-value    uint32
notifications:
   +---n link-failure
   |  +--ro topology-id     leafref
   |  +--ro link-id         leafref
   |  +--ro admin-status?   leafref
   |  +--ro oper-status     leafref
   +---n node-failure
      +--ro topology-id    leafref
      +--ro link-id        leafref


4.1.1. The node and link list
   The Layer One Topology module contains all the nodes and links
   information pertaining to a layer one network. The node is
   identified by the node-id, which is unique within the network.
   Within the nodes, all the interfaces pertaining to this node and
   their potential capabilities/constraints SHOULD be present. Besides
   this, the constraints associated with a node as a whole SHOULD also
   be present, such as the connectivity constraints introduced due to
   abstraction or due to the hardware limitations. The link is
   identified by the link-id, which is unique within a node. It
   includes the association with nodes as well as interfaces. Moreover,
   it includes information that is of interest to the I2RS client, for
   purposes, such as path computation, monitoring etc.

4.1.2. Notification

   Two types of notifications are introduced: node failure and link
   failure.

4.2. YANG Code

<CODE BEGINS> file "l1topo.yang"



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module ietf-layer1topology {
  yang-version 1;

  namespace
    "urn:ietf:params:xml:ns:yang:ietf-layer1topology";
  prefix "l1topo";

  import ietf-inet-types {
    prefix "inet";
  }
  import ietf-interfaces {
    prefix "if";
  }

  organization
    "Internet Engineering Task Force (IETF) I2RS WG";
  contact
    "ID-draft editor: zhang.xian@huawei.com";

  description
    "This module defines a data-plan technology/protocol
    independent Layer One topology data model.";

  revision 2015-03-09 {
    description
      "Initial version.";
    reference
      "draft-zhang-i2rs-l1-topo-yang-model-01.txt";
  }

  /*
  * Typedefs
  */

  typedef topology-id {
    type inet:uri;
    description "the identifier for a topology";
  }

  typedef node-id {
    type inet:ip-address;
    description
      "the identifier for a node";
  }

  typedef interface-id {
    type union {


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      type inet:ip-address; // IPv4 or IPv6 address
      type int32;          // Un-numbered
    }
  description
    "the identifier of an interface within a node, supporting both
    numbered/unnumbered";
  }

  typedef link-id {
    type inet:ip-address; // IPv4 or IPv6 address
    description "the identifier of a link";
  }

  typedef switching-capabilities {
    type enumeration {
      enum "psc-1" {
        value 1;
        description
          "Packet-Switch Capable-1 (PSC-1)";
      }
      enum "evpl" {
        value 30;
        description
          "Ethernet Virtual Private Line (EVPL)";
      }

      enum "pbb-te"{
        value 40;
        description
          "802_1 PBB-TE";
      }

      enum "l2sc" {
        value 51;
        description
          "Layer-2 Switch Capable (L2SC)";
      }
      enum "tdm" {
        value 100;
        description
          "Time-Division-Multiplex Capable (TDM)";
      }
      enum "otn-tdm" {
        value 110;
        description
          "OTN-TDM Capable";
      }


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      enum "lsc" {
        value 150;
        description
          "Lambda-Switch Capable (LSC)";
      }
      enum "fsc" {
        value 200;
        description
          "Fiber-Switch Capable (FSC)";
      }
    }

    description
      "Switching capability of an interface.
      Only a subset of the above-mentioned values are applicable
      to Layer 1 network.
      Here it is included for completeness and will later be
      updated if a base model is augmented to create layer 1
      network topology YANG data model.";

    reference
      "The definition of switching types, their values and the
      relevant RFCs can be found at:
      http://www.iana.org/assignments/gmpls-sig-parameters/gmpls
      -sig-parameters.xhtml#gmpls-sig-parameters-3";
  }

  typedef encoding-types {
    type enumeration {
      enum "packet" {
        value 1;
        description "Packet";
      }
      enum "ethernet" {
        value 2;
        description "Ethernet";
      }
      enum "pdh" {
        value 3;
        description "PDH";
      }
      enum "sdh-sonet" {
        value 5;
        description "SDH/SONET";
      }
      enum "digital-wrapper" {
        value 7;


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        description "Digital Wrapper";
      }
      enum "lambda" {
        value 8;
        description "Lambda(photonic)";
      }
      enum "fiber" {
        value 9;
        description "Fiber";
      }
      enum "fiber-channel" {
        value 11;
        description "FiberChannel";
      }
      enum "oduk" {
        value 12;
        description
          "G.709 OKUk (Digital Path)";
      }
      enum "optical-channel" {
        value 13;
        description "G.709 Optical Channel";
      }
      enum "line" {
        value 14;
        description "Line (e.g., 8B/10B)";
      }
    }
    description
      "The encoding type supported by an interface or link.
      Not all encoding types are applicable to Layer one network
      nodes. They are included here for completeness and will be
      updated if a base model is available to augment
      so as to build a layer-one specific YANG data model.";
    reference
      "The definition of encoding types, their values and the
      relevant RFCs can be found at http://www.iana.org/
      assignments/gmpls-sig-parameters/gmpls-sig-parameters.xhtml#
      gmpls-sig-parameters-3";
  }

  /*
   * Groupings
  */

  grouping srlg-attribute {
    description


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      "Shared Risk Link Group Attributes";
    reference
      "RFC 4203: OSPF Extensions in Support of Generalized
      Multi-Protocol Label Switching (GMPLS)";
    list srlg-values {
      key "srlg-value";
      leaf srlg-value {
        type uint32;
        description "SRLG value";
      }
    description
      "the SRLG value list";
    }
  }

  /*
   * Configuration data nodes
   */

  container layer-one-topology {
    description
      "this container holds all the inforamtion to layer
      one network. It includes one or multiple topologies";

    list topology {
      key "topology-id";

      description
        "This contains all the information to one topoogy";

      leaf topology-id {
        type topology-id;
        description "topology identifier";
      }

      leaf name {
        type string;
        description "topology name";
      }

      list supporting-topology {
        key "topo-ref";
        leaf topo-ref {
          type leafref {
            path "/layer-one-topology/topology/topology-id";
          }
          description


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            "a Layer-One network might be supported by a lower
            layer network and this is a pointer to the suporting
            topology if there is one";
        }
        description "underlaying topology information";
      }

      list node {
        key "node-id";
        description "the list of nodes within the topology";

        leaf node-id {
          type node-id;
          description "node identifier";
        }

        list interface {
          key "interface-id";
          leaf interface-id {
            type interface-id;
            description "interface identifier";
          }
          leaf interface-name {
            type if:interface-state-ref;
            description
            "Name of the incoming interface.";
          }
          container adaptation-capability {
            description
            "TBD -to add for technology specific information";
          }
          description "interface list pertaining to a node";
        }

        list connectivity-matrix {
          key "id";

          description
            "This describes the connectivity contraints within
            a node in the network. It can be one matrix or a set
            of matrixes. Further details, read the reference
            provided below.";
          reference
            "https://tools.ietf.org/html/draft-ietf-ccamp-general
            -constraint-encode-16 Section 2.1";

          leaf id {


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            type uint32;
            description "matrix id";
          }
          leaf type {
            type enumeration {
              enum fixed {
                value 0;
                description "Fixed";
              }
              enum dynamic {
                value 1;
                description "Dynamic/changeable";
              }
            }
            description
              "This field describes the attribute of a
              connectivity matrix, i.e., whether it is
              fixed or switched.";
          }
          list in-interface {
            key "interface-ref";

            description
              "This list describes a (sub)-set of ingoing
              interfaces within a node that may have
              connectivity constraints.
              Note: directionality may not be relevant
               and it is decided by the dir parameter.";

            leaf interface-ref {
              type leafref {
                path "/layer-one-topology/topology/node/" +
                "interface/interface-id";
              }
              description "reference to an incoming interface";
            }
          }
          list out-interface {
            key "interface-ref";

            description
              "This list describes a (sub)-set of outgoing
              interfaces within a node that may have
              connectivity constraints.
              Note: directionality may not be relevant and
              it is decided by the dir parameter.";



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            leaf interface-ref {
              type leafref {
                path "/layer-one-topology/topology/node/"+
                "interface/interface-id";
              }
              description "reference to an outgoing interface";
            }
          }
          leaf dir{
            type enumeration{
              enum "uni-dir"{
                description
                "the matrix is unidirectional.";
              }
              enum "bi-dir"{
                description
                "this matrix is bidirecdtional.";
              }
            }
            description
             "the directionality attribute of a connc. matrix.";
          }
        }
      }// end of node data node

      list link {
        key "link-id";

        description "list of the links within a topology";

        leaf link-id {
          type link-id;
          description
            "remaining issue: if there is no IP addresses
             associated with this link, what would be the key?";
        }

        container local {
          description "near end information for this link";

          leaf local-node {
            type leafref {
              path "/l1topo:layer-one-topology/topology"+
              "/node/node-id";
            }
            mandatory true;
            description "refence to the local node";


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          }
          leaf local-interface {
            type leafref {
              path "/l1topo:layer-one-topology/topology/node/"
              +"interface/interface-id";
            }
            mandatory true;
            description "reference to the local interface";
          }
        }
        container remote {
          description "far end information of this link";

          leaf remote-node {
            type leafref {
              path "/l1topo:layer-one-topology/topology"+
              "/node/node-id";
            }
            mandatory true;
            description "reference to the remote node";
          }
          leaf remote-interface {
            type leafref {
              path "/l1topo:layer-one-topology/topology/node/"
              + "interface/interface-id";
            }
            mandatory true;
            description "reference to the remote interface";
          }
        }
        list supporting-path {
          key "supporting-path-index";

          description
            "information pertaining to the underlying path if
             there is any";

          leaf supporting-path-index {
            type uint32;
            description "the identifer of the supporting path";
          }
          leaf topo-ref {
            type leafref {
              path "/l1topo:layer-one-topology/"+
              "topology/topology-id";
            }
            description "reference to the underlying topology";


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          }
          container server-path-identifier {
            description "TBD";
          }
          container server-path-srlg {
            uses srlg-attribute;
            description "the SRLG values of the server path";
          }
        }

        container attributes {

          description "additional information of the link";

          leaf information-source {
            type enumeration {
              enum "unknown" {
                description "The source is unknown";
              }
              enum "locally-configured" {
                description "Configured TE link";
              }
              enum "ospfv2" {
                description "OSPFv2";
              }
              enum "ospfv3" {
                description "OSPFv3";
              }
              enum "isis" {
                description "ISIS";
              }
            }
            config false;

            description
              "Indicates the source of the information about
              the link. remaining issue: if configuration of
              a link is allowed, what additional types are
              needed to add?";
          }
          leaf credibility-preference {
            type uint16;
            config false;
            description "the level of credibility";
          }
          leaf admin-status {
            type enumeration {


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              enum up {
                value 1;
                description "up";
              }
              enum down {
                value 2;
                description "down";
              }
              enum testing {
                value 3;
                description "testing - in some test mode.";
              }
            }
            description
              "The adminstrative state of the link.";
            reference
              "RFC2863: The Interfaces Group MIB.";
          }
          leaf oper-status {
            type enumeration {
              enum up {
                value 1;
                description "up";
              }
              enum down {
                value 2;
                description "down";
              }
              enum testing {
                value 3;
                description "testing - in some test mode";
              }
              enum unknown {
                value 4;
                description "unknown - status cannot be
                determined for some reason.";
              }
              enum dormant{
                value 5;
                description "dormant";
              }
            }
            config false;
            description
              "The current operational state of the link.";
            reference
              "RFC2863: The Interfaces Group MIB.";


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          }
          leaf area-id {
            type binary {
              length 1..13;
            }
            description
              "This object indicates the area identifier of
              the IGP. If OSPF is used to advertise LSA,
              this represents an ospfArea. If IS-IS is used,
               this represents an area address.
               Otherwise, this is zero.";
            reference
              "RFC4920: Crankback Signaling Extensions for MPLS
              and GMPLS RSVP-TE.";
          }

          leaf max-link-bandwidth {
            type decimal64 {
              fraction-digits 2;
            }
            description
              "the max bandwidth supported by this link";
          }

          list unreserved-bandwidth {
            key "priority";
            max-elements "8";

            description
              "This describes the unreserved bandwidth (in
              Bytes/second) on a level basis ( level 0-7).";

            leaf priority {
              type uint8{
                range "0..7";
              }
              description "priority level";
            }
            leaf bandwidth {
              type decimal64 {
                fraction-digits 2;
              }
              description "badnwidth per priority";
            }
          }

          leaf distance {


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            type  uint32;
            units "kilometers";

            config false;
            description
              "the distance this link spans.";
          }
          leaf te-metric {
            type uint32;
            description "the metric supported by the link";
          }

          leaf link-protection-type {
            type enumeration {
              enum "extra-traffic" {
                value 1;
                description "Extra traffic";
              }
              enum "unprotected" {
                value 2;
                description "unprotected";
              }
              enum "shared" {
                 value 4;
                description "Shared";
              }
              enum "1-for-1" {
                value 8;
                description "Dedicated one for one protection";
              }
              enum "1-plus-1" {
                value 16;
               description "Dedicated one plus one protection";
              }
              enum "enhanced" {
                value 32;
                description "a protection type that is
                more reliable than Dedicated 1+1,
                e.g.,4 fiber BLSR/MS-SPRING.";
              }
            }
            description
              "Link Protection Type configured for this link";
            reference
              "RFC3471: Generalized MUlti-Protocol Label
               Switching (GMPLS) Signaling Functional
               Description.";


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          }

          leaf switching-capability {
            type switching-capabilities;
            description
              "the switching capability supported by the link";
          }
          leaf encoding {
            type encoding-types;
            description
              "the encoding type supported by this link.";
          }

          container switching-capability-specific {
            description
            "TBD - to add for technology specific information";
          }
          container srlg {
            uses srlg-attribute;
            description " the SRLG values of a link";
          }
        }// end of link attributes
      }// end of link leaf data node
    }
  }// end of configuring data nodes

  /*
  * notifications - only provide operational change information.
  * reply to topology/node/link creation is acked via rpc-reply.
  */

  notification link-failure {
    leaf topology-id {
      type leafref {
        path "/layer-one-topology/topology/topology-id";
      }
      mandatory true;
      description "";
    }
    leaf link-id {
      type leafref {
        path
          "/layer-one-topology/topology[topology-id="+
          "current ()/../topology-id]/link/link-id";
      }
      mandatory true;
      description "";


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    }
    leaf admin-status {
      type leafref {
        path
          "/layer-one-topology/topology/link[link-id =" +
          "current()/../link-id]/attributes/admin-status";
      }
      description "";
    }
    leaf oper-status {
      type leafref {
        path
          "/layer-one-topology/topology/" +
          "link[link-id = current()/../link-id]"
          + "/attributes/oper-status";
      }
      mandatory true;
      description "";
    }
    description
      "link failure information";
  } //notification

  notification node-failure {
    leaf topology-id {
      type leafref {
        path "/layer-one-topology/topology/topology-id";
      }
      mandatory true;
      description "";
    }
    leaf link-id {
      type leafref {
        path
          "/layer-one-topology/topology[topology-id= "
          + "current ()/../topology-id]/node/node-id";
      }
      mandatory true;
      description "";
    }
    description
    "node failure information";
  } //notification
}//module

<CODE ENDS>



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5. Security Considerations

   Since the data model defined in this draft is manipulated vis the
   I2RS interface. The security concerns mentioned in [draft-ietf-i2rs-
   architecture] also applies to this draft.

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory-to-implement secure
   transport is SSH [RFC6242].  The NETCONF access control model
   [RFC6536] provides the means to restrict access for particular
   NETCONF users to a pre-configured subset of all available NETCONF
   protocol operations and content.

   There are a number of data nodes defined in the YANG module which
   are writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or ulnerable
   in some network environments.  Write operations (e.g., <edit-config>)
   to these data nodes without proper protection can have a negative
   effect on network operations.

   [Editor's note: to List specific subtrees and data nodes and their
   sensitivity/vulnerability.]

6. Manageability Considerations

   TBD.

7. IANA Considerations

   TBD.

8. Acknowledgements

   The initial YANG model specified in this draft is based on draft-
   clemm-i2rs-yang-network-topo but it is modified according to the
   features of the layer one networks.

   We would like to thank the authors of the above mentioned draft for
   their helpful discussion during the creation of this draft.




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9. References

9.1. Normative References

   [RFC2119] S. Bradner, "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

   [RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
             Network Configuration Protocol (NETCONF)", RFC 6020,
             October 2010.

9.2. Informative References

   [draft-ietf-i2rs-architecture] Atlas, A., Halpern, J., Hares, S.,
             Ward, D., Nadeau T., "An Architecture for the Interface to
             the Routing System", draft-ietf-i2rs-architecture-08, work
             in progress, January 2015;

   [draft-clemm-i2rs-yang-network-topo] Clemm A., Medved J., Tkacik T.,
             Varga R., et al, "A YANG Data Model for Network
             Topologies", draft-clemm-i2rs-yang-network-topo-01, work
             in progress, October 2014;

   [ietf-netmod-rfc6087bis] Bierman, A., "Guidelines for Authors and
             Reviewers of YANG  Data Model Documents", draft-ietf-
             netmod-rfc6087bis-01, work in progress, October 2014.

   [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
             Bierman, "Network Configuration Protocol (NETCONF)",
             RFC6241, June 2011.

   [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
             Shell (SSH)", RFC 6242, June 2011.

   [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
             Protocol (NETCONF) Access Control Model", RFC 6536, March
             2012.

10. Contributors' Addresses

   TBD.

11. Authors' Addresses

   Xian Zhang
   Huawei Technologies
   Email: zhang.xian@huawei.com


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   Baoquan Rao
   Huawei Technologies
   raobaoquan@huawei.com

   Xufeng Liu
   Ericsson
   xufeng.liu@ericsson.com








































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