module ietf-network-topology {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-network-topology";
  prefix nt;

  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-network {
    prefix nw;
    reference
      "RFC 8345: A YANG Data Model for Network Topologies";
  }

  organization
    "IETF I2RS (Interface to the Routing System) Working Group";

  contact
    "WG Web:    <https://datatracker.ietf.org/wg/i2rs/>
     WG List:   <mailto:i2rs@ietf.org>

     Editor:    Alexander Clemm
                <mailto:ludwig@clemm.org>

     Editor:    Jan Medved
                <mailto:jmedved@cisco.com>

     Editor:    Robert Varga
                <mailto:robert.varga@pantheon.tech>

     Editor:    Nitin Bahadur
                <mailto:nitin_bahadur@yahoo.com>

     Editor:    Hariharan Ananthakrishnan
                <mailto:hari@packetdesign.com>

     Editor:    Xufeng Liu
                <mailto:xufeng.liu.ietf@gmail.com>";

  description
    "This module defines a common base model for a network topology,
     augmenting the base network data model with links to connect
     nodes, as well as termination points to terminate links
     on nodes.

     Copyright (c) 2018 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject
     to the license terms contained in, the Simplified BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC 8345;
     see the RFC itself for full legal notices.";

  revision 2018-02-26 {
    description
      "Initial revision.";
    reference
      "RFC 8345: A YANG Data Model for Network Topologies";
  }

  typedef link-id {
    type inet:uri;
    description
      "An identifier for a link in a topology.  The precise
       structure of the link-id will be up to the implementation.
       The identifier SHOULD be chosen such that the same link in a
       real network topology will always be identified through the
       same identifier, even if the data model is instantiated in
       separate datastores.  An implementation MAY choose to capture
       semantics in the identifier -- for example, to indicate the
       type of link and/or the type of topology of which the link is
       a part.";
  }

  typedef tp-id {
    type inet:uri;
    description
      "An identifier for termination points on a node.  The precise
       structure of the tp-id will be up to the implementation.
       The identifier SHOULD be chosen such that the same termination
       point in a real network topology will always be identified
       through the same identifier, even if the data model is
       instantiated in separate datastores.  An implementation MAY
       choose to capture semantics in the identifier -- for example,
       to indicate the type of termination point and/or the type of
       node that contains the termination point.";
  }

  grouping link-ref {
    description
      "This grouping can be used to reference a link in a specific
       network.  Although it is not used in this module, it is
       defined here for the convenience of augmenting modules.";
    leaf link-ref {
      type leafref {
        path "/nw:networks/nw:network[nw:network-id=current()/../"+
          "network-ref]/nt:link/nt:link-id";
        require-instance false;
      }
      description
        "A type for an absolute reference to a link instance.
         (This type should not be used for relative references.
         In such a case, a relative path should be used instead.)";
    }
    uses nw:network-ref;
  }

  grouping tp-ref {
    description
      "This grouping can be used to reference a termination point
       in a specific node.  Although it is not used in this module,
       it is defined here for the convenience of augmenting
       modules.";
    leaf tp-ref {
      type leafref {
        path "/nw:networks/nw:network[nw:network-id=current()/../"+
          "network-ref]/nw:node[nw:node-id=current()/../"+
          "node-ref]/nt:termination-point/nt:tp-id";
        require-instance false;
      }
      description
        "A type for an absolute reference to a termination point.
         (This type should not be used for relative references.
         In such a case, a relative path should be used instead.)";
    }
    uses nw:node-ref;
  }

  augment "/nw:networks/nw:network" {
    description
      "Add links to the network data model.";
    list link {
      key "link-id";
      description
        "A network link connects a local (source) node and
         a remote (destination) node via a set of the respective
         node's termination points.  It is possible to have several
         links between the same source and destination nodes.
         Likewise, a link could potentially be re-homed between
         termination points.  Therefore, in order to ensure that we
         would always know to distinguish between links, every link
         is identified by a dedicated link identifier.  Note that a
         link models a point-to-point link, not a multipoint link.";
      leaf link-id {
        type link-id;
        description
          "The identifier of a link in the topology.
           A link is specific to a topology to which it belongs.";
      }
      container source {
        description
          "This container holds the logical source of a particular
           link.";
        leaf source-node {
          type leafref {
            path "../../../nw:node/nw:node-id";
            require-instance false;
          }
          description
            "Source node identifier.  Must be in the same topology.";
        }
        leaf source-tp {
          type leafref {
            path "../../../nw:node[nw:node-id=current()/../"+
              "source-node]/termination-point/tp-id";
            require-instance false;
          }
          description
            "This termination point is located within the source node
             and terminates the link.";
        }
      }

      container destination {
        description
          "This container holds the logical destination of a
           particular link.";
        leaf dest-node {
          type leafref {
            path "../../../nw:node/nw:node-id";
          require-instance false;
          }
          description
            "Destination node identifier.  Must be in the same
             network.";
        }
        leaf dest-tp {
          type leafref {
            path "../../../nw:node[nw:node-id=current()/../"+
              "dest-node]/termination-point/tp-id";
            require-instance false;
          }
          description
            "This termination point is located within the
             destination node and terminates the link.";
        }
      }
      list supporting-link {
        key "network-ref link-ref";
        description
          "Identifies the link or links on which this link depends.";
        leaf network-ref {
          type leafref {
            path "../../../nw:supporting-network/nw:network-ref";
          require-instance false;
          }
          description
            "This leaf identifies in which underlay topology
             the supporting link is present.";
        }

        leaf link-ref {
          type leafref {
            path "/nw:networks/nw:network[nw:network-id=current()/"+
              "../network-ref]/link/link-id";
            require-instance false;
          }
          description
            "This leaf identifies a link that is a part
             of this link's underlay.  Reference loops in which
             a link identifies itself as its underlay, either
             directly or transitively, are not allowed.";
        }
      }
    }
  }
  augment "/nw:networks/nw:network/nw:node" {
    description
      "Augments termination points that terminate links.
       Termination points can ultimately be mapped to interfaces.";
    list termination-point {
      key "tp-id";
      description
        "A termination point can terminate a link.
         Depending on the type of topology, a termination point
         could, for example, refer to a port or an interface.";
      leaf tp-id {
        type tp-id;
        description
          "Termination point identifier.";
      }
      list supporting-termination-point {
        key "network-ref node-ref tp-ref";
        description
          "This list identifies any termination points on which a
           given termination point depends or onto which it maps.
           Those termination points will themselves be contained
           in a supporting node.  This dependency information can be
           inferred from the dependencies between links.  Therefore,
           this item is not separately configurable.  Hence, no
           corresponding constraint needs to be articulated.
           The corresponding information is simply provided by the
           implementing system.";

        leaf network-ref {
          type leafref {
            path "../../../nw:supporting-node/nw:network-ref";
          require-instance false;
          }
          description
            "This leaf identifies in which topology the
             supporting termination point is present.";
        }
        leaf node-ref {
          type leafref {
            path "../../../nw:supporting-node/nw:node-ref";
          require-instance false;
          }
          description
            "This leaf identifies in which node the supporting
             termination point is present.";
        }
        leaf tp-ref {
          type leafref {
            path "/nw:networks/nw:network[nw:network-id=current()/"+
              "../network-ref]/nw:node[nw:node-id=current()/../"+
              "node-ref]/termination-point/tp-id";
            require-instance false;
          }
          description
            "Reference to the underlay node (the underlay node must
             be in a different topology).";
        }
      }
    }
  }
}