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RFC 6095 - Extending YANG with Language Abstractions


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Internet Engineering Task Force (IETF)                       B. Linowski
Request for Comments: 6095                    TCS/Nokia Siemens Networks
Category: Experimental                                          M. Ersue
ISSN: 2070-1721                                   Nokia Siemens Networks
                                                               S. Kuryla
                                                    360 Treasury Systems
                                                              March 2011

               Extending YANG with Language Abstractions

Abstract

   YANG -- the Network Configuration Protocol (NETCONF) Data Modeling
   Language -- supports modeling of a tree of data elements that
   represent the configuration and runtime status of a particular
   network element managed via NETCONF.  This memo suggests enhancing
   YANG with supplementary modeling features and language abstractions
   with the aim to improve the model extensibility and reuse.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6095.

Copyright Notice

   Copyright (c) 2011 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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Key Words  . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Modeling Improvements with Language Abstractions . . . . .  5
     1.4.  Design Approach  . . . . . . . . . . . . . . . . . . . . .  6
     1.5.  Modeling Resource Models with YANG . . . . . . . . . . . .  6
       1.5.1.  Example of a Physical Network Resource Model . . . . .  6
       1.5.2.  Modeling Entity MIB Entries as Physical Resources  . . 12
   2.  Complex Types  . . . . . . . . . . . . . . . . . . . . . . . . 15
     2.1.  Definition . . . . . . . . . . . . . . . . . . . . . . . . 15
     2.2.  complex-type Extension Statement . . . . . . . . . . . . . 15
     2.3.  instance Extension Statement . . . . . . . . . . . . . . . 17
     2.4.  instance-list Extension Statement  . . . . . . . . . . . . 18
     2.5.  extends Extension Statement  . . . . . . . . . . . . . . . 19
     2.6.  abstract Extension Statement . . . . . . . . . . . . . . . 19
     2.7.  XML Encoding Rules . . . . . . . . . . . . . . . . . . . . 20
     2.8.  Type Encoding Rules  . . . . . . . . . . . . . . . . . . . 20
     2.9.  Extension and Feature Definition Module  . . . . . . . . . 21
     2.10. Example Model for Complex Types  . . . . . . . . . . . . . 24
     2.11. NETCONF Payload Example  . . . . . . . . . . . . . . . . . 25
     2.12. Update Rules for Modules Using Complex Types . . . . . . . 26
     2.13. Using Complex Types  . . . . . . . . . . . . . . . . . . . 26
       2.13.1. Overriding Complex Type Data Nodes . . . . . . . . . . 26
       2.13.2. Augmenting Complex Types . . . . . . . . . . . . . . . 27
       2.13.3. Controlling the Use of Complex Types . . . . . . . . . 28
   3.  Typed Instance Identifier  . . . . . . . . . . . . . . . . . . 29
     3.1.  Definition . . . . . . . . . . . . . . . . . . . . . . . . 29
     3.2.  instance-type Extension Statement  . . . . . . . . . . . . 29
     3.3.  Typed Instance Identifier Example  . . . . . . . . . . . . 30
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 31
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 31

   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 32
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 32
   Appendix A.  YANG Modules for Physical Network Resource Model
                and Hardware Entities Model . . . . . . . . . . . . . 34
   Appendix B.  Example YANG Module for the IPFIX/PSAMP Model . . . . 40
     B.1.  Modeling Improvements for the IPFIX/PSAMP Model with
           Complex Types and Typed Instance Identifiers . . . . . . . 40
     B.2.  IPFIX/PSAMP Model with Complex Types and Typed
           Instance Identifiers . . . . . . . . . . . . . . . . . . . 41

1.  Introduction

   YANG -- the NETCONF Data Modeling Language [RFC6020] -- supports
   modeling of a tree of data elements that represent the configuration
   and runtime status of a particular network element managed via
   NETCONF.  This document defines extensions for the modeling language
   YANG as new language statements, which introduce language
   abstractions to improve the model extensibility and reuse.  The
   document reports from modeling experience in the telecommunication
   industry and gives model examples from an actual network management
   system to highlight the value of proposed language extensions,
   especially class inheritance and recursiveness.  The language
   extensions defined in this document have been implemented with two
   open source tools.  These tools have been used to validate the model
   examples through the document.  If this experimental specification
   results in successful usage, it is possible that the language
   extensions defined herein could be updated to incorporate
   implementation and deployment experience, then pursued on the
   Standards Track, possibly as part of a future version of YANG.

1.1.  Key Words

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

1.2.  Motivation

   Following are non-exhaustive motivation examples highlighting usage
   scenarios for language abstractions.

   o  Many systems today have a Management Information Base (MIB) that
      in effect is organized as a tree build of recursively nested
      container nodes.  For example, the physical resources in the
      ENTITY-MIB conceptually form a containment tree.  The index

      entPhysicalContainedIn points to the containing entity in a flat
      list.  The ability to represent nested, recursive data structures
      of arbitrary depth would enable the representation of the primary
      containment hierarchy of physical entities as a node tree in the
      server MIB and in the NETCONF payload.

   o  A manager scanning the network in order to update the state of an
      inventory management system might be only interested in data
      structures that represent a specific type of hardware.  Such a
      manager would then look for entities that are of this specific
      type, including those that are an extension or specialization of
      this type.  To support this use case, it is helpful to bear the
      corresponding type information within the data structures, which
      describe the network element hardware.

   o  A system that is managing network elements is concerned, e.g.,
      with managed objects of type "plug-in modules" that have a name, a
      version, and an activation state.  In this context, it is useful
      to define the "plug-in module" as a concept that is supposed to be
      further detailed and extended by additional concrete model
      elements.  In order to realize such a system, it is worthwhile to
      model abstract entities, which enable reuse and ease concrete
      refinements of that abstract entity in a second step.

   o  As particular network elements have specific types of components
      that need to be managed (OS images, plug-in modules, equipment,
      etc.), it should be possible to define concrete types, which
      describe the managed object precisely.  By using type-safe
      extensions of basic concepts, a system in the manager role can
      safely and explicitly determine that e.g., the "equipment" is
      actually of type "network card".

   o  Currently, different SDOs are working on the harmonization of
      their management information models.  Often, a model mapping or
      transformation between systems becomes necessary.  The
      harmonization of the models is done e.g., by mapping of the two
      models on the object level or integrating an object hierarchy into
      an existing information model.  On the one hand, extending YANG
      with language abstractions can simplify the adoption of IETF
      resource models by other SDOs and facilitate the alignment with
      other SDOs' resource models (e.g., TM Forum SID [SID_V8]).  On the
      other hand, the proposed YANG extensions can enable the
      utilization of the YANG modeling language in other SDOs, which
      usually model complex management systems in a top-down manner and
      use high-level language features frequently.

   This memo specifies additional modeling features for the YANG
   language in the area of structured model abstractions, typed
   references, as well as recursive data structures, and it discusses
   how these new features can improve the modeling capabilities of YANG.

   Section 1.5.1 contains a physical resource model that deals with some
   of the modeling challenges illustrated above.  Section 1.5.2 gives an
   example that uses the base classes defined in the physical resource
   model and derives a model for physical entities defined in the Entity
   MIB.

1.3.  Modeling Improvements with Language Abstractions

   As an enhancement to YANG 1.0, complex types and typed instance
   identifiers provide different technical improvements on the modeling
   level:

   o  In case the model of a system that should be managed with NETCONF
      makes use of inheritance, complex types enable an almost one-to-
      one mapping between the classes in the original model and the YANG
      module.

   o  Typed instance identifiers allow representing associations between
      the concepts in a type-safe way to prevent type errors caused by
      referring to data nodes of incompatible types.  This avoids
      referring to a particular location in the MIB.  Referring to a
      particular location in the MIB is not mandated by the domain
      model.

   o  Complex types allow defining complete, self-contained type
      definitions.  It is not necessary to explicitly add a key
      statement to lists, which use a grouping that defines the data
      nodes.

   o  Complex types simplify concept refinement by extending a base
      complex type and make it superfluous to represent concept
      refinements with workarounds such as huge choice-statements with
      complex branches.

   o  Abstract complex types ensure correct usage of abstract concepts
      by enforcing the refinement of a common set of properties before
      instantiation.

   o  Complex types allow defining recursive structures.  This enables
      representing complex structures of arbitrary depth by nesting
      instances of basic complex types that may contain themselves.

   o  Complex types avoid introducing metadata types (e.g., type code
      enumerations) and metadata leafs (e.g., leafs containing a type
      code) to indicate which concrete type of object is actually
      represented by a generic container in the MIB.  This also avoids
      explicitly ruling out illegal use of subtype-specific properties
      in generic containers.

   o  Complex type instances include the type information in the NETCONF
      payload.  This allows determining the actual type of an instance
      during the NETCONF payload parsing and avoids the use in the model
      of additional leafs, which provide the type information as
      content.

   o  Complex types may be declared explicitly as optional features,
      which is not possible when the actual type of an entity
      represented by a generic container is indicated with a type code
      enumeration.

   Appendix B, "Example YANG Module for the IPFIX/PSAMP Model", lists
   technical improvements for modeling with complex types and typed
   instance identifiers and exemplifies the usage of the proposed YANG
   extensions based on the IP Flow Information Export (IPFIX) / Packet
   Sampling (PSAMP) configuration model in [IPFIXCONF].

1.4.  Design Approach

   The proposed additional features for YANG in this memo are designed
   to reuse existing YANG statements whenever possible.  Additional
   semantics is expressed by an extension that is supposed to be used as
   a substatement of an existing statement.

   The proposed features don't change the semantics of models that is
   valid with respect to the YANG specification [RFC6020].

1.5.  Modeling Resource Models with YANG

1.5.1.  Example of a Physical Network Resource Model

   The diagram below depicts a portion of an information model for
   manageable network resources used in an actual network management
   system.

   Note: The referenced model (UDM, Unified Data Model) is based on key
   resource modeling concepts from [SID_V8] and is compliant with
   selected parts of SID Resource Abstract Business Entities domain
   [UDM].

   The class diagram in Figure 1 and the corresponding YANG module
   excerpt focus on basic resource ("Resource" and the distinction
   between logical and physical resources) and hardware abstractions
   ("Hardware", "Equipment", and "EquipmentHolder").  Class attributes
   were omitted to achieve decent readability.

+--------+
|Resource|
+--------+
 /\   /\
 --   --
 |    |
 |  +---------------+
 |  |LogicalResource|
 |  +---------------+
 |
 | +--------+
 | |Physical|      +-----------+
 '-|Resource|<|-+-|PhysicalLink|
   +---- ---+   | +------------+
                |     |0..* physicalLink
                |     |                                       equipment
                |     |                                       Holder
                |     |                                       0..*
                |     |                                       +-------+
                |     |0..* hardware                          |       |
                | +--------+     +---------------+     +---------+    |
                '-|Hardware|<|-+-|ManagedHardware|<|-+-|Equipment|<>--+
                  +--------+   | +---------------+   | | Holder  |0..1
                      <>       |                     | +---------+
                  0..1|        |                     |   <>
                      |        |                     |   |0..* equipment
                      |        |                     |   |     Holder
                      |        |                     |   |
                      |        |                     |   |0..* equipment
                      |        |                     |   |
                      |        |                     |   |    equipment
                      |        |                     |   |    0..*
                      |        |                     |   |    +-------+
                      |        |                     |   |    |       |
                      |        |                     | +---------+    |
                      |        |                     '-|Equipment|<>--+
                      |        |                       +---------+0..1
                      |        |                    compositeEquipment
                      |        |
                      |        | +-----------------+
                      |        '-|PhysicalConnector|----+0..* source
                      '----------+-----------------+    |     Physical
           physicalConnector 0..*           |           |     Connector
                                            |           |
                                            +-----------+
                                            0..* targetPhysicalConnector

                 Figure 1: Physical Network Resource Model

   Since this model is an abstraction of network-element-specific MIB
   topologies, modeling it with YANG creates some challenges.  Some of
   these challenges and how they can be addressed with complex types are
   explained below:

   o  Modeling of abstract concepts: Classes like "Resource" represent
      concepts that primarily serve as a base class for derived classes.
      With complex types, such an abstract concept could be represented
      by an abstract complex type (see "complex-type extension
      statement" and "abstract extension statement").

   o  Class Inheritance: Information models for complex management
      domains often use class inheritance to create specialized classes
      like "PhysicalConnector" from a more generic base class (here,
      "Hardware"), which itself might inherit from another base class
      ("PhysicalResource"), etc.  Complex types allow creating enhanced
      versions of an existing (abstract or concrete) base type via an
      extension (see "extends extension statement").

   o  Recursive containment: In order to specify containment
      hierarchies, models frequently contain different aggregation
      associations, in which the target (contained element) is either
      the containing class itself or a base class of the containing
      class.  In the model above, the recursive containment of
      "EquipmentHolder" is an example of such a relationship (see the
      description for the "complex-type EquipmentHolder" in the example
      model "udmcore" below).

   o  Complex types support such a containment by using a complex type
      (or one of its ancestor types) as the type of an instance or
      instance list that is part of its definition (see "instance(-list)
      extension statement").

   o  Reference relationships: A key requirement on large models for
      network domains with many related managed objects is the ability
      to define inter-class associations that represent essential
      relationships between instances of such a class.  For example, the
      relationship between "PhysicalLink" and "Hardware" tells which
      physical link is connecting which hardware resources.  It is
      important to notice that this kind of relationship does not
      mandate any particular location of the two connected hardware
      instances in any MIB module.  Such containment-agnostic
      relationships can be represented by a typed instance identifier
      that embodies one direction of such an association (see Section 3,
      "Typed Instance Identifier").

   The YANG module excerpt below shows how the challenges listed above
   can be addressed by the Complex Types extension (module import prefix
   "ct:").  The complete YANG module for the physical resource model in
   Figure 1 can be found in Appendix A, "YANG Modules for Physical
   Network Resource Model and Hardware Entities Model".

   Note: The YANG extensions proposed in this document have been
   implemented as the open source tools "Pyang Extension for Complex
   Types" [Pyang-ct], [Pyang], and "Libsmi Extension for Complex Types"
   [Libsmi].  All model examples in the document have been validated
   with the tools Pyang-ct and Libsmi.

<CODE BEGINS>

module udmcore {

   namespace "http://example.com/udmcore";
   prefix "udm";

   import ietf-complex-types {prefix "ct"; }

        // Basic complex types...

   ct:complex-type PhysicalResource {
      ct:extends Resource;
        ct:abstract true;
        // ...
        leaf serialNumber {
         type string;
         description "'Manufacturer-allocated part number' as
           defined in SID, e.g., the part number of a fiber link
           cable.";
      }
   }

   ct:complex-type Hardware {
      ct:extends PhysicalResource;
        ct:abstract true;
        // ...
       leaf-list physicalLink {
          type instance-identifier {ct:instance-type PhysicalLink;}
       }
       ct:instance-list containedHardware {
       ct:instance-type Hardware;
}
       ct:instance-list physicalConnector {
       ct:instance-type PhysicalConnector;

}
   }

   ct:complex-type PhysicalLink {
       ct:extends PhysicalResource;
       // ...
       leaf-list hardware {
          type instance-identifier {ct:instance-type Hardware;}
       }
   }

   ct:complex-type ManagedHardware {
      ct:extends Hardware;
        ct:abstract true;
        // ...
   }

   ct:complex-type PhysicalConnector {
      ct:extends Hardware;
        leaf location {type string;}
        // ...
      leaf-list sourcePhysicalConnector {
         type instance-identifier {ct:instance-type PhysicalConnector;}
      }
      leaf-list targetPhysicalConnector {
         type instance-identifier {ct:instance-type PhysicalConnector;}
      }
   }

   ct:complex-type Equipment {
      ct:extends ManagedHardware;
        // ...
      ct:instance-list equipment {
    ct:instance-type Equipment;
}
   }

   ct:complex-type EquipmentHolder {
      ct:extends ManagedHardware;
      description "In the SID V8 definition, this is a class based on
        the M.3100 specification.  A base class that represents physical
        objects that are both manageable as well as able to host,
        hold, or contain other physical objects.  Examples of physical

        objects that can be represented by instances of this object
        class are Racks, Chassis, Cards, and Slots.
        A piece of equipment with the primary purpose of containing
        other equipment.";
        leaf vendorName {type string;}
        // ...
      ct:instance-list equipment {
       ct:instance-type Equipment;
        }
      ct:instance-list equipmentHolder {
       ct:instance-type EquipmentHolder;
       }
   }
   // ...
}

<CODE ENDS>

1.5.2.  Modeling Entity MIB Entries as Physical Resources

   The physical resource module described above can now be used to model
   physical entities as defined in the Entity MIB [RFC4133].  For each
   physical entity class listed in the "PhysicalClass" enumeration, a
   complex type is defined.  Each of these complex types extends the
   most specific complex type already available in the physical resource
   module.  For example, the type "HWModule" extends the complex type
   "Equipment" as a hardware module.  Physical entity properties that
   should be included in a physical entity complex type are combined in
   a grouping, which is then used in each complex type definition of an
   entity.

   This approach has following benefits:

   o  The definition of the complex types for hardware entities becomes
      compact as many of the features can be reused from the basic
      complex type definition.

   o  Physical entities are modeled in a consistent manner as predefined
      concepts are extended.

   o  Entity-MIB-specific attributes as well as vendor-specific
      attributes can be added without having to define separate
      extension data nodes.

                            Module udmcore  :  Module hardware-entities
                                            :
                                equipment   :
                                Holder      :
                                0..*        :
                                +-------+   :
                                |       |   :
   +---------------+     +---------+    |   :
   |ManagedHardware|<|-+-|Equipment|<>--+   :
   +---------------+   | | Holder  |0..1    :     +-------+
                       | |         |<|---------+--|Chassis|
                       | +---------+        :  |  +-------+
                       |   <>               :  |
                       |   |0..* equipment  :  |  +---------+
                       |   |     Holder     :  '--|Container|
                       |   |                :     +---------+
                       |   |0..* equipment  :
                       |   |                :
                       |   |    equipment   :
                       |   |    0..*        :
                       |   |    +-------+   :
                       |   |    |       |   :
                       | +---------+    |   :
                       '-|Equipment|<>--+   :     +--------+
                         |         |<|---------+--|HWModule|
                         +---------+        :  |  +--------+
                      compositeEquipment    :  |
                                            :  |  +---------+
                                            :  |--|Backplane|
                                            :     +---------+

                     Figure 2: Hardware Entities Model

   Below is an excerpt of the corresponding YANG module using complex
   types to model hardware entities.  The complete YANG module for the
   Hardware Entities model in Figure 2 can be found in Appendix A, "YANG
   Modules for Physical Network Resource Model and Hardware Entities
   Model".

<CODE BEGINS>

module hardware-entities {

   namespace "http://example.com/hardware-entities";
   prefix "hwe";

   import ietf-yang-types {prefix "yt";}
   import ietf-complex-types {prefix "ct";}
   import udmcore {prefix "uc";}

   grouping PhysicalEntityProperties {
      // ...
      leaf mfgDate {type yang:date-and-time; }
      leaf-list uris {type string; }
   }

   // Physical entities representing equipment

   ct:complex-type HWModule {
      ct:extends uc:Equipment;
      description "Complex type representing module entries
                   (entPhysicalClass = module(9)) in entPhysicalTable";
      uses PhysicalEntityProperties;
   }

   // ...

   // Physical entities representing equipment holders

   ct:complex-type Chassis {
      ct:extends uc:EquipmentHolder;
      description "Complex type representing chassis entries
                   (entPhysicalClass = chassis(3)) in entPhysicalTable";
      uses PhysicalEntityProperties;
   }

   // ...
}

<CODE ENDS>

2.  Complex Types

2.1.  Definition

   YANG type concept is currently restricted to simple types, e.g.,
   restrictions of primitive types, enumerations, or union of simple
   types.

   Complex types are types with a rich internal structure, which may be
   composed of substatements defined in Table 1 (e.g., lists, leafs,
   containers, choices).  A new complex type may extend an existing
   complex type.  This allows providing type-safe extensions to existing
   YANG models as instances of the new type.

   Complex types have the following characteristics:

   o  Introduction of new types, as a named, formal description of a
      concrete manageable resource as well as abstract concepts.

   o  Types can be extended, i.e., new types can be defined by
      specializing existing types and adding new features.  Instances of
      such an extended type can be used wherever instances of the base
      type may appear.

   o  The type information is made part of the NETCONF payload in case a
      derived type substitutes a base type.  This enables easy and
      efficient consumption of payload elements representing complex
      type instances.

2.2.  complex-type Extension Statement

   The extension statement "complex-type" is introduced; it accepts an
   arbitrary number of statements that define node trees, among other
   common YANG statements ("YANG Statements", Section 7 of [RFC6020]).

                    +------------------+-------------+
                    |   substatement   | cardinality |
                    +------------------+-------------+
                    |     abstract     |     0..1    |
                    |      anyxml      |     0..n    |
                    |      choice      |     0..n    |
                    |     container    |     0..n    |
                    |    description   |     0..1    |
                    |    ct:instance   |     0..n    |
                    | ct:instance-list |     0..n    |
                    |    ct:extends    |     0..1    |
                    |     grouping     |     0..n    |
                    |    if-feature    |     0..n    |
                    |        key       |     0..1    |
                    |       leaf       |     0..n    |
                    |     leaf-list    |     0..n    |
                    |       list       |     0..n    |
                    |       must       |     0..n    |
                    |    ordered-by    |     0..n    |
                    |     reference    |     0..1    |
                    |      refine      |     0..n    |
                    |      status      |     0..1    |
                    |      typedef     |     0..n    |
                    |       uses       |     0..n    |
                    +------------------+-------------+

                   Table 1: complex-type's Substatements

   Complex type definitions may appear at every place where a grouping
   may be defined.  That includes the module, submodule, rpc, input,
   output, notification, container, and list statements.

   Complex type names populate a distinct namespace.  As with YANG
   groupings, it is possible to define a complex type and a data node
   (e.g., leaf, list, instance statements) with the same name in the
   same scope.  All complex type names defined within a parent node or
   at the top level of the module or its submodules share the same type
   identifier namespace.  This namespace is scoped to the parent node or
   module.

   A complex type MAY have an instance key.  An instance key is either
   defined with the "key" statement as part of the complex type or is
   inherited from the base complex type.  It is not allowed to define an
   additional key if the base complex type or one of its ancestors
   already defines a key.

   Complex type definitions do not create nodes in the schema tree.

2.3.  instance Extension Statement

   The "instance" extension statement is used to instantiate a complex
   type by creating a subtree in the management information node tree.
   The instance statement takes one argument that is the identifier of
   the complex type instance.  It is followed by a block of
   substatements.

   The type of the instance is specified with the mandatory "ct:
   instance-type" substatement.  The type of an instance MUST be a
   complex type.  Common YANG statements may be used as substatements of
   the "instance" statement.  An instance is optional by default.  To
   make an instance mandatory, "mandatory true" has to be applied as a
   substatement.

                    +------------------+-------------+
                    |   substatement   | cardinality |
                    +------------------+-------------+
                    |    description   |     0..1    |
                    |      config      |     0..1    |
                    | ct:instance-type |      1      |
                    |    if-feature    |     0..n    |
                    |     mandatory    |     0..1    |
                    |       must       |     0..n    |
                    |     reference    |     0..1    |
                    |      status      |     0..1    |
                    |       when       |     0..1    |
                    |      anyxml      |     0..n    |
                    |      choice      |     0..n    |
                    |     container    |     0..n    |
                    |    ct:instance   |     0..n    |
                    | ct:instance-list |     0..n    |
                    |       leaf       |     0..n    |
                    |     leaf-list    |     0..n    |
                    |       list       |     0..n    |
                    +------------------+-------------+

                     Table 2: instance's Substatements

   The "instance" and "instance-list" extension statements (see
   Section 2.4, "instance-list Extension Statement") are similar to the
   existing "leaf" and "leaf-list" statements, with the exception that
   the content is composed of subordinate elements according to the
   instantiated complex type.

   It is also possible to add additional data nodes by using the
   corresponding leaf, leaf-list, list, and choice-statements, etc., as
   substatements of the instance declaration.  This is an in-place

   augmentation of the used complex type confined to a complex type
   instantiation (see also Section 2.13, "Using Complex Types", for
   details on augmenting complex types).

2.4.  instance-list Extension Statement

   The "instance-list" extension statement is used to instantiate a
   complex type by defining a sequence of subtrees in the management
   information node tree.  In addition, the "instance-list" statement
   takes one argument that is the identifier of the complex type
   instances.  It is followed by a block of substatements.

   The type of the instance is specified with the mandatory "ct:
   instance-type" substatement.  In addition, it can be defined how
   often an instance may appear in the schema tree by using the "min-
   elements" and "max-elements" substatements.  Common YANG statements
   may be used as substatements of the "instance-list" statement.

   In analogy to the "instance" statement, YANG substatements like
   "list", "choice", "leaf", etc., MAY be used to augment the "instance-
   list" elements at the root level with additional data nodes.

                    +------------------+-------------+
                    |   substatementc  | cardinality |
                    +------------------+-------------+
                    |    description   |     0..1    |
                    |      config      |     0..1    |
                    | ct:instance-type |      1      |
                    |    if-feature    |     0..n    |
                    |   max-elements   |     0..1    |
                    |   min-elements   |     0..1    |
                    |       must       |     0..n    |
                    |    ordered-by    |     0..1    |
                    |     reference    |     0..1    |
                    |      status      |     0..1    |
                    |       when       |     0..1    |
                    |      anyxml      |     0..n    |
                    |      choice      |     0..n    |
                    |     container    |     0..n    |
                    |    ct:instance   |     0..n    |
                    | ct:instance-list |     0..n    |
                    |       leaf       |     0..n    |
                    |     leaf-list    |     0..n    |
                    |       list       |     0..n    |
                    +------------------+-------------+

                  Table 3: instance-list's Substatements

   In case the instance list represents configuration data, the used
   complex type of an instance MUST have an instance key.

   Instances as well as instance lists may appear as arguments of the
   "deviate" statement.

2.5.  extends Extension Statement

   A complex type MAY extend exactly one existing base complex type by
   using the "extends" extension statement.  The keyword "extends" MAY
   occur as a substatement of the "complex-type" extension statement.
   The argument of the "complex-type" extension statement refers to the
   base complex type via its name.  In case a complex type represents
   configuration data (the default), it MUST have a key; otherwise, it
   MAY have a key.  A key is either defined with the "key" statement as
   part of the complex type or is inherited from the base complex type.

                      +--------------+-------------+
                      | substatement | cardinality |
                      +--------------+-------------+
                      |  description |     0..1    |
                      |   reference  |     0..1    |
                      |    status    |     0..1    |
                      +--------------+-------------+

                      Table 4: extends' Substatements

2.6.  abstract Extension Statement

   Complex types may be declared to be abstract by using the "abstract"
   extension statement.  An abstract complex type cannot be
   instantiated, meaning it cannot appear as the most specific type of
   an instance in the NETCONF payload.  In case an abstract type extends
   a base type, the base complex type MUST be also abstract.  By
   default, complex types are not abstract.

   The abstract complex type serves only as a base type for derived
   concrete complex types and cannot be used as a type for an instance
   in the NETCONF payload.

   The "abstract" extension statement takes a single string argument,
   which is either "true" or "false".  In case a "complex-type"
   statement does not contain an "abstract" statement as a substatement,
   the default is "false".  The "abstract" statement does not support
   any substatements.

2.7.  XML Encoding Rules

   An "instance" node is encoded as an XML element, where an "instance-
   list" node is encoded as a series of XML elements.  The corresponding
   XML element names are the "instance" and "instance-list" identifiers,
   respectively, and they use the same XML namespace as the module.

   Instance child nodes are encoded as subelements of the instance XML
   element.  Subelements representing child nodes defined in the same
   complex type may appear in any order.  However, child nodes of an
   extending complex type follow the child nodes of the extended complex
   type.  As such, the XML encoding of lists is similar to the encoding
   of containers and lists in YANG.

   Instance key nodes are encoded as subelements of the instance XML
   element.  Instance key nodes must appear in the same order as they
   are defined within the "key" statement of the corresponding complex
   type definition and precede all other nodes defined in the same
   complex type.  That is, if key nodes are defined in an extending
   complex type, XML elements representing key data precede all other
   XML elements representing child nodes.  On the other hand, XML
   elements representing key data follow the XML elements representing
   data nodes of the base type.

   The type of the actual complex type instance is encoded in a type
   element, which is put in front of all instance child elements,
   including key nodes, as described in Section 2.8 ("Type Encoding
   Rules").

   The proposed XML encoding rules conform to the YANG XML encoding
   rules in [RFC6020].  Compared to YANG, enabling key definitions in
   derived hierarchies is a new feature introduced with the complex
   types extension.  As a new language feature, complex types also
   introduce a new payload entry for the instance type identifier.

   Based on our implementation experience, the proposed XML encoding
   rules support consistent mapping of YANG models with complex types to
   an XML schema using XML complex types.

2.8.  Type Encoding Rules

   In order to encode the type of an instance in the NETCONF payload,
   XML elements named "type" belonging to the XML namespace
   "urn:ietf:params:xml:ns:yang:ietf-complex-type-instance" are added to
   the serialized form of instance and instance-list nodes in the
   payload.  The suggested namespace prefix is "cti".  The "cti:type"
   XML elements are inserted before the serialized form of all members
   that have been declared in the corresponding complex type definition.

   The "cti:type" element is inserted for each type in the extension
   chain to the actual type of the instance (most specific last).  Each
   type name includes its corresponding namespace.

   The type of a complex type instance MUST be encoded in the reply to
   NETCONF <get> and <get-config> operations, and in the payload of a
   NETCONF <edit-config> operation if the operation is "create" or
   "replace".  The type of the instance MUST also be specified in case
   <copy-config> is used to export a configuration to a resource
   addressed with an URI.  The type of the instance has to be specified
   in user-defined remote procedure calls (RPCs).

   The type of the instance MAY be specified in case the operation is
   "merge" (either because this is explicitly specified or no operation
   attribute is provided).

   In case the node already exists in the target configuration and the
   type attribute (type of a complex type instance) is specified but
   differs from the data in the target, an <rpc-error> element is
   returned with an <error-app-tag> value of "wrong-complex-type".  In
   case no such element is present in the target configuration but the
   type attribute is missing in the configuration data, an <rpc-error>
   element is returned with an <error-tag> value of "missing-attribute".

   The type MUST NOT be specified in case the operation is "delete".

2.9.  Extension and Feature Definition Module

   The module below contains all YANG extension definitions for complex
   types and typed instance identifiers.  In addition, a "complex-type"
   feature is defined, which may be used to provide conditional or
   alternative modeling, depending on the support status of complex
   types in a NETCONF server.  A NETCONF server that supports the
   modeling features for complex types and the XML encoding for complex
   types as defined in this document MUST advertise this as a feature.
   This is done by including the feature name "complex-types" in the
   feature parameter list as part of the NETCONF <hello> message as
   described in Section 5.6.4 in [RFC6020].

 <CODE BEGINS> file "ietf-complex-types@2011-03-15.yang"

 module ietf-complex-types {

    namespace "urn:ietf:params:xml:ns:yang:ietf-complex-types";
    prefix "ct";

    organization

      "NETMOD WG";

    contact
      "Editor:  Bernd Linowski
                <bernd.linowski.ext@nsn.com>
       Editor:  Mehmet Ersue
                <mehmet.ersue@nsn.com>
       Editor:  Siarhei Kuryla
                <s.kuryla@gmail.com>";

    description
       "YANG extensions for complex types and typed instance
       identifiers.

       Copyright (c) 2011 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
       (http://trustee.ietf.org/license-info).

       This version of this YANG module is part of RFC 6095; see
       the RFC itself for full legal notices.";

        revision 2011-03-15 {
            description "Initial revision.";
        }

         extension complex-type {
             description "Defines a complex-type.";
             reference "Section 2.2, complex-type Extension Statement";
             argument type-identifier {
                 yin-element true;
             }
         }

         extension extends {
             description "Defines the base type of a complex-type.";
             reference "Section 2.5, extends Extension Statement";
             argument base-type-identifier {
                 yin-element true;
             }
         }

         extension abstract {
             description "Makes the complex-type abstract.";
             reference "Section 2.6, abstract Extension Statement";
             argument status;
         }

         extension instance {
             description "Declares an instance of the given
                  complex type.";
             reference "Section 2.3, instance Extension Statement";
             argument ct-instance-identifier {
                 yin-element true;
             }
         }

         extension instance-list {
             description "Declares a list of instances of the given
                  complex type";
             reference "Section 2.4, instance-list Extension Statement";
             argument ct-instance-identifier {
                 yin-element true;
             }
         }

         extension instance-type {
             description "Tells to which type instance the instance
                          identifier refers.";
             reference "Section 3.2, instance-type Extension Statement";
             argument target-type-identifier {
                 yin-element true;
             }
         }

         feature complex-types {
             description "Indicates that the server supports
                          complex types and instance identifiers.";
         }

    }

 <CODE ENDS>

2.10.  Example Model for Complex Types

   The example model below shows how complex types can be used to
   represent physical equipment in a vendor-independent, abstract way.
   It reuses the complex types defined in the physical resource model in
   Section 1.5.1.

   <CODE BEGINS>

   module hw {

      namespace "http://example.com/hw";
      prefix "hw";

      import ietf-complex-types {prefix "ct"; }
      import udmcore {prefix "uc"; }

      // Holder types

      ct:complex-type Slot {
              ct:extends uc:EquipmentHolder;
              leaf slotNumber { type uint16; config false; }
                // ...
      }

      ct:complex-type Chassis {
              ct:extends uc:EquipmentHolder;
              leaf numberOfChassisSlots { type uint32; config false; }
                // ..
      }

      // Equipment types

      ct:complex-type Card {
              ct:extends uc:Equipment;
              leaf position { type uint32; mandatory true; }
                leaf slotsRequired {type unit32; }
      }

      // Root Element
       ct:instance hardware { type uc:ManagedHardware; }

   } // hw module

   <CODE ENDS>

2.11.  NETCONF Payload Example

   Following example shows the payload of a reply to a NETCONF <get>
   command.  The actual type of managed hardware instances is indicated
   with the "cti:type" elements as required by the type encoding rules.
   The containment hierarchy in the NETCONF XML payload reflects the
   containment hierarchy of hardware instances.  This makes filtering
   based on the containment hierarchy possible without having to deal
   with values of leafs of type leafref that represent the tree
   structure in a flattened hierarchy.

 <hardware>
     <cti:type>uc:BasicObject</cti:type>
     <distinguishedName>/R-T31/CH-2</distinguishedName>
     <globalId>6278279001</globalId>
     <cti:type>uc:Resource</cti:type>
     <cti:type>uc:PhysicalResource</cti:type>
     <otherIdentifier>Rack R322-1</otherIdentifier>
     <serialNumber>R-US-3276279a</serialNumber>
     <cti:type>uc:Hardware</cti:type>
     <cti:type>uc:ManagedHardware</cti:type>
     <cti:type>hw:EquipmentHolder</cti:type>
     <equipmentHolder>
         <cti:type>uc:BasicObject</cti:type>
         <distinguishedName>/R-T31/CH-2/SL-1</distinguishedName>
         <globalId>548872003</globalId>
         <cti:type>uc:Resource</cti:type>
         <cti:type>uc:PhysicalResource</cti:type>
         <otherIdentifier>CU-Slot</otherIdentifier>
         <serialNumber>T-K4733890x45</serialNumber>
         <cti:type>uc:Hardware</cti:type>
         <cti:type>uc:ManagedHardware</cti:type>
         <cti:type>uc:EquipmentHolder</cti:type>
         <equipment>
             <cti:type>uc:BasicObject</cti:type>
             <distinguishedName>/R-T31/CH-2/SL-1/C-3</distinguishedName>
             <globalId>89772001</globalId>
             <cti:type>uc:Resource</cti:type>
             <cti:type>uc:PhysicalResource</cti:type>
             <otherIdentifier>ATM-45252</otherIdentifier>
             <serialNumber>A-778911-b</serialNumber>
             <cti:type>uc:Hardware</cti:type>
             <cti:type>uc:ManagedHardware</cti:type>
             <cti:type>uc:Equipment</cti:type>
             <installed>true</installed>
             <version>A2</version>
             <redundancy>1</redundancy>
             <cti:type>hw:Card</cti:type>

             <usedSlots>1</usedSlots>
         </equipment>
         <cti:type>hw:Slot</cti:type>
         <slotNumber>1</slotNumber>
     </equipmentHolder>
     <cti:type>hw:Chassis</cti:type>
     <numberOfChassisSlots>6</numberOfChassisSlots>
     // ...
 </hardware>

2.12.  Update Rules for Modules Using Complex Types

   In addition to the module update rules specified in Section 10 in
   [RFC6020], modules that define complex types, instances of complex
   types, and typed instance identifiers must obey following rules:

   o  New complex types MAY be added.

   o  A new complex type MAY extend an existing complex type.

   o  New data definition statements MAY be added to a complex type only
      if:

      *  they are not mandatory or

      *  they are not conditionally dependent on a new feature (i.e.,
         they do not have an "if-feature" statement that refers to a new
         feature).

   o  The type referred to by the instance-type statement may be changed
      to a type that derives from the original type only if the original
      type does not represent configuration data.

2.13.  Using Complex Types

   All data nodes defined inside a complex type reside in the complex
   type namespace, which is their parent node namespace.

2.13.1.  Overriding Complex Type Data Nodes

   It is not allowed to override a data node inherited from a base type.
   That is, it is an error if a type "base" with a leaf named "foo" is
   extended by another complex type ("derived") with a leaf named "foo"
   in the same module.  In case they are derived in different modules,
   there are two distinct "foo" nodes that are mapped to the XML
   namespaces of the module, where the complex types are specified.

   A complex type that extends a basic complex type may use the "refine"
   statement in order to improve an inherited data node.  The target
   node identifier must be qualified by the module prefix to indicate
   clearly which inherited node is refined.

   The following refinements can be done:

   o  A leaf or choice node may have a default value, or a new default
      value if it already had one.

   o  Any node may have a different "description" or "reference" string.

   o  A leaf, anyxml, or choice node may have a "mandatory true"
      statement.  However, it is not allowed to change from "mandatory
      true" to "mandatory false".

   o  A leaf, leaf-list, list, container, or anyxml node may have
      additional "must" expressions.

   o  A list, leaf-list, instance, or instance-list node may have a
      "min-elements" statement, if the base type does not have one or
      does not have one with a value that is greater than the minimum
      value of the base type.

   o  A list, leaf-list, instance, or instance-list node may have a
      "max-elements" statement, if the base type does not have one or
      does not have one with a value that is smaller than the maximum
      value of the base type.

   It is not allowed to refine complex-type nodes inside "instance" or
   "instance-list" statements.

2.13.2.  Augmenting Complex Types

   Augmenting complex types is only allowed if a complex type is
   instantiated in an "instance" or "instance-list" statement.  This
   confines the effect of the augmentation to the location in the schema
   tree where the augmentation is done.  The argument of the "augment"
   statement MUST be in the descendant form (as defined by the rule
   "descendant-schema-nodeid" in Section 12 in [RFC6020]).

      ct:complex-type Chassis {
              ct:extends EquipmentHolder;
              container chassisInfo {
                     config false;
                     leaf numberOfSlots { type uint16; }
                     leaf occupiedSlots { type uint16; }
                     leaf height {type unit16;}
                     leaf width {type unit16;}
                }
      }

      ct:instance-list chassis {
              type Chassis;
              augment "chassisInfo" {
                     leaf modelId { type string; }
              }
      }

   When augmenting a complex type, only the "container", "leaf", "list",
   "leaf-list", "choice", "instance", "instance-list", and "if-feature"
   statements may be used within the "augment" statement.  The nodes
   added by the augmentation MUST NOT be mandatory nodes.  One or many
   "augment" statements may not cause the creation of multiple nodes
   with the same name from the same namespace in the target node.

   To achieve less-complex modeling, this document proposes the
   augmentation of complex type instances without recursion.

2.13.3.  Controlling the Use of Complex Types

   A server might not want to support all complex types defined in a
   supported module.  This issue can be addressed with YANG features as
   follows:

   o  Features are defined that are used inside complex type definitions
      (by using "if-feature" as a substatement) to make them optional.
      In this case, such complex types may only be instantiated if the
      feature is supported (advertised as a capability in the NETCONF
      <hello> message).

   o  The "deviation" statement may be applied to node trees, which are
      created by "instance" and "instance-list" statements.  In this
      case, only the substatement "deviate not-supported" is allowed.

   o  It is not allowed to apply the "deviation" statement to node tree
      elements that may occur because of the recursive use of a complex
      type.  Other forms of deviations ("deviate add", "deviate
      replace", "deviate delete") are NOT supported inside node trees
      spanned by "instance" or "instance-list".

   As complex type definitions do not contribute by themselves to the
   data node tree, data node declarations inside complex types cannot be
   the target of deviations.

   In the example below, client applications are informed that the leaf
   "occupiedSlots" is not supported in the top-level chassis.  However,
   if a chassis contains another chassis, the contained chassis may
   support the leaf that reports the number of occupied slots.

     deviation "/chassis/chassisSpec/occupiedSlots" {
        deviate not-supported;
     }

3.  Typed Instance Identifier

3.1.  Definition

   Typed instance identifier relationships are an addition to the
   relationship types already defined in YANG, where the leafref
   relationship is location dependent, and the instance-identifier does
   not specify to which type of instances the identifier points.

   A typed instance identifier represents a reference to an instance of
   a complex type without being restricted to a particular location in
   the containment tree.  This is done by using the extension statement
   "instance-type" as a substatement of the existing "type instance
   identifier" statement.

   Typed instance identifiers allow referring to instances of complex
   types that may be located anywhere in the schema tree.  The "type"
   statement plays the role of a restriction that must be fulfilled by
   the target node, which is referred to with the instance identifier.
   The target node MUST be of a particular complex type, either the type
   itself or any type that extends this complex type.

3.2.  instance-type Extension Statement

   The "instance-type" extension statement specifies the complex type of
   the instance to which the instance-identifier refers.  The referred
   instance may also instantiate any complex type that extends the
   specified complex type.

   The instance complex type is identified by the single name argument.
   The referred complex type MUST have a key.  This extension statement
   MUST be used as a substatement of the "type instance-identifier"
   statement.  The "instance-type" extension statement does not support
   any substatements.

3.3.  Typed Instance Identifier Example

   In the example below, a physical link connects an arbitrary number of
   physical ports.  Here, typed instance identifiers are used to denote
   which "PhysicalPort" instances (anywhere in the data tree) are
   connected by a "PhysicalLink".

        // Extended version of type Card
        ct:complex-type Card {
           ct:extends Equipment;
           leaf usedSlot { type uint16; mandatory true; }
           ct:instance-list port {
               type PhysicalPort;
           }
        }

        ct:complex-type PhysicalPort {
           ct:extends ManagedHardware;
           leaf portNumber { type int32; mandatory true; }
        }

        ct:complex-type PhysicalLink {
           ct:extends ManagedHardware;
           leaf media { type string; }
           leaf-list connectedPort {
              type instance-identifier {
                ct:instance-type PhysicalPort;
              }
              min-elements 2;
           }
        }

   Below is the XML encoding of an element named "link" of type
   "PhysicalLink":

       <link>
           <objectId>FTCL-771</objectId>
           <media>Fiber</media>
           <connectedPort>/hw:hardware[objectId='R-11']
             /hw:equipment[objectId='AT22']/hw:port[objectId='P12']
           </connectedPort>
           <connectedPort>/hw:hardware[objectId='R-42]
             /hw:equipment[objectId='AT30']/hw:port[objectId='P3']
           </connectedPort>
           <serialNumber>F-7786828</serialNumber>
           <commonName>FibCon 7</commonName>
       </link>

4.  IANA Considerations

   This document registers two URIs in the IETF XML registry.  IANA
   registered the following URIs, according to [RFC3688]:

   URI: urn:ietf:params:xml:ns:yang:ietf-complex-types
   URI: urn:ietf:params:xml:ns:yang:ietf-complex-type-instance

   Registrant Contact:
   Bernd Linowski (bernd.linowski.ext@nsn.com)
   Mehmet Ersue (mehmet.ersue@nsn.com)
   Siarhei Kuryla (s.kuryla@gmail.com)

   XML: N/A, the requested URIs are XML namespaces.

   This document registers one module name in the "YANG Module Names"
   registry, defined in [RFC6020].
      name: ietf-complex-types

      namespace: urn:ietf:params:xml:ns:yang:ietf-complex-types

      prefix: ct

      RFC: 6095

5.  Security Considerations

   The YANG module "complex-types" in this memo defines YANG extensions
   for complex types and typed instance identifiers as new language
   statements.

   Complex types and typed instance identifiers themselves do not have
   any security impact on the Internet.

   The security considerations described throughout [RFC6020] apply here
   as well.

6.  Acknowledgements

   The authors would like to thank to Martin Bjorklund, Balazs Lengyel,
   Gerhard Muenz, Dan Romascanu, Juergen Schoenwaelder, and Martin
   Storch for their valuable review and comments on different versions
   of the document.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

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

7.2.  Informative References

   [IPFIXCONF]
              Muenz, G., Claise, B., and P. Aitken, "Configuration Data
              Model for IPFIX and PSAMP", Work in Progress, March 2011.

   [Libsmi]   Kuryla, S., "Libsmi Extension for Complex Types",
              April 2010, <http://www.ibr.cs.tu-bs.de/svn/libsmi>.

   [Pyang]    Bjorklund, M., "An extensible YANG validator and converter
              in python", October 2010,
              <http://code.google.com/p/pyang/>.

   [Pyang-ct]
              Kuryla, S., "Complex type extension for an extensible YANG
              validator and converter in python", April 2010,
              <http://code.google.com/p/pyang-ct/>.

   [RFC4133]  Bierman, A. and K. McCloghrie, "Entity MIB (Version 3)",
              RFC 4133, August 2005.

   [SID_V8]   TeleManagement Forum, "GB922, Information Framework (SID)
              Solution Suite, Release 8.0", July 2008, <http://
              www.tmforum.org/DocumentsInformation/
              GB922InformationFramework/35499/article.html>.

   [UDM]      NSN, "Unified Data Model SID Compliance Statement",
              May 2010, <http://www.tmforum.org/InformationFramework/
              NokiaSiemensNetworks/8815/home.html>.

Appendix A.  YANG Modules for Physical Network Resource Model and
             Hardware Entities Model

   YANG module for the 'Physical Network Resource Model':

   <CODE BEGINS>

   module udmcore {

      namespace "http://example.com/udmcore";
      prefix "udm";

      import ietf-yang-types {prefix "yang";}
      import ietf-complex-types {prefix "ct";}

      ct:complex-type BasicObject {
         ct:abstract true;
         key "distinguishedName";
           leaf globalId {type int64;}
           leaf distinguishedName {type string; mandatory true;}
      }

      ct:complex-type ManagedObject {
         ct:extends BasicObject;
         ct:abstract true;
         leaf instance {type string;}
         leaf objectState {type int32;}
         leaf release {type string;}
      }

      ct:complex-type Resource {
               ct:extends ManagedObject;
               ct:abstract true;
         leaf usageState {type int16;}
         leaf managementMethodSupported {type string;}
         leaf managementMethodCurrent {type string;}
         leaf managementInfo {type string;}
         leaf managementDomain {type string;}
         leaf version {type string;}
         leaf entityIdentification {type string;}
         leaf description {type string;}
         leaf rootEntityType {type string;}
      }

      ct:complex-type LogicalResource {
         ct:extends Resource;
         ct:abstract true;
         leaf lrStatus {type int32;}
         leaf serviceState {type int32;}
         leaf isOperational {type boolean;}
      }

      ct:complex-type PhysicalResource {
         ct:extends Resource;
         ct:abstract true;
         leaf manufactureDate {type string;}
         leaf otherIdentifier {type string;}
         leaf powerState {type int32;}
         leaf serialNumber {type string;}
         leaf versionNumber {type string;}
      }

      ct:complex-type Hardware {
         ct:extends PhysicalResource;
         ct:abstract true;
         leaf width {type string;}
         leaf height {type string;}
         leaf depth {type string;}
         leaf measurementUnits {type int32;}
         leaf weight {type string;}
         leaf weightUnits {type int32;}
         leaf-list physicalLink {
            type instance-identifier {
               ct:instance-type PhysicalLink;
            }
         }
         ct:instance-list containedHardware {
            ct:instance-type Hardware;
         }
         ct:instance-list physicalConnector {
            ct:instance-type PhysicalConnector;
         }
      }

      ct:complex-type PhysicalLink {
         ct:extends PhysicalResource;
         leaf isWireless {type boolean;}
         leaf currentLength {type string;}
         leaf maximumLength {type string;}

         leaf mediaType {type int32;}
         leaf-list hardware {
            type instance-identifier {
               ct:instance-type Hardware;
            }
         }
      }

      ct:complex-type ManagedHardware {
         ct:extends Hardware;
         leaf additionalinfo {type string;}
         leaf physicalAlarmReportingEnabled {type boolean;}
         leaf pyhsicalAlarmStatus {type int32;}
         leaf coolingRequirements {type string;}
         leaf hardwarePurpose {type string;}
         leaf isPhysicalContainer {type boolean;}
      }

      ct:complex-type AuxiliaryComponent {
         ct:extends ManagedHardware;
         ct:abstract true;
      }

      ct:complex-type PhysicalPort {
         ct:extends ManagedHardware;
         leaf portNumber {type int32;}
         leaf duplexMode {type int32;}
         leaf ifType {type int32;}
         leaf vendorPortName {type string;}
      }

      ct:complex-type PhysicalConnector {
         ct:extends Hardware;
         leaf location {type string;}
         leaf cableType {type int32;}
         leaf gender {type int32;}
         leaf inUse {type boolean;}
         leaf pinDescription {type string;}
         leaf typeOfConnector {type int32;}
         leaf-list sourcePhysicalConnector {
            type instance-identifier {
               ct:instance-type PhysicalConnector;
            }
         }

         leaf-list targetPhysicalConnector {
            type instance-identifier {
               ct:instance-type PhysicalConnector;
            }
         }
      }

      ct:complex-type Equipment {
         ct:extends ManagedHardware;
         leaf installStatus {type int32;}
         leaf expectedEquipmentType {type string;}
         leaf installedEquipmentType {type string;}
         leaf installedVersion {type string;}
         leaf redundancy {type int32;}
         leaf vendorName {type string;}
         leaf dateOfLastService {type yang:date-and-time;}
         leaf interchangeability {type string;}
         leaf identificationCode {type string;}
         ct:instance-list equipment {
            ct:instance-type Equipment;
         }
      }

      ct:complex-type EquipmentHolder {
         ct:extends ManagedHardware;
         leaf vendorName {type string;}
         leaf locationName {type string;}
         leaf dateOfLastService {type yang:date-and-time;}
         leaf partNumber {type string;}
         leaf availabilityStatus {type int16;}
         leaf nameFromPlanningSystem {type string;}
         leaf modelNumber {type string;}
         leaf acceptableEquipmentList {type string;}
         leaf isSolitaryHolder {type boolean;}
         leaf holderStatus {type int16;}
         leaf interchangeability {type string;}
         leaf equipmentHolderSpecificType {type string; }
         leaf position {type string;}
         leaf atomicCompositeType {type int16;}
         leaf uniquePhysical {type boolean;}
         leaf physicalDescription {type string;}
         leaf serviceApproach {type string;}
         leaf mountingOptions {type int32;}
         leaf cableManagementStrategy {type string;}
         leaf isSecureHolder {type boolean;}
         ct:instance-list equipment {

            ct:instance-type Equipment;
               }
         ct:instance-list equipmentHolder {
            ct:instance-type EquipmentHolder;
         }
      }

      // ... other resource complex types ...

   }
   <CODE ENDS>

   YANG module for the 'Hardware Entities Model':

   <CODE BEGINS>

   module hardware-entities {

      namespace "http://example.com/:hardware-entities";
      prefix "hwe";

      import ietf-yang-types {prefix "yang";}
      import ietf-complex-types {prefix "ct";}
      import udmcore {prefix "uc";}

      grouping PhysicalEntityProperties {
         leaf hardwareRev {type string; }
         leaf firmwareRev {type string; }
         leaf softwareRev {type string; }
         leaf serialNum {type string; }

         leaf mfgName {type string; }
         leaf modelName {type string; }
         leaf alias {type string; }
         leaf ssetID{type string; }
         leaf isFRU {type boolean; }
         leaf mfgDate {type yang:date-and-time; }
         leaf-list uris {type string; }
      }

      // Physical entities representing equipment

      ct:complex-type Module {
         ct:extends uc:Equipment;
         description "Complex type representing module entries

            (entPhysicalClass = module(9)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      ct:complex-type Backplane {
         ct:extends uc:Equipment;
         description "Complex type representing backplane entries
            (entPhysicalClass = backplane(4)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      // Physical entities representing auxiliary hardware components

      ct:complex-type PowerSupply {
         ct:extends uc:AuxiliaryComponent;
         description "Complex type representing power supply entries
            (entPhysicalClass = powerSupply(6)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      ct:complex-type Fan {
         ct:extends uc:AuxiliaryComponent;
         description "Complex type representing fan entries
            (entPhysicalClass = fan(7)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      ct:complex-type Sensor {
         ct:extends uc:AuxiliaryComponent;
         description "Complex type representing sensor entries
            (entPhysicalClass = sensor(8)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      // Physical entities representing equipment holders

      ct:complex-type Chassis {
         ct:extends uc:EquipmentHolder;
         description "Complex type representing chassis entries
            (entPhysicalClass = chassis(3)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      ct:complex-type Container {
         ct:extends uc:EquipmentHolder;
         description "Complex type representing container entries

            (entPhysicalClass = container(5)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      ct:complex-type Stack {
         ct:extends uc:EquipmentHolder;
         description "Complex type representing stack entries
            (entPhysicalClass = stack(11)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      // Other kinds of physical entities

      ct:complex-type Port {
         ct:extends uc:PhysicalPort;
         description "Complex type representing port entries
            (entPhysicalClass = port(10)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

      ct:complex-type CPU {
         ct:extends uc:Hardware;
         description "Complex type representing cpu entries
            (entPhysicalClass = cpu(12)) in entPhysicalTable";
         uses PhysicalEntityProperties;
      }

   }
   <CODE ENDS>

Appendix B.  Example YANG Module for the IPFIX/PSAMP Model

B.1.  Modeling Improvements for the IPFIX/PSAMP Model with Complex Types
      and Typed Instance Identifiers

   The module below is a variation of the IPFIX/PSAMP configuration
   model, which uses complex types and typed instance identifiers to
   model the concept outlined in [IPFIXCONF].

   When looking at the YANG module with complex types and typed instance
   identifiers, various technical improvements on the modeling level
   become apparent.

   o  There is almost a one-to-one mapping between the domain concepts
      introduced in IPFIX and the complex types in the YANG module.

   o  All associations between the concepts (besides containment) are
      represented with typed identifiers.  That avoids having to refer
      to a particular location in the tree.  Referring to a particular
      in the tree is not mandated by the original model.

   o  It is superfluous to represent concept refinement (class
      inheritance in the original model) with containment in the form of
      quite big choice-statements with complex branches.  Instead,
      concept refinement is realized by complex types extending a base
      complex type.

   o  It is unnecessary to introduce metadata identities and leafs
      (e.g., "identity cacheMode" and "leaf cacheMode" in "grouping
      cacheParameters") that just serve the purpose of indicating which
      concrete subtype of a generic type (modeled as grouping, which
      contains the union of all features of all subtypes) is actually
      represented in the MIB.

   o  Ruling out illegal use of subtype-specific properties (e.g., "leaf
      maxFlows") by using "when" statements that refer to a subtype
      discriminator is not necessary (e.g., when "../cacheMode !=
      'immediate'").

   o  Defining properties like the configuration status wherever a so
      called "parameter grouping" is used is not necessary.  Instead,
      those definitions can be put inside the complex type definition
      itself.

   o  Separating the declaration of the key from the related data nodes
      definitions in a grouping (see use of "grouping
      selectorParameters") can be avoided.

   o  Complex types may be declared as optional features.  If the type
      is indicated with an identity (e.g., "identity immediate"), this
      is not possible, since "if-feature" is not allowed as a
      substatement of "identity".

B.2.  IPFIX/PSAMP Model with Complex Types and Typed Instance
      Identifiers

<CODE BEGINS>
module ct-ipfix-psamp-example {
     namespace "http://example.com/ns/ct-ipfix-psamp-example";
     prefix ipfix;

     import ietf-yang-types { prefix yang; }
     import ietf-inet-types { prefix inet; }
     import ietf-complex-types {prefix "ct"; }

     description "Example IPFIX/PSAMP Configuration Data Model
       with complex types and typed instance identifiers";

     revision 2011-03-15 {
        description "The YANG Module ('YANG Module of the IPFIX/PSAMP
          Configuration Data Model') in [IPFIXCONF] modeled with
          complex types and typed instance identifiers.
          Disclaimer: This example model illustrates the use of the
          language extensions defined in this document and does not
          claim to be an exact reproduction of the original YANG
          model referred above. The original description texts have
          been shortened to increase the readability of the model
          example.";
    }

     /*****************************************************************
     * Features
     *****************************************************************/

     feature exporter {
       description "If supported, the Monitoring Device can be used as
         an Exporter.  Exporting Processes can be configured.";
     }

     feature collector {
       description "If supported, the Monitoring Device can be used as
         a Collector.  Collecting Processes can be configured.";
     }

     feature meter {
       description "If supported, Observation Points, Selection
         Processes, and Caches can be configured.";
     }

     feature psampSampCountBased {
       description "If supported, the Monitoring Device supports
         count-based Sampling...";
     }

     feature psampSampTimeBased {
       description "If supported, the Monitoring Device supports
         time-based Sampling...";
     }

     feature psampSampRandOutOfN {
       description "If supported, the Monitoring Device supports
         random n-out-of-N Sampling...";
     }

     feature psampSampUniProb {
       description "If supported, the Monitoring Device supports
         uniform probabilistic Sampling...";
     }

     feature psampFilterMatch {
       description "If supported, the Monitoring Device supports
         property match Filtering...";
     }

     feature psampFilterHash {
       description "If supported, the Monitoring Device supports
         hash-based Filtering...";
     }

     feature cacheModeImmediate {
       description "If supported, the Monitoring Device supports
         Cache Mode 'immediate'.";
     }

     feature cacheModeTimeout {
       description "If supported, the Monitoring Device supports
         Cache Mode 'timeout'.";
     }

     feature cacheModeNatural {
       description "If supported, the Monitoring Device supports
         Cache Mode 'natural'.";
     }

     feature cacheModePermanent {
       description "If supported, the Monitoring Device supports
         Cache Mode 'permanent'.";
     }

     feature udpTransport {
       description "If supported, the Monitoring Device supports UDP
         as transport protocol.";
     }

     feature tcpTransport {
       description "If supported, the Monitoring Device supports TCP
         as transport protocol.";
     }

     feature fileReader {
       description "If supported, the Monitoring Device supports the
         configuration of Collecting Processes as File Readers.";

     }

     feature fileWriter {
       description "If supported, the Monitoring Device supports the
         configuration of Exporting Processes as File Writers.";
     }

     /*****************************************************************
     * Identities
     *****************************************************************/

     /*** Hash function identities ***/
     identity hashFunction {
       description "Base identity for all hash functions...";
     }
     identity BOB {
       base "hashFunction";
       description "BOB hash function";
       reference "RFC 5475, Section 6.2.4.1.";
     }
     identity IPSX {
       base "hashFunction";
       description "IPSX hash function";
       reference "RFC 5475, Section 6.2.4.1.";
     }
     identity CRC {
       base "hashFunction";
       description "CRC hash function";
       reference "RFC 5475, Section 6.2.4.1.";
     }

     /*** Export mode identities ***/
     identity exportMode {
       description "Base identity for different usages of export
         destinations configured for an Exporting Process...";
     }
     identity parallel {
       base "exportMode";
       description "Parallel export of Data Records to all
         destinations configured for the Exporting Process.";
     }
     identity loadBalancing {
       base "exportMode";
       description "Load-balancing between the different
         destinations...";
     }
     identity fallback {
       base "exportMode";

       description "Export to the primary destination...";
     }

     /*** Options type identities ***/
     identity optionsType {
       description "Base identity for report types exported
          with options...";
     }
     identity meteringStatistics {
       base "optionsType";
       description "Metering Process Statistics.";
       reference "RFC 5101, Section 4.1.";
     }
     identity meteringReliability {
       base "optionsType";
       description "Metering Process Reliability Statistics.";
       reference "RFC 5101, Section 4.2.";
     }
     identity exportingReliability {
       base "optionsType";
       description "Exporting Process Reliability
         Statistics.";
       reference "RFC 5101, Section 4.3.";
     }
     identity flowKeys {
       base "optionsType";
       description "Flow Keys.";
       reference "RFC 5101, Section 4.4.";
     }
     identity selectionSequence {
       base "optionsType";
       description "Selection Sequence and Selector Reports.";
       reference "RFC 5476, Sections 6.5.1 and 6.5.2.";
     }
     identity selectionStatistics {
       base "optionsType";
       description "Selection Sequence Statistics Report.";
       reference "RFC 5476, Sections 6.5.3.";
     }
     identity accuracy {
       base "optionsType";
       description "Accuracy Report.";
       reference "RFC 5476, Section 6.5.4.";
     }
     identity reducingRedundancy {
       base "optionsType";
       description "Enables the utilization of Options Templates to
         reduce redundancy in the exported Data Records.";

       reference "RFC 5473.";
     }
     identity extendedTypeInformation {
       base "optionsType";
       description "Export of extended type information for
         enterprise-specific Information Elements used in the
         exported Templates.";
       reference "RFC 5610.";
     }

     /*****************************************************************
     * Type definitions
     *****************************************************************/

     typedef nameType {
       type string {
         length "1..max";
         pattern "\S(.*\S)?";
       }
       description "Type for 'name' leafs...";
     }

     typedef direction {
       type enumeration {
         enum ingress {
           description "This value is used for monitoring incoming
             packets.";
         }
         enum egress {
           description "This value is used for monitoring outgoing
             packets.";
         }
         enum both {
           description "This value is used for monitoring incoming and
             outgoing packets.";
         }
       }
       description "Direction of packets going through an interface or
         linecard.";
     }

     typedef transportSessionStatus {
       type enumeration {
         enum inactive {
           description "This value MUST be used for...";
         }
         enum active {
           description "This value MUST be used for...";

         }
         enum unknown {
           description "This value MUST be used if the status...";
         }
       }
       description "Status of a Transport Session.";
       reference "RFC 5815, Section 8 (ipfixTransportSessionStatus).";
     }

     /*****************************************************************
     * Complex types
     *****************************************************************/

     ct:complex-type ObservationPoint {
       description "Observation Point";
       key name;
       leaf name {
         type nameType;
         description "Key of an observation point.";
       }
       leaf observationPointId {
         type uint32;
         config false;
         description "Observation Point ID...";
         reference "RFC 5102, Section 5.1.10.";
       }
       leaf observationDomainId {
         type uint32;
         mandatory true;
         description "The Observation Domain ID associates...";
         reference "RFC 5101.";
       }
       choice OPLocation {
         mandatory true;
         description "Location of the Observation Point.";
         leaf ifIndex {
           type uint32;
           description "Index of an interface...";
           reference "RFC 2863.";
         }
         leaf ifName {
           type string;
           description "Name of an interface...";
           reference "RFC 2863.";
         }
         leaf entPhysicalIndex {
           type uint32;
           description "Index of a linecard...";

           reference "RFC 4133.";
         }
         leaf entPhysicalName {
           type string;
           description "Name of a linecard...";
           reference "RFC 4133.";
         }
       }
       leaf direction {
         type direction;
         default both;
         description "Direction of packets....";
       }
       leaf-list selectionProcess {
         type instance-identifier { ct:instance-type SelectionProcess; }
         description "Selection Processes in this list process packets
           in parallel.";
       }
     }

     ct:complex-type Selector {
       ct:abstract true;
       description "Abstract selector";
       key name;
       leaf name {
           type nameType;
           description "Key of a selector";
       }
       leaf packetsObserved {
         type yang:counter64;
         config false;
         description "The number of packets observed ...";
         reference "RFC 5815, Section 8
           (ipfixSelectionProcessStatsPacketsObserved).";
       }
       leaf packetsDropped {
         type yang:counter64;
         config false;
         description "The total number of packets discarded ...";
         reference "RFC 5815, Section 8
           (ipfixSelectionProcessStatsPacketsDropped).";
       }
       leaf selectorDiscontinuityTime {
         type yang:date-and-time;
         config false;
         description "Timestamp of the most recent occasion at which
           one or more of the Selector counters suffered a
           discontinuity...";

         reference "RFC 5815, Section 8
           (ipfixSelectionProcessStatsDiscontinuityTime).";
       }
     }

     ct:complex-type SelectAllSelector {
       ct:extends Selector;
       description "Method that selects all packets.";
     }

     ct:complex-type SampCountBasedSelector {
           if-feature psampSampCountBased;
           ct:extends Selector;
           description "Selector applying systematic count-based
             packet sampling to the packet stream.";
           reference "RFC 5475, Section 5.1;
             RFC 5476, Section 6.5.2.1.";
           leaf packetInterval {
             type uint32;
             units packets;
             mandatory true;
             description "The number of packets that are consecutively
               sampled between gaps of length packetSpace.
               This parameter corresponds to the Information Element
               samplingPacketInterval.";
             reference "RFC 5477, Section 8.2.2.";
           }
           leaf packetSpace {
             type uint32;
             units packets;
             mandatory true;
             description "The number of unsampled packets between two
               sampling intervals.
               This parameter corresponds to the Information Element
               samplingPacketSpace.";
             reference "RFC 5477, Section 8.2.3.";
           }
     }

     ct:complex-type SampTimeBasedSelector {
           if-feature psampSampTimeBased;
           ct:extends Selector;
           description "Selector applying systematic time-based
             packet sampling to the packet stream.";
           reference "RFC 5475, Section 5.1;
             RFC 5476, Section 6.5.2.2.";
           leaf timeInterval {
             type uint32;

             units microseconds;
             mandatory true;
             description "The time interval in microseconds during
               which all arriving packets are sampled between gaps
               of length timeSpace.
               This parameter corresponds to the Information Element
               samplingTimeInterval.";
             reference "RFC 5477, Section 8.2.4.";
           }
           leaf timeSpace {
             type uint32;
             units microseconds;
             mandatory true;
             description "The time interval in microseconds during
               which no packets are sampled between two sampling
               intervals specified by timeInterval.
               This parameter corresponds to the Information Element
               samplingTimeInterval.";
             reference "RFC 5477, Section 8.2.5.";
           }
     }

     ct:complex-type SampRandOutOfNSelector {
           if-feature psampSampRandOutOfN;
           ct:extends Selector;
           description "This container contains the configuration
             parameters of a Selector applying n-out-of-N packet
             sampling to the packet stream.";
           reference "RFC 5475, Section 5.2.1;
             RFC 5476, Section 6.5.2.3.";
           leaf size {
             type uint32;
             units packets;
             mandatory true;
             description "The number of elements taken from the parent
               population.
               This parameter corresponds to the Information Element
               samplingSize.";
             reference "RFC 5477, Section 8.2.6.";
           }
           leaf population {
             type uint32;
             units packets;
             mandatory true;
             description "The number of elements in the parent
               population.
               This parameter corresponds to the Information Element
               samplingPopulation.";

             reference "RFC 5477, Section 8.2.7.";
           }
     }

     ct:complex-type SampUniProbSelector {
           if-feature psampSampUniProb;
           ct:extends Selector;
           description "Selector applying uniform probabilistic
             packet sampling (with equal probability per packet) to the
             packet stream.";
           reference "RFC 5475, Section 5.2.2.1;
             RFC 5476, Section 6.5.2.4.";
           leaf probability {
             type decimal64 {
               fraction-digits 18;
               range "0..1";
             }
             mandatory true;
             description "Probability that a packet is sampled,
               expressed as a value between 0 and 1.  The probability
               is equal for every packet.
               This parameter corresponds to the Information Element
               samplingProbability.";
             reference "RFC 5477, Section 8.2.8.";
           }
     }

     ct:complex-type FilterMatchSelector {
           if-feature psampFilterMatch;
           ct:extends Selector;
           description "This container contains the configuration
             parameters of a Selector applying property match filtering
             to the packet stream.";
           reference "RFC 5475, Section 6.1;
             RFC 5476, Section 6.5.2.5.";
           choice nameOrId {
             mandatory true;
             description "The field to be matched is specified by
               either the name or the ID of the Information
               Element.";
             leaf ieName {
               type string;
               description "Name of the Information Element.";
             }
             leaf ieId {
               type uint16 {
                 range "1..32767" {
                   description "Valid range of Information Element

                       identifiers.";
                   reference "RFC 5102, Section 4.";
                 }
               }
               description "ID of the Information Element.";
             }
           }
           leaf ieEnterpriseNumber {
             type uint32;
             description "If present, ... ";
           }
           leaf value {
             type string;
             mandatory true;
             description "Matching value of the Information Element.";
           }
     }

     ct:complex-type FilterHashSelector {
           if-feature psampFilterHash;
           ct:extends Selector;
           description "This container contains the configuration
             parameters of a Selector applying hash-based filtering
             to the packet stream.";
           reference "RFC 5475, Section 6.2;
             RFC 5476, Section 6.5.2.6.";
           leaf hashFunction {
             type identityref {
               base "hashFunction";
             }
             default BOB;
             description "Hash function to be applied.  According to
               RFC 5475, Section 6.2.4.1, BOB hash function must be
               used in order to be compliant with PSAMP.";
           }
           leaf ipPayloadOffset {
             type uint64;
             units octets;
             default 0;
             description "IP payload offset ... ";
             reference "RFC 5477, Section 8.3.2.";
           }
           leaf ipPayloadSize {
             type uint64;
             units octets;
             default 8;
             description "Number of IP payload bytes ... ";
             reference "RFC 5477, Section 8.3.3.";

           }
           leaf digestOutput {
             type boolean;
             default false;
             description "If true, the output ... ";
             reference "RFC 5477, Section 8.3.8.";
           }
           leaf initializerValue {
             type uint64;
             description "Initializer value to the hash function.
               If not configured by the user, the Monitoring Device
               arbitrarily chooses an initializer value.";
             reference "RFC 5477, Section 8.3.9.";
           }
           list selectedRange {
             key name;
             min-elements 1;
             description "List of hash function return ranges for
               which packets are selected.";
             leaf name {
               type nameType;
               description "Key of this list.";
             }
             leaf min {
               type uint64;
               description "Beginning of the hash function's selected
                 range.
                 This parameter corresponds to the Information Element
                 hashSelectedRangeMin.";
               reference "RFC 5477, Section 8.3.6.";
             }
             leaf max {
               type uint64;
               description "End of the hash function's selected range.
                 This parameter corresponds to the Information Element
                 hashSelectedRangeMax.";
               reference "RFC 5477, Section 8.3.7.";
             }
           }
     }

     ct:complex-type Cache {
       ct:abstract true;
       description "Cache of a Monitoring Device.";
       key name;
       leaf name {
         type nameType;
         description "Key of a cache";

       }
       leaf-list exportingProcess {
         type leafref { path "/ipfix/exportingProcess/name"; }
         description "Records are exported by all Exporting Processes
           in the list.";
       }
       description "Configuration and state parameters of a Cache.";
       container cacheLayout {
         description "Cache Layout.";
         list cacheField {
           key name;
           min-elements 1;
           description "List of fields in the Cache Layout.";
           leaf name {
             type nameType;
             description "Key of this list.";
           }
           choice nameOrId {
             mandatory true;
             description "Name or ID of the Information Element.";
             reference "RFC 5102.";
             leaf ieName {
               type string;
               description "Name of the Information Element.";
             }
             leaf ieId {
               type uint16 {
                 range "1..32767" {
                   description "Valid range of Information Element
                       identifiers.";
                   reference "RFC 5102, Section 4.";
                 }
               }
               description "ID of the Information Element.";
             }
           }
           leaf ieLength {
             type uint16;
             units octets;
             description "Length of the field ... ";
             reference "RFC 5101, Section 6.2; RFC 5102.";
           }
           leaf ieEnterpriseNumber {
             type uint32;
             description "If present, the Information Element is
               enterprise-specific. ... ";
             reference "RFC 5101; RFC 5102.";
           }

           leaf isFlowKey {
             when "(../../../cacheMode != 'immediate')
               and
               ((count(../ieEnterpriseNumber) = 0)
               or
               (../ieEnterpriseNumber != 29305))" {
               description "This parameter is not available
                 for Reverse Information Elements (which have
                 enterprise number 29305) or if the Cache Mode
                 is 'immediate'.";
             }
             type empty;
             description "If present, this is a flow key.";
           }
         }
       }
       leaf dataRecords {
         type yang:counter64;
         units "Data Records";
         config false;
         description "The number of Data Records generated ... ";
         reference "RFC 5815, Section 8
           (ipfixMeteringProcessCacheDataRecords).";
       }
       leaf cacheDiscontinuityTime {
         type yang:date-and-time;
         config false;
         description "Timestamp of the ... ";
         reference "RFC 5815, Section 8
           (ipfixMeteringProcessCacheDiscontinuityTime).";
       }
     }

     ct:complex-type ImmediateCache {
       if-feature cacheModeImmediate;
       ct:extends Cache;
     }

     ct:complex-type NonImmediateCache {
       ct:abstract true;
       ct:extends Cache;
       leaf maxFlows {
         type uint32;
         units flows;
         description "This parameter configures the maximum number of
           Flows in the Cache ... ";
       }

       leaf activeFlows {
         type yang:gauge32;
         units flows;
         config false;
         description "The number of Flows currently active in this
           Cache.";
         reference "RFC 5815, Section 8
           (ipfixMeteringProcessCacheActiveFlows).";
       }
       leaf unusedCacheEntries {
         type yang:gauge32;
         units flows;
         config false;
         description "The number of unused Cache entries in this
           Cache.";
         reference "RFC 5815, Section 8
           (ipfixMeteringProcessCacheUnusedCacheEntries).";
       }
    }

    ct:complex-type NonPermanentCache {
      ct:abstract true;
      ct:extends NonImmediateCache;
      leaf activeTimeout {
        type uint32;
        units milliseconds;
        description "This parameter configures the time in
          milliseconds after which ... ";
      }
      leaf inactiveTimeout {
        type uint32;
        units milliseconds;
        description "This parameter configures the time in
          milliseconds after which ... ";
      }
    }

    ct:complex-type NaturalCache {
      if-feature cacheModeNatural;
      ct:extends NonPermanentCache;
    }

    ct:complex-type TimeoutCache {
      if-feature cacheModeTimeout;
      ct:extends NonPermanentCache;
    }

    ct:complex-type PermanentCache {

      if-feature cacheModePermanent;
      ct:extends NonImmediateCache;
      leaf exportInterval {
        type uint32;
        units milliseconds;
        description "This parameter configures the interval for
          periodical export of Flow Records in milliseconds.
          If not configured by the user, the Monitoring Device sets
          this parameter.";
       }
    }

    ct:complex-type ExportDestination {
      ct:abstract true;
      description "Abstract export destination.";
      key name;
      leaf name {
        type nameType;
        description "Key of an export destination.";
      }
    }

    ct:complex-type IpDestination {
      ct:abstract true;
      ct:extends ExportDestination;
      description "IP export destination.";
      leaf ipfixVersion {
         type uint16;
         default 10;
         description "IPFIX version number.";
       }
       leaf destinationPort {
         type inet:port-number;
         description "If not configured by the user, the Monitoring
           Device uses the default port number for IPFIX, which is
           4739 without Transport Layer Security, and 4740 if Transport
           Layer Security is activated.";
       }
       choice indexOrName {
         description "Index or name of the interface ... ";
         reference "RFC 2863.";
         leaf ifIndex {
           type uint32;
           description "Index of an interface as stored in the ifTable
             of IF-MIB.";
           reference "RFC 2863.";
         }
         leaf ifName {

           type string;
           description "Name of an interface as stored in the ifTable
             of IF-MIB.";
           reference "RFC 2863.";
         }
       }
       leaf sendBufferSize {
         type uint32;
         units bytes;
         description "Size of the socket send buffer.
           If not configured by the user, this parameter is set by
           the Monitoring Device.";
       }
       leaf rateLimit {
         type uint32;
         units "bytes per second";
         description "Maximum number of bytes per second ... ";
         reference "RFC 5476, Section 6.3";
       }
       container transportLayerSecurity {
         presence "If transportLayerSecurity is present, DTLS is
           enabled if the transport protocol is SCTP or UDP, and TLS
           is enabled if the transport protocol is TCP.";
         description "Transport Layer Security configuration.";
         uses transportLayerSecurityParameters;
       }
       container transportSession {
         config false;
         description "State parameters of the Transport Session
           directed to the given destination.";
         uses transportSessionParameters;
       }
    }

     ct:complex-type SctpExporter {
       ct:extends IpDestination;
       description "SCTP exporter.";
       leaf-list sourceIPAddress {
         type inet:ip-address;
         description "List of source IP addresses used ... ";
         reference "RFC 4960, Section 6.4
           (Multi-Homed SCTP Endpoints).";
       }
       leaf-list destinationIPAddress {
         type inet:ip-address;
         min-elements 1;
         description "One or multiple IP addresses ... ";
         reference "RFC 4960, Section 6.4

           (Multi-Homed SCTP Endpoints).";
       }
       leaf timedReliability {
         type uint32;
         units milliseconds;
         default 0;
         description "Lifetime in milliseconds ... ";
         reference "RFC 3758; RFC 4960.";
       }
     }

     ct:complex-type UdpExporter {
       ct:extends IpDestination;
       if-feature udpTransport;
       description "UDP parameters.";
       leaf sourceIPAddress {
         type inet:ip-address;
         description "Source IP address used by the Exporting
            Process ...";
       }
       leaf destinationIPAddress {
         type inet:ip-address;
         mandatory true;
         description "IP address of the Collection Process to which
           IPFIX Messages are sent.";
       }
       leaf maxPacketSize {
         type uint16;
         units octets;
         description "This parameter specifies the maximum size of
           IP packets ... ";
       }
       leaf templateRefreshTimeout {
         type uint32;
         units seconds;
         default 600;
         description "Sets time after which Templates are resent in the
           UDP Transport Session. ... ";
         reference "RFC 5101, Section 10.3.6; RFC 5815, Section 8
           (ipfixTransportSessionTemplateRefreshTimeout).";
       }
       leaf optionsTemplateRefreshTimeout {
         type uint32;
         units seconds;
         default 600;
         description "Sets time after which Options Templates are
           resent in the UDP Transport Session. ... ";
         reference "RFC 5101, Section 10.3.6; RFC 5815, Section 8

           (ipfixTransportSessionOptionsTemplateRefreshTimeout).";
       }
       leaf templateRefreshPacket {
         type uint32;
         units "IPFIX Messages";
         description "Sets number of IPFIX Messages after which
           Templates are resent in the UDP Transport Session. ... ";
         reference "RFC 5101, Section 10.3.6; RFC 5815, Section 8
           (ipfixTransportSessionTemplateRefreshPacket).";
       }
       leaf optionsTemplateRefreshPacket {
         type uint32;
         units "IPFIX Messages";
         description "Sets number of IPFIX Messages after which
           Options Templates are resent in the UDP Transport Session
           protocol. ... ";
         reference "RFC 5101, Section 10.3.6; RFC 5815, Section 8
           (ipfixTransportSessionOptionsTemplateRefreshPacket).";
       }
    }

     ct:complex-type TcpExporter {
       ct:extends IpDestination;
       if-feature tcpTransport;
       description "TCP exporter";
       leaf sourceIPAddress {
         type inet:ip-address;
         description "Source IP address used by the Exporting
           Process...";
       }
       leaf destinationIPAddress {
         type inet:ip-address;
         mandatory true;
         description "IP address of the Collection Process to which
           IPFIX Messages are sent.";
       }
     }

     ct:complex-type FileWriter {
       ct:extends ExportDestination;
       if-feature fileWriter;
       description "File Writer.";
       leaf ipfixVersion {
         type uint16;
         default 10;
         description "IPFIX version number.";
       }
       leaf file {

         type inet:uri;
         mandatory true;
         description "URI specifying the location of the file.";
       }
       leaf bytes {
         type yang:counter64;
         units octets;
         config false;
         description "The number of bytes written by the File
           Writer...";
       }
       leaf messages {
         type yang:counter64;
         units "IPFIX Messages";
         config false;
         description "The number of IPFIX Messages written by the File
           Writer. ... ";
       }
       leaf discardedMessages {
         type yang:counter64;
         units "IPFIX Messages";
         config false;
         description "The number of IPFIX Messages that could not be
           written by the File Writer ... ";
       }
       leaf records {
         type yang:counter64;
         units "Data Records";
         config false;
         description "The number of Data Records written by the File
           Writer. ... ";
       }
       leaf templates {
         type yang:counter32;
         units "Templates";
         config false;
         description "The number of Template Records (excluding
           Options Template Records) written by the File Writer.
           ... ";
       }
       leaf optionsTemplates {
         type yang:counter32;
         units "Options Templates";
         config false;
         description "The number of Options Template Records written
           by the File Writer. ... ";
       }
       leaf fileWriterDiscontinuityTime {

         type yang:date-and-time;
         config false;
         description "Timestamp of the most recent occasion at which
           one or more File Writer counters suffered a discontinuity.
           ... ";
       }
       list template {
         config false;
         description "This list contains the Templates and Options
           Templates that have been written by the File Reader. ... ";
         uses templateParameters;
       }
     }

     ct:complex-type ExportingProcess {
       if-feature exporter;
       description "Exporting Process of the Monitoring Device.";
       key name;
       leaf name {
         type nameType;
         description "Key of this list.";
       }
       leaf exportMode {
         type identityref {
           base "exportMode";
         }
         default parallel;
         description "This parameter determines to which configured
           destination(s) the incoming Data Records are exported.";
       }
       ct:instance-list destination {
         ct:instance-type ExportDestination;
         min-elements 1;
         description "Export destinations.";
       }
       list options {
         key name;
         description "List of options reported by the Exporting
           Process.";
         leaf name {
           type nameType;
           description "Key of this list.";
         }
         leaf optionsType {
           type identityref {
             base "optionsType";
           }
           mandatory true;

           description "Type of the exported options data.";
         }
         leaf optionsTimeout {
           type uint32;
           units milliseconds;
           description "Time interval for periodic export of the options
             data. ... ";
         }
       }
     }

     ct:complex-type CollectingProcess {
       description "A Collecting Process.";
       key name;
       leaf name {
         type nameType;
         description "Key of a collecing process.";
       }
       ct:instance-list sctpCollector {
         ct:instance-type SctpCollector;
         description "List of SCTP receivers (sockets) on which the
           Collecting Process receives IPFIX Messages.";
       }
       ct:instance-list udpCollector {
         if-feature udpTransport;
         ct:instance-type UdpCollector;
         description "List of UDP receivers (sockets) on which the
           Collecting Process receives IPFIX Messages.";
       }
       ct:instance-list tcpCollector {
         if-feature tcpTransport;
         ct:instance-type TcpCollector;
         description "List of TCP receivers (sockets) on which the
           Collecting Process receives IPFIX Messages.";
       }
       ct:instance-list fileReader {
         if-feature fileReader;
         ct:instance-type FileReader;
         description "List of File Readers from which the Collecting
           Process reads IPFIX Messages.";
       }
       leaf-list exportingProcess {
         type instance-identifier { ct:instance-type ExportingProcess; }
         description "Export of received records without any
           modifications.  Records are processed by all Exporting
           Processes in the list.";
       }
     }

     ct:complex-type Collector {
         ct:abstract true;
         description "Abstract collector.";
         key name;
         leaf name {
           type nameType;
           description "Key of collectors";
         }
     }

     ct:complex-type IpCollector {
       ct:abstract true;
       ct:extends Collector;
       description "Collector for IP transport protocols.";
       leaf localPort {
         type inet:port-number;
         description "If not configured, the Monitoring Device uses the
           default port number for IPFIX, which is 4739 without
           Transport Layer Security, and 4740 if Transport Layer
           Security is activated.";
       }
       container transportLayerSecurity {
         presence "If transportLayerSecurity is present, DTLS is enabled
           if the transport protocol is SCTP or UDP, and TLS is enabled
           if the transport protocol is TCP.";
         description "Transport Layer Security configuration.";
         uses transportLayerSecurityParameters;
       }
       list transportSession {
         config false;
         description "This list contains the currently established
           Transport Sessions terminating at the given socket.";
         uses transportSessionParameters;
       }
     }

     ct:complex-type SctpCollector {
       ct:extends IpCollector;
       description "Collector listening on an SCTP socket";
       leaf-list localIPAddress {
         type inet:ip-address;
         description "List of local IP addresses ... ";
         reference "RFC 4960, Section 6.4
           (Multi-Homed SCTP Endpoints).";
       }
     }

     ct:complex-type UdpCollector {

       ct:extends IpCollector;
       description "Parameters of a listening UDP socket at a
         Collecting Process.";
       leaf-list localIPAddress {
         type inet:ip-address;
         description "List of local IP addresses on which the Collecting
           Process listens for IPFIX Messages.";
       }
       leaf templateLifeTime {
         type uint32;
         units seconds;
         default 1800;
         description "Sets the lifetime of Templates for all UDP
           Transport Sessions ... ";
         reference "RFC 5101, Section 10.3.7; RFC 5815, Section 8
           (ipfixTransportSessionTemplateRefreshTimeout).";
       }
       leaf optionsTemplateLifeTime {
         type uint32;
         units seconds;
         default 1800;
         description "Sets the lifetime of Options Templates for all
           UDP Transport Sessions terminating at this UDP socket.
           ... ";
         reference "RFC 5101, Section 10.3.7; RFC 5815, Section 8
           (ipfixTransportSessionOptionsTemplateRefreshTimeout).";
       }
       leaf templateLifePacket {
         type uint32;
         units "IPFIX Messages";
         description "If this parameter is configured, Templates
           defined in a UDP Transport Session become invalid if ...";
         reference "RFC 5101, Section 10.3.7; RFC 5815, Section 8
           (ipfixTransportSessionTemplateRefreshPacket).";
       }
       leaf optionsTemplateLifePacket {
         type uint32;
         units "IPFIX Messages";
         description "If this parameter is configured, Options
           Templates defined in a UDP Transport Session become
           invalid if ...";
         reference "RFC 5101, Section 10.3.7; RFC 5815, Section 8
           (ipfixTransportSessionOptionsTemplateRefreshPacket).";
       }
     }

     ct:complex-type TcpCollector {
       ct:extends IpCollector;

       description "Collector listening on a TCP socket.";
       leaf-list localIPAddress {
         type inet:ip-address;
         description "List of local IP addresses on which the Collecting
           Process listens for IPFIX Messages.";
       }
     }

     ct:complex-type FileReader {
       ct:extends Collector;
       description "File Reading collector.";
       leaf file {
         type inet:uri;
         mandatory true;
         description "URI specifying the location of the file.";
       }
       leaf bytes {
         type yang:counter64;
         units octets;
         config false;
         description "The number of bytes read by the File Reader.
           ... ";
       }
       leaf messages {
         type yang:counter64;
         units "IPFIX Messages";
         config false;
         description "The number of IPFIX Messages read by the File
           Reader. ... ";
       }
       leaf records {
         type yang:counter64;
         units "Data Records";
         config false;
         description "The number of Data Records read by the File
           Reader. ... ";
       }
       leaf templates {
         type yang:counter32;
         units "Templates";
         config false;
         description "The number of Template Records (excluding
           Options Template Records) read by the File Reader. ...";
       }
       leaf optionsTemplates {
         type yang:counter32;
         units "Options Templates";
         config false;

         description "The number of Options Template Records read by
           the File Reader. ... ";
       }
       leaf fileReaderDiscontinuityTime {
         type yang:date-and-time;
         config false;
         description "Timestamp of the most recent occasion ... ";
       }
       list template {
         config false;
         description "This list contains the Templates and Options
           Templates that have been read by the File Reader.
           Withdrawn or invalidated (Options) Templates MUST be removed
           from this list.";
         uses templateParameters;
       }
     }

     ct:complex-type SelectionProcess {
         description "Selection Process";
         key name;
         leaf name {
           type nameType;
           description "Key of a selection process.";
         }
         ct:instance-list selector {
           ct:instance-type Selector;
           min-elements 1;
           ordered-by user;
           description "List of Selectors that define the action of the
             Selection Process on a single packet.  The Selectors are
             serially invoked in the same order as they appear in this
             list.";
         }
         list selectionSequence {
           config false;
           description "This list contains the Selection Sequence IDs
             which are assigned by the Monitoring Device ... ";
           reference "RFC 5476.";
           leaf observationDomainId {
             type uint32;
             description "Observation Domain ID for which the
               Selection Sequence ID is assigned.";
           }
           leaf selectionSequenceId {
             type uint64;
             description "Selection Sequence ID used in the Selection
               Sequence (Statistics) Report Interpretation.";

           }
         }
         leaf cache {
           type instance-identifier { ct:instance-type Cache; }
           description "Cache which receives the output of the
             Selection Process.";
         }
       }

     /*****************************************************************
     * Groupings
     *****************************************************************/

     grouping transportLayerSecurityParameters {
       description "Transport layer security parameters.";
       leaf-list localCertificationAuthorityDN {
         type string;
         description "Distinguished names of certification authorities
           whose certificates may be used to identify the local
           endpoint.";
       }
       leaf-list localSubjectDN {
         type string;
         description "Distinguished names that may be used in the
           certificates to identify the local endpoint.";
       }
       leaf-list localSubjectFQDN {
         type inet:domain-name;
         description "Fully qualified domain names that may be used to
           in the certificates to identify the local endpoint.";
       }
       leaf-list remoteCertificationAuthorityDN {
         type string;
         description "Distinguished names of certification authorities
           whose certificates are accepted to authorize remote
           endpoints.";
       }
       leaf-list remoteSubjectDN {
         type string;
         description "Distinguished names that are accepted in
           certificates to authorize remote endpoints.";
       }
       leaf-list remoteSubjectFQDN {
         type inet:domain-name;
         description "Fully qualified domain names that are accepted in
           certificates to authorize remote endpoints.";
       }
     }

     grouping templateParameters {
       description "State parameters of a Template used by an Exporting
         Process or received by a Collecting Process ... ";
       reference "RFC 5101; RFC 5815, Section 8 (ipfixTemplateEntry,
         ipfixTemplateDefinitionEntry, ipfixTemplateStatsEntry)";
       leaf observationDomainId {
         type uint32;
         description "The ID of the Observation Domain for which this
           Template is defined.";
         reference "RFC 5815, Section 8
           (ipfixTemplateObservationDomainId).";
       }
       leaf templateId {
         type uint16 {
           range "256..65535" {
             description "Valid range of Template Ids.";
             reference "RFC 5101";
           }
         }
         description "This number indicates the Template Id in the IPFIX
           message.";
         reference "RFC 5815, Section 8 (ipfixTemplateId).";
       }
       leaf setId {
         type uint16;
         description "This number indicates the Set Id of the Template.
           ... ";
         reference "RFC 5815, Section 8 (ipfixTemplateSetId).";
       }
       leaf accessTime {
         type yang:date-and-time;
         description "Used for Exporting Processes, ... ";
         reference "RFC 5815, Section 8 (ipfixTemplateAccessTime).";
       }
       leaf templateDataRecords {
         type yang:counter64;
         description "The number of transmitted or received Data
           Records ... ";
         reference "RFC 5815, Section 8 (ipfixTemplateDataRecords).";
       }
       leaf templateDiscontinuityTime {
         type yang:date-and-time;
         description "Timestamp of the most recent occasion at which
           the counter templateDataRecords suffered a discontinuity.
           ... ";
         reference "RFC 5815, Section 8
           (ipfixTemplateDiscontinuityTime).";
       }

       list field {
         description "This list contains the (Options) Template
           fields of which the (Options) Template is defined.
           ... ";
         leaf ieId {
           type uint16 {
             range "1..32767" {
               description "Valid range of Information Element
                   identifiers.";
               reference "RFC 5102, Section 4.";
             }
           }
           description "This parameter indicates the Information
             Element Id of the field.";
           reference "RFC 5815, Section 8 (ipfixTemplateDefinitionIeId);
             RFC 5102.";
         }
         leaf ieLength {
           type uint16;
           units octets;
           description "This parameter indicates the length of the
             Information Element of the field.";
           reference "RFC 5815, Section 8
             (ipfixTemplateDefinitionIeLength); RFC 5102.";
         }
         leaf ieEnterpriseNumber {
           type uint32;
           description "This parameter indicates the IANA enterprise
             number of the authority ... ";
           reference "RFC 5815, Section 8
             (ipfixTemplateDefinitionEnterpriseNumber).";
         }
         leaf isFlowKey {
           when "../../setId = 2" {
             description "This parameter is available for non-Options
               Templates (Set Id is 2).";
           }
           type empty;
           description "If present, this is a Flow Key field.";
           reference "RFC 5815, Section 8
             (ipfixTemplateDefinitionFlags).";
         }
         leaf isScope {
           when "../../setId = 3" {
             description "This parameter is available for Options
               Templates (Set Id is 3).";
           }
           type empty;

           description "If present, this is a scope field.";
           reference "RFC 5815, Section 8
             (ipfixTemplateDefinitionFlags).";
         }
       }
     }

     grouping transportSessionParameters {
       description "State parameters of a Transport Session ... ";
       reference "RFC 5101; RFC 5815, Section 8
         (ipfixTransportSessionEntry,
          ipfixTransportSessionStatsEntry)";
       leaf ipfixVersion {
         type uint16;
         description "Used for Exporting Processes, this parameter
           contains the version number of the IPFIX protocol ... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionIpfixVersion).";
       }
       leaf sourceAddress {
         type inet:ip-address;
         description "The source address of the Exporter of the
           IPFIX Transport Session... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionSourceAddressType,
           ipfixTransportSessionSourceAddress).";
       }
       leaf destinationAddress {
         type inet:ip-address;
         description "The destination address of the Collector of
           the IPFIX Transport Session... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionDestinationAddressType,
           ipfixTransportSessionDestinationAddress).";
       }
       leaf sourcePort {
         type inet:port-number;
         description "The transport protocol port number of the
           Exporter of the IPFIX Transport Session.";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionSourcePort).";
       }
       leaf destinationPort {
         type inet:port-number;
         description "The transport protocol port number of the
           Collector of the IPFIX Transport Session... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionDestinationPort).";

       }
       leaf sctpAssocId {
         type uint32;
         description "The association id used for the SCTP session
           between the Exporter and the Collector ... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionSctpAssocId),
           RFC 3871";
       }
       leaf status {
         type transportSessionStatus;
         description "Status of the Transport Session.";
         reference "RFC 5815, Section 8 (ipfixTransportSessionStatus).";
       }
       leaf rate {
         type yang:gauge32;
         units "bytes per second";
         description "The number of bytes per second transmitted by the
           Exporting Process or received by the Collecting Process.
           This parameter is updated every second.";
         reference "RFC 5815, Section 8 (ipfixTransportSessionRate).";
       }
       leaf bytes {
         type yang:counter64;
         units bytes;
         description "The number of bytes transmitted by the
           Exporting Process or received by the Collecting
           Process ... ";
         reference "RFC 5815, Section 8 (ipfixTransportSessionBytes).";
       }
       leaf messages {
         type yang:counter64;
         units "IPFIX Messages";
         description "The number of messages transmitted by the
           Exporting Process or received by the Collecting Process... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionMessages).";
       }
       leaf discardedMessages {
         type yang:counter64;
         units "IPFIX Messages";
         description "Used for Exporting Processes, this parameter
           indicates the number of messages that could not be
           sent ...";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionDiscardedMessages).";
       }
       leaf records {

         type yang:counter64;
         units "Data Records";
         description "The number of Data Records transmitted ... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionRecords).";
       }
       leaf templates {
         type yang:counter32;
         units "Templates";
         description "The number of Templates transmitted by the
           Exporting Process or received by the Collecting Process.
           ... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionTemplates).";
       }
       leaf optionsTemplates {
         type yang:counter32;
         units "Options Templates";
         description "The number of Option Templates transmitted by the
           Exporting Process or received by the Collecting Process...";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionOptionsTemplates).";
       }
       leaf transportSessionStartTime {
         type yang:date-and-time;
         description "Timestamp of the start of the given Transport
           Session... ";
       }
       leaf transportSessionDiscontinuityTime {
         type yang:date-and-time;
         description "Timestamp of the most recent occasion at which
           one or more of the Transport Session counters suffered a
           discontinuity... ";
         reference "RFC 5815, Section 8
           (ipfixTransportSessionDiscontinuityTime).";
       }
       list template {
         description "This list contains the Templates and Options
           Templates that are transmitted by the Exporting Process
           or received by the Collecting Process.
           Withdrawn or invalidated (Options) Templates MUST be removed
           from this list.";
         uses templateParameters;
       }
     }

     /*****************************************************************
     * Main container

     *****************************************************************/

     container ipfix {
       description "Top-level node of the IPFIX/PSAMP configuration
         data model.";
       ct:instance-list collectingProcess {
         if-feature collector;
         ct:instance-type CollectingProcess;
       }

       ct:instance-list observationPoint {
         if-feature meter;
         ct:instance-type ObservationPoint;
       }

       ct:instance-list selectionProcess {
         if-feature meter;
         ct:instance-type SelectionProcess;
       }

       ct:instance-list cache {
         if-feature meter;
         description "Cache of the Monitoring Device.";
         ct:instance-type Cache;
       }

       ct:instance-list exportingProcess {
         if-feature exporter;
         description "Exporting Process of the Monitoring Device.";
         ct:instance-type ExportingProcess;
       }

     }
}
<CODE ENDS>

Authors' Addresses

   Bernd Linowski
   TCS/Nokia Siemens Networks
   Heltorfer Strasse 1
   Duesseldorf  40472
   Germany

   EMail: bernd.linowski.ext@nsn.com

   Mehmet Ersue
   Nokia Siemens Networks
   St.-Martin-Strasse 76
   Munich  81541
   Germany

   EMail: mehmet.ersue@nsn.com

   Siarhei Kuryla
   360 Treasury Systems
   Grueneburgweg 16-18
   Frankfurt am Main  60322
   Germany

   EMail: s.kuryla@gmail.com

 

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