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RFC 4258 - Requirements for Generalized Multi-Protocol Label Swi

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Network Working Group                                   D. Brungard, Ed.
Request for Comments: 4258                                           ATT
Category: Informational                                    November 2005

  Requirements for Generalized Multi-Protocol Label Switching (GMPLS)
     Routing for the Automatically Switched Optical Network (ASON)

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   The Generalized Multi-Protocol Label Switching (GMPLS) suite of
   protocols has been defined to control different switching
   technologies as well as different applications.  These include
   support for requesting Time Division Multiplexing (TDM) connections
   including Synchronous Optical Network (SONET)/Synchronous Digital
   Hierarchy (SDH) and Optical Transport Networks (OTNs).

   This document concentrates on the routing requirements placed on the
   GMPLS suite of protocols in order to support the capabilities and
   functionalities of an Automatically Switched Optical Network (ASON)
   as defined by the ITU-T.

Table of Contents

   1. Introduction ....................................................2
   2. Conventions Used in This Document ...............................4
   3. ASON Routing Architecture and Requirements ......................4
      3.1. Multiple Hierarchical Levels of ASON Routing Areas (RAs) ...5
      3.2. Hierarchical Routing Information Dissemination .............6
      3.3. Configuration ..............................................8
           3.3.1. Configuring the Multi-Level Hierarchy ...............8
           3.3.2. Configuring RC Adjacencies ..........................8
      3.4. Evolution ..................................................8
      3.5. Routing Attributes .........................................8
           3.5.1. Taxonomy of Routing Attributes ......................9
           3.5.2. Commonly Advertised Information .....................9
           3.5.3. Node Attributes ....................................10
           3.5.4. Link Attributes ....................................11
   4. Security Considerations ........................................12
   5. Conclusions ....................................................12
   6. Contributors ...................................................15
   7. Acknowledgements ...............................................15
   8. References .....................................................16
      8.1. Normative References ......................................16
      8.2. Informative References ....................................16

1.  Introduction

   The Generalized Multi-Protocol Label Switching (GMPLS) suite of
   protocols provides, among other capabilities, support for controlling
   different switching technologies.  These include support for
   requesting TDM connections utilizing SONET/SDH (see [T1.105] and
   [G.707], respectively) as well as Optical Transport Networks (OTNs,
   see [G.709]).  However, there are certain capabilities that are
   needed to support the ITU-T G.8080 control plane architecture for an
   Automatically Switched Optical Network (ASON).  Therefore, it is
   desirable to understand the corresponding requirements for the GMPLS
   protocol suite.  The ASON control plane architecture is defined in
   [G.8080]; ASON routing requirements are identified in [G.7715] and in
   [G.7715.1] for ASON link state protocols.  These Recommendations
   apply to all [G.805] layer networks (e.g., SDH and OTN), and provide
   protocol-neutral functional requirements and architecture.

   This document focuses on the routing requirements for the GMPLS suite
   of protocols to support the capabilities and functionality of ASON
   control planes.  This document summarizes the ASON requirements using
   ASON terminology.  This document does not address GMPLS applicability
   or GMPLS capabilities.  Any protocol (in particular, routing)

   applicability, design, or suggested extensions are strictly outside
   the scope of this document.  ASON (Routing) terminology sections are
   provided in Appendixes 1 and 2.

   The ASON routing architecture is based on the following assumptions:

   -  A network is subdivided based on operator decision and criteria
      (e.g., geography, administration, and/or technology); the network
      subdivisions are defined in ASON as Routing Areas (RAs).

   -  The routing architecture and protocols applied after the network
      is subdivided are an operator's choice.  A multi-level hierarchy
      of RAs, as defined in ITU-T [G.7715] and [G.7715.1], provides for
      a hierarchical relationship of RAs based on containment; i.e.,
      child RAs are always contained within a parent RA.  The
      hierarchical containment relationship of RAs provides for routing
      information abstraction, thereby enabling scalable routing
      information representation.  The maximum number of hierarchical RA
      levels to be supported is not specified (outside the scope of this

   -  Within an ASON RA and for each level of the routing hierarchy,
      multiple routing paradigms (hierarchical, step-by-step, source-
      based), centralized or distributed path computation, and multiple
      different routing protocols MAY be supported.  The architecture
      does not assume a one-to-one correspondence between a routing
      protocol and an RA level, and allows the routing protocol(s) used
      within different RAs (including child and parent RAs) to be
      different.  The realization of the routing paradigm(s) to support
      the hierarchical levels of RAs is not specified.

   -  The routing adjacency topology (i.e., the associated Protocol
      Controller (PC) connectivity) and transport topology are NOT
      assumed to be congruent.

   -  The requirements support architectural evolution, e.g., a change
      in the number of RA levels, as well as aggregation and
      segmentation of RAs.

   The description of the ASON routing architecture provides for a
   conceptual reference architecture, with definition of functional
   components and common information elements to enable end-to-end
   routing in the case of protocol heterogeneity and facilitate
   management of ASON networks.  This description is only conceptual: no
   physical partitioning of these functions is implied.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   Although [RFC2119] describes interpretations of these key words in
   terms of protocol specifications and implementations, they are used
   in this document to describe design requirements for protocol

3.  ASON Routing Architecture and Requirements

   The fundamental architectural concept is the RA and its related
   functional components (see Appendix 2 on terminology).  The routing
   services offered by an RA are provided by a Routing Performer (RP).
   An RP is responsible for a single RA, and it MAY be functionally
   realized using distributed Routing Controllers (RCs).  The RC,
   itself, MAY be implemented as a cluster of distributed entities (ASON
   refers to the cluster as a Routing Control Domain (RCD)).  The RC
   components for an RA receive routing topology information from their
   associated Link Resource Manager(s) (LRMs) and store this information
   in the Routing Information Database (RDB).  The RDB is replicated at
   each RC bounded to the same RA, and MAY contain information about
   multiple transport plane network layers.  Whenever the routing
   topology changes, the LRM informs the corresponding RC, which in turn
   updates its associated RDB.  In order to ensure RDB synchronization,
   the RCs cooperate and exchange routing information.  Path computation
   functions MAY exist in each RC, MAY exist on selected RCs within the
   same RA, or MAY be centralized for the RA.

   In this context, communication between RCs within the same RA is
   realized using a particular routing protocol (or multiple protocols).
   In ASON, the communication component is represented by the protocol
   controller (PC) component(s) and the protocol messages are conveyed
   over the ASON control plane's Signaling Control Network (SCN).  The
   PC MAY convey information for one or more transport network layers
   (refer to the note in Section 3.2).  The RC is protocol independent,
   and RC communications MAY be realized by multiple, different PCs
   within an RA.

   The ASON routing architecture defines a multi-level routing hierarchy
   of RAs based on a containment model to support routing information
   abstraction.  [G.7715.1] defines the ASON hierarchical link state
   routing protocol requirements for communication of routing
   information within an RA (one level) to support hierarchical routing
   information dissemination (including summarized routing information

   for other levels).  The communication between any of the other
   functional component(s) (e.g., SCN, LRM, and between RCDs (RC-RC
   communication between RAs)) is outside the scope of [G.7715.1]
   protocol requirements and, thus, is also outside the scope of this

   ASON routing components are identified by identifiers that are drawn
   from different name spaces (see [G.7715.1]).  These are control plane
   identifiers for transport resources, components, and SCN addresses.
   The formats of those identifiers in a routing protocol realization
   SHALL be implementation specific and outside the scope of this

   The failure of an RC, or the failure of communications between RCs,
   and the subsequent recovery from the failure condition MUST NOT
   disrupt calls in progress (i.e., already established) and their
   associated connections.  Calls being set up MAY fail to complete, and
   the call setup service MAY be unavailable during recovery actions.

3.1.  Multiple Hierarchical Levels of ASON Routing Areas (RAs)

   [G.8080] introduces the concept of a Routing Area (RA) in reference
   to a network subdivision.  RAs provide for routing information
   abstraction.  Except for the single RA case, RAs are hierarchically
   contained: a higher-level (parent) RA contains lower-level (child)
   RAs that in turn MAY also contain RAs, etc.  Thus, RAs contain RAs
   that recursively define successive hierarchical RA levels.

   However, the RA containment relationship describes only an
   architectural hierarchical organization of RAs.  It does not restrict
   a specific routing protocol's realization (e.g., OSPF multi-areas,
   path computation, etc.).  Moreover, the realization of the routing
   paradigm to support a hierarchical organization of RAs and the number
   of hierarchical RA levels to be supported is routing protocol
   specific and outside the scope of this document.

   In a multi-level hierarchy of RAs, it is necessary to distinguish
   among RCs for the different levels of the RA hierarchy.  Before any
   pair of RCs establishes communication, they MUST verify that they are
   bound to the same parent RA (see Section 3.2).  An RA identifier (RA
   ID) is required to provide the scope within which the RCs can
   communicate.  To distinguish between RCs bound to the same RA, an RC
   identifier (RC ID) is required; the RC ID MUST be unique within its
   containing RA.

   An RA represents a partition of the data plane, and its identifier
   (i.e., RA ID) is used within the control plane as a reference to the
   data plane partition.  Each RA within a carrier's network SHALL be

   uniquely identifiable.  RA IDs MAY be associated with a transport
   plane name space, whereas RC IDs are associated with a control plane
   name space.

3.2.  Hierarchical Routing Information Dissemination

   Routing information can be exchanged between RCs bound to adjacent
   levels of the RA hierarchy, i.e., Level N+1 and N, where Level N
   represents the RAs contained by Level N+1.  The links connecting RAs
   may be viewed as external links (inter-RA links), and the links
   representing connectivity within an RA may be viewed as internal
   links (intra-RA links).  The external links to an RA at one level of
   the hierarchy may be internal links in the parent RA.  Intra-RA links
   of a child RA MAY be hidden from the parent RA's view.

   The physical location of RCs for adjacent RA levels, their
   relationship, and their communication protocol(s) are outside the
   scope of this document.  No assumption is made regarding how RCs
   communicate between adjacent RA levels.  If routing information is
   exchanged between an RC, its parent, and its child RCs, it SHOULD
   include reachability (see Section 3.5.3) and MAY include, upon policy
   decision, node and link topology.  Communication between RAs only
   takes place between RCs with a parent/child relationship.  RCs of one
   RA never communicate with RCs of another RA at the same level.  There
   SHOULD not be any dependencies on the different routing protocols
   used within an RA or in different RAs.

   Multiple RCs bound to the same RA MAY transform (filter, summarize,
   etc.) and then forward information to RCs at different levels.
   However, in this case, the resulting information at the receiving
   level must be self-consistent (i.e., ensure consistency between
   transform operations performed on routing information at different
   levels to ensure proper information processing).  This MAY be
   achieved using a number of mechanisms.

   Note: There is no implied relationship between multi-layer transport
   networks and multi-level routing.  Implementations MAY support a
   hierarchical routing topology (multi-level) with a single routing
   protocol instance for multiple transport switching layers or a
   hierarchical routing topology for one transport switching layer.

   1. Type of Information Exchanged

      The type of information flowing upward (i.e., Level N to Level
      N+1) and the information flowing downward (i.e., Level N+1 to
      Level N) are used for similar purposes, namely, the exchange of
      reachability information and summarized topology information to

      allow routing across multiple RAs.  The summarization of topology
      information may impact the accuracy of routing and may require
      additional path calculation.

      The following information exchanges are expected:

      -  Level N+1 visibility to Level N reachability and topology (or
         upward information communication) allowing RC(s) at Level N+1
         to determine the reachable endpoints from Level N.

      -  Level N visibility to Level N+1 reachability and topology (or
         downward information communication) allowing RC(s) bounded to
         an RA at Level N to develop paths to reachable endpoints
         outside of the RA.

   2. Interactions between Upward and Downward Communication

      When both upward and downward information exchanges contain
      endpoint reachability information, a feedback loop could
      potentially be created.  Consequently, the routing protocol MUST
      include a method to:

      -  prevent information propagated from a Level N+1 RA's RC into
         the Level N RA's RC from being re-introduced into the Level N+1
         RA's RC, and

      -  prevent information propagated from a Level N-1 RA's RC into
         the Level N RA's RC from being re-introduced into the Level N-1
         RA's RC.

      The routing protocol SHALL differentiate the routing information
      originated at a given-level RA from derived routing information
      (received from external RAs), even when this information is
      forwarded by another RC at the same level.  This is a necessary
      condition to be fulfilled by routing protocols to be loop free.

   3. Method of Communication

      Two approaches exist for communication between Level N and N+1:

      -  The first approach places an instance of a Level N routing
         function and an instance of a Level N+1 routing function in the
         same system.  The communications interface is within a single
         system and is thus not an open interface subject to
         standardization.  However, information re-advertisement or
         leaking MUST be performed in a consistent manner to ensure
         interoperability and basic routing protocol correctness (e.g.,
         cost/metric value).

      -  The second approach places the Level N routing function on a
         separate system from the Level N+1 routing function.  In this
         case, a communication interface must be used between the
         systems containing the routing functions for different levels.
         This communication interface and mechanisms are outside the
         scope of this document.

3.3.  Configuration

3.3.1.  Configuring the Multi-Level Hierarchy

   The RC MUST support static (i.e., operator assisted) and MAY support
   automated configuration of the information describing its
   relationship to its parent and its child within the hierarchical
   structure (including RA ID and RC ID).  When applied recursively, the
   whole hierarchy is thus configured.

3.3.2.  Configuring RC Adjacencies

   The RC MUST support static (i.e., operator assisted) and MAY support
   automated configuration of the information describing its associated
   adjacencies to other RCs within an RA.  The routing protocol SHOULD
   support all the types of RC adjacencies described in Section 9 of
   [G.7715].  The latter includes congruent topology (with distributed
   RC) and hubbed topology (e.g., note that the latter does not
   automatically imply a designated RC).

3.4.  Evolution

   The containment relationships of RAs may change, motivated by events
   such as mergers, acquisitions, and divestitures.

   The routing protocol SHOULD be capable of supporting architectural
   evolution in terms of the number of hierarchical levels of RAs, as
   well as the aggregation and segmentation of RAs.  RA ID uniqueness
   within an administrative domain may facilitate these operations.  The
   routing protocol is not expected to automatically initiate and/or
   execute these operations.  Reconfiguration of the RA hierarchy may
   not disrupt calls in progress, though calls being set up may fail to
   complete, and the call setup service may be unavailable during
   reconfiguration actions.

3.5.  Routing Attributes

   Routing for transport networks is performed on a per-layer basis,
   where the routing paradigms MAY differ among layers and within a
   layer.  Not all equipment supports the same set of transport layers
   or the same degree of connection flexibility at any given layer.  A

   server layer trail may support various clients, involving different
   adaptation functions.  In addition, equipment may support variable
   adaptation functionality, whereby a single server layer trail
   dynamically supports different multiplexing structures.  As a result,
   routing information MAY include layer-specific, layer-independent,
   and client/server adaptation information.

3.5.1.  Taxonomy of Routing Attributes

   Attributes can be organized according to the following categories:

   -  Node related or link related

   -  Provisioned, negotiated, or automatically configured

   -  Inherited or layer specific (client layers can inherit some
      attributes from the server layer, while other attributes such as
      Link Capacity are specified by layer)

   (Component) link attributes MAY be statically or automatically
   configured for each transport network layer.  This may lead to
   unnecessary repetition.  Hence, the inheritance property of
   attributes MAY also be used to optimize the configuration process.

   ASON uses the term SubNetwork Point (SNP) for the control plane
   representation of a transport plane resource.  The control plane
   representation and transport plane topology are NOT assumed to be
   congruent; the control plane representation SHALL not be restricted
   by the physical topology.  The relational grouping of SNPs for
   routing is termed an SNP Pool (SNPP).  The routing function
   understands topology in terms of SNPP links.  Grouping MAY be based
   on different link attributes (e.g., SRLG information, link weight,

   Two RAs may be linked by one or more SNPP links.  Multiple SNPP links
   may be required when component links are not equivalent for routing
   purposes with respect to the RAs to which they are attached, to the
   containing RA, or when smaller groupings are required.

3.5.2.  Commonly Advertised Information

   Advertisements MAY contain the following common set of information
   regardless of whether they are link or node related:

   -  RA ID of the RA to which the advertisement is bounded

   -  RC ID of the entity generating the advertisement

   -  Information to uniquely identify advertisements

   -  Information to determine whether an advertisement has been updated

   -  Information to indicate when an advertisement has been derived
      from a different level RA

3.5.3.  Node Attributes

   All nodes belong to an RA; hence, the RA ID can be considered an
   attribute of all nodes.  Given that no distinction is made between
   abstract nodes and those that cannot be decomposed any further, the
   same attributes MAY be used for their advertisement.  In the
   following tables, Capability refers to the level of support required
   in the realization of a link state routing protocol, whereas Usage
   refers to the degree of operational control that SHOULD be available
   to the operator.

   The following Node Attributes are defined:

      Attribute        Capability      Usage
      -----------      -----------     ---------
      Node ID          REQUIRED        REQUIRED
      Reachability     REQUIRED        OPTIONAL

               Table 1. Node Attributes

   Reachability information describes the set of endpoints that are
   reachable by the associated node.  It MAY be advertised as a set of
   associated external (e.g., User Network Interface (UNI))
   address/address prefixes or a set of associated SNPP link IDs/SNPP ID
   prefixes, the selection of which MUST be consistent within the
   applicable scope.  These are control plane identifiers; the formats
   of these identifiers in a protocol realization are implementation
   specific and outside the scope of this document.

   Note: No distinction is made between nodes that may have further
   internal details (i.e., abstract nodes) and those that cannot be
   decomposed any further.  Hence, the attributes of a node are not
   considered as only single-switch attributes but MAY apply to a node
   at a higher level of the hierarchy that represents a subnetwork.

3.5.4.  Link Attributes

   The following Link Attributes are defined:

      Link Attribute                   Capability      Usage
      ---------------                  -----------     ---------
      Local SNPP link ID               REQUIRED        REQUIRED
      Remote SNPP link ID              REQUIRED        REQUIRED
      Layer Specific Characteristics   see Table 3

                        Table 2. Link Attributes

   The SNPP link ID MUST be sufficient to uniquely identify (within the
   Node ID scope) the corresponding transport plane resource, taking
   into account the separation of data and control planes (see Section
   3.5.1; the control plane representation and transport plane topology
   are not assumed to be congruent).  The SNPP link ID format is routing
   protocol specific.

   Note: When the remote end of an SNPP link is located outside of the
   RA, the remote SNPP link ID is OPTIONAL.

   The following link characteristic attributes are defined:

   -  Signal Type: This identifies the characteristic information of the
      layer network.

   -  Link Weight: This is the metric indicating the relative
      desirability of a particular link over another, e.g., during path

   -  Resource Class: This corresponds to the set of administrative
      groups assigned by the operator to this link.  A link MAY belong
      to zero, one, or more administrative groups.

   -  Local Connection Types: This attribute identifies whether the
      local SNP represents a Termination Connection Point (CP), a
      Connection Point (CP), or can be flexibly configured as a TCP.

   -  Link Capacity: This provides the sum of the available and
      potential bandwidth capacity for a particular network transport
      layer.  Other capacity measures MAY be further considered.

   -  Link Availability: This represents the survivability capability
      such as the protection type associated with the link.

   -  Diversity Support: This represents diversity information such as
      the SRLG information associated with the link.

   -  Local Adaptation Support: This indicates the set of client layer
      adaptations supported by the TCP associated with the local SNPP.
      This is applicable only when the local SNP represents a TCP or can
      be flexibly configured as a TCP.

      Link Characteristics            Capability      Usage
      -----------------------         ----------      ---------
      Signal Type                     REQUIRED        OPTIONAL
      Link Weight                     REQUIRED        OPTIONAL
      Resource Class                  REQUIRED        OPTIONAL
      Local Connection Types          REQUIRED        OPTIONAL
      Link Capacity                   REQUIRED        OPTIONAL
      Link Availability               OPTIONAL        OPTIONAL
      Diversity Support               OPTIONAL        OPTIONAL
      Local Adaptation Support        OPTIONAL        OPTIONAL

                     Table 3. Link Characteristics

   Note: Separate advertisements of layer-specific attributes MAY be
   chosen.  However, this may lead to unnecessary duplication.  This can
   be avoided using the inheritance property, so that the attributes
   derivable from the local adaptation information do not need to be
   advertised.  Thus, an optimization MAY be used when several layers
   are present by indicating when an attribute is inheritable from a
   server layer.

4.  Security Considerations

   The ASON routing protocol MUST deliver the operational security
   objectives where required.  The overall security objectives (defined
   in ITU-T Recommendation [M.3016]) of confidentiality, integrity, and
   accountability may take on varying levels of importance.  These
   objectives do not necessarily imply requirements on the routing
   protocol itself, and MAY be met by other established means.

   Note: A threat analysis of a proposed routing protocol SHOULD address
   masquerade, eavesdropping, unauthorized access, loss or corruption of
   information (including replay attacks), repudiation, forgery, and
   denial of service attacks.

5.  Conclusions

   The description of the ASON routing architecture and components is
   provided in terms of routing functionality.  This description is only
   conceptual: no physical partitioning of these functions is implied.

   In summary, the ASON routing architecture assumes:

   -  A network is subdivided into ASON RAs, which MAY support multiple
      routing protocols; no one-to-one relationship SHALL be assumed.

   -  Routing Controllers (RCs) provide for the exchange of routing
      information (primitives) for the RA.  The RC is protocol
      independent and MAY be realized by multiple, different protocol
      controllers within an RA.  The routing information exchanged
      between RCs SHALL be subject to policy constraints imposed at
      reference points (External- and Internal-NNI).

   -  In a multi-level RA hierarchy based on containment, communication
      between RCs of different RAs happens only when there is a
      parent/child relationship between the RAs.  RCs of child RAs never
      communicate with the RCs of other child RAs.  There SHOULD not be
      any dependencies on the different routing protocols used within a
      child RA and that of its parent.  The routing information
      exchanged within the parent RA SHALL be independent of both the
      routing protocol operating within a child RA and any control
      distribution choice(s), e.g., centralized, fully distributed.

   -  For an RA, the set of RCs is referred to as an ASON routing
      (control) domain.  The routing information exchanged between
      routing domains (inter-RA, i.e., inter-domain) SHALL be
      independent of both the intra-domain routing protocol(s) and the
      intra-domain control distribution choice(s), e.g., centralized,
      fully distributed.  RCs bounded to different RA levels MAY be
      collocated within the same physical element or physically

   -  The routing adjacency topology (i.e., the associated PC
      connectivity topology) and the transport network topology SHALL
      NOT be assumed to be congruent.

   -  The routing topology SHALL support multiple links between nodes
      and RAs.

   In summary, the following functionality is expected from GMPLS
   routing to instantiate the ASON hierarchical routing architecture
   realization (see [G.7715] and [G.7715.1]):

   -  RAs SHALL be uniquely identifiable within a carrier's network,
      each having a unique RA ID within the carrier's network.

   -  Within an RA (one level), the routing protocol SHALL support
      dissemination of hierarchical routing information (including
      summarized routing information for other levels) in support of an

      architecture of multiple hierarchical levels of RAs; the number of
      hierarchical RA levels to be supported by a routing protocol is
      implementation specific.

   -  The routing protocol SHALL support routing information based on a
      common set of information elements as defined in [G.7715] and
      [G.7715.1], divided between attributes pertaining to links and
      abstract nodes (each representing either a subnetwork or simply a
      node).  [G.7715] recognizes that the manner in which the routing
      information is represented and exchanged will vary with the
      routing protocol used.

   -  The routing protocol SHALL converge such that the distributed RDBs
      become synchronized after a period of time.

   To support hierarchical routing information dissemination within an
   RA, the routing protocol MUST deliver:

   -  Processing of routing information exchanged between adjacent
      levels of the hierarchy (i.e., Level N+1 and N) including
      reachability and, upon policy, decision summarized topology

   -  Self-consistent information at the receiving level resulting from
      any transformation (filter, summarize, etc.) and forwarding of
      information from one RC to RC(s) at different levels when multiple
      RCs are bound to a single RA.

   -  A mechanism to prevent the re-introduction of information
      propagated into the Level N RA's RC back to the adjacent level
      RA's RC from which this information has been initially received.

   In order to support operator-assisted changes in the containment
   relationships of RAs, the routing protocol SHALL support evolution in
   terms of the number of hierarchical levels of RAs.  For example:
   support of non-disruptive operations such as adding and removing RAs
   at the top/bottom of the hierarchy, adding or removing a hierarchical
   level of RAs in or from the middle of the hierarchy, as well as
   aggregation and segmentation of RAs.  The number of hierarchical
   levels to be supported is routing protocol specific and reflects a
   containment relationship; e.g., an RA insertion involves supporting a
   different routing protocol domain in a portion of the network.

   Reachability information (see Section 3.5.3) of the set of endpoints
   reachable by a node may be advertised either as a set of UNI
   Transport Resource addresses/address prefixes or a set of associated
   SNPP link IDs/SNPP link ID prefixes, assigned and selected
   consistently in their applicability scope.  The formats of the

   control plane identifiers in a protocol realization are
   implementation specific.  Use of a routing protocol within an RA
   should not restrict the choice of routing protocols for use in other
   RAs (child or parent).

   As ASON does not restrict the control plane architecture choice used,
   either a collocated architecture or a physically separated
   architecture may be used.  A collection of links and nodes such as a
   subnetwork or RA MUST be able to represent itself to the wider
   network as a single logical entity with only its external links
   visible to the topology database.

6.  Contributors

   This document is the result of the CCAMP Working Group ASON Routing
   Requirements design team joint effort.  The following are the design
   team member authors who contributed to the present document:

      Wesam Alanqar (Sprint)
      Deborah Brungard (ATT)
      David Meyer (Cisco Systems)
      Lyndon Ong (Ciena)
      Dimitri Papadimitriou (Alcatel)
      Jonathan Sadler (Tellabs)
      Stephen Shew (Nortel)

7.  Acknowledgements

   The authors would like to thank Kireeti Kompella for having initiated
   the proposal of an ASON Routing Requirement Design Team and the ITU-T
   SG15/Q14 for their careful review and input.

8.  References

8.1.  Normative References

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

8.2.  Informative References

   For information on the availability of the following documents,
   please see http://www.itu.int:

   [G.707]    ITU-T Rec. G.707/Y.1322, "Network Node Interface for the
              Synchronous Digital Hierarchy (SDH)", December 2003.

   [G.709]    ITU-T Rec. G.709/Y.1331, "Interfaces for the Optical
              Transport Network (OTN)", March 2003.

   [G.7715]   ITU-T Rec. G.7715/Y.1306, "Architecture and Requirements
              for the Automatically Switched Optical Network (ASON)",
              June 2002.

   [G.7715.1] ITU-T Draft Rec. G.7715.1/Y.1706.1, "ASON Routing
              Architecture and Requirements for Link State Protocols",
              November 2003.

   [G.805]    ITU-T Rec. G.805, "Generic Functional Architecture of
              Transport Networks", March 2000.

   [G.8080]   ITU-T Rec. G.8080/Y.1304, "Architecture for the
              Automatically Switched Optical Network (ASON)", November
              2001 (and Revision, January 2003).

   [M.3016]   ITU-T Rec. M.3016.0, "Security for the Management Plane:
              Overview", May 2005.

   [T1.105]   ANSI T1.105, "Synchronous Optical Network (SONET) - Basic
              Description including Multiplex Structure, Rates, and
              Formats", 2001.

Appendix 1: ASON Terminology

   This document makes use of the following terms:

   Administrative domain (see Recommendation [G.805]): For the purposes
   of [G.7715.1], an administrative domain represents the extent of
   resources that belong to a single player such as a network operator,
   a service provider, or an end-user.  Administrative domains of
   different players do not overlap amongst themselves.

   Adaptation function (see Recommendation [G.805]): A "transport
   processing function" that processes the client layer information for
   transfer over a server layer trail.

   Client/Server relationship: The association between layer networks
   that is performed by an "adaptation" function to allow the link
   connection in the client layer network to be supported by a trail in
   the server layer network.

   Control plane: Performs the call control and connection control
   functions.  Through signaling, the control plane sets up and releases
   connections and may restore a connection in case of a failure.

   (Control) Domain: Represents a collection of (control) entities that
   are grouped for a particular purpose.  The control plane is
   subdivided into domains matching administrative domains.  Within an
   administrative domain, further subdivisions of the control plane are
   recursively applied.  A routing control domain is an abstract entity
   that hides the details of the RC distribution.

   External NNI (E-NNI): Interfaces are located between protocol
   controllers between control domains.

   Internal NNI (I-NNI): Interfaces are located between protocol
   controllers within control domains.

   Link (see Recommendation [G.805]): A "topological component" that
   describes a fixed relationship between a "subnetwork" or "access
   group" and another "subnetwork" or "access group".  Links are not
   limited to being provided by a single server trail.

   Management plane: Performs management functions for the transport
   plane, the control plane, and the system as a whole.  It also
   provides coordination between all the planes.  The following
   management functional areas are performed in the management plane:
   performance, fault, configuration, accounting, and security

   Management domain (see Recommendation [G.805]): A management domain
   defines a collection of managed objects that are grouped to meet
   organizational requirements according to geography, technology,
   policy, or other structure, and for a number of functional areas such
   as configuration, security, (FCAPS), for the purpose of providing
   control in a consistent manner.  Management domains can be disjoint,
   contained, or overlapping.  As such, the resources within an
   administrative domain can be distributed into several possible
   overlapping management domains.  The same resource can therefore
   belong to several management domains simultaneously, but a management
   domain shall not cross the border of an administrative domain.

   Multiplexing (see Recommendation [G.805]): Multiplexing techniques
   are used to combine client layer signals.  The many-to-one
   relationship represents the case of several link connections of
   client layer networks supported by one server layer trail at the same

   Subnetwork Point (SNP): The SNP is a control plane abstraction that
   represents an actual or potential transport plane resource.  SNPs (in
   different subnetwork partitions) may represent the same transport
   resource.  A one-to-one correspondence should not be assumed.

   Subnetwork Point Pool (SNPP): A set of SNPs that are grouped together
   for the purposes of routing.

   Termination Connection Point (TCP): A TCP represents the output of a
   Trail Termination function or the input to a Trail Termination Sink

   Trail (see Recommendation [G.805]): A "transport entity" that
   consists of an associated pair of "unidirectional trails" capable of
   simultaneously transferring information in opposite directions
   between their respective inputs and outputs.

   Transport plane: Provides bi-directional or unidirectional transfer
   of user information, from one location to another.  It can also
   provide transfer of some control and network management information.
   The transport plane is layered; it is equivalent to the Transport
   Network defined in the [G.805] Recommendation.

   User Network Interface (UNI): Interfaces are located between protocol
   controllers between a user and a control domain.  Note: there is no
   routing function associated with a UNI reference point.

   Variable adaptation function: A single server layer trail may
   dynamically support different multiplexing structures, i.e., link
   connections for multiple client layer networks.

Appendix 2: ASON Routing Terminology

   This document makes use of the following terms:

   Routing Area (RA): An RA represents a partition of the data plane,
   and its identifier is used within the control plane as the
   representation of this partition.  Per [G.8080], an RA is defined by
   a set of subnetworks, the links that interconnect them, and the
   interfaces representing the ends of the links exiting that RA.  An RA
   may contain smaller RAs inter-connected by links.  The limit of
   subdivision results in an RA that contains two subnetworks
   interconnected by a single link.

   Routing Database (RDB): Repository for the local topology, network
   topology, reachability, and other routing information that is updated
   as part of the routing information exchange and may additionally
   contain information that is configured.  The RDB may contain routing
   information for more than one Routing Area (RA).

   Routing Components: ASON routing architecture functions.  These
   functions can be classified as protocol independent (Link Resource
   Manager or LRM, Routing Controller or RC) and protocol specific
   (Protocol Controller or PC).

   Routing Controller (RC): Handles (abstract) information needed for
   routing and the routing information exchange with peering RCs by
   operating on the RDB.  The RC has access to a view of the RDB.  The
   RC is protocol independent.

   Note: Since the RDB may contain routing information pertaining to
   multiple RAs (and possibly to multiple layer networks), the RCs
   accessing the RDB may share the routing information.

   Link Resource Manager (LRM): Supplies all the relevant component and
   Traffic Engineering (TE) link information to the RC.  It informs the
   RC about any state changes of the link resources it controls.

   Protocol Controller (PC): Handles protocol-specific message exchanges
   according to the reference point over which the information is
   exchanged (e.g., E-NNI, I-NNI), and internal exchanges with the RC.
   The PC function is protocol dependent.

Authors' Addresses

   Wesam Alanqar

   EMail: wesam.alanqar@mail.sprint.com

   Deborah Brungard, Ed.
   Rm. D1-3C22 - 200 S. Laurel Ave.
   Middletown, NJ 07748, USA

   Phone: +1 732 4201573
   EMail: dbrungard@att.com

   David Meyer
   Cisco Systems

   EMail: dmm@1-4-5.net

   Lyndon Ong
   Ciena Corporation
   5965 Silver Creek Valley Rd,
   San Jose, CA 95128, USA

   Phone: +1 408 8347894
   EMail: lyong@ciena.com

   Dimitri Papadimitriou
   Francis Wellensplein 1,
   B-2018 Antwerpen, Belgium

   Phone: +32 3 2408491
   EMail: dimitri.papadimitriou@alcatel.be

   Jonathan Sadler
   1415 W. Diehl Rd
   Naperville, IL 60563

   EMail: jonathan.sadler@tellabs.com

   Stephen Shew
   Nortel Networks
   PO Box 3511 Station C
   Ottawa, Ontario, CANADA K1Y 4H7

   Phone: +1 613 7632462
   EMail: sdshew@nortelnetworks.com

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