Network Working Group                           Deborah Brungard (ATT)
Internet Draft                                                  Editor
Category: Informational
Expiration Date: April 2005                               October 2004

             Requirements for Generalized MPLS (GMPLS) Routing
             for Automatically Switched Optical Network (ASON)


Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.


   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 on the GMPLS
   suite of protocols to support the capabilities and functionalities
   for an Automatically Switched Optical Network (ASON) as defined by

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Table of Contents

   Status of this Memo .............................................. 1
   Abstract ......................................................... 1
   Table of Contents ................................................ 2
   1. Contributors .................................................. 2
   2. Conventions used in this document ............................. 2
   3. Introduction .................................................. 2
   4. ASON Routing Architecture and Requirements .................... 4
   4.1 Multiple Hierarchical Levels of ASON Routing Areas (RAs) ..... 5
   4.2 Hierarchical Routing Information Dissemination ............... 5
   4.3 Configuration ................................................ 7
   4.3.1 Configuring the Multi-Level Hierarchy ...................... 7
   4.3.2 Configuring RC Adjacencies ................................. 8
   4.4 Evolution .................................................... 8
   4.5 Routing Attributes ........................................... 8
   4.5.1 Taxonomy of Routing Attributes ............................. 8
   4.5.2 Commonly Advertised Information ............................ 9
   4.5.3 Node Attributes ............................................ 9
   4.5.4 Link Attributes ........................................... 10
   5. Security Considerations ...................................... 11
   6. Conclusions .................................................. 12
   7. Acknowledgements ............................................. 13
   8. References ................................................... 14
   8.1 Normative References ........................................ 14
   8.2 Informative References ...................................... 14
   9. Author's Addresses ........................................... 14
   Appendix 1: ASON Terminology .................................... 16
   Appendix 2: ASON Routing Terminology ............................ 18
   Intellectual Property Statement ................................. 19
   Disclaimer of Validity .......................................... 19
   Copyright Statement ............................................. 19

1. 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 that 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)

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].

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   While [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 extensions.

3. 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 ANSI T1.105/ITU-T
   G.707, respectively) as well as Optical Transport Networks (OTN, see
   ITU-T G.709). However, there are certain capabilities that are needed
   to support the ITU-T G.8080 control plane architecture for
   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 is strictly outside the
   scope of this document. ASON (Routing) terminology sections are
   provided in Appendix 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 is 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).
   - 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 of a routing protocol
     and a 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

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     hierarchical levels of RAs is not specified.
   - The routing adjacency topology (i.e. the associated Protocol
     Controller (PC) connectivity) and transport topology is 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.

4. 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 a RA are provided by a Routing Performer (RP). A
   RP is responsible for a single RA, and it MAY be functionally
   realized using distributed Routing Controllers (RC). 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 a 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 assure RDB synchronization, the RCs
   co-operate 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 Section 4.2 Note). The RC is protocol independent and RC
   communications MAY be realized by multiple, different PCs within a

   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

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   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 a 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.

4.1 Multiple Hierarchical Levels of ASON Routing Areas (RAs)

   [G.8080] introduces the concept of 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 they are
   bound to the same parent RA (see Section 4.2). A 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.

   A 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.

4.2 Hierarchical Routing Information Dissemination

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   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 a RA may be viewed as internal links
   (intra-RA links). The external links to a 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 a RC, its parent, and its child RCs, it SHOULD
   include reachability (see Section 4.5.3) 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 a 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

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        downward information communication) allowing RC(s) bounded to a
        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.

4.3 Configuration

4.3.1 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

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   structure (including RA ID and RC ID). When applied recursively, the
   whole hierarchy is thus configured.

4.3.2 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 a 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 designated RC).

4.4 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 number of hierarchical levels of RAs, as well
   as 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

4.5 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. Additionally, 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.

4.5.1 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 like
     Link Capacity are specified by layer).

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   (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 is 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 a 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, etc).

   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 they are attached to, or to the
   containing RA, or when smaller groupings are required.

4.5.2 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.

4.5.3 Node Attributes

   All nodes belong to a 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

   The following Node Attributes are defined:

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

                Table 1. Node Attributes

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   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. 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 is implementation specific and outside the scope of this

   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 only as single switch attributes but MAY apply to a node
   at a higher level of the hierarchy that represents a sub-network.

4.5.4 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 separation of data and control planes (see Section 4.5.1, the
   control plane representation and transport plane topology is not
   assumed to be congruent). The SNPP link ID format is routing protocol

   Note: when the remote end of a 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: The metric indicating the relative desirability of a
     particular link over another e.g. during path computation.

   - 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.

   - 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.

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   - 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 only applicable 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

5. Security Considerations

   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,
   accountability may take on varying level 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 (includes replay attacks), repudiation, forgery and
   denial of service attacks.

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6. 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 assumes.
   - Routing Controllers (RC) 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 a 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 only happens 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 a 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 co-located
     within the same physical element or physically distributed.
   - 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 a 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 sub-network or simply a

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     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 bound to a single RA.
   - A mechanism to prevent 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 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. a RA insertion involves supporting a different
   routing protocol domain in a portion of the network.

   Reachability information (see Section 4.5.3) 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 a RA should not restrict
   the choice of routing protocols for use in other RAs (child or

   As ASON does not restrict the control plane architecture choice used,
   either a co-located architecture or a physically separated
   architecture may be used. A collection of links and nodes such as a
   sub-network 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.

7. Acknowledgements

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   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

   [RFC2026]    S.Bradner, "The Internet Standards Process --
                Revision 3", BCP 9, RFC 2026, October 1996.

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

   [RFC3667]    S.Bradner, "IETF Rights in Contributions", BCP 78,
                RFC 3667, February 2004.

   [RFC3668]    S.Bradner, Ed., "Intellectual Property Rights in IETF
                Technology", BCP 79, RFC 3668, February 2004.

8.2 Informative References

   For information on the availability of the following documents,
   please see

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

9. Author's Addresses

   Wesam Alanqar (Sprint)

   Deborah Brungard (AT&T)
   Rm. D1-3C22 - 200 S. Laurel Ave.
   Middletown, NJ 07748, USA
   Phone: +1 732 4201573

   David Meyer (Cisco Systems)

   Lyndon Ong (Ciena Corporation)

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   5965 Silver Creek Valley Rd,
   San Jose, CA 95128, USA
   Phone: +1 408 8347894

   Dimitri Papadimitriou (Alcatel)
   Francis Wellensplein 1,
   B-2018 Antwerpen, Belgium
   Phone: +32 3 2408491

   Jonathan Sadler
   1415 W. Diehl Rd
   Naperville, IL 60563

   Stephen Shew (Nortel Networks)
   PO Box 3511 Station C
   Ottawa, Ontario, CANADA K1Y 4H7
   Phone: +1 613 7632462

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Appendix 1: ASON Terminology

   This document makes use of the following terms:

   Administrative domain: (see Recommendation G.805) for the purposes of
   [G7715.1] an administrative domain represents the extent of resources
   which 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" which 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" which
   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

   Management domain: (see Recommendation G.805) a management domain
   defines a collection of managed objects which 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

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   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 time.

   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" which 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 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.

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Appendix 2: ASON Routing Terminology

   This document makes use of the following terms:

   Routing Area (RA): a 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] a RA is defined by a set of sub-
   networks, the links that interconnect them, and the interfaces
   representing the ends of the links exiting that RA. A RA may contain
   smaller RAs inter-connected by links. The limit of subdivision
   results in a RA that contains two sub-networks 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
   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.

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