CCAMP Working Group                             Wesam Alanqar (Sprint)
Internet Draft                                  Deborah Brungard (ATT)
Category: Informational                     Dave Meyer (Cisco Systems)
                                                    Lyndon Ong (Ciena)
Expiration Date: May 2004              Dimitri Papadimitriou (Alcatel)
                                             Jonathan Sadler (Tellabs)
                                                 Stephen Shew (Nortel)

                                                         December 2003

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


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC-2026.

   Internet-Drafts are working documents of the Internet Engineering
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   The Generalized MPLS (GMPLS) suite of protocols has been defined to
   control different switching technologies as well as different
   applications. These include support for requesting TDM connections
   including SONET/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
   of an Automatically Switched Optical Network (ASON).

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1. Contributors

   This document is the result of the CCAMP Working Group ASON Routing
   Requirements design team joint effort.

2. Conventions used in this document

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

3. Introduction

   The GMPLS suite of protocol provides support for controlling
   different switching technologies as well as different applications.
   These include support for requesting TDM connections including
   SONET/SDH (see ANSI T1.105/ITU-T G.707) as well as Optical Transport
   Networks (see ITU-T G.709). However, there are certain capabilities
   that are needed to support the ITU-T G.8080 control plane
   architecture for the 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] and ASON routing requirements
   are identified in [G.7715] and refined in [G.7715.1] for link state
   architectures. These recommendations provide functional requirements
   and architecture, they provide a protocol neutral approach.

   This document focuses on the routing requirements for the GMPLS
   suite of protocols to support the capabilities and functionalities
   of ASON control planes. It discusses the requirements for GMPLS
   routing that MAY subsequently lead to additional backward compatible
   extensions to support the capabilities specified in the above
   referenced document. A description of backward compatibility
   considerations is provided in Section 5. Nonetheless, any protocol
   (in particular, routing) design or suggested protocol extensions is
   strictly outside the scope of this document. An ASON (Routing)
   terminology section is provided in Appendix 1 and Appendix 2.

   The ASON model distinguishes reference points (representing points
   of protocol information exchange) defined (1) between an
   administrative domain and a user (user-network interface or UNI),
   (2) between administrative domains or within an administrative
   domain between different control domains (external network-network
   interface or E-NNI) and, (3) within the same administrative domain
   between control components (or simply controllers) of the same
   control domain (internal network-network interface or I-NNI). The
   ASON model allows for the protocols used within different control
   domains to be different; and for the protocol used between control
   domains to be different than the protocols used within control
   domains. I-NNI interfaces are located between protocol controllers
   within a control domain. E-NNI interfaces are located on protocol
   controllers between control domains.

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   The term routing information refers to the abstract representation
   of network routing related information such as node and link
   attributes (see Section 4.5). No routing information is passed over
   the UNI. Routing information exchanged over the NNI is subject to
   the policy constraints at individual NNIs. The routing information
   exchanged over the E-NNI encapsulates the common semantics of the
   individual domain information while allowing different
   representation within each domain.

   The ASON routing architecture is based on the following assumptions:
   - A carrier's network is subdivided as Routing Areas (RAs). Each RA
     shall be uniquely identifiable within a carrier's network (i.e.
     administrative domain). Partitioning into RAs provides for routing
     information abstraction, thereby enabling scalable routing.
   - Routing Controllers (RC) provide for the exchange of routing
     information between and within a RA. The routing information
     exchanged between RCs is subject to policy constraints imposed at
     reference points (E-NNI and I-NNI).
   - A RA MAY support different routing protocols. There SHOULD NOT be
     any dependencies on the different routing protocols used.
   - For a RA, the cluster of RCs is referred to as a routing domain.
     The routing information exchanged between routing domains (i.e.
     inter-domain) is independent of both the intra-domain routing
     protocol and the intra-domain control distribution choice(s), e.g.
     centralized, fully distributed.
   - The routing adjacency topology and transport network topology
     SHALL NOT be assumed to be congruent.

   The following functionality is expected from GMPLS routing to
   instantiate ASON routing realization (see [G.7715]):
   - support multiple hierarchical levels of RAs
   - support hierarchical routing information dissemination including
     summarized routing information
   - support for multiple links between nodes and RAs (allowing for
     link and node diversity)
   - support architectural evolution in terms of the number of levels
     of hierarchies, aggregation and segmentation of RAs
   - 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 node). [G.7715]
     recognizes that the manner in which the routing information is
     represented and exchanged will vary with the routing protocol

   Also, the behaviour of GMPLS routing is expected to be such that:
   - it is scalable with respect to the number of links, nodes and RAs
   - in response to a routing event (e.g. topology update, reachability
     update), it delivers convergence and damping against flapping
   - it fulfils the operational security objectives where required

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4. ASON Requirements for GMPLS Routing

   The description of the ASON routing components (see Appendix 2) is
   provided in terms of routing functionality. This description is only
   conceptual: no physical partitioning of these functions is implied.

   The Routing Controller (RC) component receive routing information
   from their associated Link Resource Manager(s) (LRMs) regarding TE
   links and store this information in the Routing Information Database
   (RDB). The RDB is replicated at each RC within the same Routing Area
   (RA), and MAY contain information about multiple transport plane
   network layers. Whenever the state of a TE link (or component link)
   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. In this context,
   communication between RCs is realized using a particular routing
   protocol represented by the protocol controller (PC) component and
   the protocol messages are conveyed over the Signaling Control
   Network (SCN). The PC MAY convey information for one or more
   transport network layers.

   Note: the RC can be thought as the function processing the TE
   database populated by the link local/remote component and TE links
   (LRM) and by the network wide TE links through the PC which
   processes the protocol specific routing exchanges. The SCN
   corresponds to the IP control plane topology enabling routing
   exchanges between GMPLS controllers (i.e. the routing adjacencies).

   The next sections detail the requirements for GMPLS routing to
   support the following ASON routing functions.

4.1 Multiple Hierarchical Levels

   Routing Areas (RAs) provide for routing information abstraction,
   thereby enabling scalable routing information representation.
   [G.7715] describes the use of hierarchy as one possible choice for
   routing area organization. RAs MAY be 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 routing levels. The
   realization of the routing paradigm to support hierarchical routing
   levels and the number of hierarchical levels to be supported is
   protocol specific and outside the scope of this document.

   Note: an RA can be considered as representing either an Autonomous
   System (AS) or a canonical IGP routing area, both are sometimes
   referred to as routing regions (or simply regions).

   ASON routing components are identified by values that MAY be drawn
   from several identifier spaces. The use of identifiers in a routing
   protocol realization is implementation specific and outside the
   scope of this document.

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   In a multi-level routing hierarchy, it is necessary to distinguish
   among RCs within a level and RCs at different levels of the routing
   hierarchy. Before any pair of RCs establishes communication, they
   must verify they belong to the same RA. An RA identifier (RA ID) is
   required to provide the scope within which the RCs can communicate.
   To distinguish between RCs within the same RA, an RC identifier (RC
   ID) is required; the RC ID must be unique within its containing RA.

   Note: 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

   Routing information MAY be exchanged between adjacent levels of the
   routing 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, and the links representing connectivity within an
   RA MAY be viewed as internal links.

   The physical location of RCs at adjacent levels, their relationship
   and their communication protocol are outside the scope of this
   document. No assumption is made regarding how RCs communicate
   between levels. Information exchange between an RC, its parent, and
   its child RCs, SHOULD include reachability and MAY include (upon
   policy decision) node and link topology.

   Multiple RCs within a 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; this MAY be achieved using a number of mechanisms.

4.2.1 Communication between Adjacent Routing Levels

   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 exchange 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) in an RA at
        Level N to develop paths to reachable endpoints outside of the

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

      The routing protocol is required to differentiate the routing
      information originated at a given level RA from the one derived
      using the routing information received from its external RAs
      (regardless of the level of the corresponding RCs). This is a
      necessary condition to be fulfilled by routing protocols to be
      loop free.

      Also, for ASON, the routing information exchange may generate
      transient loops at the data plane if no route recording is used
      during signaling. So, at the data plane, it is not the routing
      exchange that guarantees (transient) loop avoidance but the
      signaling protocol by recording the route until the node where
      computation occurs (by excluding segments already traversed).

   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

      - 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.

4.2.2 Configuring the Routing Hierarchy

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

4.2.3 Configuring RC Adjacencies

   The RC MUST support static (i.e. operator assisted) and MAY support
   automated configuration of the information describing its control

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   adjacencies to other RCs within an RA. The protocol SHOULD support
   all the types of adjacencies described in Section 9 of [G.7715].

4.3 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, as well as
   aggregation and segmentation of RAs. RA IDs uniqueness within an
   administrative domain MAY facilitate these operations. The routing
   protocol is not expected to automatically initiate and/or execute
   these operations.

4.4 Multiple Links between Nodes and RAs

   See Section 4.5.3

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 equipments support the same set of transport layers
   nor 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 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).

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

   TE links are configured through grouping of component links.
   Grouping MAY be based on different link attributes (e.g., SRLG
   information, link weight, etc).

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   Two RAs may be linked by one or more TE links. Multiple TE 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 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 source external to the routing area

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.

   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 address prefixes or a set of associated TE link IDs,
   consistently assigned within an administrative domain.

   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.

4.5.4 Link Attributes

   The following Link Attributes are defined:

       Link Attribute                   Capability      Usage
       ---------------                  -----------     ---------
       Local TE link ID                 REQUIRED        REQUIRED
       Remote TE link ID                REQUIRED        REQUIRED
       TE Link Characteristics          Table 3

                Table 2. Link Attributes

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   The TE link ID must be sufficient to uniquely identify the
   corresponding transport plane resource taking into account
   separation of data and control planes. The TE link ID format is
   routing protocol specific.

   Note: when the remote end of a TE link is located outside of the RA,
   the remote TE link ID is OPTIONAL.

   The following TE 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 allows identification of whether the local
     component link is at a border or within an LSP region (see [HIER])

   - 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 local component link associated to
     the local TE link. This can only exist when the "Local Connection
     Type" indicates crossing of an LSP Region or can be flexibly
     assigned to be at a border or within an LSP region (see [HIER]).

        TE 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. TE link Characteristics

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   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 attributes
   derivable from the local adaptation information do not need to be

5. Backward Compatibility

   Any particular realization of the ASON routing requirements MUST be
   backward compatible with the considered routing protocol(s).

   Backward compatibility means that at any level of the routing
   hierarchy, nodes, some of which support the requirements described
   in this document, and some of which do not, must still be capable to
   operate as mandated by the OSPF, IS-IS, and/or IDR IETF WG and their
   corresponding GMPLS extensions (as mandated by the CCAMP IETF WG).

   Additionally, nodes (that do not support these requirements) are
   made part of a multi-level routing hierarchy from their containing
   RA(s), must be capable of:
   - rejecting any incoming routing information that would be
     addressed to them in a way that is not detrimental to the
     network as a whole
   - communicating (at a given level) with any other node located
     at the same level and that implements these requirements
   This assumes that such nodes do not communicate directly either with
   lower or upper level nodes.

6. Security Considerations


7. Acknowledgements

   The authors would like to thank Kireeti Kompella for having
   initiated the proposal of an ASON Routing Requirement Design Team.

8. Intellectual Property Considerations

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances
   of licenses to be made available, or the result of an attempt made
   to obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification
   can be obtained from the IETF Secretariat.

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   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive

9. References

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

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

   [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).

   [HIER]       K.Kompella and Y.Rekhter, "LSP Hierarchy with
                Generalized MPLS TE," Internet draft (work in
                progress), draft-ietf-mpls-lsp-hierarchy, Sept'02.

10. 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)
   5965 Silver Creek Valley Rd,
   San Jose, CA 95128, USA
   Phone: +1 408 8347894

   Dimitri Papadimitriou (Alcatel)

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   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.

   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 entities that are
   grouped for a particular purpose. G.8080 applies this G.805
   recommendation concept (that defines two particular forms, the
   administrative domain and the management domain) to the control
   plane in the form of a control domain. The entities that are grouped
   in a control domain are components of the control plane.

   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.

   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.

   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.

   User Network Interface (UNI): interfaces are located between
   protocol controllers between a user and a control domain.

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Appendix 2 - ASON Routing Terminology

   This document makes use of the following terms:

   Routing Area (RA): represents functionally either an Autonomous
   System (AS) or a canonical IGP routing area, both are sometimes
   referred to as routing regions (or simply regions).

   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 hence possibly 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.

   Internal Links: links that are fully encapsulated by a routing area
   at a given level of hierarchy. Internal links to a child RA may be
   hidden from the parent RAs view.

   External Links: links that are incident upon the routing area. Note
   that external links to a routing area at one level of the hierarchy
   may be internal links in the parent routing area.

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W.Alanqar et al. - Expires May 2004                                 15