CCAMP Working Group                         D. Papadimitriou (Alcatel)
Internet Draft                          Z. Lin (New York City Transit)
Category: Informational                                      J. Drake (Calient)
Category: Informational                                   J. Ash (ATT)
Expiration Date: March 2004
                                        A. Farrel (Old Dog Consulting)
Expiration Date: April 2004                             L. Ong (Ciena)


                                                          October 2003

         Requirements for Generalized MPLS (GMPLS) Signaling Usage
     and Extensions 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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1. Abstract

   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 signaling aspects of the GMPLS
   suite of protocols. It identifies the features to be covered by the
   GMPLS signaling protocol to support the capabilities of an
   Automatically Switched Optical Network (ASON). This document
   provides a problem statement and additional requirements on the
   GMPLS signaling protocol to support the ASON functionality.

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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 specifications 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 and ITU-T G.707, respectively)
   as well as Optical Transport Networks (see ITU-T G.709). In
   addition, there are certain capabilities that are needed to support
   Automatically Switched Optical Networks control planes (their
   architecture is defined in [ITU-T G.8080]). These include generic
   capabilities such as call and connection separation, and more
   specific capabilities such as support of soft permanent connections.

   This document concentrates on the signaling aspects of the GMPLS
   suite of protocols. It discusses the functional requirements that
   lead to additional and backward compatible extensions to GMPLS
   signaling (see [RFC 3471] and [RFC 3473]) to support the
   capabilities as specified in the above referenced document. A
   description of backward compatibility considerations is provided in
   Section 5. A terminology section is provided in the Appendix.

   Problem Statement:

   The Automatically Switched Optical Network (ASON) architecture
   describes the application of an automated control plane for
   supporting both call and connection management services (for a
   detailed description see [ITU-T G.8080]).

   Also, the ASON model distinguishes reference points (representing
   points of protocol information exchange) defined (1) between an
   administrative domain and a user a.k.a. user-network interface
   (UNI), (2) between (and when needed within) administrative domains
   a.k.a. external network-network interface (E-NNI) and, (3) between
   areas of the same administrative domain and when needed between
   control components (or simply controllers) within areas a.k.a.
   internal network-network interface (I-NNI). A full description of
   the ASON terms and relationship between ASON model and GMPLS
   protocol suite may be found in [IPO-ASON].

   This document describes the use of GMPLS signaling (in particular,
   [RFC 3471] and [RFC 3473]) to provide call and connection management
   (see [ITU-T G.7713]). The following functionality is expected to be
   supported and to be backward compatible with the GMPLS protocol
   suite as currently defined by the IETF:
   (a) soft permanent connection capability
   (b) call and connection separation

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   (c) call segments
   (d) extended restart capabilities during control plane failures

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   (e) extended label usage association
   (f) crankback capability
   (g) additional error cases.

4. Requirements for Extending Applicability of GMPLS to ASON

   The applicability statements regarding how the GMPLS suite of
   protocols may be applied to the ASON architecture can be found in
   [IPO-ASON] and [IPO-REQS]. The former includes a summary of the ASON
   functions as well as a detailed discussion of the applicability of
   the GMPLS protocol suite.

   The next sections detail the signaling protocol requirements concerning for
   GMPLS to support the functions
   including: following ASON functions:

      - Support for soft permanent connection capability
      - Support for call and connection separation
      - Support for call segments
      - Support for extended restart capabilities during control plane
      - Support for extended label usage association
      - Support for crankback capability
      - Support for additional error cases

   Also, the

   The support of these functions is must be strictly independent of and
   must be
   agnostic of to any user-to-network interface (UNI) and therefore not be
   constrained or restricted by its the implementation specifics of the UNI
   (see [ITU-
   T [ITU-T G.8080] and [ITU-T G.7713]).

   In support of the G.8080 end-to-end call model across different
   signaling domains, end-to-end signaling should be facilitated
   regardless of the administrative boundaries and protocols within the
   network. The resulting requirement being This implies that there needs to be a clear mapping of
   signaling requests between GMPLS control domains and non-GMPLS
   control domains. This document provides signalling requirements for
   G.8080 distributed call and connection management based on GMPLS,
   within a GMPLS based control domain and between GMPLS based control
   domains. It does not restrict use of other protocols within a
   control domain. Interworking aspects, including mapping of non-GMPLS
   protocol signaling requests and support of non-
   GMPLS non-GMPLS address
   formats, are strictly under the responsibility of the non-GMPLS
   control domain, and thus outside the scope of this document.

   Any User-Network Interface (UNI) that is compliant with [RFC-3473], [RFC 3473],
   e.g. [GMPLS-OVERLAY] and [GMPLS-VPN] is considered, by definition,
   to be a GMPLS UNI and must be supported.

   Compatibility aspects of non-GMPLS systems (nodes) within a GMPLS
   control domain i.e. the support of GMPLS systems and other systems
   which utilize other signaling protocols or some which may not
   support any signaling protocols is described. For instance, Section

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   4.5 'Support for Extended Label Usage' Association' covers the requirements
   when a non-GMPLS capable sub-network is introduced or when nodes do
   not support any signaling protocols.

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4.1 Support for Soft Permanent Connection (SPC) Capability

   An SPC is a combination of a permanent connection at the source
   user-to-network side, a permanent connection at the destination
   user-to-network side, and a switched connection within the network.
   An Element Management System (EMS) or a Network Management System
   (NMS) typically initiates the establishment of the switched
   connection by communicating with the node that initiates the
   switched connection (also known as the ingress node). The latter
   then sets the connection using the distributed GMPLS signaling
   protocol. For the SPC, the communication method between the EMS/NMS
   and the ingress node is beyond the scope of this document (so it is
   for any other function described in this document).

   The end-to-end connection is thus created by associating the
   incoming interface of the ingress node with the switched connection
   within the network, and the outgoing interface of the switched
   connection terminating network node (also referred to as egress
   node). An SPC connection is illustrated in the following Figure,
   which Figure.
   This shows user's node A connected to a provider's node B via link
   #1, user's node Z connected to a provider's node Y via link #3, and
   an abstract link #2 connecting provider's node B and node Y.  Nodes
   B and Y are referred to as the ingress and egress (respectively) of
   the network switched connection.

    ---       ---                 ---       ---
   | A |--1--| B |-----2-//------| Y |--3--| Z |
    ---       ---                 ---       ---

   In this instance, the connection on link #1 and link #3 are both
   provisioned (permanent connections that may be simple links). In
   contrast, the connection over link #2 is set up using the
   distributed control plane. Thus the SPC is composed of the splicing
   of link #1, #2 and #3.

   Thus, to support the capability to request an SPC connection:
   - The GMPLS signaling protocol must be capable of supporting the
     ability to indicate the outgoing link and label information used
     when setting up the destination provisioned connection.
   - In addition, due to the inter-domain applicability of ASON
     networks, the GMPLS signaling protocol should also support
     indication of the service level requested for the SPC. In the case
     where an SPC spans multiple domains, indication of both source and
     destination endpoints controlling the SPC request may be needed.
     These may be done via the source and destination signaling
     controller addresses.

   Note that the association at the ingress node between the permanent
   connection and the switched connection is an implementation matter
   under the control of the EMS/NMS and is not within the scope of the

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   signaling protocol. It is, therefore, outside the scope of this

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4.2 Support for Call and Connection Separation

   A call may be simply described as "An association between endpoints
   that supports an instance of a service" [ITU-T G.8080]. Thus, it can
   be considered as a service provided between two end-points, where
   several calls may exist between them. Multiple connections may be
   associated to each call. The call concept provides an abstract
   relationship between two users, where this relationship describes
   (or verifies) to what extent the users are willing to offer (or
   accept) service to each other. Therefore, a call does not provide
   the actual connectivity for transmitting user traffic, but only
   builds a relationship by which subsequent connections may be made.

   A property of a call is to contain zero, one or multiple
   connections. Within the same call, connections may be of different
   types and each connection may exist independently of other
   connections, i.e., each connection is setup and released with
   separate Path/Resv signaling messages. For example, a call may contain a set
   of basic connections and virtually concatenated connections (see
   [GMPLS-SONET] for corresponding connection signaling extensions).

   The concept of the call allows for a better flexibility in how end-
   points set up connections and how networks offer services to users.
   In essence, a call allows:
   - Support for virtual concatenation where each connection can travel
     on different diverse paths
   - An upgrade strategy for control plane operations, where a call
     control component (service provisioning) may be separate from the
     actual nodes hosting the connections (where the connection control
     component may reside)
   - Identification of the call initiator (with both network call
     controller as well as destination user) prior to connection, which
     may result in decreasing contention during resource reservation
   - General treatment of multiple connections which may be associated
     for several purposes; for example a pair of working and recovery
     connections may belong to the same call.

   To support the introduction of the call concept, GMPLS signaling
   should include a call identification mechanism and allow for end-to-
   end call capability exchange.

   For instance, a feasible structure for the call identifier (to
   guarantee global uniqueness) may concatenate a globally unique fixed
   ID (e.g., may be composed of country code, carrier code) with an
   operator specific ID (where the operator specific ID may be composed
   of a unique access point code - such as source node address - and a
   local identifier). Other formats shall also be possible depending on
   the call identification conventions between parties involved in the
   call setup process.

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4.3 Support for Call Segments

   As described in [ITU-T G.8080], call segmentation may be applied
   when a call crosses several administrative domains. As such, an end-
   to-end call may consist of multiple call segments, when the call
   traverses multiple administrative domains. Each call segment can
   have one or more associated connections and the number of
   connections associated with each call segment may not be the same
   for a given end-to-end call.

   The initiating caller interacts with a called party by means of one
   or more intermediate call controllers located at the network edge
   between administrative domains (i.e., inter-domain reference point)
   and in particular at the user-to-network reference point. Their
   functions are defined by the policies associated by interactions
   between the administrative domain boundaries and between users and
   the network.

   This capability allows for independent (policy based) choices of
   signaling, concatenation, data plane protection and control plane
   driven recovery paradigms in different administrative domains.

4.4 Support for Extended Restart Capabilities

   Various types of failures may occur affecting the ASON control
   plane. Requirements placed on the control plane failure recovery by
   [ITU-T G.8080] include:
   - Any control plane failure must not result in releasing established
     calls and connections.
   - Upon recovery from a control plane failure, the recovered node
     must have the ability to recover the status of the calls and
     connections established before failure occurrence.
   - Upon recovery from a control plane failure, the recovered node
     must have the ability to recover the connectivity information of
     its neighbors.
   - Upon recovery from a control plane failure, calls and connections
     in the process of being established (i.e. pending call/connection
     setup requests) should be released or continued (with setup).
   - Upon recovery from a control plane failure, calls and connections
     in the process of being released must be released.
   - Upon recovery from a control plane failure, a call must have
     the ability to re-synchronize with its associated connections.

4.5 Support for Extended Label Usage Association

   Labels are defined in GMPLS (see [RFC 3471]) to provide information
   on the resources used on link local basis for a particular
   connection. The labels may range from specifying a particular
   timeslot, a particular wavelength to a particular port/fiber.

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   In the ASON context, the value of a label MAY not be consistently
   the same across a link. For example, the figure below illustrates

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   the case where two GMPLS capable nodes (A and Z) are interconnected
   across two non-GMPLS capable nodes (B and C), where these nodes are
   all SONET/SDH nodes providing, e.g., a VC-4 service.

    -----                     -----
   |     |    ---     ---    |     |
   |  A  |---| B |---| C |---|  Z  |
   |     |    ---     ---    |     |
    -----                     -----

   Labels have an associated implicit imposed structure based on
   [GMPLS-SONET] and [GMPLS-OTN]. Thus, once the local label is
   exchanged with its neighboring control plane node, the structure of
   the local label MAY not be significant to the neighbor node since
   the association between the local and the remote label may not
   necessarily be the same. This issue does not present a problem in
   simple point-to-point connections between two control plane-enabled
   nodes where the timeslots are mapped 1:1 across the interface.
   However, once a non-GMPLS capable sub-network is introduced between
   these nodes (as in the above figure, where the sub-network provides
   re-arrangement capability for the timeslots) label scoping MAY
   become an issue.

   In this context, there is an implicit assumption that the data plane
   connections between the GMPLS capable edges already exist prior to
   any connection request. For instance, node A's outgoing VC-4's
   timeslot #1 (with SUKLM label=[1,0,0,0,0]) as defined in [GMPLS-
   SONET]) may be mapped onto node B's outgoing VC-4's timeslot #6
   (label=[6,0,0,0,0]) may be mapped onto node C's outgoing VC-4's
   timeslot #4 (label=[4,0,0,0,0]). Thus by the time node Z receives
   the request from node A with label=[1,0,0,0,0], the node Z's local
   label and the timeslot no longer corresponds to the received label
   and timeslot information.

   As such, to support this capability, a label association mechanism
   has to be used by the control plane node to map the received
   (remote) label into a locally significant label. The information
   necessary to allow mapping from received label value to a locally
   significant label value may be derived in several ways including:

   - Manual provisioning of the label association
   - Discovery of the label association

   Either method may be used. In case of dynamic association, this
   implies that the discovery mechanism operates at the timeslot/label
   level before the connection request is processed at the ingress
   node. Note that in the case where two nodes are directly connected,
   no association is required. In particular, for directly connected
   TDM interfaces no mapping function (at all) is required due to the
   implicit label structure (see [GMPLS-SONET] and [GMPLS-OTN]). In

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   such instances, the label association function provides a one-to-one
   mapping of the received to local label values.

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4.6 Support for Crankback

   Crankback has been identified as an important requirement for ASON
   networks. It allows a connection setup request to be retried on an
   alternate path that detours around a blocked link or node upon a
   setup failure, for instance, because a link or a node along the
   selected path has insufficient resources.

   Crankback mechanisms may also be applied during connection recovery
   by indicating the location of the failed link or node. This would
   significantly improve the successful recovery ratio for failed
   connections, especially in situations where a large number of setup
   requests are simultaneously triggered.

   The following mechanisms are assumed during crankback signaling (see
   also [GMPLS-CRANK]): signaling:
   - the blocking resource (link or node) must be identified and
     returned in the error response message towards the repair node
     (that may or may not be the ingress node); it is also assumed that
     this process will occur within a limited period of time
   - the computation (from the repair node) of an alternate path around
     the blocking link or node satisfying the initial connection
   - the re-initiation of the connection setup request from the repair
     node (i.e. the node that has intercepted and processed the error
     response message)

   The following properties are expected for crankback signaling (see
   [GMPLS-CRANK]): signaling:

   - Error information persistence: the entity that computes the
     alternate (re-routing) path should store the identifiers of the
     blocking resources as indicated in the error message until the
     connection is successfully established or until the node abandons
     rerouting attempts. Since crankback may happen more than once
     while establishing a specific connection, the history of all
     experienced blockages for this connection should be maintained (at
     least until the routing protocol updates the state of this
     information) to perform an accurate path computation avoiding all

   - Rerouting attempts limitation: to prevent an endless repetition of
     connection setup attempts (using crankback information), the
     number of retries should be strictly limited. The maximum number
     of crankback rerouting attempts allowed can be limited per
     connection, per node, per area or even per administrative domain.
        - When the number of retries at a particular node or area is
          exceeded, the node currently handling the failure reports the
          error message upstream to the next repair node where further
          rerouting attempts may be performed. It is important that the

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          crankback information provided indicates that re-routing
          through this node will not succeed.
        - When the maximum number of retries for a specific connection
          has been exceeded, the repair node handling the current

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          failure should send an error message upstream indicating
          "Maximum number of re-routings exceeded". This error message
          will be sent back to the ingress node with no further
          rerouting attempts. Then, the ingress node may choose to
          retry the connection setup according to local policy but also
          re-use its original path or compute a path that avoids the
          blocking resources.

   Note: after several retries, a given repair point may be unable to
   compute a path to the destination node that avoids all of the
   blockages. In this case, it must pass the error message upstream to
   the next repair point.

4.7 Support for Additional Error Cases

   To support the ASON network, the following additional category of
   error cases are defined:
   - Errors associated with basic call and soft permanent connection
     support. For example, these may include incorrect assignment of
     IDs for the Call or an invalid interface ID for the soft permanent
   - Errors associated with policy failure during processing of the new
     call and soft permanent connection capabilities. These may include
     unauthorized request for the particular capability.
   - Errors associated with incorrect specification of the service

5. Backward Compatibility

   As noted above, any extensions to the GMPLS signaling protocol in
   support of the requirements described in this document must be
   backward compatible.

   Backward compatibility means that in a network of nodes, some of
   which support GMPLS signaling extensions to facilitate the functions
   described in this document, and some of which do not, it must be
   possible to set up conventional connections (as described by [RFC
   3473]) between any arbitrary pair of nodes and traversing any
   arbitrary set of nodes. Further, the use of any GMPLS signaling
   extensions to set up calls or connections that support the functions
   described in this document must not perturb existing conventional

   Additionally, when transit nodes, that do not need to participate in
   the new functions described in this document, lie on the path of a
   call or connection, the GMPLS signaling extensions must be such that
   those transit nodes are able to participate in the establishment of

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   the call or connection by passing the setup information onwards,

   Lastly, when a transit or egress node is called upon to support a
   function described in this document, but does not, the GMPLS

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   signaling extensions must be such that they can be rejected by pre-
   existing GMPLS signaling mechanisms in a way that is not detrimental
   to the network as a whole.

6. Security Considerations

   Per [ITU-T G.8080], it is not possible to establish a connection cannot be established
   until the associated call has been set up. Also, policy and
   authentication procedures are applied prior to the establishment of
   the call (and can then also be restricted to connection
   establishment in the context of this call).

   This document introduces no new security requirements to GMPLS
   signaling (see [RFC3471]). [RFC 3471]).

7. Acknowledgements

   The authors would like to thank Nic Larkin, Osama Aboul-Magd and
   Dimitrios Pendarakis for their comments and contributions contribution to the previous version
   of this document, Zhi-Wei Lin for his contribution to this document,
   Deborah Brungard for her input and guidance in our understanding of
   the ASON model, and Gert Grammel for his decryption effort during
   the redaction of some parts of this document.

8. References

8.1 Normative 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.


   [RFC 3209]     D.Awduche et al., "RSVP-TE: Extensions to RSVP for
                  LSP Tunnels," RFC 3209, December 2001.


   [RFC 3471]     L.Berger (Editor) et al., "Generalized Multi-
                  Protocol Label Switching (GMPLS) - Signaling
                  Functional Description," RFC 3471, January 2003.


   [RFC 3473]     L.Berger (Editor) et al., "Generalized Multi-Protocol
                  Label Switching (GMPLS) Signaling - Resource
                  ReserVation Protocol-Traffic Engineering (RSVP-TE)
                  Extensions," RFC 3473, January 2003.


   [ITU-T G.8080] ITU-T Rec. G.8080/Y.1304, "Architecture for the

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                  Automatically Switched Optical Network (ASON),"
                  November 2001 (and Revision, January 2003).

   [GMPLS-CRANK]  A.Farrel (Editor), "Crankback Routing Extensions for
                  MPLS Signaling," Work in Progress, draft-iwata-mpls-
                  crankback-06.txt, June 2003.

   [GMPLS-SONET]  E.Mannie and

D.Papadimitriou (Editors), "GMPLS
                  Extensions for SONET and SDH Control, Work in
                  Progress," draft-ietf-ccamp-gmpls-sonet-sdh-08.txt,
                  February 2003. et al. - Expires March 2004                         10

8.2 Informative References

   [GMPLS-OTN]    D.Papadimitriou (Editor), "GMPLS Signaling Extensions
                  for G.709 Optical Transport Networks Control," Work
                  in progress, draft-ietf-ccamp-gmpls-g709-04.txt, May

   [GMPLS-OVERLAY]G.Swallow et al., "GMPLS RSVP Support for Overlay
                  Model," Work in Progress, draft-ietf-ccamp-gmpls-
                  overlay-01.txt, February 2003.

   [GMPLS-SONET]  E.Mannie and D.Papadimitriou (Editors), "GMPLS
                  Extensions for SONET and SDH Control, Work in
                  Progress," draft-ietf-ccamp-gmpls-sonet-sdh-08.txt,
                  February 2003.

   [GMPLS-VPN]    H.Ould-Brahim and Y.Rekhter (Editor), "GVPN Services:
                  Generalized VPN Services using BGP and GMPLS
                  Toolkit," Work in Progress, draft-ouldbrahim-ppvpn-
                  gvpn-bgpgmpls-03.txt, March 2003.

8.2 Informative References

   [IPO-ASON]     Aboul-Magd (Editor) et al., "Automatic Switched
                  Optical Network (ASON) Architecture and Its Related
                  Protocols," Work in progress, draft-ietf-ipo-ason-
                  02.txt, March 2002.

   [IPO-REQS]     Y.Xue (Editor) et al., "Optical Network Service
                  Requirements," Work in progress, draft-ietf-ipo-


   [ITU-T G.7713] ITU-T Rec. G.7713/Y.1304, "Distributed Call and
                  Connection Management," November 2001.

9. Author's Addresses

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

   Zhi-Wei Lin (New York City Transit)
   2 Broadway, Room C3.25
   New York, NY 10004, USA

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   John Drake (Calient)
   5853 Rue Ferrari,
   San Jose, CA 95138, USA

   Adrian Farrel (Old
   Old Dog Consulting)
   Email: Consulting
   Phone:  +44 (0) 1978 860944

   Gerald R. Ash (ATT)
   AT&T Labs, Room MT D5-2A01
   200 Laurel Avenue
   Middletown, NJ 07748, USA

   Lyndon Ong (Ciena)
   5965 Silver Creek Valley Road
   San Jose, CA 95138, USA

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Appendix - Terminology

   This document makes use of the following terms:

   Administrative domain: See Recommendation G.805.

   Call: association between endpoints that supports an instance of a

   Connection: concatenation of link connections and sub-network
   connections that allows the transport of user information between
   the ingress and egress points of a sub-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 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: NNI (E-NNI): interfaces are located between protocol
   controllers between control domains.

   Internal NNI: 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.

D.Papadimitriou et al. - Expires March 2004                         13                         12

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D.Papadimitriou et al. - Expires March 2004                         14                         13