Network Working Group                 Eric Mannie (Ebone) - Editor
   Internet Draft
   Expiration date: Dec. 2001            Peter Ashwood-Smith (Nortel)
                                               Daniel Awduche (Movaz)
                                              Ayan Banerjee (Calient)
                                           Debashis Basak (Accelight)
                                                   Lou Berger (Movaz)
                                               Greg Bernstein (Ciena)
                                                 John Drake (Calient)
                                                 Yanhe Fan (Axiowave)
                                                   Don Fedyk (Nortel)
                                               Gert Grammel (Alcatel)
                                           Kireeti Kompella (Juniper)
                                             Alan Kullberg (NetPlane)
                                           Jonathan P. Lang (Calient)
                                                  Fong Liaw (Zaffire)
                                             Thomas D. Nadeau (Cisco)
                                      Dimitri Papadimitriou (Alcatel)
                                       Dimitrios Pendarakis (Tellium)
                                           Bala Rajagopalan (Tellium)
                                              Yakov Rekhter (Juniper)
                                              Debanjan Saha (Tellium)
                                                 Hal Sandick (Nortel)
                                             Vishal Sharma (Metanoia)
                                               George Swallow (Cisco)
                                                 Z. Bo Tang (Tellium)
                                                    John Yu (Zaffire)
                                                   Alex Zinin (Cisco)

                                                            June 2001

      Generalized Multi-Protocol Label Switching (GMPLS) Architecture


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time. It is inappropriate to use Internet- Drafts as
   reference material or to cite them other than as "work in progress."

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   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Table of Contents

   1. Abstract........................................................4
   1.1 List of open issues............................................4
   2. Conventions used in this document...............................4
   3. Introduction....................................................4
   3.1. Acronyms & abbreviations......................................5
   3.2. Multiple Types of Switching and Forwarding Hierarchies........5
   3.3. Extension of the MPLS Control Plane...........................7
   3.4. Key Differences Between MPLS-TE and GMPLS....................10
   4. Routing and addressing model...................................11
   4.1 Addressing of PSC and non-PSC layers..........................12
   4.2 GMPLS scalability enhancements................................12
   4.3 Extensions to IP TE routing protocols.........................13
   5. Unnumbered links...............................................14
   5.1 Unnumbered Forwarding Adjacencies.............................15
   6. Link bundling..................................................15
   6.1 Restrictions on bundling......................................16
   6.2 Routing considerations for bundling...........................16
   6.3 Signaling considerations......................................17
   6.3.1 Mechanism 1: Implicit Indication............................17
   6.3.2 Mechanism 2: Explicit Indication by IP Address..............17
   6.3.3 Mechanism 3: Explicit Indication by Component Interface ID..17
   6.4 Unnumbered Bundled Link.......................................18
   6.5 Forming TE links..............................................18
   7. UNI and NNI....................................................19
   7.1 OIF UNI versus GMPLS..........................................19
   7.2 Routing at the UNI............................................20
   8. Link Management................................................20
   8.1 Control channel and control channel management................21
   8.2 Link property correlation.....................................22
   8.3 Link connectivity verification................................22
   8.4 Fault management..............................................23
   9. Generalized Signaling..........................................23
   9.1. Overview: How to Request an LSP..............................25
   9.2. Generalized Label Request....................................26
   9.3. SONET/SDH Traffic Parameters.................................27
   9.4. Bandwidth Encoding...........................................28
   9.5. Generalized Label............................................28
   9.6. Waveband Switching...........................................29
   9.7. Label Suggestion by the Upstream.............................29
   9.8. Label Restriction by the Upstream............................29
   9.9. Bi-directional LSP...........................................30
   9.10. Bi-directional LSP Contention Resolution....................31
   9.11. Rapid Notification of Failure...............................31
   9.12. Link Protection.............................................31
   9.13. Explicit Routing and Explicit Label Control.................32
   9.14. LSP modification and LSP re-routing.........................33

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   9.15. Route recording.............................................33
   10. Forwarding Adjacencies (FA)...................................34
   10.1 Routing and Forwarding Adjacencies...........................34
   10.2. Signaling aspects...........................................35
   10.3 Cascading of Forwarding Adjacencies..........................35
   11.1 Network Management Systems (NMS).............................36
   12. Security considerations.......................................38
   13. Acknowledgements..............................................39
   14. References....................................................39
   15. Author's Addresses............................................41
   Full Copyright Statement..........................................43
   Appendix 1 Brief overview of the ITU-T work on G.ASTN/G.ASON......45
   A.1 Terminology issues............................................45
   A.2 Common Equipment Management [G.cemr]..........................45
   A.3 Data Communications Network [G.dcn]...........................46
   A.4 Distributed Connection Management [G.dcm].....................46
   A.5 Generalized Automatic Neighbor Discovery [G.ndisc]............47
   A.6 Generalized Automatic Service Discovery [G.sdisc].............47
   A.7 OTN routing [G.rtg]...........................................47
   A.8 OTN Connection Admission Control [G.cac]......................47
   A.9 OTN Link Management [G.lm]....................................48

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1. Abstract

   Future data and transmission networks will consist of elements such
   as routers, switches, DWDM systems, Add-Drop Multiplexors (ADMs),
   photonic cross-connects (PXCs), optical cross-connects (OXCs), etc
   that will use Generalized MPLS (GMPLS) to dynamically provision
   resources and to provide network survivability using protection and
   restoration techniques.

   This document describes the architecture of GMPLS. GMPLS extends
   MPLS to encompass time-division (e.g. SDH/SONET, PDH, G.709),
   wavelength (lambdas), and spatial switching (e.g. incoming port or
   fiber to outgoing port or fiber). The main focus of GMPLS is on the
   control plane of these various layers since each of them can use
   physically diverse data or forwarding planes. The intention is to
   cover both the signaling and the routing part of that control plane.

1.1 List of open issues

   This section lists several open issues on which the various people
   are currently working.

   - Inter-domain operations (e.g. routing with BGP-4).
   - Protection and restoration for GMPLS.
   - Multicasting in GMPLS.
   - Extensions for new technologies like G.709.
   - VPN support.

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 [2].

3. Introduction

   The architecture presented in this document covers the main building
   blocks needed to build a consistent control plane for multiple
   switching layers. It does not restrict the way that these layers
   work together. Different models can be applied: e.g. overlay,
   augmented or integrated. Moreover, each pair of contiguous layer may
   work jointly in a different way, resulting in a number of possible
   combinations, at the discretion of manufacturers and operators.

   This document is a generalization of the MPLS architecture [MPLS-
   ARCH], and in some cases may differ slightly from that architecture
   since non packet-based forwarding planes are now considered. It is
   not the intention of this document to describe concepts already
   described in the current MPLS architecture. The goal is to describe
   specific concepts of Generalized MPLS (GMPLS).

   However, some of the concepts explained hereafter are not part of
   the current MPLS architecture and are applicable to both MPLS and
   GMPLS (i.e. link bundling, unnumbered links, and LSP hierarchy).

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   Since these concepts were introduced together with GMPLS and since
   they are of paramount importance for an operational GMPLS network,
   they will be discussed here.

   The organization of the remainder of this draft is as follows.  We
   begin with an introduction of GMPLS.  We then present the specific
   GMPLS building blocks and explain how they can be combined together
   to build an operational GMPLS networks.  Specific details of the
   separate building blocks can be found in the corresponding

3.1. Acronyms & abbreviations

   ABR          Area Border Router
   AS           Autonomous System
   ASBR         Autonomous System Boundary Router
   BGP          Border Gateway Protocol
   CR-LDP       Constraint-based Routing LDP
   CSPF         Constraint-based Shortest Path First
   DWDM         Dense Wavelength Division Multiplexing
   FA           Forwarding Adjacency
   GMPLS        Generalized Multi-Protocol Label Switching
   IGP          Interior Gateway Protocol
   LDP          Label Distribution Protocol
   LMP          Link Management Protocol
   LSA          Link State Advertisement
   LSR          Label Switching Router
   LSP          Label Switched Path
   MIB          Management Information Base
   MPLS         Multi-Protocol Label Switching
   NMS          Network Management System
   OXC          Optical Cross-Connect
   PXC          Photonic Cross-Connect
   RSVP         ReSource reserVation Protocol
   SDH          Synchronous Digital Hierarchy
   STM(-N)      Synchronous Transport Module (-N)
   STS(-N)      Synchronous Transport Signal-Level N (SONET)
   TE           Traffic Engineering

3.2. Multiple Types of Switching and Forwarding Hierarchies

   Generalized MPLS (GMPLS) differs from traditional MPLS in that it
   supports multiple types of switching, i.e. the addition of support
   for TDM, lambda, and fiber (port) switching. The support for the
   additional types of switching has driven GMPLS to extend certain
   base functions of traditional MPLS and, in some cases, to add
   functionality.  These changes and additions impact basic LSP
   properties, how labels are requested and communicated, the
   unidirectional nature of LSPs, how errors are propagated, and
   information provided for synchronizing the ingress and egress LSRs.

   The MPLS architecture [MPLS-ARCH] was defined to support the
   forwarding of data based on a label. In this architecture, Label
   Switching Routers (LSRs) were assumed to have a forwarding plane

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   that is capable of (a) recognizing either packet or cell boundaries,
   and (b) being able to process either packet headers (for LSRs
   capable of recognizing packet boundaries) or cell headers (for LSRs
   capable of recognizing cell boundaries).

   The original MPLS architecture is here being extended to include
   LSRs whose forwarding plane recognizes neither packet, nor cell
   boundaries, and therefore, can't forward data based on the
   information carried in either packet or cell headers. Specifically,
   such LSRs include devices where the forwarding decision is based on
   time slots, wavelengths, or physical ports. So, the new set of LSRs,
   or more precisely interfaces on these LSRs, can be subdivided into
   the following classes:

   1. Packet Switch Capable (PSC) interfaces:

   Interfaces that recognize packet boundaries and can forward data
   based on the content of the packet header. Examples include
   interfaces on routers that forward data based on the content of the
   IP header and interfaces on routers that forward data based on the
   content of the MPLS "shim" header.

   2. Layer-2 Switch Capable (L2SC) interfaces:

   Interfaces that recognize frame/cell boundaries and can forward data
   based on the content of the frame/cell header. Examples include
   interfaces on Ethernet bridges that forward data based on the
   content of the MAC header and interfaces on ATM-LSRs that forward
   data based on the ATM VPI/VCI.

   3. Time-Division Multiplex Capable (TDM) interfaces:

   Interfaces that forward data based on the data's time slot in a
   repeating cycle.  An example of such an interface is that of a
   SDH/SONET Cross-Connect (XC), Terminal Multiplexer (TM), or Add-Drop
   Multiplexer (ADM). Other examples include interfaces implementing
   G.709 (the "digital wrapper") and PDH interfaces.

   4. Lambda Switch Capable (LSC) interfaces:

   Interfaces that forward data based on the wavelength on which the
   data is received.  An example of such an interface is that of a
   Photonic Cross-Connect (PXC) or Optical Cross-Connect (OXC) that can
   operate at the level of an individual wavelength. Additional
   examples include PXC interfaces that can operate at the level of a
   group of wavelengths, i.e. a waveband.

   5. Fiber-Switch Capable (FSC) interfaces:

   Interfaces that forward data based on a position of the data in the
   real world physical spaces.  An example of such an interface is that
   of a PXC or OXC that can operate at the level of a single or
   multiple fibers.

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   A circuit can be established only between, or through, interfaces of
   the same type. Depending on the particular technology being used for
   each interface, different circuit names can be used, e.g. SDH
   circuit, optical trail, light path, etc. In the context of GMPLS,
   all these circuits are referenced by a common name: Label Switched
   Path (LSP).

   The concept of nested LSP (LSP within LSP), already available in the
   traditional MPLS, facilitates building a forwarding hierarchy, i.e.
   a hierarchy of LSPs. This hierarchy of LSPs can occur on the same
   interface, or between different interfaces.

   For example, a hierarchy can be built if an interface is capable of
   multiplexing several LSPs from the same technology (layer), e.g. a
   lower order SDH/SONET LSP (VC-12) nested in a higher order SDH/SONET
   LSP (VC-4). Several levels of signal (LSP) nesting are defined in
   the SDH/SONET multiplexing hierarchy.

   The nesting can also occur between interfaces. At the top of the
   hierarchy are FSC interfaces, followed by LSC interfaces, followed
   by TDM interfaces, followed by L2SC, and followed by PSC interfaces.
   This way, an LSP that starts and ends on a PSC interface can be
   nested (together with other LSPs) into an LSP that starts and ends
   on a L2SC interface. This LSP, in turn, can be nested (together with
   other LSPs) into an LSP that starts and ends on an TDM interface,
   which in turn can be nested (together with other LSPs) into an LSP
   that starts and ends on a LSC interface, which in turn can be nested
   (together with other LSPs) into an LSP that starts and ends on a FSC

3.3. Extension of the MPLS Control Plane

   The establishment of LSPs that span only Packet Switch Capable (PSC)
   or Layer-2 Switch Capable (L2SC) interfaces is defined for the
   original MPLS and/or MPLS-TE control planes. GMPLS extends these
   control planes to support each of the five classes of interfaces
   (i.e. layers) defined in the previous section.

   Note that the GMPLS control plane supports an overlay model, an
   augmented model, and a peer (integrated) model. In the near term,
   GMPLS is very suitable for controlling each layer independently.
   This elegant approach will facilitate the future deployment of other

   The GMPLS control plane is made of several building blocks are
   described in more detail in the following sections. These building
   blocks are based on well-known signaling and routing protocols that
   have been extended and/or modified to support GMPLS. They use IPv4
   and/or IPv6 addresses. Only one new specialized protocol is required
   to support the operations of GMPLS, a signaling protocol for link
   management [LMP].

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   GMPLS is indeed based on the Traffic Engineering (TE) extensions to
   MPLS, a.k.a. MPLS-TE. This is because most of the technologies that
   can be used below the PSC level require some traffic engineering.
   The placement of LSPs at these levels needs in general to take
   several constraints into consideration (such as framing, bandwidth,
   protection capability, etc) and to bypass the legacy Shortest-Path
   First (SPF) algorithm. Note, however, that this is not mandatory and
   that in some cases SPF routing can be applied.

   In order to facilitate constrained-based SPF routing of LSPs, the
   nodes performing LSP establishment need more information about the
   links in the network than standard intra-domain routing protocols
   provide. These TE attributes are distributed using the transport
   mechanisms already available in IGPs (e.g. flooding) and taken into
   consideration by the LSP routing algorithm. Optimization of the LSP
   trajectories may also require some external simulations using
   heuristics that serve as input for the actual path calculation and
   LSP establishment process.

   Extensions to traditional routing protocols and algorithms are
   needed to uniformly encode and carry TE link information, and
   explicit routes (e.g. source routes) are required in the signaling.
   In addition, the signaling must now be capable of transporting the
   required circuit (LSP) parameters such as the bandwidth, the type of
   signal, the desired protection, the position in a particular
   multiplex, etc. Most of these extensions have already been defined
   for PSC and L2SC traffic engineering with MPLS. GMPLS primarily adds
   additional extensions for TDM, LSC, and FSC traffic engineering.
   Only a very few elements are technology specific.

   Thus, GMPLS extends the two signaling protocols defined for MPLS-TE
   signaling, i.e. RSVP-TE and CR-LDP. However, GMPLS does not specify
   which one of these two signaling protocols must be used. It is the
   role of manufacturers and operators to evaluate the two possible
   solutions for their own interest.

   Since GMPLS is based on RSVP-TE and CR-LDP, it mandates a
   downstream-on-demand label allocation and distribution, with an
   ingress initiated ordered control. Liberal label retention is
   normally used, but conservative label retention mode could also be
   used. Furthermore, there is no restriction on the label allocation
   strategy, it can be request/signaling driven (obvious for circuit
   switching technologies), traffic/data driven, or even topology
   driven. There is also no restriction on the route selection;
   explicit routing is normally used (strict or loose) but hop-by-hop
   routing could be used as well.

   GMPLS also extends two traditional intra-domain link-state routing
   protocols already extended for TE, i.e. OSPF-TE and IS-IS-TE.
   However, if explicit (source) routing is used, the routing
   algorithms used by these protocols no longer need to be
   standardized. Extensions for inter-domain routing (e.g. BGP) are for
   further study.

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   The use of technologies like DWDM (Dense Wavelength Division
   Multiplexing) implies that we can now have a very large number of
   parallel links between two directly adjacent nodes (hundreds of
   wavelengths, or even thousands of wavelengths if multiple fibers are
   used). Such a large number of links was not originally considered
   for an IP or MPLS control plane. Some slight adaptations of that
   control plane are thus required if we want to reuse it in the GMPLS

   For instance, the traditional IP routing model assumes the
   establishment of a routing adjacency over each link connecting two
   adjacent nodes. Having such a large number of adjacencies does not
   scale well. Each node needs to maintain each of its adjacencies one
   by one, and link state routing information must be flooded
   throughout the network.

   To solve this issue the concept of link bundling was introduced.
   Moreover, the manual configuration and control of these links, even
   if they are unnumbered, becomes impractical. The Link Management
   Protocol (LMP) was specified to solve these issues.

   LMP runs between data-plane adjacent nodes and is used to manage TE
   links.  Specifically, LMP provides mechanisms to maintain control
   channel connectivity, verify the physical connectivity of the data-
   bearing links, correlate the link property information, and manage
   link failures. A unique feature of LMP is that it is able to
   localize faults in both opaque and transparent networks, independent
   of the encoding scheme and bit rate used for the data.

   LMP is defined in the context of GMPLS, but is specified
   independently of the GMPLS signaling specification since it is a
   local protocol run between data-plane adjacent nodes. As a result,
   LMP can be reused in other contexts with non-GMPLS signaling

   The MPLS signaling and routing protocols require at least one bi-
   directional control channel to communicate even if two adjacent
   nodes are connected by unidirectional links. Several control
   channels can be used. LMP can be used to establish, maintain and
   manage these control channels.

   GMPLS does not specify how these control channels must be
   implemented, but GMPLS requires IP to transport the signaling and
   routing protocols over them. Control channels can be either in-band
   or out-of-band, and several solutions can be used to carry IP. Note
   also that one type of LMP message is used in-band in the data plane
   and may not be transported over IP, but this is a particular case,
   needed to verify connectivity in the data plane.

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3.4. Key Differences Between MPLS-TE and GMPLS

   Some key differences between MPLS-TE and GMPLS are highlighted in
   the following. Some of them are key advantages of GMPLS to control
   TDM, LSC and FSC layers.

   - In MPLS-TE, links traversed by an LSP can include an intermix of
   links with heterogeneous label encoding (e.g. links between routers,
   links between routers and ATM-LSRs, and links between ATM-LSRs.
   GMPLS extends this by including links where the label is encoded as
   a time slot, or a wavelength, or a position in the real world
   physical space.

   - In MPLS-TE, an LSP that carries IP has to start and end on a
   router. GMPLS extends this by requiring an LSP to start and end on
   similar type of LSR.

   - The type of a payload that can be carried in GMPLS by an LSP is
   extended to allow such payloads as SONET/SDH, G.709, 1 or 10Gb
   Ethernet, etc.

   - For TDM, LSC and FSC interfaces, bandwidth allocation for an LSP
   can be performed only in discrete units.

   - It is expected to have (much) fewer labels on TDM, LSC or FSC
   links than on PSC or L2SC links.

   - The use of Forwarding Adjacencies (FA), provides a mechanism that
   can improve bandwidth utilization, when bandwidth allocation can be
   performed only in discrete units, as well as a mechanism to
   aggregate forwarding state, thus allowing the number of required
   labels to be reduced

   - GMPLS allows for a label to be suggested by an upstream node to
   reduce the setup latency. This suggestion may be overridden by a
   downstream node but, in some cases, at the cost of higher LSP setup

   - GMPLS extends on the notion of restricting the range of labels
   that may be selected by a downstream node. In GMPLS, an upstream
   node may restrict the labels for an LSP along either a single hop or
   along the entire LSP path. This feature is useful in photonic
   networks where wavelength conversion may not be available.

   - While traditional TE-based (and even LDP-based) LSPs are
   unidirectional, GMPLS supports the establishment of bi-directional

   - GMPLS supports the termination of an LSP on a specific egress
   port, i.e. the port selection at the destination side.

   - GMPLS with RSVP-TE supports an RSVP specific mechanism for rapid
   failure notification.

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4. Routing and addressing model

   GMPLS is based on the IP routing and addressing models. This assumes
   that IPv4 and/or IPv6 addresses are used to identify interfaces and
   that traditional (distributed) IP routing protocols are also reused.
   Indeed, the discovery of the topology and the resource state of all
   links in a routing domain is achieved via these routing protocols.

   Since control and data planes are de-coupled in GMPLS, one cannot do
   anymore the assumption that control-plane neighbors (i.e. IGP-learnt
   neighbors) are data-plane neighbors, hence mechanisms like LMP are
   needed to associate TE links with neighboring nodes.

   IP addresses are not used only to identify interfaces of IP hosts
   and routers, but more generally to identify any PSC and non-PSC
   interfaces. Similarly, IP routing protocols are used to find routes
   for IP datagrams with a SPF algorithm, and are also used to find
   routes for non-PSC circuits by using a CSPF algorithm.

   However, some additional mechanisms are needed to increase the
   scalability of these models and to deal with specific traffic
   engineering requirements of non-PSC layers. These mechanisms will be
   introduced in the following.

   Re-using existing IP routing protocols allows for non-PSC layers to
   take advantages of all the valuable developments that took place
   since years for IP routing, in particular in the context of intra-
   domain routing (link-state routing) and inter-domain routing (policy

   Each particular non-PSC layer can be seen as a set of Autonomous
   Systems (ASs) interconnected in an arbitrary way. Similarly to the
   traditional IP routing, each AS is managed by a single
   administrative authority. For instance, an AS can be an SDH/SONET
   network operated by a given carrier. The set of interconnected ASs
   being an SDH/SONET Internetwork.

   Exchange of routing information between ASs can be done via an
   inter-domain routing protocol like BGP-4. There is obviously a huge
   value of re-using well-known policy routing facilities provided by
   BGP in a non-PSC context. Extensions for BGP traffic engineering in
   the context of non-PSC layers are for further study.

   Each AS can be subdivided in different routing domains, and each can
   run a different intra-domain routing protocol. In turn, each
   routing-domain can be divided in areas.

   A routing domain is made of GMPLS nodes. These nodes can be either
   edge nodes (i.e. hosts, ingress LSRs or egress LSRs), or internal
   LSRs. An example of non-PSC host is an SDH/SONET Terminal
   Multiplexer (TM). Another example, is an SDH/SONET interface card
   within an IP router or ATM switch.

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   Note that traffic engineering in the intra-domain requires the use
   of link-state routing protocols like OSPF or IS-IS.

   GMPLS defines extensions to these protocols. These extensions are
   needed to disseminate specific TDM, LSC and FSC static and dynamic
   characteristics related to nodes and links. The current focus is on
   intra-area traffic engineering. However, inter-area traffic
   engineering is also under investigation.

4.1 Addressing of PSC and non-PSC layers

   The fact that IPv4 and/or IPv6 addresses are used doesn't imply at
   all that they should be allocated in the same addressing space than
   public IPv4 and/or IPv6 addresses used for the Internet. Each layer
   could have a different addressing authority responsible for address
   allocation and re-using the full addressing space, completely

   Private IP addresses can be used if they don't require to be
   exchanged with any other operator, public IP addresses are otherwise
   required. Of course, if an integrated model is used, two layers
   could share the same addressing space.

   Note that there is a benefit of using public IPv4 and/or IPv6
   Internet addresses for non-PSC layers if an integrated model with
   the IP layer is foreseen.

   If we consider the scalability enhancements proposed in the next
   section, the IPv4 (32 bits) and the IPv6 (128 bits) addressing
   spaces are both more than sufficient to accommodate any non-PSC
   layer. We can reasonably expect to have much less non-PSC devices
   (e.g. SDH/SONET nodes) than we have today IP hosts and routers.

   Other kinds of addressing schemes (e.g. NSAP) are not considered
   here since this would imply a modification of the already existing
   signaling and routing protocols that uses IPv4 and/or IPv6
   addresses. This would be incompatible to our objectives of re-using
   existing IP protocols.

4.2 GMPLS scalability enhancements

   TDM, LSC and FSC layers introduce new constraints on the IP
   addressing and routing models since several hundreds of parallel
   physical links (e.g. wavelengths) can now connect two nodes. Most of
   the carriers already have today several tens of wavelengths per
   fiber between two nodes. New generation of DWDM systems will allow
   several hundreds of wavelengths per fiber.

   It becomes rather impractical to associate an IP address with each
   end of each physical link, to represent each link as a separate
   routing adjacency, and to advertise and to maintain link states for
   each of these links. For that purpose, GMPLS enhances the MPLS
   routing and addressing models to increase their scalability.

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   Two optional mechanisms can be used to increase the scalability of
   the addressing and the routing: unnumbered links and link bundling.
   These two mechanisms can also be combined. They require extensions
   to signaling (RSVP-TE and CR-LDP) and routing (OSPF-TE and IS-IS-TE)

4.3 Extensions to IP TE routing protocols

   Traditionally, a TE link is advertised as an adjunct to a "regular"
   OSPF or IS-IS link, i.e., an adjacency is brought up on the link,
   and when the link is up, both the regular IGP properties of the link
   (basically, the SPF metric) and the TE properties of the link are
   then advertised.

   However, GMPLS challenges this notion in three ways:

   - First, links that are non-PSC may yet have TE properties; however,
   an OSPF adjacency cannot be brought up directly on such links.

   - Second, an LSP can be advertised as a point-to-point TE link in
   the routing protocol, i.e. as a Forwarding Adjacency (FA); thus, an
   advertised TE link need no longer be between two OSPF direct
   neighbors. Forwarding Adjacencies (FA) are further described in a
   separate section.

   - Third, a number of links may be advertised as a single TE link
   (e.g. for improved scalability), so again, there is no longer a one-
   to-one association of a regular adjacency and a TE link.

   Thus we have a more general notion of a TE link. A TE link is a
   logical link that has TE properties, some of which may be configured
   on the advertising LSR, others which may be obtained from other LSRs
   by means of some protocol, and yet others which may be deduced from
   the component(s) of the TE link.

   An important TE property of a TE link is related to the bandwidth
   accounting for that link. GMPLS will define different accounting
   rules for different non-PSC layers. Generic bandwidth attributes are
   however defined by the TE routing extensions and by GMPLS, such as
   the unreserved bandwidth, the maximum reservable bandwidth, the
   maximum LSP bandwidth.

   It is expected in a dynamic environment to have frequent changes of
   bandwidth accounting information. A flexible policy for triggering
   link state updates based on bandwidth thresholds and link-dampening
   mechanism can be implemented.

   TE properties associated with a link should also capture protection
   and restoration related characteristics. For instance, shared
   protection can be elegantly combined with bundling. Protection and
   restoration are mainly generic mechanisms also applicable to MPLS.
   It is expected that they will first be developed for MPLS and later
   on generalized to GMPLS.

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   A TE link between a pair of LSRs doesn't imply the existence of an
   IGP adjacency between these LSRs. A TE link must also have some
   means by which the advertising LSR can know of its liveness (e.g. by
   using LMP hellos). When an LSR knows that a TE link is up, and can
   determine the TE link's TE properties, the LSR may then advertise
   that link to its GMPLS enhanced OSPF or IS-IS neighbors using the TE
   objects/TLVs. We call the interfaces over which GMPLS enhanced OSPF
   or ISIS adjacencies are established "control channels".

5. Unnumbered links

   Unnumbered links (or interfaces) are links (or interfaces) that do
   not have IP addresses. Using such links involves two capabilities:
   the ability to specify unnumbered links in MPLS TE signaling, and
   the ability to carry (TE) information about unnumbered links in IGP
   TE extensions of ISIS-TE and OSPF-TE.

   A. The ability to specify unnumbered links in MPLS TE signaling
   requires extensions to RSVP-TE and CR-LDP. The MPLS-TE signaling
   doesn't provide support for unnumbered links, because it doesnÆt
   provide a way to indicate an unnumbered link in its Explicit Route
   Object/TLV and in its Record Route Object (there is no such TLV for
   CR-LDP). GMPLS defines simple extensions to indicate an unnumbered
   link in these two Objects/TLVs, using a new Unnumbered Interface ID

   Since unnumbered links are not identified by an IP address, then for
   the purpose of MPLS TE each end need some other identifier, local to
   the LSR to which the link belongs. Note that links are directed,
   i.e., a link l is from some LSR A to some other LSR B. LSR A chooses
   the interface identifier for link l, we call this the "outgoing
   interface identifier from LSR A's point of view". If there is a
   reverse link from LSR B to LSR A, B chooses the outgoing interface
   identifier for the reverse link, we call this the linkÆs "incoming
   interface identifier" from LSR AÆs point of view. There is no a
   priori relationship between the two interface identifiers. Both ends
   must also agree on each of these identifiers.

   The new Unnumbered Interface ID sub-object/sub-TLV for the ER
   Object/TLV contains the Router ID of the LSR at the upstream end of
   the unnumbered link and the outgoing interface identifier with
   respect to that upstream LSR.

   The new Unnumbered Interface ID sub-object/sub-TLV for the RR Object
   contains the outgoing interface identifier with respect to the LSR
   that adds it in the RR Object.

   B. The ability to carry (TE) information about unnumbered links in
   IGP TE extensions requires new sub-TLVs for the extended IS
   reachability TLV defined in ISIS-TE and for the TE LSA (which is an
   opaque LSA) defined in OSPF-TE. An Outgoing Interface Identifier
   sub-TLV and an Incoming Interface Identifier sub-TLV are defined.

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5.1 Unnumbered Forwarding Adjacencies

   If an LSR that originates an LSP advertises this LSP as an
   unnumbered FA in IS-IS or OSPF, the LSR must allocate an Interface
   ID to that FA. If the LSP is bi-directional, the tail end LSR
   advertises the reverse LSP as an unnumbered FA, the tail end LSR
   must allocate an Interface ID to the reverse FA.

   Signaling has been enhanced to carry the Interface ID. When an LSP
   is created which will be advertised as an FA, the head-end LSR
   includes its Interface ID in the Path/REQUEST. The tail end LSR
   responds by including its reverse LSPÆs Interface ID in the

   The Interface ID is transported in the new LSP Tunnel Interface ID
   object/TLV called the Forward Interface ID when it appears in a
   Path/REQUEST message, and the Reverse Interface ID when it appears
   in the Resv/MAPPING message.

   The LSP Tunnel Interface ID object/TLV contains the Router ID of the
   LSR that generates it, and the Interface ID. Note that if the
   forward or reverse LSP is part of a bundled link, the Interface ID
   is set to the Component Interface ID of that LSP (as defined in the
   next section).

6. Link bundling

   The concept of link bundling is essential in certain networks
   employing the GMPLS control plane. A typical example is an optical
   meshed network where adjacent optical cross-connects (LSRs) are
   connected by several hundreds of parallel wavelengths. In this
   network, consider the application of link state routing protocols,
   like OSPF or IS-IS, with suitable extensions for resource discovery
   and dynamic route computation. Each wavelength must be advertised
   separately in order to be used, except if link bundling is used.

   When a pair of LSRs is connected by multiple links, it is possible
   to advertise several (or all) of these links as a single link into
   OSPF and/or IS-IS. This process is called link bundling, or just
   bundling. The resulting logical link is called a bundled link as its
   physical links are called component links.

   The purpose of link bundling is to improve routing scalability by
   reducing the amount of information that has to be handled by OSPF
   and/or IS-IS. This reduction is accomplished by performing
   information aggregation/abstraction. As with any other information
   aggregation/abstraction, this results in losing some of the
   information. To limit the amount of losses one need to restrict the
   type of the information that can be aggregated/abstracted.

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6.1 Restrictions on bundling

   The following restrictions are required for bundling links. All
   component links in a bundle must begin and end on the same pair of
   LSRs; and share some common characteristics or properties, i.e. they
   must have the same:

   - Link Type (i.e. point-to-point or multi-access) [OSPF-TE/ISIS-TE],
   - TE Metric (i.e. an administrative cost) [OSPF- TE/ISIS-TE],
   - Set of Resource Classes (i.e. colors) [OSPF-TE/ISIS-TE],
   - Link Multiplex Capability (e.g. FSC, LSC or TDM) [HIERARCHY].

   Note that bundling may be applied recursively; a component link may
   itself be a bundled link. An FA may also be a component link. In
   fact, a bundle can consist of a mix of point-to-point links, FAs,
   and bundled links, but all sharing some common properties.

6.2 Routing considerations for bundling

   A bundled link is just another kind of TE link such as those defined
   by OSPF-TE or IS-IS-TE. The liveness of the bundled link is
   determined by the liveness of each of the component links within the
   bundled link. The liveness of a component link can be determined by
   any of several means: IS-IS or OSPF hellos over the component link,
   or RSVP Hello (hop local), or LMP hellos (link local), or from layer
   1 or layer 2 indications.

   Note that according to the RSVP-TE Tunnel specification the RSVP
   Hello mechanism is intended to be used when notification of link
   layer failures is not available and unnumbered links are not used,
   or when the failure detection mechanisms provided by the link layer
   are not sufficient for timely node failure detection.

   Once a bundled link is determined to be alive, it can be advertised
   as a TE link and the TE information can be flooded.  If IS-IS/OSPF
   hellos are run over the component links, IS-IS/OSPF flooding can be
   restricted to just one of the component links.

   Note that advertising a (bundled) TE link between a pair of LSRs
   doesn't imply that there is an IGP adjacency between these LSRs that
   is associated with just that link. In fact, in certain cases a TE
   link between a pair of LSRs could be advertised even if there is no
   IGP adjacency at all between the LSR (e.g. when the TE link is an

   Forming a bundled link consist in aggregating the identical TE
   parameters of each individual component link to produce aggregated
   TE parameters. A TE link as defined by [OSPF-TE-GMPLS] and [ISIS-TE-
   GMPLS] has many parameters, adequate aggregation rules must be
   defined for each one.

   Some parameters can be sums of component characteristics such as the
   unreserved bandwidth and the maximum reservable bandwidth. Bandwidth

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   information is an important part of a bundle advertisement and it
   must be clearly defined since an abstraction is done.

   A GMPLS node with bundled links must apply admission control on a
   per-component link basis.

6.3 Signaling considerations

   Typically, an LSP's explicit route (contained in an explicit route)
   will choose the bundled link to be used for the LSP, but not the
   component link(s), since information about the bundled link is
   flooded, but information about the component links is kept local to
   the LSR.

   The choice of the component link to use is always made by an
   upstream node. If the LSP is bidirectional, the upstream node
   chooses a component link in each direction.

   Three mechanisms for indicating this choice to the downstream node
   are possible.

6.3.1 Mechanism 1: Implicit Indication

   This mechanism requires that each component link has a dedicated
   signaling channel (e.g. the link is a Sonet/SDH link using the DCC
   for in-band signaling). The upstream node tells the receiver which
   component link to use by sending the message over the chosen
   component link's dedicated signaling channel. Note that this
   signaling channel can be in-band or out-of-band. In this last case,
   the association between the signaling channel and that component
   link need to be explicitly configured.

6.3.2 Mechanism 2: Explicit Indication by IP Address

   This mechanism requires that each component link has a unique remote
   IP address. The upstream node can either send messages addressed to
   the remote IP address for the component link or encapsulate messages
   in an IP header whose destination address is the remote IP address.
   This mechanism does not require each component link to have its own
   control channel. In fact, it doesn't even require the whole
   (bundled) link to have its own control channel.

6.3.3 Mechanism 3: Explicit Indication by Component Interface ID

   With this mechanism, each component link in unnumbered and is
   assigned a unique Component Interface Identifier (32 bits value).
   The two LSRs at each end of the bundled link exchange these
   identifiers. An upstream node indicates the choice of a component
   link by including the corresponding identifier in signaling

   Discovering Component Interface Identifiers at bootstrap may be
   accomplished by configuration, by means of a protocol such as LMP
   (preferred solution), by means of RSVP/CR-LDP (especially in the

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   case where a component link is a Forwarding Adjacency), or by means
   of IS-IS or OSPF extensions.

   New objects are needed to indicate Component Interface Identifiers
   in signaling. GMPLS defines one Component Upstream Interface ID
   object/TLV used to indicate the component interface to be used for
   traffic flowing in the upstream direction; and one Component
   Downstream Interface ID object/TLV used to indicate the component
   interface to be used for traffic flowing in the downstream
   direction. Since the choice of the component link to use is always
   made by an upstream node, these objects/TLVs are included in the
   Path/REQUEST message send downstream. With RSVP-TE they are included
   in the sendor descriptor of the Path message.

6.4 Unnumbered Bundled Link

   A bundled link may itself be numbered or unnumbered independent of
   whether the component links are numbered or not. This affects how
   the bundled link is advertised in IS-IS/OSPF, and the format of LSP
   EROs that traverse the bundled link. Furthermore, unnumbered
   Interface Identifiers for all unnumbered outgoing links of a given
   LSR (whether component links, Forwarding Adjacencies or bundled
   links) MUST be unique in the context of that LSR.

6.5 Forming TE links

   The generic rule for bundling component links is to place those
   links that are correlated in some manner in the same bundle. If
   links may be correlated based on multiple properties then the
   bundling may be applied sequentially based on these properties. For
   instance, links may be first grouped based on the first property.
   Each of these groups may be then divided into smaller groups based
   on the second property and so on. The main principle followed in
   this process is that the properties of the resulting bundles should
   be concisely summarizable. Link bundling may be done automatically
   or by configuration. Automatic link bundling can apply bundling
   rules sequentially to produce bundles.

   For instance, the first property on which component links may be
   correlated could be the Link Multiplex Capability, the second
   property could be the Link Type, the third property could be the
   Administrative Weight (cost), the fourth property could be the
   Resource Classes and finally links may be correlated based on other
   metrics such as SRLG (Shared Risk Link Groups) or delay.

   When routing an alternate path for protection purposes, the general
   principle followed is that the alternate path is not routed over any
   link belonging to an SRLG that some link in the primary path belongs
   to. Thus, the rule to be followed is to group links belonging to
   exactly the same set of SRLGs.

   This type of sequential sub-division may result in a number of
   bundles between two adjacent nodes. In practice, however, the link
   properties may not be very heterogeneous among component links

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   between two adjacent nodes. Thus, the number of bundles in practice
   may not be large.

7. UNI and NNI

   The interface between an edge GMPLS node and a GMPLS LSR on the
   network side may be referred to as a User to Network Interface
   (UNI), while the interface between two network side LSRs may be
   referred to as a Network to Network Interface (NNI).

   GMPLS does not specify separately a UNI and an NNI. Edge nodes are
   connected to LSRs on the network side, and these LSRs are in turn
   connected between them. Of course, the behavior of an edge node is
   not exactly the same as the behavior of an LSR on the network side.
   Note also, that an edge node may run a routing protocol, however it
   is expected that in most of the cases it will not (see also section
   7.2 and the section about signaling with an explicit route).

   Conceptually, a difference between UNI and NNI make sense either if
   both interface uses completely different protocols, or if they use
   the same protocols but with some outstanding differences. In the
   first case, separate protocols are often defined successively, with
   more or less success.

   The GMPLS approach consisted in building a consistent model from day
   one, considering both the UNI and NNI interfaces at the same time.
   For that purpose a very few specific UNI particularities have been
   ignored in a first time. GMPLS is being enhanced to support such
   particularities at the UNI by some other standardization bodies,
   like the OIF.

7.1 OIF UNI versus GMPLS

   The current OIF UNI specification [OIF-UNI] defines an interface
   between a client SDH/SONET equipment and an SDH/SONET network, each
   belonging to a distinct administrative authority. The OIF UNI
   defines additional mechanisms on the top of GMPLS for the UNI.

   For instance, the OIF service discovery procedure is a precursor to
   obtaining UNI services. Service discovery allows a client to
   determine the static parameters of the interconnection with the
   network, including the UNI signaling protocols, the type of
   concatenation, the transparency levels as well as the type of
   diversity (node, link, SRLG) supported by the network.

   Since the current OIF UNI interface does not cover photonic
   networks, G.709 Digital Wrapper, etc, it is a sub-set of the GMPLS

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7.2 Routing at the UNI

   This section discusses the selection of an explicit route by an edge
   node. The selection of the first LSR by an edge node connected to
   multiple LSRs is part of that problem.

   An edge node (host or LSR) can participate more or less deeply in
   the GMPLS routing. Four different routing models can be supported at
   the UNI: configuration based, partial peering, silent listening and
   full peering.

   - Configuration based: this routing model requires the manual or
   automatic configuration of an edge node with a list of neighbor LSRs
   sorted by preference order. Automatic configuration can be achieved
   using DHCP for instance. No routing information is exchanged at the
   UNI, except maybe the ordered list of LSRs. The only routing
   information used by the edge node is that list. The edge node sends
   by default an LSP request to the preferred LSR. ICMP redirects could
   be send by this LSR to redirect some LSP requests to another LSR
   connected to the edge node. GMPLS does not preclude that model.

   - Partial peering: limited routing information (mainly reachability)
   can be exchanged across the UNI using some extensions in the
   signaling plane. The reachability information exchanged at the UNI
   may be used to initiate edge node specific routing decision over the
   network. GMPLS does not have any capability to support this model

   - Silent listening: the edge node can silently listen to routing
   protocols and take routing decisions based on the information
   obtained. An edge node receives the full routing information,
   including traffic engineering extensions. One LSR should forward
   transparently all routing pdus to the edge node. An edge node can
   now compute a complete explicit route taking into consideration all
   the end-to-end routing information. GMPLS does not preclude this

   - Full peering: In addition to silent listening, the edge node
   participates within the routing, establish adjacencies with its
   neighbors and advertises LSAs. This is useful only if there are
   benefits for edge nodes to advertise themselves traffic engineering
   information. GMPLS does not preclude this model.

8. Link Management

   In the context of GMPLS, a pair of nodes (e.g., a photonic switch)
   may be connected by tens of fibers, and each fiber may be used to
   transmit hundreds of wavelengths if DWDM is used. Multiple fibers
   and/or multiple wavelengths may also be combined into one or more
   bundled links for routing purposes. Furthermore, to enable
   communication between nodes for routing, signaling, and link
   management, control channels must be established between a node

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   Link management is a collection of useful procedures between
   adjacent nodes that provide local services such as control channel
   management, link connectivity verification, link property
   correlation, and fault management. The Link Management Protocol
   (LMP) has been defined to fulfill these operations. LMP was
   initiated in the context of GMPLS but is a generic toolbox that can
   be also used in other contexts.

   Control channel management and link property correlation are
   mandatory procedures of LMP. Link connectivity verification and
   fault management are optional procedures.

8.1 Control channel and control channel management

   LMP control channel management is used to establish and maintain
   control channels between nodes. Control channels exist independently
   of TE links, and can be used to exchange MPLS control-plane
   information such as signaling, routing, and link management

   An "LMP adjacency" is formed between two nodes that support the same
   LMP capabilities. Multiple control channels may be active
   simultaneously for each adjacency. A control channel can be either
   explicitly configured or automatically selected, however, LMP
   currently assume that control channels are explicitly configured.

   For the purposes of LMP, the exact implementation of the control
   channel is left unspecified. The control channel(s) between two
   adjacent nodes is no longer required to use the same physical medium
   as the data-bearing links between those nodes. For example, a
   control channel could use a separate wavelength or fiber, an
   Ethernet link, or an IP tunnel through a separate management

   A consequence of allowing the control channel(s) between two nodes
   to be physically diverse from the associated data-bearing links is
   that the health of a control channel does not necessarily correlate
   to the health of the data-bearing links, and vice-versa. Therefore,
   new mechanisms must be developed to manage links, both in terms of
   link provisioning and fault isolation.

   LMP does not specify how control channels are implemented, however
   it states that messages transported over a control channel must be
   IP encoded. Furthermore, since the messages are IP encoded, the link
   level encoding is not part of LMP. A 32-bit non-zero integer control
   channel identifier (CCId) is assigned to each direction of a control

   Each control channel individually negotiates its control channel
   parameters and maintains connectivity using a fast Hello protocol.
   The latter is required if lower-level mechanisms are not available
   to detect link failures.

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   The Hello protocol of LMP is intended to be a lightweight keep-alive
   mechanism that will react to control channel failures rapidly so
   that IGP Hellos are not lost and the associated link-state
   adjacencies are not removed unnecessarily.

   The Hello protocol consists of two phases: a negotiation phase and a
   keep-alive phase. The negotiation phase allows negotiation of some
   basic Hello protocol parameters, like the Hello frequency. The keep-
   alive phase consists of a fast lightweight bi-directional Hello
   message exchange.

   If a group of control channels share a common node pair and support
   the same LMP capabilities, then LMP control channel messages (except
   Configuration messages, and Hello) may be transmitted over any of
   the active control channels without coordination between the local
   and remote nodes.

   For LMP, it is essential that at least one control channel is always
   available. In the event of a control channel failure, it may be
   possible to use an alternate active control channel without

8.2 Link property correlation

   As part of LMP, a link property correlation exchange is defined.
   The exchange is used to aggregate multiple data-bearing links (i.e.
   component links) into a bundled link and exchange, correlate, or
   change TE link parameters. The link property correlation exchange
   may be done at any time a link is up and not in the Verification
   process (see next section).

   It allows for instance to add component links to a link bundle,
   change a link's protection mechanism, change port identifiers, or
   change component identifiers in a bundle. This mechanism is
   supported by an exchange of link summary messages.

8.3 Link connectivity verification

   Link connectivity verification is an optional procedure that may be
   used to verify the physical connectivity of data-bearing links as
   well as to exchange the link identifiers that are used in the GMPLS

   The use of this procedure is negotiated as part of the configuration
   exchange that take place during the negotiation phase of the Hello
   protocol. This procedure should be done initially when a data-
   bearing link is first established, and subsequently, on a periodic
   basis for all unallocated (free) data-bearing links.

   The verification procedure consists of sending Test messages in-band
   over the data-bearing links. This requires that the unallocated
   links must be opaque; however, multiple degrees of opaqueness (e.g.,
   examining overhead bytes, terminating the payload, etc.), and hence
   different mechanisms to transport the Test messages, are specified.

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   Note that the Test message is the only LMP message that is
   transmitted over the link, and that Hello messages continue to be
   exchanged over the control channel during the link verification
   process. Data-bearing links are tested in the transmit direction as
   they are unidirectional. As such, it is possible for both nodes to
   exchange the Test messages simultaneously.

   To initiate the link verification procedure, a node must first
   notify the adjacent node that it will begin sending Test messages
   over a particular data-bearing link, or over the component links of
   a particular bundled link. The node must also indicate the number of
   data-bearing links that are to be verified; the interval at which
   the test messages will be sent; the encoding scheme, the transport
   mechanism that are supported, data rate for Test messages; and, in
   the case where the data-bearing links correspond to fibers, the
   wavelength over which the Test messages will be transmitted.
   Furthermore, the local and remote bundled link identifiers are
   transmitted at this time to perform the component link association
   with the bundled link identifiers.

8.4 Fault management

   Fault management is an important requirement from the operational
   point of view. When a failure occurs an operator needs to know
   exactly where it happened. It can also be used to support some
   specific local protection/restoration mechanisms. Logically, fault
   localization can occur only after a fault is detected. LMP provides
   a fault notification procedure that can be used to rapidly localize
   link failures.

   In new technologies such as transparent photonic switching currently
   no method is defined to locate a fault, and the mechanism by which
   the fault information is propagated must be sent "out of band" (via
   the control plane).

   As part of the fault notification procedure, the downstream LMP
   neighbor that detects data link failures will send an LMP message to
   its upstream neighbor notifying it of the failure.  When an upstream
   node receives a failure notification, it can correlate the failure
   with the corresponding input ports to determine if the failure is
   between the two nodes. Once the failure has been localized, the
   signaling protocols can be used to initiate span or path
   protection/restoration procedures.

9. Generalized Signaling

   The GMPLS signaling extends certain base functions of the RSVP-TE
   and CR-LDP signaling and, in some cases, adds functionality. These
   changes and additions impact basic LSP properties, how labels are
   requested and communicated, the unidirectional nature of LSPs, how
   errors are propagated, and information provided for synchronizing
   the ingress and egress.

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   The core GMPLS signaling specification is available in three parts:

      1. A signaling functional description [GMPLS-SIG].
      2. RSVP-TE extensions [RSVP-TE-GMPLS].
      3. CR-LDP extensions [CR-LDP-GMPLS].

   In addition, independent parts are available per technology:

      1. GMPLS extensions for SONET and SDH control [SONETSDH-GMPLS].

   The following MPLS profile applies to GMPLS:

      - Downstream-on-demand label allocation and distribution.
      - Ingress initiated ordered control.
      - Liberal (typical), or conservative (could) label retention
      - Request, traffic/data, or topology driven label allocation
      - Explicit routing (typical), or hop-by-hop routing (could).

   The GMPLS signaling defines the following new building blocks on the
   top of MPLS-TE:

      1. A new generic label request format.
      2. Labels for TDM, LSC and FSC interfaces, generically known as
         Generalized Label.
      3. Waveband switching support.
      4. Label suggestion by the upstream for optimization purposes
         (e.g. latency).
      5. Label restriction by the upstream to support some optical
      6. Bi-directional LSP establishment with contention
      7. Rapid failure notification to ingress node.
      8. Protection information currently focusing on link protection,
         plus primary and secondary LSP indication.
      9. Explicit routing with explicit label control for a fine
         degree of control.
     10. Specific traffic parameters per technology.

   These building blocks will be described in mode details in the
   following. A complete specification can be found in the
   corresponding documents.

   Note that GMPLS is highly generic and has many options. Only
   building blocks 1, 2 and 10 are mandatory, and only within the
   specific format that is needed. Typically building blocks 6 and 9
   should be implemented. Building blocks 3, 4, 5, 7 and 8 are

   A typical SDH/SONET switching network would implement building
   blocks: 1, 2 (the SDH/SONET label), 6, 9 and 10. Building blocks 7
   and 8 are optional since the protection/restoration can be achieved
   using SDH/SONET overhead bytes.

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   A typical wavelength switching network would implement building
   blocks: 1, 2 (the generic format), 4, 5, 6, 7, 8 and 9. Building
   block 3 is only needed in the particular case of waveband switching.

   A typical fiber switching network would implement building blocks:
   1, 2 (the generic format), 6, 7, 8 and 9.

   A typical MPLS-IP network would not implement any of these building
   blocks, since the absence of building block 1 would indicate regular
   MPLS-IP. Note however that building block 1 and 8 can be used to
   signal MPLS-IP as well. In that case, the MPLS-IP network can
   benefit from the link protection type (not available in CR-LDP, some
   very basic form being available in RSVP-TE). Building block 2 is
   here a regular MPLS label and no new label format is required.

   GMPLS does not specify any profile for RSVP-TE and CR-LDP
   implementations that have to support GMPLS - except for what is
   directly related to GMPLS procedures. It is to the manufacturer to
   decide which are the optional elements and procedures of RSVP-TE and
   CR-LDP that need to be implemented. Some optional MPLS-TE elements
   can be useful for TDM, LSC and FSC layers, for instance the setup
   and holding priorities that are inherited from MPLS-TE.

9.1. Overview: How to Request an LSP

   A TDM, LSC or FSC LSP is established by sending a PATH/Label Request
   message downstream to the destination. This message contains a
   Generalized Label Request with the type of LSP (i.e. the layer
   concerned), and its payload type. An Explicit Route (ERO) is also
   normally added to the message, but this can be added and/or
   completed by the first/default LSR.

   The requested bandwidth is encoded in the RSVP-TE SENDER_TSPEC
   object, or in the CR-LDP Traffic Parameters TLV. Specific parameters
   for a given technology are given in these traffic parameters, such
   as the type of signal, concatenation and/or transparency for a
   SDH/SONET LSP. For some other technology there could just one
   bandwidth parameter indicating the bandwidth as a floating-point

   The requested local protection per link may be requested using the
   Protection Information Object/TLV. The end-to-end protection type is
   for further study.

   If the LSP is a bi-directional LSP, an Upstream Label is also
   specified in the Path/Label request message. This label will be the
   one to use in the downstream to upstream direction.

   Additionally, a Suggested Label, a Label Set and a Waveband Label
   can also be included in the message. Other operations are defined in

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   The downstream node will send back a Resv/Label Mapping message
   including one Generalized Label object/TLV that can contain several
   Generalized Labels. For instance, if a concatenated SDH/SONET signal
   is requested, several labels can be returned.

   In case of SDH/SONET virtual concatenation, a list of labels is
   returned. Each label identifying one element of the virtual
   concatenated signal. This limits virtual concatenation to remain
   within a single (component) link.

   In case of any type of SDH/SONET contiguous concatenation, only one
   label is returned. That label is the lowest signal of the contiguous
   concatenated signal (given an order specified in [SONETSDH-GMPLS]).

   In case of SDH/SONET "multiplication", i.e. co-routing of circuits
   of the same type but without concatenation but all belonging to the
   same LSP, the explicit list of all signals that take part in the LSP
   is returned.

9.2. Generalized Label Request

   The Generalized Label Request is a new object/TLV to be added in an
   RSVP-TE Path message instead of the regular Label Request, or in a
   CR-LDP Request message in addition to the already existing TLVs.
   Only one label request can be used per message, so a single LSP can
   be requested at a time per signaling message.

   The Generalized Label Request gives two major characteristics
   (parameters) required to support the LSP being requested: the LSP
   encoding type, and the LSP payload type called Generalized PID (G-

   The LSP encoding type indicates the encoding type that will be used
   with the data associated with the LSP, i.e. the type of technology
   being considered. For instance, it can be SDH, SONET, Ethernet, ANSI
   PDH, etc. It represents the nature of the LSP, and not the nature of
   the links that the LSP traverses. This is used hop-by-hop by each

   A link may support a set of encoding formats, where support means
   that a link is able to carry and switch a signal of one or more of
   these encoding formats.

   The LSP payload type (G-PID) identifies the payload carried by the
   LSP, i.e. an identifier of the client layer of that LSP. For some
   technologies it also indicates the mapping used by the client layer,
   e.g. byte synchronous mapping of E1. This must be interpreted
   according to the LSP encoding type of the LSP and is used by the
   nodes at the endpoints of the LSP to know to which client layer a
   request is destined, and in some cases by the penultimate hop.

   Other technology specific parameters are not transported in the
   Generalized Label Request but in technology specific traffic

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   parameters as explained hereafter. Currently, only one specific set
   of traffic parameters is defined, for SONET/SDH.

   Note that it is expected than specific traffic parameters will be
   defined in the future for photonic (all optical) switching.

9.3. SONET/SDH Traffic Parameters

   The SDH/SONET traffic parameters [SONETSDH-GMPLS] specify indeed a
   powerful set of capabilities for SONET (ANSI T1.105) and SDH (ITU-T
   G.707). Optional non-standard capabilities are also available.

   The first traffic parameter specifies the type of the elementary
   SONET/SDH signal that comprises the requested LSP, e.g. VC-11, VT6,
   VC-4, STS-3c, etc. Several transforms can then be applied
   successively on the elementary Signal to build the final signal
   being actually requested for the LSP.

   These transforms are the contiguous concatenation, the virtual
   concatenation, the transparency and the multiplication. Each one is
   optional. They must be applied strictly in the following order:

   - First, contiguous concatenation can be optionally applied on the
     Elementary Signal, resulting in a contiguously concatenated
   - Second, virtual concatenation can be optionally applied either
     directly on the elementary Signal, or on the contiguously
     concatenated signal obtained from the previous phase.
   - Third, some transparency can be optionally specified when
     requesting a frame as signal rather than a container. Several
     transparency packages are defined.
   - Fourth, a multiplication can be optionally applied either directly
     on the elementary Signal, or on the contiguously concatenated
     signal obtained from the first phase, or on the virtually
     concatenated signal obtained from the second phase, or on these
     signals combined with some transparency.

   For RSVP-TE, the SONET/SDH traffic parameters are carried in a new
   SENDER-TSPEC and FLOWSPEC. The same format is used for both. There
   is no Adspec associated with the SENDER_TSPEC, either it is omitted
   or a default value is used. The content of the FLOWSPEC object
   received in a Resv message must be identical to the content of the
   SENDER_TSPEC of the corresponding Path message. In other words, the
   receiver is not allowed to change the values of the traffic
   parameters. However some level of negotiation may be achieved as
   explained in [SONETSDH-GMPLS]

   For CR-LDP, the SONET/SDH traffic parameters are simply carried in a
   new TLV.

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9.4. Bandwidth Encoding

   Some technologies that do not have (yet) specific traffic parameters
   just require a bandwidth encoding transported in a generic form.
   Bandwidth is carried in 32-bit number in IEEE floating-point format
   (the unit is bytes per second). Values are carried in a per protocol
   specific manner. For non-packet LSPs, it is useful to define
   discrete values to identify the bandwidth of the LSP.

   It should be noted that this bandwidth encoding do not apply to
   SONET/SDH, for which bandwidth the traffic parameters fully defined
   the requested SONET/SDH signal.

   The bandwidth is coded in the Peak Data Rate field of Int-Serv
   objects for RSVP-TE and in the Peak and Committed Data Rate fields
   of the CR-LDP Traffic Parameters TLV.

9.5. Generalized Label

   The Generalized Label extends the traditional MPLS label by allowing
   the representation of not only labels that travel in-band with
   associated data packets, but also (virtual) labels that identify
   time-slots, wavelengths, or space division multiplexed positions.

   For example, the Generalized Label may identify (a) a single fiber
   in a bundle, (b) a single waveband within fiber, (c) a single
   wavelength within a waveband (or fiber), or (d) a time-slot within a
   wavelength (or fiber). It may also be a generic MPLS label, a Frame
   Relay label, or an ATM label (VCI/VPI). The format of a label can be
   as simple as an integer value such as a wavelength label or can be
   more elaborated such as an SDH/SONET label.

   SDH and SONET define each a multiplexing structure. These
   multiplexing structures will be used as naming trees to create
   unique labels. Such a label will identify the exact position (times-
   lot(s)) of a signal in a multiplexing structure. Since the SONET
   multiplexing structure may be seen as a subset of the SDH
   multiplexing structure, the same format of label is used for SDH and

   Since the nodes sending and receiving the Generalized Label know
   what kinds of link they are using, the Generalized Label does not
   identify its type, instead the nodes are expected to know from the
   context what type of label to expect.

   A Generalized Label only carries a single level of label, i.e. it is
   non-hierarchical. When multiple levels of labels (LSPs within LSPs)
   are required, each LSP must be established separately.

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9.6. Waveband Switching

   A special case of wavelength switching is waveband switching. A
   waveband represents a set of contiguous wavelengths, which can be
   switched together to a new waveband. For optimization reasons it may
   be desirable for a photonic cross-connect to optically switch
   multiple wavelengths as a unit. This may reduce the distortion on
   the individual wavelengths and may allow tighter separation of the
   individual wavelengths. A Waveband label is defined to support this
   special case.

   Waveband switching naturally introduces another level of label
   hierarchy and as such the waveband is treated the same way all other
   upper layer labels are treated. As far as the MPLS protocols are
   concerned there is little difference between a waveband label and a
   wavelength label except that semantically the waveband can be
   subdivided into wavelengths whereas the wavelength can only be
   subdivided into time or statistically multiplexed labels.

9.7. Label Suggestion by the Upstream

   GMPLS allows for a label to be optionally suggested by an upstream
   node. This suggestion may be overridden by a downstream node but in
   some cases, at the cost of higher LSP setup time. The suggested
   label is valuable when establishing LSPs through certain kinds of
   optical equipment where there may be a lengthy (in electrical terms)
   delay in configuring the switching fabric. For example micro mirrors
   may have to be elevated or moved, and this physical motion and
   subsequent damping takes time. If the labels and hence switching
   fabric are configured in the reverse direction (the norm) the
   MAPPING/Resv message may need to be delayed by 10's of milliseconds
   per hop in order to establish a usable forwarding path. It can be
   important for restoration purposes where alternate LSPs may need to
   be rapidly established as a result of network failures.

9.8. Label Restriction by the Upstream

   An upstream node can optionally restrict (limit) the choice of label
   of a downstream node to a set of acceptable labels. Giving lists
   and/or ranges of inclusive (acceptable) or exclusive (unacceptable)
   labels in a Label Set provides this restriction. If not applied, all
   labels from the valid label range may be used. There are four cases
   where a label restriction is useful in the "optical" domain.

   1. The first case is where the end equipment is only capable of
   transmitting and receiving on a small specific set of

   2. The second case is where there is a sequence of interfaces, which
   cannot support wavelength conversion and require the same wavelength
   be used end-to-end over a sequence of hops, or even an entire path.

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   3. The third case is where it is desirable to limit the amount of
   wavelength conversion being performed to reduce the distortion on
   the optical signals.

   4. The last case is where two ends of a link support different sets
   of wavelengths.

   The receiver of a Label Set must restrict its choice of labels to
   one that is in the Label Set. A Label Set may be present across
   multiple hops. In this case each node generates it's own outgoing
   Label Set, possibly based on the incoming Label Set and the node's
   hardware capabilities. This case is expected to be the norm for
   nodes with conversion incapable interfaces.

9.9. Bi-directional LSP

   GMPLS allows establishment of bi-directional symmetric LSPs (not of
   asymmetric LSPs). A symmetric bi-directional LSP has the same
   traffic engineering requirements including fate sharing, protection
   and restoration, LSRs, and resource requirements (e.g., latency and
   jitter) in each direction.

   In the remainder of this section, the term "initiator" is used to
   refer to a node that starts the establishment of an LSP and the term
   "terminator" is used to refer to the node that is the target of the
   LSP. For a bi-directional LSPs, there is only one initiator and one

   Normally to establish a bi-directional LSP when using [RSVP-TE] or
   [CR-LDP] two unidirectional paths must be independently established.
   This approach has the following disadvantages:

   1. The latency to establish the bi-directional LSP is equal to one
   round trip signaling time plus one initiator-terminator signaling
   transit delay. This not only extends the setup latency for
   successful LSP establishment, but it extends the worst-case latency
   for discovering an unsuccessful LSP to as much as two times the
   initiator-terminator transit delay. These delays are particularly
   significant for LSPs that are established for restoration purposes.

   2. The control overhead is twice that of a unidirectional LSP. This
   is because separate control messages (e.g. Path and Resv) must be
   generated for both segments of the bi-directional LSP.

   3. Because the resources are established in separate segments, route
   selection is complicated. There is also additional potential race
   for conditions in assignment of resources, which decreases the
   overall probability of successfully establishing the bi-directional

   4. It is more difficult to provide a clean interface for SDH/SONET
   equipment that may rely on bi-directional hop-by-hop paths for
   protection switching. Note that existing SDH/SONET gear transmits
   the control information in-band with the data.

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   5. Bi-directional optical LSPs (or lightpaths) are seen as a
   requirement for many optical networking service providers.

   With bi-directional LSPs both the downstream and upstream data
   paths, i.e. from initiator to terminator and terminator to
   initiator, are established using a single set of signaling messages.
   This reduces the setup latency to essentially one initiator-
   terminator round trip time plus processing time, and limits the
   control overhead to the same number of messages as a unidirectional

   For bi-directional LSPs, two labels must be allocated. Bi-
   directional LSP setup is indicated by the presence of an Upstream
   Label in the appropriate signaling message.

9.10. Bi-directional LSP Contention Resolution

   Contention for labels may occur between two bi-directional LSP setup
   requests traveling in opposite directions. This contention occurs
   when both sides allocate the same resources (ports) at effectively
   the same time. The GMPLS signaling defines a procedure to resolve
   that contention, basically the node with the higher node ID will win
   the contention. To reduce the probability of contention, some
   mechanisms are also suggested.

9.11. Rapid Notification of Failure

   GMPLS defines three signaling extensions for RSVP-TE that enable
   expedited notification of failures and other events to nodes
   responsible for restoring failed LSPs, and modify error handling.
   For CR-LDP there is not currently a similar mechanism.

   The first extension identifies where event notifications are to be
   sent. The second provides for general expedited event notification.
   Such extensions can be used by fast restoration mechanisms.

   The final extension is an RSVP optimization to allow the faster
   removal of intermediate states in some cases.

9.12. Link Protection

   Protection information is carried in the new optional Protection
   Information Object/TLV. It currently indicates the desired link
   protection for each link of an LSP. If a particular protection type,
   i.e., 1+1, or 1:N, is requested, then a connection request is
   processed only if the desired protection type can be honored. Note
   that GMPLS advertises the protection capabilities of a link in the
   routing protocols. Path computation algorithms may take this
   information into account when computing paths for setting up LSPs.

   Protection information also indicates if the LSP is a primary or
   secondary LSP. A secondary LSP is a backup to a primary LSP. The
   resources of a secondary LSP are normally not used until the primary

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   LSP fails, but they may be used by other LSPs until the primary LSP
   fails over the secondary LSP. At that point, any LSP that is using
   the resources for the secondary LSP must be preempted.

   Six link protection types are currently defined as individual flags
   and can be combined: enhanced, dedicated 1+1, dedicated 1:1, shared,
   unprotected, extra traffic. See [GMPLS-SIG] section 7.1 for a
   precise definition of each.

9.13. Explicit Routing and Explicit Label Control

   Using an explicit route can control the path taken by an LSP more or
   less precisely. Typically, the node at the head-end of an LSP finds
   a more or less precise explicit route and builds an Explicit Route
   Object (ERO)/ Explicit Route (ER) TLV that contains that route.
   Possibly, the edge node doesnÆt build any explicit route, and just
   transmit a signaling request to a default neighbor LSR (as IP hosts
   today). For instance, an explicit route could be added to a
   signaling message by the first switching node, on behalf of the edge
   node. Note also that an explicit route is altered by intermediate
   LSRs during its progression towards the destination.

   The explicit route is originally defined by MPLS-TE as a list of
   abstract nodes (i.e. groups of nodes) along the explicit route. Each
   abstract node can be an IPv4 address prefix, an IPv6 address prefix,
   or an AS number. This capability allows the generator of the
   explicit route to have imperfect information about the details of
   the path. In the simplest case, an abstract node can be a full IP
   address (32 bits) that identifies a specific node (called a simple
   abstract node).

   MPLS-TE allows strict and loose abstract nodes. The path between a
   strict node and its preceding node must include only network nodes
   from the strict node and its preceding abstract node. The path
   between a loose node and its preceding node may include other
   network nodes that are not part of the strict node or its preceding
   abstract node.

   This explicit route was extended to include interface numbers as
   abstract nodes to support unnumbered interfaces; and further
   extended by GMPLS to include labels as abstract nodes. Having labels
   in an explicit route is an important feature that allows controlling
   the placement of an LSP with a very fine granularity. This is more
   likely to be used for TDM, LSC and FSC links.

   In particular, the explicit label control in the explicit route
   allows terminating an LSP on a particular outgoing port to an egress

   This can also be used when it is desirable to "splice" two LSPs
   together, i.e. where the tail of the first LSP would be "spliced"
   into the head of the second LSP.

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   Another use is when an optimization algorithm is used for an
   SDH/SONET network. This algorithm can provide very detailed explicit
   routes, including the label (time-slot) to use on a link, in order
   to minimize the fragmentation of the SDH/SONET multiplex on the
   corresponding interface.

   Another use is when the label indicates a particular component in a
   bundle in order to stay diverse with other components of that
   bundle, i.e. to control the usage of components in a bundle for
   different LSPs.

9.14. LSP modification and LSP re-routing

   LSP modification and re-routing are two features already available
   in MPLS-TE. GMPLS does not add anything new. Elegant re-routing is
   possible with the concept of "make-before-break" whereby an old path
   is still used while a new path is set up by avoiding double
   reservation of resources. Then, the node performing the re-routing
   can swap on the new path and close the old path. This feature is
   supported with RSVP-TE (using shared explicit filters) and CR-LDP
   (using the action indicator flag).

   LSP modification consists in changing some LSP parameters, but
   normally without changing the route. It is supported using the same
   mechanism as re-routing. However, the semantic of LSP modification
   will differ from one technology to the other. For instance, further
   studies are required to understand the impact of dynamically
   changing some SDH/SONET circuit characteristics such as the
   bandwidth, the protection type, the transparency, the concatenation,

9.15. Route recording

   In order to improve the reliability and the manageability of the LSP
   being established, the concept of the route recording was introduced
   in RSVP-TE to function as:

   - First, a loop detection mechanism to discover L3 routing loops, or
   loops inherent in the explicit route (this mechanism is strictly
   exclusive with the use of explicit routing objects).

   - Second, a route recording mechanism collects up-to-date detailed
   path information on a hop-by-hop basis during the LSP setup process.
   This mechanism provides valuable information to the source and
   destination nodes. Any intermediate routing change at setup time, in
   case of loose explicit routing, will be reported.

   - Third, a recorded route can be used as input for an explicit
   route. This is useful if a source node receives the recorded route
   from a destination node and applies it as an explicit route in order
   to "pin down the path".

   Within the GMPLS architecture only the second and third functions
   are mainly applicable for TDM, LSC and FSC layers.

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10. Forwarding Adjacencies (FA)

   To improve scalability of MPLS TE (and thus GMPLS) it may be useful
   to aggregate multiple TE LSPs inside a bigger TE LSP. Intermediate
   nodes see the external LSP only, they don't have to maintain
   forwarding states for each internal LSP, less signaling messages
   need to be exchanged and the external LSP can be somehow protected
   instead (or in addition) to the internal LSPs. This can considerably
   increase the scalability of the signaling.

   The aggregation is accomplished by (a) an LSR creating a TE LSP, (b)
   the LSR forming a forwarding adjacency out of that LSP (advertising
   this LSP as a unidirectional link into ISIS/OSPF), (c) allowing
   other LSRs to use forwarding adjacencies for their path computation,
   and (d) nesting of LSPs originated by other LSRs into that LSP (e.g.
   by using the label stack construct in the case of IP).

   An LSR may (under its local configuration control) announce an LSP
   as a link into ISIS/OSPF.  When this link is advertised into the
   same instance of ISIS/OSPF as the one that determines the route
   taken by the LSP, we call such a link a "forwarding adjacency" (FA).
   We refer to the LSP as the "forwarding adjacency LSP", or just FA-
   LSP.  Note that since the advertised entity is a link in ISIS/OSPF,
   both the endpoint LSRs of the FA-LSP must belong to the same ISIS
   level/OSPF area (intra-area improvement of scalability).

   In general, creation/termination of a FA and its FA-LSP could be
   driven either by mechanisms outside of MPLS (e.g., via configuration
   control on the LSR at the head-end of the adjacency), or by
   mechanisms within MPLS (e.g., as a result of the LSR at the head-end
   of the adjacency receiving LSP setup requests originated by some
   other LSRs).

   ISIS/OSPF floods the information about FAs just as it floods the
   information about any other links.  As a result of this flooding, an
   LSR has in its TE link state database the information about not just
   conventional links, but FAs as well.

   An LSR, when performing path computation, uses not just conventional
   links, but FAs as well.  Once a path is computed, the LSR uses RSVP-
   TE/CR-LDP for establishing label binding along the path. FAs need
   simple extensions to signaling and routing protocols.

10.1 Routing and Forwarding Adjacencies

   Forwarding adjacencies may be represented as either unnumbered or
   numbered links. A FA can also be a bundle of LSPs between two nodes.

   FAs are advertised as GMPLS TE links such as defined in [HIERARCHY].
   GMPLS TE links are advertised in OSPF and ISIS such as defined in
   [OSPF-TE-GMPLS] and [ISIS-TE-GMPLS]. These last two specifications
   enhance [OSPF-TE] and [ISIS-TE] that defines a base TE link.

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   When a FA is created dynamically, its TE attributes are inherited
   from the FA-LSP that induced its creation. [HIERARCHY] specifies how
   each TE parameter of the FA is inherited from the FA-LSP. Note that
   the bandwidth of the FA must be at least as big as the FA-LSP that
   induced it, but may be bigger if only discrete bandwidths are
   available for the FA-LSP. In general, for dynamically provisioned
   forwarding adjacencies, a policy-based mechanism may be needed to
   associate attributes to forwarding adjacencies.

   A FA advertisement could contain the information about the path
   taken by the FA-LSP associated with that FA. Other LSRs may use this
   information for path computation. This information is carried in a
   new OSPF and IS-IS TLV called the Path TLV.

   It is possible that the underlying path information might change
   over time, via configuration updates, or dynamic route
   modifications, resulting in the change of that TLV.

   If forwarding adjacencies are bundled (via link bundling), and if
   the resulting bundled link carries a Path TLV, the underlying path
   followed by each of the FA-LSPs that form the component links must
   be the same.

   It is expected that forwarding adjacencies will not be used for
   establishing ISIS/OSPF peering relation between the routers at the
   ends of the adjacency.

10.2. Signaling aspects

   For the purpose of processing the explicit route in a Path/Request
   message of an LSP that is to be tunneled over a forwarding
   adjacency, an LSR at the head-end of the FA-LSP views the LSR at the
   tail of that FA-LSP as adjacent (one IP hop away).

10.3 Cascading of Forwarding Adjacencies

   With an integrated model several layers are controlled using the
   same routing and signaling protocols. A network may then have links
   with different multiplexing/demultiplexing capabilities. For
   example, a node may be able to multiplex/demultiplex individual
   packets on a given link, and may be able to multiplex/demultiplex
   channels within a SONET payload on other links.

   A new OSPF and IS-IS sub-TLV has been defined to advertise the
   multiplexing capability of each interface: PSC, L2SC, TDM, LSC or
   FSC. This sub-TLV is named the Link Multiplex Capability sub-TLV and
   complements the sub-TLVs defined in [OSPF-TE-GMPLS] and [ISIS-TE-
   GMPLS]. The information carried in this sub-TLV is used to construct
   LSP regions, and determine regionÆs boundaries.

   Path computation may take into account region boundaries when
   computing a path for an LSP. For example, path computation may
   restrict the path taken by an LSP to only the links whose
   multiplexing/demultiplexing capability is PSC. When an LSP need to

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   cross a region boundary, it can trigger the establishment of an FA
   at the underlying layer (i.e. the L2SC layer). This can trigger a
   cascading of FAs between layers with the following obvious order:
   L2SC, then TDM, then LSC, and then finally FSC.

11. Network Management

   Service Providers (SPs) use network management extensively to
   configure, monitor or provision various devices in their network. It
   is important to note that a SPÆs equipment may be distributed across
   geographically separate sites, making distributed management even
   more important. The service provider should utilize an NMS system
   and standard management protocols such as SNMP [RFC1901] [RFC1902]
   [RFC1903] [RFC1904] [RFC1905] [RFC1906] and its associated MIBs as
   standard interfaces to configure, monitor and provision devices at
   various locations. The service provider may also wish to use the
   command line interface (CLI) provided by vendors with their devices,
   but this however, is not a standard or recommended solution due to
   the fact that there is no standard CLI language or interface, which
   results in N different CLIÆs in a network with devices from N
   different vendors. In the context of GMPLS, it is extremely
   important for standard interfaces to the SPÆs devices (SNMP) to
   exist due to the nature of the technology itself. Since GMPLS
   comprises many different layers of control-plane and data-plane
   technology, it is important for management interfaces in this area
   to be flexible enough to allow the manager to manage GMPLS easily,
   and in a standard way.

11.1 Network Management Systems (NMS)

   The NMS system should maintain the collective information about each
   device within the system. Note that the NMS system may actually be
   comprised of several distributed applications (i.e.: alarm
   aggregators, configuration consoles, polling applications, etc...)
   that collectively comprises the SPÆs NMS. In this way, it can make
   provisioning and maintenance decisions with the full knowledge of
   the entire SP network. Configuration or provisioning information
   (i.e.: requests for new services) could be entered into the NMS and
   subsequently distributed via SNMP to the remote devices, making the
   SPÆs job of managing the network much more compact and effortless
   than having to manage each device individually (i.e.: via CLI).
   Security and access control can be achieved through the use of
   SNMPv3 and the View Access Control Model [SNMPv3VACM]. This approach
   can be very effectively used within an SP network, since the SP has
   access to and control over all devices within its domain.
   Standardized MIBs will need to be developed before this approach can
   be used ubiquitously to provision, configure and monitor devices in
   non-heterogeneous networks or across SP boundaries.

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11.2 Management Information Base (MIB)

   In the context of GMPLS, it is extremely important for standard
   interfaces to devices to exist due to the nature of the technology
   itself. Since GMPLS comprises many different layers of control-plane
   technology, it is important for SNMP MIBs in this area to be
   flexible enough to allow the manager to manage the entire control
   plane. This should be through a set of MIBs that may cooperate
   (i.e.: coordinated row-creation on the agent), or through more
   generalized MIBs that aggregate some of the desired actions to be
   taken and push those details down to the devices. It is important to
   note that in certain circumstances, it may be necessary to duplicate
   some small subset of manageable objects in new MIBs for the
   convenience of management. Control of some parts of GMPLS may also
   be achieved though the use of existing MIB interfaces (i.e.:
   existing SONET MIB), or though separate ones, which are yet to be
   defined. MIBs may have been previously defined in the IETF or ITU.
   Existing MIBs may need to be extended to facilitate some of the new
   functionality desired by GMPLS. In these cases, the working group
   should work on new versions of these MIBs so that these extensions
   can be added.

11.3 Tools

   As in traditional networks, standard tools such as traceroute
   [RFC1393] and ping [RFC1739] are needed for debugging and
   performance monitoring of GMPLS networks, and mainly for the control
   plane topology that will mimic the data plane topology. Furthermore,
   such tools provide network reachability information. The GMPLS
   control protocols will need to expose certain pieces of information
   in order for these tools to function properly and to provide
   information germane to GMPLS. These tools should be made available
   via the CLI. These tools should also be made available for remote
   invocation via the SNMP interface [RFC2925].

11.4 Fault Correlation Between Multiple Layers

   Due to the nature of GMPLS and the fact that potential layers may be
   involved in the control and transmission of GMPLS data and control
   information, it is therefore required that a fault in one layer be
   passed to the adjacent higher and lower layers in an effort to
   notify them of the fault. However, due to nature of these many
   layers, it is possible and even probable, that hundreds or even
   thousands of notifications may need to transpire between layers.
   This is undesirable for several reasons. First, these notifications
   will overwhelm the device. Second, if the device(s) are programmed
   to emit SNMP Notifications [RFC1901] then the large number of
   notifications the device may attempt to emit may overwhelm the
   network with a storm of notifications. Furthermore, even if the
   device emits the notifications, the NMS that must process these
   notifications will either be overwhelmed, or will be processing
   redundant information. That is, if 1000 interfaces at layer B are
   stacked above a single interface below it at layer A, and the
   interface at A goes down, the interfaces at layer B should not emit

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   notifications. Instead, the interface at layer A should emit a
   single notification. The NMS receiving this notification should be
   able to correlate the fact that this interface has many others
   stacked above it and take appropriate action, if necessary.

   Devices that support GMPLS should provide mechanisms for
   aggregating, summarizing, enabling and disabling of inter-layer
   notifications for the reasons described above. In the context of
   SNMP MIBs, all MIBs that are used by GMPLS must provide
   enable/disable objects for all notification objects. Furthermore,
   these MIBs must also provide notification summarization objects or
   functionality (as described above) as well. NMS systems and standard
   tools which process notifications or keep track of the many layers
   on any given devices must be capable of processing the vast amount
   of information which may potentially be emitted by network devices
   running GMPLS at any point in time.

12. Security considerations

   GMPLS defines a new control plane architecture for multiple types of
   network elements. In general, since LSPs established using GMPLS are
   expected to carry high volumes of data and consume significant
   network resources, security mechanisms are required to safeguard the
   underlying network against attacks on the control plane and/or
   unauthorized usage of data transport resources.

   Security requirements depend on the level of trust between nodes
   that exchange GMPLS control messages as well as the exposure of the
   control channel to third parties. In general, a network node may
   apply more relaxed security requirements when exchanging GMPLS
   control messages with nodes under the same administrative domain
   than when talking to nodes in a different domain. In this respect,
   network to user (UNI) and network-to-network interfaces are expected
   to have higher security requirements than node-to-node interfaces.

   Security mechanisms can provide two main properties: authentication
   and confidentiality. Authentication can provide origin verification,
   message integrity and replay protection, while confidentiality
   ensures that a third party cannot decipher the contents of a
   message. In situations where GMPLS deployment requires primarily
   authentication, the respective authentication mechanisms of the
   GMPLS component protocols may be used ([RFC2747], [LDP], [RFC2385],
   [LMP]). Additionally, the IPSEC suite of protocols ([RFC2402],
   [RFC2406], [RFC2409]) may be used to provide authentication,
   confidentiality or both, for a GMPLS control channel; this option
   offers the benefit of combined protection of all GMPLS component

   Note however that GMPLS itself introduces no new security
   considerations to the current MPLS-TE signaling (RSVP-TE, CR-LDP),
   routing protocols (OSPF-TE, IS-IS-TE) or network management
   protocols (SNMP).

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13. Acknowledgements

   This draft is the work of numerous authors and consists of a
   composition of a number of previous drafts in this area.

   Many thanks to Ben Mack-Crane (Tellabs) for all the useful SDH/SONET
   discussions that we had together. Thanks also to Pedro Falcao
   (Ebone) and Michael Moelants (Ebone) for their SDH/SONET and optical
   technical advice and support. Finally, many thanks also to Krishna
   Mitra (Calient) and Curtis Villamizar (Avici).

   A list of the drafts from which material and ideas were incorporated

   [GMPLS-SIG]     draft-ietf-mpls-generalized-signaling-04.txt
                   Generalized MPLS - Signaling Functional Description

   [RSVP-TE-GMPLS] draft-ietf-mpls-generalized-rsvp-te-03.txt
                   Generalized MPLS Signaling - RSVP-TE Extensions

   [CR-LDP-GMPLS]  draft-ietf-mpls-generalized-cr-ldp-03.txt
                   Generalized MPLS Signaling - CR-LDP Extensions

   [SONETSDH-GMPLS] draft-ietf-ccamp-gmpls-sonet-sdh-01.txt
                    GMPLS Extensions for SONET and SDH Control

   [LMP]           draft-ietf-mpls-lmp-01.txt
                   Link Management Protocol (LMP)

   [HIERARCHY]     draft-ietf-mpls-lsp-hierarchy-02.txt
                   LSP Hierarchy with MPLS TE

   [RSVP-TE-UNNUM] draft-ietf-mpls-rsvp-unnum-01.txt
                   Signalling Unnumbered Links in RSVP-TE

   [CR-LDP-UNNUM]  draft-ietf-mpls-crldp-unnum-01.txt
                   Signalling Unnumbered Links in CR-LDP

   [BUNDLE]        draft-kompella-mpls-bundle-05.txt
                   Link Bundling in MPLS Traffic Engineering

   [OSPF-TE-GMPLS] draft-kompella-ospf-gmpls-extensions-01.txt
                   OSPF Extensions in Support of Generalized MPLS

   [ISIS-TE-GMPLS] draft-ietf-isis-gmpls-extensions-02.txt
                   IS-IS Extensions in Support of Generalized MPLS

14. References

   [RFC1393]    G. Malkin, "Traceroute Using an IP Option", IETF
                RFC 1393, January 1993.

   [RFC1901]    Case, J., McCloghrie, K., Rose, M., and S.
                Waldbusser, "Introduction to Community-based

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                SNMPv2", IETF RFC 1901, January 1996.

   [RFC1902]    Case, J., McCloghrie, K., Rose, M., and S.
                Waldbusser, "Structure of Management Information for
                Version 2 of the Simple Network Management Protocol
                (SNMPv2)", IETF RFC 1901, January 1996.

   [RFC1903]    Case, J., McCloghrie, K., Rose, M., and S.
                Waldbusser, "Textual Conventions for Version 2 of the
                Simple Network Management Protocol (SNMPv2)",
                IETF RFC 1901, January 1996.

   [RFC1904]    Case, J., McCloghrie, K., Rose, M., and S.
                Waldbusser, "Conformance Statements for Version 2 of
                the Simple Network Management Protocol (SNMPv2)",
                IETF RFC 1901, January 1996.

   [RFC1905]    Case, J., McCloghrie, K., Rose, M., and S.
                Waldbusser, "Protocol Operations for Version 2 of
                the Simple Network Management Protocol (SNMPv2)",
                IETF RFC 1905, January 1996.

   [RFC1906]    Case, J., McCloghrie, K., Rose, M., and S.
                Waldbusser, "Transport Mappings for Version 2 of
                the Simple Network Management Protocol (SNMPv2)",
                IETF RFC 1906, January 1996.

   [SNMPv3VACM] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-
                based Access Control Model (VACM) for the Simple
                Network Management Protocol (SNMP)", IETF RFC 2575,
                April 1999.

   [RFC1739]    G. Kessler, S. Shepard , "A Primer On Internet and
                TCP/IP Tools", RFC1739, December 1994.

  [RFC2328]    J. Moy, "OSPF Version 2", RFC 2328, Standard
               Track, April 1998.

   [RFC2370]    R. Coltun, "The OSPF Opaque LSA Option", RFC 2370
                Standard Track, July 1998.

   [RFC2385]    A. Heffernan, "Protection of BGP Sessions via the TCP
                MD5 Signature Option," IETF RFC 2385.

   [RFC2402]    S. Kent and R. Atkinson, "IP Authentication Header,"
                RFC 2402.

   [RFC2406]    S. Kent and R. Atkinson, "IP Encapsulating Security
                Payload (ESP)," IETF RFC 2406.

   [RFC2409]    D. Harkins and D. Carrel, "The Internet Key Exchange
               (IKE)", IETF RFC 2409.

   [RFC2747]    F. Baker et al. "RSVP Cryptographic Authentication",

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                IETF RFC 2747.

   [RFC2925]    K. White , "Definitions of Managed Objects for Remote
                Ping, Traceroute, and Lookup Operations", IETF RFC
                2925, September 2000.

   [LPD]        L. Andersson, P. Doolan, N. Feldman, A. Fredette,
                B. Thomas, "LDP Specification", IETF RFC 3036, January

   [OSPF-TE]    D. Katz, D. Yeung, and K. Kompella, "Traffic
                Engineering Extensions to OSPF" draft-katz-yeung-ospf-

   [LMP-WDM]    A. Fredette et al., "Link Management Protocol (LMP) for
                WDM Transmission Systems," Internet Draft, Work in
                Progress, draft-fredette-lmp-wdm-01.txt, March 2001.

  [MPLS-TEO]   D. Awduche et al., "Multi-Protocol Lambda Switching:
                Combining MPLS Traffic Engineering Control With Optical
                Crossconnects," Internet Draft, Work in Progress,
                draft-awduche-mpls-te-optical-03.txt, April 2001.

15. Author's Addresses

   Peter Ashwood-Smith                Eric Mannie (editor)
   Nortel Networks Corp.              Ebone (GTS)
   P.O. Box 3511 Station C,           Terhulpsesteenweg 6A
   Ottawa, ON K1Y 4H7                 1560 Hoeilaart
   Canada                             Belgium
   Phone: +1 613 763 4534             Phone: +32 2 658 56 52
   Email:                             Email:

   Daniel O. Awduche                  Thomas D. Nadeau
   Movaz Networks                     Cisco Systems, Inc.
   7296 Jones Branch Drive            250 Apollo Drive
   Suite 615                          Chelmsford, MA 01824
   McLean, VA 22102                   USA
   USA                                Phone: +1 978 244 3051
   Phone: +1 703 847-7350             Email:

   Ayan Banerjee                      Dimitri Papadimitriou
   Calient Networks                   Alcatel - IPO NSG
   5853 Rue Ferrari                   Francis Wellesplein, 1
   San Jose, CA 95138                 B-2018 Antwerpen
   USA                                Belgium
   Phone: +1 408 972-3645             Phone: +32 3 240-84-91
   Email:       Email:

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   Debashis Basak                     Dimitrios Pendarakis
   Accelight Networks                 Tellium, Inc.
   70 Abele Road, Bldg.1200           2 Crescent Place
   Bridgeville, PA 15017              P.O. Box 901
   USA                                Oceanport, NJ 07757-0901
   Phone: +1 412 220-2102 (ext115)    USA
   email:        Email:

   Lou Berger                         Bala Rajagopalan
   Movaz Networks, Inc.               Tellium, Inc.
   7926 Jones Branch Drive            2 Crescent Place
   Suite 615                          P.O. Box 901
   MCLean VA, 22102                   Oceanport, NJ 07757-0901
   USA                                USA
   Phone: +1 703 847-1801             Phone: +1 732 923 4237
   Email:           Email:

   Greg Bernstein                     Yakov Rekhter
   Ciena Corporation                  Juniper
   10480 Ridgeview Court              Email:
   Cupertino, CA 94014
   Phone: +1 408 366 4713

   John Drake                         Hal Sandick
   Calient Networks                   Nortel Networks
   5853 Rue Ferrari                   Email:
   San Jose, CA 95138       
   Phone: +1 408 972 3720

   Yanhe Fan                          Debanjan Saha
   Axiowave Networks, Inc.            Tellium Optical Systems
   100 Nickerson Road                 2 Crescent Place
   Marlborough, MA 01752              Oceanport, NJ 07757-0901
   USA                                USA
   Phone: +1 508 460 6969 Ext. 627    Phone: +1 732 923 4264
   Email:           Email:

   Don Fedyk                          Vishal Sharma
   Nortel Networks Corp.              Metanoia, Inc.
   600 Technology Park Drive          335 Elan Village Lane
   Billerica, MA 01821                San Jose, CA 95134
   USA                                USA
   Phone: +1-978-288-4506             Phone:  +1 408 943 1794
   Email:                             Email:

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   Gert Grammel                       George Swallow
   Alcatel                            Cisco Systems, Inc.
   Via Trento, 30                     250 Apollo Drive
   20059 Vimercate (Mi)               Chelmsford, MA 01824
   Italy                              USA
   Email:     Phone: +1 978 244 8143

   Kireeti Kompella                   Z. Bo Tang
   Juniper Networks, Inc.             Tellium, Inc.
   1194 N. Mathilda Ave.              2 Crescent Place
   Sunnyvale, CA 94089                P.O. Box 901
   USA                                Oceanport, NJ 07757-0901
   Email:         USA
                                      Phone: +1 732 923 4231

   Alan Kullberg                      John Yu
   NetPlane Systems, Inc.             Zaffire Inc.
   888 Washington                     2630 Orchard Parkway
   St.Dedham, MA 02026                San Jose, CA 95134
   USA                                USA
   Phone: +1 781 251-5319             Email:

   Jonathan P. Lang                   Alex Zinin
   Calient Networks                   Cisco Systems
   25 Castilian                       150 W. Tasman Dr.
   Goleta, CA 93117                   San Jose, CA 95134
   Email:         Email:

   Fong Liaw
   Zaffire Inc.
   2630 Orchard Parkway
   San Jose, CA 95134

Full Copyright Statement

   "Copyright (C) The Internet Society (date). All Rights Reserved.
   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

E. Mannie et. al.    Internet-Draft December 2001               43

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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

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Appendix 1 Brief overview of the ITU-T work on G.ASTN/G.ASON

   This appendix gives a brief overview of the work performed in ITU-T
   related to the control plane for transport networks, and briefly
   links it to the IETF related work.

   In ITU-T the work is performed in Study Group (SG) 13/Question 10
   for G.astn, SG15/Q12 for G.ason and SG15/Q14 for G.dcn, G.dcm,
   G.ndisc, G.sdisc and G.cemr.

   G.astn describes the network level requirements for the control plane
   of Automatically Switched Transport Networks (ASTNs). Such a network
   provides a set of control functions for the purpose of setting up and
   releasing connections across a network. It is recognized that
   transport networks support multiple clients. As such, ASTNs are
   intended to be client independent.

A.1 Terminology issues

   A common misunderstanding is related to the usage of terms like
   layer, LSP and client/server. In IETF the expression "layer" is
   attached to a technology present in a network like e.g. OTN, SDH,
   ATM, IP. However ITU-T uses the term "layer" for any kind of
   mapping. This includes the mapping between different technologies
   like SDH/SONET in OTN as well as internal mappings like SDH/SONET
   low order layer and high order layer. In this case a client server
   relationship between layers is automatically present. In order to
   avoid misunderstandings the term "technology" is used hereafter to
   represent the IETF understanding of a layer.

   In GMPLS the notion of Label Switched Path (LSP) is defined to
   describe connections between two Label Switch Routers (LSRs). In
   packet switched networks LSPs can be "tunneled" by encapsulating a
   packet into another packet within the same technology (also known as
   "label stacking"). What is considered to be encapsulation in IETF is
   considered to be a mapping in ITU-T that implies the use of a
   client-server layer relationship.

   In ITU-T the terms "client" and "server" are used to define the role
   of a layer with respect to another layer e.g. SDH can be the client
   layer of an OTN server layer network. This distinction is not used
   in IETF where a layer is associated to a certain type of technology.
   Instead the term "client" is used for a customer device attached to
   a service provider network, both belonging to distinct
   administrative authorities.

A.2 Common Equipment Management [G.cemr]

   The G.cemr recommendation specifies those Equipment Management
   Functions (EMF) requirements that are common for SDH and OTN.
   The equipment management function (EMF) provides the means through
   which a Network Element Level manager manages the Network Element
   Function (NEF).

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   These kinds of functions are not detailed in the current GMPLS work
   since it is focused on control plane related aspects. Network
   Management aspects are subject of other working groups in IETF.

A.3 Data Communications Network [G.dcn]

   According to G.dcn the various functions, which constitute a
   telecommunications network, can be classified into two broad
   functional groups. One is the transport functional group, which
   transfers any telecommunications information from one point to
   another point(s). The other is the control functional group, which
   realizes various ancillary services and operations and maintenance

   The Data Communications Network (DCN) provides transport for the
   applications associated with the control functional group. Examples
   of such applications that are transported by the DCN are: transport
   network operations/management applications, DCN
   operations/management applications, Automatic Switched Transport
   Services (ASTN) control plane applications, voice communications,

   The IP-based DCN provides Layer 1 (physical), Layer 2 (data-link)
   and Layer 3 (network) functionality and consists of
   routing/switching functionality interconnected via links. These
   links can be implemented over various interfaces, including WAN and
   LAN interfaces.

   This recommendation provides the architecture requirements for an
   IP-based DCN, the requirements for inter-working between an IP-based
   DCN and an OSI-based DCN, and the IP-based DCN interface

   Since in GMPLS the signaling and management plane are orthogonal to
   each other, different kinds of networks can be used for both tasks.
   In GMLS, LMP defines mechanisms for the control channel management,
   which is used to establish and maintain control channels between
   nodes. However, GMPLS assume that messages are transported by IP but
   doesnÆt specify how the DCN should be implemented.

A.4 Distributed Connection Management [G.dcm]

   The G.dcm Recommendation covers the areas associated with the
   signaling aspects of automatic switched transport network, such as
   attribute specifications, the message sets, the interface
   requirements, the DCM state diagrams, and the interworking functions
   for the distributed connection management

   This is the main purpose of the GMPLS signaling, using extensions to
   protocols like CR-LDP and RSVP-TE.

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A.5 Generalized Automatic Neighbor Discovery [G.ndisc]

   The G.ndisc Recommendation provides the requirements and message
   sets for the automatic neighbor for the User-to-Network Interface
   (UNI), Internal Node-to-Node Interface (I-NNI), External Node-to-
   Node Interface (E-NNI) and Physical Interface (PI). These
   requirements determine the discovery process across these interfaces
   that aid automated connection management.

   GMPLS is an IP centric control plane incorporating protocols defined
   for routing and neighbor discovery such OSPF and IS-IS. In addition,
   LMP fulfills some of these requirements as well, especially for the
   component links of bundled link.

A.6 Generalized Automatic Service Discovery [G.sdisc]

   The G.sdisc Recommendation provides the requirements and message
   sets for the automatic service discovery for the User-to-Network
   Interface (UNI), Internal Node-to-Node Interface (I-NNI), External
   Node-to-Node Interface (E-NNI) and Physical Interface (PI). These
   requirements determine the discovery process across these interfaces
   that aid automated connection management.

   GMPLS signaling and routing protocols LMP allows some level of
   automatic service discovery.

A.7 OTN routing [G.rtg]

   No ITU-T contribution available yet.

   IP based intra-domain (e.g. OSPF, IS-IS) and inter-domain (e.g. BGP-
   4) routing protocols are the strength of a GMPLS control plane.
   Moreover, BGP-4 is the only practical solution for policy routing
   between different operators that was proved on a very large scale.
   GMPLS extends the TE extensions to OSPF and IS-IS. Work on BGP-4 is

A.8 OTN Connection Admission Control [G.cac]

   According to G.astn, Connection Admission Control (CAC) is necessary
   for authentication of the user and controlling access to network
   resources. CAC shall be provided as part of the control plane
   functionality. It is the role of the CAC function to determine if
   there is sufficient free resource available to allow a new
   connection. If there is, the CAC may permit the connection request to
   proceed, alternatively, if there is not, it shall notify the
   originator of the connection request that the request has been
   denied. Connections may be denied on the basis of available free
   capacity or alternatively on the basis of prioritization. CAC
   policies are outside the scope of standardization.

   GMPLS achieves authentication (and other security related features)
   using the broad range of security mechanisms available in the GMPLS
   protocols themselves and/or using IPSEC.

E. Mannie et. al.    Internet-Draft December 2001               47

 draft-ietf-ccamp-gmpls-architecture-00.txt              June 2001

A.9 OTN Link Management [G.lm]

   No ITU-T contribution available yet.

   The Link Management Protocol (LMP) of GMPLS is a collection of
   procedures between adjacent nodes that provide local services such
   as control channel management, link connectivity verification, link
   property correlation, and fault management.

E. Mannie et. al.    Internet-Draft December 2001               48