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   CCAMP Working Group                                 D. Papadimitriou
                                                           M. Vigoureux
   Internet Draft                                             (Alcatel)
                                                            K. Shiomoto
   Expiration Date: August 2004                                   (NTT)

                                                            D. Brungard

                                                           J.L. Le Roux

                                                          February 2004

          Generalized MPLS Architecture for Multi-Region Networks


Status of this Memo

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

   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- Drafts.
   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".

   The list of current Internet-Drafts can be accessed at

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


   Most of the initial efforts on Generalized MPLS (GMPLS) have been
   related to environments of single switching capability devices e.g.
   one data plane layer, as such, the complexity raised by the control
   of such data planes is similar to the one expected in classical
   IP/MPLS networks. The fundamental reason being that an IP-based
   control plane protocol suite for Label Switch Routers (LSR) or
   Optical Cross-Connects (OXC) has exactly the same Level (i.e. single
   data plane layer) complexity.

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   The present document analyses the various GMPLS signaling and routing
   aspects when considering network environments consisting of multiple
   switching data layers e.g. supporting combined Packet/Layer-2
   Switching - OXC devices. The examples provide an overview of the
   tradeoffs in using a GMPLS control plane for combined Ethernet MAC -
   opaque, service transparent, and/or fully transparent data planes.
   The intent of this memo is also to demonstrate that these aspects may
   not be as straightforward as they may first appear.

Table of Contents

   Conventions used in this document.................................2
   1. Introduction...................................................3
      1.1 Context and Motivations....................................3
      1.2 Rationales for Multi-Region Networks:......................4
      1.3 Problem statement..........................................5
   2. Routing over Forwarding Adjacencies............................5
      2.1 Scalability of Single Region Networks......................6
      2.2 Scalability of Multi-Region Networks.......................7
      2.3 Emulating Data Plane Overlays using FAs....................7
      2.4 FA Attributes Inheritance..................................8
      2.5 FA Abstraction for Recovery................................9
   3. Cross Region Considerations....................................9
      3.1 Interface adaptation capability descriptor................10
      3.2 Regeneration capability...................................15
      3.3 Dedicated Traffic Parameters..............................16
      3.4 Applications..............................................16
   4. Extended Scope of Switching Capabilities......................17
      4.1 L2SC Switching............................................17
      4.2 Example...................................................19
      4.3 Waveband switching........................................20
   5. Conclusion....................................................20
   Security Considerations..........................................21
   Author’s Addresses...............................................23

Conventions used in this document

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

   In addition the reader is assumed to be familiar with the concepts
   developed in [GMPLS-ARCH], [RFC-3471], and [GMPLS-RTG] as well as
   [MPLS-HIER] and [MPLS-BDL].

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1. Introduction

   Generalized Multi-Protocol Label Switching (GMPLS) facilitates the
   realization of seamless control integration of IP/MPLS networks with
   SONET/SDH (see [T1.105]/[G.707]) or G.709 (see [G.709]) optical
   transport networks. In particular, the applicability of GMPLS to both
   packet/frame and circuit switching technologies (i.e. unified control
   plane architecture) provides a unified control management approach
   for both provisioning resources and restoration techniques.

   One of the additional advantages driving the construction of a
   unified GMPLS control plane is the desire to support multi LSP-
   region [MPLS-HIER] routing and traffic engineering capability. This
   would enable effective network resource utilization of both the
   Packet/Layer2 LSP regions and the Time Division Multiplexing (TDM) or
   Lambda (Optical Channels) LSP regions in high capacity networks.

1.1 Context and Motivations

   Vertical integration refers (see [TE-WG]) to the definition of
   collaborative mechanisms within a single control plane instance
   driving multiple (but at least two) data planes (also referred in the
   scope of GMPLS as switching layers). Horizontal integration is
   defined when each entity constituting the network environment
   includes at least one common (data plane) switching capability and
   the control plane topology extends over several partitions being
   either areas or autonomous systems (see [INTER-AREA-AS]). In this
   latter case, the integration is thus defined between nodes hosting
   the same switching capability. For instance, the control plane
   interconnection between lambda switching capable routing areas
   defines an horizontal integration. On the other hand, an environment
   in which at least two different switching capabilities are present
   and where these capabilities are both hosted by the same device
   and/or hosted by different devices involves a vertical integration
   within the GMPLS control plane. Such multi-switching layer capable
   networks are referred to as Multi LSP-Region Networks or simply
   Multi-Region Networks (MRN).

   Note here that, the CCAMP Working Group is currently actively working
   on extensions to this horizontal integration (the initial iteration
   being the single area context worked out over the past few years) by
   considering common multi-area and multi-AS traffic engineering
   techniques and protocol extensions [INTER-AREA-AS]. As a first phase
   vertical integration, as proposed in this document, we focus on
   single area only environments.

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   From the control plane viewpoint (as defined in [MPLS-HIER]) a data
   plane layer is mapped to an LSP region. Following this approach, a
   Traffic Engineering link or simply TE Link (at the control plane
   level) maps exactly the definition proposed in the canonical layered
   model (see [G.805]) where a link is defined as a link bundle (using
   the IETF terminology). More generically, the TE link notion is now
   recursively defined and accepted implying that the link bundle term
   will be used only when referring to a set of component links or
   ports. Therefore, the TE Link concept opens the door for a clear
   separation between the routing adjacencies and the data plane bearer
   links (or channels). Furthermore, TE Links have been extended to non
   adjacent devices by introducing the Forwarding Adjacency (FA) concept
   enabling in turn to decrease the number of control plane instances to
   control N transport layers. Last, the bundling of FA is also defined
   in [MPLS-BDL] allowing for additional flexibility in controlling
   large scale backbone networks.

   Using the Forwarding Adjacency, a node may (under its  local control
   policy configuration) advertise an LSP as a TE link into the same
   OSPF/ISIS instance as the one that induces this LSP. Such a link is
   referred to as a "Forwarding Adjacency" (FA) and the corresponding
   LSP to as a "Forwarding Adjacency LSP", or simply FA-LSP. Since the
   advertised entity appears as a TE link in OSPF/ISIS, both end-point
   nodes of the FA-LSP must belong to the same OSPF area/ISIS level
   (intra-area improvement of scalability). Afterwards, OSPF/ISIS floods
   the link-state information about FAs just as it floods the
   information about any other TE Link. This allows other nodes to use
   FAs as any other TE Links for path computation purposes.

1.2 Rationales for Multi-Region Networks:

   The rationales for investigating vertical integration (and thus
   multi-region networks) in the GMPLS distributed control plane context
   can be summarized as follows:

   - The maintenance of multiple instances of the control plane on
   devices hosting more than one switching capability not only (and
   obviously) increases the complexity of their interactions but also
   increases the total amount of processing individual instances would

   - The merge of both data and control plane addressing spaces helps in
   avoiding multiple identification for the same object (a link for
   instance or more generally any network resource), on the other hand
   such aggregation does not impact the separation between the control
   and the data plane.

   - The collaboration between associated control planes (packet/framed
   data planes) and non-associated control planes (SONET/SDH, G.709,

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   etc.) is facilitated due to the capability of hooking the associated
   in-band signaling to the IP terminating interfaces of the control

   - Resource management and policies to be applied at the edges of such
   environment would be facilitated (less control to management
   interactions) and more scalable (through the use of aggregated

   In this context, Hybrid Photonic Networks (HPN) can be differentiated
   from Multi-Region Networks (MRN). The main difference between nodes
   included in an HPN environment and nodes included in an MRN
   environment can be expressed as follows: some of the former MUST
   include at least for some (but at least two) of their interfaces an
   LSC switching capability with "lambda" (photonic) encoding.

1.3 Problem statement

   The control by a single GMPLS instance of at least two different
   switching capabilities rises some issues with regards to the control
   plane scalability as well as inter-working issues between these
   switching capabilities. Typically, devices present in an MRN will
   have the information about all the TE-Links corresponding to the
   different switching capabilities present in the environment. This
   will lead, in turn, to the maintenance of large LSDB resulting in
   CSPF computation time possibly exceeding reasonable value.
   Scalability also concerns the maintenance of a very large number of
   signaling sessions. Section 4 addresses these types of issues while
   section 5 covers issues resulting from devices hosting at least two
   different switching capabilities, or, more broadly, cross layer

2. Routing over Forwarding Adjacencies

   In order to extend MPLS to support non-packet TE attributes within
   the scope of an integrated (routing) model encompassing several data
   planes, GMPLS needs to support control of several data plane layers
   (or switching layers) using the same protocol instance.

   Forwarding Adjacencies (FAs) as described in [MPLS-HIER] are a useful
   and powerful tool for improving the scalability of Generalized MPLS
   (GMPLS) Traffic Engineering (TE) capable networks.
   Through the aggregation of TE Label Switched Paths (LSPs) this
   concept enables the creation of a vertical (nested) TE-LSP Hierarchy.
   Forwarding Adjacency LSPs (FA-LSP) may be advertised as TE link (or
   simply FA) into the same instance of OSPF/ISIS as the one that was
   used to create, initiate or trigger this LSP, allowing other LSRs to
   use FAs as TE links for their path computation. As such, forwarding
   adjacency LSPs have characteristics of both TE links and LSPs.

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   While this definition is in perfect alignment for non-packet LSP
   regions and boundaries, the same concept(s) can also be re-used in
   the MPLS LSP context but with a major difference. The mapping goes in
   the opposite direction i.e. from the control to the IP/MPLS
   forwarding plane, since in the packet domain FA-LSPs are purely
   abstract objects that would, if well tailored, provide additional
   scalability within a routing plane instance (i.e. define virtual TE
   links without increasing the number of routing adjacencies). Indeed,
   the use of FAs provides a mechanism for improving bandwidth (or more
   generally any resource) utilization when its dynamic allocation can
   be performed in discrete units; it also enables aggregating
   forwarding state, and in turn, reducing significantly the number of
   required labels as well as the number of signaling sessions.
   Therefore, FAs may significantly improve the scalability of GMPLS TE-
   capable control planes, and allow the creation of a TE-LSP hierarchy.

   From this, and when combining multi-region environments, the
   challenges that arise are related to the combination of both types of
   mappings (and in particular their control) for both super-classes of
   LSPs i.e. packet LSPs and circuit-oriented LSPs (a.k.a. non-packet
   LSPs) from or to the same control plane instance.

2.1 Scalability of Single Region Networks

   The main issue arising with FAs is related to the mapping
   directionality (from the data to the control plane). FAs allow
   avoiding the well-known O(N^2) at the control plane level by using
   the mechanisms defined in [MPLS-HIER] but requires a specific
   policing at the LSP region edges (or boundaries) in order to avoid
   full meshes both at the data plane level and control plane level.

   Currently, and as specified in [MPLS-HIER], it is expected that FAs
   will not be used for establishing OSPF/ISIS peering relation between
   the routers at the ends of the adjacency thus clearly avoiding N
   square problem at the control plane level. On the other hand,
   specific policies would be required to avoid a full mesh of FAs. A
   full mesh of FAs would lead, at the control plane level, to a full
   mesh of signaling sessions while, at the data plane, it would lead to
   poor resource utilization. Avoiding full meshes can be accomplished
   by setting the default metric of the FA to max[1, (the TE metric of
   the FA-LSP path - 1)] so that it attracts traffic in preference to
   setting up a new LSP. Such policing clearly states that FA-LSPs are
   driven by a most fit approach: do not create new FA-LSPs as long as
   existing ones are not filled up. The main issue with this approach is
   definitely related to "what to advertise and originate at LSP region
   boundaries". For instance, fully filled FA-LSPs should not be
   advertised (if preemption is not allowed), while, attracting traffic
   should be provided in some coordinated manner in order to avoid sub-

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   optimal FA-LSP setup. Moreover, nothing precludes the maintenance of
   several partially filled FA-LSPs that are kept unused indefinitely
   (even if their metric is set optimally) in particular when the
   bandwidth of the FA-LSP can not (due to its discrete bandwidths
   units) be exactly set to the incoming LSP request.

   Note: the latter suggests filtering of the corresponding LSAs at the
   regions' boundaries. In OSPF this can be accomplished by not
   advertising the link as a regular LSA, but only as a TE opaque LSA
   (see [RFC-2370]).

2.2 Scalability of Multi-Region Networks

   The Shortest Path First (SPF) computation complexity is, in classical
   cases, proportional to L Log(N) where L is the number of links (here,
   more precisely TE links) and N the number of address prefixes. As
   such, the full mesh scalability issues can be solved in two ways
   either by improving the computational capabilities of the (C-)SPF
   algorithms or simply by keeping existing Log(N) complexity but then
   by improving collaboration between data planes.
   The former can be achieved for instance by using Fibonacci heaps with
   Log(Log(N)) complexity for instance, which in turn, allows for a
   number of TE links greater than 1E6 (versus 1E3 with classical
   implementations). The latter can be achieved by considering M
   regions, over the same control plane topology and without using any
   heuristics, one increases this complexity to M x L (Log (M x N)).

   However, since TE Links can advertise multiple Interface Switching
   Capabilities (ISC), the number of links can be limited (by
   combination) by using specific topological maps referred to as
   Virtual Network Topologies (VNT). The introduction of virtual
   topological maps leads us to consider the concept of emulation of
   data plane overlays [MAMLTE]. Therefore, the expectation here is to
   reduce the overall computational complexity to L Log(M+1) x Log
   (Log(M+1) x N) (note: with M = 1 it brings L Log(N)).

2.3 Emulating Data Plane Overlays using FAs

   According to [MPLS-HIER] ISC ordering, we can use the following
   terminology: FA-LSP(1) corresponds to TE Links for which the ISC is
   equal to PSC-1, FA-LSP(2) to PSC-2, FA-LSP(3) to PSC-3, FA-LSP(4) =
   PSC-4, FA-LSP(5) to LS2SC, FA-LSP(6) to TDM, FA-LSP(7) to LSC and FA-
   LSP(8) to FSC.

   FA-LSP(i) is routed over the FA-LSP(i+j) with j >= 1. In other words
   a set of FA-LSPs(i+j) with j fixed provides a Virtual Network
   Topology (VNT) for routing FA-LSPs(i). The virtual network topology
   offered by a set of FA-LSPs(i) is denoted by VNT(i) in this document.
   The virtual network topology is changed by setting up and/or tearing

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   down one (or more) FA-LSP(i). The change of the VNT(i) affects the
   routing of FA-LSPs(i-j). It is expected that boundary LSRs of VNT(i)
   will behave consistently with respect to any internal (LSP/link
   recovery) or external (LSP/link provisioning) triggering event.

   Routing is dependent on the network topology and associated link
   state. Routing stability may be impaired if the Virtual Network
   Topology frequently changes and/or if the status of links in the
   Virtual Network Topology frequently changes. In this context,
   robustness of the Virtual Network Topology is defined as the
   capability to smooth changes that may occur and avoid their
   subsequent propagation. Changes of the Virtual Network Topology may
   be caused by the creation and/or deletion of several LSPs. Creation
   and deletion of LSPs may be triggered by adjacent regions or through
   operational actions to meet change of traffic demand. Routing
   robustness should be traded with adaptability with respect to the
   change of incoming traffic requests.

2.4 FA Attributes Inheritance

   Several FA-LSPs(i) between LSRs over LSP region(i+1) are already
   established, and several FA-LSPs(i-1) have been setup over this
   topology and are partially filled up. One of the latter LSR regions
   sees an incoming LSP request. It can be demonstrated that the TE
   metric (in addition to the Maximum LSP Bandwidth and Unreserved
   Bandwidth see [GMPLS-RTG]) alone is not a sufficient metric to
   compute the best path between these regions. This suggests that the
   inheritance process over which the TE-Metric of the FA is not as
   straightforward as proposed in [MPLS-HIER].

   The best example is a packet LSP (PSC-1) to be multiplexed into PSC-
   2 region that lies over an LSC region. The metric MUST not take only
   into account packet boundaries interface features, properties and
   traffic engineering attributes such as delay or bit-rate but also for
   instance the distance over the LSP region that this LSP will have to
   travel. As such, the TE Metric for the Lambda LSP (in this example,
   FA-LSP(i+1)) must be at least defined as a combination of the bit-
   rate and the distance, classically the bit-rate times the distance
   with some weighting factors. The main issue from this perspective is
   that joined Path TE Metric wouldn't in such a case tackle
   simultaneously both packet and optical specifics.

   This suggests the definition of more flexible TE Metric, at least the
   definition of a TE Metric per ISC. Simply adjust the TE Metric to the
   (TE Metric of the FA-LSP path - 1) is a valid approach between LSP
   over the same region class (PSC-1, PSC-2, ... , PSC-N, for instance)
   but not necessarily between PSC and LSC region.

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   Other TE attributes that need a specific processing during
   inheritance are the Shared Risk Link Groups (SRLG) (see for instance
   [SRLG]) Resource Class/Color (i.e. Administrative Groups) and
   Protection (see Section 2.5).

   The next section will describe the specific TE attributes to be
   considered for devices hosting at least two switching capabilities,
   in particular the interface switching adaptation capabilities.

2.5 FA Abstraction for Recovery

   In multi switching environments the inheritance of protection and
   restoration related TE link attributes must also be considered.

   1) Considering a 1:1 end-to-end LSP recovery scheme, two FA-LSPs may
   be set up to form a single FA. To enhance the availability of the FA,
   the primary and the secondary LSPs are set up. The primary LSP is
   used to carry the normal traffic (see [TERM] and [E2E-RECOVERY]).
   Once the failure occurs affecting the primary LSP, the normal traffic
   is carried over the secondary LSP. From the routing perspective,
   there is no topological change to carry the traffic. These two LSPs
   should, therefore, be advertised within the scope of a single FA TE
   link advertisement with link protection type of 1:1. This FA will be
   processed by an upper layer as a span protected link.

   2) Considering now a single FA-LSP, span protected over each link
   (i.e. at the underlying layer).
   The question that arises is how should this span protected FA-LSP be
   advertised in the IGP. A link protection type of 1:1 could also be
   used for this advertisement but then, an upper layer would have no
   means to differentiate the two cases. However, these two recovery
   schemes (end-to-end and span) have major differences in terms of
   recovery delay and robustness [RECOVERY].

   Therefore, abstraction and summarization must be performed when
   advertising FA-LSPs as TE links (to an upper layer) but using the
   Link Protection Type flags and applying simple attribute inheritance
   might not be sufficient to distinguish different recovery schemes.

3. Cross Region Considerations

   In an MRN, as described here above, some LSR could contain, under the
   control of a single GMPLS instance, multiple interface switching
   capabilities such as PSC and Time-Division-Multiplexing (TDM) or PSC
   and Lambda Switching Capability (LSC) or LSC and Waveband Switching
   Capability WBSC).

   These LSRs, hosting multiple Interface Switching Capabilities (ISC),
   are required to hold and advertise resource information on link

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   states and topology. They also may have to consider certain portions
   of internal LSR resources to terminate hierarchical label switched
   paths (LSPs), since circuit switch capable units such as TDMs, LSCs,
   and FSCs require rigid resources.

   For example, an LSR with PSC+LSC switching capability can switch a
   Lambda LSP but can never terminate the Lambda LSP if there is no
   unused adaptation capability between the LSC and the PSC layers.

   Therefore, within multi-region LSR networks, the advertisement the
   so-called adaptation capability to terminate LSPs  provides critical
   information to take into account when performing multi-region path
   computation. This concept enables a local LSR to discriminate remote
   LSRs (and thus allows their selection during path computation) with
   respect to their adaptation capability e.g. to terminate Lambda LSPs
   at the PSC level.

   Hence, here we introduce the idea of discriminating the (internal)
   adaptation capability from the (interface) switching capability by
   considering an interface adaptation capability descriptor.

3.1 Interface adaptation capability descriptor

   The interface adaptation capability descriptor can be interpreted
   either as the adaptation capability information from an incoming
   interface or as the adaptation capability to an outgoing interface
   for a given interface switching capability. By introducing such an
   additional descriptor (as a sub-object of the ISC sub-TLV, for
   instance), the local GMPLS control plane can swiftly search which
   LSRs can terminate a certain encoding type of LSP and successfully
   establish an LSP tunnel between two PSCs.

   As an example, consider for instance a multiple LSP-region domain
   comprising simultaneously PSC LSRs, LSC LSRs, PSC+LSC LSRs and
   PSC+TDM+LSC LSRs. The LSRs discriminate the type of the links
   connecting these LSRs by interpreting the interface switching
   capability descriptor included in the TE Link TLV of the TE opaque

   The interface switching capability at both ends of a TE link between
   LSRs for which individual resources (lambdas) are represented by
   wavelength labels shall be [LSC, LSC], [{TDM|PSC}, LSC], or [LSC,
   {TDM|PSC}]. On the other hand, the interface switching capability at
   both ends of a TE link shall be [PSC,PSC] for LSPs "carrying" a shim
   header label, or shall be [TDM, TDM], [TDM,PSC] or [PSC,TDM] for TE
   links whose individual resources (timeslots) are represented by TDM
   labels. Thus, based on the interface switching capability descriptor,
   the LSRs can impose proper constraints in order to compute the paths
   of the LSPs. For example, LSRs can understand that a remote TDM LSR

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   with [LSC,TDM] link cannot be a lambda LSP intermediate link with the
   exception that it can initiate or terminate lambda LSPs and switch
   "TDM timeslots".

   However, LSRs cannot infer the internal LSP switching capability of
   remote LSRs, especially if the LSRs have a multi-switching capability
   architecture such as a PSC+TDM+LSC as shown below or more generally,
   more than two ISC capabilities. In the LSR, LSC may have a direct
   inner interface not only to TDM but also to PSC. The LSP can be
   interfaced at both TDM or PSC. This kind of multi-switching
   architecture may become very common in optical networks.

                   .                        .
                   .          --------      .
                   .         |        |     .
                   .         |  ISC2  |     .
                   .   -<->--|        |     .
                   .  |      |        |     .
                   .  |       --------      .
                   .  |                     .
                   .  |       --------      .
                   .  |      |        |     .
                   .   -<->--|  ISC1  |     .
                   .         |        |     .
              -----<---------|        |     .
              ----->---------|        |     .
                   .          --------      .

   In the above figure, the switching capabilities ISC1 and ISC2 can be
   grouped in a single TE link, and the bandwidth information defined as
   Let X be the initial Unreserved Bandwidth of the TE link then the Max
   LSP bandwidth can be equal to X for the ISC1 (as advertised in the
   ISC1 sub-TLV) and equal to Y12 for the ISC2 (as advertised in the
   ISC2 sub-TLV). Y12 represents the link bandwidth between the two
   ISCs. The bandwidth accounting/updating is then dependent of the
   inner architecture. In this case no specific adaptation capability
   descriptor is required.

   The following cases, however, highlight the limitations of such
   procedure and the need for an enhanced switching adaptation


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                   .                        .
              TE2  .          --------      .
              ----->---------|        |     .
              -----<---------|  ISC2  |     .
                   .   --->--|        |     .
                   .  | --<--|        |     .
                   .  ||      --------      .
                   .  ||                    .
                   .  ||      --------      .
                   .  | -->--|        |     .
                   .   ---<--|  ISC1  |     .
              TE1  .         |        |     .
              ----->---------|        |     .
              -----<---------|        |     .
                   .          --------      .

   For the above picture, two cases can be considered  regarding the
   switching capability configuration. Note that both TE1 and TE2 belong
   to the same physical link.

   Let the triplet <TE, ISC1, ISC2> represent respectively the
   Unreserved Bandwidth of the TE link, the Maximum LSP Bandwidth of
   ISC1 and the Maximum LSP Bandwidth of ISC2.

   In a first scheme the switching capabilities can be declared as two
   separate TE links:  for TE link 1 (TE_1) and TE link 2 (TE_2): <X1,
   X1, Y12> and <X2, X2, Y21>

   In a second scheme, the capabilities are described as part of a
   single TE Link: <X, X+Y12, X+Y21>.

   While the first case rises some issues concerning bandwidth
   accounting coordination between the two TE Links, the later is
   confronted to an over-provisioning issue being, in addition, highly
   dependent on the Minimum LSP bandwidth value. Also, these approaches
   are limited 1) by the number of switching capabilities hosted by a
   single system and 2) by the number of ways these switching
   capabilities interacts (i.e. the number of ways data can be
   encapsulated/decapsulated when passing from one switching capability
   to another).

   1) Number of Switching Capabilities:

                       ------|       |------
                      |      |  PSC  |      |

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                      |    --|       |--    |
                      |   |   -------   |   |
                      |  \|/           /|\  |
                      |   |   -------   |   |
                      |    --|       |--    |
                     \|/     |  TDM  |     /|\
                      |    --|       |--    |
                      |   |   -------   |   |
                      |  \|/           /|\  |
                      |   |   -------   |   |
                      |    --|       |--_   |
                       ------|       |------
                             |       |
                        /|---|       |---|\  Fiber #1
               ========| |---|  LSC  |---| |========
               ========| |---|       |---| |========
                        \|---|       |---|/  Fiber #N

   Referring to this figure, the problem with the use of the interface
   switching capability descriptor at the PSC+TDM+LSC LSR, is the
   shortage of LSP termination capability information. The PSC+TDM+LSC
   LSR provides only switching capability information by abstracting the
   internal node capabilities. Therefore, remote LSRs cannot accurately
   determine which switching capability can be switched and/or
   terminated at the PSC+TDM+LSC LSR. For such a node supporting LSC,
   TDM and PSC switching capability, the determination of the resource
   made available to cross for instance the LSC to PSC region boundary
   (LSC -> PSC) may involve one of the following region cross- over: LSC
   -> PSC and LSC -> TDM -> PSC. This can be represented as follows:

                             |       |
                         ----|  PSC  |----
                        |    |       |    |
                      -----   -------   -----
                     |     |           |     |
                      -----   -------   -----
                       | |   |       |   | |
                       |  ---|  TDM  |---  |
                       |  ---|       |---  |
                       | |   |       |   | |
                      -----   -------   -----
                     |     |           |     |
                      -----   -------   -----
                       | |   |       |  _| |
                       |  ---|  LSC  |---  |
                        -----|       |-----

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   2) Number of adaptation capabilities:

   In addition, the LSP Encoding Type (representing the nature of the
   link that the LSP traverses) is "lambda". Therefore, as depicted in
   the following figure, this issue become more complex once each
   switching capability supports multiple framing, for instance, at PSC,
   Ethernet-MAC framing and PPP framing.

                             |       |
                 ------------|  PSC  |------------
                |        ----|       |----        |
                |       |    |       |    |       |
              -----   -----   -------   -----   -----
             | ETH | | PPP |           | PPP | | ETH |
              -----   -----   -------   -----   -----
               | |     | |   |       |   | |     | |
               | |     |  ---|  TDM  |---  |     | |
               |  -----------|       |-----------  |
               |       |     |       |     |       |

   Another example occurs when L2SC (Ethernet) switching can be adapted
   in LAPS X.86 and GFP for instance before reaching the TDM switching

                             |       |
                 ------------| L2SC  |------------
                |        ----|       |----        |
                |       |    |       |    |       |
              -----   -----   -------   -----   -----
             | X86 | | GFP |           | GFP | | X86 |
              -----   -----   -------   -----   -----
               | |     | |   |       |   | |     | |
               | |     |  ---|  TDM  |---  |     | |
               |  -----------|       |-----------  |
               |       |     |       |     |       |

   Similar circumstances can occur, if a switching fabric that supports
   both PSC and L2SC functionalities is assembled with LSC interfaces
   enabling "lambda" (photonic) encoding. In the switching fabric, some
   interfaces can terminate Lambda LSPs and perform frame (or cell)
   switching whilst other interfaces can terminate Lambda LSPs and
   perform packet switching.

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   Thus, the interface switching capability descriptor provides the
   information for the forwarding (or switching) capability only. In
   order for remote LSRs to understand properly the termination
   capability of the other LSRs, additional information to the existing
   interface switching capability descriptor is essential in achieving
   seamless multi-region routing. In turn, adequate processing of this
   additional information will allow the signaling of packet LSP set- up
   combined with an automated triggering of new Lambda LSPs between LSRs
   that do not yet have a preferred Lambda LSP to carry the Packet LSP.
   (see [MLRT]).
   Note that in the context of Hybrid Photonic Networks, additional
   constraints such as the regeneration capability drive even more the
   need for an adaptation switching capability descriptor.

3.2 Regeneration capability

   In an HPN context, the lower LSP region provides to the upper LSP
   region a regeneration/conversion function (using for instance opto-
   electronic interfaces). More precisely a regeneration function can
   deliver conversion (within a given pre- determined range or not)
   while conversion may be delivered independently of the existence of
   any regeneration capability.

   The following classification applies from the definition of the
   regeneration function:

   1. If the regeneration function is defined as an Interface Switching
   Capability (or simply ISC see [GMPLS-RTG] and [MPLS-HIER]), then if
   this ISC value is lower or equal to the incoming LSP switching type,
   the request may be processed by the network. Otherwise if the LSP
   Switching Type > ISC value of the region, the LSP request can not be
   processed and is simply rejected (see [MPLS-HIER] for a definition of
   the relationship between ISC values).

   2. If the regeneration function is not defined as an interface
   switching capability (pure regeneration without any connection
   function defined) then the following alternative applies depending on
   the encoding type defined at its entry points. If the regeneration
   depends on the encoding type of the incoming LSP request the latter
   must be the same as the one provided by the regeneration function.
   Otherwise the LSP request is simply rejected or tunneled toward the
   next hop (if feasible). Notice here that forwarding an LSP request to
   the next hop and expecting the latter would provide enough
   regeneration capacity for this incoming LSP is a complex problem,
   since one can not, with the currently available GMPLS tools,
   guarantee that this request will not itself be forwarded to the next
   hop, and so on.

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   Moreover, by extending the knowledge of the interface capability to
   terminate (adapt) a given signal, it would be possible for instance
   to characterize more precisely the interfaces (physical) distance
   coverage. This may be achieved by considering information such as the
   transmission distance range (Short Haul, Long Haul, Ultra Long Haul,
   etc.) or even the signal modulation format. This would provide
   dynamic interface resource management (versus the current Network
   Management techniques). In turn, this would decrease the time needed
   for selecting resources during path computation.

3.3 Dedicated Traffic Parameters

   This point is related to whether or not dedicated traffic parameters
   should be defined for LSPs established in MRN environments such as
   the ones defined for Sonet/SDH (see [SONET-SDH] and G.709 (see

   With respect to spatial routing the LSP Encoding Type, Switching Type
   and G-PID (see [RFC-3471] for the corresponding definitions) provides
   the required information to pertinently setup such LSPs. It is
   nevertheless expected here to see some additional capability allowing
   for intermediate states, in particular when the regeneration function
   is defined as a switching layer (see also Section 6.2).

   With respect to spectral routing the main issue raises from the
   passing of external physical constraints between conversion points.
   In addition to the Multiplier usage that may help in establishing/
   deleting parallel LSPs, additional information concerning the
   physical constraint each sub-path MUST fulfill should be considered
   e.g. maximum distance and BER per (sub-path). A parameter equivalent
   to the Transparency level may also help in providing a hop-by-hop
   negotiation of the regeneration capability to be used.

3.4 Applications

   In multi-region environments, crossing LSP regions during
   provisioning can occur for two main reasons: grooming or regeneration
   (when delivered by a switching capable layer).

   1. Grooming

   LSP grooming deals with the optimization of network resource
   utilization. Multi-region environments are particularly well adapted
   for this feature as they may provide different switching
   granularities allowing for the tunnelling of several finer grained
   LSPs into a coarser grained LSP. In this context, it can be useful
   from the control plane viewpoint not to terminate the multiplexed LSP
   and simply tunnel this LSP into a lower-region LSP viewed as a common
   segment for each incoming LSPs.

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   However, this raises the problem of the representation of the newly
   established LSP at the control plane level. In particular, concerning
   the maintenance of the two LSPs (head-end and tail-end LSPs) that
   forms the newly spliced LSPs. Further consideration on grooming are
   left for further study as it includes aspects leading to the
   definition of multipoint-to-point LSPs (beyond the scope of this

   2. Regeneration

   Due to the constraints of optical transmission, the optical signal
   may have to be regenerated along the LSP path. Some multi-region
   network may require to cross a region boundary to access the
   regeneration function. This rises the question of the so-called LSP
   integrity when crossing region boundaries.

   Consider for instance a Lambda LSP in a LSC+PSC multi-region network.
   For a given reason the LSP needs to be regenerated at an intermediate
   node. It will thus use the O/E/O interfaces present in the PSC
   region. From the control plane viewpoint either two Lambda LSPs are
   seen (ingress to intermediate and intermediate to egress) or a single
   one (ingress to egress).

   Keeping a single Lambda LSP would prevent from maintaining, at the
   control plane level, several entities for a single connection. It
   should be also noted here that one assumes that regeneration is
   delivered between LSPs (from ingress to intermediate and intermediate
   to egress) defined within regions of the same switching capability
   (i.e. LSC-PSC-LSC). This would in turn facilitate the processing of
   both the regenerated entities and the (pool of) regeneration
   resources that would need to be marked.

4. Extended Scope of Switching Capabilities

   When considering multi-region environments, two common examples of
   multi-switching combinations are:
   - Packet(LSR)/Layer-2(Switch) with TDM (SONET/SDH) or LSC (OXC)
   - Multi-Granularity OXC (including opaque and transparent switching
   capabilities at different granularity levels)

   The first implies some considerations with respect to Layer-2
   Switching Capable interfaces and L2SC environments. The latter
   implies further considerations on Waveband Switching aspects.

4.1 L2SC Switching

   Layer 2 Switching capable interfaces and Layer 2 LSPs are in the
   scope of GMPLS (see [GMPLS-ARCH], [GMPLS-RTG] and [RFC-3471]). Such

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   interfaces are defined as capable to recognize frame/cell boundaries
   and can forward data based on the content of the frame/cell header.
   They include mainly interfaces on Ethernet bridges that forward data
   based on the content of the MAC header. This section provides an
   overview of the issues to be considered when introducing GMPLS in
   Ethernet MAC-based networks.

   In this context, the possible development of a GMPLS signaling
   profile for Ethernet networks, involves the definition of a label
   space. From this perspective, two questions arise: 1) what the label
   value space represents and is the corresponding label value space
   semantic-full (see [GMPLS-SONET-SDH]) or semantic-less (see [RFC-
   3471]) and 2) how is the label value space implemented (i.e.
   associated with data plane or non-associated and therefore exchanged
   over dedicated signaling channels or even a combination of both). A
   contiguous problem arises that the set of potential solutions must be
   backward compatible meaning that non-GMPLS controlled Ethernet
   interfaces should be capable to inter-work with GMPLS controlled
   Ethernet interfaces.
   In addition to the label considerations, an additional problem
   appears due to the type of environment in which these Ethernet
   interfaces are considered. These interfaces may be either so-called
   LAN PHY's (thus implying a broadcast capable environment) or WAN
   PHY's (thus implying point-to-point links). On the other side, one
   has to consider MAC-based capable interfaces over Non-Broadcast
   Multiple Access (NBMA) technologies such as MPLS (Ethernet-over-
   MPLS) and over circuit-oriented technologies such as SDH and OTN
   (through different adaptation technologies such as LAPS X.86 and
   GFP). This by taking into account that the MAC Address space is by
   definition non-hierarchical. The latter implies the definition of an
   identification space translating the topological location of the
   Ethernet end-points from an IP-based perspective and this optimally
   independently of the underlying bearer technology of the Ethernet

   The ideal situation would be to define a "one size fits all"
   solution. However, it is clear that inferring label value space from
   the bearer technology implies the development of so-called snooping
   approaches, while on the other side LAN PHY's would not scale such a
   solution implying the transformation of Broadcast Access (BA)
   environment into a NBMA one (using star, hub-and-spoke, or multi-
   tree approaches). Therefore, a heuristic has to be provided to solve
   these problems while avoiding introduction of complex address
   resolution mechanisms for such environments. Broadcasts are mainly
   used in LAN environments for address resolution (ARP) and
   bootstrapping (DHCP) reasons. Thus a potential solution would be to
   let the network operate in a BA mode for such operations and bring
   its operational mode back to an NBMA mode for unicast/multicast frame
   processing. The same would apply for unknown unicast frames.

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   Therefore, a first step towards a solution would be reached, if one
   can guarantee a dual operational mode for these environments: 1)
   first mode being backward compatible with the broadcast exchanges as
   defined by the IEEE (using IEEE 802.1d and related, thus using an
   associated control plane) and 2) the second mode being GMPLS
   compatible (thus using a non-associated IP-based distributed control
   plane) for the unicast operations

   The next issue relates to the realization of resource reservation
   over Ethernet interfaces using GMPLS signaling techniques and its
   applicability. For more detailed considerations see [L2SC-LSP].

4.2 Example

   The following example details the usage of the concepts presented in
   the previous sections of this document in delivering a virtual
   topology for L2SC-over-LSC nodes.

   Consider the following network topology:

              1       2
              |       |
          |   |   |   |
          |   E---F   |
          |   |   |   |
          |       |
          7       8

   In this topology each node identified with a letter is a dual
   switching capable node (L2SC/LSC or L2SC/WBSC) and nodes identified
   with a number refers to L2SC capable devices.

   An Lambda LSP is established covering all dual-switching nodes [A-B-
   This FA-LSP constitutes the virtual topology for the dual switching
   nodes. This is viewed from the L2SC level as a L2SC capable multi-
   access link that may be accessed (upon local policy basis) from each
   node constituting the topology. Another example, would be, for
   instance, a Lambda LSP routed over [A-B-C-D-J] but precluding access
   to node C.

   Afterwards, each node (more precisely the L2SC region) may trigger
   the establishment of L2SC LSPs on top of this multi-access FA-LSP
   that would allow setting up multi-partitioning of the bandwidth
   capacity made available by the "fat pipe" having a higher ISC value.

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   These L2SC LSP's may be for instance, using the above example, [A-B-
   C-D], [A-B-D-J-I-G] or [J-I-F-E], even if the latter wouldn't be
   usable by any incoming LSP. Each of these L2SC LSP's are simply L2SC
   FA-LSP's forming a L2SC-capable virtual topology. This topology can
   be subsequently used by external devices to establish L2SC LSP's
   using these FA's as links.

   Bandwidth accounting is performed on a per FA basis, translating into
   intermediate node bandwidth aggregation accounted on a per priority
   basis. In turn, this accounting translates into restriction over the
   accessibility of each of the links constituting the Lambda LSP.

   The above example implies that currently defined ISCs (see [GMPLS-
   RTG]) such as L2SC might be extended to more than one value with the
   following relationship L2SC (=L2SC-1) < L2SC-2 < L2SC-3 < L2SC-4 <
   TDM. The (data plane) flow aggregation mechanisms for L2SC LSPs being
   out of scope of the present document.

4.3 Waveband switching

   The GMPLS protocol suite, as currently defined, supports waveband
   switching through inverse multiplexing or switching of individual
   (contiguous) wavelength components. It may be thus appropriate to
   integrate wavebands in the switching hierarchy in order to reflect,
   at the control plane level, waveband physical components
   (multiplexer/demultiplexer) availability at the data plane [WBEXT].
   Also, depending on the (passive/active) components used in an optical
   network, wavelength spacing in the optical multiplex can vary. Some
   components like multiplexer/demultiplexer impose or depend on that
   spacing. Therefore, it may be appropriate to detail the component
   capability with respect to spacing, and/or to indicate the number of
   supported wavelengths per waveband. Moreover, one may also expect in
   case of (standardized) waveband nominal frequency values some
   simplification during the corresponding wavelength assignment.

   In the MRN context, the main issue with Waveband Switching can be
   viewed as follows. If the LSRs support in addition to waveband
   switching an ISC in the set {PSC, L2SC, TDM, FSC} then waveband
   switching can be assumed (from the control plane processing
   viewpoint) as being equivalent to Lambda Switching, if one considers
   labels as described here above. However if the additional switching
   capability within a single device, or even network, includes
   interfaces with LSC capability then either links should have a
   specific resource class assigned or dedicated values should be
   considered for the LSP Encoding Type, Switching Type and G-PID (when
   bands are carried over fibers).

5. Conclusion

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   In this draft, we address the issues when using the GMPLS protocol
   suite as a unified control plane for MRN environments. Several
   proposals for enhancing the current GMPLS mechanisms are presented.
   The proposals are based on current GMPLS mechanisms and in alignment
   with GMPLS architecture (see [GMPLS-ARCH]). This memo analyzes the
   suitability of the GMPLS protocol suite for the MRN environment,
   keeping a strict and full alignment with the current and preferred
   suite of signaling and routing protocols (in particular, OSPF, IS-IS,
   RSVP-TE and LMP).
   By starting from a single area context, the expectations coming out
   from the first release of this memo, are clearly intended to open the
   field to a more detailed description of the collaborative processes
   within the GMPLS protocol suite.

   The main guideline of this work is backward compatibility with the
   current GMPLS protocols suite. The second guideline is limiting and
   efficiently handling the complexity introduced. This memo provides an
   introduction to MRNs and aspects to be considered. We invite the
   CCAMP community to collaborate on progressing this critical GMPLS
   topic: an integrated control plane supporting multiple data layers.

Security Considerations

   In its current version, this memo does not introduce new security
   consideration from the ones already detailed in the GMPLS protocol


   [G.707]      ITU-T, "Network node interface for the Synchronous
                Digital Hierarchy", Recommendation G.707

   [G.709]      ITU-T, "Interfaces for the Optical Transport Network"
                 Recommendation G.709

   [G.805]      ITU-T, "Generic functional architecture of transport
                networks", Recommendation G.805

   [GMPLS-RTG]  K. Kompella (Editor), Y. Rekhter (Editor) et al.
                "Routing Extensions in Support of Generalized MPLS",
                Internet Draft, Work in Progress,

   [GMPLS-G709] D. Papadimitriou (Editor) et al. "Generalized MPLS
                Signaling Extensions for G.709 Optical Transport
                Networks Control", Internet Draft, Work in Progress,

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   [LSP-HIER]   K. Kompella and Y. Rekhter, "LSP Hierarchy with
                Generalized MPLS TE", Internet Draft, Work in Progress,

   [RECOVERY]   CCAMP P&R Design Team, Analysis of Generalized Multi-
                Protocol Label Switching (GMPLS)-based Recovery
                Mechanisms (including Protection and Restoration),
                Work in Progress,

   [INTER-AREA-AS] A. Ayyangar, J. Vasseur, " Inter-area and Inter-AS
                   MPLS Traffic Engineering", Internet Draft, Work in

   [L2SC-LSP]   D. Papadimitriou, et. Al., "Generalized MPLS Signaling
                for Layer-2 Label Switched Paths (LSP)", Internet Draft,
                Work in Progress,

   [MAMLTE]     K. Shiomoto et al., "Multi-area multi-layer traffic
                engineering using hierarchical LSPs in GMPLS networks",
                Internet Draft, Work in Progress

   [MLRT]       W. Imajuku et al., "Multilayer routing using multilayer
                switch capable LSRs, Internet Draft, Work in Progress,

   [MPLS-BDL]   K. Kompella, Y. Rekhter and Lou Berger, "Link Bundling
                in MPLS Traffic Engineering", Internet Draft, Work in

   [RFC-2370]   R. Coltun, "The OSPF Opaque LSA Option",
                IETF RFC 2370

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

   [SONET-SDH]  E. Mannie and D. Papadimitriou et al., "Generalized
                Multi-Protocol Label Switching Extensions for SONET and
                SDH Control", Internet Draft, Work in Progress,

   [SRLG]       D. Papadimitriou et al. "Shared Risk Link Groups
                Inference and Processing", Internet Draft, Work in

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   [SURVEY]     L. Berger, Y. Rekhter et al., "Generalized MPLS
                Signaling - Implementation Survey",
                Internet Draft, Work in Progress,

   [WBEXT]      R. Douville et al., "Extensions to Generalized MPLS for
                Waveband Switching", Internet Draft, Work in Progress


   We would like to thank here, Sven Van Den Bosch, Richard Douville,
   Olivier Audouin, Amaury Jourdan, Emmanuel Desmet and Bernard sales.

   The authors would like to thank Mr. Wataru Imajuku for the
   discussions on adaptation between regions [MLRT].

Author’s Addresses

   Dimitri Papadimitriou (Alcatel)
   Francis Wellensplein 1,
   B-2018 Antwerpen, Belgium
   Phone : +32 3 240 8491
   E-mail: dimitri.papadimitriou@alcatel.be

   Martin Vigoureux (Alcatel)
   Route de Nozay,
   91461 Marcoussis cedex, France
   Phone: +33 (0)1 69 63 18 52
   E-mail: martin.vigoureux@alcatel.fr

   Kohei Shiomoto (NTT Network Innovation Laboratories)
   3-9-11 Midori-cho
   Musashino-shi, Tokyo 180-8585, Japan
   Phone: +81 422 59 4402
   E-mail: shiomoto.kohei@lab.ntt.co.jp

   Deborah Brungard (AT&T)
   Rm. D1-3C22 - 200 S. Laurel Ave.
   Middletown, NJ 07748, USA
   Phone: +1 732 420 1573
   E-mail: dbrungard@att.com

   Jean-Louis Le Roux (FTRD/DAC/LAN)
   Avenue Pierre Marzin
   22300 Lannion, France
   Phone: +33 (0)2 96 05 30 20

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   Eiji Oki (NTT Network Innovation Laboratories)
   3-9-11 Midori-cho
   Musashino-shi, Tokyo 180-8585, Japan
   Phone : +81 422 59 3441
   E-mail: oki.eiji@lab.ntt.co.jp

   Nobuaki Matsuura (NTT Network Service Systems Laboratories)
   3-9-11 Midori-cho
   Musashino-shi, Tokyo 180-8585, Japan
   Phone : +81 422 59 3758
   E-mail: matsuura.nobuaki@lab.ntt.co.jp

   Emmanuel Dotaro (Alcatel)
   Route de Nozay,
   91461 Marcoussis cedex, France
   Phone : +33 1 6963 4723
   E-mail: emmanuel.dotaro@alcatel.fr

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