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Versions: (draft-oki-pce-inter-layer-frwk) 00 01 02 03 04 05 06 07 08 09 10 RFC 5623

     Network Working Group                                         E. Oki
     Internet Draft                                                   NTT
     Category: Informational                                  J-L Le Roux
     Expires: March 2008                                   France Telecom
                                                                A. Farrel
                                                       Old Dog Consulting
                                                           September 2007
  
         Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic
                                Engineering
  
                   draft-ietf-pce-inter-layer-frwk-05.txt
  
  
  
     Status of this Memo
  
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     http://www.ietf.org/ietf/1id-abstracts.txt.
  
     The list of Internet-Draft Shadow Directories can be accessed at
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     Abstract
  
     A network may comprise multiple layers. It is important to
     globally optimize network resource utilization, taking into
     account all layers, rather than optimizing resource utilization at
     each layer independently. This allows better network efficiency to
     be achieved through a process that we call inter-layer traffic
     engineering. The Path Computation Element (PCE) can be a powerful
     tool to achieve inter-layer traffic engineering.
  
  
  
  
  
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     This document describes a framework for applying the PCE-based
     architecture to inter-layer Multiprotocol Label Switching (MPLS)
     and Generalized MPLS (GMPLS) traffic engineering. It provides
     suggestions for the deployment of PCE in support of multi-layer
     networks. This document also describes network models where PCE
     performs inter-layer traffic engineering, and the relationship
     between PCE and a functional component called the Virtual Network
     Topology Manager (VNTM).
  
  
     Table of Contents
  
    1. Introduction....................................................3
    1.1.  Terminology..................................................4
    2. Inter-Layer Path Computation....................................4
    3. Inter-layer Path Computation Models.............................6
    3.1.  Single PCE Inter-Layer Path Computation......................6
    3.2.  Multiple PCE Inter-Layer Path Computation....................7
    3.3.  General Observations.........................................9
    4. Inter-Layer Path Control........................................9
    4.1.  VNT Management...............................................9
    4.2.  Inter-Layer Path Control Models..............................9
    4.2.1.  PCE-VNTM Cooperation Model................................10
    4.2.2.  Higher-Layer Signaling Trigger Model......................12
    4.2.3.  NMS-VNTM Cooperation Model................................15
    4.2.4.  Possible Combinations of Inter-Layer Path Computation and
    Inter-Layer Path Control Models....................................17
    5. Choosing Between Inter-Layer Path Control Models...............18
    5.1.  VNTM Functions:.............................................18
    5.2.  Border LSR Functions:.......................................19
    5.3.  Complete Inter-Layer LSP Setup Time:........................20
    5.4.  Network Complexity..........................................20
    5.5.  Separation of Layer Management..............................21
    6. Manageability Considerations...................................21
    6.1.  Control of Function and Policy..............................22
    6.1.1.  Control of Inter-Layer Computation Function...............22
    6.1.2.  Control of Per-Layer Policy...............................22
    6.1.3.  Control of Inter-Layer Policy.............................22
    6.2.  Information and Data Models.................................23
    6.3.  Liveness Detection and Monitoring...........................23
    6.4.  Verifying Correct Operation.................................24
    6.5.  Requirements on Other Protocols and Functional Components...24
    6.6.  Impact on Network Operation.................................25
    7. Security Considerations........................................25
    8. Acknowledgments................................................26
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
    9. References.....................................................26
    9.1.  Normative Reference.........................................26
    9.2.  Informative Reference.......................................27
    10.  AuthorsEAddresses...........................................28
    11.  Intellectual Property Statement..............................28
  
  1. Introduction
  
     A network may comprise multiple layers. These layers may represent
     separations of technologies (e.g., packet switch capable (PSC),
     time division multiplex (TDM), or lambda switch capable (LSC))
     [RFC3945], separation of data plane switching granularity levels
     (e.g., PSC-1, PSC-2, VC4, or VC12) [MLN-REQ], or a distinction
     between client and server networking roles. In this multi-layer
     network, Label Switched Paths (LSPs) in a lower layer are used to
     carry higher-layer LSPs across the lower-layer network. The
     network topology formed by lower-layer LSPs and advertised as
     traffic engineering links (TE links) to the higher layer is called
     the Virtual Network Topology (VNT) [MLN-REQ].
  
     It may be effective to optimize network resource utilization
     globally, i.e., taking into account all layers, rather than
     optimizing resource utilization at each layer independently. This
     allows better network efficiency to be achieved and is what we
     call inter-layer traffic engineering. This includes mechanisms
     allowing the computation of end-to-end paths across layers (known
     as inter-layer path computation), and mechanisms for control and
     management of the Virtual Network Topology (VNT) by setting up and
     releasing LSPs in the lower layers [MLN-REQ].
  
     Inter-layer traffic engineering is included in the scope of the
     Path Computation Element (PCE)-based architecture [RFC4655], and
     PCE can provide a suitable mechanism for resolving inter-layer
     path computation issues.
  
     PCE Communication Protocol requirements for inter-layer traffic
     engineering are set out in [PCE-INTER-LAYER-REQ].
  
     This document describes a framework for applying the PCE-based
     architecture to inter-layer traffic engineering. It provides
     suggestions for the deployment of PCE in support of multi-layer
     networks. This document also describes network models where PCE
     performs inter-layer traffic engineering, and the relationship
     between PCE and a functional component in charge of the control
     and management of the VNT, called the Virtual Network Topology
     Manager (VNTM).
  
  
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
  1.1. Terminology
  
     This document uses terminology from the PCE-based path computation
     architecture [RFC4655] and also common terminology from Multi
     Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS
     (GMPLS) [RFC3945] and Multi-Layer Networks [MLN-REQ].
  
  2. Inter-Layer Path Computation
  
     This section describes key topics of inter-layer path computation
     in MPLS and GMPLS networks.
  
     [RFC4206] defines a way to signal a higher-layer LSP, which has an
     explicit route that includes hops traversed by LSPs in lower
     layers. The computation of end-to-end paths across layers is
     called Inter-Layer Path Computation.
  
     A Label Switching Router (LSR) in the higher-layer might not have
     information on the topology of the lower-layer, particularly in an
     overlay or augmented model deployment, and hence may not be able
     to compute an end-to-end path across layers.
  
     PCE-based Inter-Layer Path Computation, consists of using one or
     more PCEs to compute an end-to-end path across layers. This could
     be achieved by a single PCE path computation where the PCE has
     topology information about multiple layers and can directly
     compute an end-to-end path across layers considering the topology
     of all of the layers. Alternatively, the inter-layer path
     computation could be performed as a multiple-PCE computation where
     each member of a set of PCEs has information about the topology of
     one or more layers (but not all layers), and the PCEs collaborate
     to compute an end-to-end path.
  
         -----    -----                  -----    -----
        | LSR |--| LSR |................| LSR |--| LSR |
        | H1  |  | H2  |                | H3  |  | H4  |
         -----    -----\                /-----    -----
                        \-----    -----/
                        | LSR |--| LSR |
                        | L1  |  | L2  |
                         -----    -----
  
     Figure 1 EA Simple Example of a Multi-Layer Network.
  
     Consider, for instance, the two-layer network shown in Figure 1,
     where the higher-layer network is a packet-based IP/MPLS or GMPLS
     network  (LSRs H1, H2, H3, and H4), and the lower-layer network
     (LSRs, H2, L1, L2, and H3) is a GMPLS optical network. An ingress
     LSR in the higher-layer network (H1)  tries to set up an LSP to an
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
     egress LSR  (H4) also in the higher-layer network across the
     lower-layer network, and needs a path in the higher-layer network.
     However, suppose that there is no TE link in the higher-layer
     network between the border LSRs located on the boundary between
     the higher-layer and lower-layer networks (H2 and H3). Suppose
     also that the ingress LSR does not have topology visibility into
     the lower layer. If a single-layer path computation is applied for
     the higher-layer, the path computation fails because of the
     missing TE link. On the other hand, inter-layer path computation
     is able to provide a route in the higher-layer (H1-H2-H3-H4) and a
     suggestion that a lower-layer LSP be set up between the border
     LSRs (H2-L1-L2-H3).
  
     Lower-layer LSPs that are advertised as TE links into the higher-
     layer network form a Virtual Network Topology (VNT) that can be
     used for routing higher-layer LSPs. Inter-layer path computation
     for end-to-end LSPs in the higher-layer network that span the
     lower-layer network may utilize the VNT, and PCE is a candidate
     for computing the paths of such higher-layer LSPs within the
     higher-layer network. Alternatively, the PCE-based path
     computation model can:
  
     - Perform a single computation on behalf of the ingress LSR using
     information gathered from more than one layer. This mode is
     referred to as Single PCE Computation in [RFC4655].
  
     - Compute a path on behalf of the ingress LSR through cooperation
     with PCEs responsible for each layer. This mode is referred to as
     Multiple PCE Computation with inter-PCE communication in [RFC4655].
  
     - Perform separate path computations on behalf of the TE-LSP head-
     end and each transit border LSR that is the entry point to a new
     layer. This mode is referred to as Multiple PCE Computation
     (without inter-PCE communication) in [RFC4655]. This option
     utilizes per-layer path computation performed independently by
     successive PCEs.
  
     The PCE invoked by the head-end LSR computes a path that the LSR
     can use to signal an MPLS-TE or GMPLS LSP once the path
     information has been converted to an Explicit Route Object (ERO)
     for use in RSVP-TE signaling. There are two options.
  
     - Option 1: Mono-layer path.
     The PCE computes a "mono-layer" path, i.e., a path that includes
     only TE links from the same layer. There are two cases for this
     option. In the first case the PCE computes a path that includes
     already established lower-layer LSPs or lower-layer LSPs to be
     established on demand. That is, the resulting ERO includes sub-
     object(s) corresponding to lower-layer hierarchical LSPs expressed
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
     as the TE link identifiers of the hierarchical LSPs when
     advertised as TE links in the higher-layer network. The TE link
     may be a regular TE link that is actually established, or a
     virtual TE link that is not established yet (see [MLN-REQ]). If it
     is a virtual TE link, this triggers a setup attempt for a new
     lower-layer LSP when signaling reaches the head-end of the lower-
     layer LSP. Note that the path of a virtual TE link is not
     necessarily known in advance, and this may require a further
     (lower-layer) path computation.
  
     The second case is that the PCE computes a path that includes a
     loose hop that spans the lower-layer network. The higher layer
     path computation selects which lower layer network to use, and
     selects the entry and exit points from that lower-layer network,
     but does not select the path across the lower-layer network. A
     transit LSR that is the entry point to the lower-layer network is
     expected to expand the loose hop (either itself or relying on the
     services of a PCE). The path expansion process on the border LSR
     may result either in the selection of an existing lower-layer LSP,
     or in the computation and setup of a new lower-layer LSP.
  
     - Option 2: Multi-layer path. The PCE computes a "multi-layer"
     path, i.e., a path that includes TE links from distinct layers
     [RFC4206]. Such a path can include the complete path of one or
     more lower-layer LSPs that already exist or are not yet
     established. In the latter case, the signaling of the higher-layer
     LSP will trigger the establishment of the lower-layer LSPs.
  
  3. Inter-layer Path Computation Models
  
     As stated in Section 2, two PCE modes defined in the PCE
     architecture can be used to perform inter-layer path computation.
     They are discussed in the sections that follow.
  
  3.1. Single PCE Inter-Layer Path Computation
  
     In this model Inter-layer path computation is performed by a
     single PCE that has topology visibility into all layers. Such a
     PCE is called a multi-layer PCE.
  
     In Figure 2, the network is comprised of two layers. LSRs H1, H2,
     H3, and H4 belong to the higher layer, and LSRs H2, H3, L1, and L2
     belong to the lower layer. The PCE is a multi-layer PCE that has
     visibility into both layers. It can perform end-to-end path
     computation across layers (single PCE path computation). For
     instance, it can compute an optimal path H1-H2-L1-L2-H3-H4, for a
     higher layer LSP from H1 to H4. This path includes the path of a
     lower layer LSP from H2 to H3, already in existence or not yet
     established.
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
  
  
                             -----
                            | PCE |
                             -----
         -----    -----                  -----    -----
        | LSR |--| LSR |................| LSR |--| LSR |
        | H1  |  | H2  |                | H3  |  | H4  |
         -----    -----\                /-----    -----
                        \-----    -----/
                        | LSR |--| LSR |
                        | L1  |  | L2  |
                         -----    -----
  
       Figure 2: Single PCE Inter-Layer Path Computation
  
  3.2.  Multiple PCE Inter-Layer Path Computation
  
     In this model there is at least one PCE per layer, and each PCE
     has topology visibility restricted to its own layer. Some
     providers may want to keep the layer boundaries due to factors
     such as organizational and/or service management issues. The
     choice for multiple PCE computation instead of single PCE
     computation may also be driven by scalability considerations, as
     in this mode a PCE only needs to maintain topology information for
     one layer (resulting in a size reduction for the Traffic
     Engineering Database (TED)).
  
     These PCEs are called mono-layer PCEs. Mono-layer PCEs collaborate
     to compute an end-to-end optimal path across layers.
  
     Figure 3 shows multiple PCE inter-layer computation with inter-PCE
     communication. There is one PCE in each layer. The PCEs from each
     layer collaborate to compute an end-to-end path across layers. PCE
     Hi is responsible for computations in the higher layer and may
     “consultEwith PCE Lo to compute paths across the lower layer. PCE
     Lo is responsible for path computation in the lower layer. A
     simple example of cooperation between the PCEs could be as
     follows:
     - LSR H1 sends a request for a path H1-H4 to PCE Hi
     - PCE Hi selects H2 as the entry point to the lower layer, and H3
     as the exit point.
     - PCE Hi requests a path H2-H3 from PCE Lo.
     - PCE Lo returns H2-L1-L2-H3 to PCE Hi.
     - PEC Hi is now able to compute the full path (H1-H2-L1-L2-H3-H4)
     and return it to H1.
  
     Of course more complex cooperation may be required if an optimal
     end-to-end path is desired.
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
  
  
                                  -----
                                 | PCE |
                                 | Hi  |
                                  --+--
                                    |
         -----    -----             |            -----    -----
        | LSR |--| LSR |............|...........| LSR |--| LSR |
        | H1  |  | H2  |            |           | H3  |  | H4  |
         -----    -----\          --+--         /-----    -----
                        \        | PCE |       /
                         \       | Lo  |      /
                          \       -----      /
                           \                /
                            \-----    -----/
                            | LSR |--| LSR |
                            | L1  |  | L2  |
                             -----    -----
  
     Figure 3: Multiple PCE Inter-Layer Path Computation with Inter-PCE
     Communication
  
     Figure 4 shows multiple PCE inter-layer path computation without
     inter-PCE communication. As described in Section 2, separate path
     computations are performed on behalf of the TE-LSP head-end and
     each transit border LSR that is the entry point to a new layer.
  
                                  -----
                                 | PCE |
                                 | Hi  |
                                  -----
  
         -----    -----                          -----    -----
        | LSR |--| LSR |........................| LSR |--| LSR |
        | H1  |  | H2  |                        | H3  |  | H4  |
         -----    -----\          -----         /-----    -----
                        \        | PCE |       /
                         \       | Lo  |      /
                          \       -----      /
                           \                /
                            \-----    -----/
                            | LSR |--| LSR |
                            | L1  |  | L2  |
                             -----    -----
  
     Figure 4: Multiple PCE Inter-layer Path Computation without Inter-
     PCE Communication
  
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
  3.3.  General Observations
  
     - Depending on implementation details, the time to perform inter-
     layer path computation in the Single PCE inter-layer path
     computation model may be less than that of the Multiple PCE model
     with cooperating mono-layer PCEs, because there is no requirement
     to exchange messages between cooperating PCEs.
  
     - When TE topology for all layer networks is visible within one
     routing domain, the single PCE inter-layer path computation model
     may be adopted because a PCE is able to collect all layersETE
     topologies by participating in only one routing domain.
  
     - As the single PCE inter-layer path computation model uses more
     TE topology information in one computation than is used by PCEs in
     the Multiple PCE path computation model, it requires more
     computation power and memory.
  
     When there are multiple candidate layer border nodes (we may say
     that the higher layer is multi-homed), optimal path computation
     requires that all the possible paths transiting different layer
     border nodes or links be examined. This is relatively simple in
     the single PCE inter-layer path computation model because the PCE
     has full visibility Ethe computation is similar to the
     computation within a single domain of a single layer. In the
     multiple PCE inter-layer path computation model, backward
     recursive techniques described in [BRPC] could be used, by
     considering layers as separate domains.
  
  4. Inter-Layer Path Control
  
  4.1.  VNT Management
  
     As a result of inter-layer path computation, a PCE may determine
     that there is insufficient bandwidth available in the higher-layer
     network to support this or future higher-layer LSPs. The problem
     might be resolved if new LSPs were provisioned across the lower-
     layer network. Furthermore, the modification, re-organization and
     new provisioning of lower-layer LSPs may enable better utilization
     of lower-layer network resources given the demands of the higher-
     layer network. In other words, the VNT needs to be controlled or
     managed in cooperation with inter-layer path computation.
  
     A VNT Manager (VNTM) is defined as a functional element that
     manages and controls the VNT. PCE and VNT Manager are distinct
     functional elements that may or may not be co-located.
  
  4.2.  Inter-Layer Path Control Models
  
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
   4.2.1.            PCE-VNTM Cooperation Model
  
        -----      ------
       | PCE |--->| VNTM |
        -----      ------
          ^           :
          :           :
          :           :
          v           V
         -----      -----                  -----      -----
        | LSR |----| LSR |................| LSR |----| LSR |
        | H1  |    | H2  |                | H3  |    | H4  |
         -----      -----\                /-----      -----
                          \-----    -----/
                          | LSR |--| LSR |
                          | L1  |  | L2  |
                           -----    -----
  
     Figure 5: PCE-VNTM Cooperation Model
  
     A multi-layer network consists of higher-layer and lower-layer
     networks. LSRs H1, H2, H3, and H4 belong to the higher-layer
     network, LSRs H2, L1, L2, and H3 belong to the lower-layer network,
     as shown in Figure 5. The case of single PCE inter-layer path
     computation is considered here to explain the cooperation model
     between PCE and VNTM, but multiple PCE path computation with or
     without inter-PCE communication can also be applied to this model.
  
     Consider that H1 requests the PCE to compute an inter-layer path
     between H1 and H4. There is no TE link in the higher-layer between
     H2 and H3 before the path computation request, so the request
     fails. But the PCE may provide information to the VNT Manager
     responsible for the lower layer network that may help resolve the
     situation for future higher-layer LSP setup.
  
     The roles of PCE and VNTM are as follows. PCE performs inter-layer
     path computation and is unable to supply a path because there is
     no TE link between H2 and H3. The computation fails, but PCE
     suggests to VNTM that a lower-layer LSP (H2-H3) could be
     established to support future LSP requests. Messages from PCE to
     VNTM contain information about the higher-layer demand (from H2 to
     H3), and may include a suggested path in the lower layer (if the
     PCE has visibility into the lower layer network). VNTM uses local
     policy and possibly management/configuration input to determine
     how to process the suggestion from PCE, and may request an ingress
     LSR (e.g. H2) to establish a lower-layer LSP. VNTM or the ingress
     LSR (H2) may themselves use a PCE with visibility into the lower
     layer to compute the path of this new LSP.
  
  
  
  
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     When the higher-layer PCE fails to compute a path and notifies
     VNTM, it may wait for the lower-layer LSP to be set up and
     advertised as a TE link. PCE may have a timer. After TED is
     updated within a specified duration, PCE will know a new TE link.
     It could then compute the complete end-to-end path for the higher-
     layer LSP and return the result to the PCC. In this case, the PCC
     may be kept waiting for some time, and it is important that the
     PCC understands this. It is also important that the PCE and VNTM
     have an agreement that the lower-layer LSP will be set up in a
     timely manner, or that the PCE will be notified by VNTM that no
     new LSP will become available. In any case, if the PCE decides to
     wait, it must operates a timeout. An example of such a cooperative
     procedure between PCE and VNTM is as follows using the example
     network in Figure 4.
  
     Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4.
  
     Step 2: The path computation fails because there is no TE link
     across the lower-layer network.
  
     Step 3: PCE suggests to VNTM that a new TE link connecting H2 and
     H3 would be useful. The PCE notifies VNTM that it will be waiting
     for the TE link to be created. VNTM considers whether lower-layer
     LSPs should be established if necessary and if acceptable within
     VNTM’s policy constraints.
  
     Step 4: VNTM requests an ingress LSR in the lower-layer network
     (e.g., H2) to establish a lower-layer LSP. The request message may
     include a lower-layer LSP route obtained from the PCE responsible
     for the lower-layer network.
  
     Step 5: The ingress LSR signals to establish the lower-layer LSP.
  
     Step 6: If the lower-layer LSP setup is successful, the ingress
     LSR notifies VNTM that the LSP is complete and supplies the tunnel
     information.
  
     Step 7: The ingress LSR (H2) advertises the new LSP as a TE link
     in the higher-layer network routing instance.
  
     Step 8: PCE notices the new TE link advertisement and recomputes
     the requested path.
  
     Step 9: PCE replies to H1 (PCC) with a computed higher-layer LSP
     route. The computed path is categorized as a mono-layer path that
     includes the already-established lower layer-LSP as a single hop
     in the higher layer. The higher-layer route is specified as H1-H2-
     H3-H4, where all hops are strict.
  
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
     Step 9: H1 initiates signaling with the computed path H2-H3-H4 to
     establish the higher-layer LSP.
  
  
  
   4.2.2.            Higher-Layer Signaling Trigger Model
  
  
        -----
       | PCE |
        -----
          ^
          :
          :
          v
         -----      -----                  -----    -----
        | LSR |----| LSR |................| LSR |--| LSR |
        | H1  |    | H2  |                | H3  |  | H4  |
         -----      -----\                /-----    -----
                          \-----    -----/
                          | LSR |--| LSR |
                          | L1  |  | L2  |
                           -----    -----
  
     Figure 6: Higher-layer Signaling Trigger Model
  
     Figure 6 shows the higher-layer signaling trigger model. The case
     of single PCE path computation is considered to explain the
     higher-layer signaling trigger model here, but multiple PCE path
     computation with/without inter-PCE communication can also be
     applied to this model.
  
  
     As in the case described in Section 4.2.1, consider that H1
     requests PCE to compute a path between H1 and H4. There is no TE
     link in the higher-layer between H2 and H3 before the path
     computation request.
  
     PCE is unable to compute a mono-layer path, but may judge that the
     establishment of a lower-layer LSP between H2 and H3 would provide
     adequate connectivity. If the PCE has inter-layer visibility it
     may return a path that includes hops in the lower layer (H1-H2-L1-
     L2-H3-H4), but if it has no visiblity into the lower layer, it may
     return a path with a loose hop from H2 to H3 (H1-H2-H3(loose)-H4).
     The former is a multi-layer path, and the latter a mono-layer path
     that includes loose hops.
  
     In the higher-layer signaling trigger model with a multi-layer
     path, the LSP route supplied by the PCE includes the route of a
  
  
  
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     lower-layer LSP that is not yet established. A border LSR that is
     located at the boundary between the higher-layer and lower-layer
     networks (H2 in this example) receives a higher-layer signaling
     message, notices that the next hop is in the lower-layer network,
     starts to setup the lower-layer LSP as described in [RFC4206].
     Note that these actions depends on a policy being applied at the
     border LSR. An example procedure of the signaling trigger model
     with a multi-layer path is as follows.
  
     Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4.
     The request indicates that inter-layer path computation is allowed.
  
     Step 2: As a result of the inter-layer path computation, PCE
     judges that a new lower-layer LSP needs to be established.
  
     Step 3: PCE replies to H1 (PCC) with a computed multi-layer route
     including higher-layer and lower-layer LSP routes. The route may
     be specified as H1-H2-L1-L2-H3-H4, where all hops are strict.
  
     Step 4: H1 initiates higher-layer signaling using the computed
     explicit router of H2-L1-L2-H3-H4.
  
     Step 5: The border LSR (H2) that receives the higher-layer
     signaling message starts lower-layer signaling to establish a
     lower-layer LSP along the specified lower-layer route of H2-L1-L2-
     H3. That is, the border LSR recognizes the hops within the
     explicit route that apply to the lower-layer network, verifies
     with local policy that a new LSP is acceptable, and establishes
     the required lower-layer LSP. Note that it is possible that a
     suitable lower-layer LSP has already been established (or become
     available) between the time that the computation was performed and
     the moment when the higher-layer signaling message reached the
     border LSR. In this case, the border LSR may select such a lower-
     layer LSP without the need to signal a new LSP provided that the
     lower-layer LSP satisfies the explicit route in the higher-layer
     signaling request.
  
     Step 6: After the lower-layer LSP is established, the higher-layer
     signaling continues along the specified higher-layer route of H2-
     H3-H4 using hierarchical signaling [RFC4206].
  
     On the other hand, in the signaling trigger model with a mono-
     layer path, a higher-layer LSP route includes a loose hop to
     traverse the lower-layer network between the two border LSRs. A
     border LSR that receives a higher-layer signaling message needs to
     determine a path for a new lower-layer LSP. It applies local
     policy to verify that a new LSP is acceptable and then either
     consults a PCE with responsibility for the lower-layer network or
     computes the path by itself, and initiates signaling to establish
  
  
  
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     the lower-layer LSP. Again, it is possible that a suitable lower-
     layer LSP has already been established (or become available). In
     this case, the border LSR may select such a lower-layer LSP
     without the need to signal a new LSP provided that the existing
     lower-layer LSP satisfies the explicit route in the higher-layer
     signaling request. Since the higher-layer signaling request used a
     loose hop without specifying any specifics of the path within the
     lower-layer network, the border LSR has greater freedom to choose
     a lower-layer LSP than in the previous example.
  
     The difference between procedures of the signaling trigger model
     with a multi-layer path and a mono-layer path is Step 5. Step 5 of
     the signaling trigger model with a mono layer path is as follows:
  
     Step 5E The border LSR (H2) that receives the higher-layer
     signaling message applies local policy to verify that a new LSP is
     acceptable and then initiates establishment of a lower-layer LSP.
     It either consults a PCE with responsibility for the lower-layer
     network or computes the route by itself to expand the loose hop
     route in the higher-layer path.
  
     Finally, note that a virtual TE link may have been advertised into
     the higher-layer network. This causes the PCE to return a path H1-
     H2-H3-H4 where all the hops are strict. But when the higher-layer
     signaling message reaches the layer border node H2 (that was
     responsible for advertising the virtual TE link) it realizes that
     the TE link does not exist yet, and signals the necessary LSP
     across the lower-layer network using its own path determination
     (just as for a loose hop in the higher layer) before continuing
     with the higher-layer signaling.
  
     PCE
      ^
      :
      :
      V
     H1--H2                  H3--H4
          \                  /
           L1==L2==L3--L4--L5
                    |
                    |
                   L6--L7
                         \
                          H5--H6
  
     Figure 7: Example of a Multi-Layer Network
  
     Examples of multi-layer EROs are explained using Figure 7. It is
     described how lower-layer LSP setup is performed in the higher-
  
  
  
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     layer signaling trigger model using an ERO that can include
     subobjects in both the higher and lower layers. It gives rise to
     several options for the ERO when it reaches the last LSR in the
     higher layer network (H2).
     1. The next subobject is a loose hop to H3 (mono layer ERO).
     2. The next subobject is a strict hop to L1 followed by a loose
     hop to H3.
     3. The next subobjects are a series of hops (strict or loose) in
     the lower-layer network followed by H3. For example, {L1(strict),
     L3(loose), L5(loose), H3(strict)}
  
     In the first example, the lower layer can utilize any LSP tunnel
     that will deliver the end-to-end LSP to H3. In the third case, the
     lower layer must select an LSP tunnel that traverses L3 and L5.
     However, this does not mean that the lower layer can or should use
     an LSP from L1 to L3 and another from L3 to L5.
  
  
  
   4.2.3.           NMS-VNTM Cooperation Model
  
         -----
        | NMS |
        |     |   -----
         -----   | PCE |
         ^   ^   | Hi  |
         :   :    -----
         :   :    ^
         :   :    :
         :   :    :
         :   v    v
         :   ------    -----                          -----    ------
         :  | LSR  |--| LSR |........................| LSR |--| LSR  |
         :  | H1   |  | H2  |                        | H3  |  | H4   |
         :   ------    -----\                        /-----    ------
         :             ^     \                      /
         :             :      \                    /
         :     --------        \                  /
         v    :                 \                /
         ------      -----       \-----    -----/
        | VNTM |<-->| PCE |      | LSR |--| LSR |
        |      |    | Lo  |      | L1  |  | L2  |
         ------      -----        -----    -----
  
     Figure 8: NMS-VNTM Cooperation Model
  
     Figure 8 show the Network Management System (NMS)-VNTM cooperation
     model. The NMS manages the upper layer. The case of multiple PCE
     computation without inter-PCE communication is used to explain the
  
  
  
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     NMS-VNTM cooperation model here, but single PCE path computation
     could also be applied to this model. Note that multiple PCE path
     computation with inter-PCE communication does not fit in with this
     model.
  
     The NMS requests a head-end LSR (H1 in this example) to set up a
     higher-layer LSP between head-end and tail-end LSRs without
     specifying any route. The head-end LSR, which is a PCC, requests
     the higher-layer PCE to compute a path between head-end and tail-
     end LSRs. There is no TE link in the higher-layer between border
     LSRs (H2 and H3 in this example). When the PCE fails to compute a
     path, it informs the PCC (i.e. head-end LSR) that notifies the NMS.
     The notification may include the information that there is no TE
     link between the border LSRs.
  
     Note that it is equally valid for the higher-layer PCE to be
     consulted by the NMS rather than by the head-end LSR. In this case,
     the result is the same Ethe NMS discovers that an end-to-end LSP
     cannot be provisioned owing to the lack of a TE link between H2
     and H3.
  
     The NMS may now suggest (or request) to the VNTM that a lower-
     layer LSP between the border LSRs could be established and could
     be advertised as a TE link in the higher layer to support future
     higher-layer LSP requests. The communication between the NMS and
     the VNTM may be performed in an automatic manner or in a manual
     manner, and is a key interaction between layers that may also be
     separate administrative domains. Thus, this communication is
     potentially a point of application of administrative, billing, and
     security policy. The NMS may wait for the lower-layer LSP to be
     set up and advertised as a TE link, or may reject the operator's
     request for the service that requires the higher-layer LSP with a
     suggestion that the operator tries again later.
  
     The VNTM requests the lower-layer PCE to compute a path, and then
     requests H2 to establish a lower-layer LSP. Alternatively, the
     VNTM may make a direct request to H2 for the LSP, and H2 may
     consult the lower-layer PCE. After the NMS is informed or notices
     that the lower-layer LSP has been established, it can request the
     head-end LSR (H1) to set up the higher-layer end-to-end LSP
     between H1 and H4.
  
     Thus, cooperation between the high layer and lower layer is
     performed though communication between NMS and VNTM. An example of
     such a procedure of the NSM-VNTM cooperation model is as follows
     using the example network in Figure 6.
  
     Step 1: NMS requests a head-end LSR (H1) to set up a higher-layer
     LSP between H1 and H4 without specifying any route.
  
  
  
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     Step 2: H1 (PCC) requests PCE to compute a path between H2 and H3.
  
     Step 3: The path computation fails because there is no TE link
     across the lower-layer network.
  
     Step 4: H1 (PCC) notifies NMS. The notification may include an
     indication that there is no TE link between H2 and H4.
  
     Step 5: NMS suggests (or requests) to VNTM that a new TE link
     connecting H2 and H3 would be useful. The NMS notifies VNTM that
     it will be waiting for the TE link to be created. VNTM considers
     whether lower-layer LSPs should be established if necessary and if
     acceptable within VNTM’s policy constraints.
  
     Step 6: VNTM requests the lower-layer PCE for path computation.
  
     Step 7: VNTM requests the ingress LSR in the lower-layer network
     (H2) to establish a lower-layer LSP. The request message includes
     a lower-layer LSP route obtained from the lower-layer PCE
     responsible for the lower-layer network.
  
     Step 5: H2 signals the lower-layer LSP.
  
     Step 6: If the lower-layer LSP setup is successful, H2 notifies
     VNTM that the LSP is complete and supplies the tunnel information.
  
     Step 7: H2 advertises the new LSP as a TE link in the higher-layer
     network routing instance.
  
     Step 8: VNTM notifies NMS that the underlying lower-layer LSP has
     been set up, and NMS notices the new TE link advertisement.
  
     Step 9: NMS again requests H1 to set up a higher-layer LSP between
     H1 and H4.
  
     Step 10: H1 requests the higher-layer PCE to compute a path and
     obtains a successful result that includes the higher-layer route
     that is specified as H1-H2-H3-H4, where all hops are strict.
  
     Step 11: H1 initiates signaling with the computed path H2-H3-H4 to
     establish the higher-layer LSP.
  
  
   4.2.4.            Possible Combinations of Inter-Layer Path Computation and
       Inter-Layer Path Control Models
  
     Table 1 summarizes the possible combinations of inter-layer path
     computation and inter-layer path control models. There are three
  
  
  
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     inter-layer path computation models: the single PCE path
     computation model; the multiple PCE path computation with inter-
     PCE communication model; and the multiple PCE path computation
     without inter-PCE communication model. There are also three inter-
     layer path control models:  the PCE-VNTM cooperation model; the
     higher-layer signaling trigger model; and the NMS-VNTM cooperation
     model. All the combinations between inter-layer path computation
     and path control models, except for the combination of the
     multiple PCE path computation with inter-layer PCE communication
     model and the NMS-VNTM cooperation model are possible.
  
     Table 1: Possible Combinations of Inter-Layer Path Computation and
     Inter-Layer Path Control Models.
  
      ----------------------------------------------------
     | Path computation  | Single | Multiple  | Multiple  |
     |      \            | PCE    | PCE with  | PCE w/o   |
     | Path control      |        | inter-PCE | inter-PCE |
     |----------------------------------------------------|
     | PCE-VNTM          |  Yes   | Yes       | Yes       |
     | cooperation       |        |           |           |
     |----------------------------+-----------+-----------|
     | Higher-layer      |  Yes   | Yes       | Yes       |
     | signaling trigger |        |           |           |
     |----------------------------------------------------|
     | NMS-VNTM          |  No*   | No        | Yes       |
     | cooperation       |        |           |           |
      -------------------+--------+-----------+-----------
  
     *Note that, in case of NSM-VNTM cooperation and single PCE inter-
     layer path computation, the PCE function used by NMS and VNTM may
     be collocated, but it will operate on separate TEDs.
  
  
  
  5. Choosing Between Inter-Layer Path Control Models
  
     This section compares the cooperation model between PCE and VNTM,
     and the higher-layer signaling trigger model, in terms of VNTM
     functions, border LSR functions, higher-layer signaling time, and
     complexity (in terms of number of states and messages). An
     appropriate model may be chosen by a network operator in different
     deployment scenarios taking all these considerations into account.
  
  5.1. VNTM Functions:
  
     VNTM functions are required in both the PCE-VNTM cooperation model
     and the NMS-VNTM model. In the PCE-VNTM cooperation model,
     communications are required between PCE and VNTM, and between VNTM
  
  
  
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     and a border LSR. Communications between a higher-layer PCE and
     the VNTM are event notifications and may use SNMP notifications
     from the PCE MIB modules [PCE-MIB]. Note that communications from
     the PCE to the VNTM do not have any acknowledgements.
  
     VNTM-LSR communication can use existing GMPLS-TE MIB modules
     [RFC4802]. In the NMS-VNTM cooperation model, communications are
     required between NMS and VNTM, between VNTM and a lower-layer PCE,
     and between VNTM and a border LSR. NMS-VNTM communications, which
     are out of scope of this document, may use proprietary or standard
     interfaces, some of which, for example, are standardized in TM
     Forum. Communications between VNTM and a lower-layer PCE use PCEP
     [PCEP]. VNTM-LSR communications are the same as in the PCE-VNTM
     cooperation model.
  
     In the higher-layer signaling trigger model, no VNTM functions are
     required, and no such communications are required.
  
     If VNTM functions are not supported in a multi-layer network, the
     higher-layer signaling trigger model has to be chosen.
  
     The inclusion of VNTM functionality allows better coordination of
     cross-network LSP tunnels and application of network-wide policy
     that is far harder to apply in the trigger model since it requires
     the coordination of policy between multiple border LSRs.
  
  5.2. Border LSR Functions:
  
     In the higher-layer signaling trigger model, a border LSR must
     have some additional functions. It needs to trigger lower-layer
     signaling when a higher-layer path message suggests that lower-
     layer LSP setup is necessary. Note that, if virtual TE links are
     used, the border LSRs must be capable of triggered signaling.
  
     If the ERO in the higher-layer Path message uses a mono-layer path
     or specifies a loose hop, the border LSR receiving the Path
     message must obtain a lower-layer route either by consulting a PCE
     or by using its own computation engine. If the ERO in the higher-
     layer Path message uses a multi-layer path, the border LSR must
     judge whether lower-layer signaling is needed.
  
     In the PCE-VNTM cooperation model and the NMS-VNTM model, no
     additional function for triggered signaling is required in border
     LSRs except when virtual TE links are used. Therefore, if these
     additional functions are not supported in border LSRs, where a
     border LSR is controlled by VNTM to set up a lower-layer LSP, the
     cooperation model has to be chosen.
  
  
  
  
  
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  5.3. Complete Inter-Layer LSP Setup Time:
  
     The complete inter-layer LSP setup time includes inter-layer path
     computation, signaling, and the communication time between PCC and
     PCE, PCE and VNTM, NSM and VNTM, and VNTM and LSR. In the PCE-VNTM
     cooperation model and the NMS-VNTM model, the additional
     communication steps are required compared with the higher-layer
     signaling trigger model. On the other hand, the cooperation model
     provides better control at the cost of a longer service setup time.
  
     Note that, in terms of higher-layer signaling time, in the higher-
     layer signaling trigger model, the required time from when higher-
     layer signaling starts to when it is completed, is more than that
     of the cooperation model except when a virtual TE link is included.
     This is because the former model requires lower-layer signaling to
     take place during the higher-layer signaling. A higher-layer
     ingress LSR has to wait for more time until the higher-layer
     signaling is completed. A higher-layer ingress LSR is required to
     be tolerant of longer path setup times.
  
  5.4. Network Complexity
  
     If the higher and lower layer networks have multiple interconnects
     then optimal path computation for end-to-end LSPs that cross the
     layer boundaries is non-trivial. The higher layer LSP must be
     routed to the correct layer border nodes to achieve optimality in
     both layers.
  
     Where the lower layer LSPs are advertised into the higher layer
     network as TE links, the computation can be resolved in the higher
     layer network. Care needs to be taken in the allocation of TE
     metrics (i.e., costs) to the lower layer LSPs as they are
     advertised as TE links into the higher layer network, and this
     might be a function for a VNT Manager component. Similarly,
     attention should be given to the fact that the LSPs crossing the
     lower-layer network might share points of common failure (e.g.,
     they might traverse the same link in the lower-layer network) and
     the shared risk link groups (SRLGs) for the TE links advertised in
     the higher-layer must be set accordingly.
  
     In the single PCE model an end-to-end path can be found in a
     single computation because there is full visibility into both
     layers and all possible paths through all layer interconnects can
     be considered.
  
     Where PCEs cooperate to determine a path, an iterative computation
     model such as [BRPC] can be used to select an optimal path across
     layers.
  
  
  
  
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     When non-cooperating mono-layer PCEs, each of which is in a
     separate layer, are used with the triggered LSP model, it is not
     possible to determine the best border LSRs, and connectivity
     cannot even be guaranteed. In this case, signaling crankback
     techniques [CRANK] can be used to eventually achieve connectivity,
     but optimality is far harder to achieve. In this model, a PCE that
     is requested by an ingress LSR to compute a path expects a border
     LSR to setup a lower-layer path triggered by high-layer signaling
     when there is no TE link between border LSRs.
  
  5.5. Separation of Layer Management
  
     Many network operators may want to provide a clear separation
     between the management of the different layer networks. In some
     cases, the lower layer network may come from a separate commercial
     arm of an organization or from a different corporate body entirely.
     In these cases, the policy applied to the establishment of LSPs in
     the lower-layer network and to the advertisement of these LSPs as
     TE links in the higher-layer network will reflect commercial
     agreements and security concerns (see next section). Since the
     capacity of the LSPs in the lower-layer network are likely to be
     significantly larger than those in the client higher-layer network
     (multiplex-server model), the administrator of the lower-layer
     network may want to exercise caution before allowing a single
     small demand in the higher layer to tie up valuable resources in
     the lower layer.
  
     The necessary policy points for this separation of administration
     and management are more easily achieved through the VNTM approach
     than by using triggered signaling. In effect, the VNTM is the
     coordination point for all lower layer LSPs and can be closely
     tied to a human operator as well as to policy and billing. Such a
     model can also be achieved using triggered signaling.
  
  6. Manageability Considerations
  
     Inter-layer MPLS or GMPLS traffic engineering must be considered
     in the light of administrative and management boundaries that are
     likely to coincide with the technology layer boundaries. That is,
     each layer network may possibly be under separate management
     control with different policies applied to the networks, and
     specific policy rules applied at the boundaries between the layers.
  
     Management mechanisms are required to make sure that inter-layer
     traffic engineering can be applied without violating the policy
     and administrative operational procedures used by the network
     operators.
  
  
  
  
  
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  6.1.  Control of Function and Policy
  
   6.1.1.           Control of Inter-Layer Computation Function
  
     PCE implementations that are capable of supporting inter-layer
     computations should provide a configuration switch to allow
     support of inter-layer path computations to be enabled or disabled.
  
     When a PCE is capable of, and configured for, inter-layer path
     computation, it should advertise this capability as described in
     [PCE-INTER-LAYER-REQ], but this advertisement may be suppressed
     through a secondary configuration option.
  
   6.1.2.           Control of Per-Layer Policy
  
     Where each layer is operated as a separate network, the operators
     must have control over the policies applicable to each network,
     and that control should be independent of the control of policies
     for other networks.
  
     Where multiple layers are operated as part of the same network,
     the operator may have a single point of control for an integrated
     policy across all layers, or may have control of separate policies
     for each layer.
  
   6.1.3.           Control of Inter-Layer Policy
  
     Probably the most important issue for inter-layer traffic
     engineering is inter-layer policy. This may cover issues such as
     under what circumstances a lower layer LSP may be established to
     provide connectivity in the higher layer network. Inter-layer
     policy may exist to protect the lower layer (high capacity)
     network from very dynamic changes in micro-demand in the higher
     layer network. It may also be used to ensure appropriate billing
     for the lower layer LSPs.
  
     Inter-layer policy SHOULD include the definition of the points of
     connectivity between the network layers, the inter-layer TE model
     to be applied (for example, the selection between the models
     described in this document), and the rules for path computation
     and LSP setup. Where inter-layer policy is defined, it MUST be
     used consistently throughout the network, and SHOULD be made
     available to the PCEs that perform inter-layer computation so that
     appropriate paths are computed. Mechanisms for providing policy
     information to PCEs are discussed in [PCE-POLICY].
  
     VNTM may provide a suitable functional component for the
     implementation of inter-layer policy. Use of VNTM allows the
     administrator of the lower layer network to apply inter-layer
  
  
  
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     policy without making that policy public to the operator of the
     higher layer network. Similarly, a cooperative PCE model (with or
     without inter-PCE communication) allows separate application of
     policy during the selection of paths.
  
  6.2. Information and Data Models
  
     Any protocol extensions to support inter-layer computations MUST
     be accompanied by the definition of MIB objects for the control
     and monitoring of the protocol extensions. These MIB object
     definitions will conventionally be placed in a separate document
     from that which defines the protocol extensions. The MIB objects
     MAY be provided in the same MIB module as used for the management
     of the base protocol that is being extended.
  
     Note that inter-layer PCE functions SHOULD, themselves, be
     manageable through MIB modules. In general, this means that the
     MIB modules for managing PCEs SHOULD include objects that can be
     used to select and report on the inter-layer behavior of each PCE.
     It MAY also be appropriate to provide statistical information that
     reports on the inter-layer PCE interactions.
  
     Where there are communications between a PCE and VNTM, additional
     MIB modules MAY be necessary to manage and model these
     communications. On the other hand, if these communications are
     provided through MIB notifications, then those notifications MUST
     form part of a MIB module definition.
  
     Policy Information Base (PIB) modules MAY also be appropriate to
     meet the requirements as described in Section 6.1 and [PCE-POLICY].
  
  6.3. Liveness Detection and Monitoring
  
     Liveness detection and monitoring is required between PCEs and
     PCCs, and between cooperating PCEs as described in [RFC4657].
     Inter-layer traffic engineering does not change this requirement.
  
     Where there are communications between a PCE and VNTM, additional
     liveness detection and monitoring MAY be required to allow the PCE
     to know whether the VNTM has received its information about failed
     path computations and desired TE links.
  
     When a lower layer LSP fails (perhaps because of the failure of a
     lower layer network resource) or is torn down as a result of lower
     layer network policy, the consequent change SHOULD be reported to
     the higher layer as a change in the VNT, although inter-layer
     policy MAY dictate that such a change is hidden from the higher
     layer. The upper layer network MAY additionally operate data plane
     failure techniques over the virtual TE links in the VNT in order
  
  
  
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     to monitor the liveness of the connections, but it should be noted
     that if the virtual TE link is advertised but not yet established
     as an LSP in the lower layer, such higher layer OAM techniques
     will report a failure.
  
  6.4. Verifying Correct Operation
  
     The correct operation of the PCE computations and interactions are
     described in [RFC4657], [PCEP], etc., and does not need further
     discussion here.
  
     The correct operation of inter-layer traffic engineering may be
     measured in several ways. First, the failure rate of higher layer
     path computations owing to an absence of connectivity across the
     lower layer may be observed as a measure of the effectiveness of
     the VNT and MAY be reported as part of the data model described in
     Section 6.2. Second, the rate of change of the VNT (i.e., the rate
     of establishment and removal of higher layer TE links based on
     lower layer LSPs) may be seen as a measure of the correct planning
     of the VNT and MAY also form part of the data model described in
     Section 6.2. Third, network resource utilization in the lower
     layer (both in terms of resource congestion, and in consideration
     of under utilization of LSPs set up to support virtual TE links)
     can indicate whether effective inter-layer traffic engineering is
     being applied.
  
     Management tools in the higher layer network SHOULD provide a view
     of which TE links are provided using planned lower layer capacity
     (that is, physical connectivity or permanent connections) and
     which TE links are dynamic and achieved through inter-layer
     traffic engineering. Management tools in the lower layer SHOULD
     provide a view of the use to which lower layer LSPs are put
     including whether they have been set up to support TE links in a
     VNT, and if so for which client network.
  
  6.5. Requirements on Other Protocols and Functional Components
  
     There are no protocols or protocol extensions defined in this
     document and so it is not appropriate to consider specific
     interactions with other protocols. It should be noted, however,
     that the objective of this document is to enable inter-layer
     traffic engineering for MPLS-TE and GMPLS networks and so it is
     assumed that the necessary features for inter-layer operation of
     routing and signaling protocols are in existence or will be
     developed.
  
     This document introduces roles for various network components (PCE,
     LSR, NMS, and VNTM). Those components are all required to play
     their part in order that inter-layer TE can be effective. That is,
  
  
  
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     an inter-layer TE model that assumes the presence and operation of
     any of these functional components obviously depends on those
     components to fulfill their roles as described in this document.
  
  6.6. Impact on Network Operation
  
     The use of a PCE to compute inter-layer paths is expected to have
     a significant and beneficial impact on network operations. Inter-
     layer traffic engineering of itself may provide additional
     flexibility to the higher layer network while allowing the lower
     layer network to support more and varied client networks in a more
     efficient way. Traffic engineering across network layers allows
     optimal use to be made of network resources in all layers.
  
     The use of PCE as described in this document may also have a
     beneficial effect on the loading of PCEs responsible for
     performing inter-layer path computation while facilitating a more
     independent operation model for the network layers.
  
  7. Security Considerations
  
     Inter-layer traffic engineering with PCE raises new security
     issues in all three inter-layer path control models.
  
     In the cooperation model between PCE and VNTM, when the PCE
     determines that a new lower-layer LSP is desirable, communications
     are needed between the PCE and VNTM and between VNTM and a border
     LSR. In this case, these communications should have security
     mechanisms to ensure authenticity, privacy and integrity of the
     information exchanged. In particular, it is important to protect
     against false triggers for LSP setup in the lower-layer network
     since such falsification could tie up lower-layer network
     resources (achieving a denial of service attack on the lower-layer
     network and on the higher layer network that is attempting to use
     it) and could result in incorrect billing for services provided by
     the lower-layer network. Where the PCE MIB modules are used to
     provide the notification exchanges between the higher-layer PCE
     and the VNTM, SNMP v3 should be used to ensure adequate security.
     Additionally, the VNTM should provide configurable or dynamic
     policy functions so that the VNTM behavior upon receiving
     notification from a higher-layer PCE can be controlled.
  
  
     The main security concern in the higher-layer signaling trigger
     model is related to confidentiality. The PCE may inform a higher-
     layer PCC about a multi-layer path that includes an ERO in the
     lower-layer network, but the PCC may not have TE topology
     visibility into the lower-layer network and might not be trusted
     with this information. A loose hop across the lower-layer network
  
  
  
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         draft-ietf-pce-inter-layer-frwk-05.txt   September 2007
  
     could be used, but this decreases the benefit of multi-layer
     traffic engineering. A better alternative may be to mask the
     lower-layer path using a path key [PATH-KEY] that can be expanded
     within the lower-layer network. Consideration must also be given
     to filtering the recorded path information from the lower-layer E
     see [RFC4208], for example.
  
     Additionally, in the higher-layer signaling trigger model,
     consideration must be given to the security of signaling at the
     inter-layer interface since the layers may belong to different
     administrative or trust domains.
  
     The NMS-VNTM cooperation model introduces communication between
     the NMS and the VNTM. Both of these components belong to the
     management plane and the communication is out of scope for this
     PCE document. Note that the NMS-VNTM cooperation model may be
     considered to address many security and policy concerns because
     the control and decision-making is placed within the sphere of
     influence of the operator in contrast to the more dynamic
     mechanisms of the other models. However, the security issues have
     simply moved, and will require authentication of operators and of
     policy.
  
     Security issues may also exist when a single PCE is granted full
     visibility of TE information that applies to multiple layers. Any
     access to the single PCE will immediately gain access to the
     topology information for all network layers Eeffectively, a
     single security breach can expose information that requires
     multiple breaches in other models.
  
  8. Acknowledgments
  
    We would like to thank Kohei Shiomoto, Ichiro Inoue, Julien Meuric,
    Jean-Francois Peltier, Young Lee, and Ina Minei for their useful
    comments.
  
  9. References
  
  9.1.  Normative Reference
  
     [RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
     "Multiprotocol Label Switching Architecture", RFC 3031, January
     2001.
     [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
     Architecture", RFC 3945, October 2004.
  
     [RFC4206] K. Kompella and Y. Rekhter, "Label Switched Paths (LSP)
     Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
     Traffic Engineering (TE)", RFC 4206, October 2005.
  
  
  
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  9.2.  Informative Reference
  
     [MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi-
     region networks (MRN)", draft-ietf-ccamp-gmpls-mln-reqs (work in
     progress).
  
     [PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication
     Requirements for Inter-Layer Traffic EngineeringE draft-ietf-pce-
     inter-layer-req (work in progress).
  
     [BRPC] JP. Vasseur et al., "A Backward Recursive PCE-based
     Computation (BRPC) procedure to compute shortest inter-domain
     Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc
     (work in progress).
  
     [CRANK] A. Farrel et al., "Crankback Signaling Extensions for MPLS
     and GMPLS RSVP-TE", RFC 4920, July 2007.
  
     [PCE-MIB] E. Stephan, "Definitions of Textual Conventions for Path
     Computation Element", draft-ietf-pce-tc-mib.txt (work in progress).
  
     [RFC4802] A. Farrel and T. Nadeau, "Generalized Multiprotocol
     Label Switching (GMPLS) Traffic Engineering Management Information
     Base", RFC 4802, February 2007.
  
     [PATH-KEY] Bradford, R., Vasseur, JP., and Farrel, A., "Preserving
     Topology Confidentiality in Inter-Domain Path Computation Using a
     Key Based Mechanism", draft-ietf-pce-path-key, work in progress.
  
     [RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Rekhter, Y.,
     " Generalized Multiprotocol Label Switching (GMPLS) User-Network
     Interface (UNI): Resource ReserVation Protocol-Traffic Engineering
     (RSVP-TE) Support for the Overlay Model", RFC 4208, October 2005.
  
     [RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
     Element (PCE)-Based Architecture", RFC 4655, August 2006.
  
     [RFC4657] J. Ash and J.L. Le Roux (Ed.), "Path Computation Element
     (PCE) Communication Protocol Generic Requirements", RFC 4657,
     September 2006.
  
     [PCE-POLICY] Bryskin, I., Papadimitriou, P., and Berger, L.,
     "Policy-Enabled Path Computation Framework", draft-ietf-pce-
     policy-enabled-path-comp, (work in progress).
  
     [PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
     communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
     (work in progress).
  
  
  
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  10.     AuthorsEAddresses
  
     Eiji Oki
     NTT
     3-9-11 Midori-cho,
     Musashino-shi, Tokyo 180-8585, Japan
     Email: oki.eiji@lab.ntt.co.jp
  
     Jean-Louis Le Roux
     France Telecom R&D,
     Av Pierre Marzin,
     22300 Lannion, France
     Email: jeanlouis.leroux@orange-ftgroup.com
  
     Adrian Farrel
     Old Dog Consulting
     Email: adrian@olddog.co.uk
  
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     IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
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