Internet DRAFT - draft-oki-pce-inter-layer-frwk

draft-oki-pce-inter-layer-frwk




     Network Working Group                                       Eiji Oki 
     Internet Draft                                                   NTT 
     Category: Informational                           Jean-Louis Le Roux 
     Expires: October 2006                                 France Telecom 
                                                            Adrian Farrel 
                                                       Old Dog Consulting 
                                                               April 2006 
      
         Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic 
                                 Engineering 
                                       
                    draft-oki-pce-inter-layer-frwk-00.txt 
      
   
                                       
     Status of this Memo 
      
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     Abstract 
      
     A network may comprise of multiple layers. It is important to 
     globally optimize network resources 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. 
      
     This document describes a framework for the PCE-based path 
     computation architecture to inter-layer MPLS and 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, 


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     and the relationship between PCE and a functional component called 
     the Virtual Network Topology Manager (VNTM). 
      
     Conventions used in this document 
      
     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
     "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in 
     this document are to be interpreted as described in RFC 2119 
     [RFC2119]. 
      
     Table of Contents 
      
    1. Terminology.....................................................2 
    2. Introduction....................................................2 
    3. Inter-Layer Path Computation....................................3 
    4. Inter-layer Path Computation Models.............................5 
    4.1.  Single PCE Inter-Layer Path Computation......................5 
    4.2.  Multiple PCE Inter-Layer Path Computation....................6 
    4.3.  General observation..........................................6 
    5. Inter-Layer Path Control........................................7 
    5.1.  VNT Management...............................................7 
    5.2.  Inter-Layer Path Control Models..............................7 
    5.2.1.  Cooperation model between PCE and VNTM.....................7 
    5.2.2.  Higher-Layer Signaling Trigger Model.......................9 
    5.2.3.  Examples of multi-layer ERO...............................11 
    6. Choosing between inter-layer path control models...............11 
    7. Security Considerations........................................13 
    8. Acknowledgment.................................................13 
    9. References.....................................................13 
    9.1.  Normative Reference.........................................13 
    9.2.  Informative Reference.......................................14 
    10.  Authors' Addresses...........................................14 
    11.  Intellectual Property Statement..............................15 
   
      
  1. Terminology 
      
     This document uses terminology from the PCE-based path computation 
     Architecture [PCE-ARCH] and also common terminology from Multi 
     Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS (GMPLS) 
     [RFC3945] and Multi-Layer Networks [MLN-REQ]. 
      
  2. Introduction 
      
     A network may comprise of multiple layers. These layers may 
     represent separations of technologies (e.g., packet switch capable 
     (PSC), time division multiplex (TDM) lambda switch capable (LSC)) 
     [RFC3945], separation of data plane switching granularity levels 
     (e.g. PSC-1, PSC-2, VC4, VC12) [MLN-REQ], or a distinction between 
     client and server networking roles. In this multi-layer network, 
     LSPs in a lower layer are used to carry higher-layer LSPs across 
       
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     the lower-layer network. The network topology formed by lower-layer 
     LSPs and advertised to the higher layer is called a Virtual Network 
     Topology (VNT) [MLN-REQ].  
      
     It is important 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 
     VNT by setting up and releasing LSPs in the lower layers [MLN-REQ]. 
      
     Inter-layer traffic engineering is included in the scope of the 
     PCE-based path computation architecture [PCE-ARCH], 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 forth in [PCE-INTER-LAYER-REQ]. 
      
     This document describes a framework for the PCE-based path 
     computation 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, and called the Virtual Network Topology 
     Manager (VNTM). 
      
  3. 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, whose 
     explicit route includes hops traversed by LSPs in lower layers. The 
     computation of end-to-end paths across layers is called Inter-Layer 
     Path Computation. 
      
     An LSR in the higher-layer may not have information on the lower-
     layer topology, particularly in an overlay or augmented model, and 
     hence may not be able to compute an end-to-end path across layers. 
      
     PCE-based inter-layer path computation, consists of relying on one 
     or more PCEs to compute an end-to-end path across layers. This 
     could rely on 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 have information about the topology of one or more 
     layers, but not all layers, and collaborate to compute an end-to-
     end path. 
       
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     Consider a two-layer network where the higher-layer network is a 
     packet-based IP/MPLS network or GMPLS network and the lower-layer 
     network is a GMPLS optical network. An ingress LSR in the higher-
     layer network tries to set up an LSP to an egress LSR 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 between border LSRs, which are located on the boundary 
     between the higher-layer and lower-layer networks, and that the 
     ingress LSR does not have topology visibility in the lower layer. 
     If a single-layer path computation is applied for the higher-layer, 
     the path computation fails. On the other hand, inter-layer path 
     computation is able to provide a route in the higher-layer and a 
     suggestion that a lower-layer LSP be setup between border LSRs, 
     considering both layers' TE topologies.  
      
     Lower-layer LSPs form a Virtual Network Topology (VNT), which can 
     be used for routing higher-layer LSPs or to carry IP traffic. 
     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. 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 [PCE-ARCH]. 
      
     - Compute a path on behalf of the ingress LSR through cooperation 
     between PCEs responsible for each layer. This mode is referred to 
     as Multiple PCE Computation with inter-PCE communication in [PCE-
     ARCH]. 
      
     - Perform separate path computations on behalf of the TE-LSP head-
     end and each transit LSR that is the entry point to a new layer. 
     This mode is referred to as Multiple PCE Computation (without 
     inter-PCE communication) in [PCE-ARCH]. This option utilizes per-
     layer path computation performed independently by successive PCEs. 
      
     The PCE computes and returns a path to the PCC that the PCC can use 
     to build an MPLS or GMPLS LSP once 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: that is the resulting ERO 
     includes sub-object(s) corresponding to lower-layer hierarchical 
     LSPs expressed as the TE link identifiers, which  can be numbered 
     or unnumbered ones, 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 regular TE link, this 
       
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     does not trigger new lower-layer LSP setup, but the utilization of 
     existing lower-layer LSPs. If it is a virtual TE link, this 
     triggers a new lower-layer LSP setup (provided that there are 
     available resources in the lower layer). A transit LSR 
     corresponding to the entry point of the virtual TE link is expected 
     to trigger the new lower-layer LSP setup. Note that the path of a 
     virtual TE link is not necessarily known in advance, and this may 
     require path computation either on the entry point or on a PCE. The 
     second case is that the PCE computes a path that includes loose 
     hop(s). The higher layer would select which lower layers to use and 
     would select the entry and exit points from those layers, but would 
     not select the path across the layers. A transit LSR corresponding 
     to the entry point is expected to expand the loose hop (either 
     itself or relying on the services of a PCE). Path expansion process 
     on 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. 
   
  4. Inter-layer Path Computation Models 
      
     As stated in Section 3, two PCE modes defined in the PCE 
     architecture can be used to perform inter-layer path computation. 
     They are discussed below.  
      
  4.1.  Single PCE Inter-Layer Path Computation 
      
     In this model Inter-layer path computation is performed by a single 
     PCE that has topology visibility in all layers. Such a PCE is 
     called a multi-layer PCE. 
      
     In Figure 1, the network is comprised of two layers. LSR H1, H2, H3 
     and H4 belong to the higher layer, and LSRs 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 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 established or not. 
      
      
                             ----- 
                            | PCE | 
                             ----- 
         -----    -----                  -----    ----- 
        | LSR |--| LSR |................| LSR |--| LSR | 
        | H1  |  | H2  |                | H3  |  | H4  | 
         -----    -----\                /-----    ----- 
       
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                        \-----    -----/ 
                        | LSR |--| LSR | 
                        | L1  |  | L2  | 
                         -----    ----- 
      
       Figure 1 : Multi-Layer PCE - A single PCE with multi-layer 
     visibility  
      
  4.2.  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. These PCEs are 
     called mono-layer PCEs. Mono-layer PCEs collaborate to compute an 
     end-to-end optimal path across layers. 
      
     In Figure 2, 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 with 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: PCE Hi requests a 
     path H2-H3 from PCE Lo. Of course more complex cooperation may be 
     required if an end-to-end optimal path is desired. 
      
                                  ----- 
                                 | PCE | 
                                 | Hi  | 
                                  --+-- 
                                    | 
         -----    -----             |            -----    ----- 
        | LSR |--| LSR |............|...........| LSR |--| LSR | 
        | H1  |  | H2  |            |           | H3  |  | H4  | 
         -----    -----\          --+--         /-----    ----- 
                        \        | PCE |       / 
                         \       | Lo  |      / 
                          \       -----      / 
                           \                / 
                            \-----    -----/ 
                            | LSR |--| LSR | 
                            | L1  |  | L2  | 
                             -----    ----- 
      
     Figure 2 : Cooperating Mono-Layer PCEs - Multiple PCEs with single-
     layer visibility 
   
      
  4.3.  General observation 
      
     - Depending on implementation details, inter-layer path computation 
     time 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. 
      
       
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     - When TE topology for all layered 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' TE 
     topologies by participating in only one routing domain. 
      
     - As the single PCE inter-layer path computation model uses more TE 
     topology information than is used by PCEs in the Multiple PCE path 
     computation model, it requires more computation power and memory. 
      
  5. Inter-Layer Path Control 
      
  5.1.  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 are provisioned across the lower-
     layer network. Further, 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 network element that manages 
     and controls the VNT. PCE and "VNT Management" are distinct 
     functions that may or may not be co-located. To describe each 
     function clearly, VNTM is considered as a functional element in 
     this draft. 
      
  5.2.  Inter-Layer Path Control Models 
      
   5.2.1. 
           Cooperation model between PCE and VNTM 
      
        -----      ------ 
       | PCE |--->| VNTM | 
        -----      ------ 
          ^           : 
          :           : 
          :           : 
          v           V 
         -----      -----                  -----      ----- 
        | LSR |----| LSR |................| LSR |----| LSR | 
        | H1  |    | H2  |                | H3  |    | H4  | 
         -----      -----\                /-----      ----- 
                          \-----    -----/ 
                          | LSR |--| LSR | 
                          | L1  |  | L2  | 
                           -----    ----- 
      
     Figure 3: Cooperation model between PCE and VNTM 
      
     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, 
       
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     as shown in Figure 3. Consider that H1 requests 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.  
      
     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 
     not TE link between H2 and H3. The computation fails, but PCE 
     suggests to VNTM that a lower-layer LSP (H2-H3) should be 
     established to support future LSP requests. 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 use a PCE with visibility into the lower layer to compute 
     the path of this new LSP. 
      
     If the PCE cannot compute a path for the higher-layer LSP without 
     the establishment of a further lower-layer LSP, the PCE may notify 
     VNTM and wait for the lower-layer LSP to be set up and advertised 
     as a TE link. It can 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 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, the PCE operates a timeout, or the PCE will be 
     notified by VNTM that no new LSP will become available. An example 
     of such a cooperative procedure between PCE and VNTM is as follows. 
      
     Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4. 
     In the request, it 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 suggests to VNTM that a new lower-layer LSP should be 
     established if necessary and if acceptable within VNTMís policy 
     constraints. The inter-layer path route computed by PCE may include 
     one or more virtual TE links. If PCE knows the inclusion of the 
     virtual TE link(s) in the inter-layer route, PCE may suggest VNTM 
     that the corresponding new lower-layer LSP(s) should be established. 
     Otherwise, new lower-layer LSP(s) may be setup according to the 
     higher-layer signaling trigger model. 
      
     Step 4: VNTM requests an ingress LSR (e.g. H2) to establish a 
     lower-layer LSP. The request message may include a pre-computed 
     lower-layer LSP route obtained from the PCE responsible for the 
     lower-layer network.  
      
     Step 5: The ingress LSR starts signaling to establish a lower-layer 
     LSP.  
      
     Step 6: If the lower-layer LSP setup is completed, the ingress LSR 
     notifies VNTM that the LSP is complete and supplies the tunnel 
     information.  
       
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     Step 7: VNTM replies to PCE to inform it that the lower-layer LSP 
     is now established, and includes the lower-layer tunnel information. 
     Alternatively, PCE may get to know about the existence of the 
     lower-layer LSP when a new TE link in the higher-layer 
     corresponding to the lower-layer LSP is advertised to PCE through 
     the IGP. 
      
     Step 8: 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. The higher-layer 
     route is specified as H2-H3-H4, where all hops are strict. 
      
     Step 9: H1 initiates signaling with the computed path H2-H3-H4 to 
     establish the higher-layer LSP. 
      
   5.2.2. 
           Higher-Layer Signaling Trigger Model 
      
        -----  
       | PCE | 
        -----  
          ^ 
          : 
          : 
          v 
         -----      -----                  -----    ----- 
        | LSR |----| LSR |................| LSR |--| LSR | 
        | H1  |    | H2  |                | H3  |  | H4  | 
         -----      -----\                /-----    ----- 
                          \-----    -----/ 
                          | LSR |--| LSR | 
                          | L1  |  | L2  | 
                           -----    ----- 
      
     Figure 4: Higher-layer signaling trigger model 
      
     Figure 4 shows the higher-layer signaling trigger model. As in the 
     case described in section 5.2.1, consider that H1 requests 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. 
      
     If PCE judges that a lower-layer LSP needs to be established based 
     on the inter-layer path computation result, a lower-layer LSP is 
     established during the higher-layer signaling procedure. After PCE 
     completes inter-layer path computation, PCE sends a reply message 
     including explicit route to the ingress LSR (PCC). There are two 
     ways to express the higher-layer LSP route, which are a multi-layer 
     path and a mono-layer path that includes loose hop(s).  
      
     In the higher-layer signaling trigger model with a multi-layer path, 
     a high-layer LSP route includes a route for a lower-layer LSP that 
     is not yet established. An LSR that is located at the boundary 
     between the higher-layer and lower-layer networks, called a border 
       
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     LSR, receives a higher-layer signaling message and then starts to 
     setup the lower-layer LSP. 
      
     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 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 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 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. 
      
     On the other hand, in the signaling trigger model with mono-layer 
     path, a higher-layer LSP route includes a loose or strict hop to 
     traverse the lower-layer network between the two border LSRs. In 
     the strict hop case, a virtual TE link may be advertised, but a 
     lower-layer LSP is not setup. 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 a lower-layer LSP. Again, it is 
     possible that a suitable lower-layer LSP has been established (or 
     become available) between the time that the higher-layer 
     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. Since the higher-layer 
       
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     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: 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.  
      
   5.2.3. 
          Examples of multi-layer ERO 
      
     PCE 
      ^ 
      : 
      : 
      V 
     H1--H2             H3--H4  
          \                  /         
           L1==L2==L3--L4--L5          
                    | 
                    | 
                   L6--L7 
                         \ 
                          H5--H6 
      
     Figure 5 Example of multi-layer network 
      
     This section describes how lower-layer LSP setup is performed in 
     the higher-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, 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. 
      
  6. Choosing between inter-layer path control models 
      
       
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     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, and higher-layer signaling time. 
      
     VNTM functions: 
      
     In the cooperation model, VNTM functions are required. In this 
     model, additional overhead communications between PCE and VNTM and 
     between VNTM and a border LSR are required.  
      
     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 not available in the trigger model. 
      
     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. The triggering signaling is also 
     required in the cooperation case when the VNTM support virtual TE 
     links. Note that, if only the cooperation model is applied, it is 
     required that a PCE knows whether a link is a regular TE link or 
     virtual TE link.  
      
     If the ERO in the higher-layer Path message uses a mono-layer path 
     or specifies loose hop, a border LSR receiving the Path message 
     MUST obtain a lower-layer route either by consulting PCE or by 
     using its own computation engine. If the ERO in the higher-layer 
     Path message uses multi-layer path, the border LSR MUST judge 
     whether lower-layer signaling is needed.  
      
     In the cooperation model, no additional function for triggered 
     signaling in border LSRs is required except when virtual TE links 
     are used. Therefore, if these additional functions are not 
     supported in border LSRs, the cooperation model, where a border LSR 
     is controlled by VNTM to set up a lower-layer LSP, has to be chosen.  
      
     Complete inter-layer LSP setup time: 
      
     Complete inter-layer LSP setup time includes inter-layer path 
     computation, signaling, and communication time between PCC and PCE, 
     PCE and VNTM, and VNTM and LSR. In the cooperation 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. 
      
       
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     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 any 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. 
      
     An appropriate model is chosen, taking into all of the above 
     considerations. 
      
  7. Security Considerations 
      
     Inter-layer traffic engineering with PCE may raise new security 
     issues in both inter-layer path control models. 
      
     In the cooperation model between PCE and VNTM, when PCE judges a 
     new lower-layer LSP, communications between PCE and VNTM and 
     between VNTM and a border LSR are needed. In this case, there are 
     some security concerns that need to be addressed for these 
     communications. These communications should have some security 
     mechanisms to ensure authenticity, privacy and integrity.  
      
     In the higher-layer signaling trigger model, there are several 
     security concerns. First, PCE may inform PCC, which is located in 
     the higher-layer network, of multi-layer path information that 
     includes an ERO in the lower-layer network, while the PCC may not 
     have TE topology visibility into the lower-layer network. This 
     raises a security concern, where lower-layer hop information is 
     known to transit LSRs supporting a higher-layer LSP. Some security 
     mechanisms to ensure authenticity, privacy and integrity may be 
     used.  
      
     Security issues may also exist when a single PCE is granted full 
     visibility of TE information that applies to multiple layers. 
      
  8. Acknowledgment 
      
    We would like to thank Kohei Shiomoto, Ichiro Inoue, Julien Meuric 
    and Jean-Francois Peltier for their useful comments. 
      
  9. References 
      
  9.1.  Normative Reference 
      
     [RFC2119] Bradner, S., "Key words for use in RFCs to indicate 
     requirements levels", RFC 2119, March 1997. 
      
     [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching 
     Architecture", RFC 3945, October 2004. 
      

       
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            draft-oki-pce-inter-layer-frwk-00.txt   April 2006 
      
     [RFC4206] Kompella, K., and Rekhter, Y., "Label Switched Paths 
     (LSP) Hierarchy with Generalized Multi-Protocol Label Switching 
     (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005. 
      
     [RFC4208] G. Swallow et al., "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. 
      
  9.2.  Informative Reference 
      
     [PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, "Path Computation 
     Element (PCE) Architecture", draft-ietf-pce-architecture (work in 
     progress). 
      
     [PCE-COM-REQ] J. Ash, J.L Le Roux et al., "PCE Communication 
     Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen-
     reqs (work in progress). 
      
     [PCE-DISC-REQ] JL Le Roux et al., "Requirements for Path 
     Computation Element (PCE) Discovery", draft-ietf-pce-discovery-reqs 
     (work in progress). 
      
     [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", draft-ietf-pce-
     inter-layer-req (work in progress). 
      
     [PCEP] JP. Vasseur et al, "Path Computation Element (PCE) 
     communication Protocol (PCEP) - Version 1 - draft-ietf-pce-pcep 
     (work in progress). 
      
  10.     Authors' Addresses 
      
     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@francetelecom.com 
      
     Adrian Farrel 
     Old Dog Consulting 
     Email: adrian@olddog.co.uk 
      

       
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