Network Working Group E. Oki
Request for Comments: 5623 University of Electro-Communications
Category: Informational T. Takeda
NTT
JL. Le Roux
France Telecom
A. Farrel
Old Dog Consulting
September 2009
Network Working Group E. Oki
Request for Comments: 5623 University of Electro-Communications
Category: Informational T. Takeda
NTT
JL. Le Roux
France Telecom
A. Farrel
Old Dog Consulting
September 2009
Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic Engineering
基于PCE的层间MPLS和GMPLS流量工程框架
Abstract
摘要
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.
网络可以包括多个层。重要的是全局优化网络资源利用率，考虑所有层，而不是单独优化每一层的资源利用率。这允许通过我们称之为层间流量工程的过程来实现更好的网络效率。路径计算单元（PCE）是实现层间流量工程的有力工具。
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).
本文档描述了将基于PCE的体系结构应用于层间多协议标签交换（MPLS）和通用MPLS（GMPLS）流量工程的框架。它为支持多层网络的PCE部署提供了建议。本文档还描述了PCE执行层间流量工程的网络模型，以及PCE与称为虚拟网络拓扑管理器（VNTM）的功能组件之间的关系。
Status of This Memo
关于下段备忘
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright and License Notice
版权及许可证公告
Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2009 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您在以下方面的权利和限制：
to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License.
请参阅本文件。从本文件中提取的代码组件必须包括《信托法律条款》第4.e节中所述的简化BSD许可文本，并且提供BSD许可中所述的代码组件时不提供任何担保。
Table of Contents
目录
1. Introduction ....................................................3
1.1. Terminology ................................................3
2. Inter-Layer Path Computation ....................................4
3. Inter-Layer Path Computation Models .............................7
3.1. Single PCE Inter-Layer Path Computation ....................7
3.2. Multiple PCE Inter-Layer Path Computation ..................7
3.3. General Observations ......................................10
4. Inter-Layer Path Control .......................................10
4.1. VNT Management ............................................10
4.2. Inter-Layer Path Control Models ...........................11
4.2.1. PCE-VNTM Cooperation Model .........................11
4.2.2. Higher-Layer Signaling Trigger Model ...............13
4.2.3. NMS-VNTM Cooperation Model .........................16
4.2.4. Possible Combinations of Inter-Layer Path
Computation and Inter-Layer Path Control Models ....21
5. Choosing between Inter-Layer Path Control Models ...............22
5.1. VNTM Functions ............................................22
5.2. Border LSR Functions ......................................23
5.3. Complete Inter-Layer LSP Setup Time .......................24
5.4. Network Complexity ........................................24
5.5. Separation of Layer Management ............................25
6. Stability Considerations .......................................25
7. Manageability Considerations ...................................26
7.1. Control of Function and Policy ............................27
7.1.1. Control of Inter-Layer Computation Function ........27
7.1.2. Control of Per-Layer Policy ........................27
7.1.3. Control of Inter-Layer Policy ......................27
7.2. Information and Data Models ...............................28
7.3. Liveness Detection and Monitoring .........................28
7.4. Verifying Correct Operation ...............................29
7.5. Requirements on Other Protocols and Functional
Components ................................................29
7.6. Impact on Network Operation ...............................30
8. Security Considerations ........................................30
9. Acknowledgments ................................................31
10. References ....................................................32
10.1. Normative Reference ......................................32
10.2. Informative Reference ....................................32
1. Introduction ....................................................3
1.1. Terminology ................................................3
2. Inter-Layer Path Computation ....................................4
3. Inter-Layer Path Computation Models .............................7
3.1. Single PCE Inter-Layer Path Computation ....................7
3.2. Multiple PCE Inter-Layer Path Computation ..................7
3.3. General Observations ......................................10
4. Inter-Layer Path Control .......................................10
4.1. VNT Management ............................................10
4.2. Inter-Layer Path Control Models ...........................11
4.2.1. PCE-VNTM Cooperation Model .........................11
4.2.2. Higher-Layer Signaling Trigger Model ...............13
4.2.3. NMS-VNTM Cooperation Model .........................16
4.2.4. Possible Combinations of Inter-Layer Path
Computation and Inter-Layer Path Control Models ....21
5. Choosing between Inter-Layer Path Control Models ...............22
5.1. VNTM Functions ............................................22
5.2. Border LSR Functions ......................................23
5.3. Complete Inter-Layer LSP Setup Time .......................24
5.4. Network Complexity ........................................24
5.5. Separation of Layer Management ............................25
6. Stability Considerations .......................................25
7. Manageability Considerations ...................................26
7.1. Control of Function and Policy ............................27
7.1.1. Control of Inter-Layer Computation Function ........27
7.1.2. Control of Per-Layer Policy ........................27
7.1.3. Control of Inter-Layer Policy ......................27
7.2. Information and Data Models ...............................28
7.3. Liveness Detection and Monitoring .........................28
7.4. Verifying Correct Operation ...............................29
7.5. Requirements on Other Protocols and Functional
Components ................................................29
7.6. Impact on Network Operation ...............................30
8. Security Considerations ........................................30
9. Acknowledgments ................................................31
10. References ....................................................32
10.1. Normative Reference ......................................32
10.2. Informative Reference ....................................32
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) [RFC5212], 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) in the higher-layer network is called the Virtual Network Topology (VNT) [RFC5212].
网络可以包括多个层。这些层可以表示技术的分离（例如，支持分组交换（PSC）、时分多路复用（TDM）或支持lambda交换（LSC））[RFC3945]、数据平面交换粒度级别的分离（例如，PSC-1、PSC-2、VC4或VC12）[RFC5212]，或者客户端和服务器联网角色之间的区别。在这种多层网络中，较低层中的标签交换路径（LSP）用于在较低层网络中承载较高层的LSP。由较低层LSP形成并在较高层网络中宣传为流量工程链路（TE链路）的网络拓扑称为虚拟网络拓扑（VNT）[RFC5212]。
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. Inter-layer traffic engineering includes using mechanisms that allow the computation of end-to-end paths across layers (known as inter-layer path computation) and mechanisms that control and manage the Virtual Network Topology (VNT) by setting up and releasing LSPs in the lower layers [RFC5212].
全局优化网络资源利用率可能是有效的，即考虑所有层，而不是单独优化每个层的资源利用率。这可以实现更好的网络效率，我们称之为层间流量工程。层间流量工程包括使用允许跨层计算端到端路径的机制（称为层间路径计算）以及通过在较低层中设置和释放LSP来控制和管理虚拟网络拓扑（VNT）的机制[RFC5212]。
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.
层间流量工程包含在基于路径计算元素（PCE）的体系结构[RFC4655]的范围内，并且PCE可以为解决层间路径计算问题提供合适的机制。
PCE Communication Protocol requirements for inter-layer traffic engineering are set out in [PCC-PCE].
层间流量工程的PCE通信协议要求见[PCC-PCE]。
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 as well as describing 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).
本文档描述了将基于PCE的体系结构应用于层间流量工程的框架。它为支持多层网络的PCE部署提供了建议。本文档还描述了PCE执行层间流量工程的网络模型，并描述了PCE与负责VNT控制和管理的功能组件（称为虚拟网络拓扑管理器（VNTM））之间的关系。
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 [RFC5212].
本文件使用基于PCE的路径计算架构[RFC4655]中的术语，以及多协议标签交换（MPLS）[RFC3031]、通用MPLS（GMPLS）[RFC3945]和多层网络[RFC5212]中的通用术语。
This section describes key topics of inter-layer path computation in MPLS and GMPLS networks.
本节介绍MPLS和GMPLS网络中层间路径计算的关键主题。
[RFC4206] defines a way to signal a higher-layer LSP that has an explicit route and includes hops traversed by LSPs in lower layers. The computation of end-to-end paths across layers is called inter-layer path computation.
[RFC4206]定义了一种向上层LSP发送信号的方法，该LSP具有显式路由，并包括下层LSP所穿越的跳。跨层端到端路径的计算称为层间路径计算。
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.
较高层中的标签交换路由器（LSR）可能没有关于较低层拓扑的信息，特别是在覆盖或增强模型部署中，因此可能无法计算跨层的端到端路径。
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.
基于PCE的层间路径计算包括使用一个或多个PCE计算跨层的端到端路径。这可以通过单个PCE路径计算实现，其中PCE具有关于多个层的拓扑信息，并且可以直接计算跨层的端到端路径，考虑到所有层的拓扑。或者，层间路径计算可以作为多个PCE计算来执行，其中一组PCE的每个成员具有关于一个或多个层（但不是所有层）的拓扑的信息，并且PCE协作以计算端到端路径。
----- ----- ----- -----
| LSR |--| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
----- ----- ----- -----
| LSR |--| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 1: A Simple Example of a Multi-Layer Network
图1：多层网络的简单示例
Consider, for instance, the two-layer network shown in Figure 1, where the higher-layer network (LSRs H1, H2, H3, and H4) is a packet-based IP/MPLS or GMPLS network, 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 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.
例如，考虑图1所示的两层网络，其中高层网络（LSRH1、H2、H3和H4）是基于分组的IP/MPLS或GMPLS网络，而下层网络（LSRs、H2、L1、L2和H3）是GMPLS光网络。更高层网络（H1）中的入口LSR尝试在更高层网络中跨更低层网络建立到出口LSR（H4）的LSP，并且需要更高层网络中的路径。然而，假设在高层网络和底层网络（H2和H3）之间的边界LSR之间的高层网络中没有TE链路。还假设入口LSR在较低层中没有拓扑可见性。
If a single-layer path computation is applied in 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 to suggest that a lower-layer LSP be set up between the border LSRs (H2-L1-L2-H3).
如果在较高层应用单层路径计算，则由于缺少TE链路，路径计算失败。另一方面，层间路径计算能够在较高层（H1-H2-H3-H4）中提供路由，并建议在边界LSR（H2-L1-L2-H3）之间建立较低层LSP。
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:
作为TE链路播发到高层网络的下层LSP形成可用于路由高层LSP的虚拟网络拓扑（VNT）。跨较低层网络的较高层网络中的端到端lsp的层间路径计算可利用VNT，并且PCE是用于计算较高层网络内的此类较高层lsp的路径的候选。或者，基于PCE的路径计算模型可以：
- 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].
- 使用从多个层收集的信息代表入口LSR执行单个计算。该模式在[RFC4655]中称为单PCE计算。
- 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].
- 通过与负责每层的PCE合作，代表入口LSR计算路径。该模式在[RFC4655]中称为具有PCE间通信的多PCE计算。
- 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, which is performed independently by successive PCEs.
- 代表TE-LSP前端和作为新层入口点的每个过渡边界LSR执行单独的路径计算。该模式在[RFC4655]中称为多PCE计算（无PCE间通信）。此选项利用逐层路径计算，该计算由连续PCE独立执行。
Note that when a network consists of more than two layers (e.g., MPLS over SONET over Optical Transport Network (OTN)) and a path traversing more than two layers needs to be computed, it is possible to combine multiple PCE-based path computation models. For example, the single PCE computation model could be used for computing a path across the SONET layer and the OTN layer, and the multiple PCE computation with inter-PCE communication model could be used for computing a path across the MPLS layer (computed by higher-layer PCE) and the SONET layer (computed by lower-layer PCE).
注意，当网络由两层以上（例如，光传输网络（OTN）上SONET上的MPLS）组成并且需要计算穿过两层以上的路径时，可以组合多个基于PCE的路径计算模型。例如，单个PCE计算模型可用于计算跨越SONET层和OTN层的路径，并且具有PCE间通信模型的多个PCE计算可用于计算跨越MPLS层（由上层PCE计算）和SONET层（由下层PCE计算）的路径。
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.
一旦路径信息已转换为显式路由对象（ERO）以用于RSVP-TE信令，由前端LSR调用的PCE计算LSR可用于向MPLS-TE或GMPLS LSP发送信号的路径。有两种选择。
- Option 1: Mono-Layer Path
- 选项1：单层路径
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 subobject(s) corresponding to lower-layer hierarchical LSPs expressed 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 [RFC5212]). 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.
PCE计算“单层”路径，即仅包括来自同一层的TE链路的路径。此选项有两种情况。在第一种情况下，PCE计算包括已经建立的较低层lsp或根据需要建立的较低层lsp的路径。也就是说，结果ERO包括对应于较低层分层lsp的子对象，当在较高层网络中作为TE链路播发时，表示为分层lsp的TE链路标识符。TE链路可以是实际建立的常规TE链路或尚未建立的虚拟TE链路（参见[RFC5212]）。如果是虚拟TE链路，则当信令到达下层LSP的前端时，会触发新下层LSP的设置尝试。注意，虚拟TE链路的路径不一定事先已知，这可能需要进一步的（较低层）路径计算。
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 the entry and exit points of 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.
第二种情况是，PCE计算的路径包括跨越较低层网络的松散跃点。较高层路径计算选择要使用的较低层网络以及该较低层网络的入口和出口点，但不选择穿过较低层网络的路径。作为低层网络入口点的公交LSR预计将扩展松散跃点（自身或依赖PCE的服务）。边界LSR上的路径扩展过程可导致选择现有的较低层LSP或计算和设置新的较低层LSP。
Note that even if a PCE computes a path with a loose hop expecting that the loose hop will be expanded across the lower-layer network, the LSR (that is an entry point to the lower-layer network) may simply expand the loose hop in the same layer. If more strict control of how the LSR establishes the path is required, mechanisms such as Path Key [RFC5520] could be applied.
注意，即使PCE计算具有松散跃点的路径，期望松散跃点将在较低层网络上扩展，LSR（作为较低层网络的入口点）也可以简单地在同一层中扩展松散跃点。如果需要对LSR如何建立路径进行更严格的控制，则可以应用路径键[RFC5520]等机制。
- Option 2: Multi-Layer Path
- 选项2：多层路径
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 that are not yet established. In the latter case, the signaling of the higher-layer LSP will trigger the establishment of the lower-layer LSPs.
PCE计算“多层”路径，即包括来自不同层的TE链路的路径[RFC4206]。这样的路径可以包括已经存在或尚未建立的一个或多个较低层lsp的完整路径。在后一种情况下，上层LSP的信令将触发下层LSP的建立。
In Section 2, three models are defined to perform PCE-based inter-layer path computation -- namely, single PCE computation, multiple PCE computation with inter-PCE communication, and multiple PCE computation without inter-PCE communication. Single PCE computation is discussed in Section 3.1 below, and multiple PCE computation (with and without inter-PCE communication) is discussed in Section 3.2 below.
在第2节中，定义了三个模型来执行基于PCE的层间路径计算——即单个PCE计算、具有PCE间通信的多个PCE计算和不具有PCE间通信的多个PCE计算。下文第3.1节讨论了单个PCE计算，下文第3.2节讨论了多个PCE计算（有和没有PCE间通信）。
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.
在该模型中，层间路径计算由单个PCE执行，该PCE具有所有层的拓扑可见性。这种PCE称为多层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 that is already in existence or not yet established.
在图2中，网络由两层组成。LSR H1、H2、H3和H4属于上层，LSR H2、H3、L1和L2属于下层。PCE是一种多层PCE，可以同时看到两层。它可以跨层执行端到端路径计算（单PCE路径计算）。例如，它可以为从H1到H4的更高层LSP计算最优路径H1-H2-L1-L2-H3-H4。该路径包括从H2到H3的较低层LSP的路径，该路径已经存在或尚未建立。
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Figure 2: Single PCE Inter-Layer Path Computation
图2：单PCE层间路径计算
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
在该模型中，每个层至少有一个PCE，并且每个PCE的拓扑可见性仅限于其自己的层。由于组织和/或服务管理问题等因素，一些提供商可能希望保留层边界。也可以选择多个PCE计算而不是单个PCE计算
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)).
受可伸缩性考虑的驱动，因为在此模式下，PCE只需要维护一层的拓扑信息（导致流量工程数据库（TED）的大小减小）。
These PCEs are called mono-layer PCEs. Mono-layer PCEs collaborate to compute an end-to-end optimal path across layers.
这些PCE称为单层PCE。单层PCE协作计算跨层的端到端最佳路径。
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" 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 as follows:
图3显示了具有PCE层间通信的多个PCE层间计算。每层中有一个PCE。每个层的PCE协作计算跨层的端到端路径。PCE Hi负责高层的计算，并可与PCE Lo“协商”以计算穿过下层的路径。PCE Lo负责下层的路径计算。PCE之间合作的一个简单例子如下：
- LSR H1 sends a request to PCE Hi for a path H1-H4.
- LSR H1向PCE Hi发送路径H1-H4的请求。
- PCE Hi selects H2 as the entry point to the lower layer and H3 as the exit point.
- PCE Hi选择H2作为下层的入口点，选择H3作为出口点。
- PCE Hi requests a path H2-H3 from PCE Lo.
- PCE Hi从PCE Lo请求路径H2-H3。
- PCE Lo returns H2-L1-L2-H3 to PCE Hi.
- PCE Lo将H2-L1-L2-H3返回至PCE Hi。
- PCE Hi is now able to compute the full path (H1-H2-L1-L2-H3-H4) and return it to H1.
- PCE Hi现在能够计算完整路径（H1-H2-L1-L2-H3-H4）并将其返回到H1。
Of course, more complex cooperation may be required if an optimal end-to-end path is desired.
当然，如果需要最佳的端到端路径，可能需要更复杂的合作。
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Figure 3: Multiple PCE Inter-Layer Path Computation with Inter-PCE Communication
图3：具有PCE层间通信的多PCE层间路径计算
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.
图4显示了没有PCE层间通信的多个PCE层间路径计算。如第2节所述，代表TE-LSP前端和作为新层入口点的每个过境边界LSR执行单独的路径计算。
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Figure 4: Multiple PCE Inter-Layer Path Computation without Inter-PCE Communication
图4：无PCE层间通信的多PCE层间路径计算
- 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.
- 根据实现细节，在单个PCE层间路径计算模型中执行层间路径计算的时间可能小于具有协作单层PCE的多个PCE模型的时间，因为不需要在协作PCE之间交换消息。
- 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' TE topologies by participating in only one routing domain.
- 当所有层网络的TE拓扑在一个路由域内可见时，可以采用单个PCE层间路径计算模型，因为PCE能够通过仅参与一个路由域来收集所有层的TE拓扑。
- 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.
- 由于单PCE层间路径计算模型在一次计算中使用的TE拓扑信息多于多PCE路径计算模型中PCE使用的TE拓扑信息，因此需要更多的计算能力和内存。
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 -- the 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 [RFC5441] could be used by considering layers as separate domains.
当存在多个候选层边界节点（我们可以说更高层是多宿主的）时，最优路径计算要求检查通过不同层边界节点或链路的所有可能路径。这在单PCE层间路径计算模型中相对简单，因为PCE具有完全可见性——计算类似于单层的单域内的计算。在多PCE层间路径计算模型中，[RFC5441]中描述的反向递归技术可通过将层视为单独的域来使用。
As a result of mono-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. 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.
作为单层路径计算的结果，PCE可以确定在更高层网络中没有足够的可用带宽来支持这个或未来的更高层lsp。如果在较低层网络上提供新的LSP，问题可能会得到解决。此外，考虑到高层网络的需求，底层lsp的修改、重新组织和新的供应可以实现底层网络资源的更好利用。换句话说，VNT需要与层间路径计算协同控制或管理。
A VNT Manager (VNTM) is defined as a functional element that manages and controls the VNT. The PCE and VNT Manager are distinct functional elements that may or may not be collocated.
VNT管理器（VNTM）定义为管理和控制VNT的功能元素。PCE和VNT管理器是不同的功能元件，可以并置，也可以不并置。
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Figure 5: PCE-VNTM Cooperation Model
图5:PCE-VNTM合作模式
A multi-layer network consists of higher-layer and lower-layer networks. LSRs H1, H2, H3, and H4 belong to the higher-layer network, and 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.
多层网络由高层网络和下层网络组成。LSR H1、H2、H3和H4属于上层网络，LSR H2、L1、L2和H3属于下层网络，如图5所示。本文考虑了单PCE层间路径计算的情况来解释PCE与VNTM之间的协作模型，但该模型也可以应用有或没有层间通信的多PCE路径计算。
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.
考虑H1请求PCE计算H1和H4之间的层间路径。在路径计算请求之前，H2和H3之间的高层没有TE链路，因此请求失败。但是PCE可以向负责较低层网络的VNT管理器提供信息，这可能有助于解决将来较高层LSP设置的情况。
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
PCE和VNTM的作用如下。PCE执行层间路径计算，无法提供路径，因为H2和H3之间没有TE链路。计算失败，但PCE向VNTM建议可以建立较低层LSP（H2-H3）来支持未来的LSP请求。从PCE到VNTM的消息包含关于高层需求（从H2到H3）的信息，并且可能包括下层中的建议路径（如果PCE可以看到下层网络）。VNTM使用本地策略和可能的管理/配置输入来确定如何处理来自PCE的建议，并可请求进入LSR（例如H2）以
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.
建立低层LSP。VNTM或入口LSR（H2）本身可以使用具有低层可视性的PCE来计算该新LSP的路径。
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 the VNTM that no new LSP will become available. In any case, if the PCE decides to wait, it must operate a timeout. An example of such a cooperative procedure between PCE and VNTM is as follows, using the example network in Figure 4.
当上层PCE无法计算路径并通知VNTM时，它可以等待下层LSP被设置并作为TE链路通告。PCE可能有一个定时器。在指定的持续时间内更新TED后，PCE将知道一个新的TE链接。然后，它可以计算更高层LSP的完整端到端路径，并将结果返回给PCC。在这种情况下，PCC可能会等待一段时间，PCC了解这一点很重要。同样重要的是，PCE和VNTM应达成协议，及时建立下层LSP，或者VNTM将通知PCE没有新的LSP可用。在任何情况下，如果PCE决定等待，它必须操作超时。PCE和VNTM之间的这种协作过程的示例如下，使用图4中的示例网络。
Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4.
步骤1:H1（PCC）请求PCE计算H1和H4之间的路径。
Step 2: The path computation fails because there is no TE link across the lower-layer network.
步骤2：路径计算失败，因为下层网络中没有TE链路。
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 acceptable within VNTM's policy constraints.
步骤3：PCE向VNTM建议，连接H2和H3的新TE链路将是有用的。PCE通知VNTM它将等待TE链路的创建。VNTM考虑是否应建立较低层LSP（如有必要且在VNTM的政策约束范围内可接受）。
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.
步骤4:VNTM请求下层网络（例如H2）中的入口LSR以建立下层LSP。请求消息可以包括从负责较低层网络的PCE获得的较低层LSP路由。
Step 5: The ingress LSR signals to establish the lower-layer LSP.
步骤5：入口LSR信号建立下层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.
步骤6：如果下层LSP设置成功，入口LSR通知VNTM LSP已完成并提供隧道信息。
Step 7: The ingress LSR (H2) advertises the new LSP as a TE link in the higher-layer network routing instance.
步骤7：入口LSR（H2）在高层网络路由实例中将新LSP作为TE链路播发。
Step 8: PCE notices the new TE link advertisement and recomputes the requested path.
步骤8：PCE注意到新的TE链接公告，并重新计算请求的路径。
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.
步骤9：PCE使用计算出的更高层LSP路由回复H1（PCC）。计算出的路径被分类为单层路径，该单层路径包括已建立的较低层LSP作为较高层中的单跳。上层路由指定为H1-H2-H3-H4，其中所有跳数都是严格的。
Step 10: H1 initiates signaling with the computed path H2-H3-H4 to establish the higher-layer LSP.
步骤10:H1使用计算出的路径H2-H3-H4发起信令以建立更高层LSP。
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Figure 6: Higher-Layer Signaling Trigger Model
图6：高层信令触发模型
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.
图6显示了更高层的信令触发模型。这里考虑单PCE路径计算的情况来解释更高层信令触发模型，但是有/没有PCE间通信的多PCE路径计算也可以应用于该模型。
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.
如在4.2.1节中所描述的情况，考虑H1请求PCE计算H1和H4之间的路径。在路径计算请求之前，H2和H3之间的高层没有TE链路。
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 visibility 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.
PCE无法计算单层路径，但可以判断在H2和H3之间建立较低层LSP将提供足够的连通性。如果PCE具有层间可视性，则其可返回包含较低层中的跃点的路径（H1-H2-L1-L2-H3-H4），但如果其对较低层没有可视性，则其可返回具有从H2到H3的松散跃点的路径（H1-H2-H3（松散）-H4）。前者是多层路径，后者是包含松散跳数的单层路径。
In the higher-layer signaling trigger model with a multi-layer path, the LSP route supplied by the PCE includes the route of a 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, and starts to set up the lower-layer LSP as described in [RFC4206]. Note that these actions depend 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.
在具有多层路径的高层信令触发模型中，由PCE提供的LSP路由包括尚未建立的下层LSP的路由。位于上层和下层网络（本例中为H2）之间边界的边界LSR接收高层信令消息，注意到下一跳在下层网络中，并开始设置下层LSP，如[RFC4206]中所述。请注意，这些操作取决于边界LSR上应用的策略。具有多层路径的信令触发模型的示例过程如下所示。
Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4. The request indicates that inter-layer path computation is allowed.
步骤1:H1（PCC）请求PCE计算H1和H4之间的路径。该请求指示允许进行层间路径计算。
Step 2: As a result of the inter-layer path computation, PCE judges that a new lower-layer LSP needs to be established.
步骤2：作为层间路径计算的结果，PCE判断需要建立新的下层LSP。
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.
步骤3：PCE使用计算的多层路由（包括高层和下层LSP路由）回复H1（PCC）。路由可以指定为H1-H2-L1-L2-H3-H4，其中所有跳数都是严格的。
Step 4: H1 initiates higher-layer signaling using the computed explicit router of H2-L1-L2-H3-H4.
步骤4:H1使用计算出的显式路由器H2-L1-L2-H3-H4启动更高层信令。
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.
步骤5：接收上层信令消息的边界LSR（H2）启动下层信令以沿H2-L1-L2-H3的指定下层路由建立下层LSP。也就是说，边界LSR识别应用于较低层网络的显式路由内的跳，使用本地策略验证新LSP是可接受的，并建立所需的较低层LSP。注意，在执行计算的时间与高层信令消息到达边界LSR的时刻之间，可能已经建立（或变得可用）合适的下层LSP。在这种情况下，边界LSR可以选择这样的低层LSP，而不需要向新LSP发送信号，前提是低层LSP满足高层信令请求中的显式路由。
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].
步骤6：在低层LSP建立之后，高层信令使用分层信令[RFC4206]沿着H2-H3-H4的指定高层路由继续。
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 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.
另一方面，在具有单层路径的信令触发模型中，高层LSP路由包括在两个边界lsr之间穿过下层网络的松散跳。接收高层信令消息的边界LSR需要确定新的下层LSP的路径。它应用本地策略来验证新的LSP是可接受的，然后咨询负责较低层网络的PCE或自行计算路径，并发起信令以建立较低层LSP。同样，可能已经建立（或变得可用）合适的较低层LSP。在这种情况下，边界LSR可以选择这样的低层LSP而不需要发信号通知新的LSP，前提是现有的低层LSP满足高层信令请求中的显式路由。由于上层信令请求使用了松散跳，而没有指定下层网络内的路径的任何细节，因此边界LSR具有比前一示例中更大的选择下层LSP的自由度。
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:
具有多层路径和单层路径的信令触发模型的过程之间的差异是步骤5。单层路径信令触发模型步骤5如下：
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.
步骤5’：接收高层信令消息的边界LSR（H2）应用本地策略来验证新LSP是否可接受，然后启动低层LSP的建立。它要么咨询负责低层网络的PCE，要么自己计算路由以在高层路径中扩展松跳路由。
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.
最后，请注意，虚拟TE链路可能已播发到更高层网络中。这导致PCE返回路径H1-H2-H3-H4，其中所有跳数都是严格的。但是，当高层信令消息到达层边界节点H2（该节点负责广告虚拟TE链路）时，它意识到TE链路还不存在，并使用其自身的路径确定（与高层中的松散跳相同）通过下层网络向必要的LSP发信号在继续高层信令之前。
PCE
^
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V
H1--H2 H3--H4
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L1==L2==L3--L4--L5
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L6--L7
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PCE
^
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L1==L2==L3--L4--L5
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L6--L7
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Figure 7: Example of a Multi-Layer Network
图7：多层网络的示例
Examples of multi-layer EROs are explained using Figure 7, which shows 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. The higher-layer signaling trigger model provides several options for the ERO when it reaches the last LSR in the higher layer higher-layer network (H2).
使用图7解释了多层ERO的示例，图7显示了如何使用ERO在高层信令触发模型中执行下层LSP设置，ERO可以包括高层和下层中的子对象。当ERO到达更高层网络（H2）中的最后一个LSR时，更高层信令触发模型为ERO提供了几个选项。
1. The next subobject is a loose hop to H3 (mono-layer ERO).
1. 下一个子对象是到H3的松散跳跃（单层ERO）。
2. The next subobject is a strict hop to L1, followed by a loose hop to H3.
2. 下一个子对象是到L1的严格跃点，然后是到H3的松散跃点。
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)}.
3. 下一个子对象是下层网络中的一系列跃点（严格或松散），然后是H3。例如，{L1（严格）、L3（松散）、L5（松散）、H3（严格）}。
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.
在第一示例中，较低层可以利用将端到端LSP传送到H3的任何LSP隧道。在第三种情况下，下层必须选择穿过L3和L5的LSP隧道。然而，这并不意味着较低层可以或应该使用从L1到L3的LSP和从L3到L5的LSP。
In this model, NMS and VNTM cooperate to establish a lower-layer LSP. There are two flavors in this model. One is where interaction between layers in path computation is performed at the PCE level. This is called "integrated flavor". The other is where interaction between layers in path computation is achieved through NMS and VNTM cooperation, which could be a point of application of administrative, billing, and security policy. This is called "separated flavor".
在该模型中，NMS和VNTM合作建立一个较低层的LSP。这种型号有两种口味。一种是在PCE级别执行路径计算中各层之间的交互。这就是所谓的“综合风味”。另一个是通过NMS和VNTM合作实现路径计算中各层之间的交互，这可能是管理、计费和安全策略的应用点。这就是所谓的“分离风味”。
o NMS-VNTM Cooperation Model (integrated flavor)
o NMS-VNTM合作模式（集成模式）
------ -----
| NMS |<-->| PCE |
| | -----
| ---- |
||VNTM||
| ---- |
------
: :
: ---------
: :
V V
----- ----- ----- -----
| LSR |----| LSR |................| LSR |----| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
------ -----
| NMS |<-->| PCE |
| | -----
| ---- |
||VNTM||
| ---- |
------
: :
: ---------
: :
V V
----- ----- ----- -----
| LSR |----| LSR |................| LSR |----| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 8: NMS-VNTM Cooperation Model (integrated flavor)
图8:NMS-VNTM合作模式（综合风味）
Figure 8 shows the NMS-VNTM cooperation model (integrated flavor). The case of single PCE path computation is considered to explain the NMS-VNTM cooperation model (integrated flavor) here, but multiple PCE path computation with inter-PCE communication can also be applied to this model. Note that multiple PCE path computation without inter-PCE communication does not fit in with this model. For this model to have meaning, the VNTM and NMS are closely coupled.
图8显示了NMS-VNTM合作模型（集成风味）。这里考虑单PCE路径计算的情况来解释NMS-VNTM合作模型（集成风味），但是具有PCE间通信的多PCE路径计算也可以应用于该模型。注意，没有PCE间通信的多PCE路径计算不适合此模型。为了使该模型有意义，VNTM和NMS是紧密耦合的。
The NMS sends the path computation request to the PCE. The PCE returns the inter-layer path computation result. When the NMS receives the path computation result, the NMS works with the VNTM and sends the request to LSR H2 to set up the lower-layer LSP. VNTM uses local policy and possibly management/configuration input to determine how to process the computation result from PCE.
NMS向PCE发送路径计算请求。PCE返回层间路径计算结果。当NMS接收到路径计算结果时，NMS与VNTM一起工作，并将请求发送到LSR H2以建立下层LSP。VNTM使用本地策略和可能的管理/配置输入来确定如何处理来自PCE的计算结果。
An example procedure of the NMS-VNTM cooperation model (integrated flavor) is as follows.
NMS-VNTM合作模型（集成风味）的示例程序如下所示。
Step 1: NMS requests PCE to compute a path between H1 and H4. The request indicates that inter-layer path computation is allowed.
步骤1：NMS请求PCE计算H1和H4之间的路径。该请求指示允许进行层间路径计算。
Step 2: PCE computes a path. The result (H1-H2-L1-L2-H3-H4) is sent back to the NMS.
步骤2：PCE计算路径。结果（H1-H2-L1-L2-H3-H4）被发送回NMS。
Step 3: NMS discovers that a lower-layer LSP is needed. NMS works with VNTM to determine whether the new TE LSP H2-L1-L2-H3 is permitted according to policy, etc.
步骤3：NMS发现需要较低层LSP。NMS与VNTM合作，根据政策等确定是否允许新的TE LSP H2-L1-L2-H3。
Step 4: VNTM requests the ingress LSR in the lower-layer network (H2) to establish a lower-layer LSP. The request message includes the lower-layer LSP route obtained from PCE.
步骤4:VNTM请求下层网络（H2）中的入口LSR建立下层LSP。请求消息包括从PCE获得的下层LSP路由。
Step 5: H2 signals to establish the lower-layer LSP.
步骤5：H2信号建立下层LSP。
Step 6: If the lower-layer LSP setup is successful, H2 notifies VNTM that the LSP is complete and supplies the tunnel information.
步骤6：如果下层LSP设置成功，H2通知VNTM LSP已完成并提供隧道信息。
Step 7: H2 advertises the new LSP as a TE link in the higher-layer network routing instance.
步骤7:H2在更高层网络路由实例中将新LSP作为TE链路播发。
Step 8: VNTM notifies NMS that the underlying lower-layer LSP has been set up, and NMS notices the new TE link advertisement.
步骤8:VNTM通知NMS底层LSP已建立，NMS通知新的TE链路公告。
Step 9: NMS requests H1 to set up a higher-layer LSP between H1 and H4 with the path computed in Step 2. The lower-layer links are replaced by the corresponding higher-layer TE link. Hence, the NMS sends the path H1-H2-H3-H4 to H1.
步骤9:NMS请求H1在H1和H4之间建立更高层LSP，路径在步骤2中计算。较低层链接被相应的较高层TE链接替换。因此，NMS将路径H1-H2-H3-H4发送到H1。
Step 10: H1 initiates signaling with the path H2-H3-H4 to establish the higher-layer LSP.
步骤10:H1通过路径H2-H3-H4发起信令以建立更高层LSP。
o NMS-VNTM Cooperation Model (separate flavor)
o NMS-VNTM合作模式（独立风格）
-----
| NMS |
| | -----
----- | PCE |
^ ^ | Hi |
: : -----
: : ^
: : :
: : :
: v v
: ------ ----- ----- ------
: | LSR |--| LSR |........................| LSR |--| LSR |
: | H1 | | H2 | | H3 | | H4 |
: ------ -----\ /----- ------
: ^ \ /
: : \ /
: -------- \ /
v : \ /
------ ----- \----- -----/
| VNTM |<-->| PCE | | LSR |--| LSR |
| | | Lo | | L1 | | L2 |
------ ----- ----- -----
-----
| NMS |
| | -----
----- | PCE |
^ ^ | Hi |
: : -----
: : ^
: : :
: : :
: v v
: ------ ----- ----- ------
: | LSR |--| LSR |........................| LSR |--| LSR |
: | H1 | | H2 | | H3 | | H4 |
: ------ -----\ /----- ------
: ^ \ /
: : \ /
: -------- \ /
v : \ /
------ ----- \----- -----/
| VNTM |<-->| PCE | | LSR |--| LSR |
| | | Lo | | L1 | | L2 |
------ ----- ----- -----
Figure 9: NMS-VNTM Cooperation Model (separate flavor)
图9:NMS-VNTM合作模式（独立风格）
Figure 9 shows the NMS-VNTM cooperation model (separate flavor). The NMS manages the higher layer. The case of multiple PCE computation without inter-PCE communication is used to explain the 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.
图9显示了NMS-VNTM合作模型（独立风格）。NMS管理更高层。这里使用多个PCE计算而不进行PCE间通信的情况来解释NMS-VNTM合作模型，但是单PCE路径计算也可以应用于该模型。注意，具有PCE间通信的多PCE路径计算不适用于此模型。
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), which notifies the NMS. The notification may include information about the reason for failure (such as that there is no TE link between the border LSRs or that computation constraints cannot be met).
NMS请求前端LSR（本例中为H1）在前端和后端LSR之间建立更高层LSP，而不指定任何路由。作为PCC的前端LSR请求更高层PCE计算前端和后端LSR之间的路径。边界LSR（本例中为H2和H3）之间的较高层中没有TE链路。当PCE无法计算路径时，它会通知PCC（即前端LSR），后者会通知NMS。通知可能包括关于失败原因的信息（例如边界LSR之间没有TE链接或无法满足计算约束）。
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 -- the NMS discovers that an end-to-end LSP cannot be provisioned owing to the lack of a TE link between H2 and H3.
请注意，NMS而不是前端LSR咨询高层PCE同样有效。在这种情况下，结果是相同的——NMS发现由于H2和H3之间缺少TE链路，无法提供端到端LSP。
The NMS may now suggest (or request) to the VNTM that a lower-layer LSP between the border LSRs be established and 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 it may reject the operator's request for the service that requires the higher-layer LSP with a suggestion that the operator try again later.
NMS现在可以向VNTM建议（或请求）在边界LSR之间建立较低层LSP，并作为较高层中的TE链路进行广告，以支持未来较高层LSP请求。NMS和VNTM之间的通信可以以自动方式或手动方式执行，并且是也可以是单独的管理域的层之间的关键交互。因此，此通信可能是管理、计费和安全策略的应用点。NMS可以等待较低层LSP被设置并作为TE链路通告，或者可以拒绝运营商对需要较高层LSP的服务的请求，并建议运营商稍后重试。
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.
VNTM请求较低层PCE计算路径，然后请求H2建立较低层LSP。可选地，VNTM可针对LSP向H2发出直接请求，并且H2可咨询较低层PCE。在通知或通知NMS下层LSP已经建立后，它可以请求前端LSR（H1）在H1和H4之间建立高层端到端LSP。
Thus, cooperation between the higher 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.
因此，通过NMS和VNTM之间的通信来执行上层和下层之间的协作。NSM-VNTM合作模型的这种过程的示例如下，使用图6中的示例网络。
Step 1: NMS requests a head-end LSR (H1) to set up a higher-layer LSP between H1 and H4 without specifying any route.
步骤1：NMS请求前端LSR（H1）在H1和H4之间建立更高层LSP，而不指定任何路由。
Step 2: H1 (PCC) requests PCE to compute a path between H2 and H3.
步骤2:H1（PCC）请求PCE计算H2和H3之间的路径。
Step 3: The path computation fails because there is no TE link across the lower-layer network.
步骤3：路径计算失败，因为下层网络中没有TE链路。
Step 4: H1 (PCC) notifies NMS. The notification may include an indication that there is no TE link between H2 and H4.
步骤4:H1（PCC）通知NMS。通知可能包括H2和H4之间没有TE链路的指示。
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 acceptable within VNTM's policy constraints.
步骤5：NMS向VNTM建议（或请求）连接H2和H3的新TE链路将是有用的。NMS通知VNTM它将等待TE链路的创建。VNTM考虑是否应建立较低层LSP（如有必要且在VNTM的政策约束范围内可接受）。
Step 6: VNTM requests the lower-layer PCE for path computation.
步骤6:VNTM请求下层PCE进行路径计算。
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.
步骤7:VNTM请求下层网络（H2）中的入口LSR建立下层LSP。请求消息包括从负责下层网络的下层PCE获得的下层LSP路由。
Step 8: H2 signals the lower-layer LSP.
步骤8:H2向下层LSP发送信号。
Step 9: If the lower-layer LSP setup is successful, H2 notifies VNTM that the LSP is complete and supplies the tunnel information.
步骤9：如果下层LSP设置成功，H2通知VNTM LSP已完成并提供隧道信息。
Step 10: H2 advertises the new LSP as a TE link in the higher-layer network routing instance.
步骤10:H2在上层网络路由实例中将新LSP作为TE链路播发。
Step 11: VNTM notifies NMS that the underlying lower-layer LSP has been set up, and NMS notices the new TE link advertisement.
步骤11:VNTM通知NMS底层LSP已经建立，NMS通知新的TE链路公告。
Step 12: NMS again requests H1 to set up a higher-layer LSP between H1 and H4.
步骤12:NMS再次请求H1在H1和H4之间建立更高层LSP。
Step 13: 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.
步骤13:H1请求高层PCE计算路径并获得成功结果，该结果包括指定为H1-H2-H3-H4的高层路由，其中所有跳数都是严格的。
Step 14: H1 initiates signaling with the computed path H2-H3-H4 to establish the higher-layer LSP.
步骤14:H1使用计算出的路径H2-H3-H4发起信令以建立更高层LSP。
4.2.4. Possible Combinations of Inter-Layer Path Computation and Inter-Layer Path Control Models
4.2.4. 层间路径计算和层间路径控制模型的可能组合
Table 1 summarizes the possible combinations of inter-layer path computation and inter-layer path control models. There are three 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 four inter-layer path control models: the PCE-VNTM cooperation model, the higher-layer signaling trigger model, the NMS-VNTM cooperation model (integrated flavor), and the NMS-VNTM cooperation model (separate flavor). 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.
表1总结了层间路径计算和层间路径控制模型的可能组合。有三种层间路径计算模型：单PCE路径计算模型、具有层间通信模型的多PCE路径计算模型和不具有层间通信模型的多PCE路径计算模型。还有四种层间路径控制模型：PCE-VNTM协作模型、高层信令触发模型、NMS-VNTM协作模型（集成模式）和NMS-VNTM协作模型（分离模式）。除了多个PCE路径计算与层间PCE通信模型和NMS-VNTM协作模型的组合之外，层间路径计算与路径控制模型之间的所有组合都是可能的。
Table 1: Possible Combinations of Inter-Layer Path Computation and Inter-Layer Path Control Models
表1：层间路径计算和层间路径控制模型的可能组合
------------------------------------------------------
| 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 | Yes | Yes | No |
| cooperation | | | |
| (integrated flavor) | | | |
|---------------------+--------+-----------+-----------|
| NMS-VNTM | No* | No | Yes |
| cooperation | | | |
| (separate flavor) | | | |
---------------------+--------+-----------+-----------
------------------------------------------------------
| 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 | Yes | Yes | No |
| cooperation | | | |
| (integrated flavor) | | | |
|---------------------+--------+-----------+-----------|
| NMS-VNTM | No* | No | Yes |
| cooperation | | | |
| (separate flavor) | | | |
---------------------+--------+-----------+-----------
* Note that, in case of NSM-VNTM cooperation (separate flavor) 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.
* 注意，在NSM-VNTM协作（独立风格）和单个PCE层间路径计算的情况下，NMS和VNTM使用的PCE函数可以并置，但它将在单独的TED上运行。
This section compares the PCE-VNTM cooperation model, the higher-layer signaling trigger model, and the NMS-VNTM cooperation 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.
本节从VNTM功能、边界LSR功能、高层信令时间和复杂性（状态数和消息数）方面比较PCE-VNTM合作模型、高层信令触发模型和NMS-VNTM合作模型。考虑到所有这些因素，网络运营商可以在不同的部署场景中选择适当的模型。
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 and a border LSR. Communications between a higher-layer PCE and the VNTM are event notifications and may use Simple Network Management Protocol (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].
PCE-VNTM合作模型和NMS-VNTM模型都需要VNTM功能。在PCE-VNTM合作模型中，PCE和VNTM之间以及VNTM和边界LSR之间需要通信。高层PCE和VNTM之间的通信是事件通知，可以使用来自PCE MIB模块[PCE-MIB]的简单网络管理协议（SNMP）通知。请注意，从PCE到VNTM的通信没有任何确认。VNTM-LSR通信可以使用现有的GMPLS-TE MIB模块[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 the Path Computation Element Communication Protocol (PCEP) [RFC5440]. VNTM-LSR communications are the same as in the PCE-VNTM cooperation model.
在NMS-VNTM合作模型中，需要在NMS和VNTM之间、VNTM和较低层PCE之间以及VNTM和边界LSR之间进行通信。超出本文件范围的NMS-VNTM通信可能使用专有或标准接口，例如，其中一些接口在TM论坛中标准化。VNTM和下层PCE之间的通信使用路径计算元素通信协议（PCEP）[RFC5440]。VNTM-LSR通信与PCE-VNTM合作模型中的通信相同。
In the higher-layer signaling trigger model, no VNTM functions are required, and no such communications are required.
在高层信令触发模型中，不需要VNTM功能，也不需要此类通信。
If VNTM functions are not supported in a multi-layer network, the higher-layer signaling trigger model has to be chosen.
如果在多层网络中不支持VNTM功能，则必须选择更高层的信令触发模型。
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.
VNTM功能的加入允许更好地协调跨网络LSP隧道和应用网络范围的策略，这在触发器模型中应用起来要困难得多，因为它需要协调多个边界LSR之间的策略。
Also, VNTM functions could be applied to establish LSPs (or connections) in non-MPLS/GMPLS networks, which do not have signaling capabilities, by configuring each node along the path from the VNTM.
此外，VNTM功能可用于通过沿VNTM路径配置每个节点，在不具有信令能力的非MPLS/GMPLS网络中建立LSP（或连接）。
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.
在高层信令触发模型中，边界LSR必须具有一些附加功能。当较高层路径消息表明需要设置较低层LSP时，它需要触发较低层信令。注意，如果使用虚拟TE链路，则边界LSR必须能够触发信令。
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.
如果高层路径消息中的ERO使用单层路径或指定松散跃点，则接收路径消息的边界LSR必须通过咨询PCE或使用其自己的计算引擎获得下层路由。如果高层路径消息中的ERO使用多层路径，则边界LSR必须判断是否需要下层信令。
In the PCE-VNTM and NMS-VNTM cooperation models, 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.
在PCE-VNTM和NMS-VNTM合作模型中，边界LSR中不需要额外的触发信令功能，除非使用虚拟TE链路。因此，如果边界LSR不支持这些附加功能，其中边界LSR由VNTM控制以建立较低层LSP，则必须选择合作模型。
The complete inter-layer LSP setup time includes inter-layer path computation, signaling, and the communication time between PCC and PCE, PCE and VNTM, NMS and VNTM, and VNTM and LSR. In the PCE-VNTM and the NMS-VNTM cooperation models, 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.
完整的层间LSP设置时间包括层间路径计算、信令以及PCC和PCE、PCE和VNTM、NMS和VNTM以及VNTM和LSR之间的通信时间。在PCE-VNTM和NMS-VNTM合作模型中，与高层信令触发模型相比，需要额外的通信步骤。另一方面，协作模型以较长的服务设置时间为代价提供了更好的控制。
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.
注意，就高层信令时间而言，在高层信令触发模型中，从高层信令开始到完成所需的时间大于协作模型的时间，除非包括虚拟TE链路。这是因为前一个模型要求在高层信令期间发生低层信令。高层入口LSR必须等待更长的时间，直到高层信令完成。需要一个更高层的入口LSR来容忍更长的路径设置时间。
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.
如果高层和下层网络具有多个互连，则跨层边界的端到端LSP的最佳路径计算是非常重要的。较高的层LSP必须路由到正确的层边界节点，以实现两层中的优化。
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.
当较低层lsp作为TE链路播发到较高层网络中时，可以在较高层网络中解决计算。在将TE度量（即，成本）分配给较低层LSP时需要小心，因为它们作为进入较高层网络的TE链路进行广告，这可能是VNT管理器组件的功能。类似地，应注意这样一个事实，即穿过较低层网络的LSP可能共享常见故障点（例如，它们可能穿过较低层网络中的同一链路），并且必须相应地设置较高层中公布的TE链路的共享风险链路组（SRLGs）。
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.
在单PCE模型中，可以在单个计算中找到端到端路径，因为这两个层都完全可见，并且可以考虑通过所有层互连的所有可能路径。
Where PCEs cooperate to determine a path, an iterative computation model such as [RFC5441] can be used to select an optimal path across layers.
在PCE合作确定路径的情况下，可以使用迭代计算模型（如[RFC5441]）来选择跨层的最佳路径。
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, crankback signaling techniques [RFC4920] 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 set up a lower-layer path triggered by high-layer signaling when there is no TE link between border LSRs.
当非合作单层PCE（每个PCE位于单独的层）与触发LSP模型一起使用时，无法确定最佳边界LSR，甚至无法保证连接性。在这种情况下，可以使用回退信令技术[RFC4920]来最终实现连接，但实现最佳性要困难得多。在该模型中，当边界LSR之间没有TE链路时，入口LSR请求PCE计算路径的PCE期望边界LSR建立由高层信令触发的低层路径。
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 Section 8). 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.
许多网络运营商可能希望在不同层网络的管理之间提供明确的分离。在某些情况下，较低层网络可能来自一个组织的一个单独的商业部门或完全不同的法人团体。在这些情况下，适用于在较低层网络中建立LSP以及在较高层网络中将这些LSP作为TE链路发布的政策将反映商业协议和安全问题（见第8节）。由于较低层网络中LSP的容量可能显著大于客户端较高层网络（多路复用服务器模型）中的容量，较低层网络的管理员可能希望在允许较高层中的单个小需求占用较低层中的有价值资源之前谨慎行事。
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.
通过VNTM方法比使用触发信令更容易实现这种管理和管理分离的必要策略点。实际上，VNTM是所有低层LSP的协调点，可以与人工操作员以及策略和计费紧密联系。这种模型也可以通过使用触发信令来实现。
Inter-layer traffic engineering needs to be managed and operated correctly to avoid introducing instability problems.
层间流量工程需要正确管理和操作，以避免引入不稳定问题。
Lower-layer LSPs are likely, by the nature of the technologies used in layered networks, to be of considerably higher capacity than the higher-layer LSPs. This has the benefit of allowing multiple higher-layer LSPs to be carried across the lower-layer network in a single lower-layer LSP. However, when a new lower-layer LSP is set up to support a request for a higher-layer LSP because there is no suitable route in the higher-layer network, it may be the case that a very large LSP is established in support of a very small traffic demand. Further, if the higher-layer LSP is short-lived, the requirement for the lower-layer LSP will go away, either leaving it in place but
根据分层网络中使用的技术的性质，较低层LSP可能比较高层LSP具有更高的容量。这具有允许在单个低层LSP中跨低层网络承载多个高层LSP的优点。然而，当由于在高层网络中没有合适的路由而建立新的低层LSP以支持对高层LSP的请求时，可能存在建立非常大的LSP以支持非常小的业务需求的情况。此外，如果较高层LSP是短期的，则对较低层LSP的要求将消失，或者使其保持原位，但是
unused or requiring it to be torn down. This may cause excessive tie-up of unused lower-layer network resources, or may introduce instability into the lower-layer network. It is important that appropriate policy controls or configuration features are available so that demand-led establishment of lower-layer LSPs (the so-called "bandwidth on demand") is filtered according to the requirements of the lower-layer network.
未使用或需要拆除的。这可能会导致未使用的下层网络资源过度占用，或者可能会给下层网络带来不稳定性。重要的是，应提供适当的策略控制或配置功能，以便根据较低层网络的要求过滤由需求引导的较低层LSP（所谓的“按需带宽”）的建立。
When a higher-layer LSP is requested to be set up, a new lower-layer LSP may be established if there is no route with the requested bandwidth for the higher-layer LSP. After the lower-layer LSP is established, existing high-layer LSPs could be re-routed to use the newly established lower-layer LSP, if using the lower-layer LSP provides a better route than that taken by the existing LSPs. This re-routing may result in lower utilization of other lower-layer LSPs that used to carry the existing higher-layer LSPs. When the utilization of a lower-layer LSP drops below a threshold (or drops to zero), the LSP is deleted according to lower-layer network policy.
当请求建立高层LSP时，如果没有具有针对高层LSP的请求带宽的路由，则可以建立新的下层LSP。在建立较低层LSP之后，如果使用较低层LSP提供比现有LSP更好的路由，则可以重新路由现有的高层LSP以使用新建立的较低层LSP。这种重新路由可能导致用于承载现有高层LSP的其他下层LSP的利用率降低。当较低层LSP的利用率降至阈值以下（或降至零）时，根据较低层网络策略删除LSP。
But consider that some other new higher-layer LSP may be requested at once, requiring the establishment or re-establishment of a lower-layer LSP. This, in turn, may cause higher-layer re-routing, making other lower-layer LSPs under-utilized in a cyclic manner. This behavior makes the higher-layer network unstable.
但是考虑到其他新的更高层LSP可能同时被请求，需要建立或重新建立下层LSP。这反过来可能导致更高层的重新路由，使得其他下层lsp以循环方式未充分利用。这种行为使高层网络不稳定。
Inter-layer traffic engineering needs to avoid network instability problems. To solve the problem, network operators may have some constraints achieved through configuration or policy, where inter-layer path control actions such as re-routing and deletion of lower-layer LSPs are not easily allowed. For example, threshold parameters for the actions are determined so that hysteresis control behavior can be performed.
层间流量工程需要避免网络不稳定问题。为了解决这个问题，网络运营商可能会通过配置或策略实现一些约束，其中不容易允许层间路径控制操作，例如重新路由和删除下层LSP。例如，确定动作的阈值参数，以便执行滞后控制行为。
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.
层间MPLS或GMPLS流量工程必须根据可能与技术层边界重合的行政和管理边界来考虑。也就是说，每个层网络可能处于单独的管理控制之下，对网络应用不同的策略，并且在层之间的边界应用特定的策略规则。
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.
需要建立管理机制，以确保在不违反网络运营商使用的政策和管理操作程序的情况下应用层间流量工程。
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.
能够支持层间计算的PCE实现应提供一个配置开关，以允许启用或禁用对层间路径计算的支持。
When a PCE is capable of, and configured for, inter-layer path computation, it should advertise this capability as described in [PCC-PCE], but this advertisement may be suppressed through a secondary configuration option.
当PCE能够并且被配置用于层间路径计算时，它应该按照[PCC-PCE]中的描述公布该能力，但是该公布可以通过辅助配置选项来抑制。
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.
如果每一层作为单独的网络运行，运营商必须控制适用于每一网络的策略，并且该控制应独立于其他网络的策略控制。
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.
当多个层作为同一网络的一部分进行操作时，运营商可以对跨所有层的集成策略具有单个控制点，或者可以对每个层的单独策略进行控制。
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 (see Section 6). It may also be used to ensure appropriate billing for the lower-layer LSPs.
层间流量工程最重要的问题可能是层间策略。这可能涵盖诸如在什么情况下可以建立较低层LSP以在较高层网络中提供连接性之类的问题。可能存在层间策略，以保护较低层（高容量）网络免受较高层网络微观需求的动态变化的影响（见第6节）。它还可用于确保较低层LSP的适当计费。
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 [RFC5394].
层间策略应包括网络层之间连接点的定义、要应用的层间TE模型（例如，本文档中描述的模型之间的选择）以及路径计算和LSP设置规则。如果定义了层间策略，则必须在整个网络中一致地使用该策略，并且应使执行层间计算的PCE能够使用该策略，以便计算适当的路径。[RFC5394]中讨论了向PCE提供政策信息的机制。
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 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.
VNTM可以为层间策略的实现提供合适的功能组件。VNTM的使用允许较低层网络的管理员应用层间策略，而无需向较高层网络的运营商公开该策略。类似地，协作PCE模型（有或没有PCE间通信）允许在路径选择期间单独应用策略。
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.
支持层间计算的任何协议扩展必须附带用于控制和监视协议扩展的MIB对象的定义。这些MIB对象定义通常与定义协议扩展的文档放在单独的文档中。MIB对象可以在用于管理正在扩展的基本协议的同一MIB模块中提供。
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.
注意，层间PCE功能本身应该可以通过MIB模块进行管理。通常，这意味着用于管理PCE的MIB模块应包括可用于选择和报告每个PCE层间行为的对象。还可以提供报告层间PCE相互作用的统计信息。
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.
如果PCE和VNTM之间存在通信，则可能需要额外的MIB模块来管理和建模这些通信。另一方面，如果这些通信是通过MIB通知提供的，那么这些通知必须构成MIB模块定义的一部分。
Policy Information Base (PIB) modules may also be appropriate to meet the requirements as described in Section 7.1 and [RFC5394].
政策信息库（PIB）模块也适用于满足第7.1节和[RFC5394]中所述的要求。
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.
PCE和PCC之间以及[RFC4657]中所述的协作PCE之间需要活性检测和监控。层间流量工程不会改变这一要求。
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.
在PCE和VNTM之间存在通信的情况下，可能需要额外的活跃度检测和监视，以允许PCE知道VNTM是否已接收到关于失败路径计算和期望TE链路的信息。
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
当较低层LSP出现故障（可能是由于较低层网络资源的故障）或由于较低层网络策略而被拆除时，应向
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 higher-layer network may additionally operate data plane failure techniques over the virtual TE links in the VNT in order 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 Operations, Administration, and Management (OAM) techniques will report a failure.
尽管层间策略可能要求对更高层隐藏这样的更改，但在VNT中更高层是一个更改。更高层网络还可以在VNT中的虚拟TE链路上操作数据平面故障技术，以便监视连接的活跃度，但是应当注意，如果虚拟TE链路在较低层中被公布但尚未建立为LSP，则此类更高层操作、管理、，和管理（OAM）技术将报告故障。
The correct operation of the PCE computations and interactions are described in [RFC4657], [RFC5440], etc., and does not need further discussion here.
[RFC4657]、[RFC5440]等中描述了PCE计算和交互的正确操作，此处无需进一步讨论。
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 7.2. 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 7.2. 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.
层间流量工程的正确运行可通过多种方式进行测量。首先，由于低层缺乏连通性而导致的高层路径计算的失败率可作为VNT有效性的一个衡量指标，并可作为第7.2节所述数据模型的一部分进行报告。其次，VNT的变化率（即，基于较低层LSP的较高层TE链路的建立和移除率）可被视为VNT正确规划的度量，也可构成第7.2节所述数据模型的一部分。第三，较低层的网络资源利用率（就资源拥塞而言，以及考虑到为支持虚拟TE链路而设置的LSP的利用率不足而言）可以表明是否正在应用有效的层间流量工程。
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.
高层网络中的管理工具应提供以下视图：哪些TE链路使用计划的低层容量（即物理连接或永久连接）提供，哪些TE链路是动态的，并通过层间流量工程实现。较低层中的管理工具应提供较低层LSP使用情况的视图，包括是否已将其设置为支持VNT中的TE链路，以及如果已设置，用于哪个客户端网络。
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.
在本文档中没有定义协议或协议扩展，因此不适合考虑与其他协议的特定交互。然而，应注意，本文件的目的是为MPLS-TE和GMPLS网络启用层间流量工程，因此假定路由和信令协议的层间操作的必要功能已经存在或将要开发。
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, 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.
本文档介绍各种网络组件（PCE、LSR、NMS和VNTM）的角色。为了使层间TE有效，这些组件都需要发挥作用。也就是说，假设这些功能组件中的任何一个的存在和运行的层间TE模型显然依赖于这些组件来完成本文档中描述的角色。
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.
使用PCE计算层间路径预计将对网络运营产生重大和有益的影响。层间流量工程本身可以向高层网络提供额外的灵活性，同时允许下层网络以更有效的方式支持更多和不同的客户端网络。跨网络层的流量工程允许优化使用所有层中的网络资源。
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.
本文件中所述的PCE的使用还可以对负责执行层间路径计算的PCE的加载产生有益的影响，同时促进网络层的更独立的操作模型。
Inter-layer traffic engineering with PCE raises new security issues in all three inter-layer path control models.
采用PCE的层间流量工程在所有三种层间路径控制模型中提出了新的安全问题。
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 the 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, SNMPv3 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.
在PCE和VNTM之间的合作模型中，当PCE确定需要新的较低层LSP时，PCE和VNTM之间以及VNTM和边界LSR之间需要通信。在这种情况下，这些通信应该具有安全机制，以确保所交换信息的真实性、隐私性和完整性。特别是，在低层网络中防止LSP设置的错误触发非常重要，因为这种伪造可能会占用低层网络资源（在低层网络和试图使用它的高层网络上实现拒绝服务攻击）并可能导致下层网络提供的服务的不正确计费。当PCE MIB模块用于提供高层PCE和VNTM之间的通知交换时，应使用SNMPv3以确保足够的安全性。此外，VNTM应提供可配置或动态策略功能，以便在接收到来自更高层PCE的通知时可以控制VNTM行为。
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
高层信令触发模型中的主要安全问题与机密性有关。PCE可将包括下层中的ERO的多层路径通知高层PCC
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 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 [RFC5520] that can be expanded within the lower-layer network. Consideration must also be given to filtering the recorded path information from the lower-layer -- see [RFC4208], for example.
网络，但PCC可能无法看到下层网络的TE拓扑，并且可能不信任此信息。可以使用跨低层网络的松散跳，但这会降低多层流量工程的效益。更好的替代方案可以是使用可在较低层网络内扩展的路径密钥[RFC5520]来屏蔽较低层路径。还必须考虑从较低层过滤记录的路径信息——例如参见[RFC4208]。
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.
此外，在高层信令触发模型中，必须考虑层间接口处信令的安全性，因为各层可能属于不同的管理或信任域。
The NMS-VNTM cooperation model introduces communication between the NMS and the VNTM. Both of these components belong to the management plane, and such 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.
NMS-VNTM合作模型引入了NMS和VNTM之间的通信。这两个组件都属于管理平面，此类通信不在本PCE文档的范围内。请注意，NMS-VNTM合作模式可被视为解决许多安全和政策问题，因为与其他模式更具动态性的机制相比，控制和决策处于运营商的影响范围内。然而，安全问题已经简单地转移了，需要对运营商和策略进行身份验证。
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 -- effectively, a single security breach can expose information that requires multiple breaches in other models.
当单个PCE被授予适用于多个层的TE信息的完全可见性时，也可能存在安全问题。对单个PCE的任何访问都将立即获得对所有网络层的拓扑信息的访问——实际上，一个单一的安全漏洞可以暴露需要在其他模型中多次漏洞的信息。
Note that, as described in Section 6, inter-layer TE can cause network stability issues, and this could be leveraged to attack either the higher- or lower-layer network. Precautionary measures, such as those described in Section 7.1.3, can be applied through policy or configuration to dampen any network oscillations.
请注意，如第6节所述，层间TE可能会导致网络稳定性问题，这可能会被用来攻击上层或下层网络。可通过政策或配置采取预防措施，如第7.1.3节所述，以抑制任何网络振荡。
We would like to thank Kohei Shiomoto, Ichiro Inoue, Julien Meuric, Jean-Francois Peltier, Young Lee, Ina Minei, Jean-Philippe Vasseur, and Franz Rambach for their useful comments.
我们要感谢大尾大雄、井上一郎、朱利安·穆里安、让·弗朗索瓦·佩尔蒂埃、杨·李、伊娜·米尼、让·菲利普·瓦瑟尔和弗兰兹·兰巴赫所作的有益评论。
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001.
[RFC3031]Rosen，E.，Viswanathan，A.，和R.Callon，“多协议标签交换体系结构”，RFC 30312001年1月。
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC3945]Mannie，E.，Ed.“通用多协议标签交换（GMPLS）体系结构”，RFC 39452004年10月。
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4206]Kompella，K.和Y.Rekhter，“具有通用多协议标签交换（GMPLS）流量工程（TE）的标签交换路径（LSP）层次结构”，RFC 4206，2005年10月。
[PCE-MIB] Stephan, E., "Definitions of Textual Conventions for Path Computation Element", Work in Progress, March 2009.
[PCE-MIB]Stephan，E.，“路径计算元素的文本约定定义”，正在进行的工作，2009年3月。
[PCC-PCE] Oki, E., Le Roux, JL., Kumaki, K., Farrel, A., and T. Takeda, "PCC-PCE Communication and PCE Discovery Requirements for Inter-Layer Traffic Engineering", Work in Progress, January 2009.
[PCC-PCE]Oki，E.，Le Roux，JL.，Kumaki，K.，Farrel，A.，和T.Takeda，“层间流量工程的PCC-PCE通信和PCE发现要求”，在建工程，2009年1月。
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter, "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.
[RFC4208]Swallow，G.，Drake，J.，Ishimatsu，H.，和Y.Rekhter，“通用多协议标签交换（GMPLS）用户网络接口（UNI）：覆盖模型的资源预留协议流量工程（RSVP-TE）支持”，RFC 4208，2005年10月。
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4655]Farrel，A.，Vasseur，J.-P.，和J.Ash，“基于路径计算元素（PCE）的体系结构”，RFC 46552006年8月。
[RFC4657] Ash, J., Ed., and J. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, September 2006.
[RFC4657]Ash，J.，Ed.，和J.Le Roux，Ed.，“路径计算元件（PCE）通信协议通用要求”，RFC 4657，2006年9月。
[RFC4802] Nadeau, T., Ed., and A. Farrel, Ed., "Generalized Multiprotocol Label Switching (GMPLS) Traffic Engineering Management Information Base", RFC 4802, February 2007.
[RFC4802]Nadeau，T.，Ed.，和A.Farrel，Ed.，“通用多协议标签交换（GMPLS）流量工程管理信息库”，RFC 4802，2007年2月。
[RFC4920] Farrel, A., Ed., Satyanarayana, A., Iwata, A., Fujita, N., and G. Ash, "Crankback Signaling Extensions for MPLS and GMPLS RSVP-TE", RFC 4920, July 2007.
[RFC4920]Farrel，A.，Ed.，Satyanarayana，A.，Iwata，A.，Fujita，N.，和G.Ash，“MPLS和GMPLS RSVP-TE的回退信令扩展”，RFC 4920，2007年7月。
[RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux, M., and D. Brungard, "Requirements for GMPLS-Based Multi-Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July 2008.
[RFC5212]Shiomoto，K.，Papadimitriou，D.，Le Roux，JL.，Vigoureux，M.，和D.Brungard，“基于GMPLS的多区域和多层网络（MRN/MLN）的要求”，RFC 52122008年7月。
[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash, "Policy-Enabled Path Computation Framework", RFC 5394, December 2008.
[RFC5394]Bryskin，I.，Papadimitriou，D.，Berger，L.，和J.Ash，“策略启用路径计算框架”，RFC 53942008年12月。
[RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009.
[RFC5440]Vasseur，JP.，Ed.，和JL。Le Roux，Ed.“路径计算元素（PCE）通信协议（PCEP）”，RFC 54402009年3月。
[RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Procedure to Compute Shortest Constrained Inter-Domain Traffic Engineering Label Switched Paths", RFC 5441, April 2009.
[RFC5441]Vasseur，JP.，Ed.，Zhang，R.，Bitar，N.，和JL。Le Roux，“计算最短约束域间流量工程标签交换路径的基于PCE的反向递归计算（BRPC）过程”，RFC 54412009年4月。
[RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel, "Preserving Topology Confidentiality in Inter-Domain Path Computation Using a Path-Key-Based Mechanism", RFC 5520, April 2009.
[RFC5520]Bradford，R.，Ed.，Vasseur，JP.，和A.Farrel，“使用基于路径密钥的机制在域间路径计算中保持拓扑机密性”，RFC 5520，2009年4月。
Authors' Addresses
作者地址
Eiji Oki University of Electro-Communications Tokyo Japan EMail: oki@ice.uec.ac.jp
东京电子通信大学东京日本电邮：oki@ice.uec.ac.jp
Tomonori Takeda NTT 3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan EMail: takeda.tomonori@lab.ntt.co.jp
武田县武藏市武藏町3-9-11 Midori cho，日本东京180-8585，电子邮件：武田。tomonori@lab.ntt.co.jp
Jean-Louis Le Roux France Telecom R&D, Av Pierre Marzin, 22300 Lannion, France EMail: jeanlouis.leroux@orange-ftgroup.com
Jean-Louis Le Roux法国电信研发部，Av Pierre Marzin，法国兰尼翁22300电子邮件：jeanlouis。leroux@orange-ftgroup.com
Adrian Farrel Old Dog Consulting EMail: adrian@olddog.co.uk
Adrian Farrel老狗咨询电子邮件：adrian@olddog.co.uk