Network Working Group V. Sharma, Ed.
Request for Comments: 3469 Metanoia, Inc.
Category: Informational F. Hellstrand, Ed.
Nortel Networks
February 2003
Network Working Group V. Sharma, Ed.
Request for Comments: 3469 Metanoia, Inc.
Category: Informational F. Hellstrand, Ed.
Nortel Networks
February 2003
Framework for Multi-Protocol Label Switching (MPLS)-based Recovery
基于多协议标签交换（MPLS）的恢复框架
Status of this Memo
本备忘录的状况
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 Notice
版权公告
Copyright (C) The Internet Society (2003). All Rights Reserved.
版权所有（C）互联网协会（2003年）。版权所有。
Abstract
摘要
Multi-protocol label switching (MPLS) integrates the label swapping forwarding paradigm with network layer routing. To deliver reliable service, MPLS requires a set of procedures to provide protection of the traffic carried on different paths. This requires that the label switching routers (LSRs) support fault detection, fault notification, and fault recovery mechanisms, and that MPLS signaling support the configuration of recovery. With these objectives in mind, this document specifies a framework for MPLS based recovery. Restart issues are not included in this framework.
多协议标签交换（MPLS）将标签交换转发模式与网络层路由相结合。为了提供可靠的服务，MPLS需要一组过程来保护在不同路径上传输的流量。这要求标签交换路由器（LSR）支持故障检测、故障通知和故障恢复机制，并且MPLS信令支持恢复配置。考虑到这些目标，本文档为基于MPLS的恢复指定了一个框架。此框架中不包括重启问题。
Table of Contents
目录
1. Introduction................................................2
1.1. Background............................................3
1.2. Motivation for MPLS-Based Recovery....................4
1.3. Objectives/Goals......................................5
2. Overview....................................................6
2.1. Recovery Models.......................................7
2.1.1 Rerouting.....................................7
2.1.2 Protection Switching..........................8
2.2. The Recovery Cycles...................................8
2.2.1 MPLS Recovery Cycle Model.....................8
2.2.2 MPLS Reversion Cycle Model...................10
2.2.3 Dynamic Re-routing Cycle Model...............12
2.2.4 Example Recovery Cycle.......................13
2.3. Definitions and Terminology..........................14
2.3.1 General Recovery Terminology.................14
1. Introduction................................................2
1.1. Background............................................3
1.2. Motivation for MPLS-Based Recovery....................4
1.3. Objectives/Goals......................................5
2. Overview....................................................6
2.1. Recovery Models.......................................7
2.1.1 Rerouting.....................................7
2.1.2 Protection Switching..........................8
2.2. The Recovery Cycles...................................8
2.2.1 MPLS Recovery Cycle Model.....................8
2.2.2 MPLS Reversion Cycle Model...................10
2.2.3 Dynamic Re-routing Cycle Model...............12
2.2.4 Example Recovery Cycle.......................13
2.3. Definitions and Terminology..........................14
2.3.1 General Recovery Terminology.................14
2.3.2 Failure Terminology..........................17
2.4. Abbreviations........................................18
3. MPLS-based Recovery Principles.............................18
3.1. Configuration of Recovery............................19
3.2. Initiation of Path Setup.............................19
3.3. Initiation of Resource Allocation....................20
3.3.1 Subtypes of Protection Switching.............21
3.4. Scope of Recovery....................................21
3.4.1 Topology.....................................21
3.4.2 Path Mapping.................................24
3.4.3 Bypass Tunnels...............................25
3.4.4 Recovery Granularity.........................25
3.4.5 Recovery Path Resource Use...................26
3.5. Fault Detection......................................26
3.6. Fault Notification...................................27
3.7. Switch-Over Operation................................28
3.7.1 Recovery Trigger.............................28
3.7.2 Recovery Action..............................29
3.8. Post Recovery Operation..............................29
3.8.1 Fixed Protection Counterparts................29
3.8.2 Dynamic Protection Counterparts..............30
3.8.3 Restoration and Notification.................31
3.8.4 Reverting to Preferred Path
(or Controlled Rearrangement)................31
3.9. Performance..........................................32
4. MPLS Recovery Features.....................................32
5. Comparison Criteria........................................33
6. Security Considerations....................................35
7. Intellectual Property Considerations.......................36
8. Acknowledgements...........................................36
9. References.................................................36
9.1 Normative References.................................36
9.2 Informative References...............................37
10. Contributing Authors.......................................37
11. Authors' Addresses.........................................39
12. Full Copyright Statement...................................40
2.3.2 Failure Terminology..........................17
2.4. Abbreviations........................................18
3. MPLS-based Recovery Principles.............................18
3.1. Configuration of Recovery............................19
3.2. Initiation of Path Setup.............................19
3.3. Initiation of Resource Allocation....................20
3.3.1 Subtypes of Protection Switching.............21
3.4. Scope of Recovery....................................21
3.4.1 Topology.....................................21
3.4.2 Path Mapping.................................24
3.4.3 Bypass Tunnels...............................25
3.4.4 Recovery Granularity.........................25
3.4.5 Recovery Path Resource Use...................26
3.5. Fault Detection......................................26
3.6. Fault Notification...................................27
3.7. Switch-Over Operation................................28
3.7.1 Recovery Trigger.............................28
3.7.2 Recovery Action..............................29
3.8. Post Recovery Operation..............................29
3.8.1 Fixed Protection Counterparts................29
3.8.2 Dynamic Protection Counterparts..............30
3.8.3 Restoration and Notification.................31
3.8.4 Reverting to Preferred Path
(or Controlled Rearrangement)................31
3.9. Performance..........................................32
4. MPLS Recovery Features.....................................32
5. Comparison Criteria........................................33
6. Security Considerations....................................35
7. Intellectual Property Considerations.......................36
8. Acknowledgements...........................................36
9. References.................................................36
9.1 Normative References.................................36
9.2 Informative References...............................37
10. Contributing Authors.......................................37
11. Authors' Addresses.........................................39
12. Full Copyright Statement...................................40
This memo describes a framework for MPLS-based recovery. We provide a detailed taxonomy of recovery terminology, and discuss the motivation for, the objectives of, and the requirements for MPLS-based recovery. We outline principles for MPLS-based recovery, and also provide comparison criteria that may serve as a basis for comparing and evaluating different recovery schemes.
本备忘录描述了基于MPLS的恢复框架。我们提供了恢复术语的详细分类，并讨论了基于MPLS的恢复的动机、目标和要求。我们概述了基于MPLS的恢复的原则，并提供了可作为比较和评估不同恢复方案的基础的比较标准。
At points in the document, we provide some thoughts about the operation or viability of certain recovery objectives. These should be viewed as the opinions of the authors, and not the consolidated views of the IETF. The document is informational and it is expected that a standards track document will be developed in the future to describe a subset of this document as to meet the needs currently specified by the TE WG.
在本文档中，我们提供了一些关于某些恢复目标的操作或可行性的想法。这些应视为作者的意见，而不是IETF的综合意见。本文件为信息性文件，预计未来将编制一份标准跟踪文件，描述本文件的一个子集，以满足TE工作组当前规定的需求。
Network routing deployed today is focused primarily on connectivity, and typically supports only one class of service, the best effort class. Multi-protocol label switching [RFC3031], on the other hand, by integrating forwarding based on label-swapping of a link local label with network layer routing allows flexibility in the delivery of new routing services. MPLS allows for using such media-specific forwarding mechanisms as label swapping. This enables some sophisticated features such as quality-of-service (QoS) and traffic engineering [RFC2702] to be implemented more effectively. An important component of providing QoS, however, is the ability to transport data reliably and efficiently. Although the current routing algorithms are robust and survivable, the amount of time they take to recover from a fault can be significant, in the order of several seconds (for interior gateway protocols (IGPs)) or minutes (for exterior gateway protocols, such as the Border Gateway Protocol (BGP)), causing disruption of service for some applications in the interim. This is unacceptable in situations where the aim is to provide a highly reliable service, with recovery times that are in the order of seconds down to 10's of milliseconds. IP routing may also not be able to provide bandwidth recovery, where the objective is to provide not only an alternative path, but also bandwidth equivalent to that available on the original path. (For some recent work on bandwidth recovery schemes, the reader is referred to [MPLS-BACKUP].) Examples of such applications are Virtual Leased Line services, Stock Exchange data services, voice traffic, video services etc, i.e., every application that gets a disruption in service long enough to not fulfill service agreements or the required level of quality.
今天部署的网络路由主要集中在连接性上，通常只支持一类服务，即尽力而为类。另一方面，多协议标签交换[RFC3031]通过将基于链路本地标签的标签交换的转发与网络层路由集成，允许灵活地提供新的路由服务。MPLS允许使用特定于媒体的转发机制，如标签交换。这使得服务质量（QoS）和流量工程[RFC2702]等一些复杂功能能够更有效地实现。然而，提供QoS的一个重要组成部分是可靠和高效地传输数据的能力。尽管当前的路由算法具有鲁棒性和可生存性，但它们从故障中恢复所需的时间可能很长，大约为几秒钟（对于内部网关协议（IGP））或几分钟（对于外部网关协议，例如边界网关协议（BGP）），在此期间导致某些应用程序的服务中断。如果目标是提供高度可靠的服务，恢复时间从几秒减少到10毫秒，这是不可接受的。IP路由也可能无法提供带宽恢复，其目标不仅是提供替代路径，而且还提供与原始路径上可用带宽相等的带宽。（关于带宽恢复方案的一些最新工作，读者可参考[MPLS-BACKUP]）此类应用的示例包括虚拟专线服务、证券交易所数据服务、语音通信、视频服务等，即。，每个应用程序的服务中断时间长到不能满足服务协议或要求的质量级别。
MPLS recovery may be motivated by the notion that there are limitations to improving the recovery times of current routing algorithms. Additional improvement can be obtained by augmenting these algorithms with MPLS recovery mechanisms [MPLS-PATH]. Since MPLS is a possible technology of choice in future IP-based transport networks, it is useful that MPLS be able to provide protection and restoration of traffic. MPLS may facilitate the convergence of network functionality on a common control and management plane. Further, a protection priority could be used as a differentiating
MPLS恢复的动机可能是，改进当前路由算法的恢复时间存在局限性。通过使用MPLS恢复机制[MPLS-PATH]增强这些算法，可以获得额外的改进。由于MPLS是未来基于IP的传输网络中可能选择的技术，因此MPLS能够提供流量保护和恢复是非常有用的。MPLS可促进网络功能在公共控制和管理平面上的融合。此外，保护优先级可以用作区别
mechanism for premium services that require high reliability, such as Virtual Leased Line services, and high priority voice and video traffic. The remainder of this document provides a framework for MPLS based recovery. It is focused at a conceptual level and is meant to address motivation, objectives and requirements. Issues of mechanism, policy, routing plans and characteristics of traffic carried by recovery paths are beyond the scope of this document.
用于要求高可靠性的高级服务的机制，例如虚拟专线服务以及高优先级语音和视频流量。本文档的其余部分提供了一个基于MPLS的恢复框架。它侧重于概念层面，旨在解决动机、目标和需求。恢复路径承载的机制、策略、路由计划和流量特性等问题超出了本文档的范围。
MPLS based protection of traffic (called MPLS-based Recovery) is useful for a number of reasons. The most important is its ability to increase network reliability by enabling a faster response to faults than is possible with traditional Layer 3 (or IP layer) approaches alone while still providing the visibility of the network afforded by Layer 3. Furthermore, a protection mechanism using MPLS could enable IP traffic to be put directly over WDM optical channels and provide a recovery option without an intervening SONET layer or optical protection. This would facilitate the construction of IP-over-WDM networks that request a fast recovery ability (Note that what is meant here is the transport of IP traffic over WDM links, not the Generalized MPLS, or GMPLS, control of a WDM link).
基于MPLS的流量保护（称为基于MPLS的恢复）非常有用，原因有很多。最重要的是，与传统的第3层（或IP层）方法相比，它能够更快地响应故障，同时仍然提供第3层提供的网络可视性，从而提高网络可靠性。此外，使用MPLS的保护机制可以使IP流量直接置于WDM光信道上，并提供恢复选项，而无需中间的SONET层或光保护。这将有助于构建要求快速恢复能力的IP over WDM网络（请注意，这里的意思是通过WDM链路传输IP流量，而不是通过通用MPLS或GMPLS控制WDM链路）。
The need for MPLS-based recovery arises because of the following:
需要基于MPLS的恢复是因为以下原因：
I. Layer 3 or IP rerouting may be too slow for a core MPLS network that needs to support recovery times that are smaller than the convergence times of IP routing protocols.
I.对于需要支持小于IP路由协议收敛时间的恢复时间的核心MPLS网络，第3层或IP重路由可能太慢。
II. Layer 3 or IP rerouting does not provide the ability to provide bandwidth protection to specific flows (e.g., voice over IP, virtual leased line services).
二,。第3层或IP重路由不能为特定流（例如IP语音、虚拟专线服务）提供带宽保护。
III. Layer 0 (for example, optical layer) or Layer 1 (for example, SONET) mechanisms may be wasteful use of resources.
三、 第0层（例如，光学层）或第1层（例如，SONET）机制可能会浪费资源。
IV. The granularity at which the lower layers may be able to protect traffic may be too coarse for traffic that is switched using MPLS-based mechanisms.
四、 较低层能够保护业务的粒度对于使用基于MPLS的机制交换的业务来说可能过于粗糙。
V. Layer 0 or Layer 1 mechanisms may have no visibility into higher layer operations. Thus, while they may provide, for example, link protection, they cannot easily provide node protection or protection of traffic transported at layer 3. Further, this may prevent the lower layers from providing restoration based on the traffic's needs. For example, fast restoration for traffic that needs it, and slower restoration (with possibly more optimal use of resources) for traffic that does not require fast
V.第0层或第1层机制可能无法看到更高层的操作。因此，尽管它们可以提供例如链路保护，但它们不能轻易地提供节点保护或在第3层传输的业务的保护。此外，这可防止较低层基于业务的需要提供恢复。例如，对于需要快速恢复的流量，可以使用快速恢复；对于不需要快速恢复的流量，可以使用较慢的恢复速度（可能更优化地使用资源）
restoration. In networks where the latter class of traffic is dominant, providing fast restoration to all classes of traffic may not be cost effective from a service provider's perspective.
恢复在后一类流量占主导地位的网络中，从服务提供商的角度来看，为所有类别的流量提供快速恢复可能不具有成本效益。
VI. MPLS has desirable attributes when applied to the purpose of recovery for connectionless networks. Specifically that an LSP is source routed and a forwarding path for recovery can be "pinned" and is not affected by transient instability in SPF routing brought on by failure scenarios.
六、 MPLS在用于无连接网络的恢复时具有理想的特性。具体来说，LSP是源路由的，用于恢复的转发路径可以“固定”，并且不受故障场景导致的SPF路由中的瞬时不稳定性的影响。
VII. Establishing interoperability of protection mechanisms between routers/LSRs from different vendors in IP or MPLS networks is desired to enable recovery mechanisms to work in a multivendor environment, and to enable the transition of certain protected services to an MPLS core.
七,。需要在IP或MPLS网络中不同供应商的路由器/LSR之间建立保护机制的互操作性，以使恢复机制能够在多供应商环境中工作，并使某些受保护的服务能够过渡到MPLS核心。
The following are some important goals for MPLS-based recovery.
以下是基于MPLS的恢复的一些重要目标。
I. MPLS-based recovery mechanisms may be subject to the traffic engineering goal of optimal use of resources.
I.基于MPLS的恢复机制可能受制于优化使用资源的流量工程目标。
II. MPLS based recovery mechanisms should aim to facilitate restoration times that are sufficiently fast for the end user application. That is, that better match the end-user's application requirements. In some cases, this may be as short as 10s of milliseconds.
二,。基于MPLS的恢复机制应旨在促进恢复时间的加快，以满足最终用户应用程序的需要。也就是说，它更符合最终用户的应用程序需求。在某些情况下，这可能短至10毫秒。
We observe that I and II may be conflicting objectives, and a trade off may exist between them. The optimal choice depends on the end-user application's sensitivity to restoration time and the cost impact of introducing restoration in the network, as well as the end-user application's sensitivity to cost.
我们注意到，一和二可能是相互冲突的目标，它们之间可能存在权衡。最佳选择取决于最终用户应用程序对恢复时间的敏感性和在网络中引入恢复的成本影响，以及最终用户应用程序对成本的敏感性。
III. MPLS-based recovery should aim to maximize network reliability and availability. MPLS-based recovery of traffic should aim to minimize the number of single points of failure in the MPLS protected domain.
三、 基于MPLS的恢复应旨在最大限度地提高网络可靠性和可用性。基于MPLS的流量恢复应旨在最大限度地减少MPLS保护域中的单点故障数量。
IV. MPLS-based recovery should aim to enhance the reliability of the protected traffic while minimally or predictably degrading the traffic carried by the diverted resources.
四、 基于MPLS的恢复应旨在提高受保护流量的可靠性，同时最小化或可预测地降低分流资源所承载的流量。
V. MPLS-based recovery techniques should aim to be applicable for protection of traffic at various granularities. For example, it should be possible to specify MPLS-based recovery for a portion of the traffic on an individual path, for all traffic
V.基于MPLS的恢复技术应旨在适用于各种粒度的流量保护。例如，应该可以为单个路径上的一部分流量以及所有流量指定基于MPLS的恢复
on an individual path, or for all traffic on a group of paths. Note that a path is used as a general term and includes the notion of a link, IP route or LSP.
在单个路径上，或对于一组路径上的所有流量。请注意，路径用作一般术语，包括链路、IP路由或LSP的概念。
VI. MPLS-based recovery techniques may be applicable for an entire end-to-end path or for segments of an end-to-end path.
六、 基于MPLS的恢复技术可适用于整个端到端路径或端到端路径的段。
VII. MPLS-based recovery mechanisms should aim to take into consideration the recovery actions of lower layers. MPLS-based mechanisms should not trigger lower layer protection switching nor should MPLS-based mechanisms be triggered when lower layer switching has or may imminently occur.
七,。基于MPLS的恢复机制应旨在考虑较低层的恢复操作。基于MPLS的机制不应触发低层保护切换，也不应在低层切换已经发生或可能即将发生时触发基于MPLS的机制。
VIII. MPLS-based recovery mechanisms should aim to minimize the loss of data and packet reordering during recovery operations. (The current MPLS specification itself has no explicit requirement on reordering.)
八,。基于MPLS的恢复机制应旨在最大限度地减少恢复操作期间的数据丢失和数据包重新排序。（当前MPLS规范本身对重新排序没有明确要求。）
IX. MPLS-based recovery mechanisms should aim to minimize the state overhead incurred for each recovery path maintained.
九、 基于MPLS的恢复机制应旨在将维护的每个恢复路径产生的状态开销降至最低。
X. MPLS-based recovery mechanisms should aim to minimize the signaling overhead to setup and maintain recovery paths and to notify failures.
X.基于MPLS的恢复机制应旨在将建立和维护恢复路径以及通知故障的信令开销降至最低。
XI. MPLS-based recovery mechanisms should aim to preserve the constraints on traffic after switchover, if desired. That is, if desired, the recovery path should meet the resource requirements of, and achieve the same performance characteristics as, the working path.
席。如果需要，基于MPLS的恢复机制应旨在保留切换后的流量限制。也就是说，如果需要，恢复路径应该满足工作路径的资源需求，并实现与工作路径相同的性能特征。
We observe that some of the above are conflicting goals, and real deployment will often involve engineering compromises based on a variety of factors such as cost, end-user application requirements, network efficiency, complexity involved, and revenue considerations. Thus, these goals are subject to tradeoffs based on the above considerations.
我们注意到，上述一些目标相互冲突，实际部署通常会涉及基于各种因素（如成本、最终用户应用程序需求、网络效率、涉及的复杂性和收入考虑）的工程妥协。因此，基于上述考虑，这些目标需要权衡。
There are several options for providing protection of traffic. The most generic requirement is the specification of whether recovery should be via Layer 3 (or IP) rerouting or via MPLS protection switching or rerouting actions.
提供交通保护有多种选择。最通用的要求是指定恢复是通过第3层（或IP）重路由还是通过MPLS保护交换或重路由操作。
Generally network operators aim to provide the fastest, most stable, and the best protection mechanism that can be provided at a reasonable cost. The higher the levels of protection, the more the
一般来说，网络运营商的目标是以合理的成本提供最快、最稳定、最好的保护机制。保护级别越高，安全性越高
resources consumed. Therefore it is expected that network operators will offer a spectrum of service levels. MPLS-based recovery should give the flexibility to select the recovery mechanism, choose the granularity at which traffic is protected, and to also choose the specific types of traffic that are protected in order to give operators more control over that tradeoff. With MPLS-based recovery, it can be possible to provide different levels of protection for different classes of service, based on their service requirements. For example, using approaches outlined below, a Virtual Leased Line (VLL) service or real-time applications like Voice over IP (VoIP) may be supported using link/node protection together with pre-established, pre-reserved path protection. Best effort traffic, on the other hand, may use path protection that is established on demand or may simply rely on IP re-route or higher layer recovery mechanisms. As another example of their range of application, MPLS-based recovery strategies may be used to protect traffic not originally flowing on label switched paths, such as IP traffic that is normally routed hop-by-hop, as well as traffic forwarded on label switched paths.
消耗的资源。因此，预计网络运营商将提供一系列服务级别。基于MPLS的恢复应该能够灵活地选择恢复机制，选择流量保护的粒度，还可以选择受保护的特定类型的流量，以便让运营商能够更好地控制这种权衡。使用基于MPLS的恢复，可以根据不同类别的服务需求为其提供不同级别的保护。例如，使用下面概述的方法，可以使用链路/节点保护以及预先建立、预先保留的路径保护来支持虚拟租用线路（VLL）服务或诸如IP语音（VoIP）之类的实时应用。另一方面，尽力而为的流量可能使用按需建立的路径保护，或者可能仅仅依赖于IP重路由或更高层的恢复机制。作为其应用范围的另一个示例，基于MPLS的恢复策略可用于保护最初不在标签交换路径上流动的流量，例如通常逐跳路由的IP流量，以及在标签交换路径上转发的流量。
There are two basic models for path recovery: rerouting and protection switching.
路径恢复有两种基本模型：重路由和保护切换。
Protection switching and rerouting, as defined below, may be used together. For example, protection switching to a recovery path may be used for rapid restoration of connectivity while rerouting determines a new optimal network configuration, rearranging paths, as needed, at a later time.
保护切换和重路由（定义见下文）可一起使用。例如，切换到恢复路径的保护可用于快速恢复连接，而重新路由可确定新的最佳网络配置，并在以后根据需要重新排列路径。
Recovery by rerouting is defined as establishing new paths or path segments on demand for restoring traffic after the occurrence of a fault. The new paths may be based upon fault information, network routing policies, pre-defined configurations and network topology information. Thus, upon detecting a fault, paths or path segments to bypass the fault are established using signaling.
通过重路由恢复被定义为在故障发生后根据需要建立新路径或路径段以恢复通信量。新路径可以基于故障信息、网络路由策略、预定义配置和网络拓扑信息。因此，在检测到故障时，使用信令建立绕过故障的路径或路径段。
Once the network routing algorithms have converged after a fault, it may be preferable, in some cases, to reoptimize the network by performing a reroute based on the current state of the network and network policies. This is discussed further in Section 3.8.
一旦网络路由算法在故障后收敛，在某些情况下，可能优选通过基于网络的当前状态和网络策略执行重新路由来重新优化网络。这将在第3.8节中进一步讨论。
In terms of the principles defined in section 3, reroute recovery employs paths established-on-demand with resources reserved-on-demand.
根据第3节中定义的原则，重路由恢复采用按需建立的路径，并按需保留资源。
Protection switching recovery mechanisms pre-establish a recovery path or path segment, based upon network routing policies, the restoration requirements of the traffic on the working path, and administrative considerations. The recovery path may or may not be link and node disjoint with the working path. However if the recovery path shares sources of failure with the working path, the overall reliability of the construct is degraded. When a fault is detected, the protected traffic is switched over to the recovery path(s) and restored.
保护交换恢复机制根据网络路由策略、工作路径上流量的恢复要求和管理考虑预先建立恢复路径或路径段。恢复路径可能与工作路径不相交，也可能与工作路径不相交。但是，如果恢复路径与工作路径共享故障源，则结构的总体可靠性会降低。当检测到故障时，受保护的通信量将切换到恢复路径并恢复。
In terms of the principles in section 3, protection switching employs pre-established recovery paths, and, if resource reservation is required on the recovery path, pre-reserved resources. The various sub-types of protection switching are detailed in Section 4.4 of this document.
根据第3节中的原则，保护切换使用预先建立的恢复路径，如果恢复路径上需要资源预留，则使用预先预留的资源。本文件第4.4节详细介绍了各种保护开关子类型。
There are three defined recovery cycles: the MPLS Recovery Cycle, the MPLS Reversion Cycle and the Dynamic Re-routing Cycle. The first cycle detects a fault and restores traffic onto MPLS-based recovery paths. If the recovery path is non-optimal the cycle may be followed by any of the two latter cycles to achieve an optimized network again. The reversion cycle applies for explicitly routed traffic that does not rely on any dynamic routing protocols to converge. The dynamic re-routing cycle applies for traffic that is forwarded based on hop-by-hop routing.
有三个定义的恢复周期：MPLS恢复周期、MPLS恢复周期和动态重路由周期。第一个周期检测故障并将流量恢复到基于MPLS的恢复路径上。如果恢复路径是非最佳的，则该循环之后可以是后两个循环中的任何一个，以再次实现优化的网络。反向周期适用于不依赖任何动态路由协议进行收敛的显式路由流量。动态重路由循环适用于基于逐跳路由转发的流量。
The MPLS recovery cycle model is illustrated in Figure 1. Definitions and a key to abbreviations follow.
MPLS恢复周期模型如图1所示。定义和缩写的关键如下。
--Network Impairment
| --Fault Detected
| | --Start of Notification
| | | -- Start of Recovery Operation
| | | | --Recovery Operation Complete
| | | | | --Path Traffic Recovered
| | | | | |
| | | | | |
v v v v v v
----------------------------------------------------------------
| T1 | T2 | T3 | T4 | T5 |
--Network Impairment
| --Fault Detected
| | --Start of Notification
| | | -- Start of Recovery Operation
| | | | --Recovery Operation Complete
| | | | | --Path Traffic Recovered
| | | | | |
| | | | | |
v v v v v v
----------------------------------------------------------------
| T1 | T2 | T3 | T4 | T5 |
Figure 1. MPLS Recovery Cycle Model
图1。MPLS恢复周期模型
The various timing measures used in the model are described below.
模型中使用的各种计时措施如下所述。
T1 Fault Detection Time T2 Fault Hold-off Time T3 Fault Notification Time T4 Recovery Operation Time T5 Traffic Recovery Time
T1故障检测时间T2故障保持时间T3故障通知时间T4恢复操作时间T5交通恢复时间
Definitions of the recovery cycle times are as follows:
恢复周期时间的定义如下：
Fault Detection Time
故障检测时间
The time between the occurrence of a network impairment and the moment the fault is detected by MPLS-based recovery mechanisms. This time may be highly dependent on lower layer protocols.
网络损坏发生与基于MPLS的恢复机制检测到故障之间的时间。这一时间可能高度依赖于较低层协议。
Fault Hold-Off Time
故障延迟时间
The configured waiting time between the detection of a fault and taking MPLS-based recovery action, to allow time for lower layer protection to take effect. The Fault Hold-off Time may be zero.
在检测到故障和采取基于MPLS的恢复操作之间配置的等待时间，以允许较低层保护生效。故障保持时间可能为零。
Note: The Fault Hold-Off Time may occur after the Fault Notification Time interval if the node responsible for the switchover, the Path Switch LSR (PSL), rather than the detecting LSR, is configured to wait.
注意：如果负责切换的节点、路径切换LSR（PSL）而不是检测LSR被配置为等待，则故障保持时间可能在故障通知时间间隔之后发生。
Fault Notification Time
故障通知时间
The time between initiation of a Fault Indication Signal (FIS) by the LSR detecting the fault and the time at which the Path Switch LSR (PSL) begins the recovery operation. This is zero if the PSL detects the fault itself or infers a fault from such events as an adjacency failure.
从检测到故障的LSR启动故障指示信号（FIS）到路径开关LSR（PSL）开始恢复操作的时间。如果PSL检测到故障本身或从邻接故障等事件推断出故障，则该值为零。
Note: If the PSL detects the fault itself, there still may be a Fault Hold-Off Time period between detection and the start of the recovery operation.
注意：如果PSL检测到故障本身，则在检测到故障和开始恢复操作之间可能仍有一段故障延迟时间。
Recovery Operation Time
恢复操作时间
The time between the first and last recovery actions. This may include message exchanges between the PSL and PML (Path Merge LSR) to coordinate recovery actions.
第一次和最后一次恢复操作之间的时间。这可能包括PSL和PML（路径合并LSR）之间的消息交换，以协调恢复操作。
Traffic Recovery Time
交通恢复时间
The time between the last recovery action and the time that the traffic (if present) is completely recovered. This interval is intended to account for the time required for traffic to once again arrive at the point in the network that experienced disrupted or degraded service due to the occurrence of the fault (e.g., the PML). This time may depend on the location of the fault, the recovery mechanism, and the propagation delay along the recovery path.
上次恢复操作与流量（如果存在）完全恢复之间的时间。此间隔旨在说明流量再次到达网络中因故障（如PML）发生而中断或降级服务的点所需的时间。这一时间可能取决于故障位置、恢复机制以及沿恢复路径的传播延迟。
Protection switching, revertive mode, requires the traffic to be switched back to a preferred path when the fault on that path is cleared. The MPLS reversion cycle model is illustrated in Figure 2. Note that the cycle shown below comes after the recovery cycle shown in Fig. 1.
保护切换，即恢复模式，要求在清除路径上的故障时将通信量切换回首选路径。MPLS恢复周期模型如图2所示。注意，下面所示的循环在图1所示的恢复循环之后。
--Network Impairment Repaired
| --Fault Cleared
| | --Path Available
| | | --Start of Reversion Operation
| | | | --Reversion Operation Complete
| | | | | --Traffic Restored on Preferred Path
| | | | | |
| | | | | |
v v v v v v
-----------------------------------------------------------------
| T7 | T8 | T9 | T10| T11|
--Network Impairment Repaired
| --Fault Cleared
| | --Path Available
| | | --Start of Reversion Operation
| | | | --Reversion Operation Complete
| | | | | --Traffic Restored on Preferred Path
| | | | | |
| | | | | |
v v v v v v
-----------------------------------------------------------------
| T7 | T8 | T9 | T10| T11|
Figure 2. MPLS Reversion Cycle Model
图2。MPLS恢复周期模型
The various timing measures used in the model are described below.
模型中使用的各种计时措施如下所述。
T7 Fault Clearing Time T8 Clear Hold-Off Time T9 Clear Notification Time T10 Reversion Operation Time T11 Traffic Reversion Time
T7故障清除时间T8清除保持时间T9清除通知时间T10恢复操作时间T11交通恢复时间
Note that time T6 (not shown above) is the time for which the network impairment is not repaired and traffic is flowing on the recovery path.
请注意，时间T6（上面未显示）是网络损坏未修复且流量在恢复路径上流动的时间。
Definitions of the reversion cycle times are as follows:
回复周期时间的定义如下：
Fault Clearing Time
故障清除时间
The time between the repair of a network impairment and the time that MPLS-based mechanisms learn that the fault has been cleared. This time may be highly dependent on lower layer protocols.
从修复网络损坏到基于MPLS的机制得知故障已被清除之间的时间。这一时间可能高度依赖于较低层协议。
Clear Hold-Off Time
清除延迟时间
The configured waiting time between the clearing of a fault and MPLS-based recovery action(s). Waiting time may be needed to ensure that the path is stable and to avoid flapping in cases where a fault is intermittent. The Clear Hold-Off Time may be zero.
在清除故障和基于MPLS的恢复操作之间配置的等待时间。可能需要等待时间，以确保路径稳定，并在间歇性故障的情况下避免抖动。清除延迟时间可能为零。
Note: The Clear Hold-Off Time may occur after the Clear Notification Time interval if the PSL is configured to wait.
注意：如果PSL配置为等待，则清除延迟时间可能在清除通知时间间隔之后出现。
Clear Notification Time
清除通知时间
The time between initiation of a Fault Recovery Signal (FRS) by the LSR clearing the fault and the time at which the path switch LSR begins the reversion operation. This is zero if the PSL clears the fault itself.
LSR清除故障时启动故障恢复信号（FRS）与路径开关LSR开始反向操作之间的时间。如果PSL本身清除故障，则该值为零。
Note: If the PSL clears the fault itself, there still may be a Clear Hold-off Time period between fault clearing and the start of the reversion operation.
注意：如果PSL本身清除故障，则在故障清除和恢复操作开始之间可能仍有一段明显的延迟时间。
Reversion Operation Time
恢复操作时间
The time between the first and last reversion actions. This may include message exchanges between the PSL and PML to coordinate reversion actions.
第一次和最后一次恢复操作之间的时间。这可能包括PSL和PML之间的消息交换，以协调恢复操作。
Traffic Reversion Time
交通恢复时间
The time between the last reversion action and the time that traffic (if present) is completely restored on the preferred path. This interval is expected to be quite small since both paths are working and care may be taken to limit the traffic disruption (e.g., using "make before break" techniques and synchronous switch-over).
最后一次恢复操作与在首选路径上完全恢复通信量（如果存在）之间的时间。由于两条路径都在工作，因此预计该间隔相当小，并且可能会注意限制交通中断（例如，使用“先通后断”技术和同步切换）。
In practice, the most interesting times in the reversion cycle are the Clear Hold-off Time and the Reversion Operation Time together with Traffic Reversion Time (or some other measure of traffic
在实践中，复归周期中最有趣的时间是净延迟时间和复归运行时间以及交通复归时间（或其他交通量度量
disruption). The first interval is to ensure stability of the repaired path and the latter one is to minimize disruption time while the reversion action is in progress.
破坏）。第一个时间间隔是确保修复路径的稳定性，后一个时间间隔是在恢复操作进行时将中断时间降至最低。
Given that both paths are available, it is better to wait to have a well-controlled switch-back with minimal disruption than have an immediate operation that may cause new faults to be introduced (except, perhaps, when the recovery path is unable to offer a quality of service comparable to the preferred path).
考虑到两条路径都可用，最好等待控制良好且中断最小的交换机返回，而不是立即进行可能导致引入新故障的操作（除非恢复路径无法提供与首选路径相当的服务质量）。
Dynamic rerouting aims to bring the IP network to a stable state after a network impairment has occurred. A re-optimized network is achieved after the routing protocols have converged, and the traffic is moved from a recovery path to a (possibly) new working path. The steps involved in this mode are illustrated in Figure 3.
动态重路由旨在使IP网络在发生网络损坏后处于稳定状态。在路由协议聚合之后，实现了重新优化的网络，并且流量从恢复路径移动到（可能的）新的工作路径。此模式中涉及的步骤如图3所示。
Note that the cycle shown below may be overlaid on the recovery cycle shown in Fig. 1 or the reversion cycle shown in Fig. 2, or both (in the event that both the recovery cycle and the reversion cycle take place before the routing protocols converge), and occurs if after the convergence of the routing protocols it is determined (based on on-line algorithms or off-line traffic engineering tools, network configuration, or a variety of other possible criteria) that there is a better route for the working path.
注意，下面所示的周期可以覆盖在图1所示的恢复周期或图2所示的恢复周期上，或者两者都覆盖（如果恢复周期和恢复周期都发生在路由协议收敛之前），并且如果在路由协议收敛之后确定，则发生（基于在线算法或离线流量工程工具、网络配置或各种其他可能的标准）工作路径存在更好的路由。
--Network Enters a Semi-stable State after an Impairment
| --Dynamic Routing Protocols Converge
| | --Initiate Setup of New Working Path between PSL
| | | and PML
| | | --Switchover Operation Complete
| | | | --Traffic Moved to New Working Path
| | | | |
| | | | |
v v v v v
-----------------------------------------------------------------
| T12 | T13 | T14 | T15 |
--Network Enters a Semi-stable State after an Impairment
| --Dynamic Routing Protocols Converge
| | --Initiate Setup of New Working Path between PSL
| | | and PML
| | | --Switchover Operation Complete
| | | | --Traffic Moved to New Working Path
| | | | |
| | | | |
v v v v v
-----------------------------------------------------------------
| T12 | T13 | T14 | T15 |
Figure 3. Dynamic Rerouting Cycle Model
图3。动态重路由循环模型
The various timing measures used in the model are described below.
模型中使用的各种计时措施如下所述。
T12 Network Route Convergence Time T13 Hold-down Time (optional) T14 Switchover Operation Time T15 Traffic Restoration Time
T12网络路由汇聚时间T13保持时间（可选）T14切换操作时间T15业务恢复时间
Network Route Convergence Time
网络路由收敛时间
We define the network route convergence time as the time taken for the network routing protocols to converge and for the network to reach a stable state.
我们将网络路由收敛时间定义为网络路由协议收敛和网络达到稳定状态所需的时间。
Holddown Time
压制时间
We define the holddown period as a bounded time for which a recovery path must be used. In some scenarios it may be difficult to determine if the working path is stable. In these cases a holddown time may be used to prevent excess flapping of traffic between a working and a recovery path.
我们将抑制期定义为必须使用恢复路径的有界时间。在某些情况下，可能难以确定工作路径是否稳定。在这些情况下，可以使用保持时间来防止工作路径和恢复路径之间的通信量过度摆动。
Switchover Operation Time
切换操作时间
The time between the first and last switchover actions. This may include message exchanges between the PSL and PML to coordinate the switchover actions.
第一次和最后一次切换操作之间的时间。这可能包括PSL和PML之间的消息交换，以协调切换操作。
Traffic Restoration Time
交通恢复时间
The time between the last restoration action and the time that traffic (if present) is completely restored on the new preferred path.
最后一次恢复操作与流量（如果存在）在新的首选路径上完全恢复之间的时间。
As an example of the recovery cycle, we present a sequence of events that occur after a network impairment occurs and when a protection switch is followed by dynamic rerouting.
作为恢复周期的一个示例，我们提供了一系列事件，这些事件发生在发生网络损坏之后，以及保护交换机之后发生动态重新路由时。
I. Link or path fault occurs II. Signaling initiated (FIS) for the detected fault III. FIS arrives at the PSL IV. The PSL initiates a protection switch to a pre-configured recovery path V. The PSL switches over the traffic from the working path to the recovery path VI. The network enters a semi-stable state VII. Dynamic routing protocols converge after the fault, and a new working path is calculated (based, for example, on some of the criteria mentioned in Section 2.1.1). VIII. A new working path is established between the PSL and the PML (assumption is that PSL and PML have not changed) IX. Traffic is switched over to the new working path.
I.发生链路或路径故障II。为检测到的故障III启动信令（FIS）。FIS到达PSL IV。PSL启动保护开关至预配置的恢复路径V。PSL将流量从工作路径切换至恢复路径VI。网络进入半稳定状态VII。动态路由协议在故障后收敛，并计算新的工作路径（例如，基于第2.1.1节中提到的一些标准）。八,。在PSL和PML之间建立了一条新的工作路径（假设PSL和PML没有改变）IX.流量切换到新的工作路径。
This document assumes the terminology given in [RFC3031], and, in addition, introduces the following new terms.
本文件采用[RFC3031]中给出的术语，此外，还引入了以下新术语。
Re-routing
改道
A recovery mechanism in which the recovery path or path segments are created dynamically after the detection of a fault on the working path. In other words, a recovery mechanism in which the recovery path is not pre-established.
一种恢复机制，其中在检测到工作路径上的故障后动态创建恢复路径或路径段。换句话说，是一种恢复机制，其中恢复路径不是预先建立的。
Protection Switching
保护开关
A recovery mechanism in which the recovery path or path segments are created prior to the detection of a fault on the working path. In other words, a recovery mechanism in which the recovery path is pre-established.
一种恢复机制，其中在检测到工作路径上的故障之前创建恢复路径或路径段。换句话说，是一种恢复机制，其中预先建立了恢复路径。
Working Path
工作路径
The protected path that carries traffic before the occurrence of a fault. The working path can be of different kinds; a hop-by-hop routed path, a trunk, a link, an LSP or part of a multipoint-to-point LSP.
故障发生前承载通信量的受保护路径。工作路径可以是不同的类型；逐跳路由路径、中继、链路、LSP或多点对点LSP的一部分。
Synonyms for a working path are primary path and active path.
工作路径的同义词是主路径和活动路径。
Recovery Path
恢复路径
The path by which traffic is restored after the occurrence of a fault. In other words, the path on which the traffic is directed by the recovery mechanism. The recovery path is established by MPLS means. The recovery path can either be an equivalent recovery path and ensure no reduction in quality of service, or be a limited recovery path and thereby not guarantee the same quality of service (or some other criteria of performance) as the working path. A limited recovery path is not expected to be used for an extended period of time.
故障发生后恢复通信量的路径。换句话说，恢复机制引导流量的路径。恢复路径是通过MPLS方式建立的。恢复路径可以是等效的恢复路径并确保服务质量不会降低，也可以是有限的恢复路径，因此不能保证与工作路径相同的服务质量（或某些其他性能标准）。有限的恢复路径预计不会在较长时间内使用。
Synonyms for a recovery path are: back-up path, alternative path, and protection path.
恢复路径的同义词有：备份路径、替代路径和保护路径。
Protection Counterpart
保护对应物
The "other" path when discussing pre-planned protection switching schemes. The protection counterpart for the working path is the recovery path and vice-versa.
讨论预先计划的保护切换方案时的“其他”路径。工作路径的保护对应物是恢复路径，反之亦然。
Path Switch LSR (PSL)
路径开关LSR（PSL）
An LSR that is responsible for switching or replicating the traffic between the working path and the recovery path.
负责在工作路径和恢复路径之间切换或复制通信量的LSR。
Path Merge LSR (PML)
路径合并LSR（PML）
An LSR that is responsible for receiving the recovery path traffic, and either merging the traffic back onto the working path, or, if it is itself the destination, passing the traffic on to the higher layer protocols.
一种LSR，负责接收恢复路径通信量，并将通信量合并回工作路径，或者，如果它本身就是目的地，则将通信量传递给更高层协议。
Point of Repair (POR)
维修点（POR）
An LSR that is setup for performing MPLS recovery. In other words, an LSR that is responsible for effecting the repair of an LSP. The POR, for example, can be a PSL or a PML, depending on the type of recovery scheme employed.
为执行MPLS恢复而设置的LSR。换句话说，负责对LSP进行修复的LSR。例如，POR可以是PSL或PML，具体取决于所采用的恢复方案的类型。
Intermediate LSR
中间LSR
An LSR on a working or recovery path that is neither a PSL nor a PML for that path.
工作或恢复路径上既不是该路径的PSL也不是该路径的PML的LSR。
Path Group (PG)
路径组（PG）
A logical bundling of multiple working paths, each of which is routed identically between a Path Switch LSR and a Path Merge LSR.
多条工作路径的逻辑捆绑，每条工作路径在路径交换机LSR和路径合并LSR之间以相同的方式路由。
Protected Path Group (PPG)
受保护路径组（PPG）
A path group that requires protection.
需要保护的路径组。
Protected Traffic Portion (PTP)
受保护流量部分（PTP）
The portion of the traffic on an individual path that requires protection. For example, code points in the EXP bits of the shim header may identify a protected portion.
单个路径上需要保护的流量部分。例如，垫片头的EXP位中的代码点可以标识受保护的部分。
Bypass Tunnel
旁通隧道
A path that serves to back up a set of working paths using the label stacking approach [RFC3031]. The working paths and the bypass tunnel must all share the same path switch LSR (PSL) and the path merge LSR (PML).
使用标签堆叠方法备份一组工作路径的路径[RFC3031]。工作路径和旁通隧道必须全部共享同一路径开关LSR（PSL）和路径合并LSR（PML）。
Switch-Over
转换
The process of switching the traffic from the path that the traffic is flowing on onto one or more alternate path(s). This may involve moving traffic from a working path onto one or more recovery paths, or may involve moving traffic from a recovery path(s) on to a more optimal working path(s).
将通信量从正在流动的路径切换到一条或多条备用路径的过程。这可能涉及将流量从工作路径移动到一个或多个恢复路径上，或者可能涉及将流量从恢复路径移动到更优化的工作路径上。
Switch-Back
调回
The process of returning the traffic from one or more recovery paths back to the working path(s).
将流量从一个或多个恢复路径返回到工作路径的过程。
Revertive Mode
回复模式
A recovery mode in which traffic is automatically switched back from the recovery path to the original working path upon the restoration of the working path to a fault-free condition. This assumes a failed working path does not automatically surrender resources to the network.
一种恢复模式，在将工作路径恢复到无故障状态后，通信量自动从恢复路径切换回原始工作路径。这假定出现故障的工作路径不会自动将资源移交给网络。
Non-revertive Mode
非回复模式
A recovery mode in which traffic is not automatically switched back to the original working path after this path is restored to a fault-free condition. (Depending on the configuration, the original working path may, upon moving to a fault-free condition, become the recovery path, or it may be used for new working traffic, and be no longer associated with its original recovery path, i.e., is surrendered to the network.)
一种恢复模式，在该路径恢复到无故障状态后，通信量不会自动切换回原始工作路径。（根据配置，在移动到无故障状态时，原始工作路径可能成为恢复路径，或者它可能用于新的工作流量，并且不再与其原始恢复路径关联，即，移交给网络。）
MPLS Protection Domain
MPLS保护域
The set of LSRs over which a working path and its corresponding recovery path are routed.
在其上路由工作路径及其相应恢复路径的一组LSR。
MPLS Protection Plan
MPLS保护计划
The set of all LSP protection paths and the mapping from working to protection paths deployed in an MPLS protection domain at a given time.
所有LSP保护路径的集合，以及在给定时间从MPLS保护域中部署的工作路径到保护路径的映射。
Liveness Message
活跃信息
A message exchanged periodically between two adjacent LSRs that serves as a link probing mechanism. It provides an integrity check of the forward and the backward directions of the link between the two LSRs as well as a check of neighbor aliveness.
作为链路探测机制，在两个相邻的LSR之间定期交换的消息。它提供对两个LSR之间链路的前向和后向的完整性检查，以及对邻居有效性的检查。
Path Continuity Test
路径连续性测试
A test that verifies the integrity and continuity of a path or path segment. The details of such a test are beyond the scope of this document. (This could be accomplished, for example, by transmitting a control message along the same links and nodes as the data traffic or similarly could be measured by the absence of traffic and by providing feedback.)
验证路径或路径段的完整性和连续性的测试。此类测试的细节超出了本文件的范围。（例如，这可以通过沿着与数据流量相同的链路和节点发送控制消息来实现，或者类似地可以通过无流量和提供反馈来测量。）
Path Failure (PF)
路径故障（PF）
Path failure is a fault detected by MPLS-based recovery mechanisms, which is defined as the failure of the liveness message test or a path continuity test, which indicates that path connectivity is lost.
路径故障是由基于MPLS的恢复机制检测到的故障，它被定义为活动性消息测试或路径连续性测试的故障，这表明路径连接丢失。
Path Degraded (PD)
路径降级（PD）
Path degraded is a fault detected by MPLS-based recovery mechanisms that indicates that the quality of the path is unacceptable.
路径降级是一种由基于MPLS的恢复机制检测到的故障，表示路径质量不可接受。
Link Failure (LF)
链路故障（LF）
A lower layer fault indicating that link continuity is lost. This may be communicated to the MPLS-based recovery mechanisms by the lower layer.
指示链路连续性丢失的下层故障。这可以由较低层传送到基于MPLS的恢复机制。
Link Degraded (LD)
链路降级（LD）
A lower layer indication to MPLS-based recovery mechanisms that the link is performing below an acceptable level.
对基于MPLS的恢复机制的较低层指示，表明链路的性能低于可接受的水平。
Fault Indication Signal (FIS)
故障指示信号（FIS）
A signal that indicates that a fault along a path has occurred. It is relayed by each intermediate LSR to its upstream or downstream neighbor, until it reaches an LSR that is setup to perform MPLS recovery (the POR). The FIS is transmitted
一种信号，指示路径上发生故障。它由每个中间LSR中继到其上游或下游邻居，直到到达设置为执行MPLS恢复的LSR（POR）。传输FIS
periodically by the node/nodes closest to the point of failure, for some configurable length of time or until the transmitting node receives an acknowledgement from its neighbor.
由最接近故障点的节点周期性地执行，持续一些可配置的时间长度，或者直到发送节点从其邻居接收到确认。
Fault Recovery Signal (FRS)
故障恢复信号（FRS）
A signal that indicates a fault along a working path has been repaired. Again, like the FIS, it is relayed by each intermediate LSR to its upstream or downstream neighbor, until is reaches the LSR that performs recovery of the original path. The FRS is transmitted periodically by the node/nodes closest to the point of failure, for some configurable length of time or until the transmitting node receives an acknowledgement from its neighbor.
指示工作路径上的故障已修复的信号。同样，与FIS一样，它由每个中间LSR中继到其上游或下游邻居，直到is到达执行原始路径恢复的LSR。FRS由距离故障点最近的节点周期性地发送，发送时间长度为可配置的时间长度，或者直到发送节点从其邻居接收到确认为止。
FIS: Fault Indication Signal. FRS: Fault Recovery Signal. LD: Link Degraded. LF: Link Failure. PD: Path Degraded. PF: Path Failure. PML: Path Merge LSR. PG: Path Group. POR: Point of Repair. PPG: Protected Path Group. PTP: Protected Traffic Portion. PSL: Path Switch LSR.
FIS：故障指示信号。FRS：故障恢复信号。链路降级。链接失败。PD:路径已降级。PF：路径失败。路径合并LSR。路径组。维修点。PPG：受保护的路径组。PTP：受保护的流量部分。路径开关LSR。
MPLS-based recovery refers to the ability to effect quick and complete restoration of traffic affected by a fault in an MPLS-enabled network. The fault may be detected on the IP layer or in lower layers over which IP traffic is transported. Fastest MPLS recovery is assumed to be achieved with protection switching and may be viewed as the MPLS LSR switch completion time that is comparable to, or equivalent to, the 50 ms switch-over completion time of the SONET layer. Further, MPLS-based recovery may provide bandwidth protection for paths that require it. This section provides a discussion of the concepts and principles of MPLS-based recovery. The concepts are presented in terms of atomic or primitive terms that may be combined to specify recovery approaches. We do not make any assumptions about the underlying layer 1 or layer 2 transport mechanisms or their recovery mechanisms.
基于MPLS的恢复是指在启用MPLS的网络中，对受故障影响的流量进行快速、完全恢复的能力。故障可在IP层或传输IP流量的较低层上检测到。假设通过保护交换实现最快的MPLS恢复，并可将其视为MPLS LSR交换完成时间，其与SONET层的50 ms切换完成时间相当或等效。此外，基于MPLS的恢复可以为需要带宽保护的路径提供带宽保护。本节讨论了基于MPLS的恢复的概念和原理。这些概念以原子或原始术语的形式呈现，这些术语可以组合起来指定恢复方法。我们不对底层1层或2层传输机制或其恢复机制进行任何假设。
An LSR may support any or all of the following recovery options on a per-path basis:
LSR可以基于每个路径支持以下任何或所有恢复选项：
Default-recovery (No MPLS-based recovery enabled): Traffic on the working path is recovered only via Layer 3 or IP rerouting or by some lower layer mechanism such as SONET APS. This is equivalent to having no MPLS-based recovery. This option may be used for low priority traffic or for traffic that is recovered in another way (for example load shared traffic on parallel working paths may be automatically recovered upon a fault along one of the working paths by distributing it among the remaining working paths).
默认恢复（未启用基于MPLS的恢复）：工作路径上的流量仅通过第3层或IP重路由或某些较低层机制（如SONET AP）恢复。这相当于没有基于MPLS的恢复。此选项可用于低优先级流量或以另一种方式恢复的流量（例如，并行工作路径上的负载共享流量可在故障发生时通过在剩余工作路径之间分配而沿其中一条工作路径自动恢复）。
Recoverable (MPLS-based recovery enabled): This working path is recovered using one or more recovery paths, either via rerouting or via protection switching.
可恢复（启用基于MPLS的恢复）：使用一个或多个恢复路径（通过重路由或保护切换）恢复此工作路径。
There are three options for the initiation of the recovery path setup. The active and recovery paths may be established by using either RSVP-TE [RFC2205][RFC3209] or CR-LDP [RFC3212], or by any other means including SNMP.
启动恢复路径设置有三个选项。可以通过使用RSVP-TE[RFC2205][RFC3209]或CR-LDP[rfc3221]或通过包括SNMP的任何其他方式来建立活动路径和恢复路径。
Pre-established:
预先确定的：
This is the same as the protection switching option. Here a recovery path(s) is established prior to any failure on the working path. The path selection can either be determined by an administrative centralized tool, or chosen based on some algorithm implemented at the PSL and possibly intermediate nodes. To guard against the situation when the pre-established recovery path fails before or at the same time as the working path, the recovery path should have secondary configuration options as explained in Section 3.3 below.
这与保护切换选项相同。在这里，在工作路径上发生任何故障之前建立恢复路径。路径选择可以由管理集中工具确定，也可以基于在PSL和可能的中间节点上实现的某些算法进行选择。为防止预先建立的恢复路径在工作路径之前或同时出现故障，恢复路径应具有第3.3节所述的辅助配置选项。
Pre-Qualified:
通过资格预审：
A pre-established path need not be created, it may be pre-qualified. A pre-qualified recovery path is not created expressly for protecting the working path, but instead is a path created for other purposes that is designated as a recovery path after determining that it is an acceptable alternative for carrying the working path traffic. Variants include the case where an optical path or trail is configured, but no switches are set.
不需要创建预先建立的路径，它可以是预先限定的。预先鉴定的恢复路径不是专门为保护工作路径而创建的，而是为其他目的而创建的路径，在确定它是承载工作路径通信量的可接受替代方案后被指定为恢复路径。变型包括配置了光路或轨迹但未设置交换机的情况。
Established-on-Demand:
按需建立：
This is the same as the rerouting option. Here, a recovery path is established after a failure on its working path has been detected and notified to the PSL. The recovery path may be pre-computed or computed on demand, which influences recovery times.
这与重新路由选项相同。这里，在检测到其工作路径上的故障并通知PSL之后，建立恢复路径。恢复路径可以预先计算或根据需要计算，这会影响恢复时间。
A recovery path may support the same traffic contract as the working path, or it may not. We will distinguish these two situations by using different additive terms. If the recovery path is capable of replacing the working path without degrading service, it will be called an equivalent recovery path. If the recovery path lacks the resources (or resource reservations) to replace the working path without degrading service, it will be called a limited recovery path. Based on this, there are two options for the initiation of resource allocation:
恢复路径可能支持与工作路径相同的流量契约，也可能不支持。我们将使用不同的加法项来区分这两种情况。如果恢复路径能够在不降低服务质量的情况下替换工作路径，则它将被称为等效恢复路径。如果恢复路径缺少资源（或资源保留），无法在不降低服务质量的情况下替换工作路径，则将其称为有限恢复路径。基于此，启动资源分配有两种选择：
Pre-reserved:
预订：
This option applies only to protection switching. Here a pre-established recovery path reserves required resources on all hops along its route during its establishment. Although the reserved resources (e.g., bandwidth and/or buffers) at each node cannot be used to admit more working paths, they are available to be used by all traffic that is present at the node before a failure occurs. The resources held by a set of recovery paths may be shared if they protect resources that are not simultaneously subject to failure.
此选项仅适用于保护切换。在这里，预先建立的恢复路径在其建立期间在其路线上的所有跃点上保留所需的资源。尽管每个节点上的保留资源（例如，带宽和/或缓冲区）不能用于接纳更多的工作路径，但在发生故障之前，它们可供节点上存在的所有流量使用。如果一组恢复路径保护不同时发生故障的资源，则可以共享这些资源。
Reserved-on-Demand:
按需预订：
This option may apply either to rerouting or to protection switching. Here a recovery path reserves the required resources after a failure on the working path has been detected and notified to the PSL and before the traffic on the working path is switched over to the recovery path.
此选项可应用于重新路由或保护切换。在这里，在检测到工作路径上的故障并将其通知给PSL之后，以及在工作路径上的通信量切换到恢复路径之前，恢复路径保留所需的资源。
Note that under both the options above, depending on the amount of resources reserved on the recovery path, it could either be an equivalent recovery path or a limited recovery path.
请注意，在上述两种选项下，根据恢复路径上保留的资源量，恢复路径可以是等效的恢复路径，也可以是有限的恢复路径。
The resources (bandwidth, buffers, processing) on the recovery path may be used to carry either a copy of the working path traffic or extra traffic that is displaced when a protection switch occurs. This leads to two subtypes of protection switching.
恢复路径上的资源（带宽、缓冲区、处理）可用于承载工作路径流量的副本或在发生保护切换时被置换的额外流量。这导致两种类型的保护切换。
In 1+1 ("one plus one") protection, the resources (bandwidth, buffers, processing capacity) on the recovery path are fully reserved, and carry the same traffic as the working path. Selection between the traffic on the working and recovery paths is made at the path merge LSR (PML). In effect the PSL function is deprecated to establishment of the working and recovery paths and a simple replication function. The recovery intelligence is delegated to the PML.
在1+1（“一加一”）保护中，恢复路径上的资源（带宽、缓冲区、处理能力）完全保留，并承载与工作路径相同的流量。在路径合并LSR（PML）中选择工作路径和恢复路径上的通信量。实际上，PSL功能不推荐用于建立工作和恢复路径以及简单的复制功能。恢复智能委托给PML。
In 1:1 ("one for one") protection, the resources (if any) allocated on the recovery path are fully available to preemptible low priority traffic except when the recovery path is in use due to a fault on the working path. In other words, in 1:1 protection, the protected traffic normally travels only on the working path, and is switched to the recovery path only when the working path has a fault. Once the protection switch is initiated, the low priority traffic being carried on the recovery path may be displaced by the protected traffic. This method affords a way to make efficient use of the recovery path resources.
在1:1（“一对一”）保护中，在恢复路径上分配的资源（如果有的话）完全可用于可抢占的低优先级流量，除非恢复路径由于工作路径上的故障而正在使用。换句话说，在1:1保护中，受保护的流量通常仅在工作路径上移动，并且仅当工作路径出现故障时才切换到恢复路径。一旦启动保护开关，恢复路径上承载的低优先级流量可能会被受保护的流量取代。此方法提供了一种有效利用恢复路径资源的方法。
This concept can be extended to 1:n (one for n) and m:n (m for n) protection.
这一概念可以扩展到1:n（一对n）和m:n（m对n）保护。
The intent of local repair is to protect against a link or neighbor node fault and to minimize the amount of time required for failure propagation. In local repair (also known as local recovery), the node immediately upstream of the fault is the one to initiate recovery (either rerouting or protection switching). Local repair can be of two types:
本地修复的目的是防止链路或邻居节点出现故障，并将故障传播所需的时间减至最少。在本地修复（也称为本地恢复）中，紧接故障上游的节点是启动恢复（重路由或保护切换）的节点。局部维修可分为两种类型：
Link Recovery/Restoration
链路恢复/恢复
In this case, the recovery path may be configured to route around a certain link deemed to be unreliable. If protection switching is used, several recovery paths may be configured for one working path, depending on the specific faulty link that each protects against.
在这种情况下，恢复路径可被配置为围绕被认为不可靠的特定链路路由。如果使用保护切换，则可能会为一条工作路径配置多个恢复路径，具体取决于每个路径所保护的特定故障链路。
Alternatively, if rerouting is used, upon the occurrence of a fault on the specified link, each path is rebuilt such that it detours around the faulty link.
或者，如果使用重新路由，在指定链路上发生故障时，将重建每条路径，使其绕故障链路绕行。
In this case, the recovery path need only be disjoint from its working path at a particular link on the working path, and may have overlapping segments with the working path. Traffic on the working path is switched over to an alternate path at the upstream LSR that connects to the failed link. Link recovery is potentially the fastest to perform the switchover, and can be effective in situations where certain path components are much more unreliable than others.
在这种情况下，恢复路径只需要在工作路径上的特定链接处与其工作路径分离，并且可能具有与工作路径重叠的段。工作路径上的流量切换到上游LSR上连接到故障链路的备用路径。链路恢复可能是执行切换的最快速度，并且在某些路径组件比其他路径组件更不可靠的情况下可能非常有效。
Node Recovery/Restoration
节点恢复/恢复
In this case, the recovery path may be configured to route around a neighbor node deemed to be unreliable. Thus the recovery path is disjoint from the working path only at a particular node and at links associated with the working path at that node. Once again, the traffic on the primary path is switched over to the recovery path at the upstream LSR that directly connects to the failed node, and the recovery path shares overlapping portions with the working path.
在这种情况下，恢复路径可被配置为围绕被认为不可靠的邻居节点进行路由。因此，恢复路径仅在特定节点处和与该节点处的工作路径相关联的链路处与工作路径不相交。再次，主路径上的业务被切换到直接连接到故障节点的上游LSR处的恢复路径，并且恢复路径与工作路径共享重叠部分。
The intent of global repair is to protect against any link or node fault on a path or on a segment of a path, with the obvious exception of the faults occurring at the ingress node of the protected path segment. In global repair, the POR is usually distant from the failure and needs to be notified by a FIS.
全局修复的目的是防止路径或路径段上的任何链路或节点故障，但发生在受保护路径段入口节点的故障明显除外。在全局维修中，POR通常距离故障较远，需要由FIS通知。
In global repair also, end-to-end path recovery/restoration applies. In many cases, the recovery path can be made completely link and node disjoint with its working path. This has the advantage of protecting against all link and node fault(s) on the working path (end-to-end path or path segment).
在全局修复中，也适用端到端路径恢复/恢复。在许多情况下，可以使恢复路径与其工作路径完全链接且节点不相交。这具有防止工作路径（端到端路径或路径段）上的所有链路和节点故障的优点。
However, it may, in some cases, be slower than local repair since the fault notification message must now travel to the POR to trigger the recovery action.
但是，在某些情况下，它可能比本地修复慢，因为故障通知消息现在必须发送到POR以触发恢复操作。
It is possible to restore service without specifically recovering the faulted path.
可以恢复服务，而无需专门恢复故障路径。
For example, for best effort IP service it is possible to select a recovery path that has a different egress point from the working path (i.e., there is no PML). The recovery path egress must simply be a router that is acceptable for forwarding the FEC carried by the working path (without creating looping). In an engineering context, specific alternative FEC/LSP mappings with alternate egresses can be formed.
例如，对于尽力而为的IP服务，可以选择与工作路径具有不同出口点的恢复路径（即，没有PML）。恢复路径出口必须是可接受的路由器，用于转发工作路径携带的FEC（而不创建循环）。在工程环境中，可以形成具有备用出口的特定备用FEC/LSP映射。
This may simplify enhancing the reliability of implicitly constructed MPLS topologies. A PSL may qualify LSP/FEC bindings as candidate recovery paths as simply link and node disjoint with the immediate downstream LSR of the working path.
这可以简化增强隐式构造的MPLS拓扑的可靠性。PSL可以将LSP/FEC绑定限定为候选恢复路径，即与工作路径的直接下游LSR不相交的链路和节点。
Multi-layer repair broadens the network designer's tool set for those cases where multiple network layers can be managed together to achieve overall network goals. Specific criteria for determining when multi-layer repair is appropriate are beyond the scope of this document.
多层修复扩展了网络设计师的工具集，适用于多个网络层可以一起管理以实现总体网络目标的情况。确定多层维修何时合适的具体标准超出了本文件的范围。
A given service may cross multiple networks and these may employ different recovery mechanisms. It is possible to concatenate protection domains so that service recovery can be provided end-to-end. It is considered that the recovery mechanisms in different domains may operate autonomously, and that multiple points of attachment may be used between domains (to ensure there is no single point of failure). Alternate egress repair requires management of concatenated domains in that an explicit MPLS point of failure (the PML) is by definition excluded. Details of concatenated protection domains are beyond the scope of this document.
给定的服务可能跨越多个网络，这些网络可能采用不同的恢复机制。可以连接保护域，以便提供端到端的服务恢复。人们认为，不同域中的恢复机制可以自主运行，域之间可以使用多个连接点（以确保没有单点故障）。备用出口修复需要管理连接的域，因为根据定义，明确的MPLS故障点（PML）被排除在外。连接的保护域的详细信息超出了本文档的范围。
Path mapping refers to the methods of mapping traffic from a faulty working path on to the recovery path. There are several options for this, as described below. Note that the options below should be viewed as atomic terms that only describe how the working and protection paths are mapped to each other. The issues of resource reservation along these paths, and how switchover is actually performed lead to the more commonly used composite terms, such as 1+1 and 1:1 protection, which were described in Section 4.3.1..
路径映射是指将流量从故障工作路径映射到恢复路径的方法。这有几个选项，如下所述。请注意，以下选项应视为仅描述工作路径和保护路径如何相互映射的原子术语。这些路径上的资源保留问题以及实际如何执行切换导致了更常用的复合术语，如1+1和1:1保护，如第4.3.1节所述。。
1-to-1 Protection
一对一保护
In 1-to-1 protection the working path has a designated recovery path that is only to be used to recover that specific working path.
在1对1保护中，工作路径具有指定的恢复路径，该路径仅用于恢复该特定工作路径。
n-to-1 Protection
n对1保护
In n-to-1 protection, up to n working paths are protected using only one recovery path. If the intent is to protect against any single fault on any of the working paths, the n working paths should be diversely routed between the same PSL and PML. In some cases, handshaking between PSL and PML may be required to complete the recovery, the details of which are beyond the scope of this document.
在n对1保护中，最多n条工作路径仅使用一条恢复路径进行保护。如果目的是防止任何工作路径上的任何单一故障，则n条工作路径应在同一PSL和PML之间分路。在某些情况下，可能需要PSL和PML之间的握手来完成恢复，其细节超出了本文档的范围。
n-to-m Protection
n-to-m保护
In n-to-m protection, up to n working paths are protected using m recovery paths. Once again, if the intent is to protect against any single fault on any of the n working paths, the n working paths and the m recovery paths should be diversely routed between the same PSL and PML. In some cases, handshaking between PSL and PML may be required to complete the recovery, the details of which are beyond the scope of this document. n-to-m protection is for further study.
在n-to-m保护中，使用m条恢复路径保护多达n条工作路径。同样，如果目的是防止n条工作路径中的任何一条出现任何单一故障，则n条工作路径和m条恢复路径应在同一PSL和PML之间分路。在某些情况下，可能需要PSL和PML之间的握手来完成恢复，其细节超出了本文档的范围。n-to-m保护有待进一步研究。
Split Path Protection
分割路径保护
In split path protection, multiple recovery paths are allowed to carry the traffic of a working path based on a certain configurable load splitting ratio. This is especially useful when no single recovery path can be found that can carry the entire traffic of the working path in case of a fault. Split path protection may require handshaking between the PSL and the PML(s), and may require the PML(s) to correlate the traffic arriving on
在分割路径保护中，允许多条恢复路径根据一定的可配置负载分割比率承载工作路径的流量。在故障情况下，如果找不到能够承载整个工作路径通信量的单一恢复路径，这一点尤其有用。分割路径保护可能需要PSL和PML之间的握手，并且可能需要PML将到达的流量关联起来
multiple recovery paths with the working path. Although this is an attractive option, the details of split path protection are beyond the scope of this document.
具有工作路径的多个恢复路径。虽然这是一个有吸引力的选项，但分割路径保护的详细信息超出了本文档的范围。
It may be convenient, in some cases, to create a "bypass tunnel" for a PPG between a PSL and PML, thereby allowing multiple recovery paths to be transparent to intervening LSRs [RFC2702]. In this case, one LSP (the tunnel) is established between the PSL and PML following an acceptable route and a number of recovery paths can be supported through the tunnel via label stacking. It is not necessary to apply label stacking when using a bypass tunnel. A bypass tunnel can be used with any of the path mapping options discussed in the previous section.
在某些情况下，为PSL和PML之间的PPG创建“旁路隧道”可能很方便，从而允许多个恢复路径对介入LSR透明[RFC2702]。在这种情况下，沿着可接受的路线在PSL和PML之间建立一个LSP（隧道），并且可以通过标签堆叠通过隧道支持多个恢复路径。使用旁通隧道时，无需应用标签堆叠。旁通隧道可与上一节讨论的任何路径映射选项一起使用。
As with recovery paths, the bypass tunnel may or may not have resource reservations sufficient to provide recovery without service degradation. It is possible that the bypass tunnel may have sufficient resources to recover some number of working paths, but not all at the same time. If the number of recovery paths carrying traffic in the tunnel at any given time is restricted, this is similar to the n-to-1 or n-to-m protection cases mentioned in Section 3.4.2.
与恢复路径一样，旁路隧道可能具有或可能不具有足够的资源预留，以在不降低服务质量的情况下提供恢复。旁通隧道可能有足够的资源来恢复一定数量的工作路径，但不能同时恢复所有路径。如果在任何给定时间隧道内承载交通量的恢复路径数量受到限制，这与第3.4.2节中提到的n对1或n对m保护情况类似。
Another dimension of recovery considers the amount of traffic requiring protection. This may range from a fraction of a path to a bundle of paths.
恢复的另一个方面考虑需要保护的通信量。这可能从路径的一小部分到路径束。
This option allows for the protection of a fraction of traffic within the same path. The portion of the traffic on an individual path that requires protection is called a protected traffic portion (PTP). A single path may carry different classes of traffic, with different protection requirements. The protected portion of this traffic may be identified by its class, as for example, via the EXP bits in the MPLS shim header or via the priority bit in the ATM header.
此选项允许保护同一路径中的一小部分流量。单个路径上需要保护的流量部分称为受保护的流量部分（PTP）。单个路径可能承载不同等级的流量，具有不同的保护要求。该业务的受保护部分可以通过其类别来识别，例如，通过MPLS垫片报头中的EXP位或通过ATM报头中的优先级位来识别。
Bundling is a technique used to group multiple working paths together in order to recover them simultaneously. The logical bundling of multiple working paths requiring protection, each of which is routed identically between a PSL and a PML, is called a protected path group
捆绑是一种用于将多个工作路径组合在一起以便同时恢复它们的技术。需要保护的多个工作路径的逻辑捆绑，每个路径在PSL和PML之间路由相同，称为受保护路径组
(PPG). When a fault occurs on the working path carrying the PPG, the PPG as a whole can be protected either by being switched to a bypass tunnel or by being switched to a recovery path.
（PPG）。当承载PPG的工作路径发生故障时，PPG作为一个整体可以通过切换到旁路隧道或切换到恢复路径来保护。
In the case of pre-reserved recovery paths, there is the question of what use these resources may be put to when the recovery path is not in use. There are two options:
在预保留恢复路径的情况下，存在一个问题，即当恢复路径未被使用时，这些资源可能会被用于什么用途。有两种选择：
Dedicated-resource: If the recovery path resources are dedicated, they may not be used for anything except carrying the working traffic. For example, in the case of 1+1 protection, the working traffic is always carried on the recovery path. Even if the recovery path is not always carrying the working traffic, it may not be possible or desirable to allow other traffic to use these resources.
专用资源：如果恢复路径资源是专用的，则它们只能用于承载工作流量。例如，在1+1保护的情况下，工作流量始终在恢复路径上进行。即使恢复路径并不总是承载工作通信量，也可能不可能或不希望允许其他通信量使用这些资源。
Extra-traffic-allowed: If the recovery path only carries the working traffic when the working path fails, then it is possible to allow extra traffic to use the reserved resources at other times. Extra traffic is, by definition, traffic that can be displaced (without violating service agreements) whenever the recovery path resources are needed for carrying the working path traffic.
允许的额外流量：如果恢复路径仅在工作路径失败时承载工作流量，则可以允许额外流量在其他时间使用保留的资源。根据定义，额外流量是指每当需要恢复路径资源来承载工作路径流量时，可以替换的流量（不违反服务协议）。
Shared-resource: A shared recovery resource is dedicated for use by multiple primary resources that (according to SRLGs) are not expected to fail simultaneously.
共享资源：共享恢复资源专用于（根据SRLGs）预期不会同时失败的多个主资源。
MPLS recovery is initiated after the detection of either a lower layer fault or a fault at the IP layer or in the operation of MPLS-based mechanisms. We consider four classes of impairments: Path Failure, Path Degraded, Link Failure, and Link Degraded.
MPLS恢复是在检测到下层故障或IP层故障或基于MPLS的机制运行时启动的。我们考虑了四类损伤：路径失效、路径退化、链路失效和链路退化。
Path Failure (PF) is a fault that indicates to an MPLS-based recovery scheme that the connectivity of the path is lost. This may be detected by a path continuity test between the PSL and PML. Some, and perhaps the most common, path failures may be detected using a link probing mechanism between neighbor LSRs. An example of a probing mechanism is a liveness message that is exchanged periodically along the working path between peer LSRs [MPLS-PATH]. For either a link probing mechanism or path continuity test to be effective, the test message must be guaranteed to follow the same route as the working or recovery path, over the segment being tested. In addition, the path continuity test must take the path merge points
路径故障（PF）是一种向基于MPLS的恢复方案指示路径连接丢失的故障。这可以通过PSL和PML之间的路径连续性测试来检测。可以使用相邻LSR之间的链路探测机制来检测一些（可能是最常见的）路径故障。探测机制的一个示例是沿着对等lsr[MPLS-path]之间的工作路径定期交换的活跃度消息。为了使链路探测机制或路径连续性测试有效，必须保证测试消息在测试段上遵循与工作或恢复路径相同的路径。此外，路径连续性测试必须采用路径合并点
into consideration. In the case of a bi-directional link implemented as two unidirectional links, path failure could mean that either one or both unidirectional links are damaged.
考虑到。在将双向链路实现为两个单向链路的情况下，路径故障可能意味着一个或两个单向链路损坏。
Path Degraded (PD) is a fault that indicates to MPLS-based recovery schemes/mechanisms that the path has connectivity, but that the quality of the connection is unacceptable. This may be detected by a path performance monitoring mechanism, or some other mechanism for determining the error rate on the path or some portion of the path. This is local to the LSR and consists of excessive discarding of packets at an interface, either due to label mismatch or due to TTL errors, for example.
路径降级（PD）是一种故障，它向基于MPLS的恢复方案/机制表明路径具有连接性，但连接质量不可接受。这可以由路径性能监视机制或用于确定路径或路径的某部分上的错误率的某个其他机制检测。这是本地的LSR，包括过度丢弃接口上的数据包，例如，由于标签不匹配或TTL错误。
Link Failure (LF) is an indication from a lower layer that the link over which the path is carried has failed. If the lower layer supports detection and reporting of this fault (that is, any fault that indicates link failure e.g., SONET LOS (Loss of Signal)), this may be used by the MPLS recovery mechanism. In some cases, using LF indications may provide faster fault detection than using only MPLS-based fault detection mechanisms.
链路故障（LF）是来自较低层的指示，表明承载路径的链路已发生故障。如果较低层支持检测和报告该故障（即，指示链路故障的任何故障，例如SONET LOS（信号丢失）），则MPLS恢复机制可以使用该故障。在某些情况下，使用LF指示可能比仅使用基于MPLS的故障检测机制提供更快的故障检测。
Link Degraded (LD) is an indication from a lower layer that the link over which the path is carried is performing below an acceptable level. If the lower layer supports detection and reporting of this fault, it may be used by the MPLS recovery mechanism. In some cases, using LD indications may provide faster fault detection than using only MPLS-based fault detection mechanisms.
链路降级（LD）是来自较低层的指示，表明承载路径的链路的性能低于可接受水平。如果较低层支持检测和报告此故障，则MPLS恢复机制可以使用它。在某些情况下，使用LD指示可能比仅使用基于MPLS的故障检测机制提供更快的故障检测。
MPLS-based recovery relies on rapid and reliable notification of faults. Once a fault is detected, the node that detected the fault must determine if the fault is severe enough to require path recovery. If the node is not capable of initiating direct action (e.g., as a point of repair, POR) the node should send out a notification of the fault by transmitting a FIS to the POR. This can take several forms:
基于MPLS的恢复依赖于快速可靠的故障通知。一旦检测到故障，检测到故障的节点必须确定故障是否严重到需要路径恢复。如果节点无法启动直接操作（例如，作为维修点，POR），则节点应通过向POR发送FIS来发送故障通知。这可以采取几种形式：
(i) control plane messaging: relayed hop-by-hop along the path upstream of the failed LSP until a POR is reached. (ii) user plane messaging: sent downstream to the PML, which may take corrective action (as a POR for 1+1) or communicate with a POR upstream (for 1:n) by any of several means: - control plane messaging - user plane return path (either through a bi-directional LSP or via other means)
(i) 控制平面消息传递：沿故障LSP的上游路径逐跳中继，直到到达POR。（ii）用户平面消息：向下游发送至PML，PML可采取纠正措施（作为1+1的POR）或通过以下几种方式之一与上游POR（1:n）通信：-控制平面消息-用户平面返回路径（通过双向LSP或通过其他方式）
Since the FIS is a control message, it should be transmitted with high priority to ensure that it propagates rapidly towards the affected POR(s). Depending on how fault notification is configured in the LSRs of an MPLS domain, the FIS could be sent either as a Layer 2 or Layer 3 packet [MPLS-PATH]. The use of a Layer 2-based notification requires a Layer 2 path direct to the POR. An example of a FIS could be the liveness message sent by a downstream LSR to its upstream neighbor, with an optional fault notification field set or it can be implicitly denoted by a teardown message. Alternatively, it could be a separate fault notification packet. The intermediate LSR should identify which of its incoming links to propagate the FIS on.
由于FIS是一条控制信息，因此应以高优先级传输该信息，以确保其快速传播到受影响的POR。根据故障通知在MPLS域的LSR中的配置方式，FIS可以作为第2层或第3层数据包[MPLS-PATH]发送。使用基于第2层的通知需要直接到POR的第2层路径。FIS的一个示例可以是下游LSR向其上游邻居发送的活跃度消息，设置了可选的故障通知字段，也可以由拆卸消息隐式表示。或者，它可以是一个单独的故障通知包。中间LSR应确定在哪个传入链路上传播FIS。
The activation of an MPLS protection switch following the detection or notification of a fault requires a trigger mechanism at the PSL. MPLS protection switching may be initiated due to automatic inputs or external commands. The automatic activation of an MPLS protection switch results from a response to a defect or fault conditions detected at the PSL or to fault notifications received at the PSL. It is possible that the fault detection and trigger mechanisms may be combined, as is the case when a PF, PD, LF, or LD is detected at a PSL and triggers a protection switch to the recovery path. In most cases, however, the detection and trigger mechanisms are distinct, involving the detection of fault at some intermediate LSR followed by the propagation of a fault notification to the POR via the FIS, which serves as the protection switch trigger at the POR. MPLS protection switching in response to external commands results when the operator initiates a protection switch by a command to a POR (or alternatively by a configuration command to an intermediate LSR, which transmits the FIS towards the POR).
在检测到或通知故障后激活MPLS保护交换机需要PSL上的触发机制。MPLS保护切换可能由于自动输入或外部命令而启动。MPLS保护交换机的自动激活源于对PSL检测到的缺陷或故障条件的响应或对PSL接收到的故障通知的响应。故障检测和触发机制可以组合，如在PSL处检测到PF、PD、LF或LD并触发到恢复路径的保护开关时的情况。然而，在大多数情况下，检测和触发机制是不同的，包括检测某些中间LSR的故障，然后通过FIS向POR传播故障通知，FIS充当POR的保护开关触发器。当操作员通过向POR发送命令（或者通过向中间LSR发送配置命令，向POR发送FIS）启动保护切换时，会产生响应于外部命令的MPLS保护切换。
Note that the PF fault applies to hard failures (fiber cuts, transmitter failures, or LSR fabric failures), as does the LF fault, with the difference that the LF is a lower layer impairment that may be communicated to MPLS-based recovery mechanisms. The PD (or LD) fault, on the other hand, applies to soft defects (excessive errors due to noise on the link, for instance). The PD (or LD) results in a fault declaration only when the percentage of lost packets exceeds a given threshold, which is provisioned and may be set based on the service level agreement(s) in effect between a service provider and a customer.
请注意，PF故障适用于硬故障（光纤切断、发射机故障或LSR结构故障），LF故障也适用于硬故障，区别在于LF是一种较低层的损伤，可以与基于MPLS的恢复机制进行通信。另一方面，PD（或LD）故障适用于软缺陷（例如，由于链路上的噪声导致的过度错误）。PD（或LD）仅当丢失数据包的百分比超过给定阈值时才会导致故障声明，该阈值是根据服务提供商和客户之间生效的服务级别协议设置的。
After a fault is detected or FIS is received by the POR, the recovery action involves either a rerouting or protection switching operation. In both scenarios, the next hop label forwarding entry for a recovery path is bound to the working path.
在检测到故障或POR接收到FIS后，恢复操作涉及重新路由或保护切换操作。在这两种情况下，恢复路径的下一跳标签转发条目都绑定到工作路径。
When traffic is flowing on the recovery path, decisions can be made as to whether to let the traffic remain on the recovery path and consider it as a new working path or to do a switch back to the old or to a new working path. This post recovery operation has two styles, one where the protection counterparts, i.e., the working and recovery path, are fixed or "pinned" to their routes, and one in which the PSL or other network entity with real-time knowledge of failure dynamically performs re-establishment or controlled rearrangement of the paths comprising the protected service.
当业务在恢复路径上流动时，可以决定是否允许业务保持在恢复路径上，并将其视为新的工作路径或切换回旧的或新的工作路径。此恢复后操作有两种类型，一种是将保护对应物（即工作和恢复路径）固定或“固定”到其路径上，以及其中具有故障实时知识的PSL或其他网络实体动态地执行包括受保护服务的路径的重新建立或受控重排。
For fixed protection counterparts the PSL will be pre-configured with the appropriate behavior to take when the original fixed path is restored to service. The choices are revertive and non-revertive mode. The choice will typically be dependent on relative costs of the working and protection paths, and the tolerance of the service to the effects of switching paths yet again. These protection modes indicate whether or not there is a preferred path for the protected traffic.
对于固定保护对应方，PSL将预先配置适当的行为，以便在原始固定路径恢复服务时采取。可选择还原和非还原模式。选择通常取决于工作和保护路径的相对成本，以及服务对切换路径影响的容忍度。这些保护模式指示是否存在受保护流量的首选路径。
If the working path always is the preferred path, this path will be used whenever it is available. Thus, in the event of a fault on this path, its unused resources will not be reclaimed by the network on failure. Resources here may include assigned labels, links, bandwidth etc. If the working path has a fault, traffic is switched to the recovery path. In the revertive mode of operation, when the preferred path is restored the traffic is automatically switched back to it.
如果工作路径始终是首选路径，则只要该路径可用，就会使用该路径。因此，如果此路径发生故障，其未使用的资源将不会在故障时被网络回收。此处的资源可能包括分配的标签、链路、带宽等。如果工作路径有故障，则流量将切换到恢复路径。在恢复操作模式下，当首选路径恢复时，流量自动切换回首选路径。
There are a number of implications to pinned working and recovery paths:
固定的工作和恢复路径有许多含义：
- upon failure and after traffic has been moved to the recovery path, the traffic is unprotected until such time as the path defect in the original working path is repaired and that path restored to service.
- 发生故障时，在通信量移动到恢复路径后，通信量将不受保护，直到修复原始工作路径中的路径缺陷并恢复该路径的服务。
- upon failure and after traffic has been moved to the recovery path, the resources associated with the original path remain reserved.
- 发生故障时，在将通信量移动到恢复路径后，与原始路径关联的资源将保留。
In the non-revertive mode of operation, there is no preferred path or it may be desirable to minimize further disruption of the service brought on by a revertive switching operation. A switch-back to the original working path is not desired or not possible since the original path may no longer exist after the occurrence of a fault on that path. If there is a fault on the working path, traffic is switched to the recovery path. When or if the faulty path (the originally working path) is restored, it may become the recovery path (either by configuration, or, if desired, by management actions).
在非回复操作模式中，没有优选路径，或者可能希望最小化回复切换操作引起的服务的进一步中断。不希望或不可能切换回原始工作路径，因为在该路径上发生故障后，原始路径可能不再存在。如果工作路径上存在故障，通信量将切换到恢复路径。当或如果故障路径（最初的工作路径）恢复时，它可能会成为恢复路径（通过配置，或者如果需要，通过管理操作）。
In the non-revertive mode of operation, the working traffic may or may not be restored to a new optimal working path or to the original working path anyway. This is because it might be useful, in some cases, to either: (a) administratively perform a protection switch back to the original working path after gaining further assurances about the integrity of the path, or (b) it may be acceptable to continue operation on the recovery path, or (c) it may be desirable to move the traffic to a new optimal working path that is calculated based on network topology and network policies. Once a new working path has been defined, an associated recovery path may be setup.
在非回复操作模式下，工作流量可能会或不会恢复到新的最佳工作路径或原始工作路径。这是因为在某些情况下，（a）在获得有关路径完整性的进一步保证后，以管理方式将保护切换回原始工作路径，或者（b）可以在恢复路径上继续操作，或者（c）可能需要将业务移动到基于网络拓扑和网络策略计算的新的最佳工作路径。定义新的工作路径后，可以设置关联的恢复路径。
For dynamic protection counterparts when the traffic is switched over to a recovery path, the association between the original working path and the recovery path may no longer exist, since the original path itself may no longer exist after the fault. Instead, when the network reaches a stable state following routing convergence, the recovery path may be switched over to a different preferred path either optimization based on the new network topology and associated information or based on pre-configured information.
对于动态保护对等方，当流量切换到恢复路径时，原始工作路径和恢复路径之间的关联可能不再存在，因为故障发生后原始路径本身可能不再存在。相反，当网络在路由会聚之后达到稳定状态时，恢复路径可以基于新的网络拓扑和相关信息或者基于预配置的信息被切换到不同的优选路径。
Dynamic protection counterparts assume that upon failure, the PSL or other network entity will establish new working paths if another switch-over will be performed.
动态保护对应方假设，一旦发生故障，PSL或其他网络实体将建立新的工作路径（如果将执行另一次切换）。
MPLS restoration deals with returning the working traffic from the recovery path to the original or a new working path. Restoration is performed by the PSL either upon receiving notification, via FRS, that the working path is repaired, or upon receiving notification that a new working path is established.
MPLS恢复处理将工作流量从恢复路径返回到原始或新的工作路径。PSL在通过FRS收到修复工作路径的通知或收到建立新工作路径的通知后执行恢复。
For fixed counterparts in revertive mode, an LSR that detected the fault on the working path also detects the restoration of the working path. If the working path had experienced a LF defect, the LSR detects a return to normal operation via the receipt of a liveness message from its peer. If the working path had experienced a LD defect at an LSR interface, the LSR could detect a return to normal operation via the resumption of error-free packet reception on that interface. Alternatively, a lower layer that no longer detects a LF defect may inform the MPLS-based recovery mechanisms at the LSR that the link to its peer LSR is operational. The LSR then transmits FRS to its upstream LSR(s) that were transmitting traffic on the working path. At the point the PSL receives the FRS, it switches the working traffic back to the original working path.
对于还原模式下的固定对应件，检测到工作路径上故障的LSR也会检测工作路径的恢复。如果工作路径经历了LF缺陷，LSR通过从其对等方接收活跃度消息来检测到恢复正常操作。如果工作路径在LSR接口处经历了LD缺陷，则LSR可以通过恢复该接口上的无错误数据包接收来检测到恢复到正常操作。或者，不再检测LF缺陷的较低层可以通知LSR处基于MPLS的恢复机制到其对等LSR的链路是可操作的。然后，LSR将FRS发送到其在工作路径上传输流量的上游LSR。在PSL接收FRS时，它将工作流量切换回原始工作路径。
A similar scheme is used for dynamic counterparts where e.g., an update of topology and/or network convergence may trigger installation or setup of new working paths and may send notification to the PSL to perform a switch over.
类似方案用于动态对应，例如，拓扑更新和/或网络融合可能触发新工作路径的安装或设置，并可能向PSL发送通知以执行切换。
We note that if there is a way to transmit fault information back along a recovery path towards a PSL and if the recovery path is an equivalent working path, it is possible for the working path and its recovery path to exchange roles once the original working path is repaired following a fault. This is because, in that case, the recovery path effectively becomes the working path, and the restored working path functions as a recovery path for the original recovery path. This is important, since it affords the benefits of non-revertive switch operation outlined in Section 4.8.1, without leaving the recovery path unprotected.
我们注意到，如果有一种方法可以沿着恢复路径将故障信息传输回PSL，并且如果恢复路径是等效的工作路径，则在故障后修复原始工作路径后，工作路径及其恢复路径就有可能交换角色。这是因为，在这种情况下，恢复路径实际上成为工作路径，并且恢复的工作路径用作原始恢复路径的恢复路径。这一点很重要，因为它提供了第4.8.1节中概述的非回复性开关操作的好处，而不会使恢复路径不受保护。
In the revertive mode, "make before break" restoration switching can be used, which is less disruptive than performing protection switching upon the occurrence of network impairments. This will minimize both packet loss and packet reordering. The controlled rearrangement of paths can also be used to satisfy traffic engineering requirements for load balancing across an MPLS domain.
在恢复模式中，可以使用“先通后断”恢复切换，这比在发生网络损坏时执行保护切换的破坏性小。这将最小化数据包丢失和数据包重新排序。路径的受控重新排列也可用于满足跨MPLS域的负载平衡的流量工程要求。
Resource/performance requirements for recovery paths should be specified in terms of the following attributes:
应根据以下属性指定恢复路径的资源/性能要求：
I. Resource Class Attribute: Equivalent Recovery Class: The recovery path has the same performance guarantees as the working path. In other words, the recovery path meets the same SLAs as the working path.
I.资源类属性：等效恢复类：恢复路径与工作路径具有相同的性能保证。换句话说，恢复路径满足与工作路径相同的SLA。
Limited Recovery Class: The recovery path does not have the same performance guarantees as the working path.
有限恢复类：恢复路径没有与工作路径相同的性能保证。
A. Lower Class: The recovery path has lower resource requirements or less stringent performance requirements than the working path.
A.较低级别：恢复路径比工作路径具有更低的资源要求或更严格的性能要求。
B. Best Effort Class: The recovery path is best effort.
B.尽力而为等级：恢复路径为尽力而为。
II. Priority Attribute: The recovery path has a priority attribute just like the working path (i.e., the priority attribute of the associated traffic trunks). It can have the same priority as the working path or lower priority.
二,。优先级属性：恢复路径具有与工作路径相同的优先级属性（即，相关流量中继的优先级属性）。它可以具有与工作路径相同的优先级或更低的优先级。
III. Preemption Attribute: The recovery path can have the same preemption attribute as the working path or a lower one.
三、 抢占属性：恢复路径可以具有与工作路径相同的抢占属性或更低的抢占属性。
The following features are desirable from an operational point of view:
从操作角度来看，以下特征是可取的：
I. It is desirable that MPLS recovery provides an option to identify protection groups (PPGs) and protection portions (PTPs).
I.希望MPLS恢复提供一种识别保护组（PPP）和保护部分（PTP）的选项。
II. Each PSL should be capable of performing MPLS recovery upon the detection of the impairments or upon receipt of notifications of impairments.
二,。在检测到损伤或收到损伤通知后，每个PSL应能够执行MPLS恢复。
III. A MPLS recovery method should not preclude manual protection switching commands. This implies that it would be possible under administrative commands to transfer traffic from a working path to a recovery path, or to transfer traffic from a recovery
三、 MPLS恢复方法不应排除手动保护切换命令。这意味着，在管理命令下，可以将通信量从工作路径传输到恢复路径，或从恢复路径传输通信量
path to a working path, once the working path becomes operational following a fault.
工作路径的路径，一旦工作路径在故障后开始工作。
IV. A PSL may be capable of performing either a switch back to the original working path after the fault is corrected or a switchover to a new working path, upon the discovery or establishment of a more optimal working path.
四、 PSL可以在故障被纠正后切换回原始工作路径，或者在发现或建立更优化的工作路径后切换到新的工作路径。
V. The recovery model should take into consideration path merging at intermediate LSRs. If a fault affects the merged segment, all the paths sharing that merged segment should be able to recover. Similarly, if a fault affects a non-merged segment, only the path that is affected by the fault should be recovered.
V.恢复模型应考虑中间LSR的路径合并。如果故障影响合并段，则共享该合并段的所有路径都应能够恢复。同样，如果故障影响未合并的段，则只应恢复受故障影响的路径。
Possible criteria to use for comparison of MPLS-based recovery schemes are as follows:
用于比较基于MPLS的恢复方案的可能标准如下：
Recovery Time
恢复时间
We define recovery time as the time required for a recovery path to be activated (and traffic flowing) after a fault. Recovery Time is the sum of the Fault Detection Time, Hold-off Time, Notification Time, Recovery Operation Time, and the Traffic Restoration Time. In other words, it is the time between a failure of a node or link in the network and the time before a recovery path is installed and the traffic starts flowing on it.
我们将恢复时间定义为故障后激活恢复路径（和流量流动）所需的时间。恢复时间是故障检测时间、延迟时间、通知时间、恢复操作时间和流量恢复时间的总和。换句话说，这是网络中的节点或链路发生故障到安装恢复路径和流量开始在其上流动之前的时间。
Full Restoration Time
完全恢复时间
We define full restoration time as the time required for a permanent restoration. This is the time required for traffic to be routed onto links, which are capable of or have been engineered sufficiently to handle traffic in recovery scenarios. Note that this time may or may not be different from the "Recovery Time" depending on whether equivalent or limited recovery paths are used.
我们将完全恢复时间定义为永久恢复所需的时间。这是将流量路由到链路所需的时间，这些链路能够或已经设计得足以处理恢复场景中的流量。请注意，此时间可能与“恢复时间”不同，也可能不不同，具体取决于使用的是等效恢复路径还是有限恢复路径。
Setup vulnerability
设置漏洞
The amount of time that a working path or a set of working paths is left unprotected during such tasks as recovery path computation and recovery path setup may be used to compare schemes. The nature of this vulnerability should be taken into account, e.g., End to End schemes correlate the vulnerability with working paths,
在恢复路径计算和恢复路径设置等任务期间，工作路径或一组工作路径未受保护的时间量可用于比较方案。应考虑此漏洞的性质，例如，端到端方案将漏洞与工作路径关联，
Local Repair schemes have a topological correlation that cuts across working paths and Network Plan approaches have a correlation that impacts the entire network.
局部修复方案具有贯穿工作路径的拓扑相关性，而网络计划方法具有影响整个网络的相关性。
Backup Capacity
备份容量
Recovery schemes may require differing amounts of "backup capacity" in the event of a fault. This capacity will be dependent on the traffic characteristics of the network. However, it may also be dependent on the particular protection plan selection algorithms as well as the signaling and re-routing methods.
发生故障时，恢复方案可能需要不同数量的“备份容量”。该容量将取决于网络的流量特性。然而，它也可能取决于特定的保护计划选择算法以及信令和重路由方法。
Additive Latency
附加延迟
Recovery schemes may introduce additive latency for traffic. For example, a recovery path may take many more hops than the working path. This may be dependent on the recovery path selection algorithms.
恢复方案可能会为流量引入附加延迟。例如，恢复路径可能比工作路径需要更多的跃点。这可能取决于恢复路径选择算法。
Quality of Protection
保护质量
Recovery schemes can be considered to encompass a spectrum of "packet survivability" which may range from "relative" to "absolute". Relative survivability may mean that the packet is on an equal footing with other traffic of, as an example, the same diff-serv code point (DSCP) in contending for the resources of the portion of the network that survives the failure. Absolute survivability may mean that the survivability of the protected traffic has explicit guarantees.
恢复方案可被视为包含“数据包生存性”的范围，其范围从“相对”到“绝对”。相对生存性可意味着分组在竞争网络中幸存故障部分的资源时，与例如相同区分服务码点（DSCP）的其他业务处于平等的地位。绝对生存性可能意味着受保护流量的生存性有明确的保证。
Re-ordering
重新订购
Recovery schemes may introduce re-ordering of packets. Also the action of putting traffic back on preferred paths might cause packet re-ordering.
恢复方案可引入分组的重新排序。此外，将流量放回首选路径的操作可能会导致数据包重新排序。
State Overhead
状态开销
As the number of recovery paths in a protection plan grows, the state required to maintain them also grows. Schemes may require differing numbers of paths to maintain certain levels of coverage, etc. The state required may also depend on the particular scheme used for recovery. The state overhead may be a function of several parameters. For example, the number of recovery paths and the number of the protected facilities (links, nodes, or shared link risk groups (SRLGs)).
随着保护计划中恢复路径数量的增加，维护这些路径所需的状态也会增加。方案可能需要不同数量的路径来保持一定的覆盖率等。所需的状态也可能取决于用于恢复的特定方案。状态开销可能是多个参数的函数。例如，恢复路径的数量和受保护设施（链路、节点或共享链路风险组（SRLGs））的数量。
Loss
丧失
Recovery schemes may introduce a certain amount of packet loss during switchover to a recovery path. Schemes that introduce loss during recovery can measure this loss by evaluating recovery times in proportion to the link speed.
在切换到恢复路径期间，恢复方案可能会引入一定数量的分组丢失。在恢复期间引入损耗的方案可以通过评估与链路速度成比例的恢复时间来测量该损耗。
In case of link or node failure a certain packet loss is inevitable.
在链路或节点发生故障的情况下，一定的数据包丢失是不可避免的。
Coverage
新闻报道
Recovery schemes may offer various types of failover coverage. The total coverage may be defined in terms of several metrics:
恢复方案可以提供各种类型的故障切换覆盖。总覆盖率可以根据几个指标来定义：
I. Fault Types: Recovery schemes may account for only link faults or both node and link faults or also degraded service. For example, a scheme may require more recovery paths to take node faults into account.
I.故障类型：恢复方案可能只考虑链路故障，或者同时考虑节点和链路故障，或者还考虑服务降级。例如，方案可能需要更多的恢复路径来考虑节点故障。
II. Number of concurrent faults: dependent on the layout of recovery paths in the protection plan, multiple fault scenarios may be able to be restored.
二,。并发故障数：根据保护计划中恢复路径的布局，可能会恢复多个故障场景。
III. Number of recovery paths: for a given fault, there may be one or more recovery paths.
三、 恢复路径数：对于给定故障，可能有一条或多条恢复路径。
IV. Percentage of coverage: dependent on a scheme and its implementation, a certain percentage of faults may be covered. This may be subdivided into percentage of link faults and percentage of node faults.
四、 覆盖率：根据方案及其实施情况，可以覆盖一定比例的故障。这可细分为链路故障百分比和节点故障百分比。
V. The number of protected paths may effect how fast the total set of paths affected by a fault could be recovered. The ratio of protection is n/N, where n is the number of protected paths and N is the total number of paths.
V.受保护路径的数量可能会影响受故障影响的路径集合的恢复速度。保护比率为n/n，其中n是受保护路径的数量，n是路径的总数。
The MPLS recovery that is specified herein does not raise any security issues that are not already present in the MPLS architecture.
此处指定的MPLS恢复不会引起MPLS体系结构中尚未出现的任何安全问题。
Confidentiality or encryption of information on the recovery path is outside the scope of this document, but any method designed to do this in other contexts may be used with the methods described in this document.
恢复路径上信息的机密性或加密不在本文档范围内，但在其他上下文中设计用于此目的的任何方法都可以与本文档中描述的方法一起使用。
The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights.
IETF已收到关于本文件所含部分或全部规范的知识产权声明。有关更多信息，请查阅在线权利主张列表。
We would like to thank members of the MPLS WG mailing list for their suggestions on the earlier versions of this document. In particular, Bora Akyol, Dave Allan, Dave Danenberg, Sharam Davari, and Neil Harrison whose suggestions and comments were very helpful in revising the document.
我们要感谢MPLS工作组邮件列表的成员对本文件早期版本的建议。特别是Bora Akyol、Dave Allan、Dave Danenberg、Sharam Davari和Neil Harrison，他们的建议和评论对修改文件非常有帮助。
The editors would like to give very special thanks to Curtis Villamizar for his careful and extremely thorough reading of the document and for taking the time to provide numerous suggestions, which were very helpful in the last couple of revisions of the document. Thanks are also due to Adrian Farrel for a through reading of the last version of the document, and to Jean-Phillipe Vasseur and Anna Charny for several useful editorial comments and suggestions, and for input on bandwidth recovery.
编辑们要特别感谢Curtis Villamizar对该文件进行了仔细和极其透彻的阅读，并花时间提出了许多建议，这些建议对该文件的最后几次修订非常有帮助。感谢Adrian Farrel通读了本文档的最后一个版本，感谢Jean Phillipe Vasseur和Anna Charny提供了一些有用的编辑评论和建议，以及对带宽恢复的投入。
[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。
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J. McManus, "Requirements for Traffic Engineering Over MPLS", RFC 2702, September 1999.
[RFC2702]Awduche，D.，Malcolm，J.，Agogbua，J.，O'Dell，M.和J.McManus，“MPLS上的流量工程要求”，RFC 2702，1999年9月。
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. and G. Swallow, "RSVP-TE Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001.
[RFC3209]Awduche，D.，Berger，L.，Gan，D.，Li，T.，Srinivasan，V.和G.Swallow，“LSP隧道RSVP-TE延伸至RSVP”，RFC 3209，2001年12月。
[RFC3212] Jamoussi, B. (Ed.), Andersson, L., Callon, R., Dantu, R., Wu, L., Doolan, P., Worster, T., Feldman, N., Fredette, A., Girish, M., Gray, E., Heinanen, J., Kilty, T. and A. Malis, "Constraint-Based LSP Setup using LDP", RFC 3212, January 2002.
[RFC3212]Jamoussi，B.（编辑），Andersson，L.，Callon，R.，Dantu，R.，Wu，L.，Doolan，P.，Worster，T.，Feldman，N.，Fredette，A.，Girish，M.，Gray，E.，Heinanen，J.，Kilty，T.和A.Malis，“使用LDP的基于约束的LSP设置”，RFC 3212，2002年1月。
[MPLS-BACKUP] Vasseur, J. P., Charny, A., LeFaucheur, F., and Achirica, "MPLS Traffic Engineering Fast reroute: backup tunnel path computation for bandwidth protection", Work in Progress.
[MPLS-BACKUP]Vasseur，J.P.，Charny，A.，LeFaucheur，F.，和Achirica，“MPLS流量工程快速重路由：用于带宽保护的备份隧道路径计算”，正在进行中。
[MPLS-PATH] Haung, C., Sharma, V., Owens, K., Makam, V. "Building Reliable MPLS Networks Using a Path Protection Mechanism", IEEE Commun. Mag., Vol. 40, Issue 3, March 2002, pp. 156-162.
[MPLS-PATH]Haung，C.，Sharma，V.，Owens，K.，Makam，V.“使用路径保护机制构建可靠的MPLS网络”，IEEE Common。《杂志》，第40卷，第3期，2002年3月，第156-162页。
[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997.
[RFC2205]Braden，R.，Zhang，L.，Berson，S.，Herzog，S.，“资源预留协议（RSVP）——版本1功能规范”，RFC 22052997年9月。
This document was the collective work of several individuals over a period of three years. The text and content of this document was contributed by the editors and the co-authors listed below. (The contact information for the editors appears in Section 11, and is not repeated below.)
这份文件是几个人在三年期间的集体工作。本文件的文本和内容由以下列出的编辑和合著者提供。（编辑的联系信息见第11节，下文不再重复。）
Ben Mack-Crane Tellabs Operations, Inc. 1415 West Diehl Road Naperville, IL 60563
伊利诺伊州纳珀维尔西迪尔路1415号Ben Mack Crane Tellabs Operations，Inc.60563
Phone: (630) 798-6197 EMail: Ben.Mack-Crane@tellabs.com
电话：（630）798-6197电子邮件：Ben.Mack-Crane@tellabs.com
Srinivas Makam Eshernet, Inc. 1712 Ada Ct. Naperville, IL 60540
Srinivas Makam Eshernet，Inc.1712 Ada Ct。伊利诺伊州纳珀维尔60540
Phone: (630) 308-3213 EMail: Smakam60540@yahoo.com
电话：（630）308-3213电子邮件：Smakam60540@yahoo.com
Ken Owens Edward Jones Investments 201 Progress Parkway St. Louis, MO 63146
肯·欧文斯·爱德华·琼斯投资公司，密苏里州圣路易斯进步大道201号，邮编63146
Phone: (314) 515-3431 EMail: ken.owens@edwardjones.com
电话：（314）515-3431电子邮件：肯。owens@edwardjones.com
Changcheng Huang Carleton University Minto Center, Rm. 3082 1125 Colonial By Drive Ottawa, Ont. K1S 5B6 Canada
长城黄卡尔顿大学明托中心，Rm。安大略省渥太华殖民大道3082 1125号。K1S 5B6加拿大
Phone: (613) 520-2600 x2477 EMail: Changcheng.Huang@sce.carleton.ca
电话：（613）520-2600 x2477电子邮件：长城。Huang@sce.carleton.ca
Jon Weil
乔恩·威尔
Brad Cain Storigen Systems 650 Suffolk Street Lowell, MA 01854
马萨诸塞州洛厄尔萨福克街650号Brad Cain Storigen Systems 01854
Phone: (978) 323-4454 EMail: bcain@storigen.com
电话：（978）323-4454电子邮件：bcain@storigen.com
Loa Andersson
安徒生酒店
EMail: loa@pi.se
EMail: loa@pi.se
Bilel Jamoussi Nortel Networks 3 Federal Street, BL3-03 Billerica, MA 01821, USA
美国马萨诸塞州比尔里卡联邦街3号比勒尔·贾穆西北电网络有限公司，邮编01821
Phone:(978) 288-4506 EMail: jamoussi@nortelnetworks.com
电话：（978）288-4506电子邮件：jamoussi@nortelnetworks.com
Angela Chiu AT&T Labs-Research 200 Laurel Ave. Rm A5-1F13 Middletown , NJ 07748
安吉拉·邱美国电话电报公司实验室研究室，地址：新泽西州米德尔顿劳雷尔大道200号A5-1F13室，邮编：07748
Phone: (732) 420-9061 EMail: chiu@research.att.com
电话：（732）420-9061电子邮件：chiu@research.att.com
Seyhan Civanlar Lemur Networks, Inc. 135 West 20th Street, 5th Floor New York, NY 10011
纽约州纽约市西20街135号5楼Seyhan Civanlar Lemur Networks，Inc.10011
Phone: (212) 367-7676 EMail: scivanlar@lemurnetworks.com
电话：（212）367-7676电子邮件：scivanlar@lemurnetworks.com
Vishal Sharma (Editor) Metanoia, Inc. 1600 Villa Street, Unit 352 Mountain View, CA 94041-1174
Vishal Sharma（编辑）Metanoia，Inc.加利福尼亚州山景城别墅街1600号352单元94041-1174
Phone: (650) 386-6723 EMail: v.sharma@ieee.org
电话：（650）386-6723电子邮件：v。sharma@ieee.org
Fiffi Hellstrand (Editor) Nortel Networks St Eriksgatan 115 PO Box 6701 113 85 Stockholm, Sweden
Fiffi Hellstrand（编辑）Nortel Networks St Eriksgatan 115邮箱6701 113 85瑞典斯德哥尔摩
Phone: +46 8 5088 3687
EMail: fiffi@nortelnetworks.com
Phone: +46 8 5088 3687
EMail: fiffi@nortelnetworks.com
Copyright (C) The Internet Society (2003). All Rights Reserved.
版权所有（C）互联网协会（2003年）。版权所有。
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
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The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
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This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。