Internet Engineering Task Force (IETF) A. Malis, Ed.
Request for Comments: 7771 L. Andersson
Updates: 6870 Huawei Technologies Co., Ltd.
Category: Standards Track H. van Helvoort
ISSN: 2070-1721 Hai Gaoming BV
J. Shin
SK Telecom
L. Wang
China Mobile
A. D'Alessandro
Telecom Italia
January 2016
Internet Engineering Task Force (IETF) A. Malis, Ed.
Request for Comments: 7771 L. Andersson
Updates: 6870 Huawei Technologies Co., Ltd.
Category: Standards Track H. van Helvoort
ISSN: 2070-1721 Hai Gaoming BV
J. Shin
SK Telecom
L. Wang
China Mobile
A. D'Alessandro
Telecom Italia
January 2016
Switching Provider Edge (S-PE) Protection for MPLS and MPLS Transport Profile (MPLS-TP) Static Multi-Segment Pseudowires
用于MPLS和MPLS传输配置文件（MPLS-TP）静态多段伪线的交换提供商边缘（S-PE）保护
Abstract
摘要
In MPLS and MPLS Transport Profile (MPLS-TP) environments, statically provisioned Single-Segment Pseudowires (SS-PWs) are protected against tunnel failure via MPLS-level and MPLS-TP-level tunnel protection. With statically provisioned Multi-Segment Pseudowires (MS-PWs), each segment of the MS-PW is likewise protected from tunnel failures via MPLS-level and MPLS-TP-level tunnel protection. However, static MS-PWs are not protected end-to-end against failure of one of the Switching Provider Edge Routers (S-PEs) along the path of the MS-PW. This document describes how to achieve this protection via redundant MS-PWs by updating the existing procedures in RFC 6870. It also contains an optional approach based on MPLS-TP Linear Protection.
在MPLS和MPLS传输配置文件（MPLS-TP）环境中，静态配置的单段伪线（SS PW）通过MPLS级和MPLS-TP级隧道保护防止隧道故障。使用静态配置的多段伪线（MS PW），MS-PW的每个段同样通过MPLS级和MPLS TP级隧道保护免受隧道故障的影响。但是，静态MS-PW没有受到端到端的保护，以防止交换提供商边缘路由器（S-PE）沿MS-PW路径出现故障。本文件描述了如何通过更新RFC 6870中的现有程序，通过冗余MS PWs实现此保护。它还包含一种基于MPLS-TP线性保护的可选方法。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7771.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc7771.
Copyright Notice
版权公告
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2016 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Extension to RFC 6870 to Protect Statically Provisioned
SS-PWs and MS-PWs . . . . . . . . . . . . . . . . . . . . . . 3
3. Operational Considerations . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Optional Linear Protection Approach . . . . . . . . 7
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 7
A.2. Encapsulation of the PSC Protocol for Pseudowires . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Extension to RFC 6870 to Protect Statically Provisioned
SS-PWs and MS-PWs . . . . . . . . . . . . . . . . . . . . . . 3
3. Operational Considerations . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Optional Linear Protection Approach . . . . . . . . 7
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 7
A.2. Encapsulation of the PSC Protocol for Pseudowires . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
In MPLS and MPLS Transport Profile (MPLS-TP) Packet Switched Networks (PSNs), pseudowires (PWs) are transported by MPLS(-TP) Label Switched Paths (LSPs), also known as tunnels.
在MPLS和MPLS传输配置文件（MPLS-TP）分组交换网络（PSN）中，伪线（PW）通过MPLS（-TP）标签交换路径（LSP）传输，也称为隧道。
As described in RFC 5659 [RFC5659], Multi-Segment Pseudowires (MS-PWs) consist of Terminating Provider Edge Routers PEs (T-PEs), one or more Switching Provider Edge Routers (S-PEs), and a sequence of tunneled PW segments that connects one of the T-PEs with its "adjacent" S-PE, connects this S-PE with the next S-PE in the sequence, and so on until the last S-PE is connected by the last PW segment to the remaining T-PE. In MPLS and MPLS-TP environments, statically provisioned Single-Segment Pseudowires (SS-PWs) are protected against tunnel failure via MPLS-level and MPLS-TP-level tunnel protection. With statically provisioned Multi-Segment
如RFC 5659[RFC5659]所述，多段伪线（MS PW）由端接提供商边缘路由器PEs（T-PEs）、一个或多个交换提供商边缘路由器（S-PEs）和一系列隧道PW段组成，这些PW段将一个T-PE与其“相邻”的S-PE连接，并将该S-PE与序列中的下一个S-PE连接，依此类推，直到最后一个S-PE通过最后一个PW段连接到剩余的T-PE。在MPLS和MPLS-TP环境中，静态配置的单段伪线（SS PW）通过MPLS级和MPLS-TP级隧道保护来防止隧道故障。使用静态配置的多段
Pseudowires (MS-PWs), each PW segment of the MS-PW is likewise protected from tunnel failure via MPLS-level and MPLS-TP-level tunnel protection. However, tunnel protection does not protect static MS-PWs from failures of S-PEs along the path of the MS-PW.
伪线（MS PWs），MS-PW的每个PW段同样通过MPLS级和MPLS TP级隧道保护免受隧道故障的影响。然而，隧道保护不能保护静态MS-PW免受MS-PW路径沿线S-PEs故障的影响。
RFC 6718 [RFC6718] provides a general framework for PW protection, and RFC 6870 [RFC6870], which is based upon that framework, describes protection procedures for MS-PWs that are dynamically signaled using LDP. This document describes how to achieve protection against S-PE failure in a static MS-PW by extending RFC 6870 to be applicable for statically provisioned MS-PWs pseudowires (PWs) as well.
RFC 6718[RFC6718]提供了PW保护的一般框架，RFC 6870[RFC6870]基于该框架，描述了使用LDP动态发送信号的MS PW的保护程序。本文档描述了如何通过扩展RFC 6870以适用于静态配置的MS-PWs伪线（PWs），实现对静态MS-PW中S-PE故障的保护。
This document also contains an OPTIONAL alternative approach based on MPLS-TP Linear Protection. This approach, described in Appendix A, MUST be identically provisioned in the PE endpoints for the protected MS-PW in order to be used. See Appendix A for further details on this alternative approach.
本文档还包含基于MPLS-TP线性保护的可选替代方法。附录A中描述的这种方法必须在受保护MS-PW的PE端点中进行相同的配置，以便使用。有关此替代方法的更多详细信息，请参见附录A。
This document differs from [PW-REDUNDANCY] in that it provides end-to-end resiliency for static MS-PWs, whereas [PW-REDUNDANCY] provides resiliency at intermediate S-PEs and resiliency for both dynamically signaled and static MS-PWs.
本文件与[PW-REDUNDANCY]的不同之处在于，它为静态MS PWs提供端到端弹性，而[PW-REDUNDANCY]为中间S-PE提供弹性，并为动态信号和静态MS PWs提供弹性。
PWs based on the Layer 2 Tunneling Protocol Version 3 (L2TPv3) are outside the scope of this document.
基于第2层隧道协议版本3（L2TPv3）的PWs不在本文件范围内。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[RFC2119]中所述进行解释。
2. Extension to RFC 6870 to Protect Statically Provisioned SS-PWs and MS-PWs
2. 扩展到RFC 6870，以保护静态供应的SS PWs和MS PWs
Section 3.2.3 of RFC 6718 and Appendix A.5 of RFC 6870 document how to use redundant MS-PWs to protect an MS-PW against S-PE failure in the case of a singly homed Customer Edge (CE), using the following network model from RFC 6718:
RFC 6718第3.2.3节和RFC 6870附录A.5说明了如何使用冗余MS PW，在单宿客户边缘（CE）的情况下，使用RFC 6718中的以下网络模型，保护MS-PW免受S-PE故障的影响：
Native |<----------- Pseudowires ----------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| |
| CE1| | |=========| |=========| | | CE2|
| | +-----+ +-----+ +-----+ | |
+----+ |.||.| |.||.| +----+
|.||.| +-----+ |.||.|
|.||.|=========| |========== .||.|
|.||...PW2-Seg1......|.PW2-Seg2...||.|
|.| ===========|S-PE2|============ |.|
|.| +-----+ |.|
|.|============+-----+============= .|
|.....PW3-Seg1.| | PW3-Seg2......|
==============|S-PE3|===============
| |
+-----+
Native |<----------- Pseudowires ----------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| |
| CE1| | |=========| |=========| | | CE2|
| | +-----+ +-----+ +-----+ | |
+----+ |.||.| |.||.| +----+
|.||.| +-----+ |.||.|
|.||.|=========| |========== .||.|
|.||...PW2-Seg1......|.PW2-Seg2...||.|
|.| ===========|S-PE2|============ |.|
|.| +-----+ |.|
|.|============+-----+============= .|
|.....PW3-Seg1.| | PW3-Seg2......|
==============|S-PE3|===============
| |
+-----+
Figure 1: Single-Homed CE with Redundant MS-PWs
图1：带冗余MS PWs的单宿CE
In this figure, Customer Edge Router 1 (CE1) is connected to T-PE1, and CE2 is connected to T-PE2 via Attachment Circuits (ACs). There are three MS-PWs. PW1 is switched at S-PE1, PW2 is switched at S-PE2, and PW3 is switched at S-PE3. This scenario provides N:1 protection against S-PE failure for the subset of the path of the emulated service from T-PE1 to T-PE2.
在此图中，客户边缘路由器1（CE1）连接到T-PE1，CE2通过连接电路（ACs）连接到T-PE2。有三个MS PW。PW1在S-PE1处切换，PW2在S-PE2处切换，PW3在S-PE3处切换。此场景为从T-PE1到T-PE2的模拟服务路径子集提供N:1保护，以防止S-PE故障。
The procedures in RFCs 6718 and 6870 rely on LDP-based PW status signaling to signal the state of the primary MS-PW that is being protected, and the precedence in which redundant MS-PW(s) should be used to protect the primary MS-PW should it fail. These procedures make use of information carried by the PW Status TLV, which, for dynamically signaled PWs, is carried by the LDP.
RFCs 6718和6870中的程序依赖于基于LDP的PW状态信令，以向受保护的主MS-PW的状态发送信号，以及在主MS-PW发生故障时应使用冗余MS-PW保护主MS-PW的优先级。这些程序利用PW状态TLV携带的信息，对于动态信号PWs，该信息由LDP携带。
However, statically provisioned PWs (SS-PWs or MS-PWs) do not use the LDP for PW setup and signaling; rather, they are provisioned by network management systems or other means at each T-PE and S-PE along their paths. They also do not use the LDP for status signaling. Rather, they use procedures defined in RFC 6478 [RFC6478] for status signaling via the PW Operations, Administration, and Maintenance (OAM) message using the PW Associated Channel Header (ACH). The PW Status TLV carried via this status signaling is itself identical to the PW Status TLV carried via LDP-based status signaling, including the identical PW Status Codes.
但是，静态配置的PW（SS PWs或MS PWs）不使用LDP进行PW设置和信令；相反，它们是由网络管理系统或其他方式沿其路径在每个T-PE和S-PE处供应的。他们也不使用LDP作为状态信令。相反，他们使用RFC 6478[RFC6478]中定义的程序，通过PW操作、管理和维护（OAM）消息，使用PW相关信道报头（ACH）发送状态信号。通过该状态信令携带的PW状态TLV本身与通过基于LDP的状态信令携带的PW状态TLV相同，包括相同的PW状态码。
Sections 6 and 7 of RFC 6870 describe the management of a primary PW and its secondary PW(s) to provide resiliency to the failure of the primary PW. They use status codes transmitted between endpoint T-PEs using the PW Status TLV transmitted by LDP. For this management to apply to statically provisioned PWs, the PW status signaling defined in RFC 6478 MUST be used for the primary and secondary PWs. In that case, the endpoint T-PEs can then use the PW status signaling provided by RFC 6478 in place of LDP-based status signaling, so that the status-signaling-based procedures in RFC 6870 operate identically to when used with LDP-based status signaling. Note that the optional S-PE Bypass Mode defined in Section 5.5 of RFC 6478 cannot be used, as it requires LDP signaling.
RFC 6870第6节和第7节描述了一次PW及其二次PW的管理，以提供对一次PW故障的恢复能力。他们使用端点T-PEs之间传输的状态码，使用LDP传输的PW状态TLV。为了使该管理适用于静态供应的PW，RFC 6478中定义的PW状态信令必须用于主PW和辅助PW。在这种情况下，端点T-PEs随后可以使用RFC 6478提供的PW状态信令来代替基于LDP的状态信令，使得RFC 6870中基于状态信令的过程在与基于LDP的状态信令一起使用时操作相同。请注意，不能使用RFC 6478第5.5节中定义的可选S-PE旁路模式，因为它需要LDP信令。
Because LDP is not used between the T-PEs for statically provisioned MS-PWs, the negotiation procedures described in RFC 6870 cannot be used. Thus, operational care must be taken so that the endpoint T-PEs are identically provisioned regarding the use of this document, specifically whether or not MS-PW redundancy is being used, and for each protected MS-PW, the identity of the primary MS-PW and the precedence of the secondary MS-PWs.
由于对于静态供应的MS PWs，T-PE之间未使用LDP，因此不能使用RFC 6870中描述的协商过程。因此，必须注意操作，以便端点T-PE在使用本文件时得到相同的规定，特别是无论是否使用MS-PW冗余，对于每个受保护的MS-PW，主要MS-PW的标识和次要MS-PW的优先级。
The security considerations defined for RFC 6478 apply to this document as well. As the security considerations in RFCs 6718 and 6870 are related to their use of LDP, they are not required for this document.
为RFC 6478定义的安全注意事项也适用于本文档。由于RFCs 6718和6870中的安全注意事项与LDP的使用有关，因此本文件不需要这些注意事项。
If the alternative approach in Appendix A is used, then the security considerations defined for RFCs 6378, 7271, and 7324 also apply.
如果使用附录A中的替代方法，则为RFC 6378、7271和7324定义的安全注意事项也适用。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，DOI 10.17487/RFC2119，1997年3月<http://www.rfc-editor.org/info/rfc2119>.
[RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher, N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378, October 2011, <http://www.rfc-editor.org/info/rfc6378>.
[RFC6378]Y.Weingarten，Ed.，Bryant，S.，Osborne，E.，Sprecher，N.，和A.Fulignoli，Ed.，“MPLS传输模式（MPLS-TP）线性保护”，RFC 6378，DOI 10.17487/RFC6378，2011年10月<http://www.rfc-editor.org/info/rfc6378>.
[RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci, "Pseudowire Status for Static Pseudowires", RFC 6478, DOI 10.17487/RFC6478, May 2012, <http://www.rfc-editor.org/info/rfc6478>.
[RFC6478]Martini，L.，Swallow，G.，Heron，G.，和M.Bocci，“静态伪线的伪线状态”，RFC 6478，DOI 10.17487/RFC6478，2012年5月<http://www.rfc-editor.org/info/rfc6478>.
[RFC6870] Muley, P., Ed. and M. Aissaoui, Ed., "Pseudowire Preferential Forwarding Status Bit", RFC 6870, DOI 10.17487/RFC6870, February 2013, <http://www.rfc-editor.org/info/rfc6870>.
[RFC6870]Muley，P.，Ed.和M.Aissaoui，Ed.，“伪线优先转发状态位”，RFC 6870，DOI 10.17487/RFC6870，2013年2月<http://www.rfc-editor.org/info/rfc6870>.
[RFC7271] Ryoo, J., Ed., Gray, E., Ed., van Helvoort, H., D'Alessandro, A., Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS-TP) Linear Protection to Match the Operational Expectations of Synchronous Digital Hierarchy, Optical Transport Network, and Ethernet Transport Network Operators", RFC 7271, DOI 10.17487/RFC7271, June 2014, <http://www.rfc-editor.org/info/rfc7271>.
[RFC7271]Ryoo，J.，Ed.，Gray，E.，Ed.，van Helvoort，H.，D'Alessandro，A.，Cheung，T.，和E.Osborne，“MPLS传输配置文件（MPLS-TP）线性保护，以满足同步数字体系、光传输网络和以太网传输网络运营商的运营期望”，RFC 7271，DOI 10.17487/RFC72712014年6月， <http://www.rfc-editor.org/info/rfc7271>.
[RFC7324] Osborne, E., "Updates to MPLS Transport Profile Linear Protection", RFC 7324, DOI 10.17487/RFC7324, July 2014, <http://www.rfc-editor.org/info/rfc7324>.
[RFC7324]Osborne，E.“MPLS传输配置文件线性保护的更新”，RFC 7324，DOI 10.17487/RFC73242014年7月<http://www.rfc-editor.org/info/rfc7324>.
[PW-REDUNDANCY] Dong, J. and H. Wang, "Pseudowire Redundancy on S-PE", Work in Progress, draft-ietf-pals-redundancy-spe-02, August 2015.
[PW-REDUNDANCY]Dong，J.和H.Wang，“S-PE上的伪线冗余”，正在进行的工作，草稿-ietf-pals-REDUNDANCY-spe-02，2015年8月。
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, DOI 10.17487/RFC5659, October 2009, <http://www.rfc-editor.org/info/rfc5659>.
[RFC5659]Bocci，M.和S.Bryant，“多段伪线边到边仿真的体系结构”，RFC 5659，DOI 10.17487/RFC5659，2009年10月<http://www.rfc-editor.org/info/rfc5659>.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire Redundancy", RFC 6718, DOI 10.17487/RFC6718, August 2012, <http://www.rfc-editor.org/info/rfc6718>.
[RFC6718]Muley，P.，Aissaoui，M.和M.Bocci，“伪线冗余”，RFC 6718，DOI 10.17487/RFC6718，2012年8月<http://www.rfc-editor.org/info/rfc6718>.
In "MPLS Transport Profile (MPLS-TP) Linear Protection" [RFC6378], as well as in the later updates of that RFC "MPLS Transport Profile (MPLS-TP) Linear Protection to Match the Operational Expectations of Synchronous Digital Hierarchy, Optical Transport Network, and Ethernet Transport Network Operators" [RFC7271] and "Updates to MPLS Transport Profile Linear Protection" [RFC7324], the Protection State Coordination (PSC) protocol was defined for MPLS LSPs only.
在“MPLS传输配置文件（MPLS-TP）线性保护”[RFC6378]以及该RFC的后续更新中，“MPLS传输配置文件（MPLS-TP）线性保护，以匹配同步数字体系、光传输网络和以太网传输网络运营商的运营期望”[RFC7271]和“更新MPLS传输配置文件线性保护”[RFC7324]，仅为MPLS LSP定义了保护状态协调（PSC）协议。
This appendix extends these RFCs to be applicable for PWs (SS-PW and MS-PW) as well. This is useful especially in the case of end-to-end static provisioned MS-PWs running over MPLS-TP where tunnel protection alone cannot be relied upon for end-to-end protection of PWs against S-PE failure. It also enables a uniform operational approach for protection at LSP and PW layers and an easier management integration for networks that already implement the approach in RFCs 6378, 7271, and 7324.
本附录扩展了这些RFC，使其也适用于PWs（SS-PW和MS-PW）。这在MPLS-TP上运行的端到端静态配置MS PWs的情况下尤其有用，在这种情况下，无法单独依靠隧道保护对PWs进行端到端保护以防止S-PE故障。它还为LSP和PW层的保护提供了统一的操作方法，并为已经在RFCs 6378、7271和7324中实施该方法的网络提供了更容易的管理集成。
The protection architectures are those defined in [RFC6378]. For the purposes of this appendix, we define the protection domain of a point-to-point PW as consisting of two terminating PEs (T-PEs) and the transport paths that connect them (see Figure 2).
保护架构是[RFC6378]中定义的架构。在本附录中，我们将点到点PW的保护域定义为由两个终端PE（T-PE）和连接它们的传输路径组成（见图2）。
+-----+ //=======================\\ +-----+
|T-PE1|// Working Path \\|T-PE2|
| /| |\ |
| ?< | | >? |
| \| |/ |
| |\\ Protection Path //| |
+-----+ \\=======================// +-----+
+-----+ //=======================\\ +-----+
|T-PE1|// Working Path \\|T-PE2|
| /| |\ |
| ?< | | >? |
| \| |/ |
| |\\ Protection Path //| |
+-----+ \\=======================// +-----+
|<-------Protection Domain------->|
|<-------Protection Domain------->|
Figure 2: Protection Domain
图2：保护域
This Appendix is an OPTIONAL alternative approach to the one in Section 2. For interoperability, all implementations MUST include the approach in Section 2, even if this alternative approach is used. The operational considerations in Section 3 continue to apply when this approach is used, and operational care must be taken so that the endpoint T-PEs are identically provisioned regarding the use of this document.
本附录是第2节所述方法的可选替代方法。对于互操作性，所有实现都必须包括第2节中的方法，即使使用了这种替代方法。当使用此方法时，第3节中的操作注意事项继续适用，并且必须采取操作注意事项，以便在使用本文件时对端点T-PE进行相同的规定。
The PSC protocol can be used to protect against defects on any LSP (segment, link, or path). In the case of MS-PW, the PSC protocol can also protect failed intermediate nodes (S-PE). Linear protection protects an LSP or PW end-to-end and if a failure is detected, switches traffic over to another (redundant) set of resources.
PSC协议可用于防止任何LSP（段、链路或路径）上的缺陷。在MS-PW的情况下，PSC协议还可以保护发生故障的中间节点（S-PE）。线性保护端到端保护LSP或PW，如果检测到故障，则将流量切换到另一组（冗余）资源。
Obviously, the protected entity does not need to be of the same type as the protecting entity. For example, it is possible to protect a link by a path. Likewise, it is possible to protect an SS-PW with an MS-PW, and vice versa.
显然，受保护实体不需要与受保护实体的类型相同。例如，可以通过路径保护链路。同样，可以用MS-PW保护SS-PW，反之亦然。
From a PSC protocol point of view, it is possible to view an SS-PW as a single-hop LSP and an MS-PW as a multiple-hop LSP. Thus, this provides end-to-end protection for the SS-PW or MS-PW. The Generic Associated Channel (G-Ach) carrying the PSC protocol information is placed in the label stack directly beneath the PW identifier. The PSC protocol will then work as specified in RFCs 6378, 7271, and 7324.
从PSC协议的角度来看，可以将SS-PW视为单跳LSP，将MS-PW视为多跳LSP。因此，这为SS-PW或MS-PW提供端到端保护。承载PSC协议信息的通用关联信道（G-Ach）被放置在PW标识符正下方的标签堆栈中。然后，PSC协议将按照RFCs 6378、7271和7324中的规定工作。
Acknowledgements
致谢
The authors would like to thank Matthew Bocci, Yaakov Stein, David Sinicrope, Sasha Vainshtein, and Italo Busi for their comments on this document.
作者感谢Matthew Bocci、Yaakov Stein、David Sinicrope、Sasha Vainstein和Italo Busi对本文件的评论。
Figure 1 and the explanatory paragraph following the figure were taken from RFC 6718. Figure 2 was adapted from RFC 6378.
图1和图后的解释性段落取自RFC 6718。图2改编自RFC 6378。
Authors' Addresses
作者地址
Andrew G. Malis (editor) Huawei Technologies Co., Ltd.
安德鲁·马利斯（编辑）华为技术有限公司。
Email: agmalis@gmail.com
Email: agmalis@gmail.com
Loa Andersson Huawei Technologies Co., Ltd.
安达信华为技术有限公司。
Email: loa@mail01.huawei.com
Email: loa@mail01.huawei.com
Huub van Helvoort Hai Gaoming BV
Huub van Helvoort Hai Gaoming BV
Email: huubatwork@gmail.com
Email: huubatwork@gmail.com
Jongyoon Shin SK Telecom
容光信SK电信
Email: jongyoon.shin@sk.com
Email: jongyoon.shin@sk.com
Lei Wang China Mobile
王磊中国移动
Email: wangleiyj@chinamobile.com
Email: wangleiyj@chinamobile.com
Alessandro D'Alessandro Telecom Italia
亚历山德罗意大利电信公司
Email: alessandro.dalessandro@telecomitalia.it
Email: alessandro.dalessandro@telecomitalia.it