Independent Submission H. van Helvoort, Ed.
Request for Comments: 7347 Huawei Technologies
Category: Informational J. Ryoo, Ed.
ISSN: 2070-1721 ETRI
H. Zhang
Huawei Technologies
F. Huang
Philips
H. Li
China Mobile
A. D'Alessandro
Telecom Italia
September 2014
Independent Submission H. van Helvoort, Ed.
Request for Comments: 7347 Huawei Technologies
Category: Informational J. Ryoo, Ed.
ISSN: 2070-1721 ETRI
H. Zhang
Huawei Technologies
F. Huang
Philips
H. Li
China Mobile
A. D'Alessandro
Telecom Italia
September 2014
Pre-standard Linear Protection Switching in MPLS Transport Profile (MPLS-TP)
MPLS传输配置文件（MPLS-TP）中的预标准线性保护交换
Abstract
摘要
The IETF Standards Track solution for MPLS Transport Profile (MPLS-TP) Linear Protection is provided in RFCs 6378, 7271, and 7324.
RFCs 6378、7271和7324中提供了用于MPLS传输配置文件（MPLS-TP）线性保护的IETF标准跟踪解决方案。
This document describes the pre-standard implementation of MPLS-TP Linear Protection that has been deployed by several network operators using equipment from multiple vendors. At the time of publication, these pre-standard implementations were still in operation carrying live traffic.
本文档描述了MPLS-TP线性保护的预标准实施，该保护已由多家网络运营商使用多家供应商的设备部署。在发布时，这些标准前实现仍在运行，可承载实时流量。
The specified mechanism supports 1+1 unidirectional/bidirectional protection switching and 1:1 bidirectional protection switching. It is purely supported by the MPLS-TP data plane and can work without any control plane.
指定机制支持1+1单向/双向保护切换和1:1双向保护切换。它完全由MPLS-TP数据平面支持，可以在没有任何控制平面的情况下工作。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
这是对RFC系列的贡献，独立于任何其他RFC流。RFC编辑器已选择自行发布此文档，并且未声明其对实现或部署的价值。RFC编辑批准发布的文件不适用于任何级别的互联网标准；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/rfc7347.
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/rfc7347.
Copyright Notice
版权公告
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2014 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.
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。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 5
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Linear Protection-Switching Overview . . . . . . . . . . . . 6
4.1. Protection Architecture Types . . . . . . . . . . . . . . 6
4.1.1. 1+1 Architecture . . . . . . . . . . . . . . . . . . 6
4.1.2. 1:1 Architecture . . . . . . . . . . . . . . . . . . 6
4.1.3. 1:n Architecture . . . . . . . . . . . . . . . . . . 7
4.2. Protection Switching Type . . . . . . . . . . . . . . . . 7
4.3. Protection Operation Type . . . . . . . . . . . . . . . . 7
5. Protection-Switching Trigger Conditions . . . . . . . . . . . 8
5.1. Fault Conditions . . . . . . . . . . . . . . . . . . . . 8
5.2. External Commands . . . . . . . . . . . . . . . . . . . . 8
5.2.1. End-to-End Commands . . . . . . . . . . . . . . . . . 8
5.2.2. Local Commands . . . . . . . . . . . . . . . . . . . 9
6. Protection-Switching Schemes . . . . . . . . . . . . . . . . 10
6.1. 1+1 Unidirectional Protection Switching . . . . . . . . . 10
6.2. 1+1 Bidirectional Protection Switching . . . . . . . . . 11
6.3. 1:1 Bidirectional Protection Switching . . . . . . . . . 12
7. APS Protocol . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. APS PDU Format . . . . . . . . . . . . . . . . . . . . . 13
7.2. APS Transmission . . . . . . . . . . . . . . . . . . . . 16
7.3. Hold-Off Timer . . . . . . . . . . . . . . . . . . . . . 17
7.4. WTR Timer . . . . . . . . . . . . . . . . . . . . . . . . 17
7.5. Command Acceptance and Retention . . . . . . . . . . . . 18
7.6. Exercise Operation . . . . . . . . . . . . . . . . . . . 18
8. Protection-Switching Logic . . . . . . . . . . . . . . . . . 19
8.1. Principle of Operation . . . . . . . . . . . . . . . . . 19
8.2. Equal Priority Requests . . . . . . . . . . . . . . . . . 21
8.3. Signal Degrade of the Protection Transport Entity . . . . 22
9. Protection-Switching State Transition Tables . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 24
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. Normative References . . . . . . . . . . . . . . . . . . 24
12.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Operation Examples of the APS Protocol . . . . . . . 26
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 5
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Linear Protection-Switching Overview . . . . . . . . . . . . 6
4.1. Protection Architecture Types . . . . . . . . . . . . . . 6
4.1.1. 1+1 Architecture . . . . . . . . . . . . . . . . . . 6
4.1.2. 1:1 Architecture . . . . . . . . . . . . . . . . . . 6
4.1.3. 1:n Architecture . . . . . . . . . . . . . . . . . . 7
4.2. Protection Switching Type . . . . . . . . . . . . . . . . 7
4.3. Protection Operation Type . . . . . . . . . . . . . . . . 7
5. Protection-Switching Trigger Conditions . . . . . . . . . . . 8
5.1. Fault Conditions . . . . . . . . . . . . . . . . . . . . 8
5.2. External Commands . . . . . . . . . . . . . . . . . . . . 8
5.2.1. End-to-End Commands . . . . . . . . . . . . . . . . . 8
5.2.2. Local Commands . . . . . . . . . . . . . . . . . . . 9
6. Protection-Switching Schemes . . . . . . . . . . . . . . . . 10
6.1. 1+1 Unidirectional Protection Switching . . . . . . . . . 10
6.2. 1+1 Bidirectional Protection Switching . . . . . . . . . 11
6.3. 1:1 Bidirectional Protection Switching . . . . . . . . . 12
7. APS Protocol . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. APS PDU Format . . . . . . . . . . . . . . . . . . . . . 13
7.2. APS Transmission . . . . . . . . . . . . . . . . . . . . 16
7.3. Hold-Off Timer . . . . . . . . . . . . . . . . . . . . . 17
7.4. WTR Timer . . . . . . . . . . . . . . . . . . . . . . . . 17
7.5. Command Acceptance and Retention . . . . . . . . . . . . 18
7.6. Exercise Operation . . . . . . . . . . . . . . . . . . . 18
8. Protection-Switching Logic . . . . . . . . . . . . . . . . . 19
8.1. Principle of Operation . . . . . . . . . . . . . . . . . 19
8.2. Equal Priority Requests . . . . . . . . . . . . . . . . . 21
8.3. Signal Degrade of the Protection Transport Entity . . . . 22
9. Protection-Switching State Transition Tables . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 24
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. Normative References . . . . . . . . . . . . . . . . . . 24
12.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Operation Examples of the APS Protocol . . . . . . . 26
The IETF Standards Track solution for MPLS Transport Profile (MPLS-TP) Linear Protection is provided in [RFC6378], [RFC7271], and [RFC7324].
[RFC6378]、[RFC7271]和[RFC7324]中提供了用于MPLS传输配置文件（MPLS-TP）线性保护的IETF标准跟踪解决方案。
This document describes the pre-standard implementation of MPLS-TP Linear Protection that has been deployed by several network operators using equipment from multiple vendors. At the time of publication, these pre-standard implementations were still in operation carrying live traffic.
本文档描述了MPLS-TP线性保护的预标准实施，该保护已由多家网络运营商使用多家供应商的设备部署。在发布时，这些标准前实现仍在运行，可承载实时流量。
This implementation was considered in the MPLS WG; however, a different path was chosen.
MPLS工作组考虑了该实施；然而，选择了一条不同的道路。
This document may be useful in the future if a vendor or operator is trying to interwork with a different vendor or operator who has deployed the pre-standard implementation, and it provides a permanent record of the pre-standard implementation. It is also worth noting that the experience gained during deployment of the implementations of this document was used to refine [RFC7271].
如果供应商或运营商试图与部署了预标准实施的其他供应商或运营商进行交互，并且提供了预标准实施的永久记录，则本文档在将来可能会很有用。还值得注意的是，在部署本文档实现过程中获得的经验用于改进[RFC7271]。
MPLS-TP is defined as the transport profile of MPLS technology to allow its deployment in transport networks. A typical feature of a transport network is that it can provide fast protection switching for end-to-end transport paths and transport path segments. The protection-switching time is generally required to be less than 50 ms to meet the strict requirements of services such as voice, private line, etc.
MPLS-TP被定义为MPLS技术的传输配置文件，以允许其在传输网络中部署。传输网络的一个典型特征是，它可以为端到端传输路径和传输路径段提供快速保护切换。保护切换时间一般要求小于50ms，以满足语音、专线等业务的严格要求。
The goal of a linear protection-switching mechanism is to satisfy the requirement of fast protection switching for an MPLS-TP network. Linear protection switching means that, for one or more working transport entities (working paths), there is one protection transport entity (protection path), which is disjoint from any of the working transport entities, ready to take over the service transmission when a working transport entity has failed.
线性保护切换机制的目标是满足MPLS-TP网络快速保护切换的要求。线性保护切换意味着，对于一个或多个工作传输实体（工作路径），有一个保护传输实体（保护路径），该实体与任何工作传输实体不相交，准备在工作传输实体发生故障时接管服务传输。
This document specifies a 1+1 unidirectional protection-switching mechanism for a unidirectional transport entity (either point to point or point to multipoint) as well as a bidirectional point-to-point transport entity and a 1+1/1:1 bidirectional protection-switching mechanism for a point-to-point bidirectional transport entity. Since bidirectional protection switching needs the coordination of the two endpoints of the transport entity, this document also specifies the Automatic Protection Switching (APS) protocol, which is used for this purpose.
本文件规定了用于单向传输实体（点对点或点对多点）的1+1单向保护切换机制，以及用于点对点双向传输实体的双向点对点传输实体和1+1/1:1双向保护切换机制。由于双向保护切换需要传输实体的两个端点的协调，因此本文档还规定了用于此目的的自动保护切换（APS）协议。
The linear protection mechanism described in this document is applicable to both Label Switched Paths (LSPs) and Pseudowires (PWs).
本文档中描述的线性保护机制适用于标签交换路径（LSP）和伪线（PW）。
The APS protocol specified in this document is based on the same principles and behavior of the APS protocol designed for Synchronous Optical Network (SONET) [T1.105.01] / Synchronous Digital Hierarchy (SDH) [G.841], Optical Transport Network (OTN) [G.873.1], and Ethernet [G.8031] and provides commonality with the established operation models utilized in transport network technologies (e.g., SDH/SONET, OTN, and Ethernet).
本文件中规定的APS协议基于为同步光网络（SONET）[T1.105.01]/同步数字体系（SDH）[G.841]、光传输网络（OTN）[G.873.1]和以太网[G.8031]设计的APS协议的相同原理和行为并与传输网络技术（如SDH/SONET、OTN和以太网）中使用的已建立的操作模型具有通用性。
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 [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
This document uses the following acronyms:
本文件使用以下首字母缩略词：
APS Automatic Protection Switching DNR Do not Revert EXER Exercise G-ACh Generic Associated Channel FS Forced Switch LO Lockout of Protection LSP Label Switched Path MPLS-TP MPLS Transport Profile MS Manual Switch MS-P Manual Switch to Protection transport entity MS-W Manual Switch to Working transport entity NR No Request OAM Operations, Administration, and Maintenance OTN Optical Transport Network PDU Protocol Data Unit PW Pseudowire RR Reverse Request SD Signal Degrade SD-P Signal Degrade on Protection transport entity SD-W Signal Degrade on Working transport entity SDH Synchronous Digital Hierarchy SF Signal Fail SF-P Signal Fail on Protection transport entity SF-W Signal Fail on Working transport entity SONET Synchronous Optical Network WTR Wait to Restore
APS自动保护切换DNR不恢复EXER练习G-ACh通用关联通道FS强制切换保护LSP锁定标签切换路径MPLS-TP MPLS传输配置文件MS手动切换MS-P手动切换到保护传输实体MS-W手动切换到工作传输实体NR无请求OAM操作，管理和维护OTN光传输网络PDU协议数据单元PW伪线RR反向请求SD信号降级SD-P信号降级保护传输实体SD-W信号降级工作传输实体SDH同步数字层次SF信号故障SF-P信号故障保护传输实体SF-W信号故障工作传输实体SONET同步光网络WTR等待恢复
To guarantee the protection-switching time for a working transport entity, its protection transport entity is always preconfigured before the failure occurs. Normally, traffic will be transmitted and received on the working transport entity. Switching to the protection transport entity is usually triggered by link or node failure, external commands, etc. Note that external commands are often used in transport networks by operators, and they are very useful in cases of service adjustment, path maintenance, etc.
为了保证工作传输实体的保护切换时间，其保护传输实体总是在故障发生之前进行预配置。通常情况下，交通将在工作运输实体上传输和接收。切换到保护传输实体通常由链路或节点故障、外部命令等触发。请注意，运营商经常在传输网络中使用外部命令，这些命令在服务调整、路径维护等情况下非常有用。
In the 1+1 architecture, the protection transport entity is associated with a working transport entity. The normal traffic is permanently bridged onto both the working transport entity and the protection transport entity at the source endpoint of the protected domain. The normal traffic on working and protection transport entities is transmitted simultaneously to the destination sink endpoint of the protected domain, where a selection between the working and protection transport entity is made based on predetermined criteria, such as signal fail and signal degrade indications.
在1+1体系结构中，保护传输实体与工作传输实体相关联。在受保护域的源端点处，正常通信量永久桥接到工作传输实体和保护传输实体上。工作和保护传输实体上的正常业务被同时传输到受保护域的目的地接收端点，其中基于预定标准（例如信号失败和信号降级指示）在工作和保护传输实体之间进行选择。
In the 1:1 architecture, the protection transport entity is associated with a working transport entity. When the working transport entity is determined to be impaired, the normal traffic MUST be transferred from the working to the protection transport entity at both the source and sink endpoints of the protected domain. The selection between the working and protection transport entities is made based on predetermined criteria, such as signal fail and signal degrade indications from the working or protection transport entity.
在1:1体系结构中，保护传输实体与工作传输实体相关联。当确定工作传输实体受损时，必须在受保护域的源和汇端点处将正常通信量从工作传输实体传输到保护传输实体。工作和保护传输实体之间的选择基于预定标准，例如来自工作或保护传输实体的信号失败和信号降级指示。
The bridge at the source endpoint can be realized in two ways: it is either a selector bridge or a broadcast bridge. With a selector bridge, the normal traffic is connected either to the working transport entity or the protection transport entity. With a broadcast bridge, the normal traffic is permanently connected to the working transport entity, and in case a protection switch is active, it is also connected to the protection transport entity. The broadcast bridge is recommended to be used in revertive mode only.
源端点处的网桥可以通过两种方式实现：选择器网桥或广播网桥。通过选择器桥接器，正常通信量连接到工作传输实体或保护传输实体。通过广播网桥，正常通信量永久连接到工作传输实体，如果保护交换机处于活动状态，它也连接到保护传输实体。建议仅在回复模式下使用广播桥。
Details for the 1:n protection-switching architecture are out of scope of this document and will be provided in a different document in the future.
1:n保护交换体系结构的详细信息不在本文件范围内，将在未来的另一份文件中提供。
It is worth noting that the APS protocol defined here is capable of supporting 1:n operations.
值得注意的是，这里定义的APS协议能够支持1:n操作。
The linear protection-switching types can be a unidirectional switching type or a bidirectional switching type.
线性保护切换类型可以是单向切换类型或双向切换类型。
o Unidirectional switching type: Only the affected direction of the working transport entity is switched to the protection transport entity; the selectors at each endpoint operate independently. This switching type is recommended to be used for 1+1 protection in this document.
o 单向切换类型：仅工作传输实体的受影响方向切换到保护传输实体；每个端点上的选择器独立运行。本文件中建议将此开关类型用于1+1保护。
o Bidirectional switching type: Both directions of the working transport entity, including the affected direction and the unaffected direction, are switched to the protection transport entity. For bidirectional switching, the APS protocol is required to coordinate the two endpoints so that both have the same bridge and selector settings, even for a unidirectional failure. This type is applicable for 1+1 and 1:1 protection.
o 双向切换类型：工作传输实体的两个方向，包括受影响方向和未受影响方向，都切换到保护传输实体。对于双向交换，APS协议需要协调两个端点，以便两者具有相同的网桥和选择器设置，即使是单向故障。该类型适用于1+1和1:1保护。
The linear protection operation types can be a non-revertive operation type or a revertive operation type.
线性保护操作类型可以是非回复操作类型或回复操作类型。
o Non-revertive operation: The normal traffic will not be switched back to the working transport entity even after a protection switching cause has cleared. This is generally accomplished by replacing the previous switch request with a "Do not Revert (DNR)" request, which has a low priority.
o 非恢复性操作：即使在清除保护切换原因后，正常通信量也不会切换回工作传输实体。这通常是通过将以前的切换请求替换为优先级较低的“请勿恢复（DNR）”请求来实现的。
o Revertive operation: The normal traffic is restored to the working transport entity after the condition(s) causing the protection switching has cleared. In the case of clearing a command (e.g., Forced Switch), this happens immediately. In the case of clearing a defect, this generally happens after the expiry of a "Wait to Restore (WTR)" timer, which is used to avoid chattering of selectors in the case of intermittent defects.
o 恢复操作：导致保护切换的条件清除后，正常通信量恢复到工作传输实体。在清除命令（例如强制开关）的情况下，这会立即发生。在清除缺陷的情况下，这通常发生在“等待恢复（WTR）”计时器到期后，该计时器用于在间歇性缺陷的情况下避免选择器抖动。
Fault conditions mean the requests generated by the local Operations, Administration, and Maintenance (OAM) function.
故障条件是指本地操作、管理和维护（OAM）功能生成的请求。
o Signal Fail (SF): If an endpoint detects a failure by an OAM function or other mechanism, it will submit a local signal failure (local SF) to the APS module to request a protection switch. The local SF could be on the working transport entity (Signal Fail on Working transport entity (SF-W)) or the protection transport entity (Signal Fail on Protection transport entity (SF-P)).
o 信号故障（SF）：如果端点通过OAM功能或其他机制检测到故障，它将向APS模块提交本地信号故障（本地SF），以请求保护开关。本地SF可能位于工作传输实体（工作传输实体信号故障（SF-W））或保护传输实体（保护传输实体信号故障（SF-P））。
o Signal Degrade (SD): If an endpoint detects signal degradation by an OAM function or other mechanism, it will submit a local signal degrade (local SD) to the APS module to request a protection switching. The local SD could be on the working transport entity (Signal Degrade on Working transport entity (SD-W)) or the protection transport entity (Signal Degrade on Protection transport entity (SD-P)).
o 信号降级（SD）：如果端点通过OAM功能或其他机制检测到信号降级，它将向APS模块提交本地信号降级（本地SD），以请求保护切换。本地SD可能位于工作传输实体（工作传输实体上的信号降级（SD-W））或保护传输实体（保护传输实体上的信号降级（SD-P））。
The external command issues an appropriate external request to the protection process.
外部命令向保护进程发出适当的外部请求。
These commands are applied to both local and remote nodes. When the APS protocol is present, these commands, except the Clear command, are signaled to the far end of the connection. In bidirectional switching, these commands affect the bridge and selector at both ends.
这些命令同时应用于本地和远程节点。当存在APS协议时，这些命令（清除命令除外）将通过信号发送到连接的远端。在双向切换中，这些命令影响两端的桥接器和选择器。
o Lockout of Protection (LO): This command is used to provide the operator a tool for temporarily disabling access to the protection transport entity.
o 保护锁定（LO）：该命令用于向操作员提供一种工具，用于临时禁用对保护传输实体的访问。
o Manual Switch (MS): This command is used to provide the operator a tool for temporarily switching normal traffic to the working transport entity (Manual Switch to Working transport entity (MS-W)) or to the protection transport entity (Manual Switch to Protection transport entity (MS-P)), unless a higher priority switch request (i.e., LO, FS, or SF) is in effect.
o 手动切换（MS）：该命令用于向操作员提供一种工具，用于将正常通信暂时切换到工作传输实体（手动切换到工作传输实体（MS-W））或保护传输实体（手动切换到保护传输实体（MS-P）），除非有更高优先级的切换请求（即LO、FS或SF）这是有效的。
o Forced Switch (FS): This command is used to provide the operator a tool for temporarily switching normal traffic from the working transport entity to the protection transport entity, unless a higher priority switch request (i.e., LO or SF-P) is in effect.
o 强制切换（FS）：该命令用于向操作员提供工具，用于临时将正常通信量从工作传输实体切换到保护传输实体，除非更高优先级的切换请求（即LO或SF-P）生效。
o Exercise (EXER): Exercise is a command to test if the APS communication is operating correctly. The EXER command SHALL NOT affect the state of the protection selector and bridge.
o 演习（EXER）：演习是测试APS通信是否正常工作的命令。EXER命令不得影响保护选择器和电桥的状态。
o Clear: This command between management and the local protection process is not a request sent by APS to other endpoints. It is used to clear the active near-end external command or WTR state.
o 清除：管理和本地保护进程之间的此命令不是AP发送给其他端点的请求。它用于清除激活的近端外部命令或WTR状态。
These commands apply only to the near end (local node) of the protection group. Even when an APS protocol is supported, they are not signaled to the far end.
这些命令仅适用于保护组的近端（本地节点）。即使支持APS协议，也不会向远端发送信号。
o Freeze: This command freezes the state of the protection group. Until the freeze is cleared, additional near-end commands are rejected, and condition changes and received APS information are ignored. When the Freeze command is cleared, the state of the protection group is recomputed based on the condition and received APS information.
o 冻结：此命令冻结保护组的状态。在清除冻结之前，其他近端命令将被拒绝，条件更改和接收到的APS信息将被忽略。清除冻结命令后，将根据条件和收到的APS信息重新计算保护组的状态。
Because the freeze is local, if the freeze is issued at one end only, a failure of protocol can occur as the other end is open to accept any operator command or fault condition.
由于冻结是本地的，如果仅在一端发出冻结，则当另一端打开以接受任何操作员命令或故障条件时，可能会发生协议故障。
o Clear Freeze: This command clears the local freeze.
o 清除冻结：此命令清除本地冻结。
+-----------+ +-----------+
| |---------------------------------------| |
| -+---------------------------------------+- |
| / |---------------------------------------| \ |
| / | Working transport entity | \ |
--+-------> | | --------+->
| \ | | |
| \ |---------------------------------------| |
| -+---------------------------------------| |
| source |---------------------------------------| sink |
+-----------+ Protection transport entity +-----------+
(normal condition)
+-----------+ +-----------+
| |---------------------------------------| |
| -+---------------------------------------+- |
| / |---------------------------------------| \ |
| / | Working transport entity | \ |
--+-------> | | --------+->
| \ | | |
| \ |---------------------------------------| |
| -+---------------------------------------| |
| source |---------------------------------------| sink |
+-----------+ Protection transport entity +-----------+
(normal condition)
+-----------+ +-----------+
| |---------------------------------------| |
| -+------------------XX-------------------+ |
| / |---------------------------------------| |
| / | Working transport entity (failure) | |
--|-------> | | --------+->
| \ | | / |
| \ |---------------------------------------| / |
| -+---------------------------------------+- |
| source |---------------------------------------| sink |
+-----------+ Protection transport entity +-----------+
(failure condition)
+-----------+ +-----------+
| |---------------------------------------| |
| -+------------------XX-------------------+ |
| / |---------------------------------------| |
| / | Working transport entity (failure) | |
--|-------> | | --------+->
| \ | | / |
| \ |---------------------------------------| / |
| -+---------------------------------------+- |
| source |---------------------------------------| sink |
+-----------+ Protection transport entity +-----------+
(failure condition)
Figure 1: 1+1 Unidirectional Linear Protection Switching
图1:1+1单向线性保护切换
1+1 unidirectional protection switching is the simplest protection switching mechanism. The normal traffic is permanently bridged on both the working and protection transport entities at the source endpoint of the protected domain. In the normal condition, the sink endpoint receives traffic from the working transport entity. If the sink endpoint detects a failure on the working transport entity, it will switch to receive traffic from the protection transport entity. 1+1 unidirectional protection switching is recommended to be used for unidirectional transport.
1+1单向保护切换是最简单的保护切换机制。正常通信量在受保护域的源端点处的工作传输实体和保护传输实体上永久桥接。在正常情况下，接收器端点接收来自工作传输实体的流量。如果接收器端点在工作传输实体上检测到故障，它将切换到从保护传输实体接收流量。单向传输建议采用1+1单向保护切换。
Note that 1+1 unidirectional protection switching does not use the APS coordination protocol since it only performs protection switching based on the local request.
注意，1+1单向保护切换不使用APS协调协议，因为它仅根据本地请求执行保护切换。
+-----------+ +-----------+
| |---------------------------------------| |
| -+<--------------------------------------+- |
| / +-------------------------------------->+ \ |
| sink / /|---------------------------------------|\ \ sink |
<-+-------/ / | Working transport entity | --\-------+->
--+--------> | | <------+--
| source \ | | / source|
| \|---------------------------------------| / |
| +-------------------------------------->| / |
| |<--------------------------------------+- |
| APS <...................................................> APS |
| |---------------------------------------+ |
+-----------+ Protection transport entity +-----------+
(normal condition)
+-----------+ +-----------+
| |---------------------------------------| |
| -+<--------------------------------------+- |
| / +-------------------------------------->+ \ |
| sink / /|---------------------------------------|\ \ sink |
<-+-------/ / | Working transport entity | --\-------+->
--+--------> | | <------+--
| source \ | | / source|
| \|---------------------------------------| / |
| +-------------------------------------->| / |
| |<--------------------------------------+- |
| APS <...................................................> APS |
| |---------------------------------------+ |
+-----------+ Protection transport entity +-----------+
(normal condition)
+-----------+ +-----------+
| |---------------------------------------| |
| +<----------------XX--------------------+- |
| +-------------------------------------->+ \ |
| /|---------------------------------------| \ |
| source / | Working transport entity (failure) | \ source|
--+--------> | | \<-----+--
<-+------- \ | | --/------+->
| sink \ \|---------------------------------------| / / sink |
| \ +-------------------------------------->+- / |
| --+<--------------------------------------+-/ |
| APS <...................................................> APS |
| |---------------------------------------+ |
+-----------+ Protection transport entity +-----------+
(failure condition)
+-----------+ +-----------+
| |---------------------------------------| |
| +<----------------XX--------------------+- |
| +-------------------------------------->+ \ |
| /|---------------------------------------| \ |
| source / | Working transport entity (failure) | \ source|
--+--------> | | \<-----+--
<-+------- \ | | --/------+->
| sink \ \|---------------------------------------| / / sink |
| \ +-------------------------------------->+- / |
| --+<--------------------------------------+-/ |
| APS <...................................................> APS |
| |---------------------------------------+ |
+-----------+ Protection transport entity +-----------+
(failure condition)
Figure 2: 1+1 Bidirectional Linear Protection Switching
图2:1+1双向线性保护切换
In 1+1 bidirectional protection switching, for each direction, the normal traffic is permanently bridged on both the working and protection transport entities at the source endpoint of the protected domain. In the normal condition, for each direction, the sink endpoint receives traffic from the working transport entity.
在1+1双向保护交换中，对于每个方向，正常流量在受保护域的源端点处的工作传输实体和保护传输实体上永久桥接。在正常情况下，对于每个方向，接收器端点接收来自工作传输实体的流量。
If the sink endpoint detects a failure on the working transport entity, it will switch to receive traffic from the protection transport entity. It will also send an APS message to inform the sink endpoint on the other direction to switch to receive traffic from the protection transport entity.
如果接收器端点在工作传输实体上检测到故障，它将切换到从保护传输实体接收流量。它还将发送一条APS消息，通知另一个方向上的接收器端点切换以接收来自保护传输实体的流量。
The APS mechanism is necessary to coordinate the two endpoints of the transport entity and to implement 1+1 bidirectional protection switching even for a unidirectional failure.
APS机制对于协调传输实体的两个端点以及实现1+1双向保护切换（即使对于单向故障）是必要的。
+-----------+ +-----------+
| |---------------------------------------| |
| -+<--------------------------------------+- |
| / +-------------------------------------->+ \ |
| sink / /|---------------------------------------|\ \ source|
<-+-------/ / | Working transport entity | \ <-------+--
--+--------> | | ---------+->
| source | | sink |
| |---------------------------------------| |
| | | |
| | | |
| APS <...................................................> APS |
| |---------------------------------------| |
+-----------+ Protection transport entity +-----------+
(normal condition)
+-----------+ +-----------+
| |---------------------------------------| |
| -+<--------------------------------------+- |
| / +-------------------------------------->+ \ |
| sink / /|---------------------------------------|\ \ source|
<-+-------/ / | Working transport entity | \ <-------+--
--+--------> | | ---------+->
| source | | sink |
| |---------------------------------------| |
| | | |
| | | |
| APS <...................................................> APS |
| |---------------------------------------| |
+-----------+ Protection transport entity +-----------+
(normal condition)
+-----------+ +-----------+
| |---------------------------------------| |
| | \/ | |
| | /\ | |
| |---------------------------------------| |
| source | Working transport entity (failure) | sink |
--+-------> | | --------+->
<-+------- \ | | / <------+--
| sink \ \ |---------------------------------------| / / source|
| \ -+-------------------------------------->+- / |
| --+<--------------------------------------+-- |
| APS <...................................................> APS |
| |---------------------------------------+ |
+-----------+ Protection transport entity +-----------+
(failure condition)
+-----------+ +-----------+
| |---------------------------------------| |
| | \/ | |
| | /\ | |
| |---------------------------------------| |
| source | Working transport entity (failure) | sink |
--+-------> | | --------+->
<-+------- \ | | / <------+--
| sink \ \ |---------------------------------------| / / source|
| \ -+-------------------------------------->+- / |
| --+<--------------------------------------+-- |
| APS <...................................................> APS |
| |---------------------------------------+ |
+-----------+ Protection transport entity +-----------+
(failure condition)
Figure 3: 1:1 Bidirectional Linear Protection Switching
图3:1:1双向线性保护切换
In 1:1 bidirectional protection switching, for each direction, the source endpoint sends traffic on either the working transport entity or the protection transport entity. The sink endpoint receives the traffic from the same transport entity on which the source endpoint sends the traffic.
在1:1双向保护切换中，对于每个方向，源端点在工作传输实体或保护传输实体上发送通信量。接收器端点从源端点发送流量的同一传输实体接收流量。
In the normal condition, for each direction, the source and sink endpoints send and receive traffic from the working transport entity.
在正常情况下，对于每个方向，源和汇端点都从工作传输实体发送和接收流量。
If the sink endpoint detects a failure on the working transport entity, it will switch to send and receive traffic from the protection transport entity. It will also send an APS message to inform the sink endpoint on another direction to switch to send and receive traffic from the protection transport entity.
如果接收器端点在工作传输实体上检测到故障，它将切换到从保护传输实体发送和接收流量。它还将发送一条APS消息，通知接收器端点另一个切换方向，以发送和接收来自保护传输实体的流量。
The APS mechanism is necessary to coordinate the two endpoints of the transport entity and implement 1:1 bidirectional protection switching even for a unidirectional failure.
APS机制对于协调传输实体的两个端点和实现1:1双向保护切换（即使是单向故障）是必要的。
This APS protocol is based upon the APS protocol defined in Section 11 of [G.8031]. See that reference for further definition of the Protocol Data Unit (PDU) fields and protocol details beyond the description in this document.
本APS协议基于[G.8031]第11节中定义的APS协议。有关协议数据单元（PDU）字段的进一步定义和本文档描述以外的协议详细信息，请参阅该参考。
APS packets MUST be sent over a Generic Associated Channel (G-ACh) as defined in [RFC5586].
APS数据包必须通过[RFC5586]中定义的通用关联信道（G-ACh）发送。
The format of APS PDU is specified in Figure 4 below.
APS PDU的格式如下图4所示。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| Channel Type (=0x7FFA) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MEL | Version | OpCode | Flags | TLV Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| APS Specific Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End TLV |
+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| Channel Type (=0x7FFA) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MEL | Version | OpCode | Flags | TLV Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| APS Specific Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End TLV |
+-+-+-+-+-+-+-+-+
Figure 4: APS PDU Format
图4:APS PDU格式
The following values MUST be used for APS PDU:
APS PDU必须使用以下值：
o Channel Type: The Channel Type MUST be configurable by the implementation. During deployment, the local system administrator provisioned the value 0x7FFA. This is a code point value in the range of experimental Channel Types as described in RFC 5586, Section 10.
o 通道类型：通道类型必须由实现配置。在部署期间，本地系统管理员设置了值0x7FFA。这是RFC 5586第10节中所述实验信道类型范围内的码点值。
o Maintenance Entity group Level (MEL): The MEL value to set and check MUST be configurable. The DEFAULT value MUST be "111". With co-routed bidirectional transport paths, the configured MEL MUST be the same in both directions.
o 维护实体组级别（MEL）：要设置和检查的MEL值必须是可配置的。默认值必须为“111”。对于共路由双向传输路径，配置的MEL在两个方向上必须相同。
o Version: 0x00
o 版本：0x00
o OpCode: 0x27 (=0d39)
o 操作码：0x27（=0d39）
o Flags: 0x00
o 标志：0x00
o TLV Offset: 4
o TLV偏移量：4
o End TLV: 0x00
o 结束TLV:0x00
The format of the APS-specific information is defined in Figure 5.
APS特定信息的格式如图5所示。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Request|Pr.Type| Requested | Bridged | | |
| / |-+-+-+-| | |T| Reserved(0)|
| State |A|B|D|R| Signal | Signal | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Request|Pr.Type| Requested | Bridged | | |
| / |-+-+-+-| | |T| Reserved(0)|
| State |A|B|D|R| Signal | Signal | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: APS-Specific Information Format
图5:APS特定信息格式
All bits defined as "Reserved" MUST be transmitted as 0 and ignored on reception.
所有定义为“保留”的位必须作为0传输，并在接收时忽略。
o Request/State:
o 请求/说明：
The four bits indicate the protection-switching request type. See Figure 6 for the code of each request/state type.
四位表示保护切换请求类型。关于每个请求/状态类型的代码，请参见图6。
In case that there are multiple protection-switching requests, only the protection-switching request with the highest priority MUST be processed.
如果存在多个保护切换请求，则只需处理优先级最高的保护切换请求。
+------------------------------------+---------------+
| Request/State | Code/Priority |
+------------------------------------+---------------+
|Lockout of Protection (LO) | 1111 (highest)|
+------------------------------------+---------------+
|Signal Fail on Protection (SF-P) | 1110 |
+------------------------------------+---------------+
|Forced Switch (FS) | 1101 |
+------------------------------------+---------------+
|Signal Fail on Working (SF-W) | 1011 |
+------------------------------------+---------------+
|Signal Degrade (SD) | 1001 |
+------------------------------------+---------------+
|Manual Switch (MS) | 0111 |
+------------------------------------+---------------+
|Wait to Restore (WTR) | 0101 |
+------------------------------------+---------------+
|Exercise (EXER) | 0100 |
+------------------------------------+---------------+
|Reverse Request (RR) | 0010 |
+------------------------------------+---------------+
|Do Not Revert (DNR) | 0001 |
+------------------------------------+---------------+
|No Request (NR) | 0000 (lowest) |
+------------------------------------+---------------+
+------------------------------------+---------------+
| Request/State | Code/Priority |
+------------------------------------+---------------+
|Lockout of Protection (LO) | 1111 (highest)|
+------------------------------------+---------------+
|Signal Fail on Protection (SF-P) | 1110 |
+------------------------------------+---------------+
|Forced Switch (FS) | 1101 |
+------------------------------------+---------------+
|Signal Fail on Working (SF-W) | 1011 |
+------------------------------------+---------------+
|Signal Degrade (SD) | 1001 |
+------------------------------------+---------------+
|Manual Switch (MS) | 0111 |
+------------------------------------+---------------+
|Wait to Restore (WTR) | 0101 |
+------------------------------------+---------------+
|Exercise (EXER) | 0100 |
+------------------------------------+---------------+
|Reverse Request (RR) | 0010 |
+------------------------------------+---------------+
|Do Not Revert (DNR) | 0001 |
+------------------------------------+---------------+
|No Request (NR) | 0000 (lowest) |
+------------------------------------+---------------+
Figure 6: Protection-Switching Request Code/Priority
图6：保护切换请求代码/优先级
o Protection Type (Pr.Type):
o 保护类型（Pr.Type）：
The four bits are used to specify the protection type.
四位用于指定保护类型。
A: reserved (set by default to 1)
B: 0 - 1+1 (permanent bridge)
1 - 1:1 (no permanent bridge)
D: 0 - Unidirectional switching
1 - Bidirectional switching
R: 0 - Non-revertive operation
1 - Revertive operation
A: reserved (set by default to 1)
B: 0 - 1+1 (permanent bridge)
1 - 1:1 (no permanent bridge)
D: 0 - Unidirectional switching
1 - Bidirectional switching
R: 0 - Non-revertive operation
1 - Revertive operation
o Requested Signal:
o 请求信号：
This byte is used to indicate the traffic that the near-end requests to be carried over the protection entity.
该字节用于指示近端请求通过保护实体传输的通信量。
value = 0: Null traffic
value = 1: Normal traffic 1
value = 2~255: Reserved
value = 0: Null traffic
value = 1: Normal traffic 1
value = 2~255: Reserved
o Bridged Signal:
o 桥接信号：
This byte is used to indicate the traffic that is bridged onto the protection entity.
此字节用于指示桥接到保护实体上的通信量。
value = 0: Null traffic
value = 1: Normal traffic 1
value = 2~255: Reserved
value = 0: Null traffic
value = 1: Normal traffic 1
value = 2~255: Reserved
o Bridge Type (T):
o 桥梁类型（T）：
This bit is used to further specify the type of non-permanent bridge for 1:1 protection switching.
该位用于进一步指定1:1保护切换的非永久性电桥类型。
value = 0: Selector bridge
value = 1: Broadcast bridge
value = 0: Selector bridge
value = 1: Broadcast bridge
o Reserved:
o 保留：
This field MUST be set to zero.
此字段必须设置为零。
The APS message MUST be transported on the protection transport entity by encapsulation with the protection transport entity label (the label of the LSP used to transport protection traffic). If an endpoint receives APS-specific information from the working transport entity, it MUST ignore this information and MUST report the failure of protocol defect (see Section 8.1) to the operator.
APS消息必须通过封装保护传输实体标签（用于传输保护通信的LSP标签）在保护传输实体上传输。如果端点从工作传输实体接收到APS特定信息，它必须忽略该信息，并且必须向操作员报告协议缺陷故障（见第8.1节）。
A new APS packet MUST be transmitted immediately when a change in the transmitted status occurs. The first three APS packets MUST be transmitted as fast as possible only if the APS information to be transmitted has been changed so that fast protection switching is possible, even if one or two APS packets are lost or corrupted. The interval of the first three APS packets SHOULD be 3.3 ms. APS packets after the first three MUST be transmitted with the interval of 5 seconds.
当传输状态发生变化时，必须立即传输新的APS数据包。前三个APS数据包必须尽可能快地传输，前提是要传输的APS信息已经更改，以便能够进行快速保护切换，即使一个或两个APS数据包丢失或损坏。前三个APS数据包的间隔应为3.3毫秒。前三个之后的APS数据包必须以5秒的间隔传输。
If no valid APS-specific information is received, the last valid received information remains applicable.
如果未收到有效的APS特定信息，则最后收到的有效信息仍然适用。
In order to coordinate timing of protection switches at multiple layers, a hold-off timer MAY be required. The purpose is to allow a server-layer protection switch to have a chance to fix the problem before switching at a client layer.
为了协调多层保护开关的定时，可能需要一个保持定时器。其目的是让服务器层保护交换机在客户端层切换之前有机会修复问题。
Each selector SHOULD have a provisioned hold-off timer. The suggested range of the hold-off timer is 0 to 10 seconds in steps of 100 ms (accuracy of +/-5 ms).
每个选择器都应该有一个已设置的保持计时器。暂停计时器的建议范围为0至10秒，步长为100毫秒（精度为+/-5毫秒）。
When a new defect or more severe defect occurs (new SF or SD) on the active transport entity (the transport entity that currently carries and selects traffic), this event will not be reported immediately to protection switching if the provisioned hold-off timer value is non-zero. Instead, the hold-off timer SHALL be started. When the hold-off timer expires, it SHALL be checked whether a defect still exists on the transport entity that started the timer. If it does, that defect SHALL be reported to protection switching. The defect need not be the same one that started the timer.
当活动传输实体（当前承载和选择流量的传输实体）上出现新的缺陷或更严重的缺陷（新的SF或SD）时，如果设置的延迟计时器值不为零，则不会立即向保护切换报告此事件。相反，应启动暂停计时器。当暂停计时器到期时，应检查启动计时器的传输实体上是否仍存在缺陷。如果存在，则应将该缺陷报告给保护开关。缺陷不一定是启动计时器的缺陷。
This hold-off timer mechanism SHALL be applied for both working and protection transport entities.
该延迟计时器机制应适用于工作和保护运输实体。
In revertive mode of operation, to prevent frequent operation of the protection switch due to an intermittent defect, a failed working transport entity MUST become fault free. After the failed working transport entity meets this criterion, a fixed period of time SHALL elapse before a normal traffic signal uses it again. This period, called a WTR period, MAY be configured by the operator in 1 minute steps between 5 and 12 minutes; the default value is 5 minutes. An SF or SD condition will override the WTR. To activate the WTR timer appropriately, even when both ends concurrently detect clearance of SF-W and SD-W, when the local state transits from SF-W or SD-W to No Request (NR) with the requested signal number 1, the previous local state, SF-W or SD-W, MUST be memorized. If both the local state and far-end state are NR with the requested signal number 1, the local state transits to WTR only when the previous local state is SF-W or SD-W. Otherwise, the local state transits to NR with the requested signal number 0.
在回复操作模式下，为了防止由于间歇性故障而频繁操作保护开关，出现故障的工作运输实体必须无故障。发生故障的工作运输实体满足该标准后，正常交通信号再次使用该实体之前，应经过一段固定的时间。该时间段称为WTR时间段，可由操作员在5到12分钟之间以1分钟的步长进行配置；默认值为5分钟。SF或SD条件将覆盖WTR。为了适当地激活WTR定时器，即使两端同时检测到SF-W和SD-W的间隙，当本地状态从SF-W或SD-W转变为无请求（NR）且请求信号号为1时，也必须记住先前的本地状态SF-W或SD-W。如果本地状态和远端状态均为NR，且请求的信号号为1，则仅当前一个本地状态为SF-W或SD-W时，本地状态才会转换为WTR。否则，本地状态转换为NR，且请求的信号号为0。
In revertive mode of operation, when the protection is no longer requested, i.e., the failed working transport entity is no longer in SF or SD condition (and assuming no other requesting transport entities), a local WTR state will be activated. Since this state becomes the highest in priority, it is indicated on the APS signal and maintains the normal traffic signal from the previously failed working transport entity on the protection transport entity. This state SHALL normally time out and become an NR state. The WTR timer deactivates earlier when any request of higher priority request preempts this state.
在回复操作模式下，当不再请求保护时，即故障工作传输实体不再处于SF或SD状态（并且假设没有其他请求传输实体），将激活本地WTR状态。由于该状态成为最高优先级，因此在APS信号上指示该状态，并在保护传输实体上保持来自先前故障工作传输实体的正常交通信号。该状态通常应超时并变为NR状态。当任何更高优先级的请求抢占此状态时，WTR计时器将提前停用。
The commands Clear, LO, FS, MS, and EXER are accepted or rejected in the context of previous commands, the condition of the working and protection entities in the protection group, and (in bidirectional switching only) the APS information received.
Clear、LO、FS、MS和EXER命令在之前的命令、保护组中工作和保护实体的条件以及（仅在双向切换中）接收到的APS信息的上下文中被接受或拒绝。
The Clear command MUST be only valid if a near-end LO, FS, MS, or EXER command is in effect or if a WTR state is present at the near end and rejected otherwise. This command will remove the near-end command or WTR state, allowing the next lower-priority condition or (in bidirectional switching) APS request to be asserted.
仅当近端LO、FS、MS或EXER命令生效，或近端存在WTR状态，否则被拒绝时，清除命令才有效。此命令将删除近端命令或WTR状态，允许断言下一个较低优先级条件或（在双向切换中）APS请求。
Other commands MUST be rejected unless they are higher priority than the previously existing command, condition, or (in bidirectional switching) APS request. If a new command is accepted, any previous, lower-priority command that is overridden MUST be forgotten. If a higher priority command overrides a lower-priority condition or (in bidirectional switching) APS request, that other request will be reasserted if it still exists at the time the command is cleared. If a command is overridden by a condition or (in bidirectional switching) APS request, that command MUST be forgotten.
必须拒绝其他命令，除非它们的优先级高于先前存在的命令、条件或（在双向切换中）APS请求。如果接受一个新命令，则必须忘记以前任何被覆盖的低优先级命令。如果较高优先级的命令覆盖较低优先级的条件或（在双向切换中）APS请求，则如果在清除该命令时该请求仍然存在，则将重新指定该请求。如果命令被条件或（在双向切换中）APS请求覆盖，则必须忘记该命令。
Exercise is a command to test if the APS communication is operating correctly. It is lower priority than any "real" switch request. It is only valid in bidirectional switching, since this is the only place where you can get a meaningful test by looking for a response.
练习是测试APS通信是否正常工作的命令。它的优先级低于任何“实际”切换请求。它仅在双向切换中有效，因为这是唯一一个可以通过查找响应获得有意义测试的地方。
The Exercise command SHALL issue the command with the same requested and bridged signal numbers of the NR, Reverse Request (RR), or DNR request that it replaces. The valid response will be an RR with the corresponding requested and bridged signal numbers. When Exercise commands are input at both ends, an EXER, instead of RR, MUST be transmitted from both ends. The standard response to DNR MUST be DNR rather than NR. When the exercise command is cleared, it MUST be
演习命令应使用其替换的NR、反向请求（RR）或DNR请求的相同请求和桥接信号号发出命令。有效响应将是带有相应请求和桥接信号号的RR。当在两端输入训练命令时，必须从两端发送EXER而不是RR。对DNR的标准响应必须是DNR而不是NR。清除演习命令时，必须是
replaced with NR or RR if the requested signal number is 0 and DNR or RR if the requested signal number is 1.
如果请求的信号号为0，则替换为NR或RR；如果请求的信号号为1，则替换为DNR或RR。
+-------------+ Persistent +----------+
SF,SD | Hold-off | fault | Local |
----------->| timer logic |----------->| request |
+-------------+ | logic |
Other local requests ----------------->| |
(LO, FS, MS, EXER, Clear) +----------+
|
| Highest
| local request
|
Remote APS V
message +-------+ Remote APS +----------------+
------------->| APS | request/state | APS process |
(received | check |-------------->| logic |
from far end) +-------+ +----------------+
| ^ | |
| | | Signaled |
| | | APS |
| | Txed | |
| | "Requested V |
| | Signal" +-----------+ |
| +-----------------| APS mess. | |
| | generator | |
| +-----------+ |
| | |
V | |
Failure of V |
protocol APS message |
detection V
Set local
bridge/selector
+-------------+ Persistent +----------+
SF,SD | Hold-off | fault | Local |
----------->| timer logic |----------->| request |
+-------------+ | logic |
Other local requests ----------------->| |
(LO, FS, MS, EXER, Clear) +----------+
|
| Highest
| local request
|
Remote APS V
message +-------+ Remote APS +----------------+
------------->| APS | request/state | APS process |
(received | check |-------------->| logic |
from far end) +-------+ +----------------+
| ^ | |
| | | Signaled |
| | | APS |
| | Txed | |
| | "Requested V |
| | Signal" +-----------+ |
| +-----------------| APS mess. | |
| | generator | |
| +-----------+ |
| | |
V | |
Failure of V |
protocol APS message |
detection V
Set local
bridge/selector
Figure 7: Protection-Switching Logic
图7：保护切换逻辑
Figure 7 describes the protection-switching logic.
图7描述了保护切换逻辑。
One or more local protection-switching requests may be active. The "local request logic" determines which of these requests is highest using the order of priority given in Figure 6. This highest local request information SHALL be passed on to the "APS process logic". Note that an accepted Clear command, clearance of SF or SD, or
一个或多个本地保护切换请求可能处于活动状态。“本地请求逻辑”使用图6中给出的优先级顺序确定这些请求中哪一个是最高的。该最高本地请求信息应传递给“APS过程逻辑”。请注意，接受的清除命令、SF或SD清除，或
expiration of the WTR timer SHALL NOT be processed by the local request logic but SHALL be considered as the highest local request and submitted to the APS process logic for processing.
WTR定时器的过期不应由本地请求逻辑处理，但应视为最高本地请求，并提交给APS处理逻辑进行处理。
The remote APS message is received from the far end and is subjected to the validity check and mismatch detection in "APS check". Failure of protocol situations are as follows:
远程APS消息从远端接收，并在“APS检查”中进行有效性检查和不匹配检测。协议失效情况如下：
o The "B" field mismatch due to incompatible provisioning;
o “B”字段不匹配是由于不兼容的配置造成的；
o The reception of the APS message from the working entity due to working/protection configuration mismatch;
o 由于工作/保护配置不匹配，从工作实体接收APS消息；
o No match in sent "Requested Signal" and received "Requested Signal" for more than 50 ms;
o 发送的“请求信号”与接收的“请求信号”不匹配超过50毫秒；
o No APS message is received on the protection transport entity during at least 3.5 times the long APS interval (e.g., at least 17.5 seconds), and there is no defect on the protection transport entity.
o 在至少3.5倍的长APS间隔期间（例如，至少17.5秒），保护传输实体上未接收到APS消息，并且保护传输实体上没有缺陷。
Provided the "B" field matches:
如果“B”字段匹配：
o If the "D" bit mismatches, the bidirectional side will fall back to unidirectional switching.
o 如果“D”位不匹配，双向侧将退回到单向切换。
o If the "R" bit mismatches, one side will clear switches to WTR and the other will clear to DNR. The two sides will interwork and the traffic is protected.
o 如果“R”位不匹配，一侧将清除WTR开关，另一侧将清除DNR开关。双方将互通，交通得到保护。
o If the "T" bit mismatches, the side using a broadcast bridge will fall back to using a selector bridge.
o 如果“T”位不匹配，则使用广播桥的一侧将退回到使用选择器桥。
The APS message with invalid information MUST be ignored, and the last valid received information remains applicable.
必须忽略包含无效信息的APS消息，并且最后收到的有效信息仍然适用。
The linear protection-switching algorithm SHALL commence immediately every time one of the input signals changes, i.e., when the status of any local request changes, or when different APS-specific information is received from the far end. The consequent actions of the algorithm are also initiated immediately, i.e., change the local bridge/selector position (if necessary), transmit new APS-specific information (if necessary), or detect the failure of protocol defect if the protection switching is not completed within 50 ms.
每次一个输入信号发生变化时，即当任何本地请求的状态发生变化时，或当从远端接收到不同的APS特定信息时，线性保护切换算法应立即开始。算法的后续动作也会立即启动，即更改本地网桥/选择器位置（如有必要）、传输新的APS特定信息（如有必要），或者如果保护切换未在50 ms内完成，则检测协议缺陷故障。
The state transition is calculated in the "APS process logic" based on the highest local request, the request of the last received "Request/State" information, and state transition tables defined in Section 9, as follows:
状态转换在“APS过程逻辑”中根据最高本地请求、最近收到的“请求/状态”信息的请求以及第9节中定义的状态转换表进行计算，如下所示：
o If the highest local request is Clear, clearance of SF or SD, or expiration of WTR, a state transition is calculated first based on the highest local request and state machine table for local requests to obtain an intermediate state. This intermediate state is the final state in case of clearance of SF-P; otherwise, starting at this intermediate state, the last received far-end request and the state machine table for far-end requests are used to calculate the final state.
o 如果最高本地请求已清除、SF或SD清除或WTR过期，则首先根据最高本地请求和本地请求的状态机表计算状态转换，以获得中间状态。该中间状态是SF-P清除时的最终状态；否则，从这个中间状态开始，最后接收的远端请求和远端请求的状态机表将用于计算最终状态。
o If the highest local request is neither Clear nor clearance of SF or of SD nor expiration of WTR, the APS process logic compares the highest local request with the request of the last received "Request/State" information based on Figure 6.
o 如果最高本地请求既不清楚，也不清除SF或SD，也不过期WTR，则APS进程逻辑将最高本地请求与最后收到的“请求/状态”信息的请求进行比较，如图6所示。
1. If the highest local request has higher or equal priority, it is used with the state transition table for local requests defined in Section 9 to determine the final state; otherwise,
1. 如果最高本地请求具有更高或同等优先级，则将其与第9节中定义的本地请求状态转换表一起使用，以确定最终状态；否则
2. The request of the last received "Request/State" information is used with the state transition table for far-end requests defined in Section 9 to determine the final state.
2. 最后收到的“请求/状态”信息的请求与第9节中定义的远端请求的状态转换表一起使用，以确定最终状态。
The "APS message generator" generates APS-specific information with the signaled APS information for the final state from the state transition calculation (with coding as described in Figure 5).
“APS消息生成器”使用状态转换计算的最终状态的信号APS信息生成特定于APS的信息（编码如图5所述）。
In general, once a switch has been completed due to a request, it will not be overridden by another request of the same priority (first-come, first-served policy). Equal priority requests from both sides of a bidirectional protection group are both considered valid, as follows:
一般来说，由于某个请求而完成的切换不会被具有相同优先级的另一个请求覆盖（先到先得策略）。双向保护组两侧的同等优先级请求均被视为有效，如下所示：
o If the local state is NR, with the requested signal number 1, and the far-end state is NR, with the requested signal number 0, the local state transits to NR with the requested signal number 0. This applies to the case when the remote request for switching to the protection transport entity has been cleared.
o 如果本地状态为NR，请求的信号号为1，远端状态为NR，请求的信号号为0，则本地状态转换为NR，请求的信号号为0。这适用于切换到保护传输实体的远程请求已被清除的情况。
o If both the local and far-end states are NR, with the requested signal number 1, the local state transits to the appropriate new state (DNR state for non-revertive mode and WTR state for revertive mode). This applies to the case when the old request has been cleared at both ends.
o 如果本地和远端状态均为NR，且请求的信号号为1，则本地状态转换为适当的新状态（非还原模式为DNR状态，还原模式为WTR状态）。这适用于在两端清除旧请求的情况。
o If both the local and far-end states are RR, with the same requested signal number, both ends transit to the appropriate new state according to the requested signal number. This applies to the case of concurrent deactivation of EXER from both ends.
o 如果本地和远端状态均为RR，且请求的信号号相同，则两端根据请求的信号号过渡到适当的新状态。这适用于从两端同时停用EXER的情况。
o In other cases, no state transition occurs, even if equal priority requests are activated from both ends. Note that if MSs are issued simultaneously to both working and protection transport entities, either as local or far-end requests, the MS to the working transport entity is considered as having higher priority than the MS to the protection transport entity.
o 在其他情况下，即使从两端激活了同等优先级的请求，也不会发生状态转换。注意，如果同时向工作传输实体和保护传输实体发出MSs（作为本地或远端请求），则工作传输实体的MS被视为具有比保护传输实体的MS更高的优先级。
Signal degrade on the protection transport entity has the same priority as signal degrade on the working transport entity. As a result, if an SD condition affects both transport entities, the first SD detected MUST NOT be overridden by the second SD detected. If the SD is detected simultaneously, either as local or far-end requests on both working and protection transport entities, then the SD on the standby transport entity MUST be considered as having higher priority than the SD on the active transport entity, and the normal traffic signal continues to be selected from the active transport entity (i.e., no unnecessary protection switching is performed).
保护传输实体上的信号降级与工作传输实体上的信号降级具有相同的优先级。因此，如果SD条件影响两个传输实体，则检测到的第一个SD不能被检测到的第二个SD覆盖。如果在工作和保护传输实体上同时检测到SD（作为本地或远端请求），则备用传输实体上的SD必须被视为具有比活动传输实体上的SD更高的优先级，并且继续从活动传输实体中选择正常交通信号（即，不进行不必要的保护切换）。
In the preceding sentence, "simultaneously" relates to the occurrence of SD on both the active and standby transport entities at input to the protection-switching process at the same time, or as long as an SD request has not been acknowledged by the remote end in bidirectional protection switching.
在前一句中，“同时”涉及在同时输入到保护切换过程时，或只要在双向保护切换中远端未确认SD请求，则在主传输实体和备用传输实体上同时发生SD。
In this section, state transition tables for the following protection switching configurations are described.
本节介绍了以下保护开关配置的状态转换表。
o 1:1 bidirectional (revertive mode, non-revertive mode);
o 1:1双向（回复模式、非回复模式）；
o 1+1 bidirectional (revertive mode, non-revertive mode);
o 1+1双向（回复模式、非回复模式）；
o 1+1 unidirectional (revertive mode, non-revertive mode).
o 1+1单向（回复模式、非回复模式）。
Note that any other global or local request that is not described in state transition tables does not trigger any state transition.
请注意，状态转换表中未描述的任何其他全局或本地请求不会触发任何状态转换。
The states specified in the state transition tables can be described as follows:
状态转换表中指定的状态可描述如下：
o NR: NR is the state entered by the local priority under all conditions where no local protection-switching requests (including WTR and DNR) are active. NR can also indicate that the highest local request is overridden by the far-end request, whose priority is higher than the highest local request. Normal traffic signal is selected from the corresponding transport entity.
o NR:NR是本地优先级在没有激活本地保护切换请求（包括WTR和DNR）的所有条件下输入的状态。NR还可以指示最高本地请求被远端请求覆盖，其优先级高于最高本地请求。从相应的运输实体中选择正常交通信号。
o LO, SF-P, SD-P: The access by the normal traffic to the protection transport entity is NOT allowed in this state. The normal traffic is carried by the working transport entity, regardless of the fault/degrade condition possibly present (due to the highest priority of the switching triggers leading to this state).
o LO、SF-P、SD-P：在此状态下，不允许正常通信访问保护传输实体。正常通信量由工作传输实体承载，不管可能存在的故障/降级情况如何（由于导致该状态的切换触发器具有最高优先级）。
o FS, SF-W, SD-W, MS-W, MS-P: A switching trigger NOT resulting in the protection transport entity unavailability is present. The normal traffic is selected either from the corresponding working transport entity or from the protection transport entity, according to the behavior of the specific switching trigger.
o FS、SF-W、SD-W、MS-W、MS-P：存在不会导致保护传输实体不可用的切换触发器。根据特定切换触发器的行为，从相应的工作传输实体或保护传输实体中选择正常通信量。
o WTR: In revertive operation, after the clearing of an SF-W or SD-W, this maintains normal traffic as selected from the protection transport entity until the WTR timer expires or another request with higher priority, including the Clear command, is received. This is used to prevent frequent operation of the selector in the case of intermittent failures.
o WTR：在恢复操作中，在清除SF-W或SD-W后，这将保持从保护传输实体中选择的正常通信量，直到WTR计时器过期或接收到另一个具有更高优先级的请求，包括清除命令。这用于防止在间歇性故障情况下频繁操作选择器。
o DNR: In non-revertive operation, this is used to maintain a normal traffic to be selected from the protection transport entity.
o DNR：在非还原操作中，用于维持从保护传输实体中选择的正常通信量。
o EXER: Exercise of the APS protocol.
o EXER：APS协议的实施。
o RR: The near end will enter and signal Reverse Request only in response to an EXER from the far end.
o RR：近端将进入并发出反向请求信号，仅响应远端的EXER。
[State transition tables are shown at the end of the PDF form of this document.]
[状态转换表显示在本文件PDF格式的末尾。]
MPLS-TP is a subset of MPLS and so builds upon many of the aspects of the security model of MPLS. MPLS networks make the assumption that it is very hard to inject traffic into a network and equally hard to cause traffic to be directed outside the network. The control-plane protocols utilize hop-by-hop security and assume a "chain-of-trust" model such that end-to-end control-plane security is not used. For more information on the generic aspects of MPLS security, see [RFC5920].
MPLS-TP是MPLS的一个子集，因此建立在MPLS安全模型的许多方面之上。MPLS网络假设很难将流量注入网络，也很难将流量定向到网络外部。控制平面协议利用逐跳安全性，并假设“信任链”模型，因此不使用端到端控制平面安全性。有关MPLS安全性的一般方面的更多信息，请参阅[RFC5920]。
This document describes a protocol carried in the G-ACh [RFC5586] and so is dependent on the security of the G-ACh, itself. The G-ACh is a generalization of the associated channel defined in [RFC4385]. Thus, this document relies heavily on the security mechanisms provided for the associated channel and described in those two documents.
本文件描述了G-ACh[RFC5586]中携带的协议，因此依赖于G-ACh本身的安全性。G-ACh是[RFC4385]中定义的相关信道的推广。因此，本文档在很大程度上依赖于为相关通道提供的、并在这两个文档中描述的安全机制。
The authors would like to thank Hao Long, Vincenzo Sestito, Italo Busi, Igor Umansky, and Andy Malis for their input to and review of the current document.
作者感谢Hao Long、Vincenzo Sestito、Italo Busi、Igor Umansky和Andy Malis对当前文件的投入和审查。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006.
[RFC4385]Bryant，S.，Swallow，G.，Martini，L.，和D.McPherson，“用于MPLS PSN的伪线仿真边到边（PWE3）控制字”，RFC 43852006年2月。
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, June 2009.
[RFC5586]Bocci，M.，Vigoureux，M.，和S.Bryant，“MPLS通用关联信道”，RFC 55862009年6月。
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010.
[RFC5920]方，L，“MPLS和GMPLS网络的安全框架”，RFC 5920，2010年7月。
[G.841] International Telecommunications Union, "Types and characteristics of SDH network protection architectures", ITU-T Recommendation G.841, October 1998.
[G.841]国际电信联盟，“SDH网络保护体系结构的类型和特征”，ITU-T建议G.841，1998年10月。
[G.873.1] International Telecommunications Union, "Optical Transport Network (OTN): Linear protection", ITU-T Recommendation G.873.1, May 2014.
[G.873.1]国际电信联盟，“光传输网络（OTN）：线性保护”，ITU-T建议G.873.1，2014年5月。
[G.8031] International Telecommunications Union, "Ethernet linear protection switching", ITU-T Recommendation G.8031/Y.1342, June 2011.
[G.8031]国际电信联盟，“以太网线性保护交换”，ITU-T建议G.8031/Y.1342，2011年6月。
[T1.105.01] American National Standards Institute, "Synchronous Optical Network (SONET) - Automatic Protection Switching", ANSI 0900105.01:2000 (R2010), March 2000.
[T1.105.01]美国国家标准协会，“同步光网络（SONET）-自动保护切换”，ANSI 0900105.01:2000（R2010），2000年3月。
[RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear Protection", RFC 6378, October 2011.
[RFC6378]Y.Weingarten、S.Bryant、E.Osborne、N.Sprecher和A.Fulignoli，“MPLS传输模式（MPLS-TP）线性保护”，RFC 6378，2011年10月。
[RFC7271] Ryoo, J., Gray, E., 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, June 2014.
[RFC7271]Ryoo，J.，Gray，E.，van Helvoort，H.，D'Alessandro，A.，Cheung，T.，和E.Osborne，“MPLS传输模式（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 7271，2014年6月。
[RFC7324] Osborne, E., "Updates to MPLS Transport Profile Linear Protection", RFC 7324, July 2014.
[RFC7324]Osborne，E.“MPLS传输配置文件线性保护的更新”，RFC 73242014年7月。
The sequence diagrams shown in this section are only a few examples of the APS operations. The first APS message, which differs from the previous APS message, is shown. The operation of hold-off timer is omitted. The fields whose values are changed during APS packet exchange are shown in the APS packet exchange. They are Request/ State, requested traffic, and bridged traffic. For an example, SF(0,1) represents an APS packet with the following field values: Request/State = SF, Requested Signal = 0, and Bridged Signal = 1. The values of the other fields remain unchanged from the initial configuration. The signal numbers 0 and 1 refer to null signal and normal traffic signal, respectively. W(A->Z) and P(A->Z) indicate the working and protection paths in the direction of A to Z, respectively.
本节所示的序列图只是APS操作的几个示例。第一条APS消息与前一条APS消息不同，如下所示。暂停计时器的操作被省略。在APS数据包交换期间其值发生变化的字段显示在APS数据包交换中。它们是请求/状态、请求流量和桥接流量。例如，SF（0,1）表示具有以下字段值的APS分组：Request/State=SF、Request Signal=0和Bridged Signal=1。与初始配置相比，其他字段的值保持不变。信号编号0和1分别表示零信号和正常交通信号。W（A->Z）和P（A->Z）分别表示A到Z方向的工作路径和保护路径。
Example 1. 1:1 bidirectional protection switching (revertive mode) - Unidirectional SF case
例1。1:1双向保护切换（回复模式）-单向SF外壳
A Z
| |
(1) |---- NR(0,0)----->|
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z->A)) |
|---- SF(1,1)----->| (3)
|<----- NR(1,1)----|
(4) | |
| |
(5) | (Recovery) |
|---- WTR(1,1)---->|
/| |
WTR timer | |
\| |
(6) |---- NR(0,0)----->| (7)
(8) |<----- NR(0,0)----|
| |
A Z
| |
(1) |---- NR(0,0)----->|
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z->A)) |
|---- SF(1,1)----->| (3)
|<----- NR(1,1)----|
(4) | |
| |
(5) | (Recovery) |
|---- WTR(1,1)---->|
/| |
WTR timer | |
\| |
(6) |---- NR(0,0)----->| (7)
(8) |<----- NR(0,0)----|
| |
(1) The protected domain is operating without any defect, and the working entity is used for delivering the normal traffic.
(1) 受保护域运行时没有任何缺陷，工作实体用于提供正常流量。
(2) Signal Fail occurs on the working entity in the Z to A direction. Selector and bridge of node A select protection entity. Node A generates an SF(1,1) message.
(2) 工作实体在Z向A方向上发生信号故障。节点的选择器和桥接器选择保护实体。节点A生成SF（1,1）消息。
(3) Upon receiving SF(1,1), node Z sets selector and bridge to protection entity. As there is no local request in node Z, node Z generates an NR(1,1) message.
(3) 在接收到SF（1,1）后，节点Z将选择器和桥接器设置为保护实体。由于节点Z中没有本地请求，因此节点Z生成NR（1,1）消息。
(4) Node A confirms that the far end is also selecting protection entity.
(4) 节点A确认远端也在选择保护实体。
(5) Node A detects clearing of the SF condition, starts the WTR timer, and sends a WTR(1,1) message.
(5) 节点A检测到SF条件的清除，启动WTR定时器，并发送WTR（1,1）消息。
(6) At expiration of the WTR timer, node A sets selector and bridge to working entity and sends an NR(0,0) message.
(6) 在WTR计时器到期时，节点A将选择器和桥接器设置为工作实体，并发送NR（0,0）消息。
(7) Node Z is notified that the far-end request has been cleared and sets selector and bridge to working entity.
(7) 节点Z被通知远端请求已被清除，并将选择器和网桥设置为工作实体。
(8) It is confirmed that the far end is also selecting working entity.
(8) 确认远端也在选择工作实体。
Example 2. 1:1 bidirectional protection switching (revertive mode) - Bidirectional SF case
例2。1:1双向保护切换（回复模式）-双向SF外壳
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z<->A)) | (2)
|<---- SF(1,1)---->|
(3) | | (3)
| |
(4) | (Recovery) | (4)
|<---- NR(1,1)---->|
(5) |<--- WTR(1,1)---->| (5)
/| |\
WTR timer | | WTR timer
\| |/
(6) |<---- NR(1,1)---->| (6)
(7) |<----- NR(0,0)--->| (7)
(8) | | (8)
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z<->A)) | (2)
|<---- SF(1,1)---->|
(3) | | (3)
| |
(4) | (Recovery) | (4)
|<---- NR(1,1)---->|
(5) |<--- WTR(1,1)---->| (5)
/| |\
WTR timer | | WTR timer
\| |/
(6) |<---- NR(1,1)---->| (6)
(7) |<----- NR(0,0)--->| (7)
(8) | | (8)
(1) The protected domain is operating without any defect, and the working entity is used for delivering the normal traffic.
(1) 受保护域运行时没有任何缺陷，工作实体用于提供正常流量。
(2) Nodes A and Z detect local SF conditions on the working entity, set selector and bridge to protection entity, and generate SF(1,1) messages.
(2) 节点A和Z检测工作实体上的局部SF条件，将选择器和桥接器设置为保护实体，并生成SF（1,1）消息。
(3) Upon receiving SF(1,1), each node confirms that the far end is also selecting protection entity.
(3) 在接收到SF（1,1）时，每个节点确认远端也在选择保护实体。
(4) Each node detects clearing of the SF condition and sends an NR(1,1) message as the last received APS message was SF.
(4) 每个节点检测SF条件的清除，并发送NR（1,1）消息，因为最后接收到的APS消息是SF。
(5) Upon receiving NR(1,1), each node starts the WTR timer and sends WTR(1,1).
(5) 在接收到NR（1,1）后，每个节点启动WTR定时器并发送WTR（1,1）。
(6) At expiration of the WTR timer, each node sends NR(1,1) as the last received APS message was WTR.
(6) 在WTR定时器到期时，每个节点发送NR（1,1），因为最后收到的APS消息是WTR。
(7) Upon receiving NR(1,1), each node sets selector and bridge to working entity and sends an NR(0,0) message.
(7) 接收到NR（1,1）后，每个节点将选择器和桥接器设置为工作实体，并发送一条NR（0,0）消息。
(8) It is confirmed that the far end is also selecting working entity.
(8) 确认远端也在选择工作实体。
Example 3. 1:1 bidirectional protection switching (revertive mode) - Bidirectional SF case - Inconsistent WTR timers
例3。1:1双向保护切换（回复模式）-双向SF情况-WTR定时器不一致
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z<->A)) | (2)
|<---- SF(1,1)---->|
(3) | | (3)
| |
(4) | (Recovery) | (4)
|<---- NR(1,1)---->|
(5) |<--- WTR(1,1)---->| (5)
/| |\
WTR timer | | |
\| | WTR timer
(6) |----- NR(1,1)---->| | (7)
| |/
(9) |<----- NR(0,0)----| (8)
|---- NR(0,0)----->| (10)
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z<->A)) | (2)
|<---- SF(1,1)---->|
(3) | | (3)
| |
(4) | (Recovery) | (4)
|<---- NR(1,1)---->|
(5) |<--- WTR(1,1)---->| (5)
/| |\
WTR timer | | |
\| | WTR timer
(6) |----- NR(1,1)---->| | (7)
| |/
(9) |<----- NR(0,0)----| (8)
|---- NR(0,0)----->| (10)
(1) The protected domain is operating without any defect, and the working entity is used for delivering the normal traffic.
(1) 受保护域运行时没有任何缺陷，工作实体用于提供正常流量。
(2) Nodes A and Z detect local SF conditions on the working entity, set selector and bridge to protection entity, and generate SF(1,1) messages.
(2) 节点A和Z检测工作实体上的局部SF条件，将选择器和桥接器设置为保护实体，并生成SF（1,1）消息。
(3) Upon receiving SF(1,1), each node confirms that the far end is also selecting protection entity.
(3) 在接收到SF（1,1）时，每个节点确认远端也在选择保护实体。
(4) Each node detects clearing of the SF condition and sends an NR(1,1) message as the last received APS message was SF.
(4) 每个节点检测SF条件的清除，并发送NR（1,1）消息，因为最后接收到的APS消息是SF。
(5) Upon receiving NR(1,1), each node starts the WTR timer and sends WTR(1,1).
(5) 在接收到NR（1,1）后，每个节点启动WTR定时器并发送WTR（1,1）。
(6) At expiration of the WTR timer in node A, node A sends an NR(1,1) message as the last received APS message was WTR.
(6) 在节点A中的WTR定时器到期时，节点A发送NR（1,1）消息，因为最后接收到的APS消息是WTR。
(7) At node Z, the received NR(1,1) is ignored as the local WTR has a higher priority.
(7) 在节点Z处，由于本地WTR具有更高的优先级，因此忽略接收到的NR（1,1）。
(8) At expiration of the WTR timer in node Z, node Z sets selector and bridge to working entity and sends an NR(0,0) message.
(8) 在节点Z中的WTR计时器到期时，节点Z将选择器和桥接器设置为工作实体，并发送NR（0,0）消息。
(9) Upon receiving NR(0,0), node A sets selector and bridge to working entity and sends an NR(0,0) message.
(9) 收到NR（0,0）后，节点A将选择器和桥接器设置为工作实体，并发送NR（0,0）消息。
(10) It is confirmed that the far end is also selecting working entity.
（10） 确认远端也在选择工作实体。
Example 4. 1:1 bidirectional protection switching (non-revertive mode) - Unidirectional SF on working followed by unidirectional SF on protection
例4。1:1双向保护切换（非回复模式）-单向SF接通工作，然后单向SF接通保护
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z->A)) |
|----- SF(1,1)---->| (3)
(4) |<----- NR(1,1)----|
| |
| |
(5) | (Recovery) |
|----- DNR(1,1)--->| (6)
|<--- DNR(1,1)---->|
| |
| |
| (SF on P(A->Z)) | (7)
(8) |<--- SF-P(0,0)----|
|---- NR(0,0)----->|
| |
| |
| (Recovery) | (9)
|<----- NR(0,0)----|
| |
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(Z->A)) |
|----- SF(1,1)---->| (3)
(4) |<----- NR(1,1)----|
| |
| |
(5) | (Recovery) |
|----- DNR(1,1)--->| (6)
|<--- DNR(1,1)---->|
| |
| |
| (SF on P(A->Z)) | (7)
(8) |<--- SF-P(0,0)----|
|---- NR(0,0)----->|
| |
| |
| (Recovery) | (9)
|<----- NR(0,0)----|
| |
(1) The protected domain is operating without any defect, and the working entity is used for delivering the normal traffic.
(1) 受保护域运行时没有任何缺陷，工作实体用于提供正常流量。
(2) Signal Fail occurs on the working entity in the Z to A direction. Selector and bridge of node A select the protection entity. Node A generates an SF(1,1) message.
(2) 工作实体在Z向A方向上发生信号故障。节点A的选择器和桥接器选择保护实体。节点A生成SF（1,1）消息。
(3) Upon receiving SF(1,1), node Z sets selector and bridge to protection entity. As there is no local request in node Z, node Z generates an NR(1,1) message.
(3) 在接收到SF（1,1）后，节点Z将选择器和桥接器设置为保护实体。由于节点Z中没有本地请求，因此节点Z生成NR（1,1）消息。
(4) Node A confirms that the far end is also selecting protection entity.
(4) 节点A确认远端也在选择保护实体。
(5) Node A detects clearing of the SF condition and sends a DNR(1,1) message.
(5) 节点A检测到SF条件的清除，并发送DNR（1,1）消息。
(6) Upon receiving DNR(1,1), node Z also generates a DNR(1,1) message.
(6) 在接收到DNR（1,1）后，节点Z还生成DNR（1,1）消息。
(7) Signal Fail occurs on the protection entity in the A to Z direction. Selector and bridge of node Z select the working entity. Node Z generates an SF-P(0,0) message.
(7) 保护实体在A到Z方向上发生信号故障。节点Z的选择器和桥接器选择工作实体。节点Z生成SF-P（0,0）消息。
(8) Upon receiving SF-P(0,0), node A sets selector and bridge to working entity and generates an NR(0,0) message.
(8) 收到SF-P（0,0）后，节点A将选择器和桥接器设置为工作实体，并生成NR（0,0）消息。
(9) Node Z detects clearing of the SF condition and sends an NR(0,0) message.
(9) 节点Z检测到SF条件的清除，并发送NR（0,0）消息。
Exmaple 5. 1:1 bidirectional protection switching (non-revertive mode) - Bidirectional SF on working followed by bidirectional SF on protection
Exmaple 5。1:1双向保护切换（非回复模式）-双向SF on工作，然后是双向SF on保护
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(A<->Z)) | (2)
(3) |<---- SF(1,1)---->| (3)
| |
| |
(4) | (Recovery) | (4)
(5) |<---- NR(1,1)---->| (5)
|<--- DNR(1,1)---->|
| |
| |
(6) | (SF on P(A<->Z)) | (6)
(7) |<--- SF-P(0,0)--->| (7)
| |
| |
(8) | (Recovery) | (8)
|<---- NR(0,0)---->|
| |
A Z
| |
(1) |---- NR(0,0)----->| (1)
|<----- NR(0,0)----|
| |
| |
(2) | (SF on W(A<->Z)) | (2)
(3) |<---- SF(1,1)---->| (3)
| |
| |
(4) | (Recovery) | (4)
(5) |<---- NR(1,1)---->| (5)
|<--- DNR(1,1)---->|
| |
| |
(6) | (SF on P(A<->Z)) | (6)
(7) |<--- SF-P(0,0)--->| (7)
| |
| |
(8) | (Recovery) | (8)
|<---- NR(0,0)---->|
| |
(1) The protected domain is operating without any defect, and the working entity is used for delivering the normal traffic.
(1) 受保护域运行时没有任何缺陷，工作实体用于提供正常流量。
(2) Nodes A and Z detect local SF conditions on the working entity, set selector and bridge to protection entity, and generate SF(1,1) messages.
(2) 节点A和Z检测工作实体上的局部SF条件，将选择器和桥接器设置为保护实体，并生成SF（1,1）消息。
(3) Upon receiving SF(1,1), each node confirms that the far end is also selecting protection entity.
(3) 在接收到SF（1,1）时，每个节点确认远端也在选择保护实体。
(4) Each node detects clearing of the SF condition and sends an NR(1,1) message as the last received APS message was SF.
(4) 每个节点检测SF条件的清除，并发送NR（1,1）消息，因为最后接收到的APS消息是SF。
(5) Upon receiving NR(1,1), each node sends DNR(1,1).
(5) 在接收到NR（1,1）后，每个节点发送DNR（1,1）。
(6) Signal Fail occurs on the protection entity in both directions. Selector and bridge of each node selects the working entity. Each node generates an SF-P(0,0) message.
(6) 保护实体在两个方向上发生信号故障。每个节点的选择器和桥接器选择工作实体。每个节点生成一条SF-P（0,0）消息。
(7) Upon receiving SF-P(0,0), each node confirms that the far end is also selecting working entity.
(7) 接收到SF-P（0,0）后，每个节点确认远端也在选择工作实体。
(8) Each node detects clearing of the SF condition and sends an NR(0,0) message.
(8) 每个节点检测SF条件的清除并发送NR（0,0）消息。
Authors' Addresses
作者地址
Huub van Helvoort (editor) Huawei Technologies
Huub van Helvoort（编辑）华为技术
EMail: huub@van-helvoort.eu
EMail: huub@van-helvoort.eu
Jeong-dong Ryoo (editor) ETRI
郑东良（编辑）ETRI
EMail: ryoo@etri.re.kr
EMail: ryoo@etri.re.kr
Haiyan Zhang Huawei Technologies
张海燕华为技术有限公司
EMail: zhanghaiyan@huawei.com
EMail: zhanghaiyan@huawei.com
Feng Huang Philips
凤凰飞利浦
EMail: feng.huang@philips.com
EMail: feng.huang@philips.com
Han Li China Mobile
韩丽中国移动
EMail: lihan@chinamobile.com
EMail: lihan@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