Internet Engineering Task Force (IETF) W. Cheng
Request for Comments: 8227 L. Wang
Category: Standards Track H. Li
ISSN: 2070-1721 China Mobile
H. van Helvoort
Hai Gaoming BV
J. Dong
Huawei Technologies
August 2017
Internet Engineering Task Force (IETF) W. Cheng
Request for Comments: 8227 L. Wang
Category: Standards Track H. Li
ISSN: 2070-1721 China Mobile
H. van Helvoort
Hai Gaoming BV
J. Dong
Huawei Technologies
August 2017
MPLS-TP Shared-Ring Protection (MSRP) Mechanism for Ring Topology
环拓扑的MPLS-TP共享环保护（MSRP）机制
Abstract
摘要
This document describes requirements, architecture, and solutions for MPLS-TP Shared-Ring Protection (MSRP) in a ring topology for point-to-point (P2P) services. The MSRP mechanism is described to meet the ring protection requirements as described in RFC 5654. This document defines the Ring Protection Switching (RPS) protocol that is used to coordinate the protection behavior of the nodes on an MPLS ring.
本文档描述了点到点（P2P）服务环形拓扑中MPLS-TP共享环保护（MSRP）的要求、体系结构和解决方案。描述了MSRP机制以满足RFC 5654中所述的环保护要求。本文档定义了环保护交换（RPS）协议，该协议用于协调MPLS环上节点的保护行为。
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 7841.
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 7841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/rfc8227.
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/rfc8227.
Copyright Notice
版权公告
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2017 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 . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 4
3. MPLS-TP Ring Protection Criteria and Requirements . . . . . . 5
4. Shared-Ring Protection Architecture . . . . . . . . . . . . . 6
4.1. Ring Tunnel . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. Establishment of the Ring Tunnel . . . . . . . . . . 8
4.1.2. Label Assignment and Distribution . . . . . . . . . . 9
4.1.3. Forwarding Operation . . . . . . . . . . . . . . . . 9
4.2. Failure Detection . . . . . . . . . . . . . . . . . . . . 10
4.3. Ring Protection . . . . . . . . . . . . . . . . . . . . . 11
4.3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . 12
4.3.2. Short-Wrapping . . . . . . . . . . . . . . . . . . . 14
4.3.3. Steering . . . . . . . . . . . . . . . . . . . . . . 17
4.4. Interconnected Ring Protection . . . . . . . . . . . . . 21
4.4.1. Interconnected Ring Topology . . . . . . . . . . . . 21
4.4.2. Interconnected Ring Protection Mechanisms . . . . . . 22
4.4.3. Ring Tunnels in Interconnected Rings . . . . . . . . 23
4.4.4. Interconnected Ring-Switching Procedure . . . . . . . 25
4.4.5. Interconnected Ring Detection Mechanism . . . . . . . 26
5. Ring Protection Coordination Protocol . . . . . . . . . . . . 27
5.1. RPS and PSC Comparison on Ring Topology . . . . . . . . . 27
5.2. RPS Protocol . . . . . . . . . . . . . . . . . . . . . . 28
5.2.1. Transmission and Acceptance of RPS Requests . . . . . 30
5.2.2. RPS Protocol Data Unit (PDU) Format . . . . . . . . . 31
5.2.3. Ring Node RPS States . . . . . . . . . . . . . . . . 32
5.2.4. RPS State Transitions . . . . . . . . . . . . . . . . 34
5.3. RPS State Machine . . . . . . . . . . . . . . . . . . . . 36
5.3.1. Switch Initiation Criteria . . . . . . . . . . . . . 36
5.3.2. Initial States . . . . . . . . . . . . . . . . . . . 39
5.3.3. State Transitions When Local Request Is Applied . . . 40
5.3.4. State Transitions When Remote Request is Applied . . 44
5.3.5. State Transitions When Request Addresses to Another
Node is Received . . . . . . . . . . . . . . . . . . 47
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
6.1. G-ACh Channel Type . . . . . . . . . . . . . . . . . . . 51
6.2. RPS Request Codes . . . . . . . . . . . . . . . . . . . . 51
7. Operational Considerations . . . . . . . . . . . . . . . . . 52
8. Security Considerations . . . . . . . . . . . . . . . . . . . 52
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
9.1. Normative References . . . . . . . . . . . . . . . . . . 53
9.2. Informative References . . . . . . . . . . . . . . . . . 54
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 55
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 4
3. MPLS-TP Ring Protection Criteria and Requirements . . . . . . 5
4. Shared-Ring Protection Architecture . . . . . . . . . . . . . 6
4.1. Ring Tunnel . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. Establishment of the Ring Tunnel . . . . . . . . . . 8
4.1.2. Label Assignment and Distribution . . . . . . . . . . 9
4.1.3. Forwarding Operation . . . . . . . . . . . . . . . . 9
4.2. Failure Detection . . . . . . . . . . . . . . . . . . . . 10
4.3. Ring Protection . . . . . . . . . . . . . . . . . . . . . 11
4.3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . 12
4.3.2. Short-Wrapping . . . . . . . . . . . . . . . . . . . 14
4.3.3. Steering . . . . . . . . . . . . . . . . . . . . . . 17
4.4. Interconnected Ring Protection . . . . . . . . . . . . . 21
4.4.1. Interconnected Ring Topology . . . . . . . . . . . . 21
4.4.2. Interconnected Ring Protection Mechanisms . . . . . . 22
4.4.3. Ring Tunnels in Interconnected Rings . . . . . . . . 23
4.4.4. Interconnected Ring-Switching Procedure . . . . . . . 25
4.4.5. Interconnected Ring Detection Mechanism . . . . . . . 26
5. Ring Protection Coordination Protocol . . . . . . . . . . . . 27
5.1. RPS and PSC Comparison on Ring Topology . . . . . . . . . 27
5.2. RPS Protocol . . . . . . . . . . . . . . . . . . . . . . 28
5.2.1. Transmission and Acceptance of RPS Requests . . . . . 30
5.2.2. RPS Protocol Data Unit (PDU) Format . . . . . . . . . 31
5.2.3. Ring Node RPS States . . . . . . . . . . . . . . . . 32
5.2.4. RPS State Transitions . . . . . . . . . . . . . . . . 34
5.3. RPS State Machine . . . . . . . . . . . . . . . . . . . . 36
5.3.1. Switch Initiation Criteria . . . . . . . . . . . . . 36
5.3.2. Initial States . . . . . . . . . . . . . . . . . . . 39
5.3.3. State Transitions When Local Request Is Applied . . . 40
5.3.4. State Transitions When Remote Request is Applied . . 44
5.3.5. State Transitions When Request Addresses to Another
Node is Received . . . . . . . . . . . . . . . . . . 47
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
6.1. G-ACh Channel Type . . . . . . . . . . . . . . . . . . . 51
6.2. RPS Request Codes . . . . . . . . . . . . . . . . . . . . 51
7. Operational Considerations . . . . . . . . . . . . . . . . . 52
8. Security Considerations . . . . . . . . . . . . . . . . . . . 52
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
9.1. Normative References . . . . . . . . . . . . . . . . . . 53
9.2. Informative References . . . . . . . . . . . . . . . . . 54
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 55
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
As described in Section 2.5.6.1 of [RFC5654], several service providers have expressed much interest in operating an MPLS Transport Profile (MPLS-TP) in ring topologies and require a high-level survivability function in these topologies. In operational transport network deployment, MPLS-TP networks are often constructed using ring topologies. This calls for an efficient and optimized ring protection mechanism to achieve simple operation and fast, sub 50 ms, recovery performance.
如[RFC5654]第2.5.6.1节所述，一些服务提供商表示对在环形拓扑中运行MPLS传输配置文件（MPLS-TP）非常感兴趣，并要求在这些拓扑中具有高级别的可生存性功能。在运营传输网络部署中，MPLS-TP网络通常使用环形拓扑结构构建。这就需要一种高效优化的环保护机制，以实现简单的操作和快速、低于50毫秒的恢复性能。
This document specifies an MPLS-TP Shared-Ring Protection mechanism that meets the criteria for ring protection and the ring protection requirements described in Section 2.5.6.1 of [RFC5654].
本文件规定了MPLS-TP共享环保护机制，该机制满足环保护标准和[RFC5654]第2.5.6.1节所述的环保护要求。
The basic concept and architecture of the MPLS-TP Shared-Ring Protection mechanism are specified in this document. This document describes the solutions for point-to-point transport paths. While the basic concept may also apply to point-to-multipoint transport paths, the solution for point-to-multipoint transport paths is out of the scope of this document.
本文件规定了MPLS-TP共享环保护机制的基本概念和体系结构。本文档介绍了点到点传输路径的解决方案。虽然基本概念也适用于点对多点传输路径，但点对多点传输路径的解决方案不在本文档范围内。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“建议”、“不建议”、“可”和“可选”在所有大写字母出现时（如图所示）应按照BCP 14[RFC2119][RFC8174]所述进行解释。
Terminology:
术语：
Ring node: All nodes in the ring topology are ring nodes, and they MUST actively participate in the ring protection.
环节点：环拓扑中的所有节点都是环节点，它们必须积极参与环保护。
Ring tunnel: A ring tunnel provides a server layer for the Label Switched Paths (LSPs) traversing the ring. The notation used for a ring tunnel is: R<d><p><X> where <d> = c (clockwise) or a (anticlockwise), <p> = W (working) or P (protecting), and <X> = the node name.
环形通道：环形通道为穿过环形通道的标签交换路径（LSP）提供服务器层。环形隧道使用的符号是：R<d><p><X>，其中<d>=c（顺时针）或a（逆时针），<p>=W（工作）或p（保护），以及<X>=节点名称。
Ring map: A ring map is present in each ring node. The ring map contains the ring topology information, i.e., the nodes in the ring, the adjacency of the ring nodes, and the status of the links between ring nodes (Intact or Severed). The ring map is used by every ring node to determine the switchover behavior of the ring tunnels.
环映射：每个环节点中都有一个环映射。环映射包含环拓扑信息，即环中的节点、环节点的邻接关系以及环节点之间链路的状态（完整或断开）。每个环节点都使用环映射来确定环隧道的切换行为。
Notation:
符号：
The following syntax will be used to describe the contents of the label stack:
以下语法将用于描述标签堆栈的内容：
1. The label stack will be enclosed in square brackets ("[]").
1. 标签堆栈将用方括号（“[]”）括起来。
2. Each level in the stack will be separated by the '|' character. It should be noted that the label stack may contain additional layers. However, we only present the layers that are related to the protection mechanism.
2. 堆栈中的每个级别将由“|”字符分隔。应注意，标签堆栈可能包含附加层。但是，我们只提供与保护机制相关的层。
3. If the label is assigned by Node X, the Node Name is enclosed in parentheses ("()").
3. 如果标签由节点X指定，则节点名称用括号（（））括起来。
The generic requirements for MPLS-TP protection are specified in [RFC5654]. The requirements specific for ring protection are specified in Section 2.5.6.1 of [RFC5654]. This section describes how the criteria for ring protection are met:
[RFC5654]中规定了MPLS-TP保护的一般要求。[RFC5654]第2.5.6.1节规定了环保护的具体要求。本节描述了如何满足环保护标准：
a. The number of Operations, Administration, and Maintenance (OAM) entities needed to trigger protection
a. 触发保护所需的操作、管理和维护（OAM）实体的数量
Each ring node requires only one instance of the RPS protocol per ring. The OAM of the links connected to the adjacent ring nodes has to be forwarded to only this instance in order to trigger protection. For detailed information, see Section 5.2.
每个环节点每个环只需要一个RPS协议实例。连接到相邻环节点的链路的OAM必须仅转发到此实例以触发保护。有关详细信息，请参见第5.2节。
b. The number of elements of recovery in the ring
b. 环中恢复的元素数
Each ring node requires only one instance of the RPS protocol and is independent of the number of LSPs that are protected. For detailed information, see Section 5.2.
每个环节点只需要一个RPS协议实例，并且与受保护的LSP数量无关。有关详细信息，请参见第5.2节。
c. The required number of labels required for the protection paths
c. 保护路径所需的标签数量
The RPS protocol uses ring tunnels, and each tunnel has a set of labels. The number of ring tunnel labels is related to the number of ring nodes and is independent of the number of protected LSPs. For detailed information, see Section 4.1.2.
RPS协议使用环形隧道，每个隧道都有一组标签。环形隧道标签的数量与环形节点的数量相关，并且与受保护LSP的数量无关。有关详细信息，请参见第4.1.2节。
d. The amount of control and management-plane transactions
d. 控制和管理平面事务的数量
Each ring node requires only one instance of the RPS protocol per ring. This means that only one maintenance operation is required per ring node. For detailed information, see Section 5.2.
每个环节点每个环只需要一个RPS协议实例。这意味着每个环节点只需要一次维护操作。有关详细信息，请参见第5.2节。
e. Minimize the signaling and routing information exchange during protection
e. 最大限度地减少保护期间的信令和路由信息交换
Information exchange during a protection switch is using the in-band RPS and OAM messages. No control-plane interactions are required. For detailed information, see Section 5.2.
保护切换期间的信息交换使用带内RPS和OAM消息。不需要控制平面交互。有关详细信息，请参见第5.2节。
This document introduces a new logical layer of the ring for shared-ring protection in MPLS-TP networks. As shown in Figure 1, the new logical layer consists of ring tunnels that provide a server layer for the LSPs traversing the ring. Once a ring tunnel is established, the forwarding and protection switching of the ring are all performed at the ring tunnel level. A port can carry multiple ring tunnels, and a ring tunnel can carry multiple LSPs.
本文档介绍了一种新的环逻辑层，用于MPLS-TP网络中的共享环保护。如图1所示，新的逻辑层由环形隧道组成，这些环形隧道为穿过环的LSP提供服务器层。一旦建立环隧道，环的转发和保护切换都在环隧道级别执行。一个端口可以承载多个环形隧道，环形隧道可以承载多个LSP。
+-------------
+-------------|
+-------------| |
===Service1===| | |
===Service2===| LSP1 | |
+-------------| |
|Ring-Tunnel1 |
+-------------| |
===Service3===| | |
===Service4===| LSP2 | |
+-------------| |
+-------------| Physical
+-------------|
+-------------| | Port
===Service5===| | |
===Service6===| LSP3 | |
+-------------| |
|Ring-Tunnel2 |
+-------------| |
===Service7===| | |
===Service8===| LSP4 | |
+-------------| |
+-------------|
+-------------
+-------------
+-------------|
+-------------| |
===Service1===| | |
===Service2===| LSP1 | |
+-------------| |
|Ring-Tunnel1 |
+-------------| |
===Service3===| | |
===Service4===| LSP2 | |
+-------------| |
+-------------| Physical
+-------------|
+-------------| | Port
===Service5===| | |
===Service6===| LSP3 | |
+-------------| |
|Ring-Tunnel2 |
+-------------| |
===Service7===| | |
===Service8===| LSP4 | |
+-------------| |
+-------------|
+-------------
Figure 1: The Logical Layers of the Ring
图1：环的逻辑层
The label stack used in the MPLS-TP Shared-Ring Protection mechanism is [Ring Tunnel Label|LSP Label|Service Label](Payload) as illustrated in Figure 2.
MPLS-TP共享环保护机制中使用的标签堆栈是[环隧道标签| LSP标签|服务标签]（有效负载），如图2所示。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ring Tunnel Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ring Tunnel Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Label Stack Used in MPLS-TP Shared-Ring Protection
图2:MPLS-TP共享环保护中使用的标签堆栈
The Ring tunnels are established based on the egress nodes. The egress node is the node where traffic leaves the ring. LSPs that have the same egress node on the ring and travel along the ring in the same direction (clockwise or anticlockwise) share the same ring tunnels. In other words, all the LSPs that traverse the ring in the same direction and exit from the same node share the same working ring tunnel and protection ring tunnel. For each egress node, four ring tunnels are established:
基于出口节点建立环形隧道。出口节点是流量离开环的节点。环上具有相同出口节点且沿环以相同方向（顺时针或逆时针）移动的LSP共享相同的环隧道。换句话说，以相同方向穿过环并从相同节点退出的所有LSP共享相同的工作环隧道和保护环隧道。对于每个出口节点，建立四个环形隧道：
o one clockwise working ring tunnel, which is protected by the anticlockwise protection ring tunnel
o 一个顺时针工作环通道，由逆时针保护环通道保护
o one anticlockwise protection ring tunnel
o 一个逆时针保护环隧道
o one anticlockwise working ring tunnel, which is protected by the clockwise protection ring tunnel
o 一个逆时针工作环通道，由顺时针保护环通道保护
o one clockwise protection ring tunnel
o 一个顺时针保护环隧道
The structure of the protection tunnels is determined by the selected protection mechanism. This will be detailed in subsequent sections.
保护隧道的结构由选定的保护机制决定。这将在后续章节中详细说明。
As shown in Figure 3, LSP1, LSP2, and LSP3 enter the ring from Node E, Node A, and Node B, respectively, and all leave the ring at Node D. To protect these LSPs that traverse the ring, a clockwise working ring tunnel (RcW_D) via E->F->A->B->C->D and its anticlockwise protection ring tunnel (RaP_D) via D->C->B->A->F->E->D are established. Also, an anticlockwise working ring tunnel (RaW_D) via C->B->A->F->E->D and its clockwise protection ring tunnel (RcP_D) via D->E->F->A->B->C->D are established. For simplicity, Figure 3 only shows RcW_D and RaP_D. A similar provisioning should be applied for any other node on the ring. In summary, for each node in Figure 3, when acting as an egress node, the ring tunnels are created as follows:
如图3所示，LSP1、LSP2和LSP3分别从节点E、节点A和节点B进入环，并在节点D处离开环。为了保护这些穿过环的LSP，通过E->F->A->B->C->D建立顺时针工作环隧道（RcW_D）和通过D->C->B->A->F->E->D建立逆时针保护环隧道（RaP_D）。此外，还建立了经C->B->A->F->E->D的逆时针工作环通道（原始D）和经D->E->F->A->B->C->D的顺时针保护环通道（RcP D）。为简单起见，图3仅显示了RcW_D和RaP_D。环上的任何其他节点都应该应用类似的配置。总之，对于图3中的每个节点，当充当出口节点时，环形隧道的创建如下所示：
o To Node A: RcW_A, RaW_A, RcP_A, RaP_A
o 至节点A：RcW_A、原始_A、RcP_A、RaP_A
o To Node B: RcW_B, RaW_B, RcP_B, RaP_B
o 到节点B：RcW_B、RaW_B、RcP_B、RaP_B
o To Node C: RcW_C, RaW_C, RcP_C, RaP_C
o 至节点C：RcW_C、原始_C、RcP_C、RaP_C
o To Node D: RcW_D, RaW_D, RcP_D, RaP_D
o 到节点D：RcW\U D、原始D、RcP\U D、RaP\U D
o To Node E: RcW_E, RaW_E, RcP_E, RaP_E
o 至节点E：RcW_E、原始_E、RcP_E、RaP_E
o To Node F: RcW_F, RaW_F, RcP_F, RaP_F
o 到节点F：RcW\U F、RaW\U F、RcP\U F、RaP\U F
+---+#############+---+
| F |-------------| A | +-- LSP2
+---+*************+---+
#/* *\#
#/* *\#
#/* *\#
+---+ +---+
LSP1 --+ | E | | B |+-- LSP3
+---+ +---+
#\ */#
#\ */#
#\ */#
+---+*************+---+
LSP1 +--| D |-------------| C |
LSP2 +---+#############+---+
LSP3
+---+#############+---+
| F |-------------| A | +-- LSP2
+---+*************+---+
#/* *\#
#/* *\#
#/* *\#
+---+ +---+
LSP1 --+ | E | | B |+-- LSP3
+---+ +---+
#\ */#
#\ */#
#\ */#
+---+*************+---+
LSP1 +--| D |-------------| C |
LSP2 +---+#############+---+
LSP3
----- Physical Links
***** RcW_D
##### RaP_D
----- Physical Links
***** RcW_D
##### RaP_D
Figure 3: Ring Tunnels in MSRP
图3：MSRP中的环形隧道
Through these working and protection ring tunnels, LSPs that enter the ring from any node can reach any egress nodes on the ring and are protected from failures on the ring.
通过这些工作和保护环隧道，从任何节点进入环的LSP都可以到达环上的任何出口节点，并受到环上故障的保护。
The ring tunnel labels are downstream-assigned labels as defined in [RFC3031]. The ring tunnel labels on each hop of the ring tunnel can be either configured statically, provisioned by a controller, or distributed dynamically via a control protocol. For an LSP that traverses the ring tunnel, the ingress ring node and the egress ring node are considered adjacent at the LSP layer, and LSP label needs to be allocated at these two ring nodes. The control plane for label distribution is outside the scope of this document.
环形隧道标签是[RFC3031]中定义的下游指定标签。环形隧道的每个跃点上的环形隧道标签可以静态配置、由控制器提供或通过控制协议动态分发。对于穿过环形隧道的LSP，入口环节点和出口环节点被认为在LSP层相邻，并且需要在这两个环节点处分配LSP标签。标签分发的控制平面不在本文档的范围内。
When an MPLS-TP transport path, i.e., an LSP, enters the ring, the ingress node on the ring pushes the working ring tunnel label that is used to reach the specific egress node and sends the traffic to the next hop. The transit nodes on the working ring tunnel swap the ring tunnel labels and forward the packets to the next hop. When the packet arrives at the egress node, the egress node pops the ring tunnel label and forwards the packets based on the inner LSP label
当MPLS-TP传输路径（即LSP）进入环时，环上的入口节点推送用于到达特定出口节点的工作环隧道标签，并将流量发送到下一跳。工作环隧道上的传输节点交换环隧道标签，并将数据包转发到下一跳。当分组到达出口节点时，出口节点弹出环形隧道标签并基于内部LSP标签转发分组
and service label. Figure 4 shows the label operation in the MPLS-TP Shared-Ring Protection mechanism. Assume that LSP1 enters the ring at Node A and exits from Node D, and the following label operations are executed.
和服务标签。图4显示了MPLS-TP共享环保护机制中的标签操作。假设LSP1在节点A进入环并从节点D退出，并执行以下标签操作。
1. Ingress node: Packets of LSP1 arrive at Node A with a label stack [LSP1] and are supposed to be forwarded in the clockwise direction of the ring. The label of the clockwise working ring tunnel RcW_D will be pushed at Node A, the label stack for the forwarded packet at Node A is changed to [RcW_D(B)|LSP1].
1. 入口节点：LSP1的数据包通过标签堆栈[LSP1]到达节点A，并应沿环的顺时针方向转发。顺时针工作环形隧道RcW_D的标签将在节点A处推送，节点A处转发的分组的标签堆栈更改为[RcW_D（B）| LSP1]。
2. Transit nodes: In this case, Nodes B and C forward the packets by swapping the working ring tunnel labels. For example, the label [RcW_D(B)|LSP1] is swapped to [RcW_D(C)|LSP1] at Node B.
2. 中转节点：在这种情况下，节点B和C通过交换工作环隧道标签转发数据包。例如，标签[RcW_D（B）| LSP1]在节点B处交换为[RcW_D（C）| LSP1]。
3. Egress node: When the packet arrives at Node D (i.e., the egress node) with label stack [RcW_D(D)|LSP1], Node D pops RcW_D(D) and subsequently deals with the inner labels of LSP1.
3. 出口节点：当数据包到达带有标签堆栈[RcW_D（D）| LSP1]的节点D（即出口节点）时，节点D弹出RcW_D（D），随后处理LSP1的内部标签。
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#[RaP_D(A)]
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ */#
[RaP_D(D)]#\ [RxW_D(C)]*/#[RaP_D(B)]
#\ */#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#[RaP_D(A)]
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ */#
[RaP_D(D)]#\ [RxW_D(C)]*/#[RaP_D(B)]
#\ */#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+
----- Physical Links
***** RcW_D
##### RaP_D
----- Physical Links
***** RcW_D
##### RaP_D
Figure 4: Label Operation of MSRP
图4:MSRP的标签操作
The MPLS-TP section-layer OAM is used to monitor the connectivity between each two adjacent nodes on the ring using the mechanisms defined in [RFC6371]. Protection switching is triggered by the failure detected on the ring by the OAM mechanisms.
MPLS-TP段层OAM用于使用[RFC6371]中定义的机制监控环上每两个相邻节点之间的连接。保护切换由OAM机制在环上检测到的故障触发。
Two ports of a link form a Maintenance Entity Group (MEG), and a MEG End Point (MEP) function is installed in each ring port. Continuity Check (CC) OAM packets are periodically exchanged between each pair of MEPs to monitor the link health. Three consecutive lost CC packets MUST be interpreted as a link failure.
链路的两个端口构成一个维护实体组（MEG），每个环端口中安装一个MEG端点（MEP）功能。连续性检查（CC）OAM数据包在每对MEP之间定期交换，以监控链路健康状况。三个连续丢失的CC数据包必须解释为链路故障。
A node failure is regarded as the failure of two links attached to that node. The two nodes adjacent to the failed node detect the failure in the links that are connected to the failed node.
节点故障被视为连接到该节点的两条链路的故障。与故障节点相邻的两个节点检测连接到故障节点的链路中的故障。
This section specifies the ring protection mechanisms in detail. In general, the description uses the clockwise working ring tunnel and the corresponding anticlockwise protection ring tunnel as an example, but the mechanism is applicable in the same way to the anticlockwise working and clockwise protection ring tunnels.
本节详细说明了环保护机制。一般情况下，本说明使用顺时针工作环隧道和相应的逆时针保护环隧道作为示例，但该机制同样适用于逆时针工作环隧道和顺时针保护环隧道。
In a ring network, each working ring tunnel is associated with a protection ring tunnel in the opposite direction, and every node MUST obtain the ring topology either by configuration or via a topology discovery mechanism. The ring topology and the connectivity (Intact or Severed) between two adjacent ring nodes form the ring map. Each ring node maintains the ring map and uses it to perform ring protection switching.
在环形网络中，每个工作环形隧道与一个相反方向的保护环形隧道相关联，每个节点必须通过配置或拓扑发现机制获得环形拓扑。环拓扑和两个相邻环节点之间的连接（完整或断开）构成环映射。每个环节点维护环映射并使用它执行环保护切换。
Taking the topology in Figure 4 as an example, LSP1 enters the ring at Node A and leaves the ring at Node D. In normal state, LSP1 is carried by the clockwise working ring tunnel (RcW_D) through the path A->B->C->D. The label operation is:
以图4中的拓扑为例，LSP1在节点A进入环，在节点D离开环。正常状态下，LSP1由顺时针工作环隧道（RcW_D）通过路径A->B->C->D携带。标签操作为：
[LSP1](Payload) -> [RCW_D(B)|LSP1](NodeA) -> [RCW_D(C)|LSP1](NodeB) -> [RCW_D(D)| LSP1](NodeC) -> [LSP1](Payload).
[LSP1]（有效负载）->[RCW|D（B）| LSP1]（节点EA）->[RCW|D（C）| LSP1]（节点EB）->[RCW|D（D）| LSP1]（节点EC）->[LSP1]（有效负载）。
Then at Node D, the packet will be forwarded based on the label stack of LSP1.
然后，在节点D处，分组将基于LSP1的标签堆栈进行转发。
Three typical ring protection mechanisms are described in this section: wrapping, short-wrapping, and steering. All nodes on the same ring MUST use the same protection mechanism. If the RPS protocol in any node detects an RPS message with a protection-switching mode that was not provisioned in that node, a failure of protocol will be reported, and the protection mechanism will not be activated.
本节介绍了三种典型的环保护机构：缠绕、短缠绕和转向。同一环上的所有节点必须使用相同的保护机制。如果任何节点中的RPS协议检测到具有该节点中未设置的保护切换模式的RPS消息，则将报告协议故障，并且保护机制将不会被激活。
Wrapping ring protection: the node that detects a failure or accepts a switch request switches the traffic impacted by the failure or the switch request to the opposite direction (away from the failure). In
环绕环保护：检测到故障或接受交换机请求的节点将受故障或交换机请求影响的流量切换到相反方向（远离故障）。在里面
this way, the impacted traffic is switched to the protection ring tunnel by the switching node upstream of the failure, then it travels around the ring to the switching node downstream of the failure through the protection ring tunnel, where it is switched back onto the working ring tunnel to reach the egress node.
通过这种方式，受影响的流量由故障上游的切换节点切换到保护环隧道，然后通过保护环隧道绕环移动到故障下游的切换节点，在那里被切换回工作环隧道以到达出口节点。
Short-wrapping ring protection provides some optimization to wrapping protection, in which the impacted traffic is only switched once to the protection ring tunnel by the switching node upstream to the failure. At the egress node, the traffic leaves the ring from the protection ring tunnel. This can reduce the traffic detour of wrapping protection.
短环绕环保护为环绕保护提供了一些优化，在这种保护中，受影响的流量仅由切换节点向故障上游切换一次到保护环隧道。在出口节点，流量从保护环隧道离开环。这可以减少包裹保护的交通绕行。
Steering ring protection implies that the node that detects a failure sends a request along the ring to the other node adjacent to the failure, and all nodes in the ring process this information. For the impacted traffic, the ingress node (which adds traffic to the ring) performs switching of the traffic from working to the protection ring tunnel, and the egress node will drop the traffic received from the protection ring tunnel.
转向环保护意味着检测到故障的节点沿着环向与故障相邻的其他节点发送请求，环中的所有节点都处理该信息。对于受影响的流量，入口节点（向环添加流量）执行从工作到保护环隧道的流量切换，出口节点将丢弃从保护环隧道接收的流量。
The following sections describe these protection mechanisms in detail.
以下各节详细介绍了这些保护机制。
With the wrapping mechanism, the protection ring tunnel is a closed ring identified by the egress node. As shown in Figure 4, the RaP_D is the anticlockwise protection ring tunnel for the clockwise working ring tunnel RcW_D. As specified in the following sections, the closed ring protection tunnel can protect both link failures and node failures. Wrapping can be applicable for the protection of Point-to-Multipoint (P2MP) LSPs on the ring; the details of which are outside the scope of this document.
通过缠绕机制，保护环隧道是由出口节点标识的闭合环。如图4所示，RaP_D是顺时针工作环形隧道RcW_D的逆时针保护环形隧道。如以下章节所述，闭合环形保护隧道可以保护链路故障和节点故障。包装可用于保护环上的点对多点（P2MP）LSP；其详细信息不在本文件范围内。
When a link failure between Nodes B and C occurs, if it is a bidirectional failure, both Nodes B and C can detect the failure via the OAM mechanism; if it is a unidirectional failure, one of the two nodes would detect the failure via the OAM mechanism. In both cases, the node at the other side of the detected failure will be determined by the ring map and informed using the RPS protocol, which is specified in Section 5. Then Node B switches the clockwise working ring tunnel (RcW_D) to the anticlockwise protection ring tunnel (RaP_D), and Node C switches the anticlockwise protection ring tunnel (RaP_D) back to the clockwise working ring tunnel (RcW_D). The
当节点B和C之间发生链路故障时，如果是双向故障，则节点B和C都可以通过OAM机制检测故障；如果是单向故障，两个节点中的一个将通过OAM机制检测故障。在这两种情况下，检测故障另一侧的节点将由环映射确定，并使用第5节中规定的RPS协议通知。然后，节点B将顺时针工作环隧道（RcW_D）切换到逆时针保护环隧道（RaP_D），节点C将逆时针保护环隧道（RaP_D）切换回顺时针工作环隧道（RcW_D）。这个
payload that enters the ring at Node A and leaves the ring at Node D follows the path A->B->A->F->E->D->C->D. The label operation is:
在节点A进入环并在节点D离开环的有效载荷遵循路径A->B->A->F->E->D->C->D。标签操作为：
[LSP1](Payload) -> [RcW_D(B)|LSP1](Node A) -> [RaP_D(A)|LSP1](Node B)
-> [RaP_D(F)|LSP1](Node A) -> [RaP_D(E)|LSP1] (Node F) ->
[RaP_D(D)|LSP1] (Node E) -> [RaP_D(C)|LSP1] (Node D) ->
[RcW_D(D)|LSP1](Node C) -> [LSP1](Payload).
[LSP1](Payload) -> [RcW_D(B)|LSP1](Node A) -> [RaP_D(A)|LSP1](Node B)
-> [RaP_D(F)|LSP1](Node A) -> [RaP_D(E)|LSP1] (Node F) ->
[RaP_D(D)|LSP1] (Node E) -> [RaP_D(C)|LSP1] (Node D) ->
[RcW_D(D)|LSP1](Node C) -> [LSP1](Payload).
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ *x#
[RaP_D(D)]#\ [RcW_D(C)]*x#RaP_D(B)
#\ *x#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ *x#
[RaP_D(D)]#\ [RcW_D(C)]*x#RaP_D(B)
#\ *x#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+
----- Physical Links xxxxx Failure Links
***** RcW_D ##### RaP_D
----- Physical Links xxxxx Failure Links
***** RcW_D ##### RaP_D
Figure 5: Wrapping for Link Failure
图5：链路故障的包装
As shown in Figure 6, when Node B fails, Node A detects the failure between A and B and switches the clockwise working ring tunnel (RcW_D) to the anticlockwise protection ring tunnel (RaP_D); Node C detects the failure between C and B and switches the anticlockwise protection ring tunnel (RaP_D) to the clockwise working ring tunnel (RcW_D). The node at the other side of the failed node will be determined by the ring map and informed using the RPS protocol specified in Section 5.
如图6所示，当节点B发生故障时，节点A检测到A和B之间的故障，并将顺时针工作环通道（RcW_D）切换到逆时针保护环通道（RaP_D）；节点C检测C和B之间的故障，并将逆时针保护环通道（RaP_D）切换到顺时针工作环通道（RcW_D）。故障节点另一侧的节点将由环映射确定，并使用第5节中规定的RPS协议通知。
The payload that enters the ring at Node A and exits at Node D follows the path A->F->E->D->C->D. The label operation is:
在节点A进入环并在节点D退出的有效载荷遵循路径A->F->E->D->C->D。标签操作为：
[LSP1](Payload)-> [RaP_D(F)|LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) -> [RaP_D(D)|LSP1](NodeE) -> [RaP_D(C)|LSP1] (NodeD) -> [RcW_D(D)|LSP1] (NodeC) -> [LSP1](Payload).
[LSP1]（有效载荷）->[RaP|D（F）| LSP1]（节点区域）->[RaP|D（E）| LSP1]（节点区域）->[RaP|D（D）| LSP1]（节点区域）->[RcW|D（D）| LSP1]（节点区域）->[LSP1]（有效载荷）。
In one special case where Node D fails, all the ring tunnels with Node D as the egress will become unusable. The ingress node will update its ring map according to received RPS messages and determine that the egress node is not reachable; thus, it will not send traffic to either the working or the protection tunnel. However, before the failure location information is propagated to all the ring nodes, the wrapping protection mechanism may cause a temporary traffic loop: Node C detects the failure and switches the traffic from the clockwise working ring tunnel (RcW_D) to the anticlockwise protection ring tunnel (RaP_D); Node E also detects the failure and switches the traffic from the anticlockwise protection ring tunnel (RaP_D) back to the clockwise working ring tunnel (RcW_D). A possible mechanism to mitigate the temporary loop problem is: the TTL of the ring tunnel label is set to 2*N by the ingress ring node of the traffic, where N is the number of nodes on the ring.
在节点D发生故障的一种特殊情况下，以节点D作为出口的所有环形隧道将变得不可用。入口节点将根据接收到的RPS消息更新其环映射，并确定出口节点不可到达；因此，它不会向工作隧道或保护隧道发送流量。然而，在故障位置信息传播到所有环节点之前，环绕保护机制可能会导致临时流量环路：节点C检测到故障并将流量从顺时针工作环隧道（RcW_D）切换到逆时针保护环隧道（RaP_D）；节点E还检测到故障，并将通信量从逆时针保护环隧道（RaP_D）切换回顺时针工作环隧道（RcW_D）。缓解临时环路问题的一种可能机制是：环形隧道标签的TTL由业务的入口环节点设置为2*N，其中N是环上的节点数。
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ xxxxx
| E | x B x
+---+ xxxxx
#\ */#
[RaP_D(D)]#\ [RcW_D(C)]*/#RaP_D(B)
#\ */#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ xxxxx
| E | x B x
+---+ xxxxx
#\ */#
[RaP_D(D)]#\ [RcW_D(C)]*/#RaP_D(B)
#\ */#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+#####[RaP_D(C)]####+---+
----- Physical Links xxxxx Failure Nodes
***** RcW_D ##### RaP_D
----- Physical Links xxxxx Failure Nodes
***** RcW_D ##### RaP_D
Figure 6: Wrapping for Node Failure
图6：节点故障的包装
With the wrapping protection scheme, protection switching is executed at both nodes adjacent to the failure; consequently, the traffic will be wrapped twice. This mechanism will cause additional latency and bandwidth consumption when traffic is switched to the protection path.
利用环绕保护方案，在故障附近的两个节点上执行保护切换；因此，交通将被包裹两次。当流量切换到保护路径时，此机制将导致额外的延迟和带宽消耗。
With short-wrapping protection, protection switching is executed only at the node upstream to the failure, and the packet leaves the ring in the protection ring tunnel at the egress node. This scheme can reduce the additional latency and bandwidth consumption when traffic is switched to the protection path. However, the two directions of a protected bidirectional LSP are no longer co-routed under the protection-switching conditions.
对于短包装保护，保护交换仅在故障上游的节点执行，并且分组在出口节点的保护环隧道中离开环。该方案可以减少流量切换到保护路径时的额外延迟和带宽消耗。然而，在保护交换条件下，受保护的双向LSP的两个方向不再被共同路由。
In the traditional wrapping solution, the protection ring tunnel is configured as a closed ring, while in the short-wrapping solution, the protection ring tunnel is configured as ended at the egress node, which is similar to the working ring tunnel. Short-wrapping is easy to implement in shared-ring protection because both the working and protection ring tunnels are terminated on the egress nodes. Figure 7 shows the clockwise working ring tunnel and the anticlockwise protection ring tunnel with Node D as the egress node.
在传统的缠绕解决方案中，保护环隧道被配置为闭合环，而在短缠绕解决方案中，保护环隧道被配置为在出口节点结束，这类似于工作环隧道。短包装在共享环保护中易于实现，因为工作环隧道和保护环隧道都在出口节点上终止。图7显示了顺时针工作环隧道和逆时针保护环隧道，其中节点D为出口节点。
As shown in Figure 7, in normal state, LSP1 is carried by the clockwise working ring tunnel (RcW_D) through the path A->B->C->D. When a link failure between Nodes B and C occurs, Node B switches the working ring tunnel RcW_D to the protection ring tunnel RaP_D in the opposite direction. The difference with wrapping occurs in the protection ring tunnel at the egress node. In short-wrapping protection, Rap_D ends in Node D, and then traffic will be forwarded based on the LSP labels. Thus, with the short-wrapping mechanism, LSP1 will follow the path A->B->A->F->E->D when a link failure between Node B and Node C happens. The protection switch at Node D is based on the information from its ring map and the information received via the RPS protocol.
如图7所示，在正常状态下，LSP1由顺时针工作环隧道（RcW_D）通过路径A->B->C->D承载。当节点B和C之间发生链路故障时，节点B将工作环隧道RcW_D切换到相反方向的保护环隧道RaP_D。与包裹的区别出现在出口节点处的保护环隧道中。在短包装保护中，Rap_D在节点D中结束，然后根据LSP标签转发流量。因此，使用短包装机制，当节点B和节点C之间发生链路故障时，LSP1将遵循路径A->B->A->F->E->D。节点D处的保护交换机基于来自其环映射的信息和通过RPS协议接收的信息。
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ *x#
[RaP_D(D)]#\ [RcW_D(C)]*x#RaP_D(B)
#\ *x#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+ +---+
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ *x#
[RaP_D(D)]#\ [RcW_D(C)]*x#RaP_D(B)
#\ *x#
+---+*****[RcW_D(D)]****+---+
LSP1 +-- | D |-------------------| C |
+---+ +---+
----- Physical Links xxxxx Failure Links
***** RcW_D ##### RaP_D
----- Physical Links xxxxx Failure Links
***** RcW_D ##### RaP_D
Figure 7: Short-Wrapping for Link Failure
图7：链路故障的短包装
For the node failure that happens on a non-egress node, the short-wrapping protection switching is similar to the link failure case as described in the previous section. This section specifies the scenario of an egress node failure.
对于发生在非出口节点上的节点故障，短包装保护切换类似于前一节中描述的链路故障情况。本节指定出口节点故障的场景。
As shown in Figure 8, LSP1 enters the ring on Node A and leaves the ring on Node D. In normal state, LSP1 is carried by the clockwise working ring tunnel (RcW_D) through the path A->B->C->D. When Node D fails, the traffic of LSP1 cannot be protected by any ring tunnels that use Node D as the egress node. The ingress node will update its ring map according to received RPS messages and determine that the egress node is not reachable; thus, it will not send traffic to either the working or the protection tunnel. However, before the failure location information is propagated to all the ring nodes using the RPS protocol, Node C switches all the traffic on the working ring tunnel RcW_D to the protection ring tunnel RaP_D in the opposite direction based on the information in the ring map. When the traffic arrives at Node E, which also detects the failure of Node D, the protection ring tunnel RaP_D cannot be used to forward traffic to Node D. With the short-wrapping mechanism, protection switching can only be performed once from the working ring tunnel to the protection ring tunnel; thus, Node E MUST NOT switch the traffic that is already carried on the protection ring tunnel back to the working
如图8所示，LSP1进入节点A上的环，离开节点D上的环。在正常状态下，LSP1由顺时针工作环隧道（RcW_D）通过路径A->B->C->D承载。当节点D发生故障时，任何使用节点D作为出口节点的环隧道都无法保护LSP1的流量。入口节点将根据接收到的RPS消息更新其环映射，并确定出口节点不可到达；因此，它不会向工作隧道或保护隧道发送流量。然而，在使用RPS协议将故障位置信息传播到所有环节点之前，节点C根据环映射中的信息将工作环隧道RcW_D上的所有通信量切换到相反方向的保护环隧道RaP_D。当流量到达节点E时，也检测到节点D的故障，保护环隧道RaP_D不能用于将流量转发到节点D。通过短包装机制，从工作环隧道到保护环隧道只能执行一次保护切换；因此，节点E不得将已经在保护环隧道上承载的业务切换回工作环
ring tunnel in the opposite direction. Instead, Node E will discard the traffic received on RaP_D locally. This can avoid the temporary traffic loop when the failure happens on the egress node of the ring tunnel. This also illustrates one of the benefits of having separate working and protection ring tunnels in each ring direction.
相反方向的环形隧道。相反，节点E将丢弃在本地RaP_D上接收的通信量。这可以避免在环形隧道的出口节点上发生故障时出现临时交通环路。这也说明了在每个环形方向上有单独的工作和保护环形隧道的好处之一。
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ */#
[RaP_D(D)]#\ [RcW_D(C)]*/#RaP_D(B)
#\ */#
xxxxx*****[RcW_D(D)]****+---+
LSP1 +-- x D x-------------------| C |
xxxxx +---+
+---+#####[RaP_D(F)]######+---+
| F |---------------------| A | +-- LSP1
+---+*****[RcW_D(A)]******+---+
#/* *\#
[RaP_D(E)]#/*[RcW_D(F)] [RcW_D(B)]*\#RaP_D(A)
#/* *\#
+---+ +---+
| E | | B |
+---+ +---+
#\ */#
[RaP_D(D)]#\ [RcW_D(C)]*/#RaP_D(B)
#\ */#
xxxxx*****[RcW_D(D)]****+---+
LSP1 +-- x D x-------------------| C |
xxxxx +---+
----- Physical Links xxxxx Failure Nodes
***** RcW_D ##### RaP_D
----- Physical Links xxxxx Failure Nodes
***** RcW_D ##### RaP_D
Figure 8: Short-Wrapping for Egress Node Failure
图8：出口节点故障的短包装
With the steering protection mechanism, the ingress node (which adds traffic to the ring) performs switching from the working to the protection ring tunnel, and at the egress node, the traffic leaves the ring from the protection ring tunnel.
通过转向保护机制，入口节点（向环添加流量）执行从工作到保护环隧道的切换，并且在出口节点，流量从保护环隧道离开环。
When a failure occurs in the ring, the node that detects the failure with an OAM mechanism sends the failure information in the opposite direction of the failure hop by hop along the ring using an RPS request message and the ring-map information. When a ring node receives the RPS message that identifies a failure, it can determine the location of the fault by using the topology information of the ring map and updating the ring map accordingly; then, it can determine whether the LSPs entering the ring locally need to switch over or not. For LSPs that need to switch over, it will switch the LSPs from the working ring tunnels to their corresponding protection ring tunnels.
当环中发生故障时，使用OAM机制检测故障的节点使用RPS请求消息和环映射信息沿环以故障的相反方向逐跳发送故障信息。当环节点接收到识别故障的RPS消息时，它可以通过使用环映射的拓扑信息并相应地更新环映射来确定故障的位置；然后，可以确定本地进入环的LSP是否需要切换。对于需要切换的LSP，它会将LSP从工作环形隧道切换到相应的保护环形隧道。
Ring Map of F +--LSP1
+-+-+-+-+-+-+-+ +---+ ###[RaP_D(F)]### +---/ +-+-+-+-+-+-+-+
|F|A|B|C|D|E|F| | F | ---------------- | A | |A|B|C|D|E|F|A|
+-+-+-+-+-+-+-+ +---+ ***[RcW_D(A)]*** +---+ +-+-+-+-+-+-+-+
|I|I|I|S|I|I| #/* *\# |I|I|S|I|I|I|
+-+-+-+-+-+-+ #/* *\# +-+-+-+-+-+-+
[RaP_D(E)] #/* [RcW_D(B)] *\# [RaP_D(A)]
#/* [RcW_D(F)] *\#
+-+-+-+-+-+-+-+ #/* *\#
|E|F|A|B|C|D|E| +---+ +---+ +-- LSP2
+-+-+-+-+-+-+-+ | E | | B | +-+-+-+-+-+-+-+
|I|I|I|I|S|I| +---+ +---+ |B|C|D|E|F|A|B|
+-+-+-+-+-+-+ #\* */# +-+-+-+-+-+-+-+
#\* [RcW_D(E)] [RcW_D(C)] */# |I|S|I|I|I|I|
[RaP_D(D)] #\* */# +-+-+-+-+-+-+
#\* */# [RaP_D(B)]
+-+-+-+-+-+-+-+ +---+ [RcW_D(D)] +---+ +-+-+-+-+-+-+-+
|D|E|F|A|B|C|D| +-- | D | xxxxxxxxxxxxxxxxx | C | |C|D|E|F|A|B|C|
+-+-+-+-+-+-+-+ LSP1 +---+ [RaP_D(C)] +---+ +-+-+-+-+-+-+-+
|I|I|I|I|I|S| LSP2 |S|I|I|I|I|I|
+-+-+-+-+-+-+ +-+-+-+-+-+-+
Ring Map of F +--LSP1
+-+-+-+-+-+-+-+ +---+ ###[RaP_D(F)]### +---/ +-+-+-+-+-+-+-+
|F|A|B|C|D|E|F| | F | ---------------- | A | |A|B|C|D|E|F|A|
+-+-+-+-+-+-+-+ +---+ ***[RcW_D(A)]*** +---+ +-+-+-+-+-+-+-+
|I|I|I|S|I|I| #/* *\# |I|I|S|I|I|I|
+-+-+-+-+-+-+ #/* *\# +-+-+-+-+-+-+
[RaP_D(E)] #/* [RcW_D(B)] *\# [RaP_D(A)]
#/* [RcW_D(F)] *\#
+-+-+-+-+-+-+-+ #/* *\#
|E|F|A|B|C|D|E| +---+ +---+ +-- LSP2
+-+-+-+-+-+-+-+ | E | | B | +-+-+-+-+-+-+-+
|I|I|I|I|S|I| +---+ +---+ |B|C|D|E|F|A|B|
+-+-+-+-+-+-+ #\* */# +-+-+-+-+-+-+-+
#\* [RcW_D(E)] [RcW_D(C)] */# |I|S|I|I|I|I|
[RaP_D(D)] #\* */# +-+-+-+-+-+-+
#\* */# [RaP_D(B)]
+-+-+-+-+-+-+-+ +---+ [RcW_D(D)] +---+ +-+-+-+-+-+-+-+
|D|E|F|A|B|C|D| +-- | D | xxxxxxxxxxxxxxxxx | C | |C|D|E|F|A|B|C|
+-+-+-+-+-+-+-+ LSP1 +---+ [RaP_D(C)] +---+ +-+-+-+-+-+-+-+
|I|I|I|I|I|S| LSP2 |S|I|I|I|I|I|
+-+-+-+-+-+-+ +-+-+-+-+-+-+
----- Physical Links
***** RcW_D
##### RaP_D
I: Intact
S: Severed
----- Physical Links
***** RcW_D
##### RaP_D
I: Intact
S: Severed
Figure 9: Steering Operation and Protection Switching When Link C-D Fails
图9：链路C-D故障时的转向操作和保护切换
As shown in Figure 9, LSP1 enters the ring from Node A while LSP2 enters the ring from Node B, and both of them have the same destination, which is Node D.
如图9所示，LSP1从节点A进入环，而LSP2从节点B进入环，两者都有相同的目的地，即节点D。
In normal state, LSP1 is carried by the clockwise working ring tunnel (RcW_D) through the path A->B->C->D, and the label operation is: [LSP1](Payload) -> [RcW_D(B)|LSP1](NodeA) -> [RcW_D(C)| LSP1](NodeB) -> [RcW_D(D)|LSP1](NodeC) -> [LSP1](Payload).
在正常状态下，LSP1由顺时针工作环隧道（RcW_D）通过路径A->B->C->D携带，标签操作为：[LSP1]（有效负载）->[RcW_D（B）| LSP1]（节点EA）->[RcW_D（C）| LSP1]（节点EB）->[RcW_D（D）| LSP1]（节点EC）->[LSP1]（有效负载）。
LSP2 is carried by the clockwise working ring tunnel (RcW_D) through the path B->C->D, and the label operation is: [LSP2](Payload) -> [RcW_D(C)|LSP2](NodeB) -> [RcW_D(D)|LSP2](NodeC) -> [LSP2](Payload).
LSP2由顺时针工作环隧道（RcW_D）通过路径B->C->D携带，标签操作为：[LSP2]（有效负载）->[RcW_D（C）| LSP2]（NodeB）->[RcW_D（D）| LSP2]（NodeC）->[LSP2]（有效负载）。
If the link between Nodes C and D fails, according to the fault detection and distribution mechanisms, Node D will find out that there is a failure in the link between C and D, and it will update the link state of its ring topology, changing the link between C and D from normal to fault. In the direction that is opposite to the failure position, Node D will send the state report message to Node E, informing Node E of the fault between C and D, and E will update the link state of its ring topology accordingly, changing the link between C and D from normal to fault. In this way, the state report message is sent hop by hop in the clockwise direction. Similar to Node D, Node C will send the failure information in the anticlockwise direction.
如果节点C和D之间的链路出现故障，根据故障检测和分配机制，节点D将发现C和D之间的链路存在故障，并更新其环形拓扑的链路状态，将C和D之间的链路从正常更改为故障。在与故障位置相反的方向上，节点D将向节点E发送状态报告消息，通知节点E C和D之间的故障，并且E将相应地更新其环形拓扑的链路状态，将C和D之间的链路从正常更改为故障。这样，状态报告消息将按顺时针方向逐跳发送。与节点D类似，节点C将逆时针方向发送故障信息。
When Node A receives the failure report message and updates the link state of its ring map, it is aware that there is a fault on the clockwise working ring tunnel to Node D (RcW_D), and LSP1 enters the ring locally and is carried by this ring tunnel; thus, Node A will decide to switch the LSP1 onto the anticlockwise protection ring tunnel to Node D (RaP_D). After the switchover, LSP1 will follow the path A->F->E->D, and the label operation is: [LSP1](Payload) -> [RaP_D(F)| LSP1](NodeA) -> [RaP_D(E)|LSP1](NodeF) -> [RaP_D(D)|LSP1](NodeE) -> [LSP1](Payload).
当节点A接收到故障报告消息并更新其环映射的链路状态时，它知道到节点D（RcW_D）的顺时针工作环隧道上存在故障，并且LSP1本地进入环并由该环隧道承载；因此，节点A将决定将LSP1切换到逆时针保护环隧道到节点D（RaP_D）。切换后，LSP1将遵循路径A->F->E->D，标签操作为：[LSP1]（有效负载）->[RaP_D（F）| LSP1]（节点EA）->[RaP_D（E）| LSP1]（节点EF）->[RaP_D（D）|LSP1]（节点对象）->[LSP1]（有效负载）。
The same procedure also applies to the operation of LSP2. When Node B updates the link state of its ring topology, and finds out that the working ring tunnel RcW_D has failed, it will switch the LSP2 to the anticlockwise protection tunnel RaP_D. After the switchover, LSP2 goes through the path B->A->F->E->D, and the label operation is: [LSP2](Payload) -> [RaP_D(A)|LSP2](NodeB) -> [RaP_D(F)|LSP2](NodeA) -> [RaP_D(E)|LSP2](NodeF) -> [RaP_D(D)|LSP2](NodeE) -> [LSP2](Payload).
同样的程序也适用于LSP2的操作。当节点B更新其环形拓扑的链路状态，发现工作环形隧道RcW|D出现故障时，它将LSP2切换到逆时针保护隧道RaP|D。切换后，LSP2通过路径B->A->F->E->D，标签操作为：[LSP2]（有效负载）->[RaP|D（A）| LSP2]（节点B）->[RaP|D（F）| LSP2]（节点EA）->[RaP|D（E）| LSP2]（NodeF）->[RaP|D（D）| LSP2]（NodeE）->[LSP2]（有效负载）。
Assume the link between Nodes A and B breaks down, as shown in Figure 10. Similar to the above failure case, Node B will detect a fault in the link between A and B, and it will update its ring map, changing the link state between A and B from normal to fault. The state report message is sent hop by hop in the clockwise direction, notifying every node that there is a fault between Nodes A and B, and every node updates the link state of its ring topology. As a result, Node A will detect a fault in the working ring tunnel to Node D, and switch LSP1 to the protection ring tunnel, while Node B determines that the working ring tunnel for LSP2 still works fine, and it will not perform the switchover.
假设节点A和B之间的链路中断，如图10所示。与上述故障情况类似，节点B将检测a和B之间链路中的故障，并更新其环映射，将a和B之间的链路状态从正常更改为故障。状态报告消息按顺时针方向逐跳发送，通知每个节点节点a和B之间存在故障，每个节点更新其环形拓扑的链路状态。结果，节点a将检测到工作环隧道到节点D的故障，并将LSP1切换到保护环隧道，而节点B确定LSP2的工作环隧道仍然工作正常，并且不会执行切换。
/+-- LSP1
+-+-+-+-+-+-+-+ +---+ ###[RaP_D(F)]#### +---/ +-+-+-+-+-+-+-+
|F|A|B|C|D|E|F| | F | ----------------- | A | |A|B|C|D|E|F|A|
+-+-+-+-+-+-+-+ +---+ ***[RcW_D(A)]**** +---+ +-+-+-+-+-+-+-+
|I|S|I|I|I|I| #/* x |S|I|I|I|I|I|
+-+-+-+-+-+-+ #/* x +-+-+-+-+-+-+
[RaP_D(E)] #/*[RcW_D(F)] [RcW_D(B)]x [RaP_D(A)]
#/* x /+-- LSP2
+-+-+-+-+-+-+-+ +---+ +---/ +-+-+-+-+-+-+-+
|E|F|A|B|C|D|E| | E | | B | |B|C|D|E|F|A|B|
+-+-+-+-+-+-+-+ +---+ +---+ +-+-+-+-+-+-+-+
|I|I|S|I|I|I| #\* */# |I|I|I|I|I|S|
+-+-+-+-+-+-+ #\*[RcW_D(E)] [RcW_D(C)] */# +-+-+-+-+-+-+
[RaP_D(D)] #\* */# [RaP_D(B)]
+-+-+-+-+-+-+-+ #\* */# +-+-+-+-+-+-+-+
|D|E|F|A|B|C|D| +---+ ***[RcW_D(D)]*** +---+ |C|D|E|F|A|B|C|
+-+-+-+-+-+-+-+ +-- | D | ---------------- | C | +-+-+-+-+-+-+-+
|I|I|I|S|I|I| LSP1 +---+ ###[RaP_D(C)]### +---+ |I|I|I|I|S|I|
+-+-+-+-+-+-+ LSP2 +-+-+-+-+-+-+
/+-- LSP1
+-+-+-+-+-+-+-+ +---+ ###[RaP_D(F)]#### +---/ +-+-+-+-+-+-+-+
|F|A|B|C|D|E|F| | F | ----------------- | A | |A|B|C|D|E|F|A|
+-+-+-+-+-+-+-+ +---+ ***[RcW_D(A)]**** +---+ +-+-+-+-+-+-+-+
|I|S|I|I|I|I| #/* x |S|I|I|I|I|I|
+-+-+-+-+-+-+ #/* x +-+-+-+-+-+-+
[RaP_D(E)] #/*[RcW_D(F)] [RcW_D(B)]x [RaP_D(A)]
#/* x /+-- LSP2
+-+-+-+-+-+-+-+ +---+ +---/ +-+-+-+-+-+-+-+
|E|F|A|B|C|D|E| | E | | B | |B|C|D|E|F|A|B|
+-+-+-+-+-+-+-+ +---+ +---+ +-+-+-+-+-+-+-+
|I|I|S|I|I|I| #\* */# |I|I|I|I|I|S|
+-+-+-+-+-+-+ #\*[RcW_D(E)] [RcW_D(C)] */# +-+-+-+-+-+-+
[RaP_D(D)] #\* */# [RaP_D(B)]
+-+-+-+-+-+-+-+ #\* */# +-+-+-+-+-+-+-+
|D|E|F|A|B|C|D| +---+ ***[RcW_D(D)]*** +---+ |C|D|E|F|A|B|C|
+-+-+-+-+-+-+-+ +-- | D | ---------------- | C | +-+-+-+-+-+-+-+
|I|I|I|S|I|I| LSP1 +---+ ###[RaP_D(C)]### +---+ |I|I|I|I|S|I|
+-+-+-+-+-+-+ LSP2 +-+-+-+-+-+-+
----- Physical Links
***** RcW_D
##### RaP_D
----- Physical Links
***** RcW_D
##### RaP_D
Figure 10: Steering Operation and Protection Switching When Link A-B Fails
图10：链路A-B故障时的转向操作和保护切换
For a node failure that happens on a non-egress node, steering protection switching is similar to the link failure case as described in the previous section.
对于发生在非出口节点上的节点故障，转向保护切换类似于前一节中描述的链路故障情况。
If the failure occurs at the egress node of the LSP, the ingress node will update its ring map according to the received RPS messages; it will also determine that the egress node is not reachable after the failure, thus it will not send traffic to either the working or the protection tunnel, and a traffic loop can be avoided.
如果故障发生在LSP的出口节点，则入口节点将根据接收到的RPS消息更新其环映射；它还将确定出口节点在故障后不可到达，因此它不会向工作隧道或保护隧道发送流量，并且可以避免流量环路。
Interconnected ring topology is widely used in MPLS-TP networks. For a given ring, the interconnection node acts as the egress node for that ring, meaning that all LSPs using the interconnection node as an egress from one specific ring to another will use the same group of ring tunnels within the ring. This document will discuss two typical interconnected ring topologies:
互连环拓扑广泛应用于MPLS-TP网络中。对于给定环，互连节点充当该环的出口节点，这意味着使用互连节点作为从一个特定环到另一个特定环的出口的所有LSP将使用环内相同的环隧道组。本文件将讨论两种典型的互连环拓扑：
1. Single-node interconnected rings
1. 单节点互连环
In single-node interconnected rings, the connection between the two rings is through a single node. Because the interconnection node is in fact a single point of failure, this topology should be avoided in real transport networks.
在单节点互连环中，两个环之间的连接是通过单个节点进行的。由于互连节点实际上是单点故障，因此在实际传输网络中应避免这种拓扑结构。
Figure 11 shows the topology of single-node interconnected rings. Node C is the interconnection node between Ring1 and Ring2.
图11显示了单节点互连环的拓扑结构。节点C是环1和环2之间的互连节点。
+---+ +---+ +---+ +---+
| A |------| B |----- -----| G |------| H |
+---+ +---+ \ / +---+ +---+
| \ / |
| \ +---+ / |
| Ring1 | C | Ring2 |
| / +---+ \ |
| / \ |
+---+ +---+ / \ +---+ +---+
| F |------| E |----- -----| J |------| I |
+---+ +---+ +---+ +---+
+---+ +---+ +---+ +---+
| A |------| B |----- -----| G |------| H |
+---+ +---+ \ / +---+ +---+
| \ / |
| \ +---+ / |
| Ring1 | C | Ring2 |
| / +---+ \ |
| / \ |
+---+ +---+ / \ +---+ +---+
| F |------| E |----- -----| J |------| I |
+---+ +---+ +---+ +---+
Figure 11: Single-Node Interconnected Rings
图11：单节点互连环
2. Dual-node interconnected rings
2. 双节点互连环
In dual-node interconnected rings, the connection between the two rings is through two nodes. The two interconnection nodes belong to both interconnected rings. This topology can recover from one interconnection node failure.
在双节点互连环中，两个环之间的连接是通过两个节点进行的。两个互连节点属于两个互连环。此拓扑可以从一个互连节点故障中恢复。
Figure 12 shows the topology of dual-node interconnected rings. Nodes C and D are the interconnection nodes between Ring1 and Ring2.
图12显示了双节点互连环的拓扑结构。节点C和D是环1和环2之间的互连节点。
+---+ +---+ +---+ +---+ +---+
| A |------| B |------| C |------| G |------| H |
+---+ +---+ +---+ +---+ +---+
| | |
| | |
| Ring1 | Ring2 |
| | |
| | |
+---+ +---+ +---+ +---+ +---+
| F |------| E |------| D |------| J |------| I |
+---+ +---+ +---+ +---+ +---+
+---+ +---+ +---+ +---+ +---+
| A |------| B |------| C |------| G |------| H |
+---+ +---+ +---+ +---+ +---+
| | |
| | |
| Ring1 | Ring2 |
| | |
| | |
+---+ +---+ +---+ +---+ +---+
| F |------| E |------| D |------| J |------| I |
+---+ +---+ +---+ +---+ +---+
Figure 12: Dual-Node Interconnected Rings
图12：双节点互连环
Interconnected rings can be treated as two independent rings. The RPS protocol operates on each ring independently. A failure that happens in one ring only triggers protection switching in the ring itself and does not affect the other ring, unless the failure is on the interconnection node. In this way, protection switching on each ring is the same as the mechanisms described in Section 4.3.
互连环可以被视为两个独立的环。RPS协议在每个环上独立运行。一个环中发生的故障只会触发环本身的保护切换，不会影响另一个环，除非故障发生在互连节点上。这样，每个环上的保护开关与第4.3节中描述的机制相同。
The service LSPs that traverse the interconnected rings use the ring tunnels in each ring; within a given ring, the tunnel is selected using normal ring-selection procedures. The traversing LSPs are stitched on the interconnection node. On the interconnection node, the ring tunnel label of the source ring is popped, then LSP label is swapped; after that, the ring tunnel label of the destination ring is pushed.
穿过互连环的服务LSP使用每个环中的环隧道；在给定环内，使用正常环选择程序选择隧道。横向LSP缝合在互连节点上。在互连节点上，弹出源环的环隧道标签，然后交换LSP标签；之后，推送目标环的环隧道标签。
In the dual-node interconnected ring scenario, the two interconnection nodes can be managed as a virtual node group. In addition to the ring tunnels to each physical ring node, each ring SHOULD assign the working and protection ring tunnels to the virtual interconnection node group. In addition, on both nodes in the virtual interconnection node group, the same LSP label is assigned for each traversed LSP. This way, any interconnection node in the virtual node group can terminate the working or protection ring tunnels targeted to the virtual node group and stitch the service LSP from the source ring tunnel to the destination ring tunnel.
在双节点互连环方案中，两个互连节点可以作为虚拟节点组进行管理。除了每个物理环节点的环隧道外，每个环还应将工作环隧道和保护环隧道分配给虚拟互连节点组。此外，在虚拟互连节点组中的两个节点上，为每个遍历的LSP分配相同的LSP标签。这样，虚拟节点组中的任何互连节点都可以终止针对虚拟节点组的工作或保护环隧道，并将服务LSP从源环隧道缝合到目标环隧道。
When the service LSP passes through the interconnected rings, the direction of the working ring tunnels used on both rings SHOULD be the same. In dual-node interconnected rings, this ensures that in normal state the traffic passes only one of the two interconnection nodes and does not pass the link between the two interconnection
当服务LSP通过互连环时，两个环上使用的工作环通道的方向应相同。在双节点互连环中，这可确保在正常状态下，流量仅通过两个互连节点中的一个，而不通过两个互连节点之间的链路
nodes. The traffic will then only be switched to the protection path if the interconnection node that is in working path fails. For example, if the service LSP uses the clockwise working ring tunnel on Ring1, when the service LSP leaves Ring1 and enters Ring2, the working ring tunnel used on Ring2 should also follow the clockwise direction.
节点。只有在工作路径中的互连节点发生故障时，通信量才会切换到保护路径。例如，如果服务LSP使用环1上的顺时针工作环通道，则当服务LSP离开环1进入环2时，环2上使用的工作环通道也应遵循顺时针方向。
The same ring tunnels as described in Section 4.1 are used in each ring of the interconnected rings. In addition, ring tunnels to the virtual interconnection node group are established on each ring of the interconnected rings, that is:
在互连环的每个环中使用第4.1节所述的相同环隧道。此外，在互连环的每个环上建立到虚拟互连节点组的环隧道，即：
o one clockwise working ring tunnel to the virtual interconnection node group
o 一个指向虚拟互连节点组的顺时针工作环隧道
o one anticlockwise protection ring tunnel to the virtual interconnection node group
o 一个到虚拟互连节点组的逆时针保护环隧道
o one anticlockwise working ring tunnel to the virtual interconnection node group
o 到虚拟互连节点组的一个逆时针工作环隧道
o one clockwise protection ring tunnel to the virtual interconnection node group
o 到虚拟互连节点组的一个顺时针保护环隧道
The ring tunnels to the virtual interconnection node group are shared by all LSPs that need to be forwarded to other rings. These ring tunnels can terminate at any node in the virtual interconnection node group.
到虚拟互连节点组的环隧道由需要转发到其他环的所有LSP共享。这些环形隧道可以终止于虚拟互连节点组中的任何节点。
For example, all the ring tunnels on Ring1 in Figure 13 are provisioned as follows:
例如，图13中Ring1上的所有环形隧道的配置如下：
o To Node A: R1cW_A, R1aW_A, R1cP_A, R1aP_A
o 至节点A：R1cW_A、R1aW_A、R1cP_A、R1aP_A
o To Node B: R1cW_B, R1aW_B, R1cP_B, R1aP_B
o 到节点B：R1cW_B、R1aW_B、R1cP_B、R1aP_B
o To Node C: R1cW_C, R1aW_C, R1cP_C, R1aP_C
o 到节点C：R1cW_C、R1aW_C、R1cP_C、R1aP_C
o To Node D: R1cW_D, R1aW_D, R1cP_D, R1aP_D
o 到节点D：R1cW\u D、R1aW\u D、R1cP\u D、R1aP\u D
o To Node E: R1cW_E, R1aW_E, R1cP_E, R1aP_E
o 到节点E:R1cW_E、R1aW_E、R1cP_E、R1aP_E
o To Node F: R1cW_F, R1aW_F, R1cP_F, R1aP_F
o 到节点F:R1cW\u F、R1aW\u F、R1cP\u F、R1aP\u F
o To the virtual interconnection node group (including Nodes F and A): R1cW_F&A, R1aW_F&A, R1cP_F&A, R1aP_F&A
o 至虚拟互连节点组（包括节点F和A）：R1cW_F&A、R1aW_F&A、R1cP_F&A、R1aP_F&A
All the ring tunnels on Ring2 in Figure 13 are provisioned as follows:
图13中Ring2上的所有环形隧道配置如下：
o To Node A: R2cW_A, R2aW_A, R2cP_A, R2aP_A
o 至节点A：R2cW_A、R2aW_A、R2cP_A、R2aP_A
o To Node F: R2cW_F, R2aW_F, R2cP_F, R2aP_F
o 到节点F:R2cW\u F、R2aW\u F、R2cP\u F、R2aP\u F
o To Node G: R2cW_G, R2aW_G, R2cP_G, R2aP_G
o 到节点G:R2cW_G、R2aW_G、R2cP_G、R2aP_G
o To Node H: R2cW_H, R2aW_H, R2cP_H, R2aP_H
o 到节点H:R2cW_H、R2aW_H、R2cP_H、R2aP_H
o To Node I: R2cW_I, R2aW_I, R2cP_I, R2aP_I
o 到节点I：R2cW_I、R2aW_I、R2cP_I、R2aP_I
o To Node J: R2cW_J, R2aW_J, R2cP_J, R2aP_J
o 到节点J：R2cW_J、R2aW_J、R2cP_J、R2aP_J
o To the virtual interconnection node group (including Nodes F and A): R2cW_F&A, R2aW_F&A, R2cP_F&A, R2aP_F&A
o 虚拟互连节点组（包括节点F和A）：R2cW_F&A、R2aW_F&A、R2cP_F&A、R2aP_F&A
+---+ccccccccccccc+---+
| H |-------------| I |--->LSP1
+---+ +---+
c/a a\
c/a a\
c/a a\
+---+ +---+
| G | Ring2 | J |
+---+ +---+
c\a a/c
c\a a/c
c\a aaaaaaaaaaaaa a/c
+---+ccccccccccccc+---+
| F |-------------| A |
+---+ccccccccccccc+---+
c/aaaaaaaaaaaaaaaaaaa a\
c/ a\
c/ a\
+---+ +---+
| E | Ring1 | B |
+---+ +---+
c\a a/c
c\a a/c
c\a a/c
+---+aaaaaaaaaaaaa+---+
LSP1--->| D |-------------| C |
+---+ccccccccccccc+---+
+---+ccccccccccccc+---+
| H |-------------| I |--->LSP1
+---+ +---+
c/a a\
c/a a\
c/a a\
+---+ +---+
| G | Ring2 | J |
+---+ +---+
c\a a/c
c\a a/c
c\a aaaaaaaaaaaaa a/c
+---+ccccccccccccc+---+
| F |-------------| A |
+---+ccccccccccccc+---+
c/aaaaaaaaaaaaaaaaaaa a\
c/ a\
c/ a\
+---+ +---+
| E | Ring1 | B |
+---+ +---+
c\a a/c
c\a a/c
c\a a/c
+---+aaaaaaaaaaaaa+---+
LSP1--->| D |-------------| C |
+---+ccccccccccccc+---+
Ring1: ccccccccccc R1cW_F&A aaaaaaaaaaa R1aP_F&A
环1:CCCCCCCCR1CW_F&A aaaaaaaaaaaaaaaaaaaaaaaP_F&A
Ring2: ccccccccccc R2cW_I aaaaaaaaaaa R2aP_I
环2:CCCCCCCCCR2CW_I aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaap_I
Figure 13: Ring Tunnels for the Interconnected Rings
图13：互连环的环形隧道
As shown in Figure 13, for the service LSP1 that enters Ring1 at Node D and leaves Ring1 at Node F and continues to enter Ring2 at Node F and leaves Ring2 at Node I, the short-wrapping protection scheme is described as below.
如图13所示，对于在节点D进入环1，在节点F离开环1，在节点F继续进入环2，在节点I离开环2的服务LSP1，短包装保护方案描述如下。
In normal state, LSP1 follows R1cW_F&A in Ring1 and R2cW_I in Ring2. At the interconnection Node F, the label used for the working ring tunnel R1cW_F&A in Ring1 is popped, the LSP label is swapped, and the label used for the working ring tunnel R2cW_I in Ring2 will be pushed based on the inner LSP label lookup. The working path that the service LSP1 follows is: LSP1->R1cW_F&A (D->E->F)->R2cW_I(F->G->H->I)->LSP1.
在正常状态下，LSP1在环1中跟随R1cW_F&A，在环2中跟随R2cW_I。在互连节点F，弹出环1中用于工作环隧道R1cW_F&A的标签，交换LSP标签，并根据内部LSP标签查找推送环2中用于工作环隧道R2cW_I的标签。服务LSP1遵循的工作路径是：LSP1->R1cW\u F&A（D->E->F）->R2cW\u I（F->G->H->I）->LSP1。
In case of link failure, for example, when a failure occurs on the link between Nodes F and E, Node E will detect the failure and execute protection switching as described in Section 4.3.2. The path that the service LSP1 follows after switching change to: LSP1->R1cW_F &A(D->E)->R1aP_F&A(E->D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1.
在链路故障的情况下，例如，当节点F和E之间的链路发生故障时，节点E将检测故障并执行第4.3.2节所述的保护切换。切换到以下位置后，服务LSP1遵循的路径：LSP1->R1cW\U F&A（D->E）->R1aP\U F&A（E->D->C->B->A）->R2cW\U I（A->F->G->H->I）->LSP1。
In case of a non-interconnection node failure, for example, when the failure occurs at Node E in Ring1, Node D will detect the failure and execute protection switching as described in Section 4.3.2. The path that the service LSP1 follows after switching becomes: LSP1->R1aP_F&A(D->C->B->A)->R2cW_I(A->F->G->H->I)->LSP1.
在非互连节点故障的情况下，例如，当故障发生在环1中的节点E时，节点D将检测故障并执行第4.3.2节所述的保护切换。切换后服务LSP1遵循的路径变为：LSP1->R1aP\U F&A（D->C->B->A）->R2cW\U I（A->F->G->H->I）->LSP1。
In case of an interconnection node failure, for example, when the failure occurs at the interconnection Node F, Node E in Ring1 will detect the failure and execute protection switching as described in Section 4.3.2. Node A in Ring2 will also detect the failure and execute protection switching as described in Section 4.3.2. The path that the service traffic LSP1 follows after switching is: LSP1->R1cW_F&A(D->E)->R1aP_F&A(E->D->C->B->A)->R2aP_I(A->J->I)->LSP1.
在互连节点故障的情况下，例如，当故障发生在互连节点F时，环1中的节点E将检测故障并执行第4.3.2节所述的保护切换。环2中的节点A还将检测故障，并按照第4.3.2节所述执行保护切换。业务流量LSP1切换后的路径为：LSP1->R1cW\U F&A（D->E）->R1aP\U F&A（E->D->C->B->A）->R2aP\U I（A->J->I）->LSP1。
As shown in Figure 13, in normal state, the service traffic LSP1 traverses D->E->F in Ring1 and F->G->H->I in Ring2. Nodes A and F are the interconnection nodes. When both links between Nodes F and G and between Nodes F and A fail, the ring tunnel from Node F to Node I in Ring2 becomes unreachable. However, the other interconnection Node A is still available, and LSP1 can still reach Node I via Node A.
如图13所示，在正常状态下，服务流量LSP1在环1中穿过D->E->F，在环2中穿过F->G->H->I。节点A和F是互连节点。当节点F和G之间以及节点F和A之间的链路都出现故障时，从节点F到Ring2中节点I的环形隧道将变得不可访问。然而，另一互连节点A仍然可用，并且LSP1仍然可以经由节点A到达节点I。
In order to achieve this, the interconnection nodes need to know the ring topology of each ring so that they can judge whether a node is reachable. This judgment is based on the knowledge of the ring map and the fault location. The ring map can be obtained from the Network Management System (NMS) or topology discovery mechanisms. The fault location can be obtained by transmitting the fault information around the ring. The nodes that detect the failure will transmit the fault information in the opposite direction hop by hop using the RPS protocol message. When the interconnection node receives the message that informs the failure, it will calculate the
为了实现这一点，互连节点需要知道每个环的环拓扑，以便能够判断节点是否可到达。该判断基于环形图和故障位置的知识。环映射可以从网络管理系统（NMS）或拓扑发现机制获得。通过在环周围传输故障信息，可以获得故障位置。检测到故障的节点将使用RPS协议消息以相反方向逐跳传输故障信息。当互连节点收到通知故障的消息时，它将计算
location of the fault according to the topology information that is maintained by itself and determines whether the LSPs entering the ring at itself can reach the destination. If the destination node is reachable, the LSP will leave the source ring and enter the destination ring. If the destination node is not reachable, the LSP will switch to the anticlockwise protection ring tunnel.
根据自身维护的拓扑信息确定故障位置，并确定在自身进入环的LSP是否能够到达目的地。如果目标节点是可到达的，LSP将离开源环并进入目标环。如果无法到达目标节点，LSP将切换到逆时针保护环隧道。
In Figure 13, Node F determines that the ring tunnel to Node I is unreachable; the service LSP1 for which the destination node on Ring2 is Node I MUST switch to the protection ring tunnel (R1aP_F&A), and consequently, the service traffic LSP1 traverses the interconnected rings at Node A. Node A will pop the ring tunnel label of Ring1 and push the ring tunnel label of Ring2 and send the traffic to Node I via the ring tunnel (R2aW_I).
在图13中，节点F确定到节点I的环形隧道不可到达；环2上的目标节点为节点I的服务LSP1必须切换到保护环隧道（R1aP_F&A），因此，服务流量LSP1在节点A处穿过互连环。节点A将弹出环1的环隧道标签，推送环2的环隧道标签，并通过环隧道将流量发送到节点I（R2aW_I）。
This section provides comparison between RPS and Protection State Coordination (PSC) [RFC6378] [RFC6974] on ring topologies. This can be helpful to explain the reason of defining a new protocol for ring protection switching.
本节对环形拓扑上的RPS和保护状态协调（PSC）[RFC6378][RFC6974]进行了比较。这有助于解释为环保护交换定义新协议的原因。
The PSC protocol [RFC6378] is designed for point-to-point LSPs, on which the protection switching can only be performed on one or both of the endpoints of the LSP. The RPS protocol is designed for ring tunnels, which consist of multiple ring nodes, and the failure could happen on any segment of the ring; thus, RPS is capable of identifying and handling the different failures on the ring and coordinating the protection-switching behavior of all the nodes on the ring. As will be specified in the following sections, this is achieved with the introduction of the "pass-through" state for the ring nodes, and the location of the protection request is identified via the node IDs in the RPS request message.
PSC协议[RFC6378]设计用于点对点LSP，在该LSP上，保护切换只能在LSP的一个或两个端点上执行。RPS协议是针对由多个环节点组成的环隧道而设计的，故障可能发生在环的任何一段上；因此，RPS能够识别和处理环上的不同故障，并协调环上所有节点的保护切换行为。如以下章节所述，这是通过引入环节点的“通过”状态来实现的，保护请求的位置通过RPS请求消息中的节点ID来识别。
Taking a ring topology with N nodes as an example:
以N个节点的环形拓扑为例：
With the mechanism specified in [RFC6974], on every ring node, a linear protection configuration has to be provisioned with every other node in the ring, i.e., with (N-1) other nodes. This means that on every ring node there will be (N-1) instances of the PSC protocol. And in order to detect faults and to transport the PSC message, each instance shall have a MEP on the working path and a MEP on the protection path, respectively. This means that every node on the ring needs to be configured with (N-1) * 2 MEPs.
根据[RFC6974]中规定的机制，在每个环节点上，必须为环中的每个其他节点（即（N-1）个其他节点）提供线性保护配置。这意味着在每个环节点上都会有（N-1）个PSC协议实例。为了检测故障和传输PSC消息，每个实例应分别在工作路径和保护路径上具有一个MEP。这意味着环上的每个节点都需要配置（N-1）*2个MEP。
With the mechanism defined in this document, on every ring node there will only be a single instance of the RPS protocol. In order to detect faults and to transport the RPS message, each node only needs to have a MEP on the section to its adjacent nodes, respectively. In this way, every ring node only needs to be configured with 2 MEPs.
根据本文档中定义的机制，在每个环节点上，只有一个RPS协议实例。为了检测故障和传输RPS消息，每个节点只需要在该段上分别有一个MEP到其相邻节点。这样，每个环节点只需要配置2个MEP。
As shown in the above example, RPS is designed for ring topologies and can achieve ring protection efficiently with minimum protection instances and OAM entities, which meets the requirements on topology-specific recovery mechanisms as specified in [RFC5654].
如上面的示例所示，RPS是为环形拓扑设计的，可以使用最少的保护实例和OAM实体高效地实现环形保护，这符合[RFC5654]中规定的拓扑特定恢复机制的要求。
The RPS protocol defined in this section is used to coordinate the protection-switching action of all the ring nodes in the same ring.
本节定义的RPS协议用于协调同一环中所有环节点的保护切换动作。
The protection operation of the ring tunnels is controlled with the help of the RPS protocol. The RPS processes in each of the individual ring nodes that form the ring MUST communicate using the Generic Associated Channel (G-ACh). The RPS protocol is applicable to all the three ring protection modes. This section takes the short-wrapping mechanism described in Section 4.3.2 as an example.
环形隧道的保护操作通过RPS协议进行控制。构成环的每个环节点中的RPS进程必须使用通用关联通道（G-ACh）进行通信。RPS协议适用于所有三种环保护模式。本节以第4.3.2节所述的短包装机制为例。
The RPS protocol is used to distribute the ring status information and RPS requests to all the ring nodes. Changes in the ring status information and RPS requests can be initiated automatically based on link status or caused by external commands.
RPS协议用于将环状态信息和RPS请求分发到所有环节点。环状态信息和RPS请求的更改可以根据链路状态自动启动，也可以由外部命令引起。
Each node on the ring is uniquely identified by assigning it a node ID. The node ID MUST be unique on each ring. The maximum number of nodes on the ring supported by the RPS protocol is 127. The node ID SHOULD be independent of the order in which the nodes appear on the ring. The node ID is used to identify the source and destination nodes of each RPS request.
环上的每个节点都通过为其分配节点ID进行唯一标识。每个环上的节点ID必须是唯一的。RPS协议支持的环上最大节点数为127。节点ID应独立于节点在环上的显示顺序。节点ID用于标识每个RPS请求的源节点和目标节点。
Every node obtains the ring topology either by configuration or via some topology discovery mechanism. The ring map consists of the ring topology information, and connectivity status (Intact or Severed) between the adjacent ring nodes, which is determined via the OAM message exchanged between the adjacent nodes. The ring map is used by every ring node to determine the switchover behavior of the ring tunnels.
每个节点通过配置或通过某种拓扑发现机制获得环形拓扑。环映射由环拓扑信息和相邻环节点之间的连接状态（完整或断开）组成，连接状态通过相邻节点之间交换的OAM消息确定。每个环节点都使用环映射来确定环隧道的切换行为。
As shown in Figure 14, when no protection switching is active on the ring, each node MUST send RPS requests with No Request (NR) to its two adjacent nodes periodically. The transmission interval of RPS requests is specified in Section 5.2.1.
如图14所示，当环上没有激活保护切换时，每个节点必须定期向其两个相邻节点发送不带请求（NR）的RPS请求。第5.2.1节规定了RPS请求的传输间隔。
+---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR)
-------| A |-------------| B |-------------| C |-------
(NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+
+---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR)
-------| A |-------------| B |-------------| C |-------
(NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+
Figure 14: RPS Communication between the Ring Nodes in Case of No Failure in the Ring
图14：环中无故障情况下环节点之间的RPS通信
As shown in Figure 15, when a node detects a failure and determines that protection switching is required, it MUST send the appropriate RPS request in both directions to the destination node. The destination node is the other node that is adjacent to the identified failure. When a node that is not the destination node receives an RPS request and it has no higher-priority local request, it MUST transfer in the same direction the RPS request as received. In this way, the switching nodes can maintain RPS protocol communication in the ring. The RPS request MUST be terminated by the destination node of the message. If an RPS request with the node itself set as the source node is received, this message MUST be dropped and not be forwarded to the next node.
如图15所示，当节点检测到故障并确定需要进行保护切换时，它必须在两个方向向目标节点发送适当的RPS请求。目标节点是与已识别故障相邻的另一个节点。当不是目标节点的节点接收到RPS请求并且没有更高优先级的本地请求时，它必须以与接收到的RPS请求相同的方向进行传输。通过这种方式，交换节点可以在环中维护RPS协议通信。RPS请求必须由消息的目标节点终止。如果接收到将节点本身设置为源节点的RPS请求，则必须删除此消息，而不是将其转发到下一个节点。
+---+ C->B(SF) +---+ B->C(SF) +---+ C->B(SF)
-------| A |-------------| B |----- X -----| C |-------
(SF)C<-B +---+ (SF)C<-B +---+ (SF)B<-C +---+
+---+ C->B(SF) +---+ B->C(SF) +---+ C->B(SF)
-------| A |-------------| B |----- X -----| C |-------
(SF)C<-B +---+ (SF)C<-B +---+ (SF)B<-C +---+
Figure 15: RPS Communication between the Ring Nodes in Case of Failure between Nodes B and C
图15：节点B和C之间发生故障时环形节点之间的RPS通信
Note that in the case of a bidirectional failure such as a cable cut, the two adjacent nodes detect the failure and send each other an RPS request in opposite directions.
请注意，在双向故障（如电缆切断）的情况下，两个相邻节点检测到故障并以相反方向相互发送RPS请求。
o In rings utilizing the wrapping protection, each node detects the failure or receives the RPS request as the destination node MUST perform the switch from/to the working ring tunnels to/from the protection ring tunnels if it has no higher-priority active RPS request.
o 在使用环绕保护的环中，每个节点检测到故障或接收到RPS请求，因为如果没有更高优先级的活动RPS请求，则目标节点必须执行从工作环隧道到保护环隧道的切换。
o In rings utilizing the short-wrapping protection, each node detects the failure or receives the RPS request as the destination node MUST perform the switch only from the working ring tunnels to the protection ring tunnels.
o 在使用短环绕保护的环中，每个节点检测故障或接收RPS请求，因为目标节点必须仅执行从工作环隧道到保护环隧道的切换。
o In rings utilizing the steering protection, when a ring switch is required, any node MUST perform the switches if its added/dropped traffic is affected by the failure. Determination of the affected traffic MUST be performed by examining the RPS requests (indicating the nodes adjacent to the failure or failures) and the stored ring map (indicating the relative position of the failure and the added traffic destined towards that failure).
o 在使用转向保护的环中，当需要环形开关时，如果其添加/丢弃的流量受到故障的影响，则任何节点都必须执行开关。必须通过检查RPS请求（指示与一个或多个故障相邻的节点）和存储的环映射（指示故障的相对位置和指向该故障的附加通信量）来确定受影响的通信量。
When the failure has cleared and the Wait-to-Restore (WTR) timer has expired, the nodes that generate the RPS requests MUST drop their respective switches and MUST generate an RPS request carrying the NR code. The node receiving such an RPS request from both directions MUST drop its protection switches.
当故障已清除且等待恢复（WTR）计时器已过期时，生成RPS请求的节点必须丢弃各自的交换机，并且必须生成带有NR代码的RPS请求。从两个方向接收此类RPS请求的节点必须断开其保护开关。
A protection switch MUST be initiated by one of the criteria specified in Section 5.3. A failure of the RPS protocol or controller MUST NOT trigger a protection switch.
保护开关必须按照第5.3节规定的标准之一启动。RPS协议或控制器故障不得触发保护开关。
Ring switches MUST be preempted by higher-priority RPS requests. For example, consider a protection switch that is active due to a manual switch request on the given link, and another protection switch is required due to a failure on another link. Then an RPS request MUST be generated, the former protection switch MUST be dropped, and the latter protection switch established.
环形交换机必须由更高优先级的RPS请求抢占。例如，考虑由于给定链路上的手动切换请求而激活的保护开关，并且由于另一链路上的故障而需要另一个保护开关。然后必须生成RPS请求，必须丢弃前一个保护开关，并建立后一个保护开关。
The MPLS-TP Shared-Ring Protection mechanism supports multiple protection switches in the ring, resulting in the ring being segmented into two or more separate segments. This may happen when several RPS requests of the same priority exist in the ring due to multiple failures or external switch commands.
MPLS-TP共享环保护机制支持环中的多个保护交换机，从而将环分割为两个或多个单独的段。由于多个故障或外部开关命令，当环中存在多个具有相同优先级的RPS请求时，可能会发生这种情况。
Proper operation of the MSRP mechanism relies on all nodes using their ring map to determine the state of the ring (nodes and links). In order to accommodate ring state knowledge, the RPS requests MUST be sent in both directions during a protection switch.
MSRP机制的正确运行依赖于所有节点使用其环映射来确定环的状态（节点和链路）。为了适应环状态知识，必须在保护切换期间向两个方向发送RPS请求。
A new RPS request MUST be transmitted immediately when a change in the transmitted status occurs.
当传输状态发生变化时，必须立即传输新的RPS请求。
The first three RPS protocol messages carrying a new RPS request MUST be transmitted as fast as possible. For fast protection switching within 50 ms, the interval of the first three RPS protocol messages SHOULD be 3.3 ms. The successive RPS requests SHOULD be transmitted with the interval of 5 seconds. A ring node that is not the destination of the received RPS message MUST forward it to the next node along the ring immediately.
携带新RPS请求的前三条RPS协议消息必须尽可能快地传输。对于50 ms内的快速保护切换，前三条RPS协议消息的间隔应为3.3 ms。连续的RPS请求应以5秒的间隔发送。不是接收到的RPS消息目的地的环节点必须立即将其转发到环上的下一个节点。
Figure 16 depicts the format of an RPS packet that is sent on the G-ACh. The Channel Type field is set to indicate that the message is an RPS message.
图16描述了在G-ACh上发送的RPS数据包的格式。通道类型字段设置为指示消息是RPS消息。
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|Version| Reserved | RPS Channel Type (0x002A) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dest Node ID | Src Node ID | Request | M | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|Version| Reserved | RPS Channel Type (0x002A) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dest Node ID | Src Node ID | Request | M | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: G-ACh RPS Packet Format
图16:G-ACh RPS数据包格式
The following fields MUST be provided:
必须提供以下字段：
o Destination Node ID: The destination node ID MUST always be set to the value of the node ID of the adjacent node. The node ID MUST be unique on each ring. Valid destination node ID values are 1-127.
o 目标节点ID：目标节点ID必须始终设置为相邻节点的节点ID值。每个环上的节点ID必须是唯一的。有效的目标节点ID值为1-127。
o Source Node ID: The source node ID MUST always be set to the ID value of the node generating the RPS request. The node ID MUST be unique on each ring. Valid source node ID values are 1-127.
o 源节点ID：源节点ID必须始终设置为生成RPS请求的节点的ID值。每个环上的节点ID必须是唯一的。有效的源节点ID值为1-127。
o Protection-Switching Mode (M): This 2-bit field indicates the protection-switching mode used by the sending node of the RPS message. This can be used to check that the ring nodes on the same ring use the same protection-switching mechanism. The defined values of the M field are listed as below:
o 保护切换模式（M）：此2位字段表示RPS消息的发送节点使用的保护切换模式。这可用于检查同一环上的环节点是否使用相同的保护切换机制。M字段的定义值如下所示：
+------------------+-----------------------------+
| Bits (MSB - LSB) | Protection-Switching Mode |
+------------------+-----------------------------+
| 0 0 | Reserved |
| 0 1 | Wrapping |
| 1 0 | Short-Wrapping |
| 1 1 | Steering |
+------------------+-----------------------------+
+------------------+-----------------------------+
| Bits (MSB - LSB) | Protection-Switching Mode |
+------------------+-----------------------------+
| 0 0 | Reserved |
| 0 1 | Wrapping |
| 1 0 | Short-Wrapping |
| 1 1 | Steering |
+------------------+-----------------------------+
Note: MSB = most significant bit LSB = least significant bit
注：MSB=最高有效位LSB=最低有效位
o RPS Request Code: A code consisting of 8 bits as specified below:
o RPS请求代码：由以下规定的8位组成的代码：
+------------------+-----------------------------+----------+
| Bits | Condition, State, | Priority |
| (MSB - LSB) | or External Request | |
+------------------+-----------------------------+----------+
| 0 0 0 0 1 1 1 1 | Lockout of Protection (LP) | highest |
| 0 0 0 0 1 1 0 1 | Forced Switch (FS) | |
| 0 0 0 0 1 0 1 1 | Signal Fail (SF) | |
| 0 0 0 0 0 1 1 0 | Manual Switch (MS) | |
| 0 0 0 0 0 1 0 1 | Wait-to-Restore (WTR) | |
| 0 0 0 0 0 0 1 1 | Exercise (EXER) | |
| 0 0 0 0 0 0 0 1 | Reverse Request (RR) | |
| 0 0 0 0 0 0 0 0 | No Request (NR) | lowest |
+------------------+-----------------------------+----------+
+------------------+-----------------------------+----------+
| Bits | Condition, State, | Priority |
| (MSB - LSB) | or External Request | |
+------------------+-----------------------------+----------+
| 0 0 0 0 1 1 1 1 | Lockout of Protection (LP) | highest |
| 0 0 0 0 1 1 0 1 | Forced Switch (FS) | |
| 0 0 0 0 1 0 1 1 | Signal Fail (SF) | |
| 0 0 0 0 0 1 1 0 | Manual Switch (MS) | |
| 0 0 0 0 0 1 0 1 | Wait-to-Restore (WTR) | |
| 0 0 0 0 0 0 1 1 | Exercise (EXER) | |
| 0 0 0 0 0 0 0 1 | Reverse Request (RR) | |
| 0 0 0 0 0 0 0 0 | No Request (NR) | lowest |
+------------------+-----------------------------+----------+
Idle state: A node is in the idle state when it has no RPS request and is sending and receiving an NR code to/from both directions.
空闲状态：当节点没有RPS请求并且正在向/从两个方向发送和接收NR代码时，节点处于空闲状态。
Switching state: A node not in the idle or pass-through states is in the switching state.
切换状态：不处于空闲或通过状态的节点处于切换状态。
Pass-through state: A node is in the pass-through state when its highest priority RPS request is a request not destined to it or generated by it. The pass-through is bidirectional.
通过状态：当节点的最高优先级RPS请求不是发送给它或由它生成的请求时，节点处于通过状态。通过是双向的。
A node in the idle state MUST generate the NR request in both directions.
处于空闲状态的节点必须在两个方向上生成NR请求。
A node in the idle state MUST terminate RPS requests that flow in both directions.
处于空闲状态的节点必须终止双向流动的RPS请求。
A node in the idle state MUST block the traffic flow on protection ring tunnels in both directions.
处于空闲状态的节点必须在两个方向阻断保护环隧道上的流量。
A node in the switching state MUST generate an RPS request to its adjacent node with its highest RPS request code in both directions when it detects a failure or receives an external command.
处于切换状态的节点在检测到故障或接收到外部命令时，必须向其相邻节点生成具有最高RPS请求代码的双向RPS请求。
In a bidirectional failure condition, both of the nodes adjacent to the failure detect the failure and send the RPS request in both directions with the destination set to each other; while each node can only receive the RPS request via the long path, the message sent via the short path will get lost due to the bidirectional failure. Here, the short path refers to the shorter path on the ring between the source and destination node of the RPS request, and the long path refers to the longer path on the ring between the source and destination node of the RPS request. Upon receipt of the RPS request on the long path, the destination node of the RPS request MUST send an RPS request with its highest request code periodically along the long path to the other node adjacent to the failure.
在双向故障条件下，与故障相邻的两个节点检测到故障并在两个方向上发送RPS请求，目的地彼此设置；虽然每个节点只能通过长路径接收RPS请求，但由于双向故障，通过短路径发送的消息将丢失。这里，短路径是指RPS请求的源节点和目标节点之间的环上的较短路径，长路径是指RPS请求的源节点和目标节点之间的环上的较长路径。在长路径上接收到RPS请求后，RPS请求的目标节点必须沿长路径周期性地向与故障相邻的另一个节点发送带有最高请求代码的RPS请求。
In a unidirectional failure condition, the node that detects the failure MUST send the RPS request in both directions with the destination node set to the other node adjacent to the failure. The destination node of the RPS request cannot detect the failure itself but will receive an RPS request from both the short path and the long path. The destination node MUST acknowledge the received RPS requests by replying with an RPS request with the RR code on the short path and an RPS request with the received RPS request code on the long path. Accordingly, when the node that detects the failure receives the RPS request with RR code on the short path, then the RPS request received from the same node along the long path SHOULD be ignored.
在单向故障条件下，检测到故障的节点必须在两个方向上发送RPS请求，并将目标节点设置为与故障相邻的另一个节点。RPS请求的目标节点本身无法检测到故障，但将从短路径和长路径接收RPS请求。目标节点必须通过在短路径上回复带有RR代码的RPS请求和在长路径上回复带有收到的RPS请求代码的RPS请求来确认收到的RPS请求。因此，当检测到故障的节点在短路径上接收到带有RR代码的RPS请求时，应忽略沿长路径从同一节点接收到的RPS请求。
A node in the switching state MUST terminate the received RPS requests in both directions and not forward it further along the ring.
处于切换状态的节点必须在两个方向上终止接收到的RPS请求，而不是沿着环进一步转发它。
The following switches as defined in Section 5.3.1 MUST be allowed to coexist:
必须允许第5.3.1节中定义的以下开关共存：
o LP and LP
o LP和LP
o FS and FS
o 财政司司长及财政司司长
o SF and SF
o SF和SF
o FS and SF
o 财政司司长及财政司司长
When multiple MS RPS requests exist at the same time addressing different links and there is no higher-priority request on the ring, no switch SHOULD be executed and existing switches MUST be dropped. The nodes MUST still signal an RPS request with the MS code.
当多个MS RPS请求同时存在，寻址不同的链路，并且环上没有更高优先级的请求时，不应执行任何交换机，并且必须丢弃现有交换机。节点仍必须使用MS代码发出RPS请求信号。
Multiple EXER requests MUST be allowed to coexist in the ring.
必须允许多个EXER请求在环中共存。
A node in a ring-switching state that receives the external command LP for the affected link MUST drop its switch and MUST signal NR for the locked link if there is no other RPS request on another link. The node still SHOULD signal a relevant RPS request for another link.
处于环路切换状态的节点接收受影响链路的外部命令LP时，必须断开其交换机，并且如果在另一链路上没有其他RPS请求，则必须发出锁定链路的NR信号。节点仍应发出另一链路的相关RPS请求信号。
When a node is in a pass-through state, it MUST transfer the received RPS request unchanged in the same direction.
当节点处于直通状态时，它必须以相同的方向传输接收到的RPS请求。
When a node is in a pass-through state, it MUST enable the traffic flow on protection ring tunnels in both directions.
当节点处于通过状态时，它必须在两个方向上启用保护环隧道上的流量。
All state transitions are triggered by an incoming RPS request change, a WTR expiration, an externally initiated command, or locally detected MPLS-TP section failure conditions.
所有状态转换都由传入的RPS请求更改、WTR过期、外部启动的命令或本地检测到的MPLS-TP段故障条件触发。
RPS requests due to a locally detected failure, an externally initiated command, or a received RPS request shall preempt existing RPS requests in the prioritized order given in Section 5.2.2, unless the requests are allowed to coexist.
由于本地检测到的故障、外部启动的命令或接收到的RPS请求引起的RPS请求应按照第5.2.2节给出的优先顺序抢占现有RPS请求，除非允许这些请求共存。
The transition from the idle state to pass-through state MUST be triggered by a valid RPS request change, in any direction, from the NR code to any other code, as long as the new request is not destined to the node itself. Both directions move then into a pass-through state, so that traffic entering the node through the protection ring tunnels are transferred transparently through the node.
从空闲状态到通过状态的转换必须由有效的RPS请求在任何方向上从NR代码更改为任何其他代码来触发，只要新请求不是以节点本身为目的地。然后，两个方向都进入直通状态，这样通过保护环隧道进入节点的流量就可以通过节点透明地传输。
A node MUST revert from pass-through state to the idle state when an RPS request with an NR code is received in both directions. Then both directions revert simultaneously from the pass-through state to the idle state.
当在两个方向上接收到带有NR代码的RPS请求时，节点必须从通过状态恢复到空闲状态。然后两个方向同时从通过状态恢复到空闲状态。
Transition of a node from the idle state to the switching state MUST be triggered by one of the following conditions:
节点从空闲状态到切换状态的转换必须由以下条件之一触发：
o A valid RPS request change from the NR code to any code received on either the long or the short path and is destined to this node
o 有效的RPS请求从NR代码更改为在长路径或短路径上接收的任何代码，并发送到此节点
o An externally initiated command for this node
o 此节点的外部启动命令
o The detection of an MPLS-TP section-layer failure at this node
o 在此节点检测MPLS-TP节层故障
Actions taken at a node in the idle state upon transition to the switching state are:
在节点过渡到切换状态时，在空闲状态下采取的措施包括：
o For all protection-switch requests, except EXER and LP, the node MUST execute the switch
o 对于所有保护开关请求（EXER和LP除外），节点必须执行开关
o For EXER, and LP, the node MUST signal the appropriate request but not execute the switch
o 对于EXER和LP，节点必须发出相应请求的信号，但不执行切换
In one of the following conditions, transition from the switching state to the idle state MUST be triggered:
在下列任一情况下，必须触发从开关状态到空闲状态的转换：
o On the node that triggers the protection switching, when the WTR time expires or an externally initiated command is cleared, the node MUST transit from switching state to Idle State and signal the NR code using RPS message in both directions.
o 在触发保护切换的节点上，当WTR时间到期或清除外部启动的命令时，节点必须从切换状态过渡到空闲状态，并在两个方向上使用RPS消息向NR代码发送信号。
o On the node that enters the switching state due to the received RPS request: upon reception of the NR code from both directions, the head-end node MUST drop its switch, transition to idle state, and signal the NR code in both directions.
o 在由于接收到RPS请求而进入切换状态的节点上：在接收到来自两个方向的NR代码后，前端节点必须放下其交换机，转换到空闲状态，并向两个方向的NR代码发送信号。
When a node that is currently executing any protection switch receives a higher-priority RPS request (due to a locally detected failure, an externally initiated command, or a ring protection switch request destined to it) for the same link, it MUST update the priority of the switch it is executing to the priority of the received RPS request.
当当前正在执行任何保护交换机的节点针对同一链路接收到更高优先级的RPS请求（由于本地检测到的故障、外部启动的命令或指向它的环形保护交换机请求），它必须将正在执行的交换机的优先级更新为接收到的RPS请求的优先级。
When a failure condition clears at a node, the node MUST enter WTR condition and remain in it for the appropriate time-out interval, unless:
当某个节点上的故障条件清除时，该节点必须进入WTR条件并在适当的超时间隔内保持该状态，除非：
o A different RPS request with a higher priority than WTR is received
o 接收到优先级高于WTR的不同RPS请求
o Another failure is detected
o 检测到另一个故障
o An externally initiated command becomes active
o 外部启动的命令变为活动状态
The node MUST send out a WTR code on both the long and short paths.
节点必须在长路径和短路径上发送WTR代码。
When a node that is executing a switch in response to an incoming SF RPS request (not due to a locally detected failure) receives a WTR code (unidirectional failure case), it MUST send out the RR code on the short path and the WTR on the long path.
当响应传入SF RPS请求（不是由于本地检测到的故障）而执行交换机的节点接收到WTR代码（单向故障情况）时，它必须在短路径上发送RR代码，在长路径上发送WTR。
When a node that is currently executing a switch receives an RPS request for a non-adjacent link of higher priority than the switch it is executing, it MUST drop its switch immediately and enter the pass-through state.
当当前正在执行交换机的节点收到RPS请求，请求非相邻链路的优先级高于其正在执行的交换机的优先级时，它必须立即放下其交换机并进入直通状态。
The transition of a node from pass-through to switching state MUST be triggered by:
节点从直通到切换状态的转换必须通过以下方式触发：
o An equal priority, a higher priority, or an allowed coexisting externally initiated command
o 同等优先级、更高优先级或允许共存的外部启动命令
o The detection of an equal priority, a higher priority, or an allowed coexisting automatic initiated command
o 检测到同等优先级、更高优先级或允许共存的自动启动命令
o The receipt of an equal, a higher priority, or an allowed coexisting RPS request destined to this node
o 接收到发送到此节点的同等、更高优先级或允许共存的RPS请求
Administrative commands can be initiated by the network operator through the Network Management System (NMS). The operator command may be transmitted to the appropriate node via the MPLS-TP RPS message.
网络运营商可通过网络管理系统（NMS）启动管理命令。操作员命令可以经由MPLS-TP RPS消息发送到适当的节点。
The following commands can be transferred by the RPS message:
以下命令可通过RPS消息传输：
o Lockout of Protection (LP): This command prevents any protection activity and prevents using ring switches anywhere in the ring. If any ring switches exist in the ring, this command causes the switches to drop.
o 锁定保护（LP）：此命令可防止任何保护活动，并防止在环中的任何位置使用环形开关。如果环中存在任何环开关，此命令将导致开关下降。
o Forced Switch (FS) to protection: This command performs the ring switch of normal traffic from the working entity to the protection entity for the link between the node at which the command is initiated and the adjacent node to which the command is directed. This switch occurs regardless of the state of the MPLS-TP section for the requested link, unless a higher-priority switch request exists.
o 强制切换（FS）到保护：该命令执行正常通信量从工作实体到保护实体的环形切换，用于启动命令的节点和命令指向的相邻节点之间的链路。除非存在更高优先级的切换请求，否则无论请求链路的MPLS-TP部分的状态如何，都会发生此切换。
o Manual Switch (MS) to protection: This command performs the ring switch of the normal traffic from the working entity to the protection entity for the link between the node at which the command is initiated and the adjacent node to which the command is directed. This occurs if the MPLS-TP section for the requested link is not satisfying an equal or higher priority switch request.
o 手动切换（MS）到保护：该命令执行正常通信量从工作实体到保护实体的环形切换，用于启动命令的节点和命令指向的相邻节点之间的链路。如果所请求链路的MPLS-TP部分不满足同等或更高优先级的交换请求，就会发生这种情况。
o Exercise (EXER): This command exercises ring protection switching on the addressed link without completing the actual switch. The command is issued and the responses (RRs) are checked, but no normal traffic is affected.
o 练习（EXER）：此命令在寻址链路上练习环形保护切换，而不完成实际切换。发出命令并检查响应（RRs），但不影响正常通信。
The following commands are not transferred by the RPS message:
以下命令不会通过RPS消息传输：
o Clear: This command clears the administrative command and WTR timer at the node to which the command was addressed. The node-to-node signaling after the removal of the externally initiated commands is performed using the NR code.
o 清除：此命令清除命令所发节点上的管理命令和WTR计时器。使用NR代码执行移除外部启动命令后的节点到节点信令。
o Lockout of Working (LW): This command prevents the normal traffic transported over the addressed link from being switched to the protection entity by disabling the node's capability of requesting a switch for this link in case of failure. If any normal traffic is already switched on the protection entity, the switch is dropped. If no other switch requests are active on the ring, the NR code is transmitted. This command has no impact on any other link. If the node receives the switch request from the adjacent node from any side, it will perform the requested switch. If the node receives the switch request addressed to the other node, it will enter the pass-through state.
o 锁定工作（LW）：该命令通过禁用节点在发生故障时请求切换该链路的能力，防止通过寻址链路传输的正常通信量切换到保护实体。如果已在保护实体上切换了任何正常通信量，则会断开该切换。如果环上没有其他激活的开关请求，则传输NR代码。此命令对任何其他链接没有影响。如果节点从任何一侧接收到来自相邻节点的切换请求，它将执行请求的切换。如果节点接收到发往另一个节点的交换机请求，它将进入直通状态。
Automatically initiated commands can be initiated based on MPLS-TP section-layer OAM indication and the received switch requests.
根据MPLS-TP段层OAM指示和接收到的交换机请求，可以启动自动启动的命令。
The node can initiate the following switch requests automatically:
节点可以自动启动以下交换机请求：
o Signal Fail (SF): This command is issued when the MPLS-TP section-layer OAM detects a signal failure condition.
o 信号故障（SF）：当MPLS-TP段层OAM检测到信号故障情况时，发出此命令。
o Wait-to-Restore (WTR): This command is issued when the MPLS-TP section detects that the SF condition has cleared. It is used to maintain the state during the WTR period unless it is preempted by a higher-priority switch request. The WTR time may be configured by the operator in 1 minute steps between 0 and 12 minutes; the default value is 5 minutes.
o 等待恢复（WTR）：当MPLS-TP部分检测到SF条件已清除时，发出此命令。它用于在WTR期间保持状态，除非它被更高优先级的切换请求抢占。WTR时间可由操作员在0到12分钟之间以1分钟的步长进行配置；默认值为5分钟。
o Reverse Request (RR): This command is transmitted to the source node of the received RPS message over the short path as an acknowledgment for receiving the switch request.
o 反向请求（RR）：此命令通过短路径传输到接收到的RPS消息的源节点，作为接收交换机请求的确认。
This section describes the possible states of a ring node, the corresponding action of the working and protection ring tunnels on the node, and the RPS request that should be generated in that state.
本节介绍环形节点的可能状态、节点上工作和保护环形隧道的相应操作，以及在该状态下应生成的RPS请求。
+-----------------------------------+----------------+
| State | Signaled RPS |
+-----------------------------------+----------------+
| A | Idle | NR |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| B | Pass-through | N/A |
| | Working: no switch | |
| | Protection: pass-through | |
+-----+-----------------------------+----------------+
| C | Switching - LP | LP |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| D | Idle - LW | NR |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| E | Switching - FS | FS |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| F | Switching - SF | SF |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| G | Switching - MS | MS |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| H | Switching - WTR | WTR |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| I | Switching - EXER | EXER |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
+-----------------------------------+----------------+
| State | Signaled RPS |
+-----------------------------------+----------------+
| A | Idle | NR |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| B | Pass-through | N/A |
| | Working: no switch | |
| | Protection: pass-through | |
+-----+-----------------------------+----------------+
| C | Switching - LP | LP |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| D | Idle - LW | NR |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| E | Switching - FS | FS |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| F | Switching - SF | SF |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| G | Switching - MS | MS |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| H | Switching - WTR | WTR |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| I | Switching - EXER | EXER |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
In the state description below, 'O' means that a new local request will be rejected because of an existing request.
在下面的状态描述中，“O”表示新的本地请求将因现有请求而被拒绝。
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP C (Switching - LP)
LW D (Idle - LW)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear N/A
WTR expires N/A
EXER I (Switching - EXER)
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-through) LP C (Switching - LP)
LW B (Pass-through)
FS O - if current state is due to
LP sent by another node
E (Switching - FS) - otherwise
SF O - if current state is due to
LP sent by another node
F (Switching - SF) - otherwise
Recover from SF N/A
MS O - if current state is due to
LP, SF, or FS sent by
another node
G (Switching - MS) - otherwise
Clear N/A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP C (Switching - LP)
LW D (Idle - LW)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear N/A
WTR expires N/A
EXER I (Switching - EXER)
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-through) LP C (Switching - LP)
LW B (Pass-through)
FS O - if current state is due to
LP sent by another node
E (Switching - FS) - otherwise
SF O - if current state is due to
LP sent by another node
F (Switching - SF) - otherwise
Recover from SF N/A
MS O - if current state is due to
LP, SF, or FS sent by
another node
G (Switching - MS) - otherwise
Clear N/A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP N/A
LW O
FS O
SF O
Recover from SF N/A
MS O
Clear A (Idle) - if there is no
failure in the ring
F (Switching - SF) - if there
is a failure at this node
B (Pass-through) - if there is
a failure at another node
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP)
LW N/A - if on the same link
D (Idle - LW) - if on another
link
FS O - if on the same link
E (Switching - FS) - if on
another link
SF O - if on the addressed link
F (Switching - SF) - if on
another link
Recover from SF N/A
MS O - if on the same link
G (Switching - MS) - if on
another link
Clear A (Idle) - if there is no
failure on addressed link
F (Switching - SF) - if there
is a failure on this link
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP N/A
LW O
FS O
SF O
Recover from SF N/A
MS O
Clear A (Idle) - if there is no
failure in the ring
F (Switching - SF) - if there
is a failure at this node
B (Pass-through) - if there is
a failure at another node
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP)
LW N/A - if on the same link
D (Idle - LW) - if on another
link
FS O - if on the same link
E (Switching - FS) - if on
another link
SF O - if on the addressed link
F (Switching - SF) - if on
another link
Recover from SF N/A
MS O - if on the same link
G (Switching - MS) - if on
another link
Clear A (Idle) - if there is no
failure on addressed link
F (Switching - SF) - if there
is a failure on this link
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP)
LW O - if on another link
D (Idle - LW) - if on the same
link
FS N/A - if on the same link
E (Switching - FS) - if on
another link
SF O - if on the addressed link
E (Switching - FS) - if on
another link
Recover from SF N/A
MS O
Clear A (Idle) - if there is no
failure in the ring
F (Switching - SF) - if there
is a failure at this node
B (Pass-through) - if there is
a failure at another node
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP)
LW O - if on another link
D (Idle - LW) - if on the same
link
FS E (Switching - FS)
SF N/A - if on the same link
F (Switching - SF) - if on
another link
Recover from SF H (Switching - WTR)
MS O
Clear N/A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP)
LW O - if on another link
D (Idle - LW) - if on the same
link
FS N/A - if on the same link
E (Switching - FS) - if on
another link
SF O - if on the addressed link
E (Switching - FS) - if on
another link
Recover from SF N/A
MS O
Clear A (Idle) - if there is no
failure in the ring
F (Switching - SF) - if there
is a failure at this node
B (Pass-through) - if there is
a failure at another node
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP)
LW O - if on another link
D (Idle - LW) - if on the same
link
FS E (Switching - FS)
SF N/A - if on the same link
F (Switching - SF) - if on
another link
Recover from SF H (Switching - WTR)
MS O
Clear N/A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP)
LW O - if on another link
D (Idle - LW) - if on the same
link
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS N/A - if on the same link
G (Switching - MS) - if on
another link, release the
switches but signal MS
Clear A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP)
LW D (Idle - W)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear A
WTR expires A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP)
LW D (Idle - W)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear A
WTR expires N/A
EXER N/A - if on the same link
I (Switching - EXER)
=====================================================================
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP)
LW O - if on another link
D (Idle - LW) - if on the same
link
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS N/A - if on the same link
G (Switching - MS) - if on
another link, release the
switches but signal MS
Clear A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP)
LW D (Idle - W)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear A
WTR expires A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP)
LW D (Idle - W)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear A
WTR expires N/A
EXER N/A - if on the same link
I (Switching - EXER)
=====================================================================
The priority of a remote request does not depend on the side from which the request is received.
远程请求的优先级不取决于从哪一方接收请求。
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR A (Idle)
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-through) LP C (Switching - LP)
FS N/A - cannot happen when there
is an LP request in the
ring
E (Switching - FS) - otherwise
SF N/A - cannot happen when there
is an LP request in the
ring
F (Switching - SF) - otherwise
MS N/A - cannot happen when there
is an LP, FS, or SF
request in the ring
G (Switching - MS) - otherwise
WTR N/A - cannot happen when there
is an LP, FS, SF, or MS
request in the ring
EXER N/A - cannot happen when there
is an LP, FS, SF, MS, or
a WTR request in the
ring
I (Switching - EXER) -
otherwise
RR N/A
NR A (Idle) - if received from
both sides
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR A (Idle)
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-through) LP C (Switching - LP)
FS N/A - cannot happen when there
is an LP request in the
ring
E (Switching - FS) - otherwise
SF N/A - cannot happen when there
is an LP request in the
ring
F (Switching - SF) - otherwise
MS N/A - cannot happen when there
is an LP, FS, or SF
request in the ring
G (Switching - MS) - otherwise
WTR N/A - cannot happen when there
is an LP, FS, SF, or MS
request in the ring
EXER N/A - cannot happen when there
is an LP, FS, SF, MS, or
a WTR request in the
ring
I (Switching - EXER) -
otherwise
RR N/A
NR A (Idle) - if received from
both sides
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP C (Switching - LP)
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP C (Switching - LP)
FS N/A - cannot happen when there
is an LP request in the
ring
SF N/A - cannot happen when there
is an LP request in the
ring
MS N/A - cannot happen when there
is an LP request in the
ring
WTR N/A
EXER N/A - cannot happen when there
is an LP request in the
ring
RR C (Switching - LP)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR D (Idle - LW)
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP)
FS E (Switching - FS)
SF E (Switching - FS)
MS N/A - cannot happen when there
is an FS request in the
ring
WTR N/A
EXER N/A - cannot happen when there
is an FS request in the
ring
RR E (Switching - FS)
NR N/A
FS N/A - cannot happen when there
is an LP request in the
ring
SF N/A - cannot happen when there
is an LP request in the
ring
MS N/A - cannot happen when there
is an LP request in the
ring
WTR N/A
EXER N/A - cannot happen when there
is an LP request in the
ring
RR C (Switching - LP)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR D (Idle - LW)
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP)
FS E (Switching - FS)
SF E (Switching - FS)
MS N/A - cannot happen when there
is an FS request in the
ring
WTR N/A
EXER N/A - cannot happen when there
is an FS request in the
ring
RR E (Switching - FS)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP)
FS F (Switching - SF)
SF F (Switching - SF)
MS N/A - cannot happen when there
is an SF request in the
ring
WTR N/A
EXER N/A - cannot happen when there
is an SF request in the
ring
RR F (Switching - SF)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS) - release
the switches but signal MS
WTR N/A
EXER N/A - cannot happen when there
is an MS request in the
ring
RR G (Switching - MS)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR H (Switching - WTR)
EXER N/A - cannot happen when there
is a WTR request in the
ring
RR H (Switching - WTR)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP)
FS F (Switching - SF)
SF F (Switching - SF)
MS N/A - cannot happen when there
is an SF request in the
ring
WTR N/A
EXER N/A - cannot happen when there
is an SF request in the
ring
RR F (Switching - SF)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS) - release
the switches but signal MS
WTR N/A
EXER N/A - cannot happen when there
is an MS request in the
ring
RR G (Switching - MS)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR H (Switching - WTR)
EXER N/A - cannot happen when there
is a WTR request in the
ring
RR H (Switching - WTR)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR I (Switching - EXER)
NR N/A
=====================================================================
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR I (Switching - EXER)
NR N/A
=====================================================================
5.3.5. State Transitions When Request Addresses to Another Node is Received
5.3.5. 收到到另一个节点的请求地址时状态转换
The priority of a remote request does not depend on the side from which the request is received.
远程请求的优先级不取决于从哪一方接收请求。
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR B (Pass-through)
EXER B (Pass-through)
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR B (Pass-through)
EXER B (Pass-through)
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-through) LP B (Pass-through)
FS N/A - cannot happen when there
is an LP request in the
ring
B (Pass-through) - otherwise
SF N/A - cannot happen when there
is an LP request in the
ring
B (Pass-through) - otherwise
MS N/A - cannot happen when there
is an LP, FS, or SF
request in the ring
B (Pass-through) - otherwise
WTR N/A - cannot happen when there
is an LP, FS, SF, or MS
request in the ring
B (Pass-through) - otherwise
EXER N/A - cannot happen when there
is an LP, FS, SF, MS, or
a WTR request in the
ring
B (Pass-through) - otherwise
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP C (Switching - LP)
FS N/A - cannot happen when there
is an LP request in the
ring
SF N/A - cannot happen when there
is an LP request in the
ring
MS N/A - cannot happen when there
is an LP request in the
ring
WTR N/A - cannot happen when there
is an LP request in the
ring
EXER N/A - cannot happen when there
is an LP request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-through) LP B (Pass-through)
FS N/A - cannot happen when there
is an LP request in the
ring
B (Pass-through) - otherwise
SF N/A - cannot happen when there
is an LP request in the
ring
B (Pass-through) - otherwise
MS N/A - cannot happen when there
is an LP, FS, or SF
request in the ring
B (Pass-through) - otherwise
WTR N/A - cannot happen when there
is an LP, FS, SF, or MS
request in the ring
B (Pass-through) - otherwise
EXER N/A - cannot happen when there
is an LP, FS, SF, MS, or
a WTR request in the
ring
B (Pass-through) - otherwise
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP C (Switching - LP)
FS N/A - cannot happen when there
is an LP request in the
ring
SF N/A - cannot happen when there
is an LP request in the
ring
MS N/A - cannot happen when there
is an LP request in the
ring
WTR N/A - cannot happen when there
is an LP request in the
ring
EXER N/A - cannot happen when there
is an LP request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR B (Pass-through)
EXER B (Pass-through)
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP B (Pass-through)
FS E (Switching - FS)
SF E (Switching - FS)
MS N/A - cannot happen when there
is an FS request in the
ring
WTR N/A - cannot happen when there
is an FS request in the
ring
EXER N/A - cannot happen when there
is an FS request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP B (Pass-through)
FS F (Switching - SF)
SF F (Switching - SF)
MS N/A - cannot happen when there
is an SF request in the
ring
WTR N/A - cannot happen when there
is an SF request in the
ring
EXER N/A - cannot happen when there
is an SF request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR B (Pass-through)
EXER B (Pass-through)
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP B (Pass-through)
FS E (Switching - FS)
SF E (Switching - FS)
MS N/A - cannot happen when there
is an FS request in the
ring
WTR N/A - cannot happen when there
is an FS request in the
ring
EXER N/A - cannot happen when there
is an FS request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP B (Pass-through)
FS F (Switching - SF)
SF F (Switching - SF)
MS N/A - cannot happen when there
is an SF request in the
ring
WTR N/A - cannot happen when there
is an SF request in the
ring
EXER N/A - cannot happen when there
is an SF request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS G (Switching - MS) - release
the switches but signal MS
WTR N/A - cannot happen when there
is an MS request in the
ring
EXER N/A - cannot happen when there
is an MS request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR N/A
EXER N/A - cannot happen when there
is a WTR request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR N/A
=====================================================================
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS G (Switching - MS) - release
the switches but signal MS
WTR N/A - cannot happen when there
is an MS request in the
ring
EXER N/A - cannot happen when there
is an MS request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR N/A
EXER N/A - cannot happen when there
is a WTR request in the
ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP B (Pass-through)
FS B (Pass-through)
SF B (Pass-through)
MS B (Pass-through)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR N/A
=====================================================================
IANA has assigned the values listed in the sections below.
IANA已分配以下各节中列出的值。
The Channel Types for G-ACh are allocated from the PW Associated Channel Type registry defined in [RFC4446] and updated by [RFC5586].
G-ACh的信道类型从[RFC4446]中定义的PW关联信道类型注册表中分配，并由[RFC5586]更新。
IANA has allocated the following new G-ACh Channel Type in the "MPLS Generalized Associated Channel (G-ACh) Types (including Pseudowire Associated Channel Types)" registry:
IANA已在“MPLS通用关联信道（G-ACh）类型（包括伪线关联信道类型）”注册表中分配了以下新的G-ACh信道类型：
Value | Description | Reference
-------+---------------------------------+--------------
0x002A | Ring Protection Switching (RPS) | this document
| Protocol |
-------+---------------------------------+--------------
Value | Description | Reference
-------+---------------------------------+--------------
0x002A | Ring Protection Switching (RPS) | this document
| Protocol |
-------+---------------------------------+--------------
IANA has created the subregistry "MPLS RPS Request Code Registry" under the "Generic Associated Channel (G-ACh) Parameters" registry. All code points within this registry shall be allocated according to the "Specification Required" procedure as specified in [RFC8126].
IANA在“通用关联通道（G-ACh）参数”注册表下创建了子区“MPLS RPS请求代码注册表”。应根据[RFC8126]中规定的“所需规范”程序分配该注册表中的所有代码点。
The RPS request field is 8 bits; the allocated values are as follows:
RPS请求字段为8位；分配的值如下所示：
Value Description Reference
------- --------------------------- -------------
0 No Request (NR) this document
1 Reverse Request (RR) this document
2 Unassigned
3 Exercise (EXER) this document
4 Unassigned
5 Wait-to-Restore (WTR) this document
6 Manual Switch (MS) this document
7-10 Unassigned
11 Signal Fail (SF) this document
12 Unassigned
13 Forced Switch (FS) this document
14 Unassigned
15 Lockout of Protection (LP) this document
16-254 Unassigned
255 Reserved
Value Description Reference
------- --------------------------- -------------
0 No Request (NR) this document
1 Reverse Request (RR) this document
2 Unassigned
3 Exercise (EXER) this document
4 Unassigned
5 Wait-to-Restore (WTR) this document
6 Manual Switch (MS) this document
7-10 Unassigned
11 Signal Fail (SF) this document
12 Unassigned
13 Forced Switch (FS) this document
14 Unassigned
15 Lockout of Protection (LP) this document
16-254 Unassigned
255 Reserved
This document describes three protection modes of the RPS protocol. Operators could choose the appropriate protection mode according to their network and service requirement.
本文档描述了RPS协议的三种保护模式。运营商可根据其网络和服务要求选择适当的保护模式。
Wrapping mode provides a ring protection mechanism in which the protected traffic will reach every node of the ring and is applicable to protect both the point-to-point LSPs and LSPs that need to be dropped in several ring nodes, i.e., the point-to-multipoint applications. When protection is inactive, the protected traffic is switched (wrapped) to/from the protection ring tunnel at both sides of the defective link/node. Due to the wrapping, the additional propagation delay and bandwidth consumption of the protection tunnel are considerable. For bidirectional LSPs, the protected traffic in both directions is co-routed.
包装模式提供了一种环保护机制，在该机制中，受保护的流量将到达环的每个节点，并适用于保护需要在多个环节点（即点对多点应用程序）中丢弃的点对点LSP和LSP。当保护处于非活动状态时，受保护的通信量在有缺陷链路/节点两侧的保护环隧道之间切换（打包）。由于缠绕，保护隧道的额外传播延迟和带宽消耗相当大。对于双向LSP，两个方向上受保护的流量是共同路由的。
Short-wrapping mode provides a ring protection mechanism that can be used to protect only point-to-point LSPs. When protection is inactive, the protected traffic is wrapped to the protection ring tunnel at the defective link/node and leaves the ring when the protection ring tunnel reaches the egress node. Compared with the wrapping mode, short-wrapping can reduce the propagation latency and bandwidth consumption of the protection tunnel. However, the two directions of a protected bidirectional LSP are not totally co-routed.
短包装模式提供了一种环保护机制，可用于仅保护点对点LSP。当保护处于非活动状态时，受保护的通信量被包装到缺陷链路/节点处的保护环隧道，并在保护环隧道到达出口节点时离开环。与包裹模式相比，短包裹可以减少保护隧道的传播延迟和带宽消耗。然而，受保护的双向LSP的两个方向不是完全共同路由的。
Steering mode provides a ring protection mechanism that can be used to protect only point-to-point LSPs. When protection is inactive, the protected traffic is switched to the protection ring tunnel at the ingress node and leaves the ring when the protection ring tunnel reaches the egress node. The steering mode has the least propagation delay and bandwidth consumption of the three modes, and the two directions of a protected bidirectional LSP can be kept co-routed.
转向模式提供了一种环形保护机制，可用于仅保护点对点LSP。当保护处于非活动状态时，受保护的流量切换到入口节点的保护环隧道，并在保护环隧道到达出口节点时离开环。转向模式具有三种模式中最小的传播延迟和带宽消耗，并且受保护的双向LSP的两个方向可以保持共路由。
Note that only one protection mode can be provisioned in the whole ring for all protected traffic.
请注意，对于所有受保护的流量，整个环中只能提供一种保护模式。
MPLS-TP is a subset of MPLS, thus it builds upon many of the aspects of the security model of MPLS. Please refer to [RFC5920] for generic MPLS security issues and methods for securing traffic privacy and integrity.
MPLS-TP是MPLS的一个子集，因此它建立在MPLS安全模型的许多方面之上。请参考[RFC5920]了解通用MPLS安全问题以及保护流量隐私和完整性的方法。
The RPS message defined in this document is used for protection coordination on the ring; if it is injected or modified by an attacker, the ring nodes might not agree on the protection action,
本文件中定义的RPS消息用于环上的保护协调；如果它被攻击者注入或修改，则环节点可能不同意保护操作，
and the improper protection-switching action may cause a temporary break to services traversing the ring. It is important that the RPS message is used within a trusted MPLS-TP network domain as described in [RFC6941].
不正确的保护切换动作可能会导致穿越环的服务暂时中断。如[RFC6941]所述，在可信MPLS-TP网络域内使用RPS消息非常重要。
The RPS message is carried in the G-ACh [RFC5586], so it 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 on the security mechanisms provided for the Associated Channel as described in those two documents.
RPS消息在G-ACh[RFC5586]中传输，因此它取决于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，本文档依赖于为相关通道提供的安全机制，如这两个文档中所述。
As described in the security considerations of [RFC6378], the G-ACh is essentially connection oriented, so injection or modification of control messages requires the subversion of a transit node. Such subversion is generally considered hard in connection-oriented MPLS networks and impossible to protect against at the protocol level. Management-level techniques are more appropriate. The procedures and protocol extensions defined in this document do not affect the security model of MPLS-TP linear protection as defined in [RFC6378].
如[RFC6378]的安全注意事项所述，G-ACh本质上是面向连接的，因此控制消息的注入或修改需要对传输节点进行颠覆。在面向连接的MPLS网络中，这种颠覆通常被认为是很难实现的，并且不可能在协议级别进行保护。管理层技术更合适。本文件中定义的程序和协议扩展不影响[RFC6378]中定义的MPLS-TP线性保护的安全模型。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://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<https://www.rfc-editor.org/info/rfc2119>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, <https://www.rfc-editor.org/info/rfc3031>.
[RFC3031]Rosen，E.，Viswanathan，A.，和R.Callon，“多协议标签交换体系结构”，RFC 3031，DOI 10.17487/RFC3031，2001年1月<https://www.rfc-editor.org/info/rfc3031>.
[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, DOI 10.17487/RFC4385, February 2006, <https://www.rfc-editor.org/info/rfc4385>.
[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 4385，DOI 10.17487/RFC4385，2006年2月<https://www.rfc-editor.org/info/rfc4385>.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, DOI 10.17487/RFC4446, April 2006, <https://www.rfc-editor.org/info/rfc4446>.
[RFC4446]Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，DOI 10.17487/RFC4446，2006年4月<https://www.rfc-editor.org/info/rfc4446>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, June 2009, <https://www.rfc-editor.org/info/rfc5586>.
[RFC5586]Bocci，M.，Ed.，Vigoureux，M.，Ed.，和S.Bryant，Ed.，“MPLS通用关联信道”，RFC 5586，DOI 10.17487/RFC55862009年6月<https://www.rfc-editor.org/info/rfc5586>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed., Sprecher, N., and S. Ueno, "Requirements of an MPLS Transport Profile", RFC 5654, DOI 10.17487/RFC5654, September 2009, <https://www.rfc-editor.org/info/rfc5654>.
[RFC5654]Niven Jenkins，B.，Ed.，Brungard，D.，Ed.，Betts，M.，Ed.，Sprecher，N.，和S.Ueno，“MPLS传输配置文件的要求”，RFC 5654，DOI 10.17487/RFC5654，2009年9月<https://www.rfc-editor.org/info/rfc5654>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8174]Leiba，B.，“RFC 2119关键词中大写与小写的歧义”，BCP 14，RFC 8174，DOI 10.17487/RFC8174，2017年5月<https://www.rfc-editor.org/info/rfc8174>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010, <https://www.rfc-editor.org/info/rfc5920>.
[RFC5920]方，L.，编辑，“MPLS和GMPLS网络的安全框架”，RFC 5920，DOI 10.17487/RFC5920，2010年7月<https://www.rfc-editor.org/info/rfc5920>.
[RFC6371] Busi, I., Ed. and D. Allan, Ed., "Operations, Administration, and Maintenance Framework for MPLS-Based Transport Networks", RFC 6371, DOI 10.17487/RFC6371, September 2011, <https://www.rfc-editor.org/info/rfc6371>.
[RFC6371]Busi，I.，Ed.和D.Allan，Ed.，“基于MPLS的传输网络的运营、管理和维护框架”，RFC 6371，DOI 10.17487/RFC63711911年9月<https://www.rfc-editor.org/info/rfc6371>.
[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, <https://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<https://www.rfc-editor.org/info/rfc6378>.
[RFC6941] Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed., and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP) Security Framework", RFC 6941, DOI 10.17487/RFC6941, April 2013, <https://www.rfc-editor.org/info/rfc6941>.
[RFC6941]Fang，L.，Ed.，Niven Jenkins，B.，Ed.，Mansfield，S.，Ed.，和R.Graveman，Ed.，“MPLS传输配置文件（MPLS-TP）安全框架”，RFC 6941，DOI 10.17487/RFC69411913年4月<https://www.rfc-editor.org/info/rfc6941>.
[RFC6974] Weingarten, Y., Bryant, S., Ceccarelli, D., Caviglia, D., Fondelli, F., Corsi, M., Wu, B., and X. Dai, "Applicability of MPLS Transport Profile for Ring Topologies", RFC 6974, DOI 10.17487/RFC6974, July 2013, <https://www.rfc-editor.org/info/rfc6974>.
[RFC6974]Weingarten，Y.，Bryant，S.，Ceccarelli，D.，Caviglia，D.，Fondelli，F.，Corsi，M.，Wu，B.，和X.Dai，“环拓扑MPLS传输配置文件的适用性”，RFC 6974，DOI 10.17487/RFC6974，2013年7月<https://www.rfc-editor.org/info/rfc6974>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.
[RFC8126]Cotton，M.，Leiba，B.，和T.Narten，“在RFC中编写IANA考虑事项部分的指南”，BCP 26，RFC 8126，DOI 10.17487/RFC8126，2017年6月<https://www.rfc-editor.org/info/rfc8126>.
Acknowledgements
致谢
The authors would like to thank Gregory Mirsky, Yimin Shen, Eric Osborne, Spencer Jackson, and Eric Gray for their valuable comments and suggestions.
作者要感谢Gregory Mirsky、沈一民、Eric Osborne、Spencer Jackson和Eric Gray提出的宝贵意见和建议。
Contributors
贡献者
The following people contributed significantly to the content of this document and should be considered co-authors:
以下人员对本文件的内容做出了重大贡献，应被视为共同作者：
Kai Liu Huawei Technologies Email: alex.liukai@huawei.com
刘凯华为技术电子邮件：alex。liukai@huawei.com
Jia He Huawei Technologies Email: hejia@huawei.com
嘉和华为技术电子邮件：hejia@huawei.com
Fang Li China Academy of Telecommunication Research MIIT China Email: lifang@catr.cn
方力中国电信研究院工信部中国电子邮件：lifang@catr.cn
Jian Yang ZTE Corporation China Email: yang.jian90@zte.com.cn
建阳中兴通讯中国有限公司电子邮件：杨。jian90@zte.com.cn
Junfang Wang Fiberhome Telecommunication Technologies Co., LTD. Email: wjf@fiberhome.com.cn
王俊芳光纤家庭通信技术有限公司电子邮件：wjf@fiberhome.com.cn
Wen Ye China Mobile Email: yewen@chinamobile.com
文烨中国移动邮箱：yewen@chinamobile.com
Minxue Wang China Mobile Email: wangminxue@chinamobile.com
王敏雪中国移动邮箱：wangminxue@chinamobile.com
Sheng Liu China Mobile Email: liusheng@chinamobile.com
刘晟中国移动电子邮件：liusheng@chinamobile.com
Guanghui Sun Huawei Technologies Email: sunguanghui@huawei.com
广汇阳光华为技术电子邮件：sunguanghui@huawei.com
Authors' Addresses
作者地址
Weiqiang Cheng China Mobile
程伟强中国移动
Email: chengweiqiang@chinamobile.com
Email: chengweiqiang@chinamobile.com
Lei Wang China Mobile
王磊中国移动
Email: wangleiyj@chinamobile.com
Email: wangleiyj@chinamobile.com
Han Li China Mobile
韩丽中国移动
Email: lihan@chinamobile.com
Email: lihan@chinamobile.com
Huub van Helvoort Hai Gaoming BV
Huub van Helvoort Hai Gaoming BV
Email: huubatwork@gmail.com
Email: huubatwork@gmail.com
Jie Dong Huawei Technologies
杰东华为技术有限公司
Email: jie.dong@huawei.com
Email: jie.dong@huawei.com