Internet Engineering Task Force (IETF) D. Frost, Ed.
Request for Comments: 5960 S. Bryant, Ed.
Category: Standards Track Cisco Systems
ISSN: 2070-1721 M. Bocci, Ed.
Alcatel-Lucent
August 2010
Internet Engineering Task Force (IETF) D. Frost, Ed.
Request for Comments: 5960 S. Bryant, Ed.
Category: Standards Track Cisco Systems
ISSN: 2070-1721 M. Bocci, Ed.
Alcatel-Lucent
August 2010
MPLS Transport Profile Data Plane Architecture
MPLS传输配置文件数据平面体系结构
Abstract
摘要
The Multiprotocol Label Switching Transport Profile (MPLS-TP) is the set of MPLS protocol functions applicable to the construction and operation of packet-switched transport networks. This document specifies the subset of these functions that comprises the MPLS-TP data plane: the architectural layer concerned with the encapsulation and forwarding of packets within an MPLS-TP network.
多协议标签交换传输配置文件（MPLS-TP）是一组MPLS协议功能，适用于分组交换传输网络的构建和运行。本文件规定了构成MPLS-TP数据平面的这些功能的子集：与MPLS-TP网络内数据包的封装和转发有关的体系结构层。
This document is a product of a joint Internet Engineering Task Force (IETF) / International Telecommunication Union Telecommunication Standardization Sector (ITU-T) effort to include an MPLS Transport Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge (PWE3) architectures to support the capabilities and functionalities of a packet transport network.
本文件是联合互联网工程任务组（IETF）/国际电信联盟电信标准化部门（ITU-T）努力的成果，旨在将MPLS传输配置文件纳入IETF MPLS和伪线仿真边到边（PWE3）中支持分组传输网络的能力和功能的体系结构。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5960.
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/rfc5960.
Copyright Notice
版权公告
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2010 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. MPLS-TP Packet Encapsulation and Forwarding . . . . . . . . . 4
3. MPLS-TP Transport Entities . . . . . . . . . . . . . . . . . . 5
3.1. Label Switched Paths . . . . . . . . . . . . . . . . . . . 5
3.1.1. LSP Packet Encapsulation and Forwarding . . . . . . . 6
3.1.2. LSP Payloads . . . . . . . . . . . . . . . . . . . . . 7
3.1.3. LSP Types . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Sections . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Pseudowires . . . . . . . . . . . . . . . . . . . . . . . 9
4. MPLS-TP Generic Associated Channel . . . . . . . . . . . . . . 10
5. Server-Layer Considerations . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 14
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. MPLS-TP Packet Encapsulation and Forwarding . . . . . . . . . 4
3. MPLS-TP Transport Entities . . . . . . . . . . . . . . . . . . 5
3.1. Label Switched Paths . . . . . . . . . . . . . . . . . . . 5
3.1.1. LSP Packet Encapsulation and Forwarding . . . . . . . 6
3.1.2. LSP Payloads . . . . . . . . . . . . . . . . . . . . . 7
3.1.3. LSP Types . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Sections . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Pseudowires . . . . . . . . . . . . . . . . . . . . . . . 9
4. MPLS-TP Generic Associated Channel . . . . . . . . . . . . . . 10
5. Server-Layer Considerations . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 14
The MPLS Transport Profile (MPLS-TP) is the set of functions that meet the requirements [RFC5654] for the application of MPLS to the construction and operation of packet-switched transport networks. MPLS-based packet-switched transport networks, and the overall architecture of the MPLS-TP, are defined and described in [RFC5921]. It is assumed that the reader is familiar with that document.
MPLS传输配置文件（MPLS-TP）是一组满足[RFC5654]要求的功能，用于将MPLS应用于分组交换传输网络的构建和运行。[RFC5921]中定义并描述了基于MPLS的分组交换传输网络以及MPLS-TP的总体架构。假定读者熟悉该文档。
This document defines the set of functions that comprise the MPLS-TP data plane: the architectural layer concerned with the encapsulation and forwarding of packets within an MPLS-TP network. This layer is based on the data plane architectures for MPLS ([RFC3031] and [RFC3032]) and for pseudowires [RFC3985].
本文档定义了组成MPLS-TP数据平面的一组功能：与MPLS-TP网络内数据包的封装和转发相关的体系结构层。该层基于MPLS（[RFC3031]和[RFC3032]）和伪线[RFC3985]的数据平面架构。
This document is a product of a joint Internet Engineering Task Force (IETF) / International Telecommunication Union Telecommunication Standardization Sector (ITU-T) effort to include an MPLS Transport Profile within the IETF MPLS and PWE3 architectures to support the capabilities and functionalities of a packet transport network.
本文件是联合互联网工程任务组（IETF）/国际电信联盟电信标准化部门（ITU-T）努力的成果，旨在将MPLS传输配置文件纳入IETF MPLS和PWE3体系结构中，以支持分组传输网络的能力和功能。
This document has the following purposes:
本文件具有以下目的：
o To identify the data plane functions within the MPLS Transport Profile; and
o 识别MPLS传输简档内的数据平面功能；和
o To indicate which of these data plane functions an MPLS-TP implementation is required to support.
o 指示MPLS-TP实现需要支持哪些数据平面功能。
This document defines the encapsulation and forwarding functions applicable to packets traversing an MPLS-TP Label Switched Path (LSP), pseudowire (PW), or section (see Section 3 for the definitions of these transport entities). Encapsulation and forwarding functions for packets outside an MPLS-TP LSP, PW, or section, and mechanisms for delivering packets to or from MPLS-TP LSPs, PWs, and sections, are outside the scope of this document.
本文档定义了适用于穿过MPLS-TP标签交换路径（LSP）、伪线（PW）或区段的数据包的封装和转发功能（这些传输实体的定义见第3节）。MPLS-TP LSP、PW或部分外部数据包的封装和转发功能，以及向MPLS-TP LSP、PWs或部分传递数据包或从MPLS-TP LSP、PWs和部分传递数据包的机制，不在本文档的范围内。
Term Definition
------- -------------------------------------------
ACH Associated Channel Header
G-ACh Generic Associated Channel
GAL G-ACh Label
LER Label Edge Router
LSE Label Stack Entry
LSP Label Switched Path
LSR Label Switching Router
MPLS-TP MPLS Transport Profile
OAM Operations, Administration, and Maintenance
PW Pseudowire
QoS Quality of Service
S-PE PW Switching Provider Edge
T-PE PW Terminating Provider Edge
TTL Time To Live
Term Definition
------- -------------------------------------------
ACH Associated Channel Header
G-ACh Generic Associated Channel
GAL G-ACh Label
LER Label Edge Router
LSE Label Stack Entry
LSP Label Switched Path
LSR Label Switching Router
MPLS-TP MPLS Transport Profile
OAM Operations, Administration, and Maintenance
PW Pseudowire
QoS Quality of Service
S-PE PW Switching Provider Edge
T-PE PW Terminating Provider Edge
TTL Time To Live
Additional definitions and terminology can be found in [RFC5921] and [RFC5654].
其他定义和术语可在[RFC5921]和[RFC5654]中找到。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[RFC2119]中所述进行解释。
MPLS-TP packet encapsulation and forwarding SHALL operate according to the MPLS data plane architecture described in [RFC3031] and [RFC3032] and to the data plane architectures for single-segment pseudowires and multi-segment pseudowires (see Section 3.3), except as noted otherwise in this document. The MPLS-TP data plane satisfies the requirements specified in [RFC5654].
MPLS-TP数据包封装和转发应根据[RFC3031]和[RFC3032]中描述的MPLS数据平面架构以及单段伪线和多段伪线的数据平面架构（见第3.3节）进行操作，除非本文件另有说明。MPLS-TP数据平面满足[RFC5654]中规定的要求。
Since an MPLS-TP packet is an MPLS packet as defined in [RFC3031] and [RFC3032], it will have an associated label stack, and the 'push', 'pop', and 'swap' label processing operations specified in those documents apply. The label stack represents a hierarchy of Label Switched Paths (LSPs). A label is pushed to introduce an additional level of LSP hierarchy and popped to remove it. Such an additional level may be introduced by any pair of LSRs, whereupon they become adjacent at this new level, and are then known as Label Edge Routers (LERs) with respect to the new LSP.
由于MPLS-TP数据包是[RFC3031]和[RFC3032]中定义的MPLS数据包，因此它将具有关联的标签堆栈，并且这些文档中指定的“推送”、“弹出”和“交换”标签处理操作适用。标签堆栈表示标签交换路径（LSP）的层次结构。推送标签以引入LSP层次结构的附加级别，并弹出标签以将其删除。这样的附加层可以由任何一对lsr引入，因此它们在该新层上成为相邻的，并且随后被称为关于新LSP的标签边缘路由器（ler）。
In contrast to, for example, Section 3.10 of [RFC3031], support for Internet Protocol (IP) host and router data plane functionality by MPLS-TP interfaces and in MPLS-TP networks is OPTIONAL.
例如，与[RFC3031]第3.10节不同，通过MPLS-TP接口和在MPLS-TP网络中支持互联网协议（IP）主机和路由器数据平面功能是可选的。
MPLS-TP forwarding is based on the label that identifies an LSP or PW. The label value specifies the processing operation to be performed by the next hop at that level of encapsulation. A swap of this label is an atomic operation in which the contents of the packet (after the swapped label) are opaque to the forwarding function. The only event that interrupts a swap operation is Time To Live (TTL) expiry.
MPLS-TP转发基于标识LSP或PW的标签。标签值指定下一跳在该封装级别执行的处理操作。该标签的交换是一种原子操作，其中数据包的内容（在交换标签之后）对转发功能是不透明的。中断交换操作的唯一事件是生存时间（TTL）到期。
At an LSR, S-PE, or T-PE, further processing to determine the context of a packet occurs when a swap operation is interrupted by TTL expiry. If the TTL of an LSP label expires, then the label with the S (Bottom of Stack) bit set is inspected to determine if it is a reserved label. If it is a reserved label, the packet is processed according to the rules of that reserved label. For example, if it is a Generic Associated Channel Label (GAL), then it is processed as a packet on the Generic Associated Channel (G-ACh); see Section 4. If the TTL of a PW expires at an S-PE or T-PE, then the packet is examined to determine if a Generic Associated Channel Header (ACH) is present immediately below the PW label. If so, then the packet is processed as a packet on the G-ACh.
在LSR、S-PE或T-PE上，当交换操作被TTL到期中断时，发生确定分组上下文的进一步处理。如果LSP标签的TTL过期，则检查设置了S（堆栈底部）位的标签，以确定其是否为保留标签。如果是保留标签，则根据该保留标签的规则处理数据包。例如，如果它是通用关联信道标签（GAL），则它作为通用关联信道（G-ACh）上的分组处理；见第4节。如果PW的TTL在S-PE或T-PE处过期，则检查分组以确定PW标签正下方是否存在通用关联信道报头（ACH）。如果是，则该分组作为G-ACh上的分组处理。
Similarly, if a pop operation at an LER exposes a reserved label at the top of the label stack, then the packet is processed according to the rules of that reserved label.
类似地，如果LER的pop操作在标签堆栈的顶部公开保留标签，则根据该保留标签的规则处理该数据包。
If no such exception occurs, the packet is forwarded according to the procedures in [RFC3031] and [RFC3032].
如果未发生此类异常，则根据[RFC3031]和[RFC3032]中的程序转发数据包。
The MPLS Transport Profile includes the following data plane transport entities:
MPLS传输配置文件包括以下数据平面传输实体：
o Label Switched Paths (LSPs)
o 标签交换路径（LSP）
o sections
o 部分
o pseudowires (PWs)
o 伪导线（PWs）
MPLS-TP LSPs are ordinary MPLS LSPs as defined in [RFC3031], except as specifically noted otherwise in this document.
MPLS-TP LSP是[RFC3031]中定义的普通MPLS LSP，除非本文件另有特别说明。
Encapsulation and forwarding of packets traversing MPLS-TP LSPs MUST follow standard MPLS packet encapsulation and forwarding as defined in [RFC3031], [RFC3032], [RFC5331], and [RFC5332], except as explicitly stated otherwise in this document.
除非本文件另有明确规定，否则通过MPLS-TP LSP的数据包的封装和转发必须遵循[RFC3031]、[RFC3032]、[RFC5331]和[RFC5332]中定义的标准MPLS数据包封装和转发。
Data plane Quality of Service capabilities are included in the MPLS-TP in the form of Traffic Engineered (TE) LSPs [RFC3209] and the MPLS Differentiated Services (Diffserv) architecture [RFC3270]. Both E-LSP and L-LSP MPLS Diffserv modes are included. The Traffic Class field (formerly the EXP field) of an MPLS label follows the definition of [RFC5462] and [RFC3270] and MUST be processed according to the rules specified in those documents.
数据平面服务质量能力以流量工程（TE）LSP[RFC3209]和MPLS区分服务（Diffserv）架构[RFC3270]的形式包含在MPLS-TP中。包括E-LSP和L-LSP MPLS区分服务模式。MPLS标签的流量类别字段（以前称为EXP字段）遵循[RFC5462]和[RFC3270]的定义，必须根据这些文档中指定的规则进行处理。
Except for transient packet reordering that may occur, for example, during fault conditions, packets are delivered in order on L-LSPs, and on E-LSPs within a specific ordered aggregate.
除了例如在故障条件下可能发生的瞬时数据包重新排序外，数据包在L-LSP和E-LSP上以特定有序聚合的顺序交付。
The Uniform, Pipe, and Short Pipe Diffserv tunneling and TTL processing models described in [RFC3270] and [RFC3443] MAY be used for MPLS-TP LSPs. Note, however, that support for the Pipe or Short Pipe models is REQUIRED for typical transport applications in which the topology and QoS characteristics of the MPLS-TP server layer are independent of the client layer. Specific applications MAY place further requirements on the Diffserv tunneling and TTL processing models an LSP can use.
[RFC3270]和[RFC3443]中描述的均匀、管道和短管Diffserv隧道和TTL处理模型可用于MPLS-TP LSP。然而，请注意，对于MPLS-TP服务器层的拓扑和QoS特性独立于客户端层的典型传输应用程序，需要支持管道或短管模型。特定应用可能对LSP可以使用的区分服务隧道和TTL处理模型提出进一步的要求。
Per-platform, per-interface, or other context-specific label space [RFC5331] MAY be used for MPLS-TP LSPs. Downstream [RFC3031] or upstream [RFC5331] label allocation schemes MAY be used for MPLS-TP LSPs. The requirements of a particular LSP type may, however, dictate which label spaces or allocation schemes LSPs of that type can use.
每个平台、每个接口或其他特定于上下文的标签空间[RFC5331]可用于MPLS-TP LSP。下游[RFC3031]或上游[RFC5331]标签分配方案可用于MPLS-TP LSP。然而，特定LSP类型的要求可能规定该类型LSP可以使用哪些标签空间或分配方案。
Equal-Cost Multi-Path (ECMP) load-balancing MUST NOT be performed on an MPLS-TP LSP. MPLS-TP LSPs as defined in this document MAY operate over a server layer that supports load-balancing, but this load-balancing MUST operate in such a manner that it is transparent to MPLS-TP. This does not preclude the future definition of new MPLS-TP LSP types that have different requirements regarding the use of ECMP in the server layer.
不得在MPLS-TP LSP上执行等成本多路径（ECMP）负载平衡。本文档中定义的MPLS-TP LSP可以在支持负载平衡的服务器层上运行，但这种负载平衡必须以对MPLS-TP透明的方式运行。这并不排除将来定义新的MPLS-TP LSP类型，这些类型在服务器层使用ECMP方面有不同的要求。
Penultimate Hop Popping (PHP) MUST be disabled by default on MPLS-TP LSPs.
默认情况下，MPLS-TP LSP上必须禁用倒数第二跳弹出（PHP）。
The MPLS-TP includes support for the following LSP payload types:
MPLS-TP包括对以下LSP有效负载类型的支持：
o Network-layer protocol packets (including MPLS-labeled packets)
o 网络层协议数据包（包括标记为MPLS的数据包）
o Pseudowire packets
o 伪线包
The rules for processing LSP payloads that are network-layer protocol packets SHALL be as specified in [RFC3032].
处理作为网络层协议包的LSP有效载荷的规则应符合[RFC3032]的规定。
The rules for processing LSP payloads that are pseudowire packets SHALL be as defined in the data plane pseudowire specifications (see Section 3.3).
处理伪线数据包LSP有效载荷的规则应符合数据平面伪线规范的规定（见第3.3节）。
The payload of an MPLS-TP LSP may be a packet that itself contains an MPLS label stack. This is true, for instance, when the payload is a pseudowire or an MPLS LSP. In such cases, the label stack is contiguous between the MPLS-TP LSP and its payload, and exactly one LSE in this stack SHALL have the S (Bottom of Stack) bit set to 1. This behavior reflects best current practice in MPLS but differs slightly from [RFC3032], which uses the S bit to identify when MPLS label processing stops and network-layer processing starts.
MPLS-TP LSP的有效载荷可以是本身包含MPLS标签堆栈的分组。例如，当有效负载是伪线或MPLS LSP时，这是正确的。在这种情况下，标签堆栈在MPLS-TP LSP及其有效负载之间是连续的，并且该堆栈中正好有一个LSE将S（堆栈底部）位设置为1。此行为反映了MPLS中当前的最佳实践，但与[RFC3032]略有不同，后者使用S位来标识MPLS标签处理何时停止，网络层处理何时开始。
The MPLS-TP includes the following LSP types:
MPLS-TP包括以下LSP类型：
o Point-to-point unidirectional
o 点对点单向
o Point-to-point associated bidirectional
o 点对点关联双向
o Point-to-point co-routed bidirectional
o 点对点双向路由
o Point-to-multipoint unidirectional
o 点对多点单向
Point-to-point unidirectional LSPs are supported by the basic MPLS architecture [RFC3031] and are REQUIRED to function in the same manner in the MPLS-TP data plane, except as explicitly stated otherwise in this document.
点对点单向LSP受基本MPLS体系结构[RFC3031]的支持，并且需要在MPLS-TP数据平面中以相同的方式运行，除非本文档中另有明确说明。
A point-to-point associated bidirectional LSP between LSRs A and B consists of two unidirectional point-to-point LSPs, one from A to B and the other from B to A, which are regarded as a pair providing a single logical bidirectional transport path.
LSR A和B之间的点到点关联双向LSP由两个单向点到点LSP组成，一个从A到B，另一个从B到A，它们被视为提供单个逻辑双向传输路径的对。
A point-to-point co-routed bidirectional LSP is a point-to-point associated bidirectional LSP with the additional constraint that its two unidirectional component LSPs in each direction follow the same path (in terms of both nodes and links). An important property of co-routed bidirectional LSPs is that their unidirectional component LSPs share fate.
点到点共路由双向LSP是点到点关联的双向LSP，附加约束是其每个方向上的两个单向组件LSP遵循相同的路径（就节点和链路而言）。共路由双向LSP的一个重要特性是其单向组件LSP共享命运。
A point-to-multipoint unidirectional LSP functions in the same manner in the data plane, with respect to basic label processing and packet-switching operations, as a point-to-point unidirectional LSP, with one difference: an LSR may have more than one (egress interface, outgoing label) pair associated with the LSP, and any packet it transmits on the LSP is transmitted out all associated egress interfaces. Point-to-multipoint LSPs are described in [RFC4875] and [RFC5332]. TTL processing and exception handling for point-to-multipoint LSPs is the same as for point-to-point LSPs and is described in Section 2.
关于基本标签处理和分组交换操作，点对多点单向LSP以与点对点单向LSP相同的方式在数据平面中工作，但有一个区别：LSR可以具有多个与LSP相关联的（出口接口、输出标签）对，并且它在LSP上发送的任何分组都被发送出所有相关的出口接口。[RFC4875]和[RFC5332]中描述了点对多点LSP。点对多点LSP的TTL处理和异常处理与点对点LSP相同，并在第2节中描述。
Two MPLS-TP LSRs are considered to be topologically adjacent at a particular layer n >= 0 of the MPLS-TP LSP hierarchy if there exists connectivity between them at the next lowest network layer, and if there is no MPLS layer processing at layer n between the two LSRs (other than at the LSRs themselves). Such connectivity, if it exists, will be either an MPLS-TP LSP (if n > 0) or a data-link provided by the underlying server layer network (if n = 0), and is referred to as an MPLS-TP section at layer n of the MPLS-TP LSP hierarchy. Thus, the links traversed by a layer n+1 MPLS-TP LSP are layer n MPLS-TP sections. Such an LSP is referred to as a client of the section layer, and the section layer is referred to as the server layer with respect to its clients.
如果两个MPLS-TP LSR之间在下一个最低网络层存在连接，并且如果两个LSR之间的第n层（LSR本身除外）没有MPLS层处理，则认为两个MPLS-TP LSR在MPLS-TP LSP层次结构的特定层n>=0处在拓扑上相邻。这种连接（如果存在）将是MPLS-TP LSP（如果n>0）或由底层服务器层网络提供的数据链路（如果n=0），并且在MPLS-TP LSP层次结构的第n层被称为MPLS-TP部分。因此，由层n+1 MPLS-TP LSP穿过的链路是层n MPLS-TP部分。这样的LSP被称为部分层的客户端，并且部分层相对于其客户端被称为服务器层。
The MPLS label stack associated with an MPLS-TP section at layer n consists of n labels, in the absence of stack optimization mechanisms. In order for two LSRs to exchange non-IP MPLS-TP control packets over a section, an additional label, the G-ACh Label (GAL) (see Section 4) MUST appear at the bottom of the label stack.
在没有栈优化机制的情况下，与第n层的MPLS-TP部分相关联的MPLS标签栈由n个标签组成。为了使两个LSR在一个部分上交换非IP MPLS-TP控制数据包，必须在标签堆栈的底部显示一个附加标签，即G-ACh标签（GAL）（参见第4节）。
An MPLS-TP section may provide one or more of the following types of service to its client layer:
MPLS-TP部分可以向其客户端层提供以下一种或多种类型的服务：
o Point-to-point bidirectional
o 点对点双向
o Point-to-point unidirectional
o 点对点单向
o Point-to-multipoint unidirectional
o 点对多点单向
The manner in which a section provides such a service is outside the scope of the MPLS-TP.
部分提供这种服务的方式不在MPLS-TP的范围内。
An LSP of any of the types listed in Section 3.1.3 may serve as a section for a client-layer transport entity as long as it supports the type of service the client requires.
第3.1.3节中列出的任何类型的LSP可作为客户层传输实体的一部分，只要它支持客户要求的服务类型。
A section MUST provide a means of identifying the type of payload it carries. If the section is a data-link, link-specific mechanisms such as a protocol type indication in the data-link header MAY be used. If the section is an LSP, this information MAY be implied by the LSP label or, if the LSP payload is MPLS-labeled, by the setting of the S bit. Additional labels MAY also be used if necessary to distinguish different payload types; see [RFC5921] for examples and further discussion.
区段必须提供一种识别其承载的有效载荷类型的方法。如果该部分是数据链路，则可以使用链路特定机制，例如数据链路报头中的协议类型指示。如果该部分是LSP，则该信息可由LSP标签暗示，或者，如果LSP有效载荷是MPLS标签，则可由S位的设置暗示。如有必要，还可使用附加标签来区分不同的有效载荷类型；有关示例和进一步讨论，请参见[RFC5921]。
The data plane architectures for single-segment pseudowires [RFC3985] and multi-segment pseudowires [RFC5659] are included in the MPLS-TP.
MPLS-TP中包括单段伪线[RFC3985]和多段伪线[RFC5659]的数据平面架构。
Data plane processing procedures for pseudowires are defined and described in a number of IETF documents. Some example pseudowire data plane procedures include:
许多IETF文件中定义并描述了伪导线的数据平面处理程序。一些伪线数据平面程序示例包括：
o Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN [RFC4385]
o 用于MPLS PSN的伪线仿真边到边（PWE3）控制字[RFC4385]
o Encapsulation Methods for Transport of Ethernet over MPLS Networks [RFC4448]
o MPLS网络上以太网传输的封装方法[RFC4448]
o Structure-Agnostic Time Division Multiplexing (TDM) over Packet (SAToP) [RFC4553]
o 结构无关的分组时分复用（TDM）（SAToP）[RFC4553]
o Encapsulation Methods for Transport of PPP/High-Level Data Link Control (HDLC) over MPLS Networks [RFC4618]
o 通过MPLS网络传输PPP/高级数据链路控制（HDLC）的封装方法[RFC4618]
o Encapsulation Methods for Transport of Frame Relay over Multiprotocol Label Switching (MPLS) Networks [RFC4619]
o 多协议标签交换（MPLS）网络上帧中继传输的封装方法[RFC4619]
o Encapsulation Methods for Transport of Asynchronous Transfer Mode (ATM) over MPLS Networks [RFC4717]
o MPLS网络上异步传输模式（ATM）传输的封装方法[RFC4717]
o Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service [RFC4816]
o 伪线仿真边到边（PWE3）异步传输模式（ATM）透明信元传输服务[RFC4816]
o Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/ SDH) Circuit Emulation over Packet (CEP) [RFC4842]
o 同步光网络/同步数字体系（SONET/SDH）分组电路仿真（CEP）[RFC4842]
o Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation Service over Packet Switched Network (CESoPSN) [RFC5086]
o 分组交换网络（CESoPSN）上的结构感知时分复用（TDM）电路仿真服务[RFC5086]
o Time Division Multiplexing over IP (TDMoIP) [RFC5087]
o IP时分多路复用（TDMoIP）[RFC5087]
o Encapsulation Methods for Transport of Fibre Channel frames Over MPLS Networks [FC-ENCAP]
o MPLS网络上光纤通道帧传输的封装方法[FC-ENCAP]
This document specifies no modifications or extensions to pseudowire data plane architectures or protocols.
本文档未指定对伪线数据平面架构或协议的修改或扩展。
The MPLS Generic Associated Channel (G-ACh) mechanism is specified in [RFC5586] and included in the MPLS-TP. The G-ACh provides an auxiliary logical data channel associated with MPLS-TP sections, LSPs, and PWs in the data plane. The primary purpose of the G-ACh in the context of MPLS-TP is to support control, management, and Operations, Administration, and Maintenance (OAM) traffic associated with MPLS-TP transport entities. The G-ACh MUST NOT be used to transport client layer network traffic in MPLS-TP networks.
MPLS通用关联信道（G-ACh）机制在[RFC5586]中规定，并包含在MPLS-TP中。G-ACh提供与数据平面中的MPLS-TP段、LSP和PW相关联的辅助逻辑数据通道。在MPLS-TP上下文中，G-ACh的主要目的是支持与MPLS-TP传输实体相关联的控制、管理以及操作、管理和维护（OAM）流量。G-ACh不得用于在MPLS-TP网络中传输客户端层网络流量。
For pseudowires, the G-ACh uses the first four bits of the PW control word to provide the initial discrimination between data packets and packets belonging to the associated channel, as described in [RFC4385]. When this first nibble of a packet, immediately following the label at the bottom of stack, has a value of '1', then this packet belongs to a G-ACh. The first 32 bits following the bottom of stack label then have a defined format called an Associated Channel Header (ACH), which further defines the content of the packet. The ACH is therefore both a demultiplexer for G-ACh traffic on the PW, and a discriminator for the type of G-ACh traffic.
对于伪线，G-ACh使用PW控制字的前四位来提供数据分组和属于相关信道的分组之间的初始区分，如[RFC4385]中所述。当数据包的第一个半字节（紧跟在堆栈底部的标签之后）的值为“1”时，则该数据包属于G-ACh。然后，堆栈底部标签后面的前32位具有称为关联通道头（ACH）的已定义格式，该格式进一步定义了数据包的内容。因此，ACH既是PW上G-ACH通信的解复用器，也是G-ACH通信类型的鉴别器。
When the control message is carried over a section or an LSP, rather than over a PW, it is necessary to provide an indication in the packet that the payload is something other than a client data packet. This is achieved by including a reserved label with a value of 13 at the bottom of the label stack. This reserved label is referred to as the G-ACh Label (GAL) and is defined in [RFC5586]. When a GAL is found, it indicates that the payload begins with an ACH. The GAL is thus a demultiplexer for G-ACh traffic on the section or the LSP, and the ACH is a discriminator for the type of traffic carried on the G-ACh. MPLS-TP forwarding follows the normal MPLS model, and thus a GAL is invisible to an LSR unless it is the top label in the label stack. The only other circumstance under which the label stack may be inspected for a GAL is when the TTL has expired. Normal packet
当控制消息通过区段或LSP而不是通过PW传送时，有必要在分组中提供有效载荷不是客户端数据分组的指示。这是通过在标签堆栈底部包含值为13的保留标签来实现的。该保留标签称为G-ACh标签（GAL），并在[RFC5586]中定义。当找到GAL时，它指示有效负载以ACH开始。因此，GAL是区段或LSP上的G-ACh业务的解复用器，并且ACh是G-ACh上承载的业务类型的鉴别器。MPLS-TP转发遵循正常的MPLS模型，因此GAL对LSR不可见，除非它是标签堆栈中的顶部标签。只有在TTL过期的情况下，才可以检查标签堆栈的GAL。正常数据包
forwarding MAY continue concurrently with this inspection. All operations on the label stack are in accordance with [RFC3031] and [RFC3032].
运输可与本次检查同时进行。标签堆栈上的所有操作均符合[RFC3031]和[RFC3032]的要求。
An application processing a packet received over the G-ACh may require packet-specific context (such as the receiving interface or received label stack). Data plane implementations MUST therefore provide adequate context to the application that is to process a G-ACh packet. The definition of the context required MUST be provided as part of the specification of the application using the G-ACh.
处理通过G-ACh接收的分组的应用程序可能需要特定于分组的上下文（例如接收接口或接收的标签堆栈）。因此，数据平面实现必须为处理G-ACh数据包的应用程序提供足够的上下文。所需上下文的定义必须作为使用G-ACh的应用程序规范的一部分提供。
The MPLS-TP network has no awareness of the internals of the server layer of which it is a client; it requires only that the server layer be capable of delivering the type of service required by the MPLS-TP transport entities that make use of it. Note that what appears to be a single server-layer link to the MPLS-TP network may be a complicated construct underneath, such as an LSP or a collection of underlying links operating as a bundle. Special care may be needed in network design and operation when such constructs are used as a server layer for MPLS-TP.
MPLS-TP网络不知道其作为客户机的服务器层的内部结构；它只要求服务器层能够提供使用它的MPLS-TP传输实体所需的服务类型。请注意，看起来是到MPLS-TP网络的单服务器层链路的可能是底层的复杂构造，例如LSP或作为捆绑运行的底层链路的集合。当这种结构用作MPLS-TP的服务器层时，在网络设计和操作中可能需要特别小心。
Encapsulation of MPLS-TP packets for transport over specific server-layer media is outside the scope of this document.
用于在特定服务器层介质上传输的MPLS-TP数据包的封装不在本文档的范围内。
The MPLS data plane (and therefore the MPLS-TP data plane) does not provide any security mechanisms in and of itself. Client layers that wish to secure data carried over MPLS-TP transport entities are REQUIRED to apply their own security mechanisms.
MPLS数据平面（因此MPLS-TP数据平面）本身不提供任何安全机制。希望保护通过MPLS-TP传输实体传输的数据的客户端层需要应用自己的安全机制。
Where management or control plane protocols are used to install label-switching operations necessary to establish MPLS-TP transport paths, those protocols are equipped with security features that network operators may use to securely create the transport paths.
当使用管理或控制平面协议来安装建立MPLS-TP传输路径所需的标签交换操作时，这些协议配备了网络运营商可用于安全创建传输路径的安全功能。
Where enhanced security is desirable, and a trust relationship exists between an LSR and its peer, the LSR MAY choose to implement the following policy for the processing of MPLS packets received from one or more of its neighbors:
在需要增强的安全性并且LSR与其对等方之间存在信任关系的情况下，LSR可以选择实施以下策略来处理从其一个或多个邻居接收的MPLS分组：
Upon receipt of an MPLS packet, discard the packet unless one of the following two conditions holds:
收到MPLS数据包后，丢弃该数据包，除非以下两种情况之一成立：
1. Any MPLS label in the packet's label stack processed at the receiving LSR, such as an LSP or PW label, has a label value that the receiving LSR has distributed to that neighbor; or
1. 在接收LSR处处理的分组的标签堆栈中的任何MPLS标签，例如LSP或PW标签，具有接收LSR已分发给该邻居的标签值；或
2. Any MPLS label in the packet's label stack processed at the receiving LSR, such as an LSP or PW label, has a label value that the receiving LSR has previously distributed to the peer beyond that neighbor (i.e., when it is known that the path from the system to which the label was distributed to the receiving system is via that neighbor).
2. 在接收LSR处处理的分组标签堆栈中的任何MPLS标签，例如LSP或PW标签，具有接收LSR先前已分发给该邻居之外的对等方的标签值（即，当已知从标签分发到接收系统的系统的路径是通过该邻居时）。
Further details of MPLS and MPLS-TP security can be found in [RFC5921] and [RFC5920].
有关MPLS和MPLS-TP安全性的更多详细信息，请参见[RFC5921]和[RFC5920]。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001.
[RFC3031]Rosen，E.，Viswanathan，A.，和R.Callon，“多协议标签交换体系结构”，RFC 30312001年1月。
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, January 2001.
[RFC3032]Rosen，E.，Tappan，D.，Fedorkow，G.，Rekhter，Y.，Farinaci，D.，Li，T.，和A.Conta，“MPLS标签堆栈编码”，RFC 3032，2001年1月。
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001.
[RFC3209]Awduche，D.，Berger，L.，Gan，D.，Li，T.，Srinivasan，V.，和G.Swallow，“RSVP-TE：LSP隧道RSVP的扩展”，RFC 3209，2001年12月。
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-Protocol Label Switching (MPLS) Support of Differentiated Services", RFC 3270, May 2002.
[RFC3270]Le Faucheur，F.，Wu，L.，Davie，B.，Davari，S.，Vaananen，P.，Krishnan，R.，Cheval，P.，和J.Heinanen，“区分服务的多协议标签交换（MPLS）支持”，RFC 32702002年5月。
[RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in Multi-Protocol Label Switching (MPLS) Networks", RFC 3443, January 2003.
[RFC3443]Agarwal，P.和B.Akyol，“多协议标签交换（MPLS）网络中的生存时间（TTL）处理”，RFC 3443，2003年1月。
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006.
[RFC4385]Bryant，S.，Swallow，G.，Martini，L.，和D.McPherson，“用于MPLS PSN的伪线仿真边到边（PWE3）控制字”，RFC 43852006年2月。
[RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron, "Encapsulation Methods for Transport of Ethernet over MPLS Networks", RFC 4448, April 2006.
[RFC4448]Martini，L.，Rosen，E.，El Aawar，N.，和G.Heron，“通过MPLS网络传输以太网的封装方法”，RFC 4448，2006年4月。
[RFC4553] Vainshtein, A. and YJ. Stein, "Structure-Agnostic Time Division Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June 2006.
[RFC4553]Vainstein，A.和YJ。Stein，“分组上的结构不可知时分复用（TDM）（SAToP）”，RFC4553，2006年6月。
[RFC4618] Martini, L., Rosen, E., Heron, G., and A. Malis, "Encapsulation Methods for Transport of PPP/High-Level Data Link Control (HDLC) over MPLS Networks", RFC 4618, September 2006.
[RFC4618]Martini，L.，Rosen，E.，Heron，G.，和A.Malis，“通过MPLS网络传输PPP/高级数据链路控制（HDLC）的封装方法”，RFC 4618，2006年9月。
[RFC4619] Martini, L., Kawa, C., and A. Malis, "Encapsulation Methods for Transport of Frame Relay over Multiprotocol Label Switching (MPLS) Networks", RFC 4619, September 2006.
[RFC4619]Martini，L.，Kawa，C.，和A.Malis，“多协议标签交换（MPLS）网络上帧中继传输的封装方法”，RFC 4619，2006年9月。
[RFC4717] Martini, L., Jayakumar, J., Bocci, M., El-Aawar, N., Brayley, J., and G. Koleyni, "Encapsulation Methods for Transport of Asynchronous Transfer Mode (ATM) over MPLS Networks", RFC 4717, December 2006.
[RFC4717]Martini，L.，Jayakumar，J.，Bocci，M.，El-Aawar，N.，Brayley，J.，和G.Koleyni，“MPLS网络上异步传输模式（ATM）传输的封装方法”，RFC 47172006年12月。
[RFC4816] Malis, A., Martini, L., Brayley, J., and T. Walsh, "Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service", RFC 4816, February 2007.
[RFC4816]Malis，A.，Martini，L.，Brayley，J.，和T.Walsh，“伪线仿真边到边（PWE3）异步传输模式（ATM）透明信元传输服务”，RFC 4816，2007年2月。
[RFC4842] Malis, A., Pate, P., Cohen, R., and D. Zelig, "Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Circuit Emulation over Packet (CEP)", RFC 4842, April 2007.
[RFC4842]Malis，A.，Pate，P.，Cohen，R.，和D.Zelig，“同步光网络/同步数字体系（SONET/SDH）分组电路仿真（CEP）”，RFC 48422007年4月。
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa, "Extensions to Resource Reservation Protocol - Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC4875]Aggarwal，R.，Papadimitriou，D.，和S.Yasukawa，“资源预留协议的扩展-点对多点TE标签交换路径（LSP）的流量工程（RSVP-TE）”，RFC 4875，2007年5月。
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream Label Assignment and Context-Specific Label Space", RFC 5331, August 2008.
[RFC5331]Aggarwal，R.，Rekhter，Y.，和E.Rosen，“MPLS上游标签分配和上下文特定标签空间”，RFC 53312008年8月。
[RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS Multicast Encapsulations", RFC 5332, August 2008.
[RFC5332]Eckert，T.，Rosen，E.，Aggarwal，R.，和Y.Rekhter，“MPLS多播封装”，RFC 5332，2008年8月。
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic Class" Field", RFC 5462, February 2009.
[RFC5462]Andersson，L.和R.Asati，“多协议标签交换（MPLS）标签堆栈条目：“EXP”字段重命名为“流量类”字段”，RFC 5462，2009年2月。
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, June 2009.
[RFC5586]Bocci，M.，Vigoureux，M.，和S.Bryant，“MPLS通用关联信道”，RFC 55862009年6月。
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, "Requirements of an MPLS Transport Profile", RFC 5654, September 2009.
[RFC5654]Niven Jenkins，B.，Brungard，D.，Betts，M.，Sprecher，N.，和S.Ueno，“MPLS传输配置文件的要求”，RFC 56542009年9月。
[FC-ENCAP] Black, D. and L. Dunbar, "Encapsulation Methods for Transport of Fibre Channel frames Over MPLS Networks", Work in Progress, June 2010.
[FC-ENCAP]Black，D.和L.Dunbar，“通过MPLS网络传输光纤通道帧的封装方法”，正在进行的工作，2010年6月。
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC3985]Bryant，S.和P.Pate，“伪线仿真边到边（PWE3）架构”，RFC 39852005年3月。
[RFC5086] Vainshtein, A., Sasson, I., Metz, E., Frost, T., and P. Pate, "Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation Service over Packet Switched Network (CESoPSN)", RFC 5086, December 2007.
[RFC5086]Vainstein，A.，Sasson，I.，Metz，E.，Frost，T.，和P.Pate，“分组交换网络上的结构感知时分多路复用（TDM）电路仿真服务（CESoPSN）”，RFC 50862007年12月。
[RFC5087] Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi, "Time Division Multiplexing over IP (TDMoIP)", RFC 5087, December 2007.
[RFC5087]Stein，Y（J.），Shashoua，R.，Insler，R.，和M.Anavi，“IP时分多路复用（TDMoIP）”，RFC 5087，2007年12月。
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, October 2009.
[RFC5659]Bocci，M.和S.Bryant，“多段伪线边到边仿真的体系结构”，RFC 5659，2009年10月。
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010.
[RFC5920]方，L，“MPLS和GMPLS网络的安全框架”，RFC 5920，2010年7月。
[RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L. Berger, "A Framework for MPLS in Transport Networks", RFC 5921, July 2010.
[RFC5921]Bocci，M.，Bryant，S.，Frost，D.，Levrau，L.，和L.Berger，“传输网络中MPLS的框架”，RFC 59212010年7月。
Authors' Addresses
作者地址
Dan Frost (editor) Cisco Systems
Dan Frost（编辑）思科系统公司
EMail: danfrost@cisco.com
EMail: danfrost@cisco.com
Stewart Bryant (editor) Cisco Systems
斯图尔特·布莱恩特（编辑）思科系统
EMail: stbryant@cisco.com
EMail: stbryant@cisco.com
Matthew Bocci (editor) Alcatel-Lucent
Matthew Bocci（编辑）阿尔卡特朗讯
EMail: matthew.bocci@alcatel-lucent.com
EMail: matthew.bocci@alcatel-lucent.com