Network Working Group L. Martini, Ed.
Request for Comments: 4448 E. Rosen
Category: Standards Track Cisco Systems, Inc.
N. El-Aawar
Level 3 Communications, LLC
G. Heron
Tellabs
April 2006
Network Working Group L. Martini, Ed.
Request for Comments: 4448 E. Rosen
Category: Standards Track Cisco Systems, Inc.
N. El-Aawar
Level 3 Communications, LLC
G. Heron
Tellabs
April 2006
Encapsulation Methods for Transport of Ethernet over MPLS Networks
MPLS网络上以太网传输的封装方法
Status of This Memo
关于下段备忘
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2006).
版权所有（C）互联网协会（2006年）。
Abstract
摘要
An Ethernet pseudowire (PW) is used to carry Ethernet/802.3 Protocol Data Units (PDUs) over an MPLS network. This enables service providers to offer "emulated" Ethernet services over existing MPLS networks. This document specifies the encapsulation of Ethernet/802.3 PDUs within a pseudowire. It also specifies the procedures for using a PW to provide a "point-to-point Ethernet" service.
以太网伪线（PW）用于通过MPLS网络承载以太网/802.3协议数据单元（PDU）。这使服务提供商能够在现有MPLS网络上提供“模拟”以太网服务。本文档规定了以太网/802.3 PDU在伪线中的封装。它还规定了使用PW提供“点对点以太网”服务的程序。
Table of Contents
目录
1. Introduction ....................................................3
2. Specification of Requirements ...................................6
3. Applicability Statement .........................................6
4. Details Specific to Particular Emulated Services ................7
4.1. Ethernet Tagged Mode .......................................7
4.2. Ethernet Raw Mode ..........................................8
4.3. Ethernet-Specific Interface Parameter LDP Sub-TLV ..........8
4.4. Generic Procedures .........................................9
4.4.1. Raw Mode vs. Tagged Mode ............................9
4.4.2. MTU Management on the PE/CE Links ..................11
4.4.3. Frame Ordering .....................................11
4.4.4. Frame Error Processing .............................11
4.4.5. IEEE 802.3x Flow Control Interworking ..............11
4.5. Management ................................................12
4.6. The Control Word ..........................................12
4.7. QoS Considerations ........................................13
5. Security Considerations ........................................14
6. PSN MTU Requirements ...........................................14
7. Normative References ...........................................15
8. Informative References .........................................15
9. Significant Contributors .......................................17
Appendix A. Interoperability Guidelines ...........................20
A.1. Configuration Options .....................................20
A.2. IEEE 802.3x Flow Control Considerations ...................21
Appendix B. QoS Details ...........................................21
B.1. Adaptation of 802.1Q CoS to PSN CoS .......................22
B.2. Drop Precedence ...........................................23
1. Introduction ....................................................3
2. Specification of Requirements ...................................6
3. Applicability Statement .........................................6
4. Details Specific to Particular Emulated Services ................7
4.1. Ethernet Tagged Mode .......................................7
4.2. Ethernet Raw Mode ..........................................8
4.3. Ethernet-Specific Interface Parameter LDP Sub-TLV ..........8
4.4. Generic Procedures .........................................9
4.4.1. Raw Mode vs. Tagged Mode ............................9
4.4.2. MTU Management on the PE/CE Links ..................11
4.4.3. Frame Ordering .....................................11
4.4.4. Frame Error Processing .............................11
4.4.5. IEEE 802.3x Flow Control Interworking ..............11
4.5. Management ................................................12
4.6. The Control Word ..........................................12
4.7. QoS Considerations ........................................13
5. Security Considerations ........................................14
6. PSN MTU Requirements ...........................................14
7. Normative References ...........................................15
8. Informative References .........................................15
9. Significant Contributors .......................................17
Appendix A. Interoperability Guidelines ...........................20
A.1. Configuration Options .....................................20
A.2. IEEE 802.3x Flow Control Considerations ...................21
Appendix B. QoS Details ...........................................21
B.1. Adaptation of 802.1Q CoS to PSN CoS .......................22
B.2. Drop Precedence ...........................................23
An Ethernet pseudowire (PW) allows Ethernet/802.3 [802.3] Protocol Data Units (PDUs) to be carried over a Multi-Protocol Label Switched [MPLS-ARCH] network. In addressing the issues associated with carrying an Ethernet PDU over a packet switched network (PSN), this document assumes that a pseudowire (PW) has been set up by using a control protocol such as the one as described in [PWE3-CTRL]. The design of Ethernet pseudowire described in this document conforms to the pseudowire architecture described in [RFC3985]. It is also assumed in the remainder of this document that the reader is familiar with RFC 3985.
以太网伪线（PW）允许以太网/802.3[802.3]协议数据单元（PDU）通过多协议标签交换[MPLS-ARCH]网络传输。在解决与通过分组交换网络（PSN）承载以太网PDU相关的问题时，本文档假设已通过使用控制协议（如[PWE3-CTRL]中所述的协议）建立了伪线（PW）。本文件中描述的以太网伪线设计符合[RFC3985]中描述的伪线体系结构。在本文件的其余部分中，还假定读者熟悉RFC 3985。
The Pseudowire Emulation Edge-to-Edge (PWE3) Ethernet PDU consists of the Destination Address, Source Address, Length/Type, MAC Client Data, and padding extracted from a MAC frame as a concatenated octet sequence in their original order [PDU].
伪线仿真边到边（PWE3）以太网PDU由目标地址、源地址、长度/类型、MAC客户端数据和从MAC帧提取的填充组成，作为原始顺序的串联八位字节序列[PDU]。
In addition to the Ethernet PDU format used within the pseudowire, this document discusses:
除了伪线中使用的以太网PDU格式外，本文档还讨论：
- Procedures for using a PW in order to provide a pair of Customer Edge (CE) routers with an emulated (point-to-point) Ethernet service, including the procedures for the processing of Provider Edge (PE)-bound and CE-bound Ethernet PDUs [RFC3985]
- 使用PW为一对客户边缘（CE）路由器提供模拟（点对点）以太网服务的程序，包括处理提供商边缘（PE）绑定和CE绑定以太网PDU的程序[RFC3985]
- Ethernet-specific quality of service (QoS) and security considerations
- 以太网特定服务质量（QoS）和安全注意事项
- Inter-domain transport considerations for Ethernet PW
- 以太网PW的域间传输注意事项
The following two figures describe the reference models that are derived from [RFC3985] to support the Ethernet PW emulated services.
以下两幅图描述了从[RFC3985]衍生的参考模型，以支持以太网PW模拟服务。
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------->| |
| | | |
| | |<-- PSN Tunnel -->| | |
| PW End V V V V PW End |
V Service +----+ +----+ Service V
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | ^ +-----+
^ | +----+ +----+ | | ^
| | Provider Edge 1 Provider Edge 2 | |
| | | |
Customer | | Customer
Edge 1 | | Edge 2
| |
| |
Attachment Circuit (AC) Attachment Circuit (AC)
native Ethernet service native Ethernet service
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------->| |
| | | |
| | |<-- PSN Tunnel -->| | |
| PW End V V V V PW End |
V Service +----+ +----+ Service V
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | ^ +-----+
^ | +----+ +----+ | | ^
| | Provider Edge 1 Provider Edge 2 | |
| | | |
Customer | | Customer
Edge 1 | | Edge 2
| |
| |
Attachment Circuit (AC) Attachment Circuit (AC)
native Ethernet service native Ethernet service
Figure 1: PWE3 Ethernet/VLAN Interface Reference Configuration
图1:PWE3以太网/VLAN接口参考配置
The "emulated service" shown in Figure 1 is, strictly speaking, a bridged LAN; the PEs have MAC interfaces, consume MAC control frames, etc. However, the procedures specified herein only support the case in which there are two CEs on the "emulated LAN". Hence we refer to this service as "emulated point-to-point Ethernet". Specification of the procedures for using pseudowires to emulate LANs with more than two CEs are out of the scope of the current document.
严格来说，图1所示的“模拟服务”是一个桥接LAN；PEs具有MAC接口，使用MAC控制帧等。然而，本文规定的程序仅支持“模拟LAN”上有两个CE的情况。因此，我们将此服务称为“模拟点对点以太网”。使用伪线模拟具有两个以上CE的LAN的过程的规范不在当前文档的范围内。
+-------------+ +-------------+
| Emulated | | Emulated |
| Ethernet | | Ethernet |
| (including | Emulated Service | (including |
| VLAN) |<==============================>| VLAN) |
| Services | | Services |
+-------------+ Pseudowire +-------------+
|Demultiplexer|<==============================>|Demultiplexer|
+-------------+ +-------------+
| PSN | PSN Tunnel | PSN |
| MPLS |<==============================>| MPLS |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
+-------------+ +-------------+
| Emulated | | Emulated |
| Ethernet | | Ethernet |
| (including | Emulated Service | (including |
| VLAN) |<==============================>| VLAN) |
| Services | | Services |
+-------------+ Pseudowire +-------------+
|Demultiplexer|<==============================>|Demultiplexer|
+-------------+ +-------------+
| PSN | PSN Tunnel | PSN |
| MPLS |<==============================>| MPLS |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
Figure 2: Ethernet PWE3 Protocol Stack Reference Model
图2：以太网PWE3协议栈参考模型
For the purpose of this document, PE1 will be defined as the ingress router, and PE2 as the egress router. A layer 2 PDU will be received at PE1, encapsulated at PE1, transported, decapsulated at PE2, and transmitted out on the attachment circuit of PE2.
在本文件中，PE1定义为入口路由器，PE2定义为出口路由器。第2层PDU将在PE1处接收，在PE1处封装，在PE2处传输、解封，并在PE2的连接电路上发送出去。
An Ethernet PW emulates a single Ethernet link between exactly two endpoints. The mechanisms described in this document are agnostic to that which is beneath the "Pseudowire" level in Figure 2, concerning itself only with the "Emulated Service" portion of the stack.
以太网PW模拟两个端点之间的单个以太网链路。本文档中描述的机制与图2中“伪线”级别下的机制无关，只涉及堆栈的“模拟服务”部分。
The following reference model describes the termination point of each end of the PW within the PE:
以下参考模型描述了PE内PW各端的终止点：
+-----------------------------------+
| PE |
+---+ +-+ +-----+ +------+ +------+ +-+
| | |P| | | |PW ter| | PSN | |P|
| |<==|h|<=| NSP |<=|minati|<=|Tunnel|<=|h|<== From PSN
| | |y| | | |on | | | |y|
| C | +-+ +-----+ +------+ +------+ +-+
| E | | |
| | +-+ +-----+ +------+ +------+ +-+
| | |P| | | |PW ter| | PSN | |P|
| |==>|h|=>| NSP |=>|minati|=>|Tunnel|=>|h|==> To PSN
| | |y| | | |on | | | |y|
+---+ +-+ +-----+ +------+ +------+ +-+
| |
+-----------------------------------+
^ ^ ^
| | |
A B C
+-----------------------------------+
| PE |
+---+ +-+ +-----+ +------+ +------+ +-+
| | |P| | | |PW ter| | PSN | |P|
| |<==|h|<=| NSP |<=|minati|<=|Tunnel|<=|h|<== From PSN
| | |y| | | |on | | | |y|
| C | +-+ +-----+ +------+ +------+ +-+
| E | | |
| | +-+ +-----+ +------+ +------+ +-+
| | |P| | | |PW ter| | PSN | |P|
| |==>|h|=>| NSP |=>|minati|=>|Tunnel|=>|h|==> To PSN
| | |y| | | |on | | | |y|
+---+ +-+ +-----+ +------+ +------+ +-+
| |
+-----------------------------------+
^ ^ ^
| | |
A B C
Figure 3: PW Reference Diagram
图3:PW参考图
The PW terminates at a logical port within the PE, defined at point B in the above diagram. This port provides an Ethernet MAC service that will deliver each Ethernet frame that is received at point A, unaltered, to the point A in the corresponding PE at the other end of the PW.
PW终止于PE内的逻辑端口，在上图中的点B处定义。该端口提供以太网MAC服务，该服务将在点A接收的每个以太网帧未经更改地传送到PW另一端相应PE中的点A。
The Native Service Processing (NSP) function includes frame processing that is required for the Ethernet frames that are forwarded to the PW termination point. Such functions may include stripping, overwriting or adding VLAN tags, physical port multiplexing and demultiplexing, PW-PW bridging, L2 encapsulation, shaping, policing, etc. These functions are specific to the Ethernet technology, and may not be required for the PW emulation service.
本机服务处理（NSP）功能包括转发到PW终端点的以太网帧所需的帧处理。此类功能可能包括剥离、覆盖或添加VLAN标记、物理端口多路复用和解多路复用、PW-PW桥接、L2封装、整形、监管等。这些功能特定于以太网技术，PW仿真服务可能不需要这些功能。
The points to the left of A, including the physical layer between the CE and PE, and any adaptation (NSP) functions between it and the PW terminations, are outside of the scope of PWE3 and are not defined here.
A左侧的点，包括CE和PE之间的物理层，以及它与PW终端之间的任何适配（NSP）功能，不在PWE3的范围内，此处不作定义。
"PW Termination", between A and B, represents the operations for setting up and maintaining the PW, and for encapsulating and decapsulating the Ethernet frames as necessary to transmit them across the MPLS network.
A和B之间的“PW终端”表示设置和维护PW的操作，以及必要时封装和解封以太网帧以通过MPLS网络传输它们的操作。
An Ethernet PW operates in one of two modes: "raw mode" or "tagged mode". In tagged mode, each frame MUST contain at least one 802.1Q [802.1Q] VLAN tag, and the tag value is meaningful to the NSPs at the two PW termination points. That is, the two PW termination points must have some agreement (signaled or manually configured) on how to process the tag. On a raw mode PW, a frame MAY contain an 802.1Q VLAN tag, but if it does, the tag is not meaningful to the NSPs, and passes transparently through them.
以太网PW以两种模式之一运行：“原始模式”或“标记模式”。在标记模式下，每个帧必须至少包含一个802.1Q[802.1Q]VLAN标记，并且标记值对两个PW端点处的NSP有意义。也就是说，两个PW端点必须就如何处理标签达成某种协议（信号或手动配置）。在原始模式PW上，帧可能包含802.1Q VLAN标记，但如果包含，则该标记对NSP没有意义，并且透明地通过NSP。
Additional terminology relevant to pseudowires and Layer 2 Virtual Private Networking may be found in [RFC4026].
与伪线和第2层虚拟专用网络相关的其他术语可在[RFC4026]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。
The Ethernet PW emulation allows a service provider to offer a "port to port" Ethernet-based service across an MPLS packet switched network (PSN) while the Ethernet VLAN PW emulation allows an "Ethernet VLAN to VLAN" based service across an MPLS packet switched network (PSN).
以太网PW仿真允许服务提供商跨MPLS分组交换网络（PSN）提供基于“端口到端口”的以太网服务，而以太网VLAN PW仿真允许跨MPLS分组交换网络（PSN）提供基于“以太网VLAN到VLAN”的服务。
The Ethernet or Ethernet VLAN PW has the following characteristics in relationship to the respective native service:
以太网或以太网VLAN PW相对于各自的本机服务具有以下特征：
- An Ethernet PW connects two Ethernet ACs while an Ethernet VLAN PW connects two Ethernet VLAN ACs, supporting bidirectional transport of variable length Ethernet frames. The ingress Native Service Processing (NSP) function strips the preamble and frame check sequence (FCS) from the Ethernet frame and transports the frame in its entirety across the PW. This is done regardless of the presence of the 802.1Q tag in the frame. The egress NSP function receives the Ethernet frame from the PW and regenerates the preamble or FCS before forwarding the frame
- 以太网PW连接两个以太网ACs，而以太网VLAN PW连接两个以太网VLAN ACs，支持可变长度以太网帧的双向传输。ingress Native Service Processing（NSP）功能从以太网帧中剥离前导码和帧检查序列（FCS），并通过PW整体传输帧。无论帧中是否存在802.1Q标记，都会执行此操作。出口NSP功能从PW接收以太网帧，并在转发帧之前重新生成前导码或FCS
to the attachment circuit. Since the FCS is not transported across either Ethernet or Ethernet VLAN PWs, payload integrity transparency may be lost. The OPTIONAL method described in [FCS] can be used to achieve payload integrity transparency on Ethernet or Ethernet VLAN PWs.
连接至附件回路。由于FCS不是通过以太网或以太网VLAN PWs传输的，因此负载完整性透明性可能会丢失。[FCS]中描述的可选方法可用于在以太网或以太网VLAN PWs上实现有效负载完整性透明。
- For an Ethernet VLAN PW, VLAN tag rewrite can be achieved by NSP at the egress PE, which is outside the scope of this document.
- 对于以太网VLAN PW，VLAN标记重写可通过出口PE处的NSP实现，这超出了本文档的范围。
- The Ethernet or Ethernet VLAN PW only supports homogeneous Ethernet frame type across the PW; both ends of the PW must be either tagged or untagged. Heterogeneous frame type support achieved with NSP functionality is outside the scope of this document.
- 以太网或以太网VLAN PW仅支持PW上的同构以太网帧类型；PW的两端必须标记或未标记。使用NSP功能实现的异构帧类型支持不在本文档范围内。
- Ethernet port or Ethernet VLAN status notification is provided using the PW Status TLV in the Label Distribution Protocol (LDP) status notification message. Loss of connectivity between PEs can be detected by the LDP session closing, or by using [VCCV] mechanisms. The PE can convey these indications back to its attached Remote System.
- 使用标签分发协议（LDP）状态通知消息中的PW status TLV提供以太网端口或以太网VLAN状态通知。可以通过LDP会话关闭或使用[VCCV]机制检测PEs之间的连接丢失。PE可将这些指示传回其连接的远程系统。
- The maximum frame size that can be supported is limited by the PSN MTU minus the MPLS header size, unless fragmentation and reassembly are used [FRAG].
- 可以支持的最大帧大小受PSN MTU减去MPLS报头大小的限制，除非使用分段和重新组装[FRAG]。
- The packet switched network may reorder, duplicate, or silently drop packets. Sequencing MAY be enabled in the Ethernet or Ethernet VLAN PW to detect lost, duplicate, or out-of-order packets on a per-PW basis.
- 分组交换网络可以重新排序、复制或静默丢弃分组。可在以太网或以太网VLAN PW中启用排序，以基于每个PW检测丢失、重复或无序数据包。
- The faithfulness of an Ethernet or Ethernet VLAN PW may be increased by leveraging Quality of Service features of the PEs and the underlying PSN. (See Section 4.7, "QoS Considerations".)
- 以太网或以太网VLAN PW的忠实性可以通过利用PEs和底层PSN的服务质量特性来提高。（参见第4.7节“QoS注意事项”。）
The Ethernet frame will be encapsulated according to the procedures defined later in this document for tagged mode. It should be noted that if the VLAN identifier is modified by the egress PE, the Ethernet spanning tree protocol might fail to work properly. If this issue is of significance, the VLAN identifier MUST be selected in such a way that it matches on the attachment circuits at both ends of the PW.
以太网帧将根据本文件后面针对标记模式定义的程序进行封装。应该注意，如果出口PE修改VLAN标识符，以太网生成树协议可能无法正常工作。如果此问题很重要，则必须选择VLAN标识符，使其与PW两端的连接电路匹配。
If the PE detects a failure on the Ethernet physical port, or the port is administratively disabled, it MUST send a PW status notification message for all PWs associated with the port.
如果PE在以太网物理端口上检测到故障，或者该端口被管理禁用，则必须为与该端口关联的所有PW发送PW状态通知消息。
This mode uses service-delimiting tags to map input Ethernet frames to respective PWs and corresponds to PW type 0x0004 "Ethernet Tagged Mode" [IANA].
此模式使用服务定界标记将输入以太网帧映射到各个PW，并对应于PW类型0x0004“以太网标记模式”[IANA]。
The Ethernet frame will be encapsulated according to the procedures defined later in this document for raw mode. If the PE detects a failure on the Ethernet input port, or the port is administratively disabled, the PE MUST send an appropriate PW status notification message to the corresponding remote PE.
以太网帧将根据本文件后面针对原始模式定义的程序进行封装。如果PE在以太网输入端口上检测到故障，或端口被管理禁用，则PE必须向相应的远程PE发送适当的PW状态通知消息。
In this mode, all Ethernet frames received on the attachment circuit of PE1 will be transmitted to PE2 on a single PW. This service corresponds to PW type 0x0005 "Ethernet" [IANA].
在此模式下，在PE1的连接电路上接收到的所有以太网帧将通过单个PW传输到PE2。此服务对应于PW类型0x0005“以太网”[IANA]。
This LDP sub-Type Length Value [LDP] specifies interface-specific parameters. When applicable, it MUST be used to validate that the PEs, and the ingress and egress ports at the edges of the circuit, have the necessary capabilities to interoperate with each other. The Interface parameter TLV is defined in [PWE3-CTRL], the IANA registry with initial values for interface parameter sub-TLV types is defined in [IANA], but the Ethernet-specific interface parameters are specified as follows:
此LDP子类型长度值[LDP]指定接口特定参数。适用时，必须使用它来验证PEs以及电路边缘的入口和出口端口是否具有相互互操作的必要能力。接口参数TLV在[PWE3-CTRL]中定义，带有接口参数子TLV类型初始值的IANA注册表在[IANA]中定义，但特定于以太网的接口参数指定如下：
- 0x06 Requested VLAN ID Sub-TLV
- 0x06请求的VLAN ID子TLV
An Optional 16-bit value indicating the requested VLAN ID. This parameter MUST be used by a PE that is incapable of rewriting the 802.1Q Ethernet VLAN tag on output. If the ingress PE receives this request, it MUST rewrite the VLAN ID contained inside the VLAN Tag at the input to match the requested VLAN ID. If this is not possible, and the VLAN ID does not already match the configured ingress VLAN ID, the PW MUST not be enabled. This parameter is applicable only to PW type 0x0004.
一个可选的16位值，指示请求的VLAN ID。此参数必须由无法在输出上重写802.1Q以太网VLAN标记的PE使用。如果入口PE收到此请求，它必须重写输入端VLAN标记内包含的VLAN ID，以匹配请求的VLAN ID。如果不可能，且VLAN ID尚未匹配配置的入口VLAN ID，则不得启用PW。此参数仅适用于PW类型0x0004。
When the NSP/Forwarder hands a frame to the PW termination function:
当NSP/转发器将帧交给PW终止功能时：
- The preamble (if any) and FCS are stripped off.
- 序言（如有）和FCS被剥离。
- The control word as defined in Section 4.6, "The Control Word", is, if necessary, prepended to the resulting frame. The conditions under which the control word is or is not used are specified below.
- 如有必要，将第4.6节“控制字”中定义的控制字添加到生成的帧之前。下面指定了使用或不使用控制字的条件。
- The proper pseudowire demultiplexer (PW Label) is prepended to the resulting packet.
- 正确的伪线解复用器（PW标签）在生成的数据包之前。
- The proper tunnel encapsulation is prepended to the resulting packet.
- 正确的隧道封装在生成的数据包之前。
- The packet is transmitted.
- 数据包被传输。
The way in which the proper tunnel encapsulation and pseudowire demultiplexer is chosen depends on the procedures that were used to set up the pseudowire.
选择合适的隧道封装和伪线解复用器的方式取决于用于设置伪线的程序。
The tunnel encapsulation depends on how the MPLS PSN is set up. This can include no label, one label, or multiple labels. The proper pseudowire demultiplexer is an MPLS label whose value is determined by the PW setup and maintenance protocols.
隧道封装取决于MPLS PSN的设置方式。这可以包括无标签、一个标签或多个标签。合适的伪线解复用器是MPLS标签，其值由PW设置和维护协议确定。
When a packet arrives over a PW, the tunnel encapsulation and PW demultiplexer are stripped off. If the control word is present, it is processed and stripped off. The resulting frame is then handed to the Forwarder/NSP. Regeneration of the FCS is considered to be an NSP responsibility.
当数据包通过PW到达时，隧道封装和PW解复用器被剥离。如果控制字存在，则对其进行处理和剥离。然后将生成的帧交给转发器/NSP。FCS的再生被视为NSP的责任。
When the PE receives an Ethernet frame, and the frame has a VLAN tag, we can distinguish two cases:
当PE接收到以太网帧，并且该帧具有VLAN标记时，我们可以区分两种情况：
1. The tag is service-delimiting. This means that the tag was placed on the frame by some piece of service provider-operated equipment, and the tag is used by the service provider to distinguish the traffic. For example, LANs from different customers might be attached to the same service provider switch, which applies VLAN tags to distinguish one customer's traffic from another's, and then forwards the frames to the PE.
1. 标记是服务定界。这意味着标签由服务提供商操作的设备放置在框架上，服务提供商使用标签来区分流量。例如，来自不同客户的LAN可能连接到同一个服务提供商交换机，该交换机应用VLAN标记来区分一个客户的流量和另一个客户的流量，然后将帧转发给PE。
2. The tag is not service-delimiting. This means that the tag was placed in the frame by a piece of customer equipment, and is not meaningful to the PE.
2. 标记不是服务定界。这意味着标签是由客户设备放置在框架中的，对PE没有意义。
Whether or not the tag is service-delimiting is determined by local configuration on the PE.
标签是否为服务定界由PE上的本地配置决定。
If an Ethernet PW is operating in raw mode, service-delimiting tags are NEVER sent over the PW. If a service-delimiting tag is present when the frame is received from the attachment circuit by the PE, it MUST be stripped (by the NSP) from the frame before the frame is sent to the PW.
如果以太网PW在原始模式下运行，则永远不会通过PW发送服务定界标记。如果PE从连接电路接收到帧时存在服务定界标签，则在将帧发送到PW之前，必须（由NSP）将其从帧中剥离。
If an Ethernet PW is operating in tagged mode, every frame sent on the PW MUST have a service-delimiting VLAN tag. If the frame as received by the PE from the attachment circuit does not have a service-delimiting VLAN tag, the PE must prepend the frame with a dummy VLAN tag before sending the frame on the PW. This is the default operating mode. This is the only REQUIRED mode.
如果以太网PW在标记模式下运行，则PW上发送的每个帧必须具有服务分隔VLAN标记。如果PE从连接电路接收到的帧没有服务定界VLAN标记，则PE必须在PW上发送帧之前使用虚拟VLAN标记预先结束该帧。这是默认的操作模式。这是唯一需要的模式。
In both modes, non-service-delimiting tags are passed transparently across the PW as part of the payload. It should be noted that a single Ethernet packet may contain more than one tag. At most, one of these tags may be service-delimiting. In any case, the NSP function may only inspect the outermost tag for the purpose of adapting the Ethernet frame to the pseudowire.
在这两种模式中，非服务定界标记作为有效负载的一部分透明地通过PW传递。应注意，单个以太网分组可能包含多个标签。最多，这些标记中的一个可能是服务定界。在任何情况下，NSP功能只能检查最外面的标签，以便将以太网帧适配到伪线。
In both modes, the service-delimiting tag values have only local significance, i.e., are meaningful only at a particular PE-CE interface. When tagged mode is used, the PE that receives a frame from the PW may rewrite the tag value, or may strip the tag entirely, or may leave the tag unchanged, depending on its configuration. When raw mode is used, the PE that receives a frame may or may not need to add a service-delimiting tag before transmitting the frame on the attachment circuit; however, it MUST not rewrite or remove any tags that are already present.
在这两种模式中，服务定界标记值仅具有局部意义，即，仅在特定PE-CE接口处有意义。当使用标记模式时，从PW接收帧的PE可以重写标记值，或者可以完全去除标记，或者可以保持标记不变，这取决于其配置。当使用原始模式时，接收帧的PE可以或不需要在附件电路上发送帧之前添加服务定界标签；但是，它不能重写或删除已经存在的任何标记。
The following table illustrates the operations that might be performed at input from the attachment circuit:
下表说明了在附件电路输入时可能执行的操作：
+-----------------------------------------------------------+
| Tag-> | service delimiting | non service delimiting|
|-------------+---------------------+-----------------------|
| Raw Mode | 1st VLAN Tag Removed| no operation performed|
|-------------+---------------------+-----------------------|
| Tagged Mode | NO OP or Tag Added | Tag Added |
+-----------------------------------------------------------+
+-----------------------------------------------------------+
| Tag-> | service delimiting | non service delimiting|
|-------------+---------------------+-----------------------|
| Raw Mode | 1st VLAN Tag Removed| no operation performed|
|-------------+---------------------+-----------------------|
| Tagged Mode | NO OP or Tag Added | Tag Added |
+-----------------------------------------------------------+
The Ethernet PW MUST NOT be enabled unless it is known that the MTUs of the CE-PE links are the same at both ends of the PW. If an egress router receives an encapsulated layer 2 PDU whose payload length (i.e., the length of the PDU itself without any of the encapsulation headers) exceeds the MTU of the destination layer 2 interface, the PDU MUST be dropped.
除非已知CE-PE链路的MTU在PW两端相同，否则不得启用以太网PW。如果出口路由器接收到一个封装的第2层PDU，其有效负载长度（即，没有任何封装头的PDU本身的长度）超过目的地第2层接口的MTU，则必须丢弃该PDU。
In general, applications running over Ethernet do not require strict frame ordering. However, the IEEE definition of 802.3 [802.3] requires that frames from the same conversation in the context of link aggregation (clause 43) are delivered in sequence. Moreover, the PSN cannot (in the general case) be assumed to provide or to guarantee frame ordering. An Ethernet PW can, through use of the control word, provide strict frame ordering. If this option is enabled, any frames that get misordered by the PSN will be dropped or reordered by the receiving PW endpoint. If strict frame ordering is a requirement for a particular PW, this option MUST be enabled.
通常，通过以太网运行的应用程序不需要严格的帧顺序。然而，802.3[802.3]的IEEE定义要求在链路聚合上下文（第43条）中来自相同会话的帧按顺序交付。此外，PSN不能（在一般情况下）被假定为提供或保证帧顺序。以太网PW可以通过使用控制字提供严格的帧顺序。如果启用此选项，则接收PW端点将丢弃PSN错误排序的任何帧或对其重新排序。如果特定PW要求严格的帧顺序，则必须启用此选项。
An encapsulated Ethernet frame traversing a pseudowire may be dropped, corrupted, or delivered out-of-order. As described in [PWE3-REQ], frame loss, corruption, and out-of-order delivery are considered to be a "generalized bit error" of the pseudowire. PW frames that are corrupted will be detected at the PSN layer and dropped.
穿过伪线的封装以太网帧可能会被丢弃、损坏或无序交付。如[PWE3-REQ]中所述，帧丢失、损坏和无序交付被认为是伪线的“广义位错误”。损坏的PW帧将在PSN层检测并丢弃。
At the ingress of the PW, the native Ethernet frame error processing mechanisms MUST be enabled. Therefore, if a PE device receives an Ethernet frame containing hardware-level Cyclic Redundancy Check (CRC) errors, framing errors, or a runt condition, the frame MUST be discarded on input. Note that defining this processing is part of the NSP function and is outside the scope of this document.
在PW入口，必须启用本机以太网帧错误处理机制。因此，如果PE设备接收到包含硬件级循环冗余校验（CRC）错误、帧错误或runt条件的以太网帧，则必须在输入时丢弃该帧。请注意，定义此处理是NSP功能的一部分，不在本文档的范围内。
In a standard Ethernet network, the flow control mechanism is optional and typically configured between the two nodes on a point-to-point link (e.g., between the CE and the PE). IEEE 802.3x PAUSE frames MUST NOT be carried across the PW. See Appendix A for notes on CE-PE flow control.
在标准以太网网络中，流量控制机制是可选的，并且通常在点到点链路上的两个节点之间配置（例如，在CE和PE之间）。IEEE 802.3x暂停帧不得通过PW传输。CE-PE流量控制说明见附录A。
The Ethernet PW management model follows the general PW management model defined in [RFC3985] and [PWE3-MIB]. Many common PW management facilities are provided here, with no additional Ethernet specifics necessary. Ethernet-specific parameters are defined in an additional MIB module, [PW-MIB].
以太网PW管理模型遵循[RFC3985]和[PWE3-MIB]中定义的通用PW管理模型。这里提供了许多常见的PW管理设施，不需要额外的以太网细节。以太网特定参数在附加MIB模块[PW-MIB]中定义。
The control word defined in this section is based on the Generic PW MPLS Control Word as defined in [PWE3-CW]. It provides the ability to sequence individual frames on the PW, avoidance of equal-cost multiple-path load-balancing (ECMP) [RFC2992], and Operations and Management (OAM) mechanisms including VCCV [VCCV].
本节中定义的控制字基于[PWE3-CW]中定义的通用PW MPLS控制字。它提供对PW上的各个帧进行排序的能力，避免等成本多路径负载平衡（ECMP）[RFC2992]，以及包括VCCV[VCCV]在内的操作和管理（OAM）机制。
[PWE3-CW] states, "If a PW is sensitive to packet misordering and is being carried over an MPLS PSN that uses the contents of the MPLS payload to select the ECMP path, it MUST employ a mechanism which prevents packet misordering." This is necessary because ECMP implementations may examine the first nibble after the MPLS label stack to determine whether the labelled packet is IP or not. Thus, if the source MAC address of an Ethernet frame carried over the PW without a control word present begins with 0x4 or 0x6, it could be mistaken for an IPv4 or IPv6 packet. This could, depending on the configuration and topology of the MPLS network, lead to a situation where all packets for a given PW do not follow the same path. This may increase out-of-order frames on a given PW, or cause OAM packets to follow a different path than actual traffic (see Section 4.4.3, "Frame Ordering").
[PWE3-CW]指出，“如果PW对数据包错序非常敏感，并且正在通过使用MPLS有效载荷的内容来选择ECMP路径的MPLS PSN进行传输，则必须采用防止数据包错序的机制。”这是必要的，因为ECMP实现可能会检查MPLS标签堆栈之后的第一个半字节，以确定标记的数据包是否为IP。因此，如果在PW上携带的以太网帧的源MAC地址（不存在控制字）以0x4或0x6开头，则可能会将其误认为IPv4或IPv6数据包。根据MPLS网络的配置和拓扑，这可能导致给定PW的所有数据包不遵循相同路径的情况。这可能会增加给定PW上的无序帧，或导致OAM数据包遵循与实际流量不同的路径（参见第4.4.3节“帧顺序”）。
The features that the control word provides may not be needed for a given Ethernet PW. For example, ECMP may not be present or active on a given MPLS network, strict frame sequencing may not be required, etc. If this is the case, the control word provides little value and is therefore optional. Early Ethernet PW implementations have been deployed that do not include a control word or the ability to process one if present. To aid in backwards compatibility, future implementations MUST be able to send and receive frames without the control word present.
给定以太网PW可能不需要控制字提供的功能。例如，ECMP在给定MPLS网络上可能不存在或不活动，可能不需要严格的帧排序等。如果是这种情况，则控制字提供的值很小，因此是可选的。早期的以太网PW实现已经部署，不包括控制字或处理控制字（如果存在）的能力。为了帮助实现向后兼容性，未来的实现必须能够在不存在控制字的情况下发送和接收帧。
In all cases, the egress PE MUST be aware of whether the ingress PE will send a control word over a specific PW. This may be achieved by configuration of the PEs, or by signaling, as defined in [PWE3-CTRL].
在所有情况下，出口PE必须知道入口PE是否将通过特定PW发送控制字。这可以通过配置PEs或通过[PWE3-CTRL]中定义的信令来实现。
The control word is defined as follows:
控制字的定义如下：
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 0| Reserved | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 0| Reserved | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the above diagram, the first 4 bits MUST be set to 0 to indicate PW data. The rest of the first 16 bits are reserved for future use. They MUST be set to 0 when transmitting, and MUST be ignored upon receipt.
在上图中，前4位必须设置为0以指示PW数据。前16位的其余部分保留供将来使用。传输时必须将其设置为0，并且在接收时必须忽略。
The next 16 bits provide a sequence number that can be used to guarantee ordered frame delivery. The processing of the sequence number field is OPTIONAL.
接下来的16位提供了一个序列号，可用于保证有序的帧传送。序列号字段的处理是可选的。
The sequence number space is a 16-bit, unsigned circular space. The sequence number value 0 is used to indicate that the sequence number check algorithm is not used. The sequence number processing algorithm is found in [PWE3-CW].
序列号空间是一个16位的无符号循环空间。序号值0用于指示未使用序号检查算法。序列号处理算法见[PWE3-CW]。
The ingress PE MAY consider the user priority (PRI) field [802.1Q] of the VLAN tag header when determining the value to be placed in a QoS field of the encapsulating protocol (e.g., the EXP fields of the MPLS label stack). In a similar way, the egress PE MAY consider the QoS field of the encapsulating protocol (e.g., the EXP fields of the MPLS label stack) when queuing the frame for transmission towards the CE.
入口PE可以在确定要放置在封装协议的QoS字段中的值（例如，MPLS标签堆栈的EXP字段）时考虑VLAN标签头的用户优先级（PRI）字段[802.1Q]。以类似的方式，外出PE可以考虑封装协议的QoS字段（例如，MPLS标签堆栈的EXP字段），当排队用于向CE传输的帧时。
A PE MUST support the ability to carry the Ethernet PW as a best-effort service over the MPLS PSN. PRI bits are kept transparent between PE devices, regardless of the QoS support of the PSN.
PE必须支持通过MPLS PSN将以太网PW作为尽力而为的服务进行传输的能力。PRI位在PE设备之间保持透明，而不考虑PSN的QoS支持。
If an 802.1Q VLAN field is added at the PE, a default PRI setting of zero MUST be supported, a configured default value is recommended, or the value may be mapped from the QoS field of the PSN, as referred to above.
如果在PE处添加802.1Q VLAN字段，则必须支持默认PRI设置为零，建议配置默认值，或者可以从PSN的QoS字段映射该值，如上所述。
A PE may support additional QoS support by means of one or more of the following methods:
PE可通过以下一种或多种方法支持额外的QoS支持：
i. One class of service (CoS) per PW End Service (PWES), mapped to a single CoS PW at the PSN. ii. Multiple CoS per PWES mapped to a single PW with multiple CoS at the PSN. iii. Multiple CoS per PWES mapped to multiple PWs at the PSN.
我每个PW终端服务（PWES）一个服务类别（CoS），映射到PSN处的单个CoS PW。二,。每个PWE的多个CoS映射到PSN处具有多个CoS的单个PW。iii.每个PWE的多个CoS映射到PSN的多个PW。
Examples of the cases above and details of the service mapping considerations are described in Appendix B.
附录B中描述了上述案例的示例和服务映射注意事项的详细信息。
The PW guaranteed rate at the MPLS PSN level is PW service provider policy based on agreement with the customer, and may be different from the Ethernet physical port rate.
MPLS PSN级别的PW保证速率是基于与客户协议的PW服务提供商策略，可能不同于以太网物理端口速率。
The Ethernet pseudowire type is subject to all of the general security considerations discussed in [RFC3985] and [PWE3-CTRL].
以太网伪线类型受[RFC3985]和[PWE3-CTRL]中讨论的所有一般安全注意事项的约束。
The Ethernet pseudowire is transported on an MPLS PSN; therefore, the security of the pseudowire itself will only be as good as the security of the MPLS PSN. The MPLS PSN can be secured by various methods, as described in [MPLS-ARCH].
以太网伪线在MPLS PSN上传输；因此，伪线本身的安全性将只与MPLS PSN的安全性一样好。如[MPLS-ARCH]中所述，MPLS PSN可以通过各种方法进行保护。
Security achieved by access control of MAC addresses is out of the scope of this document. Additional security requirements related to the use of PW in a switching (virtual bridging) environment are not discussed here as they are not within the scope of this document.
通过MAC地址访问控制实现的安全性不在本文档范围内。与在交换（虚拟桥接）环境中使用PW相关的其他安全要求在此不讨论，因为它们不在本文档的范围内。
The MPLS PSN MUST be configured with an MTU that is large enough to transport a maximum-sized Ethernet frame that has been encapsulated with a control word, a pseudowire demultiplexer, and a tunnel encapsulation. With MPLS used as the tunneling protocol, for example, this is likely to be 8 or more bytes greater than the largest frame size. The methodology described in [FRAG] MAY be used to fragment encapsulated frames that exceed the PSN MTU. However, if [FRAG] is not used and if the ingress router determines that an encapsulated layer 2 PDU exceeds the MTU of the PSN tunnel through which it must be sent, the PDU MUST be dropped.
MPLS PSN必须配置足够大的MTU，以传输已用控制字、伪线解复用器和隧道封装封装的最大尺寸以太网帧。例如，使用MPLS作为隧道协议时，这可能比最大帧大小大8个或更多字节。[FRAG]中描述的方法可用于分割超过PSN MTU的封装帧。然而，如果未使用[FRAG]，并且如果入口路由器确定封装的第2层PDU超过必须通过其发送的PSN隧道的MTU，则必须丢弃PDU。
[PWE3-CW] Bryant, S., Swallow, G., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006.
[PWE3-CW]Bryant，S.，Swallow，G.，和D.McPherson，“在MPLS PSN上使用的伪线仿真边到边（PWE3）控制字”，RFC 4385，2006年2月。
[IANA] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[IANA]Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，2006年4月。
[PWE3-CTRL] Martini, L., El-Aawar, N., Heron, G., Rosen, E., Tappan, D., and T. Smith, "Pseudowire Setup and Maintenance using the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[PWE3-CTRL]Martini，L.，El Aawar，N.，Heron，G.，Rosen，E.，Tappan，D.，和T.Smith，“使用标签分发协议（LDP）的伪线设置和维护”，RFC 4447，2006年4月。
[MPLS-ARCH] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001.
[MPLS-ARCH]Rosen，E.，Viswanathan，A.，和R.Callon，“多协议标签交换体系结构”，RFC 30312001年1月。
[802.3] IEEE802.3-2005, ISO/IEC 8802-3: 2000 (E), "IEEE Standard for Information technology -- Telecommunications and information exchange between systems -- Local and metropolitan area networks -- Specific requirements -- Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications", 2005.
[802.3]IEEE802.3-2005，ISO/IEC 8802-3:2000（E），“IEEE信息技术标准——系统间电信和信息交换——局域网和城域网——具体要求——第3部分：带冲突检测的载波侦听多址（CSMA/CD）接入方法和物理层规范”，2005
[802.1Q] ANSI/IEEE Standard 802.1Q-2005, "IEEE Standards for Local and Metropolitan Area Networks: Virtual Bridged Local Area Networks", 2005.
[802.1Q]ANSI/IEEE标准802.1Q-2005，“局域网和城域网的IEEE标准：虚拟桥接局域网”，2005年。
[PDU] IEEE Std 802.3, 1998 Edition, "Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications" figure 3.1, 1998
[PDU]IEEE标准802.3，1998版，“第3部分：带冲突检测的载波侦听多址接入（CSMA/CD）接入方法和物理层规范”，图3.11998
[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。
[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。
[PW-MIB] Zelig, D. and T. Nadeau, "Ethernet Pseudo Wire (PW) Management Information Base", Work in Progress, February 2006.
[PW-MIB]Zelig，D.和T.Nadeau，“以太网伪线（PW）管理信息库”，正在进行的工作，2006年2月。
[PWE3-REQ] Xiao, X., McPherson, D., and P. Pate, "Requirements for Pseudo-Wire Emulation Edge-to-Edge (PWE3)", RFC 3916, September 2004.
[PWE3-REQ]Xiao，X.，McPherson，D.，和P.Pate，“伪线仿真边到边（PWE3）的要求”，RFC 39162004年9月。
[PWE3-MIB] Zelig, D., Ed. and T. Nadeau, Ed., "Pseudo Wire (PW) Management Information Base", Work in Progress, February 2006.
[PWE3-MIB]Zelig，D.，Ed.和T.Nadeau，Ed.，“伪线路（PW）管理信息库”，正在进行的工作，2006年2月。
[LDP] Andersson, L., Doolan, P., Feldman, N., Fredette, A., and B. Thomas, "LDP Specification", RFC 3036, January 2001.
[LDP]Andersson，L.，Doolan，P.，Feldman，N.，Fredette，A.，和B.Thomas，“LDP规范”，RFC 3036，2001年1月。
[FRAG] Malis, A. and W. Townsley, "PWE3 Fragmentation and Reassembly", Work in Progress, February 2005.
[FRAG]Malis，A.和W.Townsley，“PWE3碎片化和重组”，正在进行的工作，2005年2月。
[FCS] Malis, A., Allan, D., and N. Del Regno, "PWE3 Frame Check Sequence Retention", Work in Progress, September 2005.
[FCS]Malis，A.，Allan，D.，和N.Del Regno，“PWE3帧检查序列保留”，正在进行的工作，2005年9月。
[VCCV] Nadeau, T., Ed. and R. Aggarwal, Ed., "Pseudo Wire Virtual Circuit Connectivity Verification (VCCV)", Work in Progress, August 2005.
[VCCV]Nadeau，T.，Ed.和R.Aggarwal，Ed.，“伪线虚拟电路连接验证（VCCV）”，正在进行的工作，2005年8月。
[RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path Algorithm", RFC 2992, November 2000.
[RFC2992]Hopps，C.，“等成本多径算法分析”，RFC 2992，2000年11月。
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, March 2005.
[RFC4026]Andersson，L.和T.Madsen，“提供商提供的虚拟专用网络（VPN）术语”，RFC 4026，2005年3月。
[L2TPv3] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[L2TPv3]Lau，J.，Townsley，M.，和I.Goyret，“第二层隧道协议-版本3（L2TPv3）”，RFC 39312005年3月。
Andrew G. Malis Tellabs 90 Rio Robles Dr. San Jose, CA 95134
安德鲁·G·马里斯·特拉伯斯90里约热内卢·罗伯斯博士，加利福尼亚州圣何塞，邮编95134
EMail: Andy.Malis@tellabs.com
EMail: Andy.Malis@tellabs.com
Dan Tappan Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, MA 01719
Dan Tappan Cisco Systems，Inc.马萨诸塞州伯斯堡马萨诸塞大道1414号，邮编01719
EMail: tappan@cisco.com
EMail: tappan@cisco.com
Steve Vogelsang ECI Telecom Omega Corporate Center 1300 Omega Drive Pittsburgh, PA 15205
宾夕法尼亚州匹兹堡欧米茄大道1300号Steve Vogelsang ECI电信欧米茄公司中心15205
EMail: stephen.vogelsang@ecitele.com
EMail: stephen.vogelsang@ecitele.com
Vinai Sirkay Reliance Infocomm Dhirubai Ambani Knowledge City Navi Mumbai 400 709 India
Vinai Sirkay Reliance Infocomm Dhirubai Ambani知识城纳维孟买400 709印度
EMail: vinai@sirkay.com
EMail: vinai@sirkay.com
Vasile Radoaca Nortel Networks 600 Technology Park Billerica MA 01821
瓦西里·拉多阿卡北电网络600技术园马里兰州比尔里卡01821
EMail: vasile@nortelnetworks.com
EMail: vasile@nortelnetworks.com
Chris Liljenstolpe Alcatel 11600 Sallie Mae Dr. 9th Floor Reston, VA 20193
Chris Liljenstolpe Alcatel 11600 Sallie Mae博士，弗吉尼亚州雷斯顿市9楼，邮编20193
EMail: chris.liljenstolpe@alcatel.com
EMail: chris.liljenstolpe@alcatel.com
Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave Sunnyvale, CA 94089
Kireeti Kompella Juniper Networks 1194 N.Mathilda Ave Sunnyvale，加利福尼亚州94089
EMail: kireeti@juniper.net
EMail: kireeti@juniper.net
Tricci So Nortel Networks 3500 Carling Ave., Nepean, Ontario, Canada, K2H 8E9.
Tricci So Nortel Networks加拿大安大略省内皮恩卡林大道3500号，K2H 8E9。
EMail: tso@nortelnetworks.com
EMail: tso@nortelnetworks.com
XiPeng Xiao Riverstone Networks 5200 Great America Parkway Santa Clara, CA 95054
加利福尼亚州圣克拉拉大美洲公园路5200号西彭肖里弗斯通网络公司，邮编95054
EMail: xxiao@riverstonenet.com
EMail: xxiao@riverstonenet.com
Christopher O. Flores T-Systems 10700 Parkridge Boulevard Reston, VA 20191 USA
克里斯托弗·弗洛雷斯T-Systems美国弗吉尼亚州莱斯顿市帕克里奇大道10700号，邮编：20191
EMail: christopher.flores@usa.telekom.de
EMail: christopher.flores@usa.telekom.de
David Zelig Corrigent Systems 126, Yigal Alon St. Tel Aviv, ISRAEL
David Zelig Corrigent Systems 126，以色列特拉维夫Yigal Alon St.特拉维夫
EMail: davidz@corrigent.com
EMail: davidz@corrigent.com
Raj Sharma Luminous Networks, Inc. 10460 Bubb Road Cupertino, CA 95014
Raj Sharma夜光网络有限公司，地址：加利福尼亚州库比蒂诺市布布路10460号，邮编95014
EMail: raj@luminous.com
EMail: raj@luminous.com
Nick Tingle TiMetra Networks 274 Ferguson Drive Mountain View, CA 94043
美国加利福尼亚州山景城弗格森大道274号Nick Tingle TiMetra Networks 94043
EMail: nick@timetra.com
EMail: nick@timetra.com
Sunil Khandekar TiMetra Networks 274 Ferguson Drive Mountain View, CA 94043
Sunil Khandekar TiMetra Networks 274 Ferguson Drive Mountain View，加利福尼亚州94043
EMail: sunil@timetra.com
EMail: sunil@timetra.com
Loa Andersson TLA-group
安达信TLA集团
EMail: loa@pi.se
EMail: loa@pi.se
The following is a list of the configuration options for a point-to-point Ethernet PW based on the reference points of Figure 3:
以下是基于图3参考点的点到点以太网PW配置选项列表：
--------------|---------------|---------------|------------------
Service and | Encap on C |Operation at B | Remarks
Encap on A | |ingress/egress |
--------------|---------------|---------------|------------------
1) Raw | Raw - Same as | |
| A | |
| | |
--------------|---------------|---------------|------------------
2) Tag1 | Tag2 |Optional change| VLAN can be
| |of VLAN value | 0-4095
| | | Change allowed in
| | | both directions
--------------|---------------|---------------|------------------
3) No Tag | Tag |Add/remove Tag | Tag can be
| |field | 0-4095
| | | (note i)
| | |
--------------|---------------|---------------|------------------
4) Tag | No Tag |Remove/add Tag | (note ii)
| |field |
| | |
| | |
--------------|---------------|---------------|------------------
--------------|---------------|---------------|------------------
Service and | Encap on C |Operation at B | Remarks
Encap on A | |ingress/egress |
--------------|---------------|---------------|------------------
1) Raw | Raw - Same as | |
| A | |
| | |
--------------|---------------|---------------|------------------
2) Tag1 | Tag2 |Optional change| VLAN can be
| |of VLAN value | 0-4095
| | | Change allowed in
| | | both directions
--------------|---------------|---------------|------------------
3) No Tag | Tag |Add/remove Tag | Tag can be
| |field | 0-4095
| | | (note i)
| | |
--------------|---------------|---------------|------------------
4) Tag | No Tag |Remove/add Tag | (note ii)
| |field |
| | |
| | |
--------------|---------------|---------------|------------------
Figure 4: Configuration Options
图4：配置选项
Allowed combinations:
允许的组合：
Raw and other services are not allowed on the same NSP virtual port (A). All other combinations are allowed, except that conflicting VLANs on (A) are not allowed. Note that in most point-to-point PW applications the NSP virtual port is the same entity as the physical port.
不允许在同一NSP虚拟端口（A）上使用原始服务和其他服务。允许所有其他组合，但不允许（A）上存在冲突的VLAN。请注意，在大多数点对点PW应用程序中，NSP虚拟端口与物理端口是同一实体。
Notes:
笔记：
i. Mode #3 MAY be limited to adding VLAN NULL only, since change of VLAN or association to specific VLAN can be done at the PW CE-bound side.
i. 模式#3可能仅限于添加VLAN NULL，因为可以在PW CE绑定端更改VLAN或与特定VLAN的关联。
ii. Mode #4 exists in layer 2 switches, but is not recommended when operating with PW since it may not preserve the user's PRI bits. If there is a need to remove the VLAN tag (for TLS at the other end of the PW), it is recommended to use mode #2 with tag2=0 (NULL VLAN) on the PW and use mode #3 at the other end of the PW.
二,。模式#4存在于第2层交换机中，但在使用PW操作时不建议使用，因为它可能不会保留用户的PRI位。如果需要删除VLAN标记（对于PW另一端的TLS），建议在PW上使用tag2=0（空VLAN）的模式#2，并在PW的另一端使用模式#3。
If the receiving node becomes congested, it can send a special frame, called the PAUSE frame, to the source node at the opposite end of the connection. The implementation MUST provide a mechanism for terminating PAUSE frames locally (i.e., at the local PE). It MUST operate as follows: PAUSE frames received on a local Ethernet port SHOULD cause the PE device to buffer, or to discard, further Ethernet frames for that port until the PAUSE condition is cleared. Optionally, the PE MAY simply discard PAUSE frames.
如果接收节点变得拥挤，它可以向连接另一端的源节点发送一个称为暂停帧的特殊帧。该实现必须提供一种在本地（即在本地PE）终止暂停帧的机制。它必须按如下操作：在本地以太网端口上接收的暂停帧应导致PE设备缓冲或丢弃该端口的更多以太网帧，直到暂停条件被清除。可选地，PE可以简单地丢弃暂停帧。
If the PE device wishes to pause data received on a local Ethernet port (perhaps because its own buffers are filling up or because it has received notification of congestion within the PSN), then it MAY issue a PAUSE frame on the local Ethernet port, but MUST clear this condition when willing to receive more data.
如果PE设备希望暂停在本地以太网端口上接收的数据（可能是因为其自身的缓冲区已满，或者因为其已在PSN内接收到拥塞通知），则其可在本地以太网端口上发出暂停帧，但在愿意接收更多数据时必须清除此条件。
Section 4.7, "QoS Considerations", describes various modes for supporting PW QOS over the PSN. Examples of the above for a point-to-point VLAN service are:
第4.7节“QoS注意事项”描述了在PSN上支持PW QoS的各种模式。点到点VLAN服务的上述示例包括：
- The classification to the PW is based on VLAN field, but the user PRI bits are mapped to different CoS markings (and network behavior) at the PW level. An example of this is a PW mapped to an E-LSP in an MPLS network.
- PW的分类基于VLAN字段，但用户PRI位在PW级别映射到不同的CoS标记（和网络行为）。这方面的一个例子是映射到MPLS网络中的E-LSP的PW。
- The classification to the PW is based on VLAN field and the PRI bits, and frames with different PRI bits are mapped to different PWs. An example is to map a PWES to different L-LSPs in MPLS PSN in order to support multiple CoS over an L-LSP-capable network, or to map a PWES to multiple L2TPv3 sessions [L2TPv3].
- PW的分类基于VLAN字段和PRI位，具有不同PRI位的帧映射到不同的PW。例如，将PWE映射到MPLS PSN中的不同L-LSP，以便在支持L-LSP的网络上支持多个CoS，或者将PWE映射到多个L2TPv3会话[L2TPv3]。
The specific value to be assigned at the PSN for various CoS is out of the scope of this document.
在PSN上为各种CoS分配的特定值不在本文件范围内。
It is not required that the PSN will have the same CoS definition of CoS as defined in [802.1Q], and the mapping of 802.1Q CoS to PSN CoS is application specific and depends on the agreement between the customer and the PW provider. However, the following principles adopted from 802.1Q, Table 8-2, MUST be met when applying the set of PSN CoS based on user's PRI bits.
不要求PSN具有与[802.1Q]中定义的CoS相同的CoS定义，并且802.1Q CoS到PSN CoS的映射是特定于应用程序的，取决于客户和PW提供商之间的协议。然而，当基于用户的PRI位应用PSN CoS集时，必须满足802.1Q表8-2中采用的以下原则。
----------------------------------
|#of available classes of service|
-------------||---+---+---+---+---+---+---+---|
User || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Priority || | | | | | | | |
===============================================
0 Best Effort|| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 2 |
(Default) || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
1 Background || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
|| | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
2 Spare || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
|| | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
3 Excellent || 0 | 0 | 0 | 1 | 1 | 2 | 2 | 3 |
Effort || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
4 Controlled || 0 | 1 | 1 | 2 | 2 | 3 | 3 | 4 |
Load || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
5 Interactive|| 0 | 1 | 1 | 2 | 3 | 4 | 4 | 5 |
Multimedia || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
6 Interactive|| 0 | 1 | 2 | 3 | 4 | 5 | 5 | 6 |
Voice || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
7 Network || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Control || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
----------------------------------
|#of available classes of service|
-------------||---+---+---+---+---+---+---+---|
User || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Priority || | | | | | | | |
===============================================
0 Best Effort|| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 2 |
(Default) || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
1 Background || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
|| | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
2 Spare || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
|| | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
3 Excellent || 0 | 0 | 0 | 1 | 1 | 2 | 2 | 3 |
Effort || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
4 Controlled || 0 | 1 | 1 | 2 | 2 | 3 | 3 | 4 |
Load || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
5 Interactive|| 0 | 1 | 1 | 2 | 3 | 4 | 4 | 5 |
Multimedia || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
6 Interactive|| 0 | 1 | 2 | 3 | 4 | 5 | 5 | 6 |
Voice || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
7 Network || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Control || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
Figure 5: IEEE 802.1Q CoS Mapping
图5:IEEE 802.1Q CoS映射
The 802.1P standard does not support drop precedence; therefore, from the PW PE-bound point of view there is no mapping required. It is, however, possible to mark different drop precedence for different PW frames based on the operator policy and required network behavior. This functionality is not discussed further here.
802.1P标准不支持删除优先级；因此，从PW PE绑定的角度来看，不需要映射。但是，可以根据运营商策略和所需的网络行为，为不同的PW帧标记不同的丢弃优先级。这里不再进一步讨论此功能。
PSN QoS support and signaling of QoS are out of the scope of this document.
PSN QoS支持和QoS信令不在本文档范围内。
Authors' Addresses
作者地址
Luca Martini, Editor Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112
卢卡·马蒂尼，思科系统公司编辑，地址：科罗拉多州恩格尔伍德东尼科尔斯大道9155号400室，邮编：80112
EMail: lmartini@cisco.com
EMail: lmartini@cisco.com
Nasser El-Aawar Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO, 80021
Nasser El Aawar三级通信有限责任公司，埃尔多拉多大道1025号。科罗拉多州布鲁姆菲尔德，80021
EMail: nna@level3.net
EMail: nna@level3.net
Giles Heron Tellabs Abbey Place 24-28 Easton Street High Wycombe Bucks HP11 1NT UK
Giles Heron Tellabs Abbey Place 24-28 Easton Street High Wycombe Bucks HP11 1NT英国
EMail: giles.heron@tellabs.com
EMail: giles.heron@tellabs.com
Eric C. Rosen Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, MA 01719
Eric C.Rosen Cisco Systems，Inc.马萨诸塞州伯斯堡马萨诸塞大道1414号，邮编01719
EMail: erosen@cisco.com
EMail: erosen@cisco.com
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确认
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