Network Working Group A. Malis
Request for Comments: 4842 Verizon Communications
Category: Standards Track P. Pate
Overture Networks
R. Cohen, Ed.
Resolute Networks
D. Zelig
Corrigent Systems
April 2007
Network Working Group A. Malis
Request for Comments: 4842 Verizon Communications
Category: Standards Track P. Pate
Overture Networks
R. Cohen, Ed.
Resolute Networks
D. Zelig
Corrigent Systems
April 2007
Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Circuit Emulation over Packet (CEP)
同步光网络/同步数字体系（SONET/SDH）分组电路仿真（CEP）
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 IETF Trust (2007).
版权所有（C）IETF信托基金（2007年）。
Abstract
摘要
This document provides encapsulation formats and semantics for emulating Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) circuits and services over MPLS.
本文档提供了通过MPLS模拟同步光网络/同步数字体系（SONET/SDH）电路和服务的封装格式和语义。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
4. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. CEP Encapsulation Format . . . . . . . . . . . . . . . . . . . 5
5.1. SONET/SDH Fragment . . . . . . . . . . . . . . . . . . . . 6
5.2. CEP Header . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 9
5.4. PSN Encapsulation . . . . . . . . . . . . . . . . . . . . 11
6. CEP Operation . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. CEP Packetizer and De-Packetizer . . . . . . . . . . . . . 11
6.2. Packet Synchronization . . . . . . . . . . . . . . . . . . 12
6.2.1. Acquisition of Packet Synchronization . . . . . . . . 13
6.2.2. Loss of Packet Synchronization . . . . . . . . . . . . 13
7. SONET/SDH Maintenance Signals . . . . . . . . . . . . . . . . 13
7.1. SONET/SDH to PSN . . . . . . . . . . . . . . . . . . . . . 13
7.1.1. CEP-AIS: AIS-P/V Indication . . . . . . . . . . . . . 13
7.1.2. Unequipped Indication . . . . . . . . . . . . . . . . 14
7.1.3. CEP-RDI: Remote Defect Indication . . . . . . . . . . 15
7.2. PSN to SONET/SDH . . . . . . . . . . . . . . . . . . . . . 15
7.2.1. CEP-AIS: AIS-P/V Indication . . . . . . . . . . . . . 15
7.2.2. Unequipped Indication . . . . . . . . . . . . . . . . 16
8. SONET/SDH Transport Timing . . . . . . . . . . . . . . . . . . 16
9. SONET/SDH Pointer Management . . . . . . . . . . . . . . . . . 17
9.1. Explicit Pointer Adjustment Relay (EPAR) . . . . . . . . . 17
9.2. Adaptive Pointer Management (APM) . . . . . . . . . . . . 19
10. CEP Performance Monitors . . . . . . . . . . . . . . . . . . . 19
10.1. Near-End Performance Monitors . . . . . . . . . . . . . . 19
10.2. Far-End Performance Monitors . . . . . . . . . . . . . . . 20
11. Payload Compression Options . . . . . . . . . . . . . . . . . 20
11.1. Dynamic Bandwidth Allocation . . . . . . . . . . . . . . . 21
11.2. Service-Specific Payload Formats . . . . . . . . . . . . . 21
11.2.1. Fractional STS-1 (VC-3) Encapsulation . . . . . . . . 21
11.2.1.1. Fractional STS-1 CEP Header . . . . . . . . . . . 23
11.2.1.2. B3 Compensation . . . . . . . . . . . . . . . . . 24
11.2.1.3. Actual Payload Size . . . . . . . . . . . . . . . 24
11.2.2. Asynchronous T3/E3 STS-1 (VC-3) Encapsulation . . . . 25
11.2.2.1. T3 Payload Compression . . . . . . . . . . . . . 25
11.2.2.2. E3 Payload Compression . . . . . . . . . . . . . 26
11.2.3. Fractional VC-4 Encapsulation . . . . . . . . . . . . 26
11.2.3.1. Fractional VC-4 Mapping . . . . . . . . . . . . . 27
11.2.3.2. Fractional VC-4 CEP Header . . . . . . . . . . . 28
11.2.3.3. B3 Compensation . . . . . . . . . . . . . . . . . 29
11.2.3.4. Actual Payload Sizes . . . . . . . . . . . . . . 30
12. Signaling of CEP Pseudowires . . . . . . . . . . . . . . . . . 30
12.1. CEP/TDM Payload Bytes . . . . . . . . . . . . . . . . . . 31
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
4. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. CEP Encapsulation Format . . . . . . . . . . . . . . . . . . . 5
5.1. SONET/SDH Fragment . . . . . . . . . . . . . . . . . . . . 6
5.2. CEP Header . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 9
5.4. PSN Encapsulation . . . . . . . . . . . . . . . . . . . . 11
6. CEP Operation . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. CEP Packetizer and De-Packetizer . . . . . . . . . . . . . 11
6.2. Packet Synchronization . . . . . . . . . . . . . . . . . . 12
6.2.1. Acquisition of Packet Synchronization . . . . . . . . 13
6.2.2. Loss of Packet Synchronization . . . . . . . . . . . . 13
7. SONET/SDH Maintenance Signals . . . . . . . . . . . . . . . . 13
7.1. SONET/SDH to PSN . . . . . . . . . . . . . . . . . . . . . 13
7.1.1. CEP-AIS: AIS-P/V Indication . . . . . . . . . . . . . 13
7.1.2. Unequipped Indication . . . . . . . . . . . . . . . . 14
7.1.3. CEP-RDI: Remote Defect Indication . . . . . . . . . . 15
7.2. PSN to SONET/SDH . . . . . . . . . . . . . . . . . . . . . 15
7.2.1. CEP-AIS: AIS-P/V Indication . . . . . . . . . . . . . 15
7.2.2. Unequipped Indication . . . . . . . . . . . . . . . . 16
8. SONET/SDH Transport Timing . . . . . . . . . . . . . . . . . . 16
9. SONET/SDH Pointer Management . . . . . . . . . . . . . . . . . 17
9.1. Explicit Pointer Adjustment Relay (EPAR) . . . . . . . . . 17
9.2. Adaptive Pointer Management (APM) . . . . . . . . . . . . 19
10. CEP Performance Monitors . . . . . . . . . . . . . . . . . . . 19
10.1. Near-End Performance Monitors . . . . . . . . . . . . . . 19
10.2. Far-End Performance Monitors . . . . . . . . . . . . . . . 20
11. Payload Compression Options . . . . . . . . . . . . . . . . . 20
11.1. Dynamic Bandwidth Allocation . . . . . . . . . . . . . . . 21
11.2. Service-Specific Payload Formats . . . . . . . . . . . . . 21
11.2.1. Fractional STS-1 (VC-3) Encapsulation . . . . . . . . 21
11.2.1.1. Fractional STS-1 CEP Header . . . . . . . . . . . 23
11.2.1.2. B3 Compensation . . . . . . . . . . . . . . . . . 24
11.2.1.3. Actual Payload Size . . . . . . . . . . . . . . . 24
11.2.2. Asynchronous T3/E3 STS-1 (VC-3) Encapsulation . . . . 25
11.2.2.1. T3 Payload Compression . . . . . . . . . . . . . 25
11.2.2.2. E3 Payload Compression . . . . . . . . . . . . . 26
11.2.3. Fractional VC-4 Encapsulation . . . . . . . . . . . . 26
11.2.3.1. Fractional VC-4 Mapping . . . . . . . . . . . . . 27
11.2.3.2. Fractional VC-4 CEP Header . . . . . . . . . . . 28
11.2.3.3. B3 Compensation . . . . . . . . . . . . . . . . . 29
11.2.3.4. Actual Payload Sizes . . . . . . . . . . . . . . 30
12. Signaling of CEP Pseudowires . . . . . . . . . . . . . . . . . 30
12.1. CEP/TDM Payload Bytes . . . . . . . . . . . . . . . . . . 31
12.2. CEP/TDM Bit Rate . . . . . . . . . . . . . . . . . . . . . 31
12.3. CEP Options . . . . . . . . . . . . . . . . . . . . . . . 32
13. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 34
14. Security Considerations . . . . . . . . . . . . . . . . . . . 34
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
17. Co-Authors . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix A. SONET/SDH Rates and Formats . . . . . . . . . . . . . 36
Appendix B. Example Network Diagrams . . . . . . . . . . . . . . 37
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
18.1. Normative References . . . . . . . . . . . . . . . . . . . 40
18.2. Informative References . . . . . . . . . . . . . . . . . . 41
12.2. CEP/TDM Bit Rate . . . . . . . . . . . . . . . . . . . . . 31
12.3. CEP Options . . . . . . . . . . . . . . . . . . . . . . . 32
13. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 34
14. Security Considerations . . . . . . . . . . . . . . . . . . . 34
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
17. Co-Authors . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix A. SONET/SDH Rates and Formats . . . . . . . . . . . . . 36
Appendix B. Example Network Diagrams . . . . . . . . . . . . . . 37
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
18.1. Normative References . . . . . . . . . . . . . . . . . . . 40
18.2. Informative References . . . . . . . . . . . . . . . . . . 41
This document provides encapsulation formats and semantics for emulating SONET/SDH circuits and services over MPLS.
本文档提供了通过MPLS模拟SONET/SDH电路和服务的封装格式和语义。
The generic requirements and architecture for Pseudowire Emulation Edge-to-Edge (PWE3) are described in [PWE3-REQ] and [PWE3-ARCH]. Additional requirements for emulation of SONET/SDH and lower-rate TDM circuits are described in [PWE3-TDM-REQ].
[PWE3-REQ]和[PWE3-ARCH]中描述了伪线仿真边到边（PWE3）的一般要求和体系结构。SONET/SDH和低速TDM电路仿真的附加要求在[PWE3-TDM-REQ]中描述。
This document provides encapsulation formats and semantics for emulating SONET/SDH circuits and services over MPLS packet-switched networks (PSNs). Emulation of the following digital signals are defined:
本文档提供了通过MPLS分组交换网络（PSN）模拟SONET/SDH电路和服务的封装格式和语义。定义了以下数字信号的仿真：
1. Synchronous Payload Envelope (SPE)/Virtual Container (VC-n): STS-1/VC-3, STS-3c/VC-4, STS-12c/VC-4-4c, STS-48c/VC-4-16c, STS-192c/ VC-4-64c, etc.
1. 同步有效载荷包络线（SPE）/虚拟容器（VC-n）：STS-1/VC-3、STS-3c/VC-4、STS-12c/VC-4-4c、STS-48c/VC-4-16c、STS-192c/VC-4-64c等。
2. Virtual Tributary (VT)/Virtual Container (VC-n): VT1.5/VC-11, VT2/VC-12, VT3, VT6/VC-2
2. 虚拟支流（VT）/虚拟容器（VC-n）：VT1.5/VC-11、VT2/VC-12、VT3、VT6/VC-2
For the remainder of this document, these constructs are referred to as SONET/SDH channels.
对于本文档的其余部分，这些结构称为SONET/SDH通道。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
ADM Add Drop Multiplexer AIS Alarm Indication Signal APM Adaptive Pointer Management AU-n Administrative Unit-n (SDH) AUG Administrative Unit Group (SDH) BIP Bit Interleaved Parity BITS Building Integrated Timing Supply CEP Circuit Emulation over Packet DBA Dynamic Bandwidth Allocation EBM Equipped Bit Mask EPAR Explicit Pointer Adjustment Relay
ADM Add Drop多路复用器AIS报警指示信号APM自适应指针管理AU-n管理单元n（SDH）AUG管理单元组（SDH）BIP位交叉奇偶校验位构建集成定时电源CEP电路仿真分组DBA动态带宽分配配备EBM的位掩码EPAR显式指针调整继电器
LOF Loss of Frame LOS Loss of Signal LTE Line Terminating Equipment POH Path Overhead PSN Packet Switched Network PTE Path Terminating Equipment PW Pseudowire RDI Remote Defect Indication SDH Synchronous Digital Hierarchy SONET Synchronous Optical Network SPE Synchronous Payload Envelope STM-n Synchronous Transport Module-n (SDH) STS-n Synchronous Transport Signal-n (SONET) TDM Time Division Multiplexing TOH Transport Overhead TU-n Tributary Unit-n (SDH) TUG-n Tributary Unit Group-n (SDH) UNEQ Unequipped VC-n Virtual Container-n (SDH) VT Virtual Tributary (SONET) VTG Virtual Tributary Group (SONET)
LOF帧丢失LOS信号丢失LTE线路终端设备POH路径开销PSN分组交换网络PTE路径终端设备PW伪线RDI远程缺陷指示SDH同步数字体系SONET同步光网络SPE同步有效载荷包络STM-n同步传输模块-n（SDH）STS-n同步传输信号-n（SONET）TDM时分复用到传输开销TU-n支路单元-n（SDH）拖船-n支路单元组-n（SDH）未配置的VC-n虚拟容器-n（SDH）VT虚拟支路（SONET）VTG虚拟支路组（SONET）
In order to transport SONET/SDH circuits through a packet-oriented network, the SPE (or VT) is broken into fragments, and a CEP header and optionally an RTP header are prepended to each fragment.
为了通过面向分组的网络传输SONET/SDH电路，SPE（或VT）被分解成片段，并且CEP报头和可选的RTP报头被预先添加到每个片段。
The basic CEP packet appears in Figure 1.
基本CEP数据包如图1所示。
+-----------------------------------+
| PSN and Multiplexing Layer |
| Headers |
+-----------------------------------+
| CEP Header |
+-----------------------------------+
| RTP Header |
| (RFC 3550) |
+-----------------------------------+
| |
| |
| SONET/SDH |
| Fragment |
| |
| |
+-----------------------------------+
+-----------------------------------+
| PSN and Multiplexing Layer |
| Headers |
+-----------------------------------+
| CEP Header |
+-----------------------------------+
| RTP Header |
| (RFC 3550) |
+-----------------------------------+
| |
| |
| SONET/SDH |
| Fragment |
| |
| |
+-----------------------------------+
Figure 1: Basic CEP Packet
图1：基本CEP数据包
The SONET/SDH fragments MUST be byte aligned with the SONET/SDH SPE or VT. The first bit received from each byte of the SONET/SDH MUST be the Most Significant Bit of each byte in the SONET/SDH fragment.
SONET/SDH片段必须与SONET/SDH SPE或VT进行字节对齐。从SONET/SDH的每个字节接收的第一位必须是SONET/SDH片段中每个字节的最高有效位。
SONET/SDH bytes are placed into the SONET/SDH fragment in the same order in which they are received.
SONET/SDH字节按接收顺序放入SONET/SDH片段中。
SONET/SDH optical interfaces use binary coding and therefore are scrambled prior to transmission to ensure an adequate number of transitions. For clarity, this scrambling is referred to as physical layer scrambling/descrambling.
SONET/SDH光接口使用二进制编码，因此在传输之前进行加扰，以确保足够数量的转换。为清楚起见，该加扰被称为物理层加扰/解扰。
In addition, many payload formats (such as for Asynchronous Transfer Mode (ATM) and High-Level Data Link Control (HDLC)) include an additional layer of scrambling to provide protection against transition density violations within the SPEs. This function is referred to as payload scrambling/unscrambling.
此外，许多有效负载格式（例如异步传输模式（ATM）和高级数据链路控制（HDLC））包括额外的加扰层，以防止SPE内的过渡密度违规。此功能称为有效负载加扰/解扰。
CEP assumes that physical layer scrambling/unscrambling occurs as part of the SONET/SDH section/line termination Native Service Processing (NSP) functions.
CEP假设物理层加扰/解扰作为SONET/SDH段/线路终端本机服务处理（NSP）功能的一部分发生。
However, CEP makes no assumption about payload scrambling. The SONET/SDH fragments MUST be constructed without knowledge or processing of any incidental payload scrambling.
然而，CEP没有对有效载荷加扰进行假设。SONET/SDH片段必须在不知道或不处理任何偶然有效负载干扰的情况下构建。
CEP implementations MUST include the H3 (or V3) byte in the SONET/SDH fragment during negative pointer adjustment events, and MUST remove the stuff byte from the SONET/SDH fragment during positive pointer adjustment events.
CEP实现必须在负指针调整事件期间在SONET/SDH片段中包含H3（或V3）字节，并且在正指针调整事件期间必须从SONET/SDH片段中删除填充字节。
VT emulation implementations MUST NOT carry the VT pointer bytes V1, V2, V3, and V4 as part of the CEP payload. The only exception is the carriage of V3 during negative pointer adjustment as described above.
VT仿真实现不得携带VT指针字节V1、V2、V3和V4作为CEP有效负载的一部分。唯一的例外是如上所述负指针调整期间V3的托架。
All CEP SPE implementations MUST support a packet size of 783 bytes and MAY support other packet sizes.
所有CEP SPE实现必须支持783字节的数据包大小，并且可以支持其他数据包大小。
VT emulation implementations MUST support payload size of full VT super-frame, and MAY support 1/2 and 1/4 VT super-frame payload sizes.
VT仿真实现必须支持完整VT超级帧的有效负载大小，并且可能支持1/2和1/4 VT超级帧有效负载大小。
Table 1 below describes single super-frame payload size per VT type.
下表1描述了每种VT类型的单个超级帧有效负载大小。
+-------------+--------------+
| VT type | Size (Bytes) |
+-------------+--------------+
| VT1.5/VC-11 | 104 |
| VT2/VC-12 | 140 |
| VT3 | 212 |
| VT6/VC-2 | 428 |
+-------------+--------------+
+-------------+--------------+
| VT type | Size (Bytes) |
+-------------+--------------+
| VT1.5/VC-11 | 104 |
| VT2/VC-12 | 140 |
| VT3 | 212 |
| VT6/VC-2 | 428 |
+-------------+--------------+
Table 1: VT Super-Frame Payload Sizes
表1:VT超级帧有效负载大小
OPTIONAL SONET/SDH Fragment formats have been defined to reduce the bandwidth requirements of the emulated SONET/SDH circuits under certain conditions. These OPTIONAL formats are included in Section 11.
已定义了可选SONET/SDH片段格式，以降低特定条件下模拟SONET/SDH电路的带宽要求。这些可选格式包含在第11节中。
The CEP header supports both a basic and extended mode. The Basic CEP header provides the minimum functionality necessary to accurately emulate a SONET/SDH circuit over a PSN. Extended headers are utilized for some of the OPTIONAL SONET/SDH fragment formats described in Section 11.
CEP标头支持基本模式和扩展模式。基本CEP报头提供了在PSN上准确模拟SONET/SDH电路所需的最低功能。扩展报头用于第11节中描述的一些可选SONET/SDH片段格式。
Enhanced functionality and commonality with other real-time Internet applications is provided by RTP encapsulation.
RTP封装提供了增强的功能和与其他实时互联网应用程序的通用性。
The CEP header has the following format:
CEP标头具有以下格式：
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|L|R|N|P|FRG|Length[0:5]| Sequence Number[0:15] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Structure Pointer[0:11]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|L|R|N|P|FRG|Length[0:5]| Sequence Number[0:15] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Structure Pointer[0:11]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: CEP Header Format
图2:CEP标题格式
L bit: CEP-AIS. This bit MUST be set to 1 to signal to the downstream PE that a failure condition has been detected on the attachment circuit. Failure conditions leading to generation of CEP-AIS and the mapping of CEP-AIS signal on the downstream attachment circuit are described in Section 7.
L位：CEP-AIS。该位必须设置为1，以向下游PE发送信号，表明已在附件电路上检测到故障状况。第7节描述了导致产生CEP-AIS的故障条件以及下游连接电路上CEP-AIS信号的映射。
R bit: CEP-RDI. This bit MUST be set to 1 to signal to the upstream PE that a loss of packet synchronization has occurred. This bit MUST be set to 0 once packet synchronization is acquired. See Section 6.2 for details.
R位：CEP-RDI。该位必须设置为1，以向上游PE发出数据包同步丢失的信号。一旦获得数据包同步，该位必须设置为0。详见第6.2节。
N and P bits: These bits are used to explicitly relay negative and positive pointer adjustments events across the PSN. The use of N and P bits is OPTIONAL. If not used, N and P bits MUST be set to 0. See Section 9 for details.
N和P位：这些位用于在PSN上显式中继正负指针调整事件。N和P位的使用是可选的。如果不使用，N和P位必须设置为0。详情见第9节。
Table 2 describes the interpretation of N and P bits settings.
表2描述了N位和P位设置的解释。
+---+---+-----------------------------+
| N | P | Interpretation |
+---+---+-----------------------------+
| 0 | 0 | No Pointer Adjustments |
| 0 | 1 | Positive Pointer Adjustment |
| 1 | 0 | Negative Pointer Adjustment |
| 1 | 1 | Loss of Pointer Alarm |
+---+---+-----------------------------+
+---+---+-----------------------------+
| N | P | Interpretation |
+---+---+-----------------------------+
| 0 | 0 | No Pointer Adjustments |
| 0 | 1 | Positive Pointer Adjustment |
| 1 | 0 | Negative Pointer Adjustment |
| 1 | 1 | Loss of Pointer Alarm |
+---+---+-----------------------------+
Table 2: Interpretation of N and P Bits
表2：N和P位的解释
FRG bits: FRG bits MUST be set to 0 by sender and ignored by receiver.
FRG位：发送方必须将FRG位设置为0，接收方必须忽略FRG位。
SONET data is continuously fragmented into packets. The structure pointer field designates the offset between the SONET SPE or VT structure and the packet boundary.
SONET数据被连续地分割成数据包。结构指针字段指定SONET SPE或VT结构与数据包边界之间的偏移量。
Length [0:5]: The Length field, if other than zero, indicates the length of the CEP header, plus the length of the RTP header if used, plus the length of the payload. The Length field MUST be set if the length of CEP header plus RTP header if used, plus payload is less than or equal to 64 bytes and MUST be set to 0 otherwise. In particular, if the payload is suppressed (e.g., DBA) the Length field MUST be set to the CEP header length plus the RTP header length if used.
长度[0:5]：长度字段（如果不是零）表示CEP标头的长度，加上RTP标头（如果使用）的长度，再加上有效负载的长度。如果CEP标头加上RTP标头（如果使用）的长度加上有效负载小于或等于64字节，则必须设置长度字段，否则必须设置为0。特别是，如果有效负载被抑制（例如DBA），则长度字段必须设置为CEP标头长度加上RTP标头长度（如果使用）。
Sequence Number [0:15]: The packet sequence number MUST continuously cycle from 0 to 0xFFFF. It is generated and processed in accordance with the rules established in [RTP].
序列号[0:15]：数据包序列号必须从0连续循环到0xFFFF。它是根据[RTP]中建立的规则生成和处理的。
Structure Pointer [0:11]: The structure pointer MUST contain the offset of the first byte of the SONET structure within the packet payload. For SPE emulation, the structure pointer locates the J1 byte within the CEP packet. For VT emulation, the structure pointer locates the V5 byte within the packet. The structure pointer value ranges between 0 to 0xFFE, where 0 represents the first byte after the CEP header. The structure pointer MUST be set to 0xFFF if a packet does not carry the J1 (or V5) byte. An arbitrary pointer change (New Data Flag (NDF) event) in the attachment circuit changes the offset of the SONET structure within the CEP packet and therefore changes the structure pointer value.
结构指针[0:11]：结构指针必须包含数据包有效负载内SONET结构的第一个字节的偏移量。对于SPE仿真，结构指针定位CEP数据包中的J1字节。对于VT仿真，结构指针定位数据包中的V5字节。结构指针值的范围在0到0xFFE之间，其中0表示CEP头之后的第一个字节。如果数据包不包含J1（或V5）字节，则结构指针必须设置为0xFFF。连接电路中的任意指针改变（新数据标志（NDF）事件）改变CEP分组内SONET结构的偏移量，因此改变结构指针值。
Reserved field: The reserved field MUST be set to 0 by the sender and ignored by receiver.
保留字段：发送方必须将保留字段设置为0，接收方必须忽略该字段。
Usage of the RTP header is OPTIONAL. Although CEP MAY employ an RTP header when explicit transfer of timing information is required, this is purely a formal reuse of the header format. RTP mechanisms, such as header extensions, contributing source (CSRC) list, padding, RTP Control Protocol (RTCP), RTP header compression, Secure Realtime Transport Protocol (SRTP), etc., are not applicable to pseudowires. CEP uses the RTP Header as shown below.
RTP头的使用是可选的。尽管当需要显式传输定时信息时，CEP可以使用RTP报头，但这纯粹是报头格式的正式重用。RTP机制，如报头扩展、贡献源（CSC）列表、填充、RTP控制协议（RTCP）、RTP报头压缩、安全实时传输协议（SRTP）等，不适用于伪线。CEP使用RTP报头，如下所示。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Synchronization Source (SSRC) Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Synchronization Source (SSRC) Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: RTP Header
图3:RTP报头
V: Version. The Version field MUST be set to 2.
V:版本。版本字段必须设置为2。
P: Padding. No padding is required. The P bit MUST be set to 0 by sender and ignored by receiver.
P:填充。不需要填充。发送方必须将P位设置为0，接收方必须忽略P位。
X: Header extension. No extensions are defined. The X bit MUST be set to 0 by sender and ignored by receiver.
X：标题扩展。没有定义任何扩展。发送方必须将X位设置为0，接收方必须忽略X位。
CC: CSRC count. The CC field MUST be set to 0 by sender and ignored by receiver.
抄送：中国证监会计数。发送方必须将CC字段设置为0，接收方必须忽略该字段。
M: Marker. The M bit MUST be set to 0 by sender and ignored by receiver.
M:马克。发送方必须将M位设置为0，接收方必须忽略M位。
PT [0:6]: Payload type. A PT value SHOULD be allocated from the range of dynamic values for each direction of the PW. The same PT value MAY be reused both for direction and between different CEP PWs.
PT[0:6]：有效负载类型。应根据PW每个方向的动态值范围分配PT值。相同的PT值可在方向和不同CEP PW之间重复使用。
Sequence Number [0:15]: The packet sequence number MUST continuously cycle from 0 to 0xFFFF. It is generated and processed in accordance with the rules established in [RTP]. The CEP receiver MUST sequence packets according to the Sequence Number field of the CEP header and MAY verify correct sequencing using RTP Sequence Number field.
序列号[0:15]：数据包序列号必须从0连续循环到0xFFFF。它是根据[RTP]中建立的规则生成和处理的。CEP接收器必须根据CEP报头的序列号字段对数据包进行排序，并且可以使用RTP序列号字段验证正确的排序。
Timestamp [0:31]: Timestamp values are used in accordance with the rules established in [RTP]. Frequency of the clock used for generating timestamps MUST be 19.44 MHz based on a local reference.
时间戳[0:31]：根据[RTP]中建立的规则使用时间戳值。基于本地参考，用于生成时间戳的时钟频率必须为19.44 MHz。
SSRC [0:31]: Synchronization source. The SSRC field MAY be used for detection of misconnections.
SSRC[0:31]：同步源。SSRC字段可用于检测错误连接。
This document defines the transport of CEP over MPLS PSNs. The bottom label in the MPLS label stack MUST be used to de-multiplex individual CEP channels. In keeping with the conventions used in [PWE3-CONTROL], this de-multiplexing label is referred to as the PW Label and the upper labels are referred to as Tunnel Labels. The CEP header follows the generic PWE3 Control Word format specified in [PWE3-MPLSCW] for use over an MPLS PSN.
本文档定义了通过MPLS PSN传输CEP。MPLS标签堆栈中的底部标签必须用于解复用单个CEP信道。根据[PWE3-CONTROL]中使用的约定，该解复用标签称为PW标签，上部标签称为隧道标签。CEP头遵循[PWE3-MPLSCW]中指定的通用PWE3控制字格式，用于MPLS PSN。
Transport of CEP over other PSN technologies is out of scope of this document.
通过其他PSN技术传输CEP不在本文件范围内。
A CEP implementation MUST support a normal mode of operation and MAY support additional bandwidth conserving modes as described in Section 11. During normal operation, SONET/SDH payloads are fragmented, prepended with the appropriate headers, and then transmitted into the packet network.
CEP实施必须支持正常操作模式，并可支持第11节所述的额外带宽节约模式。在正常操作过程中，SONET/SDH有效负载被分段，用适当的报头预先封装，然后传输到分组网络。
As with all adaptation functions, CEP has two distinct components: adapting TDM SONET/SDH into a CEP packet stream, and converting the CEP packet stream back into a TDM SONET/SDH. The first function is referred to as CEP packetizer or sender and the second as CEP de-packetizer or receiver. This terminology is illustrated below.
与所有适配功能一样，CEP有两个不同的组件：将TDM SONET/SDH适配为CEP分组流，以及将CEP分组流转换回TDM SONET/SDH。第一个函数称为CEP打包器或发送器，第二个函数称为CEP反打包器或接收器。这一术语如下所示。
+------------+ +---------------+
| | | |
SONET --> | CEP | --> PSN --> | CEP | --> SONET
SDH | Packetizer | | De-Packetizer | SDH
| | | |
+------------+ +---------------+
(sender) (receiver)
+------------+ +---------------+
| | | |
SONET --> | CEP | --> PSN --> | CEP | --> SONET
SDH | Packetizer | | De-Packetizer | SDH
| | | |
+------------+ +---------------+
(sender) (receiver)
Figure 4: CEP Terminology
图4：CEP术语
The CEP de-packetizer requires a buffering mechanism to account for delay variation in the CEP packet stream. This buffering mechanism is generically referred to as the CEP jitter buffer.
CEP解包器需要缓冲机制来考虑CEP包流中的延迟变化。这种缓冲机制通常称为CEP抖动缓冲。
During normal operation, the CEP packetizer receives a fixed-rate byte stream from a SONET/SDH interface. When a packet worth of data is received from a SONET/SDH channel, the necessary headers are prepended to the SPE fragment and the resulting CEP packet is transmitted into the packet network. Because all CEP packets
在正常操作期间，CEP打包器从SONET/SDH接口接收固定速率字节流。当从SONET/SDH信道接收到相当于数据包的数据时，必要的报头被预先添加到SPE片段中，并且产生的CEP数据包被传输到数据包网络中。因为所有的CEP包
associated with a specific SONET/SDH channel have the same length, the transmission of CEP packets for that channel SHOULD occur at regular intervals.
与具有相同长度的特定SONET/SDH信道相关，该信道的CEP数据包的传输应定期进行。
At the far end of the packet network, the CEP de-packetizer receives packets into a jitter buffer and then plays out the received byte stream at a fixed rate onto the corresponding SONET/SDH channel. The jitter buffer SHOULD be adjustable in length to account for varying network delay behavior. On average, the receive packet rate from the packet network should be balanced by the transmission rate onto the SONET/SDH channel.
在分组网络的远端，CEP解分组器将分组接收到抖动缓冲器中，然后以固定速率将接收到的字节流播放到相应的SONET/SDH信道上。抖动缓冲区的长度应可调，以考虑不同的网络延迟行为。平均而言，来自分组网络的接收分组速率应与SONET/SDH信道上的传输速率相平衡。
The CEP sequence numbers provide a mechanism to detect lost and/or misordered packets. The sequence number in the CEP header MUST be used when transmission of the RTP header is suppressed. The CEP de-packetizer MUST detect lost or misordered packets. The CEP de-packetizer SHOULD play out an all-ones pattern (AIS) in place of any dropped packets. The CEP de-packetizer SHOULD re-order packets received out of order. If the CEP de-packetizer does not support re-ordering, it MUST drop misordered packets.
CEP序列号提供了一种检测丢失和/或错序数据包的机制。当RTP报头的传输被抑制时，必须使用CEP报头中的序列号。CEP解包器必须检测丢失或排序错误的数据包。CEP去分组器应该播放一个all-ones模式（AIS）来代替任何丢弃的数据包。CEP反打包器应重新排序无序接收的数据包。如果CEP反打包器不支持重新排序，它必须丢弃错误排序的数据包。
A key component in declaring the state of a CEP service is whether or not the CEP de-packetizer is in or out of packet synchronization. The following paragraphs describe how that determination is made.
声明CEP服务状态的一个关键组件是CEP反打包器是否处于数据包同步状态。以下段落描述了如何作出该决定。
As packets are received from the PSN, they are placed into a jitter buffer prior to play out on the SONET/SDH interface. If a CEP de-packetizer supports re-ordering, any packet received before its play out time will still be considered valid.
当从PSN接收数据包时，在SONET/SDH接口上播放之前，数据包被放入抖动缓冲区。如果CEP解包器支持重新排序，则在其播放时间之前收到的任何数据包仍将被视为有效。
The determination of acquisition or loss of packet synchronization is always made at SONET/SDH play out time. During SONET/SDH play out, the CEP de-packetizer will play received CEP packets onto the SONET/ SDH interface. However, if the jitter buffer is empty or the packet to be played out has not been received, the CEP de-packetizer will play out an 'empty packet' composed of an all-ones AIS pattern onto the SONET/SDH interface in place of the unavailable packet.
始终在SONET/SDH播放时间确定数据包同步的获取或丢失。在SONET/SDH播放期间，CEP解包器将在SONET/SDH接口上播放接收到的CEP数据包。但是，如果抖动缓冲区为空或未接收到要播放的数据包，CEP解包器将在SONET/SDH接口上播放由all ones AIS模式组成的“空数据包”，以代替不可用的数据包。
The acquisition of packet synchronization is based on the number of sequential CEP packets that are played onto the SONET/SDH interface. Loss of packet synchronization is based on the number of sequential 'empty' packets that are played onto the SONET/SDH interface. Specific details of these two cases are described below.
数据包同步的获取基于在SONET/SDH接口上播放的顺序CEP数据包的数量。数据包同步丢失基于在SONET/SDH接口上播放的连续“空”数据包的数量。这两起案件的具体细节如下所述。
At startup, a CEP de-packetizer will be out of packet synchronization by default. To declare packet synchronization at startup or after a loss of packet synchronization, the CEP de-packetizer must play out a configurable number of CEP packets with sequential sequence numbers towards the SONET/SDH interface.
在启动时，默认情况下，CEP反打包器将失去数据包同步。要在启动时或数据包同步丢失后声明数据包同步，CEP解包器必须向SONET/SDH接口播放具有序列号的可配置数量的CEP数据包。
Once a CEP de-packetizer is in packet synchronization state, it may encounter a set of events that will cause it to lose packet synchronization.
一旦CEP解包器处于数据包同步状态，它可能会遇到一组事件，导致其丢失数据包同步。
If the CEP de-packetizer encounters more than a configurable number of sequential empty packets, the CEP de-packetizer MUST declare a Loss of Packet Synchronization (LOPS) defect.
如果CEP解包器遇到超过可配置数量的连续空数据包，则CEP解包器必须声明数据包同步丢失（LOPS）缺陷。
LOPS failure is declared after 2.5 +/- 0.5 seconds of LOPS defect, and cleared after 10 seconds free of LOPS defect state. The circuit is considered down as long as LOPS failure is declared.
LOPS故障在LOPS缺陷出现2.5+/-0.5秒后宣布，并在10秒后清除LOPS缺陷状态。只要宣布LOPS故障，电路即被视为停机。
This section describes the mapping of maintenance and alarm signals between the SONET/SDH network and the CEP pseudowire. For clarity, the mappings are split into two groups: SONET/SDH to PSN, and PSN to SONET/SDH.
本节描述SONET/SDH网络和CEP伪线之间的维护和报警信号映射。为清楚起见，映射分为两组：SONET/SDH到PSN，以及PSN到SONET/SDH。
For coherent failure detection, isolation, monitoring, and troubleshooting, SONET/SDH failure indications MUST be transferred correctly over the CEP pseudowire, and CEP connection failures MUST be mapped to SONET/SDH SPE/VT failure indications. Failure detection capabilities and performance monitoring capabilities are dependent on the NSP functionality, e.g., LTE, PTE, Tandem Connection Monitoring [G.707], or Non-intrusive Monitoring (intermediate connection monitoring).
对于一致性故障检测、隔离、监测和故障排除，SONET/SDH故障指示必须通过CEP伪线正确传输，CEP连接故障必须映射到SONET/SDH SPE/VT故障指示。故障检测能力和性能监控能力取决于NSP功能，例如LTE、PTE、串联连接监控[g.707]或非侵入性监控（中间连接监控）。
The following sections describe the mapping of SONET/SDH Maintenance Signals and Alarm conditions into CEP pseudowire indications.
以下章节描述了SONET/SDH维护信号和报警条件到CEP伪线指示的映射。
SONET/SDH Path outages are signaled by using maintenance alarms such as Path AIS (AIS-P). AIS-P, in particular, indicates that the SONET/ SDH Path is not currently transmitting valid end-user data, and the
SONET/SDH路径中断通过使用路径AIS（AIS-P）等维护警报发出信号。AIS-P特别指出SONET/SDH路径当前未传输有效的最终用户数据，并且
SPE contains all ones. Similarly, AIS-V indicates that the VT is not currently transmitting valid end-user data, and the VT contains all ones.
SPE包含所有的。类似地，AIS-V表示VT当前未传输有效的最终用户数据，并且VT包含所有数据。
It should be noted that nearly every type of service-affecting section or line defect would result in an AIS-P/V condition.
应注意的是，几乎所有影响区段或线路缺陷的服务类型都会导致AIS-P/V状况。
The mapping of SONET/SDH failures into the SPE/VT layer is considered part of the NSP function and is based on the principles specified in [GR253], [SONET], [G.707], [G.806], and [G.783]. For example, should the SONET Section Layer detect a Loss of Signal (LOS) or Loss of Frame (LOF) or Section Trace Mismatch (TIM) conditions, an AIS-L is sent up to the Line Layer. If the Line Layer detects AIS-L or Loss of Pointer (LOP), an AIS-P is sent to the Path Layer. If the Path is terminated at the PE (i.e., a PTE) and the Path Layer detects AIS-P or UNEQ-P or TIM-P or PLM-P an AIS-V is sent to the VT Layer.
将SONET/SDH故障映射到SPE/VT层被视为NSP功能的一部分，并基于[GR253]、[SONET]、[G.707]、[G.806]和[G.783]中规定的原则。例如，如果SONET区段层检测到信号丢失（LOS）或帧丢失（LOF）或区段跟踪不匹配（TIM）情况，则向线路层发送AIS-L。如果线路层检测到AIS-L或指针丢失（LOP），则向路径层发送AIS-P。如果路径在PE（即PTE）处终止，并且路径层检测到AIS-P或UNEQ-P或TIM-P或PLM-P，则AIS-V被发送到VT层。
The AIS-P/V indication is transferred to the CEP packetizer. During AIS-P/V, CEP packets are generated as usual. The L bit in the CEP header MUST be set to 1 to signal AIS-P/V explicitly through the packet network. The N and P bits SHOULD be set to 1 to indicate loss of pointer indication.
AIS-P/V指示被传输到CEP包装器。在AIS-P/V期间，CEP数据包照常生成。CEP报头中的L位必须设置为1，以便通过分组网络显式发送AIS-P/V信号。N和P位应设置为1，以指示指针指示丢失。
If DBA has been enabled for AIS-P/V, only the necessary headers and optional padding are transmitted into the packet network. The Length field MUST be set to the size of the CEP header plus the size of the RTP header if used.
如果已为AIS-P/V启用DBA，则仅将必要的报头和可选填充传输到数据包网络。长度字段必须设置为CEP标头的大小加上RTP标头的大小（如果使用）。
Unequipped indication is used for bandwidth conserving modes defined in Section 11 as a trigger for payload removal.
未装备指示用于第11节中定义的带宽节约模式，作为有效负载移除的触发器。
The declaration of the SPE/VT channel as Unequipped MUST conform to [GR253], [SONET], [G.806], and [G.783]. Unequipped circuits do not carry valid end-user data, but MAY be used for transporting valid information in the SPE/VT overhead bytes. Supervisory Unequipped signals and Tandem Connection transport are two such applications:
SPE/VT通道未配备的声明必须符合[GR253]、[SONET]、[G.806]和[G.783]的规定。未装备的电路不携带有效的最终用户数据，但可用于传输SPE/VT开销字节中的有效信息。监控未配备信号和串联连接传输是两种此类应用：
Supervisory Unequipped signal (called TEST-P in [SONET]) is used to provide a test signal for pre-service testing or in-service supervision of a path connection to a remote PTE from a PTE or an intermediate non-terminating path network element. Both Unequipped and Supervisory Unequipped signals carry Unequipped Signal Label defined to be zero. To distinguish between Unequipped and Supervisory Unequipped signals, [G.806] recommends that the SPE/VT Trace bytes J1/J2 be set to a non-zero value in Supervisory Unequipped signals.
监控未装备信号（在[SONET]中称为TEST-P）用于提供测试信号，用于对从PTE或中间非端接路径网元到远程PTE的路径连接进行服务前测试或服务中监控。未配备信号和监控未配备信号均带有定义为零的未配备信号标签。为了区分未装备信号和监控未装备信号，[G.806]建议在监控未装备信号中将SPE/VT跟踪字节J1/J2设置为非零值。
The SPE/VT overhead bytes N1/Z6 (SDH refers to Z6 as N2) optionally transport Tandem Connection signals between intermediate network elements. Unequipped signals transporting Tandem Connection would have non-zero N1 or N2/Z6 bytes.
SPE/VT开销字节N1/Z6（SDH将Z6称为N2）可选地在中间网络元件之间传输串联连接信号。传输串联连接的未装备信号将具有非零N1或N2/Z6字节。
Therefore, the CEP packetizer MUST declare a circuit unequipped only if the Signal Label, Trace (J1/J2), and Tandem Connection (N1/N2/Z6) bytes all have zero value.
因此，只有当信号标签、记录道（J1/J2）和串联连接（N1/N2/Z6）字节均为零值时，CEP封装器才必须声明电路未装备。
During SPE/VT Unequipped, the N and P bits MUST be interpreted as usual. The SPE/VT MUST be transmitted into the packet network along with the appropriate headers.
在SPE/VT未配备期间，N位和P位必须按常规进行解释。SPE/VT必须与适当的报头一起传输到数据包网络。
If DBA has been enabled for Unequipped SPE/VT, only the necessary headers and optional padding are transmitted into the packet network. The Length field MUST be set to the size of the CEP header plus the size of the RTP header if used. The N and P bits MAY be used to signal pointer adjustments as normal.
如果已为未装备的SPE/VT启用DBA，则只有必要的报头和可选填充才会传输到数据包网络。长度字段必须设置为CEP标头的大小加上RTP标头的大小（如果使用）。N位和P位可正常用于发出指针调整信号。
The CEP function MUST send CEP-RDI indication towards the packet network during loss of packet synchronization by setting the R bit to one in the CEP header. The CEP function SHOULD clear the R bit once packet synchronization is restored.
在分组同步丢失期间，CEP功能必须通过在CEP报头中将R位设置为1，向分组网络发送CEP-RDI指示。一旦恢复数据包同步，CEP功能应清除R位。
The following sections describe the mapping of pseudowire indications to SONET/SDH Maintenance Signals and Alarm conditions.
以下章节描述了伪线指示到SONET/SDH维护信号和报警条件的映射。
There are several conditions in the packet network that cause the CEP de-packetization function to play out an AIS-P/V indication towards a SONET/SDH channel. The CEP de-packetizer MUST play out one packet's worth of all ones for each packet received, and MUST set the SONET/ SDH Overhead to signal AIS-P/V as defined in [SONET], [GR253], and [G.707].
分组网络中有几种情况导致CEP去分组功能向SONET/SDH信道播放AIS-P/V指示。CEP解包器必须为接收到的每个数据包播放所有数据包中的一个数据包，并且必须按照[SONET]、[GR253]和[G.707]中的定义，将SONET/SDH开销设置为信号AIS-P/V。
The first of these is the receipt of CEP packets with the L bit set to one indicating that the far end has detected an error leading to declaration of AIS-P/V alarm. In addition to the play out of AIS-P/V, the CEP de-packetizer SHOULD set the pointer value to all-ones value.
第一个是接收CEP数据包，L位设置为1，表示远端检测到错误，导致声明AIS-P/V报警。除了AIS-P/V的播放外，CEP反打包器还应将指针值设置为“所有1”值。
The second case that will cause a CEP de-packetization function to play out an AIS-P/V indication onto a SONET/SDH channel is during loss of packet synchronization.
第二种情况将导致CEP去分组功能在SONET/SDH信道上播放AIS-P/V指示，这是在数据包同步丢失期间。
The third case is the receipt of CEP packets with both the N and P bits set to 1. This is an explicit indication of Loss of Pointer LOP-P/V received at the far-end of the packet network. In addition to play out of AIS-P/V, the CEP de-packetizer SHOULD set the pointer value to all-ones value.
第三种情况是接收N位和P位都设置为1的CEP分组。这是在分组网络远端接收到的指针LOP-P/V丢失的明确指示。除了播放AIS-P/V外，CEP反打包器还应将指针值设置为all ones值。
There are several conditions in the packet network that cause the CEP function to transmit Unequipped indications onto the SONET/SDH channel.
分组网络中有几种情况导致CEP功能将未装备的指示传输到SONET/SDH信道。
The first, which is transparent to CEP, is the receipt of regular CEP packets that happen to carry an SPE/VT containing the appropriate Path overhead or VT overhead set to Unequipped. This case does not require any special processing on the part of the CEP de-packetizer.
第一个对CEP是透明的，它是常规CEP数据包的接收，这些数据包碰巧携带SPE/VT，其中包含设置为未装备的适当路径开销或VT开销。这种情况不需要CEP去包装商进行任何特殊处理。
The second case is the receipt of CEP packets with the Length field indicating that the payload was removed by DBA, while the L bit is set to 0, indicating that the DBA was triggered by an Unequipped indication and not by an AIS-P/V indication. The CEP de-packetizer MUST use this information to transmit a packet of all zeros onto the SONET/SDH interface.
第二种情况是接收CEP数据包，其长度字段指示DBA删除了有效负载，而L位设置为0，指示DBA是由未装备的指示触发的，而不是由AIS-P/V指示触发的。CEP解包器必须使用此信息将全零数据包传输到SONET/SDH接口。
The third case when a CEP de-packetizer MUST play out an SPE/VT Unequipped indication towards the SONET/SDH interface is when the circuit has been de-provisioned.
第三种情况是，当CEP解包器必须向SONET/SDH接口播放SPE/VT未配备指示时，电路已解配。
It is assumed that the distribution of SONET/SDH transport timing information is addressed either through external mechanisms such as Building Integrated Timing Supply (BITS), Stand Alone Synchronization Equipment (SASE), Global Positioning System (GPS), or other such methods, or is obtained through an adaptive timing recovery mechanism.
假定SONET/SDH传输定时信息的分布通过外部机制（如楼宇集成定时电源（BITS）、独立同步设备（SASE）、全球定位系统（GPS）或其他此类方法）来解决，或者通过自适应定时恢复机制来获得。
Details about specific adaptive algorithms for recovery of SONET/SDH transport timing are not considered to be within scope for this document. The wander and jitter limits for networks based on the SDH hierarchy are defined in [G.825] and for the SONET hierarchy in [GR253]. The wander and jitter limits specified in these standards must be maintained when CEP PWs are used.
有关SONET/SDH传输定时恢复的特定自适应算法的详细信息不在本文件范围内。基于SDH层次结构的网络的漂移和抖动限制在[G.825]中定义，SONET层次结构在[GR253]中定义。使用CEP PWs时，必须保持这些标准中规定的漂移和抖动限制。
A pointer management system is defined as part of the definition of SONET/SDH. Details on SONET/SDH pointer management can be found in [SONET], [GR253], [G.707], and [G.783]. If there is a frequency offset between the frame rate of the transport overhead and that of the SONET/SDH SPE, the alignment of the SPE will periodically slip back or advance in time through positive or negative stuffing. Similarly, if there is a frequency offset between the SPE rate and the VT rate it carries, the alignment of the VT will periodically slip back or advance in time through positive or negative stuffing within the SPE.
指针管理系统是SONET/SDH定义的一部分。有关SONET/SDH指针管理的详细信息，请参见[SONET]、[GR253]、[G.707]和[G.783]。如果传输开销的帧速率与SONET/SDH SPE的帧速率之间存在频率偏移，则SPE的对齐将通过正或负填充周期性地在时间上后退或前进。类似地，如果SPE速率与其承载的VT速率之间存在频率偏移，则VT的校准将通过SPE内的正或负填充周期性地向后滑动或在时间上向前移动。
The emulation of this aspect of SONET/SDH networks may be accomplished using a variety of techniques including Explicit Pointer Adjustment Relay (EPAR) and Adaptive Pointer Management (APM).
SONET/SDH网络的这一方面的仿真可以使用各种技术完成，包括显式指针调整中继（EPAR）和自适应指针管理（APM）。
In any case, the handling of the SPE or VT data by the CEP packetizer is the same.
在任何情况下，CEP打包器对SPE或VT数据的处理都是相同的。
During a negative pointer adjustment event, the CEP packetizer MUST incorporate the H3 (or V3) byte from the SONET/SDH stream into the CEP packet payload in order with the rest of the SPE (or VT). During a positive pointer adjustment event, the CEP packetizer MUST strip the stuff byte from the CEP packet payload.
在负指针调整事件期间，CEP打包器必须将SONET/SDH流中的H3（或V3）字节合并到CEP数据包有效负载中，以便与SPE（或VT）的其余部分一起使用。在正指针调整事件期间，CEP数据包生成器必须从CEP数据包有效负载中删除填充字节。
When playing out a negative pointer adjustment event, the appropriate byte of the CEP payload MUST be placed into the H3 (or V3) byte of the SONET/SDH stream. When playing out a positive pointer adjustment, the CEP de-packetizer MUST insert a stuff byte into the appropriate position within the SONET/SDH stream.
播放负指针调整事件时，CEP有效负载的相应字节必须放入SONET/SDH流的H3（或V3）字节中。当播放正指针调整时，CEP反打包器必须在SONET/SDH流中的适当位置插入一个填充字节。
The details regarding the use of the H3 (and V3) byte and stuff byte during positive and negative pointer adjustments can be found in [SONET], [GR253], and [G.707].
有关在正负指针调整期间使用H3（和V3）字节和填充字节的详细信息，请参见[SONET]、[GR253]和[G.707]。
CEP provides an OPTIONAL mechanism to explicitly relay pointer adjustment events from one side of the PSN to the other. This technique is referred to as Explicit Pointer Adjustment Relay (EPAR). EPAR is only effective when both ends of the PW have access to a common timing reference.
CEP提供了一种可选机制，可将指针调整事件从PSN的一侧显式中继到另一侧。这种技术称为显式指针调整继电器（EPAR）。EPAR仅在PW两端都可以访问公共定时基准时有效。
The following text only applies to CEP implementations that choose to implement EPAR. Any CEP implementation that does not support EPAR MUST set the N and P bits to 0.
以下EPA仅适用于CEPA实施的文本。任何不支持EPAR的CEP实现都必须将N和P位设置为0。
The pointer adjustment event MUST be transmitted in three consecutive packets by the packetizer. The de-packetizer MUST play out the pointer adjustment event when any one packet with N/P bit set is received. The CEP de-packetizer MUST utilize the CEP sequence numbers to ensure that SONET/SDH pointer adjustment events are not played any more frequently than once per every three CEP packets transmitted by the remote CEP packetizer.
指针调整事件必须由打包器以三个连续数据包的形式传输。当接收到任何一个设置了N/P位的数据包时，解包器必须播放指针调整事件。CEP解包器必须利用CEP序列号，以确保SONET/SDH指针调整事件的播放频率不会超过远程CEP包器传输的每三个CEP包播放一次。
The VT EPAR packetizer MUST relay pointer adjustment indications received at the SPE level in addition to relaying VT pointer adjustment indications. Because of the rate differences between VT and SPE, the magnitude of a VT pointer adjustment is much larger than that of an SPE adjustment. Therefore, the VT EPAR packetizer has to convert multiple SPE pointer adjustments to fewer VT pointer adjustment indications signaled over the PSN using the N and P CEP header bits. A simple algorithm can be used for this purpose using an accumulator (counter):
VT EPAR打包机除了中继VT指针调整指示外，还必须中继SPE级别接收到的指针调整指示。由于VT和SPE之间的速率差异，VT指针调整的幅度远大于SPE调整的幅度。因此，VT EPAR打包器必须将多个SPE指针调整转换为使用N和P CEP头位通过PSN发出信号的较少VT指针调整指示。为此，可使用累加器（计数器）使用简单算法：
The accumulator value is reset to 0 when the circuit is in Loss of Packet Synchronization (LOPS) state.
当电路处于数据包同步丢失（LOPS）状态时，累加器值重置为0。
A positive pointer adjustment indication increases the accumulator value by a fixed quota, while negative pointer adjustment subtracts the same quota from the accumulator. A VT pointer adjustment changes the accumulator value by 783 units (one STS-1 SPE size). An SPE pointer adjustment changes the accumulator value by quota that depends on the VT emulation type. The quota is 1/4 of the VT size as defined in Table 1, e.g., 26 bytes for VT1.5 emulation and 35 bytes for VT2 emulation.
正指针调整指示将累加器值增加固定配额，而负指针调整将从累加器中减去相同配额。VT指针调整将累加器值更改783个单位（一个STS-1 SPE大小）。SPE指针调整根据VT仿真类型的配额更改累加器值。配额为表1中定义的VT大小的1/4，例如，VT1.5仿真为26字节，VT2仿真为35字节。
When the accumulator value is larger than or equal to 783 units, a positive pointer adjustment is signaled towards the PSN using the CEP header P bit and 783 units are subtracted from the accumulator.
当累加器值大于或等于783个单位时，使用CEP头P位向PSN发出正指针调整信号，并从累加器中减去783个单位。
When the accumulator value is smaller than or equal to minus 783 units, a negative pointer adjustment is signaled towards the PSN using the CEP header N bit and 783 units are added to the accumulator.
当累加器值小于或等于-783个单位时，使用CEP头N位向PSN发送负指针调整信号，并向累加器添加783个单位。
The same algorithm is applicable for SDH Virtual Container carried in VC-4, i.e., positive VC-4 pointer adjustment adds 35 units to a VC-12 accumulator, while positive VC-12 pointer adjustment adds 783 units to the accumulator.
同样的算法也适用于VC-4中携带的SDH虚拟容器，即正VC-4指针调整将向VC-12累加器添加35个单位，而正VC-12指针调整将向累加器添加783个单位。
If both N and P bits are set, then a Loss of Pointer event has been detected at the PW ingress, making the pointer invalid. The de-packetizer MUST play out an AIS-P/V indication and SHOULD set the pointer value to all-ones value.
如果同时设置了N位和P位，则在PW入口检测到指针丢失事件，使指针无效。反包装器必须播放AIS-P/V指示，并应将指针值设置为所有值。
Another OPTIONAL method that may be used to emulate SONET/SDH pointer management is Adaptive Pointer Management (APM). In basic terms, APM uses information about the depth of the CEP jitter buffers to introduce pointer adjustments in the reassembled SONET/SDH SPE.
另一种可用于模拟SONET/SDH指针管理的可选方法是自适应指针管理（APM）。基本上，APM使用有关CEP抖动缓冲器深度的信息在重新组装的SONET/SDH SPE中引入指针调整。
Details about specific APM algorithms are not considered to be within scope for this document.
有关特定APM算法的详细信息不在本文件范围内。
SONET/SDH as defined in [SONET], [GR253], [G.707], and [G.784] includes a definition of several counters used to monitor the performance of SONET/SDH services. These counters are referred to as Performance Monitors.
[SONET]、[GR253]、[G.707]和[G.784]中定义的SONET/SDH包括用于监控SONET/SDH服务性能的几个计数器的定义。这些计数器称为性能监视器。
In order for CEP to be utilized by traditional SONET/SDH network operators, CEP SHOULD provide similar functionality. The following sections describe a number of counters that are collectively referred to as CEP Performance Monitors.
为了让传统SONET/SDH网络运营商使用CEP，CEP应提供类似的功能。以下各节描述了一些计数器，这些计数器统称为CEP性能监视器。
These performance monitors are maintained by the CEP de-packetizer during reassembly of the SONET/SDH stream.
在SONET/SDH流重新组装期间，这些性能监视器由CEP解包器维护。
The performance monitors are based on two types of defects.
性能监视器基于两种类型的缺陷。
Type 1: missing or dropped packet.
类型1：丢失或丢弃的数据包。
Type 2: buffer underrun, buffer overrun, LOPS, missing packets above predefined configurable threshold.
类型2：缓冲区不足、缓冲区溢出、LOPS、丢失的数据包超过预定义的可配置阈值。
The specific performance monitors defined for CEP are as follows:
为CEP定义的具体性能监视器如下：
ES-CEP - CEP Errored Seconds SES-CEP - CEP Severely Errored Seconds UAS-CEP - CEP Unavailable Seconds
ES-CEP-CEP错误秒SES-CEP-CEP严重错误秒UAS-CEP-CEP不可用秒
Each second that contains at least one type 1 defect SHALL be declared as ES-CEP. Each second that contains at least one type 2 defect SHALL be declared as SES-CEP.
每秒钟至少包含一个1类缺陷应声明为ES-CEP。包含至少一个2类缺陷的每秒钟应声明为SES-CEP。
UAS-CEP SHALL be declared after configurable number of consecutive SES-CEP, and cleared after a configurable number of consecutive seconds without SES-CEP. Default value for each is 10 seconds.
UAS-CEP应在连续SES-CEP的可配置数量后声明，并在无SES-CEP的可配置连续秒数后清除。每个的默认值为10秒。
Once unavailability is declared, ES and SES counts SHALL be inhibited up to the point where the unavailability was started. Once unavailability is removed, ES and SES that occurred along the clearing period SHALL be added to the ES and SES counts.
一旦宣布不可用，ES和SES计数应被抑制，直至不可用开始。一旦取消不可用性，应将清算期间发生的ES和SES添加到ES和SES计数中。
CEP-NE failure is declared after 2.5 +/- 0.5 seconds of CEP-NE type 2 defect, and cleared after 10 seconds free of CEP-NE defect state. Sending notification to the OS for CEP-NE failure is local policy.
CEP-NE故障在CEP-NE 2类缺陷出现2.5+/-0.5秒后宣布，并在10秒后清除CEP-NE缺陷状态。向操作系统发送CEP-NE故障通知是本地策略。
Far-end performance monitors provide insight into the CEP de-packetizer at the far end of the PSN.
远端性能监视器提供对PSN远端CEP解包器的深入了解。
Far-end statistics are based on the CEP-RDI indication carried in the CEP header R bit. CEP-FE defect is declared when CEP-RDI is set in the incoming CEP packets.
远端统计数据基于CEP报头R位中携带的CEP-RDI指示。CEP-FE缺陷在传入CEP数据包中设置CEP-RDI时声明。
CEP-FE failure is declared after 2.5 +/- 0.5 seconds of CEP-FE defect, and cleared after 10 seconds free of CEP-FE defect state. Sending notification to the OS for CEP-FE failure is local policy.
CEP-FE故障在CEP-FE缺陷出现2.5+/-0.5秒后宣布，并在10秒后清除CEP-FE缺陷状态。向操作系统发送CEP-FE故障通知是本地策略。
In addition to pure emulation, CEP also offers a number of options for reducing the total bandwidth utilized by the emulated circuit. These options fall into two categories: Dynamic Bandwidth Allocation (DBA) and Service-Specific Payload Formats.
除了纯仿真之外，CEP还提供了许多选项，用于减少仿真电路使用的总带宽。这些选项分为两类：动态带宽分配（DBA）和特定于服务的有效负载格式。
DBA suppresses transmission of the CEP payload altogether under certain circumstances such as AIS-P/V and SPE/VT Unequipped. The use of DBA is dependent on network architectures, e.g., support of Tandem Connection Monitoring, test signals (TEST-P) [SONET], or Supervisory Unequipped [G.806] signals.
DBA在某些情况下（如AIS-P/V和SPE/VT未配备）完全抑制CEP有效载荷的传输。DBA的使用取决于网络体系结构，例如，支持串联连接监控、测试信号（test-P）[SONET]或监控未配备的[g.806]信号。
Service-Specific Payload Formats reduce bandwidth by suppressing transmission of portions of the SPE based on specific knowledge of the SPE payload.
特定于服务的有效负载格式通过基于SPE有效负载的特定知识抑制SPE部分的传输来减少带宽。
Details on these payload compression options are described in the following subsections.
有关这些有效负载压缩选项的详细信息，请参见以下小节。
Dynamic Bandwidth Allocation (DBA) is an OPTIONAL mechanism for suppressing the transmission of the SPE (or VT) fragment when one of two trigger conditions are met, AIS-P/V or SPE/VT Unequipped.
动态带宽分配（DBA）是一种可选机制，用于在满足两个触发条件之一（AIS-P/V或SPE/VT未装备）时抑制SPE（或VT）片段的传输。
Implementations that support DBA MUST include a mechanism for disabling DBA on a channel-by-channel basis to allow for interoperability with implementations that do not support DBA.
支持DBA的实现必须包括一种机制，用于逐个通道禁用DBA，以允许与不支持DBA的实现进行互操作。
When a DBA trigger is recognized at PW ingress, the CEP payload will be suppressed. The CEP Length field MUST be set to the CEP header length plus the RTP header length if used, and padding bytes SHOULD be added if the intervening packet network has a minimum packet size that is larger than the payload-suppressed DBA packet.
当在PW入口识别DBA触发器时，CEP有效负载将被抑制。CEP长度字段必须设置为CEP报头长度加上RTP报头长度（如果使用），如果中间分组网络的最小分组大小大于有效负载抑制的DBA分组，则应添加填充字节。
Other than the suppression of the CEP payload, the CEP behavior during DBA should be equivalent to normal CEP behavior. In particular, the packet transmission rate during DBA should be equivalent to the normal packet transmission rate.
除了抑制CEP有效载荷外，DBA期间的CEP行为应等同于正常CEP行为。特别是，DBA期间的数据包传输速率应等于正常数据包传输速率。
In addition to the standard payload encapsulations for SPE and VT transport, several OPTIONAL payload formats have been defined to provide varying amounts of payload compression depending on the type and amount of user traffic present within the SPE. These are described below.
除了SPE和VT传输的标准有效负载封装外，还定义了几种可选的有效负载格式，以根据SPE中存在的用户通信的类型和数量提供不同数量的有效负载压缩。下文对这些问题进行了说明。
Fractional STS-1 (VC-3) encapsulation carries only a selected set of VTs within an STS-1 container. This mode is applicable for STS-1 with POH signal label byte C2=2 (VT-structured SPE) and for C2=3 (Locked VT mode).
部分STS-1（VC-3）封装仅在STS-1容器中携带一组选定的VT。该模式适用于POH信号标签字节C2=2（VT结构化SPE）的STS-1和C2=3（锁定VT模式）。
Implementations of fractional STS-1 (VC-3) encapsulation MUST support payload length of one SPE and MAY support payload length of 1/3 SPE.
分数STS-1（VC-3）封装的实现必须支持一个SPE的有效负载长度，并且可以支持1/3 SPE的有效负载长度。
The mapping of VTs into an STS-1 container is described in Section 3.2.4 of [GR253], and the mapping into VC-3 is defined in Section 7.2.4 in [G.707]. The CEP packetizer removes all fixed column bytes (columns 30 and 59) and all bytes belonging to the removed VTs. Only
[GR253]第3.2.4节描述了VTs到STS-1容器的映射，而[G.707]第7.2.4节定义了到VC-3的映射。CEP打包器删除所有固定列字节（第30列和第59列）以及属于已删除VT的所有字节。只有
STS-1 POH bytes and bytes that belong to the selected VTs are carried within the payload. The CEP de-packetizer adds the fixed stuff bytes and generates unequipped VT data replacing the removed VT bytes.
STS-1 POH字节和属于所选VT的字节在有效负载内携带。CEP反打包器添加固定的填充字节，并生成未装备的VT数据来替换删除的VT字节。
The figure below illustrates VT1.5 mapping into an STS-1 SPE.
下图说明了VT1.5到STS-1 SPE的映射。
1 2 3 * * * 29 30 31 32 * * * 58 59 60 61 * * * 87
+--+------------------+-+------------------+-+------------------+
1 |J1| Byte 1 (V1-V4) |R| | | | |R| | | | |
+--+---+---+------+---+-+------------------+-+------------------+
2 |B3|VT | | | |R| | | | |R| | | | |
+--+1.5| | | +-+---+---+------+---+-+------------------+
3 |C2| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
4 |G1| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
5 |F2| | | | |R| | | | |R| | | | |
+--|1-1|2-1| * * *|7-4|-|1-1|2-1| * * *|7-4|-|1-1|2-1| * * *|7-4|
6 |H4| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
7 |Z3| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
8 |Z4| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
9 |Z5| | | | |R| | | | |R| | | | |
+--+---+---+------+---+-+---+---+------+---+-+------------------+
| | |
+-- Path Overhead +--------------------+-- Fixed Stuffs
1 2 3 * * * 29 30 31 32 * * * 58 59 60 61 * * * 87
+--+------------------+-+------------------+-+------------------+
1 |J1| Byte 1 (V1-V4) |R| | | | |R| | | | |
+--+---+---+------+---+-+------------------+-+------------------+
2 |B3|VT | | | |R| | | | |R| | | | |
+--+1.5| | | +-+---+---+------+---+-+------------------+
3 |C2| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
4 |G1| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
5 |F2| | | | |R| | | | |R| | | | |
+--|1-1|2-1| * * *|7-4|-|1-1|2-1| * * *|7-4|-|1-1|2-1| * * *|7-4|
6 |H4| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
7 |Z3| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
8 |Z4| | | | |R| | | | |R| | | | |
+--+ | | | +-+---+---+------+---+-+------------------+
9 |Z5| | | | |R| | | | |R| | | | |
+--+---+---+------+---+-+---+---+------+---+-+------------------+
| | |
+-- Path Overhead +--------------------+-- Fixed Stuffs
Figure 5: SONET SPE Mapping of VT1.5
图5:VT1.5的SONET SPE映射
The SPE always contains seven interleaved VT groups (VTGs). Each VTG contains a single type of VT, and each VTG occupies 12 columns (108 bytes) within each SPE. A VTG can contain 4 VT1.5s (T1s), 3 VT2s (E1s), 2 VT3s, or a single VT6. Altogether, the SPE can carry 28 T1s or carry 21 E1s.
SPE始终包含七个交错VT组（VTG）。每个VTG包含单一类型的VT，每个VTG在每个SPE中占用12列（108字节）。一个VTG可以包含4个VT1.5（T1s）、3个VT2（E1s）、2个VT3或一个VT6。SPE总共可以携带28个T1s或21个E1s。
The fractional STS-1 encapsulation can optionally carry a bit mask that specifies which VTs are carried within the STS-1 payload and which VTs have been removed. This optional bit mask attribute allows the ingress circuit emulation node to remove an unequipped VT on the fly, providing the egress circuit emulation node enough information for reconstructing the VTs in the right order. The use of bit mask enables on-the-fly compression, whereby only equipped VTs (carrying actual data) are sent.
分数STS-1封装可以选择性地携带位掩码，该位掩码指定在STS-1有效负载内携带哪些VT以及哪些VT已被移除。此可选位掩码属性允许入口电路仿真节点动态移除未装备的VT，从而为出口电路仿真节点提供足够的信息，以便以正确的顺序重建VT。使用位掩码可实现动态压缩，因此仅发送配备的VT（携带实际数据）。
The fractional STS-1 CEP header uses the STS-1 CEP header encapsulation as defined in this document. Optionally, an additional 4-byte header extension word is added.
分数STS-1 CEP标头使用本文档中定义的STS-1 CEP标头封装。（可选）添加额外的4字节头扩展字。
The extended header has the following format:
扩展标头具有以下格式：
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|L|R|N|P|FRG|Length[0:5]| Sequence Number[0:15] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Structure Pointer[0:11]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0| Equipped Bit Mask (EBM) [0:27] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|L|R|N|P|FRG|Length[0:5]| Sequence Number[0:15] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Structure Pointer[0:11]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0| Equipped Bit Mask (EBM) [0:27] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Extended Fractional STS-1 Header
图6：扩展分数STS-1标头
The L, R, N, P, FRG, Length, Sequence Number, and Structured Pointer fields are used as defined in this document for STS-1 encapsulation.
L、R、N、P、FRG、长度、序列号和结构化指针字段按照本文档中的定义用于STS-1封装。
Each bit within the Equipped Bit Mask (EBM) field refers to a different VT within the STS-1 container. A bit set to 1 indicates that the corresponding VT is equipped, hence carried within the fractional STS-1 payload.
配备的位掩码（EBM）字段中的每个位都表示STS-1容器中的不同VT。位设置为1表示配备了相应的VT，因此在分数STS-1有效载荷内携带。
The STS-1 EBM has the following format:
STS-1 EBM具有以下格式：
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTG7 | VTG6 | VTG5 | VTG4 | VTG3 | VTG2 | VTG1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTG7 | VTG6 | VTG5 | VTG4 | VTG3 | VTG2 | VTG1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Equipped Bit Mask (EBM) for Fractional STS-1
图7：分数STS-1配备的位掩码（EBM）
The 28 bits of the EBM are divided into groups of 4 bits, each corresponding to a different VTG within the STS container. All 4 bits are used to indicate whether VT1.5 (T1) tributaries are carried within a VTG. The first 3 bits read from right to left are used to indicate whether VT2 (E1) tributaries are carried within a VTG. The first 2 bits are used to indicate whether VT3 (DS1C) tributaries are carried within a VTG. The rightmost bit is used to indicate whether a VT6 (DS2) is carried within the VTG. The VTs within the VTG are numbered from right to left, starting from the first VT as the first bit on the right. For example, the EBM of a fully occupied STS-1
EBM的28位被分成4位的组，每一位对应于STS容器内的不同VTG。所有4位用于指示VTG中是否携带VT1.5（T1）支路。从右向左读取的前3位用于指示VTG中是否携带VT2（E1）支路。前2位用于指示VTG中是否携带VT3（DS1C）支路。最右边的位用于指示VTG中是否携带VT6（DS2）。VTG内的VT从右向左编号，从第一个VT开始，作为右侧的第一位。例如，完全占用的STS-1的EBM
with VT1.5 tributaries is all ones, while that of an STS-1 fully occupied with VT2 (E1) tributaries has the binary value 0111011101110111011101110111.
VT1.5支流为全1，而完全占用VT2（E1）支流的STS-1支流为二进制值0111011110111101110111。
Fractional STS-1 encapsulation can be implemented in Line Terminating Equipment (LTE) or in Path Terminating Equipment (PTE). PTE implementations terminate the path layer at the ingress PE and generate a new path layer at the egress PE.
部分STS-1封装可在线路终端设备（LTE）或路径终端设备（PTE）中实现。PTE实现在入口PE处终止路径层，并在出口PE处生成新的路径层。
LTE implementations do not terminate the path layer, and therefore need to keep the content and integrity of the POH bytes across the PSN. In LTE implementations, special care must be taken to maintain the B3 bit-wise parity POH byte. The B3 compensation algorithm is defined below.
LTE实现不终止路径层，因此需要在PSN上保持POH字节的内容和完整性。在LTE实现中，必须特别注意保持B3位奇偶校验POH字节。B3补偿算法定义如下。
Since the BIP-8 value in a given frame reflects the parity check over the previous frame, the changes made to BIP-8 bits in the previous frame shall also be considered in the compensation of BIP-8 in the current frame. Therefore, the following equation shall be used for compensation of the individual bits of the BIP-8:
由于给定帧中的BIP-8值反映了对前一帧的奇偶校验，因此在当前帧中对BIP-8进行补偿时，还应考虑对前一帧中的BIP-8位所做的更改。因此，应使用以下等式对BIP-8的各个位进行补偿：
B3[i]'(t) = B3[i](t-1) || B3[i]'(t-1) || B3[i](t) || B*3[i](t-1)
B3[i]'(t) = B3[i](t-1) || B3[i]'(t-1) || B3[i](t) || B*3[i](t-1)
Where:
哪里：
B3[i] = the existing B3[i] value in the incoming signal B3[i]' = the new (compensated) B3[i] value B3*[i] = the B3[i] value of the unequipped VTs in the incoming signal || = exclusive OR operator t = the time of the current frame t-1 = the time of the previous frame
B3[i]=输入信号中现有的B3[i]值B3[i]'=新的（补偿的）B3[i]值B3*[i]=输入信号中未装备VT的B3[i]值| |=异或运算符t=当前帧的时间t-1=前一帧的时间
The egress PE MUST reconstruct the unequipped VTs and modify the B3 parity value in the same manner to accommodate the additional VTs added. In this way, the end-to-end BIP is preserved.
出口PE必须重建未配备的VT，并以相同的方式修改B3奇偶校验值，以适应添加的额外VT。这样，将保留端到端BIP。
The actual CEP payload size depends on the number of virtual tributaries carried within the fractional SPE. The contributions of each tributary to the fractional STS-1 payload size as well as the path overhead contribution are described below.
实际CEP有效负载大小取决于分数SPE中承载的虚拟支路的数量。各支路对分数STS-1有效负载大小的贡献以及路径开销贡献如下所述。
Each VT1.5 contributes 27 bytes
每个VT1.5贡献27个字节
Each VT2 contributes 36 bytes
每个VT2贡献36个字节
Each VT3 contributes 54 bytes
每个VT3贡献54个字节
Each VT6 contributes 108 bytes
每个VT6贡献108字节
STS-1 POH contributes 9 bytes
STS-1 POH贡献9个字节
For example, a fractional STS-1 carrying 7 VT2 circuit in full-SPE encapsulation would have an actual size of 261=36*7+9 bytes. Divide by 3 to calculate the third-SPE encapsulation actual payload sizes.
例如，在完全SPE封装中携带7个VT2电路的分数STS-1的实际大小为261=36*7+9字节。除以3计算第三个SPE封装的实际有效负载大小。
Asynchronous T3/E3 STS-1 (VC-3) encapsulation is applicable for signals with POH signal label byte C2=4, carrying asynchronously mapped T3 or E3 signals.
异步T3/E3 STS-1（VC-3）封装适用于POH信号标签字节C2=4的信号，承载异步映射的T3或E3信号。
Implementations of asynchronous T3/E3 STS-1 (VC-3) encapsulation MUST support payload length of one SPE and MAY support payload length of 1/3 SPE.
异步T3/E3 STS-1（VC-3）封装的实现必须支持一个SPE的有效负载长度，并且可以支持1/3 SPE的有效负载长度。
A T3 is encapsulated asynchronously into an STS-1 SPE using the format defined in Section 3.4.2.1 of [GR253]. The STS-1 SPE is then encapsulated as defined in this document.
T3使用[GR253]第3.4.2.1节中定义的格式异步封装到STS-1 SPE中。然后按照本文档中的定义封装STS-1 SPE。
Optionally, the STS-1 SPE can be compressed by removing the fixed columns leaving only data columns. STS-1 columns are numbered 1 to 87, starting from the POH column numbered 1. The following columns have fixed values and are removed: 2, 3, 30, 31, 59, and 60.
或者，可以通过删除只留下数据列的固定列来压缩STS-1 SPE。STS-1列从编号为1的POH列开始编号为1至87。以下列具有固定值并已删除：2、3、30、31、59和60。
Bandwidth saving is approximately 7% (6 columns out of 87). The B3 parity byte need not be modified as the parity of the fixed columns amounts to 0. The actual payload size for full-SPE encapsulation would be 729 bytes and 243 bytes for third-SPE encapsulation.
带宽节省约7%（87列中有6列）。B3奇偶校验字节不需要修改，因为固定列的奇偶校验为0。完整SPE封装的实际有效负载大小为729字节，第三个SPE封装的实际有效负载大小为243字节。
A T3 is encapsulated asynchronously into a VC-3 container as described in Section 10.1.2.1 of [G.707]. VC-3 container has only 85 data columns, which is identical to the STS-1 container with the two fixed stuff columns 30 and 59 removed. Other than that, the mapping is identical.
T3异步封装到VC-3容器中，如[G.707]第10.1.2.1节所述。VC-3容器只有85个数据列，这与删除了两个固定填充列30和59的STS-1容器相同。除此之外，映射是相同的。
An E3 is encapsulated asynchronously into a VC-3 SPE using the format defined in Section 10.1.2.2 of [G.707]. The VC-3 SPE is then encapsulated as defined in this document.
E3使用[G.707]第10.1.2.2节中定义的格式异步封装到VC-3 SPE中。然后按照本文档中的定义封装VC-3 SPE。
Optionally, the VC-3 SPE can be compressed by removing the fixed columns leaving only data columns. VC-3 columns are numbered 1 to 85 (and not 87), starting from the POH column numbered 1. The following columns have fixed values and are removed: 2, 6, 10, 14, 18, 19, 23, 27, 31, 35, 39, 44, 48, 52, 56, 60, 61, 65, 69, 73, 77, and 81.
或者，可以通过删除只留下数据列的固定列来压缩VC-3 SPE。VC-3列从编号为1的POH列开始编号为1到85（而不是87）。以下列具有固定值并将被删除：2、6、10、14、18、19、23、27、31、35、39、44、48、52、56、60、61、65、69、73、77和81。
Bandwidth saving is approximately 28% (24 columns out of 85). The B3 parity byte need not be modified as the parity of the fixed columns amounts to 0. The actual payload size for full-SPE encapsulation would be 567 bytes and 189 bytes for third-SPE encapsulation.
带宽节省约为28%（85列中有24列）。B3奇偶校验字节不需要修改，因为固定列的奇偶校验为0。完整SPE封装的实际有效负载大小为567字节，第三个SPE封装的实际有效负载大小为189字节。
SDH defines a mapping of VC-11, VC-12, VC-2, and VC-3 directly into VC-4. This mapping does not have an equivalent within the SONET hierarchy. The VC-4 mapping is common in SDH implementations.
SDH定义了VC-11、VC-12、VC-2和VC-3直接映射到VC-4的映射。此映射在SONET层次结构中没有等效项。VC-4映射在SDH实现中很常见。
VC-4 <--x3-- TUG-3 <--------x1-------- TU-3 <-- VC-3 <---- E3/T3
|
+--x7-- TUG-2 <--x1-- TU-2 <-- VC-2 <---- DS2
|
+----x3---- TU-12 <-- VC-12<---- E1
|
+----x4---- TU-11 <-- VC-11<---- T1
VC-4 <--x3-- TUG-3 <--------x1-------- TU-3 <-- VC-3 <---- E3/T3
|
+--x7-- TUG-2 <--x1-- TU-2 <-- VC-2 <---- DS2
|
+----x3---- TU-12 <-- VC-12<---- E1
|
+----x4---- TU-11 <-- VC-11<---- T1
Figure 8: Mapping of VCs into VC-4
图8：VCs到VC-4的映射
Figure 8 describes the mapping options of VCs into VC-4. A VC-4 contains three TUG-3s. Each TUG-3 is composed of either a single TU-3 or 7 TUG-2s. A TU-3 contains a single VC-3. A TUG-2 contains either 4 VC-11s (T1s), 3 VC-12s (E1s), or one VC-2. Therefore, a VC-4 may contain 3 VC-3s, 1 VC-3 and 42 VC-12s, 63 VC-12s, etc.
图8描述了VCs到VC-4的映射选项。VC-4包含三个拖船-3。每艘拖轮-3由一艘TU-3或7艘拖轮-2组成。TU-3包含一个VC-3。拖船-2包含4个VC-11s（T1s）、3个VC-12s（E1s）或一个VC-2。因此，一个VC-4可能包含3个VC-3、1个VC-3和42个VC-12s、63个VC-12s等。
Fractional VC-4 encapsulation carries only a selected set of VCs within a VC-4 container. This mode is applicable for VC-4 with POH signal label byte C2=2 (TUG structure) and for C2=3 (Locked TU-n). The mapping of VCs into a VC-4 container is described in Section 7.2 of [G.707]. The CEP packetizer removes all fixed column bytes and all bytes that belong to the removed VCs. Only VC-4 POH bytes and bytes that belong to the selected VCs are carried within the payload. The CEP de-packetizer adds the fixed stuff bytes and generates unequipped VC data replacing the removed VC bytes.
部分VC-4封装仅在VC-4容器中携带一组选定的VC。该模式适用于POH信号标签字节C2=2（拖船结构）和C2=3（锁定TU-n）的VC-4。[G.707]第7.2节描述了VCs到VC-4容器的映射。CEP打包器删除所有固定列字节和属于已删除VCs的所有字节。有效负载中仅携带VC-4 POH字节和属于所选VCs的字节。CEP反打包器添加固定的填充字节，并生成未配置的VC数据来替换删除的VC字节。
The fractional VC-4 encapsulation can optionally carry a bit mask that specifies which VCs are carried within the VC-4 payload and which VCs have been removed. This optional bit mask attribute allows the ingress circuit emulation node to remove unequipped VCs on the fly, providing the egress circuit emulation node enough information for reconstructing the VCs in the right order. The use of bit mask enables on-the-fly compression, whereby only equipped VCs (carrying actual data) are sent.
分数VC-4封装可以选择性地携带位掩码，该位掩码指定在VC-4有效负载内携带哪些VCs以及哪些VCs已被移除。此可选位掩码属性允许入口电路仿真节点动态移除未装备的VCs，从而为出口电路仿真节点提供足够的信息，以便以正确的顺序重建VCs。使用位掩码可实现动态压缩，因此仅发送配备的VCs（携带实际数据）。
VC-3 carrying asynchronous T3/E3 signals within the VC-4 container can optionally be compressed by removing the fixed column bytes as described in Section 11.2.2, providing additional bandwidth saving.
在VC-4容器内承载异步T3/E3信号的VC-3可选择性地通过删除第11.2.2节中所述的固定列字节进行压缩，从而提供额外的带宽节约。
Implementations of fractional VC-4 encapsulation MUST support payload length of 1/3 SPE and MAY support payload lengths of 4/9, 5/9, 6/9, 7/9, 8/9, and full SPE. The actual payload size of fractional VC-4 encapsulation depends on the number of VCs carried within the payload.
分数VC-4封装的实现必须支持1/3 SPE的有效负载长度，并且可以支持4/9、5/9、6/9、7/9、8/9和完整SPE的有效负载长度。分数VC-4封装的实际有效负载大小取决于有效负载内携带的VCs数量。
[G.707] defines the mapping of TUG-3 to a VC-4 in Section 7.2.1. Each TUG-3 includes 86 columns. TUG-3#1, TUG-3#2, and TUG-3#3 are byte multiplexed, starting from column 4. Column 1 is the VC-4 POH, while columns 2 and 3 are fixed and therefore removed in the fractional VC-4 encapsulation.
[G.707]定义了第7.2.1节中拖船-3至VC-4的映射。每艘拖船-3包括86根立柱。从第4列开始，TUG-3#1、TUG-3#2和TUG-3#3是字节多路复用的。第1列是VC-4 POH，而第2列和第3列是固定的，因此在部分VC-4封装中被移除。
The mapping of TU-3 into TUG-3 is defined in Section 7.2.2 of [G.707]. The TU-3 consists of the VC-3 with a 9-byte VC-3 POH and the TU-3 pointer. The first column of the 9-row-by-86-column TUG-3 is allocated to the TU-3 pointer (bytes H1, H2, H3) and fixed stuff. The phase of the VC-3 with respect to the TUG-3 is indicated by the TU-3 pointer.
[G.707]第7.2.2节定义了TU-3到TUG-3的映射。TU-3由带9字节VC-3 POH的VC-3和TU-3指针组成。9行86列的TUG-3的第一列被分配给TU-3指针（字节H1、H2、H3）和固定内容。VC-3相对于拖船-3的相位由TU-3指针指示。
The mapping of TUG-2 into TUG-3 is defined in Section 7.2.3 of [G.707]. The first two columns of the TUG-3 are fixed and therefore removed in the fractional VC-4 encapsulation. The 7 TUG-2s, each 12 columns wide, are byte multiplexed starting from column 3 of the TUG-3. This is the equivalent of multiplexing 7 VTGs within STS-1 container in SONET terminology, except for the location of the fixed columns.
[G.707]第7.2.3节规定了将2号拖船映射为3号拖船。TUG-3的前两列是固定的，因此在部分VC-4封装中移除。7个TUG-2，每个12列宽，从TUG-3的第3列开始进行字节多路复用。在SONET术语中，这相当于在STS-1容器中复用7个VTG，但固定列的位置除外。
The static fractional VC-4 mapping assumes that both the ingress and egress nodes are preconfigured with the set of equipped VCs carried within the fractional VC-4 encapsulation. The ingress emulation edge removes the fixed columns as well as columns of the VCs agreed upon by the two edges, and updates the B3 VC-4 byte. The egress side adds the fixed columns and the unequipped VCs and updates B3.
静态分数VC-4映射假设入口和出口节点都预先配置了分数VC-4封装中携带的一组配备的VCs。入口模拟边缘删除固定列以及两个边缘同意的VCs列，并更新B3 VC-4字节。出口侧添加固定柱和未配备的VCs，并更新B3。
The fractional VC-4 CEP header uses the VC-4 CEP header defined in this document. Optionally, an additional 12-byte header extension word is added.
部分VC-4 CEP标头使用本文档中定义的VC-4 CEP标头。可选地，添加额外的12字节头扩展字。
The extended header has the following format:
扩展标头具有以下格式：
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|L|R|N|P|FRG|Length[0:5]| Sequence Number[0:15] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Structure Pointer[0:11]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Equipped Bit Mask #1 (EBM) [0:29] TUG-3#1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Equipped Bit Mask #2 (EBM) [0:29] TUG-3#2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Equipped Bit Mask #3 (EBM) [0:29] TUG-3#3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|L|R|N|P|FRG|Length[0:5]| Sequence Number[0:15] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Structure Pointer[0:11]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Equipped Bit Mask #1 (EBM) [0:29] TUG-3#1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Equipped Bit Mask #2 (EBM) [0:29] TUG-3#2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Equipped Bit Mask #3 (EBM) [0:29] TUG-3#3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Extended Fractional VC-4 Header
图9：扩展分数VC-4标题
The L, R, N, P, FRG, Length, Sequence Number, and Structured Pointer fields are used as defined in this document for STS-1 encapsulation.
L、R、N、P、FRG、长度、序列号和结构化指针字段按照本文档中的定义用于STS-1封装。
Each bit within the Equipped Bit Mask (EBM) field refers to a different tributary within the VC-4 container. A bit set to 1 indicates that the corresponding tributary is equipped, hence carried within the fractional VC-4 payload.
配备的位掩码（EBM）字段中的每个位都表示VC-4容器中的不同支路。位设置为1表示配备了相应的支路，因此在分数VC-4有效负载内携带。
Three EBM fields are used. Each EBM field corresponds to a different TUG-3 within the VC-4. The EBM includes 7 groups of 4 bits per TUG-2. A bit set to 1 indicates that the corresponding VC is equipped, hence carried within the fractional VC-4 payload. An additional 2 bits within the EBM indicate whether VC-3 carried within the TUG-3 is equipped and whether it is in AIS mode.
使用三个EBM字段。每个EBM字段对应于VC-4内的不同拖船-3。EBM包括7组，每组4位，每拖轮2。位设置为1表示配备了相应的VC，因此在分数VC-4有效载荷内携带。EBM中的另外2位表示拖船-3内携带的VC-3是否配备以及是否处于AIS模式。
The VC-4 EBM has the following format:
VC-4 EBM具有以下格式：
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|T|TUG2#7 |TUG2#6 |TUG2#5 |TUG2#4 |TUG2#3 |TUG2#2 |TUG2#1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|T|TUG2#7 |TUG2#6 |TUG2#5 |TUG2#4 |TUG2#3 |TUG2#2 |TUG2#1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Equipped Bit Mask (EBM) for Fractional VC-4
图10：分数VC-4配备的位掩码（EBM）
The 30 bits of the EBM are divided into 2 bits that control the VC-3 within the TUG-3 and 7 groups of 4 bits, each corresponding to a different TUG-2 within the TUG-3 container.
EBM的30位分为2位，控制TUG-3内的VC-3和7组4位，每组对应于TUG-3集装箱内的不同TUG-2。
For a TUG-3 containing TUG-2, the first two A and T bits MUST be set to 0. The TUG-2 bits indicate whether the VCs within the TUG-2 are equipped. All 4 bits are used to indicate whether VC-11 (T1) tributaries are carried within a TUG-2. The first 3 bits read right to left are used to indicate whether VC-12 (E1) tributaries are carried within a TUG-2. The first bit is used to indicate that a VC-2 is carried within a TUG-2. The VCs within the TUG-2 are numbered from right to left, starting from the first VC as the first bit on the right. For example, 28 bits of the EBM of a fully occupied TUG-3 with VC-11 tributaries are all ones, while that of a TUG-3 fully occupied with VC-12 tributaries has the binary value 000111011101110111011101110111.
对于包含TUG-2的TUG-3，前两个a和T位必须设置为0。TUG-2位指示是否配备了TUG-2内的VCs。所有4位用于指示VC-11（T1）支流是否在拖船-2内运输。从右至左读取的前3位用于指示VC-12（E1）支路是否在拖船-2内传输。第一位用于指示VC-2在拖船-2内运载。TUG-2内的VCs从右向左编号，从第一个VC开始，作为右侧的第一位。例如，具有VC-11支路的完全占用的TUG-3的EBM的28位均为1，而具有VC-12支路的完全占用的TUG-3的EBM的28位具有二进制值00011011101111011101111。
For a TUG-3 containing VC-3, all TUG-2 bits MUST be set to 0. The A and T bits are defined as follows:
对于包含VC-3的TUG-3，所有TUG-2位必须设置为0。A和T位的定义如下：
T: TUG-3 carried bit. If set to 1, the VC-3 payload is carried within the TUG-3 container. If set to 0, all the TUG-3 columns are not carried within the fractional VC-4 encapsulation. The TUG-3 columns are removed either because the VC-3 is unequipped or in AIS mode.
T:TUG-3携带钻头。如果设置为1，则VC-3有效载荷在拖船-3集装箱内运输。如果设置为0，则所有TUG-3列不在分数VC-4封装内。由于VC-3未配备设备或处于AIS模式，拖船-3立柱被拆除。
A: VC-3 AIS bit. The A bit MUST be set to 0 when the T bit is 1 (i.e., when the TUG-3 columns are carried within the fractional VC-4 encapsulation). The A bit indicate the reason for removal of the entire TUG-3 columns. If set to 0, the TUG-3 columns were removed because the VC-3 is unequipped. If set to 1, the TUG-3 columns were removed because the VC-3 is in AIS mode.
A:VC-3 AIS位。当T位为1时（即，在分数VC-4封装中携带TUG-3列时），A位必须设置为0。A位表示拆除整个拖船-3立柱的原因。如果设置为0，则由于VC-3未配备设备，拖船-3立柱被移除。如果设置为1，则由于VC-3处于AIS模式，因此删除了TUG-3立柱。
Fractional VC-4 encapsulation can be implemented in Line Terminating Equipment (LTE) or in Path Terminating Equipment (PTE). PTE implementations terminate the path layer at the ingress PE and
部分VC-4封装可在线路终端设备（LTE）或路径终端设备（PTE）中实现。PTE实现在入口PE处终止路径层，并
generate a new path layer at the egress PE. LTE implementations do not terminate the path layer, and therefore need to keep the content and integrity of the POH bytes across the PSN. In LTE implementations, special care must be taken to maintain the B3 bit-wise parity POH byte. The same procedures for B3 compensation as described in Section 11.2.1.2 for fractional STS-1 encapsulation are used.
在出口PE处生成新路径层。LTE实现不终止路径层，因此需要在PSN上保持POH字节的内容和完整性。在LTE实现中，必须特别注意保持B3位奇偶校验POH字节。使用第11.2.1.2节中描述的分数STS-1封装B3补偿程序。
The actual CEP payload size depends on the number of virtual tributaries carried within the fractional SPE. The contributions of each tributary to the fractional VC-4 payload length as well as the path overhead contribution are described below.
实际CEP有效负载大小取决于分数SPE中承载的虚拟支路的数量。各支路对分数VC-4有效负载长度的贡献以及路径开销贡献如下所述。
Each VC-11 contributes 27 bytes
每个VC-11贡献27个字节
Each VC-12 contributes 36 bytes
每个VC-12贡献36个字节
Each VC-2 contributes 108 bytes
每个VC-2贡献108字节
Each VC-3(T3) contributes 738 bytes
每个VC-3（T3）贡献738字节
Each VC-3(E3) contributes 576 bytes
每个VC-3（E3）贡献576字节
Each VC-3(uncompressed) contributes 774 bytes
每个VC-3（未压缩）贡献774字节
VC-4 POH contributes 9 bytes
VC-4 POH贡献了9个字节
The VC-3 contribution includes the AU-3 pointer. For example, the payload size of a fractional VC-4 configured to third-SPE encapsulation that carries a single compressed T3 VC-3 and 6 VC-12s would be: 321=(9 + 6*36 + 738) / 3 bytes payload per each packet.
VC-3贡献包括AU-3指针。例如，对于第三个有效负载，每个VC-736的部分有效负载将被配置为VC-736个字节，并且对于第三个有效负载，每个VC-736的部分有效负载将被配置为VC-736个字节。
[PWE3-CONTROL] specifies the use of the MPLS Label Distribution Protocol, LDP, as a protocol for setting up and maintaining pseudowires. In particular, it provides a way to bind a de-multiplexer field value to a pseudo-wire, specifying procedures for reporting pseudowire status changes and for releasing the bindings. [PWE3-CONTROL] assumes that the pseudowire de-multiplexer field is an MPLS label; however, the PSN tunnel itself can be either an IP or MPLS PSN.
[PWE3-CONTROL]指定使用MPLS标签分发协议LDP作为建立和维护伪线的协议。特别是，它提供了一种将解复用器字段值绑定到伪线的方法，指定了报告伪线状态更改和释放绑定的过程。[PWE3-CONTROL]假设伪线解复用器字段是MPLS标签；但是，PSN隧道本身可以是IP或MPLS PSN。
The use of LDP for setting up and maintaining CEP pseudowires is OPTIONAL. This section describes the use of the CEP-specific fields and error codes.
使用LDP设置和维护CEP伪线是可选的。本节介绍CEP特定字段和错误代码的使用。
The PW Type field in PWid Forwarding Equivalence Class (FEC) and PW generalized ID FEC elements MUST be set to SONET/SDH Circuit Emulation over Packet (CEP) [PWE3-IANA].
PWid转发等价类（FEC）和PW通用ID FEC元素中的PW类型字段必须设置为SONET/SDH分组电路仿真（CEP）[PWE3-IANA]。
The control word is REQUIRED for CEP pseudowires. Therefore, the C bit in PWid FEC and PW generalized ID FEC elements MUST be set. If the C bit is not set, the pseudowire MUST not be established and a Label Release MUST be sent with an Illegal C bit status code [PWE3-IANA].
CEP伪导线需要控制字。因此，必须设置PWid FEC和PW通用ID FEC元素中的C位。如果未设置C位，则不得建立伪线，并且必须发送带有非法C位状态代码[PWE3-IANA]的标签释放。
The PWid FEC and PW generalized ID FEC elements can include one or more Interface Parameters fields. The Interface Parameters fields are used to validate that the two ends of the pseudowire have the necessary capabilities to interoperate with each other. The CEP-specific Interface Parameters fields are the CEP/TDM Payload Bytes, the CEP/TDM Bit Rate, and the CEP Options parameters.
PWid FEC和PW通用ID FEC元素可以包括一个或多个接口参数字段。接口参数字段用于验证伪线的两端是否具有相互操作所需的功能。CEP特定接口参数字段是CEP/TDM有效负载字节、CEP/TDM比特率和CEP选项参数。
This parameter MUST contain the expected CEP payload size in bytes. The payload size does not include network headers, CEP header or padding. If payload compression is used, the CEP/TDM Payload Bytes parameter MUST be set to the uncompressed payload size as if payload compression was disabled. In particular, when Fractional SPE (STS-1/ VC-3 or VC-4) payload compression is used, the Payload Bytes parameter MUST be set to the payload size before removal of the unequipped VT containers and fixed value columns. Therefore, when fractional SPE mode is used, the actual (i.e., on the wire) packet length would normally be less than advertised, and in dynamic fractional SPE, even change while the connection is active. Similarly, when DBA payload compression is used, the CEP/TDM Payload Bytes parameter MUST be set to the payload size prior to compression.
此参数必须包含预期的CEP有效负载大小（以字节为单位）。有效负载大小不包括网络标头、CEP标头或填充。如果使用有效负载压缩，则CEP/TDM有效负载字节参数必须设置为未压缩的有效负载大小，就像有效负载压缩已禁用一样。特别是，当使用分数SPE（STS-1/VC-3或VC-4）有效负载压缩时，在移除未装备的VT容器和固定值列之前，必须将有效负载字节参数设置为有效负载大小。因此，当使用分数SPE模式时，实际（即在线）数据包长度通常会小于公布的长度，在动态分数SPE中，甚至在连接处于活动状态时会发生变化。类似地，当使用DBA有效负载压缩时，CEP/TDM有效负载字节参数必须设置为压缩前的有效负载大小。
The CEP/TDM Payload Bytes parameter is OPTIONAL. Default payload sizes are assumed if this parameter is not included as part of the Interface Parameters fields. The default payload size for VT is a single super frame. The default payload size for SPE is 783 bytes.
CEP/TDM有效负载字节参数是可选的。如果此参数未作为接口参数字段的一部分包含，则假定默认有效负载大小。VT的默认有效负载大小是单个超级帧。SPE的默认有效负载大小为783字节。
A PE that receives a label-mapping request with request for a CEP/TDM Payload Bytes value that is not locally supported MUST return CEP/TDM misconfiguration status error code [PWE3-IANA], and the pseudowire MUST not be established.
接收标签映射请求并请求本地不支持的CEP/TDM有效负载字节值的PE必须返回CEP/TDM错误配置状态错误代码[PWE3-IANA]，并且不得建立伪线。
The CEP/TDM Bit Rate parameter MUST be set to the data rate in 64- Kbps units of the CEP payload. If payload compression is used, the CEP/TDM Bit Rate parameter MUST be set to the uncompressed payload
CEP/TDM比特率参数必须设置为CEP有效负载的64-Kbps单位的数据速率。如果使用有效负载压缩，则CEP/TDM比特率参数必须设置为未压缩的有效负载
data rate as if payload compression was disabled. Table 3 specifies the CEP/TDM Bit Rate parameters that MUST be set for each of the pseudowire circuits.
数据速率，如同有效负载压缩已禁用。表3规定了必须为每个伪线电路设置的CEP/TDM比特率参数。
+-------------+-----------------------+
| Circuit | Bit Rate Parameter |
+-------------+-----------------------+
| VT1.5/VC-11 | 26 |
| VT2/VC-12 | 35 |
| VT3 | 53 |
| VT6/VC-2 | 107 |
| STS-Nc | 783*N N=1,3,12,48,192 |
+-------------+-----------------------+
+-------------+-----------------------+
| Circuit | Bit Rate Parameter |
+-------------+-----------------------+
| VT1.5/VC-11 | 26 |
| VT2/VC-12 | 35 |
| VT3 | 53 |
| VT6/VC-2 | 107 |
| STS-Nc | 783*N N=1,3,12,48,192 |
+-------------+-----------------------+
Table 3: CEP/TDM Bit Rates
比特率：3 CEP表
The CEP/TDM Bit Rate parameter is REQUIRED. Attempts to establish a pseudowire between two peers with different bit rates MUST be rejected with incompatible bit rate status error code [PWE3-IANA], and the pseudowire MUST not be established.
需要CEP/TDM比特率参数。必须使用不兼容的比特率状态错误代码[PWE3-IANA]拒绝在具有不同比特率的两个对等方之间建立伪线的尝试，并且不得建立伪线。
The CEP Options parameter is REQUIRED. The format of the CEP Options parameter is described below:
CEP Options参数是必需的。CEP Options参数的格式如下所述：
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|AIS|UNE|RTP|EBM| Reserved [0:6] | CEP Type | Async |
| | | | | | [0:2] |T3 |E3 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|AIS|UNE|RTP|EBM| Reserved [0:6] | CEP Type | Async |
| | | | | | [0:2] |T3 |E3 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 11: CEP Options
图11:CEP选项
AIS: When set, indicates that the PE sending the label-mapping request is configured to send DBA packets when AIS indication is detected.
AIS：设置时，表示发送标签映射请求的PE配置为在检测到AIS指示时发送DBA数据包。
UNE: When set, indicates that the PE sending the label-mapping request is configured to send DBA packets when unequipped circuit indication is detected.
UNE：设置时，表示发送标签映射请求的PE配置为在检测到未设置的电路指示时发送DBA数据包。
RTP: When set, indicates that the PE sending the label-mapping request is configured to send packets with RTP header.
RTP：设置时，表示发送标签映射请求的PE配置为发送带有RTP头的数据包。
EBM: When set, indicates that the PE sending the label-mapping request is configured to send packets with EBM extension header.
EBM：设置时，表示发送标签映射请求的PE配置为发送带有EBM扩展头的数据包。
CEP Type: indicates the CEP connection type:
CEP类型：表示CEP连接类型：
0x0 SPE mode (STS-1/STS-Mc)
0x0 SPE模式（STS-1/STS Mc）
0x1 VT mode (VT1.5/VT2/VT3/VT6)
0x1 VT mode (VT1.5/VT2/VT3/VT6)
0x2 Fractional SPE (STS-1/VC-3/VC-4)
0x2分数SPE（STS-1/VC-3/VC-4）
Async Type: indicates the Async E3/T3 bandwidth reduction configuration. Relevant only when CEP type is set to fractional SPE, and fractional SPE is expected to carry Asynchronous T3/E3 payload:
异步类型：表示异步E3/T3带宽缩减配置。仅当CEP类型设置为分数SPE时相关，分数SPE预计携带异步T3/E3有效负载：
T3: When set, indicates that the PE sending the label-mapping request is configured to send Fractional SPE packets with T3 bandwidth reduction.
T3：设置时，表示发送标签映射请求的PE配置为发送T3带宽减少的分数SPE数据包。
E3: When set, indicates that the PE sending the label-mapping request is configured to send Fractional SPE packets with E3 bandwidth reduction.
E3：设置时，表示发送标签映射请求的PE配置为发送E3带宽减少的分数SPE数据包。
Reserved field: MUST be set to 0 by the PE sending the label-mapping request and ignored by the receiver.
保留字段：必须由发送标签映射请求的PE设置为0，并由接收方忽略。
A PE that does not support one of the CEP options set in the label-mapping request MUST send a label-release message with status code of CEP/TDM misconfiguration [PWE3-IANA], report to the operator, and wait for a new consistent label-mapping. A PE MUST send a new label-mapping request once it is reconfigured or when it receives a label-mapping request from its peer with consistent configuration.
不支持标签映射请求中设置的CEP选项之一的PE必须发送状态代码为CEP/TDM错误配置[PWE3-IANA]的标签发布消息，向操作员报告，并等待新的一致标签映射。PE在重新配置后或从具有一致配置的对等方接收到标签映射请求时，必须发送新的标签映射请求。
A pseudowire can be configured asymmetrically. One PE can be configured to use bandwidth reduction modes, while the other PE can be configured to send the entire circuit unmodified. A PE can compare the CEP Options settings received in the label-mapping request with its own configuration and detect an asymmetric pseudowire configuration. A PE that identifies an asymmetric configuration MAY report it to the operator.
伪线可以不对称配置。一个PE可以配置为使用带宽减少模式，而另一个PE可以配置为不经修改地发送整个电路。PE可以将标签映射请求中接收的CEP选项设置与其自身的配置进行比较，并检测非对称伪线配置。识别非对称配置的PE可向操作员报告。
The PSN carrying the CEP PW may be subject to congestion. Congestion considerations for PWs are described in Section 6.5 of [PWE3-ARCH]. CEP PWs represent inelastic constant bit rate (CBR) flows and cannot respond to congestion in a TCP-friendly manner prescribed by [CONG]. CEP PWs SHOULD be carried across traffic-engineered PSNs that provide either bandwidth reservation and admission control or forwarding prioritization and boundary traffic conditioning mechanisms. Intserv-enabled domains [INTSERV] supporting Guaranteed Service [GS] and Diffserv-enabled domains [DIFFSERV] supporting Expedited Forwarding [EF] provide examples of such PSNs. It is expected that PWs emulating high-rate SONET STS-Nc or SDH virtual circuits will be tunneled over traffic-engineered MPLS PSN.
承载CEP PW的PSN可能会出现拥塞。[PWE3-ARCH]第6.5节描述了PWs的拥堵考虑因素。CEP PWs代表非弹性恒定比特率（CBR）流，不能以[CONG]规定的TCP友好方式响应拥塞。CEP PWs应跨提供带宽预留和准入控制或转发优先级和边界流量调节机制的流量工程PSN进行。支持保证服务[GS]的支持Intserv的域[Intserv]和支持快速转发[EF]的支持Diffserv的域[Diffserv]提供了此类PSN的示例。预计模拟高速SONET STS Nc或SDH虚拟电路的PWs将通过流量工程MPLS PSN进行隧道传输。
CEP PWs SHOULD monitor packet loss in order to detect "severe congestion". If such a condition is detected, a CEP PW SHOULD shut down bi-directionally. This specification does not define the exact criteria for detecting "severe congestion" using the CEP packet loss rate and the consequent restart criteria after a suitable delay. This is left for further study.
CEP PWs应监控数据包丢失，以检测“严重拥塞”。如果检测到这种情况，CEP PW应双向关闭。本规范未定义使用CEP丢包率检测“严重拥塞”的确切标准，以及在适当延迟后的后续重启标准。这有待进一步研究。
If the CEP PW has been set up using the PWE3 control protocol [PWE3-CONTROL], the regular PW teardown procedures SHOULD be used upon detection of "severe congestion".
如果已使用PWE3控制协议[PWE3-control]设置CEP PW，则在检测到“严重拥塞”时，应使用常规PW拆卸程序。
The SONET/SDH services emulated by CEP PWs have high availability objectives that MUST be taken into account when deciding on temporary shutdown of CEP PWs. CEP performance monitoring provides entry and exit criteria for the CEP PW unavailable state (UAS-CEP). Detection of "severe congestion" MAY be based on unavailability criteria of the CEP PW.
CEP PWs模拟的SONET/SDH服务具有高可用性目标，在决定临时关闭CEP PWs时必须将其考虑在内。CEP性能监控为CEP PW不可用状态（UAS-CEP）提供进入和退出标准。“严重拥堵”的检测可能基于CEP PW的不可用标准。
The CEP encapsulation is subject to all of the general security considerations discussed in [PWE3-ARCH]. In addition, this document specifies only encapsulations, and not the protocols used to carry the encapsulated packets across the PSN. Each such protocol may have its own set of security issues, but those issues are not affected by the encapsulations specified herein. Note that the security of the transported CEP service will only be as good as the security of the PSN. This level of security may be less rigorous than that available from a native TDM service due to the inherent differences between circuit-switched and packet-switched public networks.
CEP封装受[PWE3-ARCH]中讨论的所有一般安全注意事项的约束。此外，本文档仅指定封装，而不指定用于跨PSN传输封装数据包的协议。每个这样的协议可能有其自己的一组安全问题，但是这些问题不受本文指定的封装的影响。请注意，传输的CEP服务的安全性仅与PSN的安全性相同。由于电路交换和分组交换公共网络之间的固有差异，这种安全级别可能不如本地TDM服务提供的安全级别严格。
Although CEP MAY employ an RTP header when explicit transfer of timing information is required, SRTP [RFC3711] mechanisms are not a substitute for securing the PW and underlying MPLS network.
尽管当需要显式传输定时信息时，CEP可以使用RTP报头，但是SRTP[RFC3711]机制不能替代保护PW和底层MPLS网络。
IANA considerations for pseudowires are covered in [PWE3-IANA]. CEP does not introduce additional requirements from IANA.
[PWE3-IANA]中介绍了伪导线的IANA注意事项。CEP并未引入IANA的额外要求。
The authors would like to thank the members of the PWE3 Working Group for their assistance on this document. We thank Sasha Vainshtein, Deborah Brungard, Juergen Heiles, and Nick Weeds for their review and valuable feedback.
作者要感谢PWE3工作组成员对本文件的帮助。我们感谢Sasha Vainstein、Deborah Brungard、Juergen Heiles和Nick Weeds的评论和宝贵反馈。
The individuals listed below are co-authors of this document. Tom Johnson from Litchfield Communications was the editor of this document from the pre-WG versions of the SONET SPE work through version 01 of this document.
下面列出的个人是本文件的共同作者。来自Litchfield Communications的Tom Johnson是本文档的编辑，从SONET SPE工作的前工作组版本一直到本文档的第01版。
Craig White Level3 Communications Ed Hallman Litchfield Communications Jeremy Brayley Laurel Networks Jim Boyle Juniper Networks John Shirron Laurel Networks Luca Martini Cisco Systems Marlene Drost Litchfield Communications Steve Vogelsang Laurel Networks Tom Johnson Litchfield Communications Ken Hsu Tellabs
Craig White Level 3 Communications Ed Hallman Litchfield Communications Jeremy Brayley Laurel Networks Jim Boyle Juniper Networks John Shirron Laurel Networks Luca Martini Cisco Systems Marlene Drost Litchfield Communications Steve Vogelsang Laurel Networks Tom Johnson Litchfield Communications Ken Hsu Tellabs
Appendix A. SONET/SDH Rates and Formats
附录A.SONET/SDH速率和格式
For simplicity, the discussion in this section uses SONET terminology, but it applies equally to SDH as well. SDH-equivalent terminology is shown in the tables.
为简单起见，本节中的讨论使用SONET术语，但它同样适用于SDH。SDH等效术语如表所示。
The basic SONET modular signal is the synchronous transport signal-level 1 (STS-1). A number of STS-1s may be multiplexed into higher-level signals denoted as STS-N, with N synchronous payload envelopes (SPEs). The optical counterpart of the STS-N is the Optical Carrier-level N, or OC-N. Table 4 lists standard SONET line rates discussed in this document.
基本SONET模块信号为1级同步传输信号（STS-1）。可以将多个STS-1复用成表示为STS-N的具有N个同步有效载荷包络（spe）的更高级别信号。STS-N的光学对应物是光载波电平N或OC-N。表4列出了本文件中讨论的标准SONET线速率。
+-------------+--------+---------+----------+-----------+-----------+
| OC Level | OC-1 | OC-3 | OC-12 | OC-48 | OC-192 |
+-------------+--------+---------+----------+-----------+-----------+
| SDH Term | - | STM-1 | STM-4 | STM-16 | STM-64 |
| Line | 51.840 | 155.520 | 622.080 | 2,488.320 | 9,953.280 |
| Rate(Mb/s) | | | | | |
+-------------+--------+---------+----------+-----------+-----------+
+-------------+--------+---------+----------+-----------+-----------+
| OC Level | OC-1 | OC-3 | OC-12 | OC-48 | OC-192 |
+-------------+--------+---------+----------+-----------+-----------+
| SDH Term | - | STM-1 | STM-4 | STM-16 | STM-64 |
| Line | 51.840 | 155.520 | 622.080 | 2,488.320 | 9,953.280 |
| Rate(Mb/s) | | | | | |
+-------------+--------+---------+----------+-----------+-----------+
Table 4: Standard SONET Line Rates
表4：标准SONET线路费率
Each SONET frame is 125us and consists of nine rows. An STS-N frame has nine rows and N*90 columns. Of the N*90 columns, the first N*3 columns are transport overhead and the other N*87 columns are SPEs. A number of STS-1s may also be linked together to form a super-rate signal with only one SPE. The optical super-rate signal is denoted as OC-Nc, which has a higher payload capacity than OC-N.
每个SONET帧为125us，由九行组成。STS-N帧有九行和N*90列。在N*90列中，前N*3列为传输开销，其他N*87列为SPE。多个STS-1也可连接在一起，以形成仅具有一个SPE的超速率信号。光学超速率信号表示为OC-Nc，其有效负载容量高于OC-N。
The first 9-byte column of each SPE is the path overhead (POH) and the remaining columns form the payload capacity with fixed stuff (STS-Nc only). The fixed stuff, which is purely overhead, is N/3-1 columns for STS-Nc. Thus, STS-1 and STS-3c do not have any fixed stuff, STS-12c has three columns of fixed stuff, and so on.
每个SPE的第一个9字节列是路径开销（POH），其余列构成固定内容的有效负载容量（仅限STS Nc）。对于STS Nc，固定内容（纯粹是开销）是N/3-1列。因此，STS-1和STS-3c没有任何固定内容，STS-12c有三列固定内容，依此类推。
The POH of an STS-1 or STS-Nc is always 9 bytes in nine rows. The payload capacity of an STS-1 is 86 columns (774 bytes) per frame. The payload capacity of an STS-Nc is (N*87)-(N/3) columns per frame. Thus, the payload capacity of an STS-3c is (3*87 - 1)*9 = 2,340 bytes per frame. As another example, the payload capacity of an STS-192c is 149,760 bytes, which is 64 times the capacity of an STS-3c.
STS-1或STS Nc的POH始终为9行9字节。STS-1的有效负载容量为每帧86列（774字节）。STS Nc的有效负载容量为每帧（N*87）-（N/3）列。因此，STS-3c的有效负载容量是（3×87-1）×9＝2340字节/帧。另一个例子是，STS-192c的有效负载容量为149760字节，是STS-3c容量的64倍。
There are 8,000 SONET frames per second. Therefore, the SPE size,
(POH plus payload capacity) of an STS-1 is 783*8*8,000 = 50.112 Mb/s.
The SPE size of a concatenated STS-3c is 2,349 bytes per frame or
There are 8,000 SONET frames per second. Therefore, the SPE size,
(POH plus payload capacity) of an STS-1 is 783*8*8,000 = 50.112 Mb/s.
The SPE size of a concatenated STS-3c is 2,349 bytes per frame or
150.336 Mb/s. The payload capacity of an STS-192c is 149,760 bytes per frame, which is equivalent to 9,584.640 Mb/s. Table 5 lists the SPE and payload rates supported.
150.336 Mb/s。STS-192c的有效负载容量为每帧149760字节，相当于9584.640 Mb/s。表5列出了支持的SPE和有效负载速率。
+-------------+--------+---------+----------+-----------+-----------+
| SONET STS | STS-1 | STS-3c | OC-12c | OC-48c | OC-192c |
| Level | | | | | |
+-------------+--------+---------+----------+-----------+-----------+
| SDH VC | VC-3 | VC-4 | VC-4-4c | VC-4-16c | VC-4-64c |
| Level | | | | | |
| Payload | 774 | 2,340 | 9,360 | 37,440 | 149,760 |
| Size(Bytes) | | | | | |
| Payload | 49.536 | 149.760 | 599.040 | 2,396.160 | 9,584.640 |
| Rate(Mb/s) | | | | | |
| SPE | 783 | 2,349 | 9,396 | 37,584 | 150,336 |
| Size(Bytes) | | | | | |
| SPE | 50.112 | 150.336 | 601.344 | 2,405.376 | 9,621.504 |
| Rate(Mb/s) | | | | | |
+-------------+--------+---------+----------+-----------+-----------+
+-------------+--------+---------+----------+-----------+-----------+
| SONET STS | STS-1 | STS-3c | OC-12c | OC-48c | OC-192c |
| Level | | | | | |
+-------------+--------+---------+----------+-----------+-----------+
| SDH VC | VC-3 | VC-4 | VC-4-4c | VC-4-16c | VC-4-64c |
| Level | | | | | |
| Payload | 774 | 2,340 | 9,360 | 37,440 | 149,760 |
| Size(Bytes) | | | | | |
| Payload | 49.536 | 149.760 | 599.040 | 2,396.160 | 9,584.640 |
| Rate(Mb/s) | | | | | |
| SPE | 783 | 2,349 | 9,396 | 37,584 | 150,336 |
| Size(Bytes) | | | | | |
| SPE | 50.112 | 150.336 | 601.344 | 2,405.376 | 9,621.504 |
| Rate(Mb/s) | | | | | |
+-------------+--------+---------+----------+-----------+-----------+
Table 5: Payload Size and Rate
表5：有效载荷大小和速率
To support circuit emulation, the entire SPE of a SONET STS or SDH VC level is encapsulated into packets, using the encapsulation defined in Section 5, for carriage across packet-switched networks.
为了支持电路仿真，SONET STS或SDH VC级别的整个SPE使用第5节中定义的封装封装到数据包中，用于跨数据包交换网络传输。
VTs are organized in SONET super-frames, where a SONET super-frame is a sequence of four SONET SPEs. The SPE path overhead byte H4 indicates the SPE number within the super-frame. The VT data can float relative to the SPE position. The overhead bytes V1, V2, and V3 are used as pointer and stuffing byte similar to the use of the H1, H2, and H3 TOH bytes.
VT在SONET超级帧中组织，其中SONET超级帧是四个SONET SPE的序列。SPE路径开销字节H4表示超级帧内的SPE编号。VT数据可以相对于SPE位置浮动。开销字节V1、V2和V3用作指针和填充字节，类似于H1、H2和H3-TOH字节的使用。
Figure 12 below illustrates a SONET interconnect example. Site A and Site B are connected back to a Hub Site, Site C by means of a SONET infrastructure. The OC-12 from Site A and the OC-12 from Site B are partially equipped. Each of them is transported through a SONET network back to a hub site C. Equipped SPEs (or VTs) are then groomed onto the OC-12 towards site C.
下面的图12说明了SONET互连示例。站点A和站点B通过SONET基础设施连接回中心站点，即站点C。现场A的OC-12和现场B的OC-12部分配备。它们中的每一个都通过SONET网络传输回中心站点C。然后，装备的SPE（或VT）被引导到OC-12上，朝向站点C。
SONET Network
____ ___ ____
/ \___/ \ _/ \__
+------+ Physical / \__/ \
|Site A| OC-12 / +---+ OC-12 \ Hub Site
| |=================|\S/|-------------+-----+ \ +------+
| | \ |/ \|=============|\ /| \ | |
+------+ /\ +---+-------------| \ / | / OC-12| |
/ | S |=========|Site C|
+------+ Physical/ +---+-------------| / \ | \ | |
|Site B| OC-12 \ |\S/|=============|/ \| \ | |
| |=================|/ \|-------------+-----+ / +------+
| | \ +---+ OC-12 __ /
+------+ \ __/ \ /
\ ___ ___ / \_/
\_/ \____/ \___/
SONET Network
____ ___ ____
/ \___/ \ _/ \__
+------+ Physical / \__/ \
|Site A| OC-12 / +---+ OC-12 \ Hub Site
| |=================|\S/|-------------+-----+ \ +------+
| | \ |/ \|=============|\ /| \ | |
+------+ /\ +---+-------------| \ / | / OC-12| |
/ | S |=========|Site C|
+------+ Physical/ +---+-------------| / \ | \ | |
|Site B| OC-12 \ |\S/|=============|/ \| \ | |
| |=================|/ \|-------------+-----+ / +------+
| | \ +---+ OC-12 __ /
+------+ \ __/ \ /
\ ___ ___ / \_/
\_/ \____/ \___/
Figure 12: SONET Interconnect Example Diagram
图12:SONET互连示例图
Figure 13 below illustrates the same pair of OC-12s being emulated over a PSN. This configuration frees up bandwidth in the grooming network, since only equipped SPEs (or VTs) are sent through the PSN. Additional bandwidth savings can be realized by taking advantage of the various payload compression options described in Section 11.
下面的图13说明了在PSN上模拟的同一对OC-12。这种配置释放了梳理网络中的带宽，因为只有装备的SPE（或VT）通过PSN发送。通过利用第11节中描述的各种有效负载压缩选项，可以实现额外的带宽节约。
SONET/TDM/Packet Network
____ ___ ____
/ \___/ \ / \__
+------+ Physical /+-+ \__/ \_
|Site A| OC-12 / | | +---+ \ Hub Site
| |=============|P|=| R | +---+ +-+ +-----+ \ +------+
| | \ |E| | |===| | | |=|\ /| \ | |
+------+ /\+-+ +---+ | | | | | \ / | / OC-12| |
/ | R |=|P| | S |=========|Site C|
+------+ Physical/ +-+ +---+ | | |E| | / \ | \ | |
|Site B| OC-12 \ |P| | R |===| | | |=|/ \| \ | |
| |=============|E|=| | +---+ +-+ +-----+ / +------+
| | \ | | +---+ __ /
+------+ \ +-+ __/ \ /
\ ___ ___ / \_/
\_/ \____/ \___/
SONET/TDM/Packet Network
____ ___ ____
/ \___/ \ / \__
+------+ Physical /+-+ \__/ \_
|Site A| OC-12 / | | +---+ \ Hub Site
| |=============|P|=| R | +---+ +-+ +-----+ \ +------+
| | \ |E| | |===| | | |=|\ /| \ | |
+------+ /\+-+ +---+ | | | | | \ / | / OC-12| |
/ | R |=|P| | S |=========|Site C|
+------+ Physical/ +-+ +---+ | | |E| | / \ | \ | |
|Site B| OC-12 \ |P| | R |===| | | |=|/ \| \ | |
| |=============|E|=| | +---+ +-+ +-----+ / +------+
| | \ | | +---+ __ /
+------+ \ +-+ __/ \ /
\ ___ ___ / \_/
\_/ \____/ \___/
Figure 13: SONET Interconnect Emulation Example Diagram
图13:SONET互连仿真示例图
Figure 14 below shows an example of T1 grooming into OC-12 in access networks. The VT encapsulation is used to transport the T1s from the Hub site to customer sites, maintaining SONET/SDH Operations and Management (OAM).
下面的图14显示了接入网络中T1梳理成OC-12的示例。VT封装用于将T1s从集线器站点传输到客户站点，以维护SONET/SDH操作和管理（OAM）。
SONET/TDM/Packet Network
____ ___ ____
/ \___/ \ / \__
+------+ Physical /+-+ \__/ \_
|Site A| T1 / | | +---+ \ Hub Site
| |=============|P|=| R | +---+ +-+ +-----+ \ +------+
| | \ |E| | |===| | | |=|\ /| \ | |
+------+ /\+-+ +---+ | | | | | \ / | / OC-12| |
/ | R |=|P| | S |=========|Site C|
+------+ Physical/ +-+ +---+ | | |E| | / \ | \ | |
|Site B| T1 \ |P| | R |===| | | |=|/ \| \ | |
| |=============|E|=| | +---+ +-+ +-----+ / +------+
| | \ | | +---+ __ /
+------+ \ +-+ __/ \ /
\ ___ ___ / \_/
\_/ \____/ \___/
SONET/TDM/Packet Network
____ ___ ____
/ \___/ \ / \__
+------+ Physical /+-+ \__/ \_
|Site A| T1 / | | +---+ \ Hub Site
| |=============|P|=| R | +---+ +-+ +-----+ \ +------+
| | \ |E| | |===| | | |=|\ /| \ | |
+------+ /\+-+ +---+ | | | | | \ / | / OC-12| |
/ | R |=|P| | S |=========|Site C|
+------+ Physical/ +-+ +---+ | | |E| | / \ | \ | |
|Site B| T1 \ |P| | R |===| | | |=|/ \| \ | |
| |=============|E|=| | +---+ +-+ +-----+ / +------+
| | \ | | +---+ __ /
+------+ \ +-+ __/ \ /
\ ___ ___ / \_/
\_/ \____/ \___/
Figure 14: T1 to OC-12 Grooming Emulation Example Diagram
图14:T1至OC-12梳理仿真示例图
[G.707] "Network Node Interface For The Synchronous Digital Hierarchy", ITU-T Recommendation G.707, December 2003.
[G.707]“同步数字体系的网络节点接口”，ITU-T建议G.707，2003年12月。
[G.783] "Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks", ITU-T Recommendation G.783, February 2004.
[G.783]“同步数字体系（SDH）设备功能块的特性”，ITU-T建议G.783，2004年2月。
[G.784] "Synchronous Digital Hierarchy (SDH) management", ITU-T Recommendation G.784, July 1999.
[G.784]“同步数字体系（SDH）管理”，ITU-T建议G.784，1999年7月。
[G.806] "Characteristics of transport equipment-Description methodology and generic functionality", ITU-T Recommendation G.806, February 2004.
[G.806]“运输设备描述方法和通用功能的特征”，ITU-T建议G.806，2004年2月。
[G.825] "The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH)", ITU-T Recommendation G.825, March 2000.
[G.825]“基于同步数字体系（SDH）的数字网络中的抖动和漂移控制”，ITU-T建议G.825，2000年3月。
[GR253] "Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria", Telcordia GR-253- CORE Issue 3, September 2000.
[GR253]“同步光网络（SONET）传输系统：通用通用标准”，Telcordia GR-253-核心问题3，2000年9月。
[MPLS] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, January 2001.
[MPLS]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。
[PWE3-CONTROL] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[PWE3-CONTROL]Martini，L.，Rosen，E.，El-Aawar，N.，Smith，T.，和G.Heron，“使用标签分发协议（LDP）的伪线设置和维护”，RFC 4447，2006年4月。
[PWE3-IANA] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[PWE3-IANA]Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，2006年4月。
[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。
[RTP] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3005, July 2003.
[RTP]Schulzrinne，H.，Casner，S.，Frederick，R.，和V.Jacobson，“RTP：实时应用的传输协议”，STD 64，RFC 3005，2003年7月。
[SONET] "Synchronous Optical Network (SONET) - Basic Description including Multiplex Structure, Rates and Formats", ANSI T1.105-2001, October 2001.
[SONET]“同步光网络（SONET）-基本说明，包括多路复用结构、速率和格式”，ANSI T1.105-2001，2001年10月。
[CONG] Floyd, S., "Congestion Control Principles", RFC 2914, September 2000.
[CONG]Floyd，S.，“拥塞控制原则”，RFC 29142000年9月。
[DIFFSERV] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and W. Weiss, "An Architecture for Differentiated Services", RFC 2475, December 1998.
[DIFFSERV]Blake，S.，Black，D.，Carlson，M.，Davies，E.，Wang，Z.，和W.Weiss，“区分服务的架构”，RFC 24751998年12月。
[EF] Davie, B., Charny, A., Bennett, J., Benson, K., Le Boudec, J., Courtney, W., Davari, S., Firoiu, V., and D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop Behavior)", RFC 3246, March 2002.
[EF]Davie，B.，Charny，A.，Bennett，J.，Benson，K.，Le Boudec，J.，Courtney，W.，Davari，S.，Firoiu，V.，和D.Stiliadis，“快速转发PHB（每跳行为）”，RFC 32462002年3月。
[GS] Shenker, S., Partridge, C., and R. Guerin, "Specification of Guaranteed Quality of Service", RFC 2212, September 1997.
[GS]Shenker，S.，Partridge，C.和R.Guerin，“保证服务质量规范”，RFC 2212，1997年9月。
[INTSERV] Braden, R., Clark, D., and S. Shenker, "Integrated Services in the Internet Architecture: an Overview", RFC 1633, June 1994.
[INTSERV]Braden，R.，Clark，D.，和S.Shenker，“互联网体系结构中的综合服务：概述”，RFC 16331994年6月。
[PWE3-ARCH] Bryant, S. and P. Pate, "PWE3 Architecture", RFC 3985, March 2005.
[PWE3-ARCH]Bryant，S.和P.Pate，“PWE3架构”，RFC 39852005年3月。
[PWE3-MPLSCW] Bryant, S., Swallow, G., and D. McPherson, "Control Word for Use over an MPLS PSN", RFC 4385, February 2006.
[PWE3-MPLSCW]Bryant，S.，Swallow，G.和D.McPherson，“MPLS PSN上使用的控制字”，RFC 43852006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-TDM-REQ] Riegel, M., "Requirements for Edge-to-Edge Emulation of TDM Circuits over Packet Switching Networks (PSN)", RFC 4197, October 2005.
[PWE3-TDM-REQ]Riegel，M.，“分组交换网络（PSN）上TDM电路的边到边仿真要求”，RFC 41972005年10月。
[RFC3711] Baugher, M., McGrew, D., Naslund, N., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[RFC3711]Baugher，M.，McGrew，D.，Naslund，N.，Carrara，E.，和K.Norrman，“安全实时传输协议（SRTP）”，RFC 37112004年3月。
Authors' Addresses
作者地址
Andrew G. Malis Verizon Communications 40 Sylvan Road Waltham, MA 02451 USA
Andrew G.Malis Verizon Communications美国马萨诸塞州沃尔瑟姆西尔文路40号，邮编02451
EMail: andrew.g.malis@verizon.com
EMail: andrew.g.malis@verizon.com
Prayson Pate Overture Networks 507 Airport Blvd, Suite 111 Morrisville, NC 27560 USA
Prayson Pate Overture Networks美国北卡罗来纳州莫里斯维尔机场大道507号111室27560
EMail: prayson.pate@overturenetworks.com
EMail: prayson.pate@overturenetworks.com
Ron Cohen (editor) Resolute Networks 15 Central Avenue Modiin, 71700 Israel
罗恩·科恩（编辑）以色列莫丁中央大道15号Resolute Networks 71700
EMail: ronc@resolutenetworks.com
EMail: ronc@resolutenetworks.com
David Zelig Corrigent Systems 126 Yigal Alon st. Tel Aviv, Israel
David Zelig Corrigent Systems以色列特拉维夫Yigal Alon st.126
EMail: davidz@corrigent.com
EMail: davidz@corrigent.com
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