Network Working Group A. Vainshtein, Ed.
Request for Comments: 5086 I. Sasson
Category: Informational Axerra Networks
E. Metz
KPN
T. Frost
Zarlink Semiconductor
P. Pate
Overture Networks
December 2007
Network Working Group A. Vainshtein, Ed.
Request for Comments: 5086 I. Sasson
Category: Informational Axerra Networks
E. Metz
KPN
T. Frost
Zarlink Semiconductor
P. Pate
Overture Networks
December 2007
Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation Service over Packet Switched Network (CESoPSN)
分组交换网络（CESoPSN）上的结构感知时分复用（TDM）电路仿真服务
Status of This Memo
关于下段备忘
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Abstract
摘要
This document describes a method for encapsulating structured (NxDS0) Time Division Multiplexed (TDM) signals as pseudowires over packet-switching networks (PSNs). In this regard, it complements similar work for structure-agnostic emulation of TDM bit-streams (see RFC 4553).
本文描述了一种通过分组交换网络（PSN）将结构化（NxDS0）时分复用（TDM）信号封装为伪线的方法。在这方面，它补充了TDM比特流的结构无关仿真的类似工作（参见RFC 4553）。
Table of Contents
目录
1. Introduction ....................................................3
2. Terminology and Reference Models ................................3
2.1. Terminology ................................................3
2.2. Reference Models ...........................................4
2.3. Requirements and Design Constraint .........................4
3. Emulated Services ...............................................5
4. CESoPSN Encapsulation Layer .....................................6
4.1. CESoPSN Packet Format ......................................6
4.2. PSN and Multiplexing Layer Headers .........................8
4.3. CESoPSN Control Word .......................................9
4.4. Usage of the RTP Header ...................................11
5. CESoPSN Payload Layer ..........................................12
5.1. Common Payload Format Considerations ......................12
5.2. Basic NxDS0 Services ......................................13
5.3. Extending Basic NxDS0 Services with CE Application
Signaling .................................................15
5.4. Trunk-Specific NxDS0 Services with CAS ....................18
6. CESoPSN Operation ..............................................20
6.1. Common Considerations .....................................20
6.2. IWF Operation .............................................20
6.2.1. PSN-Bound Direction ................................20
6.2.2. CE-Bound Direction .................................20
6.3. CESoPSN Defects ...........................................23
6.4. CESoPSN PW Performance Monitoring .........................24
7. QoS Issues .....................................................25
8. Congestion Control .............................................25
9. Security Considerations ........................................27
10. IANA Considerations ...........................................27
11. Applicability Statement .......................................27
12. Acknowledgements ..............................................29
13. Normative References ..........................................30
14. Informative References ........................................31
Appendix A. A Common CE Application State Signaling Mechanism .....33
Appendix B. Reference PE Architecture for Emulation of NxDS0
Services ......................................................34
Appendix C. Old Mode of CESoPSN Encapsulation Over L2TPV3 .........36
1. Introduction ....................................................3
2. Terminology and Reference Models ................................3
2.1. Terminology ................................................3
2.2. Reference Models ...........................................4
2.3. Requirements and Design Constraint .........................4
3. Emulated Services ...............................................5
4. CESoPSN Encapsulation Layer .....................................6
4.1. CESoPSN Packet Format ......................................6
4.2. PSN and Multiplexing Layer Headers .........................8
4.3. CESoPSN Control Word .......................................9
4.4. Usage of the RTP Header ...................................11
5. CESoPSN Payload Layer ..........................................12
5.1. Common Payload Format Considerations ......................12
5.2. Basic NxDS0 Services ......................................13
5.3. Extending Basic NxDS0 Services with CE Application
Signaling .................................................15
5.4. Trunk-Specific NxDS0 Services with CAS ....................18
6. CESoPSN Operation ..............................................20
6.1. Common Considerations .....................................20
6.2. IWF Operation .............................................20
6.2.1. PSN-Bound Direction ................................20
6.2.2. CE-Bound Direction .................................20
6.3. CESoPSN Defects ...........................................23
6.4. CESoPSN PW Performance Monitoring .........................24
7. QoS Issues .....................................................25
8. Congestion Control .............................................25
9. Security Considerations ........................................27
10. IANA Considerations ...........................................27
11. Applicability Statement .......................................27
12. Acknowledgements ..............................................29
13. Normative References ..........................................30
14. Informative References ........................................31
Appendix A. A Common CE Application State Signaling Mechanism .....33
Appendix B. Reference PE Architecture for Emulation of NxDS0
Services ......................................................34
Appendix C. Old Mode of CESoPSN Encapsulation Over L2TPV3 .........36
This document describes a method for encapsulating structured (NxDS0) Time Division Multiplexed (TDM) signals as pseudowires over packet-switching networks (PSN). In this regard, it complements similar work for structure-agnostic emulation of TDM bit-streams [RFC4553].
本文描述了一种通过分组交换网络（PSN）将结构化（NxDS0）时分复用（TDM）信号封装为伪线的方法。在这方面，它补充了TDM比特流的结构无关仿真的类似工作[RFC4553]。
Emulation of NxDS0 circuits provides for saving PSN bandwidth, and supports DS0-level grooming and distributed cross-connect applications. It also enhances resilience of CE devices to effects of loss of packets in the PSN.
NxDS0电路仿真可节省PSN带宽，并支持DS0级梳理和分布式交叉连接应用。它还增强了CE设备对PSN中数据包丢失影响的恢复能力。
The CESoPSN solution presented in this document fits the Pseudowire Emulation Edge-to-Edge (PWE3) architecture described in [RFC3985], satisfies the general requirements put forth in [RFC3916], and specific requirements for structured TDM emulation put forth in [RFC4197].
本文档中介绍的CESoPSN解决方案适合[RFC3985]中描述的伪线仿真边到边（PWE3）体系结构，满足[RFC3916]中提出的一般要求，以及[RFC4197]中提出的结构化TDM仿真的具体要求。
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。
The terms defined in [RFC3985], Section 1.4, and in [RFC4197], Section 3, are consistently used without additional explanations.
[RFC3985]第1.4节和[RFC4197]第3节中定义的术语一致使用，无需额外解释。
This document uses some terms and acronyms that are commonly used in conjunction with TDM services. In particular:
本文档使用了TDM服务中常用的一些术语和首字母缩略词。特别地：
o Loss of Signal (LOS) is a common term denoting a condition where a valid TDM signal cannot be extracted from the physical layer of the trunk. Actual criteria for detecting and clearing LOS are described in [G.775].
o 信号丢失（LOS）是一个常用术语，表示无法从中继的物理层提取有效TDM信号的情况。[G.775]中描述了检测和清除服务水平的实际标准。
o Frame Alignment Signal (FAS) is a common term denoting a special periodic pattern that is used to impose TDM structures on E1 and T1 circuits. These patterns are described in [G.704].
o 帧对齐信号（FAS）是一个通用术语，表示用于在E1和T1电路上施加TDM结构的特殊周期模式。[G.704]中描述了这些模式。
o Out of Frame Synchronization (OOF) is a common term denoting the state of the receiver of a TDM signal when it failed to find valid FAS. Actual criteria for declaring and clearing OOF are described in [G.706]. Handling of this condition includes invalidation of the TDM data.
o 帧外同步（OOF）是一个常用术语，表示TDM信号接收机在找不到有效的FAS时的状态。[G.706]中描述了宣布和清除OOF的实际标准。这种情况的处理包括TDM数据的失效。
o Alarm Indication Signal (AIS) is a common term denoting a special bit pattern in the TDM bit stream that indicates presence of an upstream circuit outage. Actual criteria for declaring and clearing the AIS condition in a TDM stream are defined in [G.775].
o 报警指示信号（AIS）是一个通用术语，表示TDM比特流中的特殊比特模式，表示存在上游电路中断。[G.775]中定义了在TDM流中声明和清除AIS条件的实际标准。
o Remote Alarm Indication (RAI) and Remote Defect Indication (RDI) are common terms (often used as synonyms) denoting a special pattern in the framing of a TDM service that is sent back by the receiver that experiences an AIS condition. This condition cannot be detected while an LOS, OOF, or AIS condition is detected. Specific rules for encoding this pattern in the TDM framing are discussed in [G.775].
o 远程报警指示（RAI）和远程缺陷指示（RDI）是通用术语（通常用作同义词），表示TDM服务帧中的特殊模式，该模式由经历AIS条件的接收器发回。当检测到LOS、OOF或AIS条件时，无法检测到该条件。[G.775]中讨论了在TDM帧中编码该模式的具体规则。
We also use the term Interworking Function (IWF) to describe the functional block that segments and encapsulates TDM into CESoPSN packets and, in the reverse direction, decapsulates CESoPSN packets and reconstitutes TDM.
我们还使用术语互通功能（IWF）来描述功能块，该功能块将TDM分段并封装到CESoPSN数据包中，并且在相反方向上，将CESoPSN数据包解封并重新构建TDM。
Generic models that have been defined in Sections 4.1, 4.2, and 4.4 of [RFC3985] are fully applicable for the purposes of this document without any modifications.
[RFC3985]第4.1、4.2和4.4节中定义的通用模型完全适用于本文件，无需任何修改。
The Network Synchronization reference model and deployment scenarios for emulation of TDM services have been described in [RFC4197], Section 4.3.
[RFC4197]第4.3节描述了TDM服务仿真的网络同步参考模型和部署场景。
Structured services considered in this document represent special cases of the "Structured bit stream" payload type defined in Section 3.3.4 of [RFC3985]. In each specific case, the basic service structures that are preserved by a CESoPSN PW are explicitly specified (see Section 3 below).
本文件中考虑的结构化服务代表[RFC3985]第3.3.4节中定义的“结构化比特流”有效负载类型的特殊情况。在每种特定情况下，明确规定了CESoPSN PW保留的基本服务结构（见下文第3节）。
In accordance with the principle of minimum intervention ([RFC3985], Section 3.3.5), the TDM payload is encapsulated without any changes.
根据最小干预原则（[RFC3985]，第3.3.5节），TDM有效载荷在没有任何变化的情况下进行封装。
The CESoPSN protocol has been designed in order to meet the following design constraints:
CESoPSN协议的设计旨在满足以下设计约束：
1. Fixed amount of TDM data per packet: All the packets belonging to a given CESoPSN PW MUST carry the same amount of TDM data. This approach simplifies compensation of a lost PW packet with a packet carrying exactly the same amount of "replacement" TDM data
1. 每个数据包的固定TDM数据量：属于给定CESoPSN PW的所有数据包必须携带相同数量的TDM数据。这种方法简化了丢失的PW数据包的补偿，而数据包携带的“替换”TDM数据量完全相同
2. Fixed end-to-end delay: CESoPSN implementations SHOULD provide the same end-to-end delay between a given pair of CEs regardless of the bit rate of the emulated service.
2. 固定端到端延迟：CESoPSN实现应在给定的一对CE之间提供相同的端到端延迟，而不管模拟服务的比特率如何。
3. Packetization latency range: a) All the implementations of CESoPSN SHOULD support packetization latencies in the range 1 to 5 milliseconds. b) CESoPSN implementations that support configurable packetization latency MUST allow configuration of this parameter with the granularity, which is a multiple of 125 microseconds.
3. 打包延迟范围：a）CESoPSN的所有实现都应支持1到5毫秒范围内的打包延迟。b） 支持可配置打包延迟的CESoPSN实现必须允许使用粒度（125微秒的倍数）配置此参数。
4. Common data path for services with and without CE application signaling (e.g., Channel-Associated Signaling (CAS)-- see [RFC4197]): If, in addition to TDM data, CE signaling must be transferred between a pair of CE devices for the normal operation of the emulated service, this signaling is passed in dedicated signaling packets specific for the signaling protocol while format and processing of the packets carrying TDM data remain unchanged.
4. 具有和不具有CE应用信令的服务的公共数据路径（例如，信道相关信令（CAS）--参见[RFC4197]）：如果除了TDM数据外，CE信令必须在一对CE设备之间传输，以便模拟服务的正常运行，该信令在特定于信令协议的专用信令分组中传递，而承载TDM数据的分组的格式和处理保持不变。
In accordance with [RFC4197], structured services considered in this specification are NxDS0 services, with and without CAS.
根据[RFC4197]，本规范中考虑的结构化服务是NxDS0服务，包括和不包括CA。
NxDS0 services are usually carried within appropriate physical trunks, and Provider Edges (PEs) providing their emulation include appropriate Native Service Processing (NSP) blocks, commonly referred to as Framers.
NxDS0服务通常在适当的物理中继内进行，提供其仿真的提供者边缘（PE）包括适当的本机服务处理（NSP）块，通常称为帧器。
The NSPs may also act as digital cross-connects, creating structured TDM services from multiple synchronous trunks. As a consequence, the service may contain more timeslots that could be carried over any single trunk, or the timeslots may not originate from any single trunk.
NSPs还可以充当数字交叉连接，从多个同步中继创建结构化TDM服务。因此，服务可能包含更多可通过任何单个中继传输的时隙，或者这些时隙可能不来自任何单个中继。
The reference PE architecture supporting these services is described in Appendix B.
支持这些服务的参考PE架构如附录B所述。
This document defines a single format for packets carrying TDM data regardless of the need to carry CAS or any other CE application signaling. The resulting "basic NxDS0 service" can be extended to carry CE application signaling (e.g., CAS) using separate signaling packets. Signaling packets MAY be carried in the same PW as the packets carrying TDM data or in a separate dedicated PW.
本文件为携带TDM数据的数据包定义了一种单一格式，而无需携带CAS或任何其他CE应用信令。由此产生的“基本NxDS0服务”可以扩展为使用单独的信令分组来承载CE应用信令（例如，ca）。信令分组可以在与承载TDM数据的分组相同的PW中承载，或者在单独的专用PW中承载。
In addition, this document also defines dedicated formats for carrying NxDS0 services with CAS in signaling sub-structures in some of the packets. These formats effectively differ for NxDS0 services that originated in different trunks so that their usage results in emulating trunk-specific NxDS0 services with CAS.
此外，本文档还定义了在某些数据包的信令子结构中使用CAS承载NxDS0服务的专用格式。对于源自不同中继的NxDS0服务，这些格式实际上是不同的，因此它们的使用会导致使用CAS模拟特定于中继的NxDS0服务。
The CESoPSN header MUST contain the CESoPSN Control Word (4 bytes) and MAY also contain a fixed RTP header [RFC3550]. If the RTP header is included in the CESoPSN header, it MUST immediately follow the CESoPSN control word in all cases except UDP demultiplexing, where it MUST precede it (see Figures 1a, 1b, and 1c below).
CESoPSN报头必须包含CESoPSN控制字（4字节），还可能包含固定RTP报头[RFC3550]。如果RTP报头包含在CESoPSN报头中，则在除UDP解复用外的所有情况下，RTP报头都必须紧跟在CESoPSN控制字之后，因为UDP解复用必须在RTP报头之前（参见下面的图1a、1b和1c）。
Note: The difference in the CESoPSN packet formats for IP PSN using UDP-based demultiplexing and the rest of the PSN and demultiplexing combinations, is based on the following considerations:
注：使用基于UDP的解复用的IP PSN的CESoPSN数据包格式与其他PSN和解复用组合的差异基于以下考虑：
1. Compliance with the existing header compression mechanisms for IPv4/IPv6 PSNs with UDP demultiplexing requires placing the RTP header immediately after the UDP header.
1. 要符合IPv4/IPv6 PSN与UDP解复用的现有报头压缩机制，需要将RTP报头放在UDP报头之后。
2. Compliance with the common PWE3 mechanisms for keeping PWs Equal Cost Multipath (ECMP)-safe for the MPLS PSN by providing for PW-IP packet discrimination (see [RFC3985], Section 5.4.3). This requires placing the PWE3 control word immediately after the PW label.
2. 遵守公共PWE3机制，通过提供PW-IP数据包鉴别，确保MPLS PSN的PWs等成本多路径（ECMP）安全（见[RFC3985]，第5.4.3节）。这需要将PWE3控制字立即放在PW标签之后。
3. Commonality of the CESoPSN packet formats for MPLS networks and IPv4/IPv6 networks with Layer 2 Tunneling Protocol Version 3 (L2TPv3) demultiplexing facilitates smooth stitching of L2TPv3- based and MPLS-based segments of CESoPSN PWs (see [PWE3-MS]).
3. MPLS网络和IPv4/IPv6网络的CESoPSN数据包格式与第2层隧道协议版本3（L2TPv3）解复用的通用性有助于平滑拼接基于L2TPv3和基于MPLS的CESoPSN PWs段（参见[PWE3-MS]）。
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| IPv4/IPv6 and UDP (demultiplexing layer) headers |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL |
+-- --+
| |
+-- --+
| Fixed RTP Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Packetized TDM data (Payload) |
| ... |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| IPv4/IPv6 and UDP (demultiplexing layer) headers |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL |
+-- --+
| |
+-- --+
| Fixed RTP Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Packetized TDM data (Payload) |
| ... |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1a. CESoPSN Packet Format for an IPv4/IPv6 PSN with UDP demultiplexing
图1a。带UDP解复用的IPv4/IPv6 PSN的CESoPSN数据包格式
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| MPLS Label Stack |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL |
+-- --+
| |
+-- --+
| Fixed RTP Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Packetized TDM data (Payload) |
| ... |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| MPLS Label Stack |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL |
+-- --+
| |
+-- --+
| Fixed RTP Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Packetized TDM data (Payload) |
| ... |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1b. CESoPSN Packet Format for an MPLS PSN
图1b。MPLS PSN的CESoPSN数据包格式
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| IPv4/IPv6 and L2TPv3 (demultiplexing layer) headers |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL |
+-- --+
| |
+-- --+
| Fixed RTP Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Packetized TDM data (Payload) |
| ... |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| IPv4/IPv6 and L2TPv3 (demultiplexing layer) headers |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL |
+-- --+
| |
+-- --+
| Fixed RTP Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Packetized TDM data (Payload) |
| ... |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1c. CESoPSN Packet Format for an IPv4/IPv6 PSN with L2TPv3 Demultiplexing
图1c。具有L2TPv3解复用功能的IPv4/IPv6 PSN的CESoPSN数据包格式
The total size of a CESoPSN packet for a specific PW MUST NOT exceed path MTU between the pair of PEs terminating this PW.
特定PW的CESoPSN数据包的总大小不得超过终止该PW的PEs对之间的路径MTU。
CESoPSN implementations working with IPv4 PSN MUST set the "Don't Fragment" flag in IP headers of the packets they generate.
使用IPv4 PSN的CESoPSN实现必须在生成的数据包的IP头中设置“不分段”标志。
Usage of MPLS and L2TPv3 as demultiplexing layers is explained in [RFC3985] and [RFC3931], respectively.
[RFC3985]和[RFC3931]分别解释了MPLS和L2TPv3作为解复用层的用法。
Setup and maintenance of CESoPSN PWs over MPLS PSN is described in [PWE3-TDM-CONTROL].
[PWE3-TDM-CONTROL]中描述了通过MPLS PSN的CESoPSN PWs的设置和维护。
Setup and maintenance of CESoPSN PWs over IPv4/IPv6 using L2TPv3 demultiplexing is defined in [L2TPEXT-TDM].
[L2TPEXT-TDM]中定义了使用L2TPv3解复用在IPv4/IPv6上设置和维护CESoPSN PWs。
The destination UDP port MUST be used to multiplex and demultiplex individual PWs between nodes. Architecturally (see [RFC3985]) this makes the destination UDP port act as the PW Label.
目标UDP端口必须用于在节点之间多路复用和解多路复用单个PW。架构上（请参见[RFC3985]）这使得目标UDP端口充当PW标签。
UDP ports MUST be manually configured by both endpoints of the PW. The configured destination port together with both the source and destination IP addresses uniquely identifies the PW for the receiver. All UDP port values that function as PW labels SHOULD be in the range of dynamically allocated UDP port numbers (49152 through 65535).
UDP端口必须由PW的两个端点手动配置。配置的目标端口与源和目标IP地址一起唯一地标识接收器的PW。用作PW标签的所有UDP端口值应在动态分配的UDP端口号范围内（49152到65535）。
While many UDP-based protocols are able to traverse middleboxes without dire consequences, the use of UDP ports as PW labels makes middlebox traversal more difficult. Hence, it is NOT RECOMMENDED to use UDP-based PWs where port-translating middleboxes are present between PW endpoints.
虽然许多基于UDP的协议能够在不造成可怕后果的情况下遍历中间箱，但将UDP端口用作PW标签会使中间箱遍历更加困难。因此，如果PW端点之间存在端口转换中间盒，则不建议使用基于UDP的PW。
The structure of the CESoPSN Control Word that MUST be used with all combinations of the PSN and demultiplexing mechanisms described in the previous section is shown in Figure 2 below.
必须与前一节中描述的PSN和解复用机制的所有组合一起使用的CESoPSN控制字的结构如下图2所示。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|L|R| M |FRG| LEN | Sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|L|R| M |FRG| LEN | Sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. Structure of the CESoPSN Control Word
图2。CESoPSN控制字的结构
The use of Bits 0 to 3 is described in [RFC4385]. These bits MUST be set to zero unless they are being used to indicate the start of an Associated Channel Header (ACH). An ACH is needed if the state of the CESoPSN PW is being monitored using Virtual Circuit Connectivity Verification [RFC5085].
[RFC4385]中描述了位0到3的使用。这些位必须设置为零，除非它们用于指示相关信道头（ACH）的开始。如果使用虚拟电路连接验证[RFC5085]监控CESoPSN PW的状态，则需要ACH。
L - if set, indicates some abnormal condition of the attachment circuit.
L-如果设置，则表示附件电路出现异常状况。
M - a 2-bit modifier field. In case of L cleared, this field allows discrimination of signaling packets and carrying RDI of the attachment circuit across the PSN. In case of L set, only the '00' value is currently defined; other values are reserved for future extensions. L and M bits can be treated as a 3-bit code point space that is described in detail in Table 1 below.
M-一个2位修饰符字段。在清除L的情况下，该字段允许区分信令分组和通过PSN承载连接电路的RDI。对于L集合，当前仅定义“00”值；其他值保留给将来的扩展。L和M位可被视为3位代码点空间，详见下表1。
R - if set by the PSN-bound IWF, indicates that its local CE-bound IWF is in the packet loss state, i.e., has lost a pre-configured number of consecutive packets. The R bit MUST be cleared by the PSN-bound IWF once its local CE-bound IWF has exited the packet loss state, i.e., has received a pre-configured number of consecutive packets.
R-如果由PSN绑定的IWF设置，则表示其本地CE绑定的IWF处于丢包状态，即丢失了预先配置数量的连续数据包。一旦绑定到PSN的IWF的本地CE的IWF退出丢包状态，即接收到预配置数量的连续数据包，则必须由绑定到PSN的IWF清除R位。
|=================================================================|
| L | M | Code Point Interpretation |
|===|=====|=======================================================|
| 0 | 00 | CESoPSN data packet - normal situation. All CESoPSN |
| | | implementations MUST recognize this code point. |
| | | Payload MUST be played out "as received". |
|---|-----|-------------------------------------------------------|
| 0 | 01 | Reserved for future extensions. |
|---|-----|-------------------------------------------------------|
| 0 | 10 | CESoPSN data packet, RDI condition of the AC. All |
| | | CESoPSN implementations MUST support this codepoint: |
| | | payload MUST be played out "as received", and, if |
| | | so configured, the receiving CESoPSN IWF instance |
| | | SHOULD be able to command the NSP to force the RDI |
| | | condition on the outgoing TDM trunk. |
|---|-----|-------------------------------------------------------|
| 0 | 11 | Reserved for CESoPSN signaling packets. |
|---|-----|-------------------------------------------------------|
| 1 | 00 | TDM data is invalid; payload MAY be omitted. All |
| | | implementations MUST recognize this code point and |
| | | insert appropriate amount of the configured "idle |
| | | code" in the outgoing attachment circuit. In addition,|
| | | if so configured, the receiving CESoPSN IWF instance |
| | | SHOULD be able to force the AIS condition on the |
| | | outgoing TDM trunk. |
|---|-----|-------------------------------------------------------|
| 1 | 01 | Reserved for future extensions |
|---|-----|-------------------------------------------------------|
| 1 | 10 | Reserved for future extensions |
|---|-----|-------------------------------------------------------|
| 1 | 11 | Reserved for future extensions |
|=================================================================|
|=================================================================|
| L | M | Code Point Interpretation |
|===|=====|=======================================================|
| 0 | 00 | CESoPSN data packet - normal situation. All CESoPSN |
| | | implementations MUST recognize this code point. |
| | | Payload MUST be played out "as received". |
|---|-----|-------------------------------------------------------|
| 0 | 01 | Reserved for future extensions. |
|---|-----|-------------------------------------------------------|
| 0 | 10 | CESoPSN data packet, RDI condition of the AC. All |
| | | CESoPSN implementations MUST support this codepoint: |
| | | payload MUST be played out "as received", and, if |
| | | so configured, the receiving CESoPSN IWF instance |
| | | SHOULD be able to command the NSP to force the RDI |
| | | condition on the outgoing TDM trunk. |
|---|-----|-------------------------------------------------------|
| 0 | 11 | Reserved for CESoPSN signaling packets. |
|---|-----|-------------------------------------------------------|
| 1 | 00 | TDM data is invalid; payload MAY be omitted. All |
| | | implementations MUST recognize this code point and |
| | | insert appropriate amount of the configured "idle |
| | | code" in the outgoing attachment circuit. In addition,|
| | | if so configured, the receiving CESoPSN IWF instance |
| | | SHOULD be able to force the AIS condition on the |
| | | outgoing TDM trunk. |
|---|-----|-------------------------------------------------------|
| 1 | 01 | Reserved for future extensions |
|---|-----|-------------------------------------------------------|
| 1 | 10 | Reserved for future extensions |
|---|-----|-------------------------------------------------------|
| 1 | 11 | Reserved for future extensions |
|=================================================================|
Table 1. Interpretation of bits L and M in the CESoPSN CW
表1。CESoPSN连续波中L位和M位的解释
Notes:
笔记：
1. Bits in the M field are shown in the same order as in Figure 2 (i.e., bit 6 of the CW followed by bit 7 of the CW).
1. M字段中的位按与图2中相同的顺序显示（即，CW的位6后跟CW的位7）。
2. Implementations that do not support the reserved code points MUST silently discard the corresponding packets upon reception.
2. 不支持保留代码点的实现必须在接收时自动丢弃相应的数据包。
The FRG bits in the CESoPSN control word MUST be cleared for all services, excluding trunk-specific NxDS0 with CAS. In case of these services, they MAY be used to denote fragmentation of the multiframe structures between CESoPSN packets as described in [RFC4623]; see Section 5.4 below.
必须为所有服务清除CESoPSN控制字中的FRG位，不包括带CAS的中继特定NxDS0。在这些服务的情况下，它们可用于表示如[RFC4623]中所述的CESoPSN分组之间的多帧结构的分段；见下文第5.4节。
LEN (bits (10 to 15) MAY be used to carry the length of the CESoPSN packet (defined as the size of the CESoPSN header + the payload size) if it is less than 64 bytes, and MUST be set to zero otherwise. Note: If fixed RTP header is used in the encapsulation, it is considered part of the CESoPSN header.
LEN（位（10到15）可用于承载CESoPSN数据包的长度（定义为CESoPSN头的大小+有效负载大小），如果小于64字节，则必须设置为零。注意：如果封装中使用固定RTP头，则它被视为CESoPSN头的一部分。
The sequence number is used to provide the common PW sequencing function, as well as detection of lost packets. It MUST be generated in accordance with the rules defined in Section 5.1 of [RFC3550] for the RTP sequence number, i.e.:
序列号用于提供公共PW排序功能，以及检测丢失的数据包。必须根据[RFC3550]第5.1节规定的RTP序列号规则生成，即：
o Its space is a 16-bit unsigned circular space
o 它的空间是一个16位无符号循环空间
o Its initial value SHOULD be random (unpredictable)
o 其初始值应为随机（不可预测）
o It MUST be incremented with each CESoPSN data packet sent in the specific PW.
o 它必须与在特定PW中发送的每个CESoPSN数据包一起递增。
Although CESoPSN MAY employ an RTP header when explicit transfer of timing information is required, this is purely 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 RTP (SRTP), etc., are not applicable to CESoPSN pseudowires.
尽管当需要显式传输定时信息时，CESoPSN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RTP（SRTP）等，不适用于CESoPSN伪线。
When a fixed RTP header (see [RFC3550], Section 5.1) is used with CESoPSN, its fields are used in the following way:
当固定RTP报头（见[RFC3550]，第5.1节）与CESoPSN一起使用时，其字段的使用方式如下：
1. V (version) is always set to 2.
1. V（版本）始终设置为2。
2. P (padding), X (header extension), CC (CSRC count), and M (marker) are always set to 0.
2. P（填充）、X（标题扩展）、CC（CSC计数）和M（标记）始终设置为0。
3. PT (payload type) is used as following:
3. PT（有效负载类型）的使用如下：
a) One PT value MUST be allocated from the range of dynamic values (see [RTP-TYPES]) for each direction of the PW. The same PT value MAY be reused for both directions of the PW and also reused between different PWs.
a) 必须从PW每个方向的动态值范围（见[RTP-TYPES]）中分配一个PT值。相同的PT值可在PW的两个方向重复使用，也可在不同PW之间重复使用。
b) The PE at the PW ingress MUST set the PT field in the RTP header to the allocated value.
b) PW入口的PE必须将RTP报头中的PT字段设置为分配值。
c) The PE at the PW egress MAY use the received value to detect malformed packets.
c) PW出口处的PE可以使用接收到的值来检测格式错误的分组。
4. Sequence number in the RTP header MUST be equal to the sequence number in the CESoPSN CW.
4. RTP报头中的序列号必须等于CESoPSN CW中的序列号。
5. Timestamps are used for carrying timing information over the network:
5. 时间戳用于通过网络传输定时信息：
a) Their values are generated in accordance with the rules established in [RFC3550].
a) 根据[RFC3550]中建立的规则生成其值。
b) Frequency of the clock used for generating timestamps MUST be an integer multiple of 8 kHz. All implementations of CESoPSN MUST support the 8 kHz clock. Other frequencies that are integer multiples of 8 kHz MAY be used if both sides agree to that.
b) 用于生成时间戳的时钟频率必须是8 kHz的整数倍。CESoPSN的所有实现必须支持8 kHz时钟。如果双方同意，可使用8 kHz整数倍的其他频率。
c) Possible modes of timestamp generation are discussed below.
c) 时间戳生成的可能模式如下所述。
6. The SSRC (synchronization source) value in the RTP header MAY be used for detection of misconnections.
6. RTP报头中的SSRC（同步源）值可用于检测错误连接。
The RTP header in CESoPSN can be used in conjunction with at least the following modes of timestamp generation:
CESoPSN中的RTP报头可至少与以下时间戳生成模式结合使用：
1. Absolute mode: the ingress PE sets timestamps using the clock recovered from the incoming TDM circuit. As a consequence, the timestamps are closely correlated with the sequence numbers. All CESoPSN implementations MUST support this mode.
1. 绝对模式：入口PE使用从输入TDM电路恢复的时钟设置时间戳。因此，时间戳与序列号密切相关。所有CESoPSN实现都必须支持此模式。
2. Differential mode: PE devices connected by the PW have access to the same high-quality synchronization source, and this synchronization source is used for timestamp generation. As a consequence, the second derivative of the timestamp series represents the difference between the common timing source and the clock of the incoming TDM circuit. Support of this mode is OPTIONAL.
2. 差分模式：通过PW连接的PE设备可以访问相同的高质量同步源，该同步源用于生成时间戳。因此，时间戳序列的二阶导数表示公共定时源和输入TDM电路的时钟之间的差。此模式的支持是可选的。
All the services considered in this document are treated as sequences of "basic structures" (see Section 3 above). The payload of a CESoPSN packet always consists of a fixed number of octets filled, octet by octet, with the data contained in the corresponding consequent basic structures that preserve octet alignment between these structures and the packet payload boundaries, in accordance with the following rules:
本文件中考虑的所有服务均被视为“基本结构”序列（见上文第3节）。根据以下规则，CESoPSN数据包的有效载荷始终由固定数量的八位字节组成，一个八位字节一个八位字节填充，数据包含在相应的后续基本结构中，这些结构和数据包有效载荷边界之间保持八位字节对齐：
1. The order of the payload octets corresponds to their order on the TDM AC.
1. 有效载荷八位字节的顺序对应于它们在TDM AC上的顺序。
2. Consecutive bits coming from the TDM AC fill each payload octet, starting from its most significant bit to the least significant one.
2. 来自TDM AC的连续位填充每个有效负载八位字节，从其最高有效位到最低有效位。
3. All the CESoPSN packets MUST carry the same amount of valid TDM data in both directions of the PW. In other words, the time that is required to fill a CESoPSN packet with the TDM data must be constant. The PE devices terminating a CESoPSN PW MUST agree on the number of TDM payload octets in the PW packets for both directions of the PW at the time of the PW setup.
3. 所有CESoPSN数据包必须在PW的两个方向上携带相同数量的有效TDM数据。换句话说，用TDM数据填充CESoPSN分组所需的时间必须是恒定的。终止CESoPSN PW的PE设备必须在PW设置时就PW两个方向的PW数据包中的TDM有效负载八位字节数达成一致。
Notes:
笔记：
1. CESoPSN packets MAY omit invalid TDM data in order to save the PSN bandwidth. If the CESoPSN packet payload is omitted, the L bit in the CESoPSN control word MUST be set.
1. CESoPSN分组可以省略无效的TDM数据以节省PSN带宽。如果省略CESoPSN数据包有效负载，则必须设置CESoPSN控制字中的L位。
2. CESoPSN PWs MAY carry CE signaling information either in separate packets or appended to packets carrying valid TDM data. If signaling information and valid TDM data are carried in the same CESoPSN packet, the amount of the former does not affect the amount of the latter.
2. CESoPSN PW可以在单独的分组中或者附加到携带有效TDM数据的分组中携带CE信令信息。如果信令信息和有效TDM数据被携带在同一个CESoPSN分组中，则前者的量不影响后者的量。
As mentioned above, the basic structure preserved across the PSN for this service consists of N octets filled with the data of the corresponding NxDS0 channels belonging to the same frame of the originating trunk(s), and the service generates 8000 such structures per second.
如上所述，为该服务跨PSN保留的基本结构由N个八位字节组成，其中填充了属于发起中继的相同帧的相应NxDS0信道的数据，并且该服务每秒生成8000个这样的结构。
CESoPSN MUST use alignment of the basic structures with the packet payload boundaries in order to carry the structures across the PSN. This means that:
CESoPSN必须使用基本结构与分组有效负载边界的对齐，以便跨PSN承载结构。这意味着：
1. The amount of TDM data in a CESoPSN packet MUST be an integer multiple of the basic structure size
1. CESoPSN数据包中的TDM数据量必须是基本结构大小的整数倍
2. The first structure in the packet MUST start immediately at the beginning of the packet payload.
2. 数据包中的第一个结构必须立即从数据包有效负载的开始处开始。
The resulting payload format is shown in Figure 3 below.
产生的有效负载格式如下图3所示。
0 1 2 3 4 5 6 7
--- +-+-+-+-+-+-+-+-+
| Timeslot 1 |
+-+-+-+-+-+-+-+-+
| Timeslot 2 |
Frame #1 | ... |
| Timeslot N |
--- +-+-+-+-+-+-+-+-+
| Timeslot 1 |
+-+-+-+-+-+-+-+-+
| Timeslot 2 |
Frame #2 | ... |
| Timeslot N |
--- +-+-+-+-+-+-+-+-+
... | ... |
--- +-+-+-+-+-+-+-+-+
| Timeslot 1 |
+-+-+-+-+-+-+-+-+
| Timeslot 2 |
Frame #m | ... |
| Timeslot N |
--- +-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
--- +-+-+-+-+-+-+-+-+
| Timeslot 1 |
+-+-+-+-+-+-+-+-+
| Timeslot 2 |
Frame #1 | ... |
| Timeslot N |
--- +-+-+-+-+-+-+-+-+
| Timeslot 1 |
+-+-+-+-+-+-+-+-+
| Timeslot 2 |
Frame #2 | ... |
| Timeslot N |
--- +-+-+-+-+-+-+-+-+
... | ... |
--- +-+-+-+-+-+-+-+-+
| Timeslot 1 |
+-+-+-+-+-+-+-+-+
| Timeslot 2 |
Frame #m | ... |
| Timeslot N |
--- +-+-+-+-+-+-+-+-+
Figure 3. The CESoPSN Packet Payload Format for the Basic NxDS0 Service
图3。基本NxDS0服务的CESoPSN数据包有效负载格式
This mode of operation complies with the recommendation in [RFC3985] to use similar encapsulations for structured bit stream and cell generic payload types.
此操作模式符合[RFC3985]中的建议，即对结构化比特流和小区通用有效负载类型使用类似的封装。
Packetization latency, number of timeslots, and payload size are linked by the following obvious relationship:
打包延迟、时隙数和有效负载大小通过以下明显关系联系起来：
L = 8*N*D
L = 8*N*D
where:
哪里：
o D is packetization latency, milliseconds
o D是打包延迟，毫秒
o L is packet payload size, octets
o L是数据包有效负载大小，八位字节
o N is number of DS0 channels.
o N是DS0通道数。
CESoPSN implementations supporting NxDS0 services MUST support the following set of configurable packetization latency values:
支持NxDS0服务的CESoPSN实现必须支持以下一组可配置的打包延迟值：
o For N = 1: 8 milliseconds (with the corresponding packet payload size of 64 bytes)
o 对于N=1:8毫秒（相应的数据包有效负载大小为64字节）
o For 2 <=N <= 4: 4 millisecond (with the corresponding packet payload size of 32*N bytes)
o 对于2<=N<=4:4毫秒（相应的数据包有效负载大小为32*N字节）
o For N >= 5: 1 millisecond (with the corresponding packet payload size of 8*N octets).
o 对于N>=5:1毫秒（对应的数据包有效负载大小为8*N个八位字节）。
Support of 5 ms packetization latency for N = 1 is RECOMMENDED.
建议支持N=1的5ms打包延迟。
Usage of any other packetization latency (packet payload size) that is compatible with the restrictions described above is OPTIONAL.
使用与上述限制兼容的任何其他包化延迟（包有效负载大小）是可选的。
Implementations that have chosen to extend the basic NxDS0 service to support CE application state signaling carry-encoded CE application state signals in separate signaling packets.
选择扩展基本NxDS0服务以支持CE应用程序状态信令的实现在单独的信令分组中携带编码的CE应用程序状态信号。
The format of the CESoPSN signaling packets over both IPv4/IPv6 and MPLS PSNs for the case when the CE maintains a separate application state per DS0 channel (e.g., CAS for the telephony applications) is shown in Figures 4a and 4b below, respectively.
当CE在每个DS0信道（例如，用于电话应用的CAS）上保持单独的应用状态时，IPv4/IPv6和MPLS PSN上的CESoPSN信令分组的格式分别如下图4a和4b所示。
Signaling packets SHOULD be carried in a separate dedicated PW. However, implementations MAY carry them in the same PW as the TDM data packets for the basic NxDS0 service. The methods of "pairing" the PWs carrying TDM data and signaling packets for the same extended NxDS0 service are out of scope of this document.
信令包应在单独的专用PW中传送。然而，实现可以将它们携带在与基本NxDS0服务的TDM数据包相同的PW中。为同一扩展NxDS0服务“配对”携带TDM数据和信令包的PW的方法不在本文件范围内。
Regardless of the way signaling packets are carried across the PSN, the following rules apply:
无论信令包在PSN中的传输方式如何，以下规则适用：
1. The CESoPSN signaling packets MUST:
1. CESoPSN信令包必须：
a) Use their own sequence numbers in the control word
a) 在控制字中使用它们自己的序列号
b) Set the flags in the control word like following:
b) 在控制字中设置标志，如下所示：
i) L = 0
i) L=0
ii) M = '11'
ii）M='11'
iii) R = 0
iii）R=0
2. If an RTP header is used in the data packets, it MUST be also used in the signaling packets with the following restrictions:
2. 如果在数据包中使用RTP报头，则它也必须在信令包中使用，并具有以下限制：
a) An additional RTP payload type (from the range of dynamically allocated types) MUST be allocated for the signaling packets.
a) 必须为信令分组分配额外的RTP有效负载类型（来自动态分配类型的范围）。
b) In addition, the signaling packets MUST use their own SSRC value.
b) 此外，信令分组必须使用它们自己的SSRC值。
The protocol used to assure reliable delivery of signaling packets is discussed in Appendix A.
用于确保信令包可靠传输的协议在附录A中讨论。
Encoding of CE application state for telephony applications using CAS follows [RFC2833] (which has since been obsoleted by [RFC4733] and [RFC4734], but they do not affect the relevant text).
使用CAS对电话应用程序的CE应用程序状态编码遵循[RFC2833]（该编码已被[RFC4733]和[RFC4734]淘汰，但不影响相关文本）。
Encoding of CE application state for telephony application using CCS will be considered in a separate document.
将在单独的文件中考虑使用CCS对电话应用的CE应用状态进行编码。
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| IPv4/IPv6 and multiplexing layer headers |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL Fixed |
+-- --+
| RTP |
+-- --+
| Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Encoded CE application state entry for the DS0 channel #1 |
+-- --+
| ... |
+-- --+
| Encoded CE application state entry for the DS0 channel #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| IPv4/IPv6 and multiplexing layer headers |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL Fixed |
+-- --+
| RTP |
+-- --+
| Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Encoded CE application state entry for the DS0 channel #1 |
+-- --+
| ... |
+-- --+
| Encoded CE application state entry for the DS0 channel #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4a. CESoPSN Signaling Packet Format over an IPv4/IPv6 PSN
图4a。IPv4/IPv6 PSN上的CESoPSN信令数据包格式
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| MPLS Label Stack |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL Fixed |
+-- --+
| RTP |
+-- --+
| Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Encoded CE application state entry for the DS0 channel #1 |
+-- --+
| ... |
+-- --+
| Encoded CE application state entry for the DS0 channel #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| MPLS Label Stack |
| ... |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| CESoPSN Control Word |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| OPTIONAL Fixed |
+-- --+
| RTP |
+-- --+
| Header (see [RFC3550]) |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| Encoded CE application state entry for the DS0 channel #1 |
+-- --+
| ... |
+-- --+
| Encoded CE application state entry for the DS0 channel #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4b. CESoPSN Signaling Packet Format over an MPLS PSN
图4b。MPLS PSN上的CESoPSN信令分组格式
The structure preserved by CESoPSN for this group of services is the trunk multiframe sub-divided into the trunk frames, and signaling information is carried appended to the TDM data using the signaling substructures defined in [ATM-CES]. These substructures comprise N consecutive nibbles, so that the i-th nibble carries CAS bits for the i-th DS0 channel, and are padded with a dummy nibble for odd values of N.
CESoPSN为这组服务保留的结构是分为中继帧的中继多帧，并且使用[ATM-CES]中定义的信令子结构将信令信息附加到TDM数据中。这些子结构包括N个连续的半字节，因此第i个半字节携带用于第i个DS0信道的CAS位，并且对于N的奇数值用虚拟半字节填充。
CESoPSN implementations supporting trunk-specific NxDS0 services with CAS MUST NOT carry more TDM data per packet than is contained in a single trunk multiframe.
支持带有CAS的特定于中继的NxDS0服务的CESoPSN实现，每个数据包的TDM数据量不得超过单个中继多帧中包含的数据量。
All CESoPSN implementations supporting trunk-specific NxDS0 with CAS MUST support the default mode, where a single CESoPSN packet carries exactly the amount of TDM data contained in exactly one trunk multiframe and appended with the signaling sub-structure. The TDM data is aligned with the packet payload. In this case:
所有支持带有CAS的中继特定NxDS0的CESoPSN实现都必须支持默认模式，其中单个CESoPSN数据包正好携带一个中继多帧中包含的TDM数据量，并附加了信令子结构。TDM数据与分组有效载荷对齐。在这种情况下：
1. Packetization latency is:
1. 打包延迟为：
a) 2 milliseconds for E1 NxDS0
a) E1 NxDS0为2毫秒
b) 3 milliseconds for T1 NxDS0
b) T1 NxDS0为3毫秒
2. The packet payload size is:
2. 数据包有效负载大小为：
a) 16*N + floor((N+1)/2) for E1-NxDS0
a) 16*N + floor((N+1)/2) for E1-NxDS0
b) 24*N + floor((N+1)/2) for T1/ESF-NxDS0 and T1/SF- NxDS0
b) 24*N + floor((N+1)/2) for T1/ESF-NxDS0 and T1/SF- NxDS0
3. The packet payload format coincides with the multiframe structure described in [ATM-CES] (Section 2.3.1.2).
3. 数据包有效载荷格式与[ATM-CES]（第2.3.1.2节）中描述的多帧结构一致。
In order to provide lower packetization latency, CESoPSN implementations for trunk-specific NxDS0 with CAS SHOULD support fragmentation of multiframe structures between multiple CESoPSN packets. In this case:
为了提供较低的分组延迟，针对具有CAS的中继特定NxDS0的CESoPSN实现应支持多个CESoPSN分组之间的多帧结构分段。在这种情况下：
1. The FRG bits MUST be used to indicate first, intermediate, and last fragment of a multiframe as described in [RFC4623].
1. 如[RFC4623]所述，FRG位必须用于指示多帧的第一个、中间和最后一个片段。
2. The amount of the TDM data per CESoPSN packet must be constant.
2. 每个CESoPSN数据包的TDM数据量必须恒定。
3. Each multiframe fragment MUST comprise an integer multiple of the trunk frames.
3. 每个多帧片段必须包含主干帧的整数倍。
4. The signaling substructure MUST be appended to the last fragment of each multiframe.
4. 信号子结构必须附加到每个多帧的最后一个片段。
Format of CESoPSN packets carrying trunk-specific NxDS0 service with CAS that do and do not contain signaling substructures is shown in Figures 5 (a) and (b), respectively. In these figures, the number of the trunk frames per multiframe fragment ("m") MUST be an integer divisor of the number of frames per trunk multiframe.
图5（a）和（b）分别显示了承载特定于中继的NxDS0服务的CESoPSN数据包的格式，这些数据包带有CA，CA包含和不包含信令子结构。在这些图中，每个多帧片段的主干帧数（“m”）必须是每个主干多帧的帧数的整数除数。
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
| Timeslot 1 | | Timeslot 1 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Timeslot 2 | | Timeslot 2 |
Frame #1 | ... | Frame #1 | ... |
| Timeslot N | | Timeslot N |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
| Timeslot 1 | | Timeslot 1 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Timeslot 2 | Frame #2 | Timeslot 2 |
Frame #2 | ... | | ... |
| Timeslot N | | Timeslot N |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
... | ... | | ... |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
| Timeslot 1 | | Timeslot 1 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Timeslot 2 | | Timeslot 2 |
Frame #m | ... | Frame #m | ... |
| Timeslot N | | Timeslot N |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
Nibbles 1,2 |A B C D|A B C D|
+-+-+-+-+-+-+-+-+
Nibbles 3,4 |A B C D|A B C D|
+-+-+-+-+-+-+-+-+
Nibble n |A B C D| (pad) |
(odd) & pad +-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
| Timeslot 1 | | Timeslot 1 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Timeslot 2 | | Timeslot 2 |
Frame #1 | ... | Frame #1 | ... |
| Timeslot N | | Timeslot N |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
| Timeslot 1 | | Timeslot 1 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Timeslot 2 | Frame #2 | Timeslot 2 |
Frame #2 | ... | | ... |
| Timeslot N | | Timeslot N |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
... | ... | | ... |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
| Timeslot 1 | | Timeslot 1 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Timeslot 2 | | Timeslot 2 |
Frame #m | ... | Frame #m | ... |
| Timeslot N | | Timeslot N |
--- +-+-+-+-+-+-+-+-+ --- +-+-+-+-+-+-+-+-+
Nibbles 1,2 |A B C D|A B C D|
+-+-+-+-+-+-+-+-+
Nibbles 3,4 |A B C D|A B C D|
+-+-+-+-+-+-+-+-+
Nibble n |A B C D| (pad) |
(odd) & pad +-+-+-+-+-+-+-+-+
(a) The packet with (b) The packet without the signaling structure the signaling structure (the last fragment of (not the last fragment the multiframe) of the multiframe)
(a) 具有（b）不具有信令结构的分组信令结构（多帧的最后一个片段（不是多帧的最后一个片段））的分组
Figure 5. The CESoPSN Packet Payload Format for Trunk-Specific NxDS0 with CAS
图5。具有CAS的中继特定NxDS0的CESoPSN数据包有效负载格式
Notes:
笔记：
1. In case of T1-NxDS0 with CAS, the signaling bits are carried in the TDM data, as well as in the signaling substructure. However, the receiver MUST use the CAS bits as carried in the signaling substructures.
1. 在带有CAS的T1-NxDS0的情况下，信令位在TDM数据以及信令子结构中携带。然而，接收机必须使用信令子结构中携带的CAS位。
2. In case of trunk-specific NxDS0 with CAS originating in a T1-SF trunk, each nibble of the signaling substructure contains A and B bits from two consecutive trunk multiframes as described in [ATM-CES].
2. 在中继特定NxDS0的情况下，CA源自T1-SF中继，信令子结构的每个半字节包含[ATM-CES]中所述的两个连续中继多帧的a和B位。
Edge-to-edge emulation of a TDM service using CESoPSN is only possible when the two PW attachment circuits are of the same type (basic NxDS0 or one of the trunk-specific NxDS0 with CAS) and bit rate. The service type and bit rate are exchanged at PW setup as described in [RFC4447].
只有当两个PW连接电路具有相同类型（基本NxDS0或一个具有CAS的中继特定NxDS0）和比特率时，才可能使用CESoPSN对TDM服务进行边到边仿真。服务类型和比特率在PW设置时交换，如[RFC4447]所述。
Once the PW is set up, the PSN-bound CESoPSN IWF operates as follows:
一旦设置了PW，绑定PSN的CESoPSN IWF将按如下方式运行：
TDM data is packetized using the configured number of payload bytes per packet.
TDM数据使用每个数据包配置的有效负载字节数进行打包。
Sequence numbers, flags, and timestamps (if the RTP header is used) are inserted in the CESoPSN headers and, for trunk-specific NxDS0 with CAS, signaling substructures are appended to the packets carrying the last fragment of a multiframe.
序列号、标志和时间戳（如果使用RTP报头）被插入CESoPSN报头中，并且对于具有CAS的中继特定NxDS0，信令子结构被附加到承载多帧的最后片段的分组。
CESoPSN, multiplexing layer, and PSN headers are prepended to the packetized service data.
CESoPSN、多路复用层和PSN报头在分组服务数据之前。
The resulting packets are transmitted over the PSN.
产生的数据包通过PSN传输。
The CE-bound CESoPSN IWF SHOULD include a jitter buffer where payload of the received CESoPSN packets is stored prior to play-out to the local TDM attachment circuit. The size of this buffer SHOULD be locally configurable to allow accommodation to the PSN-specific packet delay variation.
绑定CE的CESoPSN IWF应包括抖动缓冲器，其中在播放到本地TDM连接电路之前存储接收到的CESoPSN分组的有效载荷。该缓冲区的大小应该是本地可配置的，以允许适应特定于PSN的数据包延迟变化。
The CE-bound CESoPSN IWF MUST detect lost and misordered packets. It SHOULD use the sequence number in the control word for these purposes but, if the RTP header is used, the RTP sequence number MAY be used instead.
绑定CE的CESoPSN IWF必须检测丢失和错误排序的数据包。出于这些目的，它应该在控制字中使用序列号，但如果使用RTP报头，则可以使用RTP序列号。
The CE-bound CESoPSN IWF MAY reorder misordered packets. Misordered packets that cannot be reordered MUST be discarded and treated as lost.
绑定CE的CESoPSN-IWF可以对错误排序的分组重新排序。不能重新排序的错误数据包必须丢弃并视为丢失。
The payload of the received CESoPSN data packets marked with the L bit set SHOULD be replaced by the equivalent amount of some locally configured "idle" bit pattern even if it has not been omitted. In addition, the CE-bound CESoPSN IWF will be locally configured to command its local NSP to perform one of the following actions:
接收到的标有L位集的CESoPSN数据包的有效载荷应替换为一些本地配置的“空闲”位模式的等量，即使它没有被省略。此外，绑定CE的CESoPSN IWF将在本地配置为命令其本地NSP执行以下操作之一：
o None (MUST be supported by all the implementations)
o 无（所有实现都必须支持）
o Transmit the AIS pattern towards the local CE on the E1 or T1 trunk carrying the local attachment circuit (support of this action is RECOMMENDED)
o 在承载本地连接电路的E1或T1中继线上向本地CE传输AIS模式（建议支持此操作）
o Send the "Channel Idle" signal to the local CE for all the DS0 channels comprising the local attachment circuit (support of this action is OPTIONAL).
o 向本地CE发送包含本地连接电路的所有DS0信道的“信道空闲”信号（支持此操作是可选的）。
If the data packets received are marked with L bit cleared and M bits set to '10' or with R bit set, the CE-bound CESoPSN IWF will be locally configured to command its local NSP to perform one of the following actions:
如果接收的数据包标记为L位清除，M位设置为“10”或R位设置，则绑定CE的CESoPSN IWF将在本地配置为命令其本地NSP执行以下操作之一：
o None (MUST be supported by all the implementations)
o 无（所有实现都必须支持）
o Transmit the RAI pattern towards the local CE on the E1 or T1 trunk carrying the local attachment circuit (support of this action is RECOMMENDED)
o 在承载本地连接电路的E1或T1中继线上向本地CE传输RAI模式（建议支持此操作）
o Send the "Channel Idle" signal to the local CE for all the DS0 channels comprising the local attachment circuit (support of this action is OPTIONAL and requires also that the CE-bound CES IWF replaces the actually received payload with the equivalent amount of the locally configured "idle" bit pattern.
o 将包括本地连接电路的所有DS0信道的“信道空闲”信号发送到本地CE（支持此操作是可选的，并且还要求绑定CE的CES IWF用本地配置的等效“空闲”位模式替换实际接收的有效负载。
Notes:
笔记：
1. If the pair of IWFs at the two ends of the PW have been configured to force the TDM trunks carrying their ACs to transmit AIS upon reception of data packets with the L bit set and to transmit RAI upon reception of data packets with the R bit set,
1. 如果PW两端的一对IWF已配置为强制承载其ACs的TDM中继在接收到具有L位集的数据分组时发送AIS，并在接收到具有R位集的数据分组时发送RAI，
or with the L bit cleared and M bits set to '10', this PW provides a bandwidth-saving emulation of a fractional E1 or T1 service between the pair of CE devices.
或者在L位被清除，M位被设置为“10”的情况下，此PW在这对CE设备之间提供分数E1或T1服务的带宽节省仿真。
2. If the pair of IWFs at the two ends of the PW have been configured to signal "Channel Idle" CE application state to its local CE upon reception of packets marked with L bit set, R bit set, or (L,M) set to '010', and to replace the actually received payload with the locally configured "idle" bit pattern, the resulting PW will comply with the requirements for Downstream Trunk conditioning as defined in [TR-NWT-170].
2. 如果PW两端的一对IWF已配置为在接收到标记为L位集、R位集或（L，M）设置为“010”的分组时向其本地CE发送“信道空闲”CE应用状态信号，并用本地配置的“空闲”位模式替换实际接收的有效载荷，产生的PW将符合[TR-NWT-170]中定义的下游干线调节要求。
3. Usage of bits R, L, and M described above additionally provides the tools for "single-ended" management of the CESoPSN pseudowires with ability to distinguish between the problems in the PSN and in the TDM attachment circuits.
3. 上述比特R、L和M的使用另外提供了用于CESoPSN伪线的“单端”管理的工具，能够区分PSN和TDM连接电路中的问题。
The payload of each lost CESoPSN data packet MUST be replaced with the equivalent amount of the replacement data. The contents of the replacement data are implementation-specific and MAY be locally configurable. By default, all CESoPSN implementations MUST support generation of the locally configurable "idle" pattern as the replacement data.
必须用等量的替换数据替换每个丢失的CESoPSN数据包的有效负载。替换数据的内容是特定于实现的，可以在本地配置。默认情况下，所有CESoPSN实现必须支持生成本地可配置的“空闲”模式作为替换数据。
Before a PW has been set up and after a PW has been torn down, the IWF MUST play out the locally configurable "idle" pattern to its TDM attachment circuit.
在设置PW之前和拆除PW之后，IWF必须向其TDM连接电路播放本地可配置的“空闲”模式。
Once the PW has been set up, the CE-bound IWF begins to receive CESoPSN packets and to store their payload in the jitter buffer, but continues to play out the locally configurable "idle" pattern to its TDM attachment circuit. This intermediate state persists until a pre-configured amount of TDM data (usually half of the jitter buffer) has been received in consecutive CESoPSN packets, or until a pre-configured intermediate state timer expires.
一旦PW被设置，绑定CE的IWF开始接收CESoPSN分组并将其有效载荷存储在抖动缓冲器中，但是继续向其TDM连接电路播放本地可配置的“空闲”模式。此中间状态持续存在，直到在连续的CESoPSN数据包中接收到预先配置的TDM数据量（通常为抖动缓冲区的一半），或者直到预先配置的中间状态计时器过期。
Once the pre-configured amount of the TDM data has been received, the CE-bound CESoPSN IWF enters its normal operation state, where it continues to receive CESoPSN packets and store their payload in the jitter buffer while playing out the contents of the jitter buffer in accordance with the required clock. In this state, the CE-bound IWF performs clock recovery, MAY monitor PW defects, and MAY collect PW performance-monitoring data.
一旦接收到预先配置的TDM数据量，绑定CE的CESoPSN IWF进入其正常操作状态，其中它继续接收CESoPSN分组并将其有效负载存储在抖动缓冲器中，同时根据所需时钟播放抖动缓冲器的内容。在这种状态下，受CE约束的IWF执行时钟恢复，可以监视PW缺陷，并且可以收集PW性能监视数据。
If the CE-bound CESoPSN IWF detects loss of a pre-configured number of consecutive packets, or if the intermediate state timer expires before the required amount of TDM data has been received, it enters its packet loss state. While in this state:
如果绑定CE的CESoPSN IWF检测到预先配置数量的连续分组丢失，或者如果中间状态计时器在接收到所需数量的TDM数据之前过期，则其进入分组丢失状态。在这种状态下：
o The locally configurable "idle" pattern SHOULD be played out to the TDM attachment circuit.
o 应向TDM连接电路播放本地可配置的“空闲”模式。
o The local PSN-bound CESoPSN IWF SHOULD mark every packet it transmits with the R bit set.
o 绑定到本地PSN的CESoPSN IWF应使用R位集标记其传输的每个数据包。
The CE-bound CESoPSN IWF leaves this state and transits to the normal one once a pre-configured number of consecutive CESoPSN packets have been received.
一旦接收到预先配置数量的连续CESoPSN数据包，绑定CE的CESoPSN IWF将离开该状态并转换为正常状态。
In addition to the packet loss state of the CE-bound CESoPSN IWF defined above, it MAY detect the following defects:
除了上面定义的CE绑定的CESoPSN IWF的分组丢失状态之外，它还可以检测以下缺陷：
o Stray packets
o 杂散数据包
o Malformed packets
o 格式错误的数据包
o Excessive packet loss rate
o 数据包丢失率过高
o Buffer overrun
o 缓冲区泛滥
o Remote packet loss.
o 远程数据包丢失。
Corresponding to each defect is a defect state of the IWF, a detection criterion that triggers transition from the normal operation state to the appropriate defect state, and an alarm that MAY be reported to the management system and, thereafter, cleared. Alarms are only reported when the defect state persists for a pre-configured amount of time (typically 2.5 seconds) and MUST be cleared after the corresponding defect is undetected for a second pre-configured amount of time (typically 10 seconds). The trigger and release times for the various alarms may be independent.
与每个缺陷相对应的是IWF的缺陷状态、触发从正常运行状态过渡到适当缺陷状态的检测标准，以及可向管理系统报告并随后清除的警报。只有当缺陷状态持续一段预先配置的时间（通常为2.5秒）时，才会报告报警，并且在第二段预先配置的时间（通常为10秒）内未检测到相应的缺陷后，必须清除报警。各种警报的触发和释放时间可能是独立的。
Stray packets MAY be detected by the PSN and multiplexing layers. When RTP is used, the SSRC field in the RTP header MAY be used for this purpose as well. Stray packets MUST be discarded by the CE-bound IWF, and their detection MUST NOT affect mechanisms for detection of packet loss.
杂散分组可由PSN和复用层检测。使用RTP时，RTP头中的SSRC字段也可用于此目的。受CE约束的IWF必须丢弃杂散数据包，其检测不得影响数据包丢失检测机制。
Malformed packets MAY be detected by mismatch between the expected packet size (taking the value of the L bit into account) and the actual packet size inferred from the PSN and multiplexing layers. When RTP is used, lack of correspondence between the PT value and that allocated for this direction of the PW MAY also be used for this purpose. Other methods of detecting malformed packets are implementation-specific. Malformed in-order packets MUST be discarded by the CE-bound IWF and replacement data generated as for lost packets.
通过预期分组大小（考虑L位的值）与从PSN和复用层推断的实际分组大小之间的不匹配，可以检测到格式错误的分组。当使用RTP时，PT值和分配给PW方向的PT值之间缺乏对应关系也可用于此目的。检测格式错误数据包的其他方法是特定于实现的。绑定CE的IWF必须丢弃格式不正确的顺序数据包，并为丢失的数据包生成替换数据。
Excessive packet loss rate is detected by computing the average packet Loss rate over a configurable amount of times and comparing it with a pre-configured threshold.
通过计算可配置次数内的平均分组丢失率并将其与预先配置的阈值进行比较，可以检测到过度分组丢失率。
Buffer overrun is detected in the normal operation state when the jitter buffer of the CE-bound IWF cannot accommodate newly arrived CESoPSN packets.
当绑定CE的IWF的抖动缓冲区不能容纳新到达的CESoPSN数据包时，在正常操作状态下检测到缓冲区溢出。
Remote packet loss is indicated by reception of packets with their R bit set.
远程数据包丢失通过接收设置了R位的数据包来表示。
Performance monitoring (PM) parameters are routinely collected for TDM services and provide an important maintenance mechanism in TDM networks. Ability to collect compatible PM parameters for CESoPSN PWs enhances their maintenance capabilities.
性能监控（PM）参数是为TDM服务定期收集的，并在TDM网络中提供重要的维护机制。为CESoPSN PWs收集兼容PM参数的能力增强了其维护能力。
Collection of the CESoPSN PW performance monitoring parameters is OPTIONAL and, if implemented, is only performed after the CE-bound IWF has exited its intermediate state.
CESoPSN PW性能监视参数的收集是可选的，如果实现，则仅在绑定CE的IWF退出其中间状态后执行。
CESoPSN defines error events, errored blocks, and defects as follows:
CESoPSN对错误事件、错误块和缺陷的定义如下：
o A CESoPSN error event is defined as insertion of a single replacement packet into the jitter buffer (replacement of payload of CESoPSN packets with the L bit set is not considered as insertion of a replacement packet).
o CESoPSN错误事件定义为将单个替换数据包插入抖动缓冲器（用L位集替换CESoPSN数据包的有效载荷不视为插入替换数据包）。
o A CESoPSN errored data block is defined as a block of data played out to the TDM attachment circuit and of size defined in accordance with the [G.826] rules for the corresponding TDM service that has experienced at least one CESoPSN error event.
o CESoPSN错误数据块被定义为向TDM连接电路播放的数据块，其大小根据[G.826]规则为经历至少一次CESoPSN错误事件的相应TDM服务定义。
o A CESoPSN defect is defined as the packet loss state of the CE-bound CESoPSN IWF.
o CESoPSN缺陷定义为绑定CE的CESoPSN IWF的丢包状态。
The CESoPSN PW PM parameters (Errored, Severely Errored, and Unavailable Seconds) are derived from these definitions, in accordance with [G.826].
CESoPSN PW PM参数（出错、严重出错和不可用秒数）根据[G.826]从这些定义中得出。
If the PSN providing connectivity between PE devices is Diffserv-enabled and provides a per-domain behavior (PDB) [RFC3086] that guarantees low-jitter and low-loss, the CESoPSN PW SHOULD use this PDB in compliance with the admission and allocation rules the PSN has put in place for that PDB (e.g., marking packets as directed by the PSN).
如果在PE设备之间提供连接的PSN启用了Diffserv，并提供了保证低抖动和低损耗的每域行为（PDB）[RFC3086]，则CESoPSN PW应根据PSN为该PDB制定的准入和分配规则使用该PDB（例如，按照PSN的指示标记数据包）。
As explained in [RFC3985], the PSN carrying the PW may be subject to congestion. CESoPSN PWs represent inelastic, constant bit rate (CBR) flows and cannot respond to congestion in a TCP-friendly manner prescribed by [RFC2914], although the percentage of total bandwidth they consume remains constant.
如[RFC3985]所述，承载PW的PSN可能会出现拥塞。CESoPSN PW代表非弹性、恒定比特率（CBR）流，不能以[RFC2914]规定的TCP友好方式响应拥塞，尽管它们消耗的总带宽百分比保持不变。
Unless appropriate precautions are taken, undiminished demand of bandwidth by CESoPSN PWs can contribute to network congestion that may impact network control protocols.
除非采取适当的预防措施，否则CESoPSN PWs对带宽的需求不减可能导致网络拥塞，从而影响网络控制协议。
Whenever possible, CESoPSN 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 supporting Guaranteed Service (GS) [RFC2212] and Diffserv-enabled domains [RFC2475] supporting Expedited Forwarding (EF) [RFC3246] provide examples of such PSNs. Such mechanisms will negate, to some degree, the effect of the CESoPSN PWs on the neighboring streams. In order to facilitate boundary traffic conditioning of CESoPSN traffic over IP PSNs, the CESoPSN IP packets SHOULD NOT use the Diffserv Code Point (DSCP) value reserved for the Default PHB [RFC2474].
只要可能，CESoPSN PW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）[RFC2212]的支持IntServ的域[RFC2475]和支持快速转发（EF）[RFC3246]的支持区分服务的域[RFC2475]提供了此类PSN的示例。这种机制将在一定程度上抵消CESoPSN PWs对相邻流的影响。为了促进IP PSN上CESoPSN流量的边界流量调节，CESoPSN IP数据包不应使用为默认PHB保留的Diffserv代码点（DSCP）值[RFC2474]。
If CESoPSN PWs run over a PSN providing best-effort service, they SHOULD monitor packet loss in order to detect "severe congestion". If such a condition is detected, a CESoPSN PW SHOULD shut down bidirectionally for some period of time as described in Section 6.5 of [RFC3985].
如果CESoPSN PW在提供尽力而为服务的PSN上运行，它们应该监控数据包丢失，以便检测“严重拥塞”。如果检测到这种情况，CESoPSN PW应双向关闭一段时间，如[RFC3985]第6.5节所述。
Note that:
请注意：
1. The CESoPSN IWF can inherently provide packet loss measurement, since the expected rate of arrival of CESoPSN packets is fixed and known
1. 由于CESoPSN数据包的预期到达率是固定且已知的，因此CESoPSN IWF可以固有地提供数据包丢失测量
2. The results of the CESoPSN packet loss measurement may not be a reliable indication of presence or absence of severe congestion if the PSN provides enhanced delivery, e.g.,:
2. 如果PSN提供增强的传送，则CESoPSN分组丢失测量的结果可能不是存在或不存在严重拥塞的可靠指示，例如：
a) If CESoPSN traffic takes precedence over non-CESoPSN traffic, severe congestion can develop without significant CESoPSN packet loss.
a) 如果CESoPSN流量优先于非CESoPSN流量，则可能会出现严重拥塞，而不会造成显著的CESoPSN数据包丢失。
b) If non-CESoPSN traffic takes precedence over CESoPSN traffic, CESoPSN may experience substantial packet loss due to a short-term burst of high-priority traffic.
b) 如果非CESoPSN流量优先于CESoPSN流量，则由于高优先级流量的短期突发，CESoPSN可能会经历大量的数据包丢失。
3. The TDM services emulated by the CESoPSN PWs have high availability objectives (see [G.826]) that MUST be taken into account when deciding on temporary shutdown of CESoPSN PWs.
3. CESoPSN PWs模拟的TDM服务具有高可用性目标（见[G.826]），在决定临时关闭CESoPSN PWs时必须将其考虑在内。
This specification does not define the exact criteria for detecting "severe congestion" using the CESoPSN packet loss rate, or the specific methods for bidirectional shutdown that the CESoPSN PWs (when such severe congestion has been detected) and their consequent restart after a suitable delay. This is left for further study. However, the following considerations may be used as guidelines for implementing the CESoPSN severe congestion shutdown mechanism:
本规范未定义使用CESoPSN数据包丢失率检测“严重拥塞”的准确标准，也未定义CESoPSN PWs（当检测到严重拥塞时）的双向关机的具体方法，以及在适当延迟后重新启动的具体方法。这有待进一步研究。但是，以下注意事项可用作实施CESoPSN严重拥塞停机机制的指南：
1. CESoPSN Performance Monitoring techniques (see Section 6.4) provide entry and exit criteria for the CESoPSN PW "Unavailable" state that make it closely correlated with the "Unavailable" state of the emulated TDM circuit as specified in [G.826]. Using the same criteria for "severe congestion" detection may decrease the risk of shutting down the CESoPSN PW while the emulated TDM circuit is still considered available by the CE.
1. CESoPSN性能监测技术（见第6.4节）为CESoPSN PW“不可用”状态提供了进入和退出标准，使其与[G.826]中规定的模拟TDM电路的“不可用”状态密切相关。在CE认为仿真TDM电路仍然可用时，使用相同的“严重拥塞”检测标准可降低关闭CESoPSN PW的风险。
2. If the CESoPSN PW has been set up using either PWE3 control protocol [RFC4447] or L2TPv3 [RFC3931], the regular PW teardown procedures of these protocols SHOULD be used.
2. 如果已使用PWE3控制协议[RFC4447]或L2TPv3[RFC3931]设置CESoPSN PW，则应使用这些协议的常规PW拆卸程序。
3. If one of the CESoPSN PW end points stops transmission of packets for a sufficiently long period, its peer (observing 100% packet loss) will necessarily detect "severe congestion" and also stop transmission, thus achieving bidirectional PW shutdown.
3. 如果其中一个CESoPSN PW端点在足够长的时间内停止数据包的传输，则其对等方（观察到100%的数据包丢失）将必然检测到“严重拥塞”并停止传输，从而实现双向PW关闭。
CESoPSN does not enhance or detract from the security performance of the underlying PSN; rather, it relies upon the PSN mechanisms for encryption, integrity, and authentication whenever required.
CESoPSN不会提高或降低基础PSN的安全性能；相反，它在需要时依赖PSN机制进行加密、完整性和身份验证。
CESoPSN PWs share susceptibility to a number of pseudowire-layer attacks, and will use whatever mechanisms for confidentiality, integrity, and authentication that are developed for general PWs. These methods are beyond the scope of this document.
CESoPSN PWs对许多伪线层攻击具有敏感性，并且将使用为通用PWs开发的任何保密性、完整性和身份验证机制。这些方法超出了本文件的范围。
Although CESoPSN PWs MAY employ an RTP header when explicit transfer of timing information is required, it is not possible to use SRTP (see [RFC3711]) mechanisms as a substitute for PW layer security.
尽管当需要显式传输定时信息时，CESoPSN PWs可采用RTP报头，但不可能使用SRTP（参见[RFC3711]）机制替代PW层安全性。
Misconnection detection capabilities of CESoPSN increase its resilience to misconfiguration and some types of DoS attacks.
CESoPSN的错误连接检测功能增强了其对错误配置和某些类型的DoS攻击的恢复能力。
Random initialization of sequence numbers, in both the control word and the optional RTP header, makes known-plaintext attacks on encrypted CESoPSN PWs more difficult. Encryption of PWs is beyond the scope of this document.
控制字和可选RTP报头中序列号的随机初始化使得加密CESoPSN PW上的已知明文攻击更加困难。PWs的加密超出了本文件的范围。
Allocation of PW Types for the corresponding CESoPSN PWs is defined in [RFC4446].
[RFC4446]中定义了相应CESoPSN PW的PW类型分配。
CESoPSN is an encapsulation layer intended for carrying NxDS0 services with or without CAS over PSN.
CESoPSN是一个封装层，用于在PSN上承载NxDS0服务，包括或不包括CAS。
CESoPSN allows emulation of certain end-to-end delay properties of TDM networks. In particular, the end-to-end delay of a TDM circuit emulated by a CESoPSN PW does not depend upon the bit rate of the service.
CESoPSN允许模拟TDM网络的某些端到端延迟特性。特别地，由CESoPSN PW仿真的TDM电路的端到端延迟不取决于服务的比特率。
CESoPSN fully complies with the principle of minimal intervention, minimizing overhead, and computational power required for encapsulation.
CESoPSN完全符合最小干预、最小化开销和封装所需计算能力的原则。
CESoPSN can be used in conjunction with various clock recovery techniques and does not presume availability of a global synchronous clock at the ends of a PW. However, if the global synchronous clock is available at both ends of a CESoPSN PW, using RTP and differential mode of timestamp generation improves the quality of the recovered clock.
CESoPSN可与各种时钟恢复技术结合使用，且不假定PW端的全局同步时钟可用。然而，如果全局同步时钟在CESoPSN PW的两端可用，则使用RTP和时间戳生成的差分模式可以提高恢复时钟的质量。
CESoPSN allows carrying CE application state signaling that requires synchronization with data in-band in separate signaling packets. A special combination of flags in the CESoPSN control word is used to distinguish between data and signaling packets, while the Timestamp field in the RTP headers is used for synchronization. This makes CESoPSN extendable to support different types of CE signaling without affecting the data path in the PE devices.
CESoPSN允许承载CE应用状态信令，该信令需要与单独信令分组中的带内数据同步。CESoPSN控制字中的标志的特殊组合用于区分数据包和信令包，而RTP报头中的时间戳字段用于同步。这使得CESoPSN可扩展以支持不同类型的CE信令，而不影响PE设备中的数据路径。
CESoPSN also allows emulation of NxDS0 services with CAS carrying the signaling information appended to (some of) the packets carrying TDM data.
CESoPSN还允许使用CA模拟NxDS0服务，CA携带附加到（一些）携带TDM数据的分组的信令信息。
CESoPSN allows the PSN bandwidth conservation by carrying only AIS and/or Idle Code indications instead of data.
CESoPSN通过仅携带AIS和/或空闲代码指示而不是数据，从而实现PSN带宽节约。
CESoPSN allows deployment of bandwidth-saving Fractional point-to-point E1/T1 applications. These applications can be described as the following:
CESoPSN允许部署节省带宽的分数点到点E1/T1应用程序。这些应用可描述为以下内容：
o The pair of CE devices operates as if it was connected by an emulated E1 or T1 circuit. In particular, it reacts to AIS and RAI states of its local ACs in the standard way.
o 这对CE设备的工作方式与模拟E1或T1电路的连接方式相同。特别是，它以标准方式对其本地ACs的AIS和RAI状态作出反应。
o The PSN carries only an NxDS0 service, where N is the number of actually used timeslots in the circuit connecting the pair of CE devices, thus saving the bandwidth.
o PSN仅承载NxDS0服务，其中N是连接CE设备对的电路中实际使用的时隙数，从而节省带宽。
Being a constant bit rate (CBR) service, CESoPSN cannot provide TCP-friendly behavior under network congestion. If the service encounters congestion, it SHOULD be temporarily shut down.
作为一种恒定比特率（CBR）服务，CESoPSN在网络拥塞情况下无法提供TCP友好行为。如果服务遇到拥塞，应暂时关闭。
CESoPSN allows collection of TDM-like faults and performance monitoring parameters; hence, emulating 'classic' carrier services of TDM circuits (e.g., SONET/SDH). Similarity with these services is increased by the CESoPSN ability to carry 'far end error' indications.
CESoPSN允许收集TDM类故障和性能监测参数；因此，模拟TDM电路的“经典”载波服务（例如SONET/SDH）。CESoPSN承载“远端错误”指示的能力增加了与这些服务的相似性。
CESoPSN provides for a carrier-independent ability to detect misconnections and malformed packets. This feature increases resilience of the emulated service to misconfiguration and DoS attacks.
CESoPSN提供了独立于运营商的能力来检测错误连接和格式错误的数据包。此功能增强了模拟服务对错误配置和DoS攻击的恢复能力。
CESoPSN provides for detection of lost packets and allows using various techniques for generation of "replacement packets".
CESoPSN用于检测丢失的数据包，并允许使用各种技术生成“替换数据包”。
CESoPSN carries indications of outages of incoming attachment circuit across the PSN, thus, providing for effective fault isolation.
CESoPSN在PSN上显示输入连接电路的中断，从而提供有效的故障隔离。
Faithfulness of a CESoPSN PW may be increased if the carrying PSN is Diffserv-enabled and implements a PDB that guarantees low loss and low jitter.
如果承载PSN启用了区分服务并且实现了保证低损耗和低抖动的PDB，则可以增加CESoPSN PW的忠实性。
CESoPSN does not provide any mechanisms for protection against PSN outages. As a consequence, resilience of the emulated service to such outages is defined by the PSN behavior. On the other hand:
CESoPSN不提供任何防止PSN中断的机制。因此，模拟服务对此类中断的恢复能力由PSN行为定义。另一方面：
o The jitter buffer and packets' reordering mechanisms associated with CESoPSN increase resilience of the emulated service to fast PSN re-convergence events
o 与CESoPSN相关的抖动缓冲区和数据包重排序机制提高了模拟服务对快速PSN重新聚合事件的恢复能力
o Remote indication of lost packets is carried backward across the PSN from the receiver (that has detected loss of packets) to transmitter. Such an indication MAY be used as a trigger for activation of proprietary, service-specific protection mechanisms.
o 丢失数据包的远程指示通过PSN从接收机（检测到数据包丢失）向后传送到发射机。此类指示可用作激活专有、特定于服务的保护机制的触发器。
Security of TDM services provided by CESoPSN across a shared PSN may be below the level of security traditionally associated with TDM services carried across TDM networks.
CESoPSN在共享PSN上提供的TDM服务的安全性可能低于传统上与TDM网络上承载的TDM服务相关联的安全性级别。
Akiva Sadovski has been an active participant of the team that co-authored early versions of this document.
Akiva Sadovski一直是该文件早期版本共同作者团队的积极参与者。
We express deep gratitude to Stephen Casner, who reviewed an early version of this document in detail, corrected some serious errors, and provided many valuable inputs.
我们对Stephen Casner深表感谢，他详细审查了本文件的早期版本，纠正了一些严重错误，并提供了许多有价值的投入。
The present version of the text of the QoS section has been suggested by Kathleen Nichols.
QoS部分的当前版本由Kathleen Nichols提出。
We thank Maximilian Riegel, Sim Narasimha, Tom Johnson, Ron Cohen, and Yaron Raz for valuable feedback.
我们感谢Maximilian Riegel、Sim Narasimha、Tom Johnson、Ron Cohen和Yaron Raz的宝贵反馈。
We thank Alik Shimelmits for many fruitful discussions.
我们感谢Alik Shimelmits进行了许多富有成果的讨论。
[ATM-CES] The ATM Forum Technical Committee. Circuit Emulation Service Interoperability Specification version 2.0 af-vtoa-0078.000, January 1997.
[ATM-CES]ATM论坛技术委员会。电路仿真服务互操作性规范版本2.0 af-vtoa-0078.000，1997年1月。
[G.704] ITU-T Recommendation G.704 (10/98) - Synchronous frame structures used at 1544, 6312, 2048, 8448 and 44 736 Kbit/s hierarchical levels
[G.704]ITU-T建议G.704（10/98）-在154463120488448和44736kbit/s分层级别上使用的同步帧结构
[G.706] ITU-T Recommendation G.706 (04/91) - Frame Alignment and Cyclic Redundancy Check (CRC) Procedures Relating to Basic Frame Structured Defined in Recommendation G.704
[G.706]ITU-T建议G.706（04/91）-与建议G.704中定义的基本帧结构相关的帧对齐和循环冗余校验（CRC）程序
[G.775] ITU-T Recommendation G.775 (10/98) - Loss of Signal (LOS), Alarm Indication Signal (AIS), and Remote Defect Indication (RDI) Defect Detection and Clearance Criteria for PDH Signals
[G.775]ITU-T建议G.775（10/98）-PDH信号的信号丢失（LOS）、报警指示信号（AIS）和远程缺陷指示（RDI）缺陷检测和清除标准
[G.826] ITU-T Recommendation G.826 (02/99) - Error performance parameters and objectives for international, constant bit rate digital paths at or above the primary rate
[G.826]ITU-T建议G.826（02/99）——基本速率或以上国际恒定比特率数字路径的错误性能参数和目标
[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。
[RFC2833] Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals", RFC 2833, May 2000.
[RFC2833]Schulzrinne，H.和S.Petrack，“DTMF数字、电话音和电话信号的RTP有效载荷”，RFC 28332000年5月。
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC 2914, September 2000.
[RFC2914]Floyd，S.，“拥塞控制原则”，BCP 41，RFC 2914，2000年9月。
[RFC3086] Nichols, K. and B. Carpenter, "Definition of Differentiated Services Per Domain Behaviors and Rules for their Specification", RFC 3086, April 2001.
[RFC3086]Nichols，K.和B.Carpenter，“每域区分服务行为的定义及其规范规则”，RFC 3086，2001年4月。
[RFC3916] Xiao, X., McPherson, D., and P. Pate, "Requirements for Pseudo-Wire Emulation Edge-to-Edge (PWE3)", RFC 3916, September 2004.
[RFC3916]Xiao，X.，McPherson，D.，和P.Pate，“伪线仿真边到边（PWE3）的要求”，RFC 39162004年9月。
[RFC4197] Riegel, M., "Requirements for Edge-to-Edge Emulation of Time Division Multiplexed (TDM) Circuits over Packet Switching Networks", RFC 4197, October 2005.
[RFC4197]Riegel，M.，“分组交换网络上时分多路复用（TDM）电路的边到边仿真要求”，RFC 4197，2005年10月。
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC3985]Bryant，S.和P.Pate，“伪线仿真边到边（PWE3）架构”，RFC 39852005年3月。
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003.
[RFC3550]Schulzrinne，H.，Casner，S.，Frederick，R.，和V.Jacobson，“RTP：实时应用的传输协议”，STD 64，RFC 35502003年7月。
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006.
[RFC4385]Bryant，S.，Swallow，G.，Martini，L.，和D.McPherson，“用于MPLS PSN的伪线仿真边到边（PWE3）控制字”，RFC 43852006年2月。
[RFC4447] Martini L. et al, Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP), RFC 4447, April 2006
[RFC4447]Martini L.等人，使用标签分发协议（LDP）的伪线设置和维护，RFC 4447，2006年4月
[RFC4623] Malis, A. and M. Townsley, "Pseudowire Emulation Edge-to-Edge (PWE3) Fragmentation and Reassembly", RFC 4623, August 2006.
[RFC4623]Malis，A.和M.Townsley，“伪线仿真边到边（PWE3）碎片化和重组”，RFC 46232006年8月。
[RTP-TYPES] RTP PARAMETERS, <http://www.iana.org/assignments/rtp-parameters>.
[RTP-TYPES]RTP参数<http://www.iana.org/assignments/rtp-parameters>.
[TR-NWT-170] Digital Cross Connect Systems - Generic Requirements and Objectives, Bellcore, TR-NWT-170, January 1993
[TR-NWT-170]数字交叉连接系统-一般要求和目标，Bellcore，TR-NWT-170，1993年1月
[L2TPEXT-TDM] Vainshtein, A. and S. Galtsur, "Layer Two Tunneling Protocol - Setup of TDM Pseudowires", Work in Progress, February 2007.
[L2TPEXT-TDM]Vainstein，A.和S.Galtsur，“第二层隧道协议-TDM伪线的设置”，正在进行的工作，2007年2月。
[PWE3-MS] Martini, L., Metz, C., Nadeau, T., and M. Duckett, "Segmented Pseudo Wire", Work in Progress, November 2007.
[PWE3-MS]Martini，L.，Metz，C.，Nadeau，T.，和M.Duckett，“分段伪线”，正在进行的工作，2007年11月。
[PWE3-TDM-CONTROL] Vainshtein, A. and Y. Stein, "Control Protocol Extensions for Setup of TDM Pseudowires in MPLS Networks", Work in Progress, November 2007.
[PWE3-TDM-CONTROL]Vainstein，A.和Y.Stein，“用于在MPLS网络中设置TDM伪线的控制协议扩展”，正在进行的工作，2007年11月。
[RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification of Guaranteed Quality of Service", RFC 2212, September 1997.
[RFC2212]Shenker，S.，Partridge，C.和R.Guerin，“保证服务质量规范”，RFC 2212，1997年9月。
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, December 1998.
[RFC2474]Nichols，K.，Blake，S.，Baker，F.，和D.Black，“IPv4和IPv6头中区分服务字段（DS字段）的定义”，RFC 2474，1998年12月。
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and W. Weiss, "An Architecture for Differentiated Service", RFC 2475, December 1998.
[RFC2475]Blake，S.，Black，D.，Carlson，M.，Davies，E.，Wang，Z.，和W.Weiss，“差异化服务架构”，RFC 24751998年12月。
[RFC3246] Davie, B., Charny, A., Bennet, J.C., 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.
[RFC3246]Davie，B.，Charny，A.，Bennet，J.C.，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。
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[RFC3711]Baugher，M.，McGrew，D.，Naslund，M.，Carrara，E.，和K.Norrman，“安全实时传输协议（SRTP）”，RFC 37112004年3月。
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC3931]Lau，J.，Townsley，M.，和I.Goyret，“第二层隧道协议-版本3（L2TPv3）”，RFC 39312005年3月。
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[RFC4446]Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，2006年4月。
[RFC4553] Vainshtein, A. and YJ. Stein, "Structure-Agnostic Time Division Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June 2006.
[RFC4553]Vainstein，A.和YJ。Stein，“分组上的结构不可知时分复用（TDM）（SAToP）”，RFC4553，2006年6月。
[RFC4733] Schulzrinne, H. and T. Taylor, "RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals", RFC 4733, December 2006.
[RFC4733]Schulzrinne，H.和T.Taylor，“DTMF数字、电话音和电话信号的RTP有效载荷”，RFC 47332006年12月。
[RFC4734] Schulzrinne, H. and T. Taylor, "Definition of Events for Modem, Fax, and Text Telephony Signals", RFC 4734, December 2006.
[RFC4734]Schulzrinne，H.和T.Taylor，“调制解调器、传真和文本电话信号事件的定义”，RFC 47342006年12月。
[RFC5085] Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", Work in Progress, RFC 5085, December 2007.
[RFC5085]Nadeau，T.，Ed.，和C.Pignataro，Ed.，“伪线虚拟电路连接验证（VCCV）：伪线的控制通道”，正在进行的工作，RFC 5085，2007年12月。
Format of the CESoPSN signaling packets is discussed in Section 5.3 above.
上述第5.3节讨论了CESoPSN信令包的格式。
The sequence number in the CESoPSN control word for the signaling packets is generated according to the same rules as for the TDM data packets.
信令分组的CESoPSN控制字中的序列号根据与TDM数据分组相同的规则生成。
If the RTP header is used in the CESoPSN signaling packets, the timestamp in this header represents the time when the CE application state has been collected.
如果在CESoPSN信令分组中使用RTP报头，则该报头中的时间戳表示收集CE应用程序状态的时间。
Signaling packets are generated by the ingress PE, in accordance with the following logic (adapted from [RFC2833]):
信令分组由入口PE根据以下逻辑（改编自[RFC2833]）生成：
1. The CESoPSN signaling packet with the same information (including the timestamp in the case RTP header is used) is sent 3 times at an interval of 5 ms under one of the following conditions:
1. 在以下条件之一下，以5ms的间隔发送具有相同信息（包括在使用RTP报头的情况下的时间戳）的CESoPSN信令分组3次：
a) The CESoPSN PW has been set up
a) CESoPSN PW已经建立
b) A change in the CE application state has been detected. If another change of the CE application state has been detected during the 10 ms period (i.e., before all 3 signaling packets reporting the previous change have been sent), this process is re-started, i.e.:
b) 检测到CE应用程序状态发生变化。如果在10ms期间（即，在报告先前改变的所有3个信令分组被发送之前）检测到CE应用状态的另一改变，则该过程被重新启动，即：
i) The unsent signaling packet(s) with the previous CE application state are discarded
i) 具有先前CE应用状态的未发送信令分组被丢弃
ii) Triple send of packets with the new CE application state begins.
ii）开始三次发送具有新CE应用程序状态的数据包。
c) Loss of packets defect has been cleared
c) 数据包丢失缺陷已清除
d) Remote Loss of Packets indication has been cleared (after previously being set)
d) 远程数据包丢失指示已清除（之前设置后）
2. Otherwise, the CESoPSN signaling packet with the current CE application state information is sent every 5 seconds.
2. 否则，每5秒发送具有当前CE应用状态信息的CESoPSN信令分组。
These rules allow fast probabilistic recovery after loss of a single signaling packet, as well as deterministic (but possibly slow) recovery following PW setup and PSN outages.
这些规则允许在单个信令包丢失后进行快速概率恢复，以及在PW设置和PSN中断后进行确定性（但可能较慢）恢复。
Structured TDM services do not exist as physical circuits. They are always carried within appropriate physical attachment circuits (AC), and the PE providing their emulation always includes a Native Service Processing Block (NSP), commonly referred to as Framer. As a consequence, the architecture of a PE device providing edge-to-edge emulation for these services includes the Framer and Forwarder blocks.
结构化TDM服务不作为物理电路存在。它们总是携带在适当的物理连接电路（AC）中，并且提供它们的仿真的PE总是包括本机服务处理块（NSP），通常称为成帧器。因此，为这些服务提供边到边仿真的PE设备的体系结构包括成帧器和转发器块。
In case of NxDS0 services (the only type of structured services considered in this document), the AC is either an E1 or a T1 trunk, and bundles of NxDS0 are cut out of it using one of the framing methods described in [G.704].
对于NxDS0服务（本文件中考虑的唯一结构化服务类型），AC是E1或T1中继，NxDS0束使用[G.704]中描述的一种成帧方法从中切断。
In addition to detecting the FAS and imposing associated structure on the "trunk" AC, E1, and T1, framers commonly support some additional functionality, including:
除了检测FAS并在“中继”AC、E1和T1上施加相关结构外，成帧器通常还支持一些附加功能，包括：
1. Detection of special states of the incoming AC (e.g., AIS, OOF, or RAI)
1. 检测输入AC的特殊状态（例如AIS、OOF或RAI）
2. Forcing special states (e.g., AIS and RAI) on the outgoing AC upon explicit request
2. 根据明确要求，强制输出AC上的特殊状态（如AIS和RAI）
3. Extraction and insertion of CE application signals that may accompany specific DS0 channel(s).
3. 提取和插入可能伴随特定DS0信道的CE应用信号。
The resulting PE architecture for NxDS0 services is shown in Figure B.1 below. In this diagram:
NxDS0服务的PE架构如下图B.1所示。在此图中：
1. In the PSN-bound direction:
1. 在PSN绑定方向：
a) The Framer:
a) 制宪者：
i) Detects frame alignment signal (FAS) and splits the incoming ACs into separate DS0 channels
i) 检测帧对齐信号（FAS）并将传入的ACs拆分为单独的DS0通道
ii) Detects special AC states
ii）检测特殊交流状态
iii) If necessary, extracts CE application signals accompanying each of the separate DS0 services
iii）如有必要，提取每个单独DS0服务附带的CE应用信号
b) The Forwarder:
b) 货代：
i) Creates one or more NxDS0 bundles
i) 创建一个或多个NxDS0捆绑包
ii) Sends the data received in each such bundle to the PSN-bound direction of a respective CESoPSN IWF instance
ii）将在每个这样的捆绑中接收的数据发送到各个CESoPSN IWF实例的PSN绑定方向
iii) If necessary, sends the current CE application state data of the DS0 services in the bundle to the PSN-bound direction of the respective CESoPSN IWF instance
iii）如有必要，将捆绑包中DS0服务的当前CE应用程序状态数据发送到相应CESoPSN IWF实例的PSN绑定方向
iv) If necessary, sends the AC state indications to the PSN-bound directions of all the CESoPSN instances associated with the given AC
iv）如有必要，向与给定AC相关联的所有CESoPSN实例的PSN绑定方向发送AC状态指示
c) Each PSN-bound PW IWF instance encapsulates the received data, application state signal, and the AC state into PW PDUs, and sends the resulting packets to the PSN
c) 每个绑定到PSN的PW IWF实例将接收到的数据、应用程序状态信号和AC状态封装到PW PDU中，并将生成的数据包发送到PSN
2. In the CE-bound direction:
2. 在CE绑定方向：
a) Each CE-bound instance of the CESoPSN IWF receives the PW PDUs from the PSN, extracts the TDM data, AC state, and CE application state signals, and sends them
a) CESoPSN IWF的每个CE绑定实例从PSN接收PW PDU，提取TDM数据、AC状态和CE应用状态信号，并发送它们
b) The Forwarder sends the TDM data, application state signals and, if necessary, a single command representing the desired AC state, to the Framer
b) 转发器向成帧器发送TDM数据、应用程序状态信号以及（如有必要）表示所需AC状态的单个命令
c) The Framer accepts all the data of one or more NxDS0 bundles possibly accompanied by the associated CE application state, and commands referring to the desired AC state, and generates a single AC accordingly with correct FAS.
c) 编帧器接受一个或多个NxDS0捆绑包的所有数据，这些数据可能伴随着相关的CE应用程序状态，以及引用所需AC状态的命令，并相应地生成具有正确FAS的单个AC。
Notes: This model is asymmetric:
注：该模型是不对称的：
o AC state indication can be forwarded from the framer to multiple instances of the CESoPSN IWF
o AC状态指示可以从成帧器转发到CESoPSN IWF的多个实例
o No more than one CESoPSN IWF instance should forward AC state-affecting commands to the framer.
o 不能有多个CESoPSN IWF实例将影响AC状态的命令转发给编帧器。
+------------------------------------------+
| PE Device |
+------------------------------------------+
| | Forwarder | |
| |---------------------| |
| | | |
| +<-- AC State---->- | |
| | | | |
| | | | |
E1 or T1 | | | | |
AC | | | | |
<=======>| |-----------------+---|--------------|
| | | | At most, one |
| | |-->+ PW IWF |
| | | instance |
... | +<---NxDS0 TDM Data-->+ imposing | PW Instance
| F | | state X<===========>
| +<---CE App State --->+ on the |
E1 or T1 | R | | outgoing AC |
AC | +<--AC Command -------+ |
<=======>o A |---------------------|--------------|
| | ... | ... | ...
| M |-----------------+---|--------------|
| | | | Zero, one or |
| E | |-->+ more PW IWF |
| | | instances |
| R +<---NxDS0 TDM Data-->+ that do not | PW Instance
| | | impose state X<===========>
| +<---CE App State --->+ on the out- |
| | | going AC |
+------------------------------------------+
+------------------------------------------+
| PE Device |
+------------------------------------------+
| | Forwarder | |
| |---------------------| |
| | | |
| +<-- AC State---->- | |
| | | | |
| | | | |
E1 or T1 | | | | |
AC | | | | |
<=======>| |-----------------+---|--------------|
| | | | At most, one |
| | |-->+ PW IWF |
| | | instance |
... | +<---NxDS0 TDM Data-->+ imposing | PW Instance
| F | | state X<===========>
| +<---CE App State --->+ on the |
E1 or T1 | R | | outgoing AC |
AC | +<--AC Command -------+ |
<=======>o A |---------------------|--------------|
| | ... | ... | ...
| M |-----------------+---|--------------|
| | | | Zero, one or |
| E | |-->+ more PW IWF |
| | | instances |
| R +<---NxDS0 TDM Data-->+ that do not | PW Instance
| | | impose state X<===========>
| +<---CE App State --->+ on the out- |
| | | going AC |
+------------------------------------------+
Figure B.1. Reference PE Architecture for NxDS0 Services
图B.1。NxDS0服务的参考PE体系结构
Previous versions of this specification defined a CESoPSN PW encapsulation over L2TPv3, which differs from one described in Section 4.1 and Figure 1c. In these versions, the RTP header, if used, precedes the CESoPSN control word.
本规范以前的版本定义了L2TPv3上的CESoPSN PW封装，这与第4.1节和图1c中描述的不同。在这些版本中，RTP头（如果使用）位于CESoPSN控制字之前。
Existing implementations of the old encapsulation mode MUST be distinguished from the encapsulations conforming to this specification via the CESoPSN PW setup.
旧封装模式的现有实现必须通过CESoPSN PW设置与符合本规范的封装进行区分。
Authors' Addresses
作者地址
Alexander ("Sasha") Vainshtein Axerra Networks 24 Raoul Wallenberg St., Tel Aviv 69719, Israel EMail: sasha@axerra.com, vainshtein.alex@gmail.com
Alexander（“Sasha”）Vainstein Axerra Networks 24 Raoul Wallenberg St.，特拉维夫69719，以色列电子邮件：sasha@axerra.com，Vainstein。alex@gmail.com
Israel Sasson Axerra Networks 24 Raoul Wallenberg St., Tel Aviv 69719, Israel EMail: israel@axerra.com
以色列Sasson Axera Networks 24 Raoul Wallenberg St.，特拉维夫69719，以色列电子邮件：israel@axerra.com
Eduard Metz KPN Regulusweg 1 2316 AC The Hague Netherlands EMail: eduard.metz@kpn.com
Eduard Metz KPN Regulusweg 1 2316 AC海牙荷兰电子邮件：Eduard。metz@kpn.com
Tim Frost Symmetricom, Inc. Tamerton Road Roborough, Plymouth PL6 7BQ, UK EMail: tfrost@symmetricom.com
Tim Frost Symmetricom，Inc.英国普利茅斯罗伯勒塔默顿路6号，邮编7BQ电子邮件：tfrost@symmetricom.com
Prayson Pate Overture Networks 507 Airport Boulevard Building 111 Morrisville, North Carolina 27560 USA EMail: prayson.pate@overturenetworks.com
Prayson Pate Overture Networks美国北卡罗来纳州莫里斯维尔111号机场大道507号楼，邮编27560电子邮件：Prayson。pate@overturenetworks.com
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