Network Working Group A. Malis
Request for Comments: 4816 Verizon
Category: Standards Track L. Martini
Cisco Systems
J. Brayley
ECI Telecom
T. Walsh
Juniper Networks
February 2007
Network Working Group A. Malis
Request for Comments: 4816 Verizon
Category: Standards Track L. Martini
Cisco Systems
J. Brayley
ECI Telecom
T. Walsh
Juniper Networks
February 2007
Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service
伪线仿真边缘到边缘（PWE3）异步传输模式（ATM）透明信元传输服务
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
The document describes a transparent cell transport service that makes use of the "N-to-one" cell relay mode for Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer-Mode (ATM) cell encapsulation.
本文档描述了一种透明信元传输服务，该服务利用“N对1”信元中继模式进行伪线仿真边缘到边缘（PWE3）异步传输模式（ATM）信元封装。
This transparent cell transport service allows migration of ATM services to a PSN without having to provision the ATM subscriber or customer edge (CE) devices. The ATM CEs will view the ATM transparent cell transport service as if they were directly connected via a Time Division Multiplexer (TDM) leased line. This service is most likely to be used as an internal function in an ATM service provider's network as a way to connect existing ATM switches via a higher-speed PSN, or to provide ATM "backhaul" services for remote access to existing ATM networks.
这种透明信元传输服务允许将ATM服务迁移到PSN，而无需提供ATM订户或客户边缘（CE）设备。ATM CEs将查看ATM透明信元传输服务，就像它们通过时分多路复用器（TDM）租用线路直接连接一样。该服务最有可能用作ATM服务提供商网络中的内部功能，作为通过高速PSN连接现有ATM交换机的一种方式，或为远程访问现有ATM网络提供ATM“回程”服务。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[1]中所述进行解释。
The transparent port service is a natural application of the "N-to-one" Virtual Circuit Connection (VCC) cell transport mode for PWE3 ATM encapsulation described in [2], and MUST be used with pseudowires of type 0x0003, "ATM transparent cell transport" [4].
透明端口服务是[2]中描述的PWE3 ATM封装的“N对1”虚拟电路连接（VCC）信元传输模式的自然应用，必须与0x0003类型的伪线“ATM透明信元传输”[4]一起使用。
The ATM transparent port service emulates connectivity between two remote ATM ports. This service is useful when one desires to connect two CEs without processing or switching at the Virtual Path Connection (VPC) or VCC layer. The ingress PE discards any idle/unassigned cells received from the ingress ATM port, and maps all other received cells to a single pseudowire.
ATM透明端口服务模拟两个远程ATM端口之间的连接。当希望连接两个CE而不在虚拟路径连接（VPC）或VCC层进行处理或切换时，此服务非常有用。入口PE丢弃从入口ATM端口接收的任何空闲/未分配的信元，并将所有其他接收的信元映射到单个伪线。
The egress PE does not change the Virtual Path Identifier (VPI), Virtual Circuit Identifier (VCI), Payload Type Identifier (PTI), or Cell Loss Priority (CLP) bits when it sends these cells on the egress ATM port. Therefore, the transparent port service appears to emulate an ATM transmission convergence layer connection between two ports. However, since the ingress PE discards idle/unassigned cells, this service benefits from statistical multiplexing bandwidth savings.
出口PE在出口ATM端口上发送这些信元时，不会更改虚拟路径标识符（VPI）、虚拟电路标识符（VCI）、有效负载类型标识符（PTI）或信元丢失优先级（CLP）位。因此，透明端口服务似乎模拟了两个端口之间的ATM传输汇聚层连接。然而，由于入口PE丢弃空闲/未分配的小区，因此该服务受益于统计复用带宽节约。
In accordance with [2], cell concatenation MAY be used for transparent cell-relay transport in order to save the PSN bandwidth. If used, it MUST be agreed between the ingress and egress PEs. In particular, if the Pseudo Wire has been set up using the PWE3 control protocol [3], the ingress PE MUST NOT exceed the value of the "Maximum Number of concatenated ATM cells" Pseudowire Interface Parameter Sub-TLV (Interface Parameter ID = 0x02 [4]) received in the Label Mapping message for the Pseudo Wire, and MUST NOT use cell concatenation if this parameter has been omitted by the egress PE.
根据[2]，小区级联可用于透明小区中继传输，以节省PSN带宽。如果使用，必须在入口和出口PEs之间达成一致。特别是，如果已经使用PWE3控制协议[3]设置了伪线，则入口PE不得超过伪线的标签映射消息中接收到的“连接的ATM信元的最大数量”伪线接口参数Sub TLV（接口参数ID=0x02[4]）的值，如果出口PE省略了此参数，则不能使用单元连接。
ATM Operations and Management (OAM) cells MUST be transported transparently, and the PEs do not act on them. If the PEs detect a PSN or pseudowire failure between them, they do not generate any OAM cells, but rather bring down the ATM interfaces to the CEs (e.g., generating LOS on the ATM port), just as if it were a transmission layer failure.
ATM操作和管理（OAM）信元的传输必须透明，PEs不会对其进行操作。如果PEs检测到它们之间的PSN或伪线故障，它们不会生成任何OAM信元，而是将ATM接口带到CEs（例如，在ATM端口上生成LOS），就像它是传输层故障一样。
Similarly, ATM Integrated Local Management Interface (ILMI) signaling from the CEs, if any, MUST be transported transparently, and the PEs do not act on it. However, the PEs must act on physical interface failure by either withdrawing the PW labels or by using pseudowire status signaling to indicate the interface failure. The procedures for both alternatives are described in [3].
类似地，来自CEs的ATM集成本地管理接口（ILMI）信令（如果有的话）必须透明传输，PEs不会对其进行操作。然而，PEs必须通过撤销PW标签或使用伪线状态信号指示接口故障来应对物理接口故障。[3]中描述了两种备选方案的程序。
This document does not introduce any new security considerations beyond those in [2] and [3]. This document defines an application that utilizes the encapsulation specified in [2], and does not specify 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 application specified herein. Note that the security of the transported ATM service will only be as good as the security of the PSN. This level of security might be less rigorous than a native ATM service.
除了[2]和[3]中的安全注意事项外，本文件未引入任何新的安全注意事项。本文档定义了一个应用程序，该应用程序使用了[2]中规定的封装，但未指定用于在PSN上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，但这些问题不受本文指定的应用程序的影响。请注意，传输的ATM服务的安全性仅与PSN的安全性相同。这种级别的安全性可能不如本机ATM服务严格。
Since this document discusses an application of the "N-to-one" VCC cell transport mode for PWE3 ATM encapsulation described in [2], the congestion control considerations are identical to those discussed in section 15 of [2]. The PWE3 Working Group is also undertaking additional work on ATM-related congestion issues, and implementers should anticipate that an RFC will be published describing additional congestion control techniques that should be applied to ATM emulation over pseudowires.
由于本文件讨论了[2]中描述的用于PWE3 ATM封装的“N对1”VCC信元传输模式的应用，因此拥塞控制注意事项与[2]第15节中讨论的相同。PWE3工作组也在进行与ATM相关的拥塞问题的额外工作，实施者应预计将发布RFC，描述应应用于伪线ATM仿真的额外拥塞控制技术。
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[1] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[2] Martini, L., Jayakumar, J., Bocci, M., El-Aawar, N., Brayley, J., and G. Koleyni, "Encapsulation Methods for Transport of Asynchronous Transfer Mode (ATM) over MPLS Networks", RFC 4717, December 2006.
[2] Martini，L.，Jayakumar，J.，Bocci，M.，El Aawar，N.，Brayley，J.，和G.Koleyni，“MPLS网络上异步传输模式（ATM）传输的封装方法”，RFC 47172006年12月。
[3] 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.
[3] 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。
[4] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[4] Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，2006年4月。
Acknowledgments
致谢
The authors would like to thank the members of the PWE3 working group for their assistance on this document, and Sasha Vainshtein of Axerra in particular for his comments and suggestions.
作者要感谢PWE3工作组成员对本文件的帮助，特别是Axerra的Sasha Vainstein的评论和建议。
Author's Addresses
作者地址
Andrew G. Malis Verizon Communications 40 Sylvan Road Waltham, MA
马萨诸塞州沃尔瑟姆Sylvan路40号安德鲁·G·马里斯威瑞森通信公司
EMail: andrew.g.malis@verizon.com
EMail: andrew.g.malis@verizon.com
Luca Martini Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112
卢卡·马蒂尼·思科系统公司，地址：科罗拉多州恩格尔伍德东尼科尔斯大道9155号400室，邮编：80112
EMail: lmartini@cisco.com
EMail: lmartini@cisco.com
Jeremy Brayley ECI Telecom Omega Corporate Center 1300 Omega Drive Pittsburgh, PA 15205
Jeremy Brayley ECI电信欧米茄公司中心宾夕法尼亚州匹兹堡欧米茄大道1300号，邮编15205
EMail: jeremy.brayley@ecitele.com
EMail: jeremy.brayley@ecitele.com
Tom Walsh Juniper Networks 1194 N Mathilda Ave Sunnyvale, CA 94089
汤姆·沃尔什·朱尼珀网络公司，加利福尼亚州桑尼维尔市马蒂尔达大道北1194号，邮编94089
EMail: twalsh@juniper.net
EMail: twalsh@juniper.net
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