Internet Engineering Task Force (IETF) A. Sajassi
Request for Comments: 7080 S. Salam
Category: Informational Cisco
ISSN: 2070-1721 N. Bitar
Verizon
F. Balus
Nuage Networks
December 2013
Internet Engineering Task Force (IETF) A. Sajassi
Request for Comments: 7080 S. Salam
Category: Informational Cisco
ISSN: 2070-1721 N. Bitar
Verizon
F. Balus
Nuage Networks
December 2013
Virtual Private LAN Service (VPLS) Interoperability with Provider Backbone Bridges
虚拟专用LAN服务（VPLS）与提供商主干网桥的互操作性
Abstract
摘要
The scalability of Hierarchical Virtual Private LAN Service (H-VPLS) with Ethernet access networks (RFC 4762) can be improved by incorporating Provider Backbone Bridge functionality in the VPLS access. Provider Backbone Bridging has been standardized as IEEE 802.1ah-2008. It aims to improve the scalability of Media Access Control (MAC) addresses and service instances in Provider Ethernet networks. This document describes different interoperability scenarios where Provider Backbone Bridge functionality is used in H-VPLS with Ethernet or MPLS access network to attain better scalability in terms of number of customer MAC addresses and number of service instances. The document also describes the scenarios and the mechanisms for incorporating Provider Backbone Bridge functionality within H-VPLS with existing Ethernet access and interoperability among them. Furthermore, the document discusses the migration mechanisms and scenarios by which Provider Backbone Bridge functionality can be incorporated into H-VPLS with existing MPLS access.
通过在VPLS接入中加入提供商主干网桥功能，可以提高具有以太网接入网络（RFC 4762）的分层虚拟专用LAN服务（H-VPLS）的可扩展性。提供商主干桥接已标准化为IEEE 802.1ah-2008。它旨在提高提供商以太网中媒体访问控制（MAC）地址和服务实例的可伸缩性。本文档描述了不同的互操作性场景，其中在具有以太网或MPLS接入网络的H-VPLS中使用提供商主干网桥功能，以在客户MAC地址数量和服务实例数量方面实现更好的可伸缩性。本文档还描述了将提供商主干网桥功能与H-VPLS中的现有以太网接入和互操作性结合在一起的场景和机制。此外，本文档还讨论了迁移机制和场景，通过这些迁移机制和场景，提供商主干网桥功能可以结合到具有现有MPLS访问的H-VPL中。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7080.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc7080.
Copyright Notice
版权公告
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2013 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Applicability ...................................................5
4. H-VPLS with Homogeneous PBBN Access .............................6
4.1. Service Interfaces and Interworking Options ................8
4.2. H-VPLS with PBBN Access: Type I Service Interface .........10
4.3. H-VPLS with PBBN Access: Type II Service Interface ........11
5. H-VPLS with Mixed PBBN Access and PBN Access ...................14
5.1. H-VPLS with Mixed PBBN and PBN Access: Modified PBN PE ....15
5.2. H-VPLS with Mixed PBBN and PBN Access: Regular PBN PE .....16
6. H-VPLS with MPLS Access ........................................17
6.1. H-VPLS with MPLS Access: PBB U-PE .........................17
6.2. H-VPLS with MPLS Access: PBB N-PE .........................19
7. H-VPLS with MPLS Access: PBB Migration Scenarios ...............21
7.1. 802.1ad Service Frames over VPLS Core .....................21
7.2. PBB Service Frames over VPLS Core .........................22
7.3. Mixed 802.1ad and PBB over VPLS Core ......................23
8. Acknowledgments ................................................24
9. Security Considerations ........................................24
10. References ....................................................24
10.1. Normative References .....................................24
10.2. Informative References ...................................25
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Applicability ...................................................5
4. H-VPLS with Homogeneous PBBN Access .............................6
4.1. Service Interfaces and Interworking Options ................8
4.2. H-VPLS with PBBN Access: Type I Service Interface .........10
4.3. H-VPLS with PBBN Access: Type II Service Interface ........11
5. H-VPLS with Mixed PBBN Access and PBN Access ...................14
5.1. H-VPLS with Mixed PBBN and PBN Access: Modified PBN PE ....15
5.2. H-VPLS with Mixed PBBN and PBN Access: Regular PBN PE .....16
6. H-VPLS with MPLS Access ........................................17
6.1. H-VPLS with MPLS Access: PBB U-PE .........................17
6.2. H-VPLS with MPLS Access: PBB N-PE .........................19
7. H-VPLS with MPLS Access: PBB Migration Scenarios ...............21
7.1. 802.1ad Service Frames over VPLS Core .....................21
7.2. PBB Service Frames over VPLS Core .........................22
7.3. Mixed 802.1ad and PBB over VPLS Core ......................23
8. Acknowledgments ................................................24
9. Security Considerations ........................................24
10. References ....................................................24
10.1. Normative References .....................................24
10.2. Informative References ...................................25
The scalability of Hierarchical Virtual Private LAN Service (H-VPLS) with Ethernet access networks [RFC4762] can be improved by incorporating Provider Backbone Bridge (PBB) functionality in the VPLS access. Provider Backbone Bridging has been standardized as IEEE 802.1ah-2008 [802.1ah], which is an amendment to IEEE 802.1Q to improve the scalability of Media Access Control (MAC) addresses and service instances in Provider Ethernet networks. This document describes interoperability scenarios where IEEE 802.1ah functionality is used in H-VPLS with Ethernet or MPLS access network to attain better scalability in terms of the number of customer MAC addresses and the number of services.
通过在VPLS接入中加入提供商主干网桥（PBB）功能，可以提高具有以太网接入网络[RFC4762]的分层虚拟专用LAN服务（H-VPLS）的可扩展性。提供商主干网桥已标准化为IEEE 802.1ah-2008[802.1ah]，这是对IEEE 802.1Q的修订，旨在提高提供商以太网中媒体访问控制（MAC）地址和服务实例的可扩展性。本文档描述了互操作性场景，其中，IEEE 802.1ah功能用于具有以太网或MPLS接入网络的H-VPLS，以在客户MAC地址数量和服务数量方面实现更好的可伸缩性。
This document also covers the interoperability scenarios for deploying H-VPLS with Provider Backbone Bridging Ethernet access when other types of access networks are deployed, including existing 802.1ad Ethernet and MPLS access in either single or multiple service domains. Furthermore, the document explores the scenarios by which an operator can gradually migrate an existing H-VPLS network to Provider Backbone Bridging over VPLS.
本文档还介绍了在部署其他类型的接入网络（包括单个或多个服务域中的现有802.1ad以太网和MPLS接入）时，使用提供商主干桥接以太网接入部署H-VPL的互操作性场景。此外，本文件还探讨了运营商可以通过VPLS逐步将现有的H-VPLS网络迁移到提供商主干网桥的场景。
Section 2 gives a quick terminology reference and Section 3 highlights the applicability of Provider Backbone Bridging interoperation with VPLS. Section 4 describes H-VPLS with homogeneous Provider Backbone Bridge Access Network. Section 5 discusses H-VPLS with mixed 802.1ah/802.1ad access. Section 6 focuses on Provider Backbone Bridging in H-VPLS with MPLS Access Network including PBB function on U-PE and on N-PE variants. Finally, Section 7 describes gradual migration scenarios from existing H-VPLS to Provider Backbone Bridging over H-VPLS.
第2节提供了一个快速的术语参考，第3节强调了提供商主干网桥接与VPL互操作的适用性。第4节描述了具有同构提供商骨干网桥接入网络的H-VPL。第5节讨论了混合802.1ah/802.1ad访问的H-VPL。第6节重点介绍了H-VPLS和MPLS接入网络中的提供商主干桥接，包括U-PE和N-PE变体上的PBB功能。最后，第7节描述了通过H-VPL从现有H-VPL到提供商主干桥接的逐步迁移场景。
802.1ad: IEEE specification for "QinQ" encapsulation and bridging of Ethernet frames.
802.1ad:IEEE以太网帧“QinQ”封装和桥接规范。
802.1ah: IEEE specification for "MAC tunneling" encapsulation and bridging of frames across a Provider Backbone Bridged Network (PBBN).
802.1ah:IEEE规范，用于跨提供商主干桥接网络（PBBN）的帧“MAC隧道”封装和桥接。
B-BEB: A backbone edge bridge positioned at the edge of a PBBN. It contains a B-component that supports bridging in the provider backbone based on B-MAC and B-TAG information.
B-BEB：位于PBBN边缘的主干边缘网桥。它包含一个B组件，支持基于B-MAC和B-TAG信息在提供商主干网中桥接。
B-MAC: The backbone source or destination MAC address fields defined in the 802.1ah provider MAC encapsulation header.
B-MAC：在802.1ah提供商MAC封装报头中定义的主干源或目标MAC地址字段。
BCB: A backbone core bridge running in the core of a provider backbone bridged network. It bridges frames based on B-TAG information just as an 802.1ad provider bridge will bridge frames based on a Service VLAN (S-VLAN) identifier.
BCB：在提供商主干桥接网络的核心中运行的主干核心桥接器。它基于B标签信息桥接帧，就像802.1ad提供商桥接器将基于服务VLAN（S-VLAN）标识符桥接帧一样。
B-Component: The backbone component of a Provider Backbone edge bridge as defined in [802.1ah].
B-Component:802.1ah中定义的提供商主干边缘网桥的主干组件。
BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It can contain an I-component, B-component, or both.
BEB：位于提供商主干桥接网络边缘的主干边缘桥接器。它可以包含I组件、B组件或两者。
B-MACs: Backbone MAC addresses -- outer MAC addresses of a PBB-encapsulated frame.
B-MAC：主干MAC地址——PBB封装帧的外部MAC地址。
B-TAG: A field defined in the 802.1ah provider MAC encapsulation header that conveys the backbone VLAN identifier information. The format of the B-TAG field is the same as that of an 802.1ad S-TAG field.
B标签：在802.1ah提供商MAC封装报头中定义的字段，用于传输主干VLAN标识符信息。B标签字段的格式与802.1ad S标签字段的格式相同。
B-Tagged Service Interface: This is the interface between a BEB and BCB in a PBB network. Frames passed through this interface contain a B-TAG field.
B标签服务接口：这是PBB网络中BEB和BCB之间的接口。通过此接口的帧包含一个B标记字段。
B-VID: This is the specific VLAN identifier carried inside a B-TAG
B-VID：这是B-TAG中携带的特定VLAN标识符
C-MACs: Customer MAC addresses are the inner MAC addresses of a PBB-encapsulated frame.
C-MAC：客户MAC地址是PBB封装帧的内部MAC地址。
H-VPLS: Hierarchical Virtual Private LAN Service.
H-VPLS：分层虚拟专用LAN服务。
I-component: A bridging component contained in a backbone edge bridge that bridges in the customer space (customer MAC addresses, S-VLAN).
I-component：包含在主干边缘网桥中的桥接组件，桥接客户空间（客户MAC地址，S-VLAN）。
IB-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains an I-component for bridging in the customer space (customer MAC addresses, S-VLAN IDs) and a B-component for bridging the provider's backbone space (B-MAC, B-TAG).
IB-BEB：位于提供商主干桥接网络边缘的主干边缘网桥。它包含一个用于在客户空间桥接的I组件（客户MAC地址、S-VLAN ID）和一个用于桥接提供商主干空间的B组件（B-MAC、B-TAG）。
I-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains an I-component for bridging in the customer space (customer MAC addresses, S-VLAN IDs).
I-BEB：位于提供商主干桥接网络边缘的主干边缘桥接器。它包含一个用于在客户空间桥接的I组件（客户MAC地址、S-VLAN id）。
I-SID: The 24-bit service instance field carried inside the I-TAG. I-SID defines the service instance that the frame should be "mapped to".
I-SID：I-TAG中携带的24位服务实例字段。I-SID定义帧应“映射到”的服务实例。
I-TAG: A field defined in the 802.1ah provider MAC encapsulation header that conveys the service instance information (I-SID) associated with the frame.
I-TAG：在802.1ah提供商MAC封装报头中定义的字段，用于传输与帧相关的服务实例信息（I-SID）。
I-Tagged Service Interface: This is the interface defined between the I-component and B-component inside an IB-BEB or between two B-BEBs. Frames passed through this interface contain an I-TAG field.
I标记服务接口：这是在IB-BEB内部的I组件和B组件之间或两个B-BEB之间定义的接口。通过此接口的帧包含一个I-TAG字段。
N-PE: Network-facing Provider Edge
N-PE：面向网络的提供商边缘
PBB: Provider Backbone Bridge
提供商主干网桥
PBBN: Provider Backbone Bridged Network
PBBN：提供商主干桥接网络
PBN: Provider Bridged Network. A network that employs 802.1ad (QinQ) technology.
PBN：提供商桥接网络。采用802.1ad（QinQ）技术的网络。
S-TAG: A field defined in the 802.1ad QinQ encapsulation header that conveys the Service VLAN (S-VLAN) identifier information.
S-TAG：在802.1ad QinQ封装头中定义的字段，用于传输服务VLAN（S-VLAN）标识符信息。
S-Tagged Service Interface: This the interface defined between the customer (CE) and the I-BEB or IB-BEB components. Frames passed through this interface contain an S-TAG field.
S标记服务接口：这是客户（CE）和I-BEB或IB-BEB组件之间定义的接口。通过此接口的帧包含一个S标记字段。
S-VLAN: The specific Service VLAN identifier carried inside an S-TAG
S-VLAN：S-TAG中携带的特定服务VLAN标识符
U-PE: User-facing Provider Edge
U-PE：面向用户的提供者边缘
VPLS: Virtual Private LAN Service
虚拟专用局域网服务
[RFC4762] describes a two-tier hierarchical solution for VPLS for the purpose of improved pseudowire (PW) scalability. This improvement is achieved by reducing the number of PE devices connected in a full-mesh topology through connecting CE devices via the lower-tier access network, which in turn is connected to the top-tier core network. [RFC4762] describes two types of H-VPLS network topologies -- one with an MPLS access network and another with an IEEE 802.1ad (QinQ) Ethernet access network. In both types of H-VPLS, the learning and forwarding of MAC addresses is based on customer MAC addresses (C-MACs), which poses scalability issues as the number of VPLS instances (and thus C-MACs) increases. Furthermore, since a set of PWs is maintained on a per customer service instance basis, the number of PWs required at N-PE devices is proportional to the number of customer service instances multiplied by the number of N-PE devices in the full-mesh set. This can result in scalability issues
[RFC4762]描述了一种用于VPLS的两层分层解决方案，以提高伪线（PW）的可伸缩性。这一改进是通过减少全网状拓扑中连接的PE设备数量来实现的，通过低层接入网络连接CE设备，而低层接入网络又连接到顶层核心网络。[RFC4762]描述了两种类型的H-VPLS网络拓扑——一种具有MPLS接入网络，另一种具有IEEE 802.1ad（QinQ）以太网接入网络。在这两种类型的H-VPL中，MAC地址的学习和转发都基于客户MAC地址（C-MAC），随着VPL实例（以及C-MAC）数量的增加，这会带来可伸缩性问题。此外，由于在每个客户服务实例的基础上维护一组PW，因此N-PE设备所需的PW数量与客户服务实例数量乘以全网格集中N-PE设备数量成正比。这可能会导致可伸缩性问题
(in terms of PW manageability and troubleshooting) as the number of customer service instances grows.
（就PW可管理性和故障排除而言）随着客户服务实例数量的增长。
In addition to the above, H-VPLS with an 802.1ad Ethernet access network has another scalability issue in terms of the maximum number of service instances that can be supported in the access network as described in [RFC4762]. Since the number of provider VLANs (S-VLANs) is limited to 4094 and each S-VLAN represents a service instance in an 802.1ad network, then the maximum number of service instances that can be supported is 4094. These issues are highlighted in [RFC6246].
除上述内容外，具有802.1ad以太网接入网络的H-VPLS在接入网络中可支持的最大服务实例数量方面存在另一个可伸缩性问题，如[RFC4762]所述。由于提供商VLAN（S-VLAN）的数量限制为4094，并且每个S-VLAN代表802.1ad网络中的一个服务实例，因此可以支持的最大服务实例数量为4094。[RFC6246]中突出了这些问题。
This document describes how IEEE 802.1ah (aka Provider Backbone Bridges) can be integrated with H-VPLS to address these scalability issues. In the case of H-VPLS with 802.1ah Ethernet access, the solution results in better scalability in terms of both number of service instances and number of C-MACs in the Ethernet access network and the VPLS core network, as well as number of PWs in VPLS core network. And in the case of H-VPLS with MPLS access, Provider Backbone Bridging functionality can be used at the U-PE or N-PE, which results in reduction of customer MAC addresses and the number of PWs in the VPLS core network.
本文档描述了如何将IEEE 802.1ah（又名提供商主干网桥）与H-VPLS集成，以解决这些可伸缩性问题。对于具有802.1ah以太网接入的H-VPLS，该解决方案在以太网接入网络和VPLS核心网络中的服务实例数量和C-MAC数量以及VPLS核心网络中的PW数量方面具有更好的可扩展性。并且，在具有MPLS接入的H-VPLS的情况下，可以在U-PE或N-PE处使用提供商主干桥接功能，这会减少VPLS核心网络中的客户MAC地址和PW数量。
The interoperability scenarios depicted in this document fall into the following two categories:
本文档中描述的互操作性场景分为以下两类：
- Scenarios in which Provider Backbone Bridging seamlessly works with current VPLS implementations (e.g., Section 4.2).
- 提供商主干桥接与当前VPLS实现无缝工作的场景（例如，第4.2节）。
- Scenarios in which VPLS-PE implementations need to be upgraded in order to work with Provider Backbone Bridging (e.g., Sections 4.3 and 5.1).
- 需要升级VPLS-PE实施以使用提供商主干桥接的场景（例如，第4.3节和第5.1节）。
PBBN access offers MAC-address-table scalability for H-VPLS PE nodes. This is due to the MAC tunneling encapsulation scheme of PBB, which only exposes the provider's own MAC addresses to PE nodes (B-MACs of Provider's PBB-capable devices in the access network), as opposed to customers' MAC addresses in conventional H-VPLS with MPLS or 802.1ad access.
PBBN访问为H-VPLS PE节点提供MAC地址表可扩展性。这是由于PBB的MAC隧道封装方案，该方案仅将提供商自己的MAC地址公开给PE节点（接入网络中提供商支持PBB的设备的B-MAC），而不是使用MPLS或802.1ad接入的传统H-VPL中客户的MAC地址。
PBBN access also offers service-instance scalability when compared to H-VPLS with 802.1Q/802.1ad access networks. This is due to the new 24-bit service identifier (I-SID) used in PBB encapsulation, which allows up to 16M services per PBB access network, compared to 4094 services per 802.1Q/802.1ad access network.
与具有802.1Q/802.1ad接入网络的H-VPLS相比，PBBN接入还提供了服务实例可扩展性。这是由于PBB封装中使用了新的24位服务标识符（I-SID），它允许每个PBB接入网络最多提供16M服务，而每个802.1Q/802.1ad接入网络最多提供4094个服务。
Another important advantage of PBBN access is that it offers clear separation between the service layer (represented by I-SID) and the network layer (represented by B-VLAN). B-VLANs segregate a PBB access network into different broadcast domains and possibly unique spanning-tree topologies, with each domain being able to carry multiple services (i.e., I-SIDs). In 802.1ad access networks, the network and service layers are the same (represented by S-VLAN).
PBBN访问的另一个重要优点是，它在服务层（由I-SID表示）和网络层（由B-VLAN表示）之间提供了清晰的分离。B-VLAN将PBB接入网络划分为不同的广播域和可能唯一的生成树拓扑，每个域能够承载多个服务（即，i-SID）。在802.1ad接入网络中，网络和服务层是相同的（由S-VLAN表示）。
This separation allows the provider to manage and optimize the PBB access network topology independent of the number of service instances that are supported.
这种分离允许提供商独立于所支持的服务实例的数量来管理和优化PBB接入网络拓扑。
In this section and those following, we look into different flavors of H-VPLS with PBBN access. This section discusses the case in which H-VPLS is deployed with homogeneous PBBN access. Section 5 describes the case in which at least one of the access networks has PBN access (QinQ/802.1ad) while the others are PBBNs.
在本节和接下来的部分中，我们将研究具有PBBN访问的不同类型的H-VPL。本节讨论H-VPLS部署为同质PBBN接入的情况。第5节描述了至少一个接入网络具有PBN接入（QinQ/802.1ad），而其他接入网络是PBBN的情况。
On a macro scale, a network that employs H-VPLS with PBBN access can be represented as shown in Figure 1 below.
在宏观层面上，采用具有PBBN接入的H-VPL的网络可以表示为如下图1所示。
+--------------+
| |
+---------+ | IP/MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| | |VPLS| |VPLS| | |--| CE |
+----+ | PBBN |---| PE | | PE |--| PBBN | +----+
+----+ | 802.1ah | +----+ +----+ | 802.1ah | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
+--------------+
| |
+---------+ | IP/MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| | |VPLS| |VPLS| | |--| CE |
+----+ | PBBN |---| PE | | PE |--| PBBN | +----+
+----+ | 802.1ah | +----+ +----+ | 802.1ah | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 1: H-VPLS with PBBN Access
图1:PBBN接入的H-VPLS
In the context of PBBN and H-VPLS interoperability, "I-SID Domain" and "B-VLAN Domain" can be defined as follows:
在PBBN和H-VPLS互操作性的上下文中，“I-SID域”和“B-VLAN域”可定义如下：
- "I-SID Domain" refers to a network administrative boundary under which all the PBB BEBs and VPLS-PE devices use the same I-SID space. That is, the I-SID assignment is carried out by the same administration. This effectively means that a given service instance has the same I-SID designation on all devices within an I-SID Domain.
- “I-SID域”是指所有PBB BEB和VPLS-PE设备使用相同I-SID空间的网络管理边界。也就是说，I-SID分配由同一管理机构执行。这实际上意味着给定服务实例在I-SID域中的所有设备上具有相同的I-SID指定。
- "B-VLAN Domain" refers to a network administrative boundary under which all the PBB BEBs and VPLS-PE devices employ consistent I-SID to B-VLAN bundling. For example, the grouping of I-SIDs to B-VLANs is the same in that domain. Although the two B-VLANs in two PBBNs that represent the same group of I-SIDs do not need to
- “B-VLAN域”是指所有PBB BEB和VPLS-PE设备采用一致的I-SID到B-VLAN绑定的网络管理边界。例如，I-SID到B-VLAN的分组在该域中是相同的。虽然两个PBBN中代表同一组I-SID的两个B-VLAN不需要
use the same B-VID value, in practice, they often use the same value because once the I-SID grouping is made identical in two PBBNs. It is very easy to make the values of the corresponding B-VIDs identical also.
使用相同的B-VID值，实际上，它们通常使用相同的值，因为一旦两个PBBN中的I-SID分组相同。很容易使相应B-VID的值也相同。
Consequently, three different kinds of "Service Domains" are defined in the following manner:
因此，以下列方式定义了三种不同类型的“服务域”：
- Tightly Coupled Service Domain - Different PBBNs' access belonging to the same I-SID Domain and B-VLAN Domain. However, the network control protocols (e.g., xSTP) run independently in each PBBN access.
- 紧密耦合服务域-属于同一I-SID域和B-VLAN域的不同PBBN访问。然而，网络控制协议（例如xSTP）在每个PBBN接入中独立运行。
- Loosely Coupled Service Domain - Different PBBNs' access belonging to the same I-SID Domain. However, each PBBN access maintains its own independent B-VLAN Domain. Again, the network control protocols (e.g., xSTP) run independently in each PBBN access.
- 松耦合服务域-属于同一I-SID域的不同PBBN访问。但是，每个PBBN访问都维护自己独立的B-VLAN域。同样，网络控制协议（例如，xSTP）在每个PBBN接入中独立运行。
- Different Service Domain - In this case, each PBBN access maintains its own independent I-SID Domain and B-VLAN Domain, with independent network control protocols (e.g., xSTP) in each PBBN access.
- 不同的服务域-在这种情况下，每个PBBN访问维护其自己的独立I-SID域和B-VLAN域，在每个PBBN访问中使用独立的网络控制协议（如xSTP）。
In general, correct service connectivity spanning networks in a Tightly Coupled Service Domain can be achieved via B-VID mapping between the networks (often even without B-VID translation). However, correct service connectivity spanning networks in a Loosely Coupled Service Domain requires I-SID to B-VID remapping (i.e., unbundling and rebundling of I-SIDs into B-VIDs). Furthermore, service connectivity spanning networks in Different Service Domains requires both I-SID translation and I-SID to B-VID remapping.
通常，在紧密耦合的服务域中，跨网络的正确服务连接可以通过网络之间的B-VID映射实现（通常甚至没有B-VID转换）。然而，在松散耦合的服务域中跨网络的正确服务连接需要I-SID到B-VID的重新映射（即，I-SID到B-VID的解绑和重新绑定）。此外，跨不同服务域网络的服务连接需要I-SID转换和I-SID到B-VID的重新映射。
Customer devices will interface with PBBN edge bridges using existing Ethernet interfaces including IEEE 802.1Q and IEEE 802.1ad. At the PBBN edge, C-MAC frames are encapsulated in a PBB header that includes service provider source and destination MAC addresses (B-MACs) and are bridged up to the VPLS-PE. The PBB-encapsulated C-MAC frame is then injected into the VPLS backbone network, delivered to the remote VPLS-PE node(s), and switched onto the remote PBBN access. From there, the PBBN bridges the encapsulated frame to a PBBN edge bridge where the PBB header is removed and the customer frame is sent to the customer domain.
客户设备将使用现有以太网接口（包括IEEE 802.1Q和IEEE 802.1ad）与PBBN边缘网桥连接。在PBBN边缘，C-MAC帧封装在PBB报头中，该报头包括服务提供商源和目标MAC地址（B-MAC），并桥接到VPLS-PE。然后将PBB封装的C-MAC帧注入VPLS骨干网，传送到远程VPLS-PE节点，并切换到远程PBBN接入。从那里，PBBN将封装的帧桥接到PBBN边缘桥接器，其中PBB报头被移除，并且客户帧被发送到客户域。
Interoperating between PBBN devices and VPLS-PE nodes can leverage the BEB functions already defined in [802.1ah]. When I-SID visibility is required at the VPLS-PE nodes, a new service interface based on I-SID tag will need to be defined.
PBBN设备和VPLS-PE节点之间的互操作可以利用[802.1ah]中已经定义的BEB功能。当VPLS-PE节点需要I-SID可见性时，需要定义基于I-SID标记的新服务接口。
Moreover, by mapping a bridge domain (e.g., B-VLAN) to a VPLS instance, and bundling multiple end-customer service instances (represented by I-SID) over the same bridge domain, service providers will be able to significantly reduce the number of full-mesh PWs required in the core. In this case, I-SID visibility is not required on the VPLS-PE and the I-SID will serve as the means of multiplexing/de-multiplexing individual service instances in the PBBN over a bundle (e.g., B-VLAN).
此外，通过将网桥域（例如，B-VLAN）映射到VPLS实例，并在同一网桥域上捆绑多个终端客户服务实例（由I-SID表示），服务提供商将能够显著减少核心中所需的全网状PW的数量。在这种情况下，VPLS-PE上不需要I-SID可见性，I-SID将作为通过捆绑包（例如，B-VLAN）复用/解复用PBBN中单个服务实例的手段。
When I-SID visibility is expected across the service interface at the VPLS-PE, the VPLS-PE can be considered to offer service-level interworking between PBBN access and the IP/MPLS core. Similarly, when the PE is not expected to have visibility of the I-SID at the service interface, the VPLS-PE can be considered to offer network-level interworking between PBBN access and the MPLS core.
当在VPLS-PE的服务接口上预期I-SID可见性时，可以认为VPLS-PE提供PBBN接入和IP/MPLS核心之间的服务级别互通。类似地，当预期PE在服务接口处不具有I-SID的可见性时，可以认为VPLS-PE提供PBBN接入和MPLS核心之间的网络级互通。
A VPLS-PE is always part of the IP/MPLS core, and it may optionally participate in the control protocols (e.g., xSTP) of the access network. When connecting to a PBBN access, the VPLS-PE needs to support one of the following two types of service interfaces:
VPLS-PE始终是IP/MPLS核心的一部分，并且它可以选择性地参与接入网络的控制协议（例如xSTP）。当连接到PBBN接入时，VPLS-PE需要支持以下两种类型的服务接口之一：
- Type I: B-Tagged Service Interface with B-VID as Service Delimiter
- 类型I:B标记的服务接口，以B-VID作为服务分隔符
The PE connects to a Backbone Core Bridge (BCB) in the PBBN access. The handoff between the BCB and the PE is B-Tagged PBB-encapsulated frames. The PE is transparent to PBB encapsulations and treats these frames as 802.1ad frames since the B-VID EtherType is the same as the S-VID EtherType. The PE does not need to support PBB functionality. This corresponds to conventional VPLS-PEs' tagged service interface. When using Type I service interface, the PE needs to support either raw mode or tagged mode Ethernet PW. Type I service interface is described in detail in Section 4.2.
PE连接到PBBN接入中的主干核心网桥（BCB）。BCB和PE之间的切换是B标记的PBB封装帧。PE对PBB封装是透明的，并将这些帧视为802.1ad帧，因为B-VID以太网类型与S-VID以太网类型相同。PE不需要支持PBB功能。这与传统VPLS PEs的标记服务接口相对应。当使用I型服务接口时，PE需要支持原始模式或标记模式以太网PW。第4.2节详细描述了I类服务接口。
- Type II: I-Tagged Service Interface with I-SID as Service Delimiter
- 类型II：以I-SID作为服务分隔符的I标记服务接口
The PE connects to a B-BEB (backbone edge bridge with B-component) in the PBBN access. The PE itself also supports the B-BEB functionality of [802.1ah]. The handoff between the B-BEB in the PBBN access and the PE is an I-Tagged PBB-encapsulated frame. With Type II service
PE连接到PBBN接入中的B-BEB（带B组件的主干边缘网桥）。PE本身也支持[802.1ah]的B-BEB功能。PBBN接入中的B-BEB与PE之间的切换是I标记的PBB封装帧。第二类服务
interface, the PE supports the existing raw mode and tagged mode PW types. Type II service interface is described in detail in Section 4.3.
接口，PE支持现有的原始模式和标记模式PW类型。第4.3节详细描述了II类服务接口。
This is a B-Tagged service interface with B-VID as service delimiter on the VPLS-PE. It does not require any new functionality on the VPLS-PE. As shown in Figure 2, the PE is always part of the IP/MPLS core. The PE may also be part of the PBBN access (e.g., VPLS-PE on right side of Figure 2) by participating in network control protocols (e.g., xSTP) of the PBBN access.
这是一个带B标签的服务接口，在VPLS-PE上以B-VID作为服务分隔符。它不需要VPLS-PE上的任何新功能。如图2所示，PE始终是IP/MPLS核心的一部分。通过参与PBBN接入的网络控制协议（例如xSTP），PE也可以是PBBN接入的一部分（例如，图2右侧的VPLS-PE）。
PBBN Access IP/MPLS Core PBBN Access
+--------------+
+---------+ | | +---------------+
| | +----+ | | |
| +---+ |VPLS| +-+ | | +---+ |
| |BCB|---| PE |---|P| | | |BCB| |
| +---+ /+----+ /+-+ | | /+---+ |
|+---+ | / +----+ / +----+ / +---+|
+--+ ||IB-| +---+/ |VPLS|/ +-+ |VPLS|/ +---+ |IB-|| +--+
|CE|-||BEB|-|BCB|---| PE |---|P|--| PE |---|BCB|-|BEB|--|CE|
+--+ |+---+ +---+ ^ +----+ +-+ +----+ ^ +---+ +---+| +--+
| | | | | | | |
+---------+ | | | +--|------------+
| +--------------+ |
| |
Type I Type I
PBBN Access IP/MPLS Core PBBN Access
+--------------+
+---------+ | | +---------------+
| | +----+ | | |
| +---+ |VPLS| +-+ | | +---+ |
| |BCB|---| PE |---|P| | | |BCB| |
| +---+ /+----+ /+-+ | | /+---+ |
|+---+ | / +----+ / +----+ / +---+|
+--+ ||IB-| +---+/ |VPLS|/ +-+ |VPLS|/ +---+ |IB-|| +--+
|CE|-||BEB|-|BCB|---| PE |---|P|--| PE |---|BCB|-|BEB|--|CE|
+--+ |+---+ +---+ ^ +----+ +-+ +----+ ^ +---+ +---+| +--+
| | | | | | | |
+---------+ | | | +--|------------+
| +--------------+ |
| |
Type I Type I
Figure 2: H-VPLS with PBBN Access and Type I Service Interface
图2：具有PBBN接入和I型服务接口的H-VPLS
Type I service interface is applicable to networks with Tightly Coupled Service Domains, where both I-SID Domains and B-VLAN Domains are the same across all PBBN access networks.
I型服务接口适用于具有紧密耦合服务域的网络，其中I-SID域和B-VLAN域在所有PBBN接入网络中都是相同的。
The BCB and the VPLS-PE will exchange PBB-encapsulated frames that include source and destination B-MACs, a B-VID, and an I-SID. The service delimiter, from the perspective of the VPLS-PE, is the B-VID; in fact, this interface operates exactly as a current 802.1Q/ad interface into a VPLS-PE does today. With Type I service interface, the VPLS-PE can be considered to provide network-level interworking between PBBN and MPLS domains, since VPLS-PE does not have visibility of I-SIDs.
BCB和VPLS-PE将交换PBB封装的帧，其中包括源和目标B-MAC、B-VID和I-SID。从VPLS-PE的角度来看，服务分隔符是B-VID；事实上，该接口的工作原理与当前VPLS-PE中的802.1Q/ad接口完全相同。对于I型服务接口，VPLS-PE可被视为提供PBBN和MPLS域之间的网络级互通，因为VPLS-PE不具备I-SID的可见性。
The main advantage of this service interface, when compared to other types, is that it allows the service provider to save on the number of full-mesh PWs required in the core. This is primarily because
与其他类型相比，此服务接口的主要优势在于，它允许服务提供商节省核心中所需的全网状PW的数量。这主要是因为
multiple service instances (I-SIDs) are bundled over a single full-mesh PW corresponding to a bridge domain (e.g., B-VID), instead of requiring a dedicated full-mesh PW per service instance. Another advantage is the MAC address scalability in the core since the core is not exposed to C-MACs.
多个服务实例（I-SID）捆绑在对应于网桥域（例如，B-VID）的单个全网格PW上，而不是每个服务实例都需要专用的全网格PW。另一个优点是核心中的MAC地址可伸缩性，因为核心不暴露于C-MAC。
The disadvantage of this interface is the comparably excessive replication required in the core: since a group of service instances share the same full-mesh of PWs, an unknown unicast, multicast, or broadcast on a single service instance will result in a flood over the core. This, however, can be mitigated via the use of flood containment per I-SID (B-MAC multicast pruning).
此接口的缺点是核心中需要的复制相对过多：由于一组服务实例共享相同的PW完整网格，单个服务实例上的未知单播、多播或广播将导致核心上的洪水。然而，这可以通过使用I-SID的洪水遏制（B-MAC多播修剪）来缓解。
Three different modes of operation are supported by Type I service interface:
I类服务接口支持三种不同的操作模式：
- Port Mode: All traffic over an interface in this mode is mapped to a single VPLS instance. Existing PW signaling and Ethernet raw mode (0x0005) PW type, defined in [RFC4447] and [RFC4448], are supported.
- 端口模式：此模式下接口上的所有流量都映射到单个VPLS实例。支持[RFC4447]和[RFC4448]中定义的现有PW信令和以太网原始模式（0x0005）PW类型。
- VLAN Mode: all traffic associated with a particular VLAN identified by the B-VID is mapped to a single VPLS instance. Existing PW signaling and Ethernet raw mode (0x0005) PW type, defined in [RFC4447] and [RFC4448], are supported.
- VLAN模式：与B-VID标识的特定VLAN相关联的所有流量都映射到单个VPLS实例。支持[RFC4447]和[RFC4448]中定义的现有PW信令和以太网原始模式（0x0005）PW类型。
- VLAN Bundling Mode: all traffic associated with a group or range of VLANs or B-VIDs is mapped to a single VPLS instance. Existing PW signaling and Ethernet raw mode (0x0005) PW type, defined in [RFC4447] and [RFC4448], are supported.
- VLAN绑定模式：与一组或一系列VLAN或B-VID关联的所有流量都映射到单个VPLS实例。支持[RFC4447]和[RFC4448]中定义的现有PW信令和以太网原始模式（0x0005）PW类型。
For the VLAN mode, it is also possible to use Ethernet tagged mode (0x0004) PW, as defined in [RFC4447] and [RFC4448], for interoperability with equipment that does not support raw mode. The use of raw mode is recommended to be the default though.
对于VLAN模式，也可以使用[RFC4447]和[RFC4448]中定义的以太网标记模式（0x0004）PW与不支持原始模式的设备进行互操作。不过，建议使用原始模式作为默认模式。
This is an I-Tagged service interface with I-SID as service delimiter on the VPLS-PE. It requires the VPLS-PE to include the B-component of PBB BEB for I-SID processing in addition to the capability to map an I-SID Bundle to a VPLS instance. As shown in Figure 3, the PE is always part of the IP/MPLS core and connects to one or more B-BEBs in the PBBN access.
这是一个I标记的服务接口，在VPLS-PE上以I-SID作为服务分隔符。它要求VPLS-PE除了能够将I-SID捆绑包映射到VPLS实例之外，还包括用于I-SID处理的PBB BEB的B组件。如图3所示，PE始终是IP/MPLS核心的一部分，并连接到PBBN接入中的一个或多个B-BEB。
PBBN Access IP/MPLS Core PBBN Access
+--------------+
+---------+ | | +---------+
| | | | | |
| +---+ +-----+ | | +---+ |
| |B- | |PE w/| +-+ | | |BCB| |
| |BEB|--|B-BEB|-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
|+---+ +---+/ +-----+/ +-----+ +---+ +---+|
+--+ ||IB-| |B- | |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||BEB|-|BEB|--|B-BEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | | | | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
Type II Type II
PBBN Access IP/MPLS Core PBBN Access
+--------------+
+---------+ | | +---------+
| | | | | |
| +---+ +-----+ | | +---+ |
| |B- | |PE w/| +-+ | | |BCB| |
| |BEB|--|B-BEB|-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
|+---+ +---+/ +-----+/ +-----+ +---+ +---+|
+--+ ||IB-| |B- | |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||BEB|-|BEB|--|B-BEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | | | | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
Type II Type II
Figure 3: H-VPLS with PBBN Access and Type II Service Interface
图3：具有PBBN接入和II型服务接口的H-VPLS
Type II service interface is applicable to Loosely Coupled Service Domains and Different Service Domains. B-VLAN Domains can be independent and the B-VID is always locally significant in each PBBN access: it does not need to be transported over the IP/MPLS core. Given the above, it should be apparent that Type II service interface is applicable to Tightly Coupled Service Domains as well.
II类服务接口适用于松散耦合的服务域和不同的服务域。B-VLAN域可以是独立的，并且B-VID在每个PBBN访问中始终在本地重要：它不需要通过IP/MPLS核心传输。鉴于上述情况，II型服务接口显然也适用于紧密耦合的服务域。
By definition, the B-BEB connecting to the VPLS-PE will remove any B-VLAN tags for frames exiting the PBBN access. The B-BEB and VPLS-PE will exchange PBB-encapsulated frames that include source and destination B-MACs and an I-SID. The service delimiter, from the perspective of the VPLS-PE, is the I-SID. Since the PE has visibility of I-SIDs, the PE provides service-level interworking between PBBN access and IP/MPLS core.
根据定义，连接到VPLS-PE的B-BEB将删除退出PBBN访问的帧的任何B-VLAN标记。B-BEB和VPLS-PE将交换PBB封装的帧，其中包括源和目标B-MAC以及I-SID。从VPLS-PE的角度来看，服务分隔符是I-SID。由于PE具有I-SID的可见性，因此PE提供PBBN接入和IP/MPLS核心之间的服务级别互通。
Type II service interface may operate in I-SID Bundling Mode: all traffic associated with a group or range of I-SIDs is mapped to a single VPLS instance. The PE maintains a mapping of I-SIDs to a PE local bridge domain (e.g., B-VID). The VPLS instance is then associated with this bridge domain. With Loosely Coupled service Domains, no I-SID translation needs to be performed. Type II Service interface also supports Different Service Domains in this mode, since the B-BEB link in the PE connecting to the local PBBN can perform the translation of PBBN-specific I-SID to a local I-SID within the IP/MPLS core, which may then be translated to the other PBBN-specific I-SID on the egress PE. Such translation can also occur in the B-BEB of PBBN access. Existing PW signaling and Ethernet raw mode (0x0005), defined in [RFC4447] and [RFC4448], is supported. It is
II类服务接口可在I-SID绑定模式下运行：与I-SID组或范围相关联的所有通信量映射到单个VPLS实例。PE维护I-SID到PE本地网桥域（如B-VID）的映射。然后，VPLS实例与该网桥域相关联。对于松散耦合的服务域，不需要执行I-SID转换。II型服务接口在此模式下还支持不同的服务域，因为连接到本地PBBN的PE中的B-BEB链路可以将特定于PBBN的I-SID转换为IP/MPLS核心内的本地I-SID，然后可以将其转换为出口PE上的其他特定于PBBN的I-SID。这种转换也可以发生在PBBN接入的B-BEB中。支持[RFC4447]和[RFC4448]中定义的现有PW信令和以太网原始模式（0x0005）。它是
also possible to use a tagged mode (0x0004) PW for purpose of interoperability with equipment that does not support raw mode.
也可以使用标记模式（0x0004）PW与不支持原始模式的设备进行互操作。
Type II service interface provides operators with the flexibility to trade off PW state for multicast flooding containment, since a full-mesh of PWs can be set up:
II类服务接口为运营商提供了在多播泛洪遏制中权衡PW状态的灵活性，因为可以设置PW的完整网格：
a. per I-SID, b. per group of I-SIDs, or c. for all I-SIDs.
a. 根据I-SID，b。每组I-SID，或c。对于所有I-SID。
For (a) and (b), the advantage that Type II service interface has compared to Type I is that it can reduce replication in the core without the need for a mechanism that provides flood containment per-I-SID (B-MAC multicast pruning). This is mainly due to the increased segregation of service instances over disjoint full meshes of PWs. For (c), both Type II and Type I service interfaces are at par with regard to flood containment.
对于（a）和（b），与类型I相比，类型II服务接口的优势在于，它可以减少核心中的复制，而不需要提供每I-SID（b-MAC多播修剪）的洪水遏制机制。这主要是由于在PWs的不相交全网格上增加了服务实例的隔离。对于（c），Type II和I型服务接口在防洪安全方面是一致的。
For (a) and (b), the disadvantage of this service interface, compared to Type I, is that it may require a larger number of full-mesh PWs in the core. For (c), both Type II and Type I service interfaces are at par with regard to PW state. However, for all three scenarios, the number of full-mesh PWs can still be fewer than the number required by H-VPLS without PBBN access, since an I-SID can multiplex many S-VLANs.
对于（a）和（b），与I型相比，该服务接口的缺点是，它可能需要在核心中使用更多的全网状PW。对于（c），Type II和I型服务接口在PW状态方面是一致的。然而，对于所有三种情况，全网状PW的数量仍然可以小于不使用PBBN访问的H-VPL所需的数量，因为I-SID可以多路复用多个S-VLAN。
It is expected that this interface type will be used for customers with significant multicast traffic (but without multicast pruning capability in the VPLS-PE) so that a separate VPLS instance is set up per group of customers with similar geographic locality (per I-SID group).
预计此接口类型将用于具有大量多播流量（但VPLS-PE中没有多播修剪功能）的客户，以便为具有类似地理位置的每组客户（每个I-SID组）设置单独的VPLS实例。
Note: Port mode is not called out in Type II service interface since it requires the mapping of I-SIDs to be identical on different I-Tagged interfaces across VPLS network. If this is indeed the case, Port mode defined in Type I service interface (Section 4.2) can be used.
注：II型服务接口中未调用端口模式，因为它要求VPLS网络上不同I标签接口上的I-SID映射相同。如果确实如此，则可以使用I类服务接口（第4.2节）中定义的端口模式。
It is foreseeable that service providers will want to interoperate their existing Provider Bridged Networks (PBNs) with Provider Backbone Bridged Networks (PBBNs) over H-VPLS. Figure 4 below shows the high-level network topology.
可以预见，服务提供商将希望通过H-VPL将其现有的提供商桥接网络（PBN）与提供商主干桥接网络（PBBN）进行互操作。下面的图4显示了高级网络拓扑。
+--------------+
| |
+---------+ | IP/MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| PBN | |VPLS| |VPLS| | |--| CE |
+----+ | (QinQ) |---| PE1| | PE2|--| PBBN | +----+
+----+ | 802.1ad | +----+ +----+ | 802.1ah | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
+--------------+
| |
+---------+ | IP/MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| PBN | |VPLS| |VPLS| | |--| CE |
+----+ | (QinQ) |---| PE1| | PE2|--| PBBN | +----+
+----+ | 802.1ad | +----+ +----+ | 802.1ah | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 4: H-VPLS with Mixed PBN and PBBN Access Networks
图4：混合PBN和PBBN接入网络的H-VPL
Referring to Figure 4 above, two possibilities come into play depending on whether the interworking is carried out at PE1 or PE2. These are described in the following subsections.
参考上面的图4，根据互通是在PE1还是PE2进行，有两种可能性发挥作用。以下各小节将对此进行说明。
As shown in Figure 5, the operation of VPLS-PE2 (connecting to the PBBN access on the right) is no different from what was discussed in Section 4. Type II service interface, as discussed in the above section, is applicable. It is the behavior of VPLS-PE1 (connecting to the PBN access on the left) that is the focus of this section.
如图5所示，VPLS-PE2（连接到右侧的PBBN接入）的操作与第4节中讨论的相同。上述章节中讨论的II类服务接口适用。VPLS-PE1（连接到左边的PBN接入）的行为是本节的重点。
PBN Access IP/MPLS Core PBBN Access
(802.1ad) +--------------+ (802.1ah)
| | +---------+
+---------+ | | | |
| | +-----+ | | +---+ |
| +---+ |PE w/| +-+ | | |BCB| |
| |PCB|--|IBBEB|-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
| | / +-----+/ +-----+ +---+ +---+|
+--+ |+---+ +---+ |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||PEB|-|PCB|--|IBBEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | |PE1 PE2| | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
S-Tagged Type II (I-Tagged)
PBN Access IP/MPLS Core PBBN Access
(802.1ad) +--------------+ (802.1ah)
| | +---------+
+---------+ | | | |
| | +-----+ | | +---+ |
| +---+ |PE w/| +-+ | | |BCB| |
| |PCB|--|IBBEB|-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
| | / +-----+/ +-----+ +---+ +---+|
+--+ |+---+ +---+ |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||PEB|-|PCB|--|IBBEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | |PE1 PE2| | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
S-Tagged Type II (I-Tagged)
Figure 5: H-VPLS with Mixed PBN and PBBN Access: Modified PBN PE
图5:PBN和PBBN混合接入的H-VPLS：改进的PBN PE
Some assumptions made for this topology include:
对该拓扑所做的一些假设包括：
- CE is directly connected to PBBN via S-Tagged or port-based interface.
- CE通过S标记或基于端口的接口直接连接到PBBN。
- I-SID in PBBN access represents the same customer as S-VID in PBN access.
- PBBN访问中的I-SID表示与PBN访问中的S-VID相同的客户。
- At S-Tagged service interface of PE with IB-BEB functionality (e.g., PE1 in Figure 5), the only viable service is 1:1 mapping of S-VID to I-SID. However, towards the core network side, the same PE can support I-SID bundling into a VPLS instance.
- 在具有IB-BEB功能的PE的S标记服务接口处（如图5中的PE1），唯一可行的服务是S-VID到I-SID的1:1映射。但是，对于核心网络端，同一个PE可以支持将I-SID绑定到VPLS实例中。
- PE1 participates in the local I-SID Domain of the IP/MPLS core so the model accommodates for the rest of the PBB network any of the three domain types described in Section 4 -- Tightly Coupled, Loosely Coupled, and Different Service Domains.
- PE1参与IP/MPLS核心的本地I-SID域，因此该模型为PBB网络的其余部分适应第4节中描述的三种域类型中的任何一种——紧耦合、松耦合和不同的服务域。
- For ease of provisioning in these disparate access networks, it is recommended to use the same I-SID Domain among the PBBN access networks and the PEs with IB-BEB functionality (those connecting to PBN).
- 为便于在这些完全不同的接入网络中进行配置，建议在PBBN接入网络和具有IB-BEB功能的PEs（那些连接到PBN的）之间使用相同的I-SID域。
This topology operates in I-SID Bundling Mode: at a PE connecting to PBN access, each S-VID is mapped to an I-SID and subsequently a group of I-SIDs is mapped to a VPLS instance. Similarly, at a PE connecting to PBBN access, each group of I-SIDs is mapped to a VPLS instance. Similar to Type II service interface, no I-SID translation is performed for the I-SID bundling case. Existing PW signaling and Ethernet raw mode (0x0005) PW type, defined in [RFC4447] and [RFC4448], are supported. It is possible to use tagged mode (0x0004) PW for backward compatibility as well.
此拓扑在I-SID绑定模式下运行：在连接到PBN访问的PE上，每个S-VID映射到一个I-SID，然后一组I-SID映射到一个VPLS实例。类似地，在连接到PBBN接入的PE上，每组I-SID映射到一个VPLS实例。与II类服务接口类似，I-SID绑定案例不执行I-SID转换。支持[RFC4447]和[RFC4448]中定义的现有PW信令和以太网原始模式（0x0005）PW类型。也可以使用标记模式（0x0004）PW实现向后兼容性。
As shown in Figure 6, the operation of VPLS-PE1 (connecting to the PBN access on the left) is no different from existing VPLS-PEs. It is the behavior of VPLS-PE2 (connecting to the PBBN access on the right) that is the focus of this section.
如图6所示，VPLS-PE1（连接到左边的PBN接入）的操作与现有的VPLS-PEs没有什么不同。VPLS-PE2（连接右侧的PBBN接入）的行为是本节的重点。
PBN Access IP/MPLS Core PBBN Access
(802.1ad) +--------------+ (802.1ah)
| | +---------+
+---------+ | | | |
| | +-----+ | | +---+ |
| +---+ | PE | +-+ | | |BCB| |
| |PCB|--| |-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
| | / +-----+/ +-----+ +---+ +---+|
+--+ |+---+ +---+ | PE | +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||PEB|-|PCB|--| |-|P|-|IBBEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | |PE1 PE2| | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
S-Tagged Type II (I-Tagged)
PBN Access IP/MPLS Core PBBN Access
(802.1ad) +--------------+ (802.1ah)
| | +---------+
+---------+ | | | |
| | +-----+ | | +---+ |
| +---+ | PE | +-+ | | |BCB| |
| |PCB|--| |-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
| | / +-----+/ +-----+ +---+ +---+|
+--+ |+---+ +---+ | PE | +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||PEB|-|PCB|--| |-|P|-|IBBEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | |PE1 PE2| | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
S-Tagged Type II (I-Tagged)
Figure 6: H-VPLS with Mixed PBN and PBBN Access: Regular PBN PE
图6:PBN和PBBN混合接入的H-VPL：常规PBN PE
Some assumptions made for this topology include:
对该拓扑所做的一些假设包括：
- The CE is directly connected to the PBBN access via an S-Tagged or port-based Interface.
- CE通过S标记或基于端口的接口直接连接到PBBN接入。
- The I-SID in the PBBN access represents the same customer as the S-VID in the PBN access.
- PBBN访问中的I-SID表示与PBN访问中的S-VID相同的客户。
- There is 1:1 mapping between the I-SID and the VPLS instance.
- I-SID和VPLS实例之间存在1:1映射。
- At the S-Tagged service interface of the PE connecting to PBN (e.g., PE1 in Figure 6), the PE only provides 1:1 mapping of S-VID to the VPLS instance. S-VID bundling is not a viable option since it does not correspond to anything in the PBBN access.
- 在连接到PBN的PE的S标记服务接口处（例如，图6中的PE1），PE仅提供S-VID到VPLS实例的1:1映射。S-VID捆绑不是可行的选择，因为它与PBBN接入中的任何内容都不对应。
- The PE connecting to the PBBN access (e.g., PE2 in Figure 6), supports IB-BEB functionality and the I-component is connected to the VPLS Forwarder (i.e., the I-component faces the IP/MPLS core whereas the B-component faces the PBBN access network). One or more I-SIDs can be grouped into a B-VID in the PBBN access.
- 连接到PBBN接入的PE（如图6中的PE2）支持IB-BEB功能，I组件连接到VPLS转发器（即，I组件面向IP/MPLS核心，而B组件面向PBBN接入网络）。在PBBN接入中，一个或多个I-SID可以分组到B-VID中。
- Since C-VID grouping in different PBBN access networks must be consistent, it is assumed that same I-SID Domain is used across these PBBN access networks.
- 由于不同PBBN接入网络中的C-VID分组必须一致，因此假设在这些PBBN接入网络中使用相同的I-SID域。
Unlike the previous case, I-SID bundling mode is not supported in this case. This is primarily because the VPLS core operates in the same manner as today. The PE with IB-BEB functionality connecting to PBBN access performs the mapping of each VPLS instance to an I-SID and one or more of these I-SIDs may be mapped onto a B-VID within the PBBN access network.
与前一种情况不同，这种情况下不支持I-SID绑定模式。这主要是因为VPLS核心的运行方式与今天相同。连接到PBBN接入的具有IB-BEB功能的PE执行每个VPLS实例到I-SID的映射，并且这些I-SID中的一个或多个可以映射到PBBN接入网络内的B-VID。
In this section, the case of H-VPLS with MPLS access network is discussed. The integration of PBB functionality into VPLS-PE for such access networks is described to improve the scalability of the network in terms of the number of MAC addresses and service instances that are supported.
在本节中，将讨论带有MPLS接入网络的H-VPLS的情况。描述了将PBB功能集成到用于此类接入网络的VPLS-PE中，以在所支持的MAC地址和服务实例的数量方面改进网络的可伸缩性。
For this topology, it is possible to embed PBB functionality in either the U-PE or the N-PE. Both of these cases are described in the following subsections.
对于这种拓扑，可以在U-PE或N-PE中嵌入PBB功能。以下小节将对这两种情况进行描述。
As stated earlier, the objective for incorporating PBB function at the U-PE is to improve the scalability of H-VPLS networks in terms of the number of MAC addresses and service instances that are supported.
如前所述，在U-PE处合并PBB功能的目的是在所支持的MAC地址和服务实例的数量方面改进H-VPLS网络的可伸缩性。
In current H-VPLS, the N-PE must learn customer MAC addresses (C-MACs) of all VPLS instances in which it participates. This can easily add up to hundreds of thousands or even millions of C-MACs at
在当前的H-VPLS中，N-PE必须了解其参与的所有VPLS实例的客户MAC地址（C-MAC）。这可以很容易地在同一时间增加数十万甚至数百万个C-Mac
the N-PE. When the U-PE performs PBB encapsulation, the N-PE only needs to learn the MAC addresses of the U-PEs, which is a significant reduction. Furthermore, when PBB encapsulation is used, many I-SIDs are multiplexed within a single bridge domain (e.g., B-VLAN). If the VPLS instance is set up per B-VLAN, then one can also achieve a significant reduction in the number of full-mesh PWs. It should be noted that this reduction in full-mesh PWs comes at the cost of potentially increased replication over the full-mesh of PWs: customer multicast and/or broadcast frames are effectively broadcasted within the B-VLAN. This may result in additional frame replication because the full-mesh PWs corresponding to a B-VLAN are most likely bigger than the full-mesh PWs corresponding to a single I-SID. However, flood containment per I-SID (B-MAC multicast pruning) can be used to remedy this drawback and have multicast traffic replicated efficiently for each customer (i.e., for each I-SID).
N-PE。当U-PE执行PBB封装时，N-PE只需要学习U-PE的MAC地址，这是一个显著的减少。此外，当使用PBB封装时，许多I-sid在单个网桥域（例如，B-VLAN）内复用。如果按照B-VLAN设置VPLS实例，则还可以显著减少全网状PW的数量。应该注意的是，全网状PW的这种减少是以在PW的全网状上潜在地增加复制为代价的：客户多播和/或广播帧在B-VLAN内有效地广播。这可能会导致额外的帧复制，因为对应于B-VLAN的全网状PW很可能比对应于单个I-SID的全网状PW大。然而，每个I-SID的泛洪遏制（B-MAC多播修剪）可用于弥补此缺陷，并为每个客户（即，每个I-SID）有效复制多播通信量。
Figure 7 below illustrates the scenario for H-VPLS with MPLS access. As illustrated, customer networks or hosts (CE) connect into the U-PE nodes using standard Ethernet interfaces [802.1D-REV], [802.1Q], or [802.1ad]. The U-PE is connected upstream to one or more VPLS N-PE nodes by MPLS PWs (per VPLS instance). These, in turn, are connected via a full mesh of PWs (per VPLS instance) traversing the IP/MPLS core. The U-PE is outfitted with PBB Backbone Edge Bridge (BEB) functions where it can encapsulate/decapsulate customer MAC frames in provider B-MACs and perform I-SID translation if needed.
下面的图7说明了具有MPLS访问的H-VPLS的场景。如图所示，客户网络或主机（CE）使用标准以太网接口[802.1D-REV]、[802.1Q]或[802.1ad]连接到U-PE节点。U-PE通过MPLS PWs（每个VPLS实例）向上游连接到一个或多个VPLS N-PE节点。反过来，它们通过穿过IP/MPLS核心的完整PWs网格（每个VPLS实例）进行连接。U-PE配备了PBB主干边缘网桥（BEB）功能，可以在提供商B-MAC中封装/解封客户MAC帧，并在需要时执行I-SID转换。
PBB PBB
BEB +----------+ BEB
| | | |
| +-----------+ | IP | +-----------+ |
| | MPLS | | MPLS | | MPLS | |
V | Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| | | | | |
+-----------+ +----------+ +-----------+
PBB PBB
BEB +----------+ BEB
| | | |
| +-----------+ | IP | +-----------+ |
| | MPLS | | MPLS | | MPLS | |
V | Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| | | | | |
+-----------+ +----------+ +-----------+
Figure 7: H-VPLS with MPLS Access Network and PBB U-PE
图7：带有MPLS接入网络和PBB U-PE的H-VPLS
The U-PE still provides the same type of services toward its customers as before and they are:
U-PE仍然向其客户提供与以前相同类型的服务，他们是：
- Port mode (either 802.1D, 802.1Q, or 802.1ad) - VLAN mode (either 802.1Q or 802.1ad) - VLAN-bundling mode (either 802.1Q or 802.1ad)
- 端口模式（802.1D、802.1Q或802.1ad）-VLAN模式（802.1Q或802.1ad）-VLAN绑定模式（802.1Q或802.1ad）
By incorporating a PBB function, the U-PE maps each of these services (for a given customer) onto a single I-SID based on the configuration at the U-PE. Many I-SIDs are multiplexed within a single bridge domain (e.g., B-VLAN). The U-PE can then map a bridge domain onto a VPLS instance and the encapsulated frames are sent over the PW associated with that VPLS instance. Furthermore, the entire Ethernet bridging operation over the VPLS network is performed as defined in [RFC4762]. In other words, MAC forwarding is based on the B-MAC address space and service delimiter is based on VLAN ID, which is B-VID in this case. There is no need to inspect or deal with I-SID values in the VPLS N-PEs.
通过合并PBB功能，U-PE根据U-PE上的配置将这些服务中的每一项（针对给定客户）映射到单个I-SID上。许多I-SID在单个网桥域（例如，B-VLAN）内多路复用。然后，U-PE可以将网桥域映射到VPLS实例上，封装的帧通过与该VPLS实例相关联的PW发送。此外，VPLS网络上的整个以太网桥接操作按照[RFC4762]中的定义执行。换句话说，MAC转发基于B-MAC地址空间，服务分隔符基于VLAN ID，在本例中为B-VID。无需检查或处理VPLS N-PEs中的I-SID值。
In the case of PBB U-PEs in a single I-SID Domain, I-SID assignment is performed globally across all MPLS access networks and therefore there is no need for I-SID translation. This scenario supports I-SID bundling mode, and it is assumed that the mapping of the I-SIDs to the bridge domain (e.g., B-VLAN) is consistent across all the participating PE devices. In the case of the I-SID bundling mode, a bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and an existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type is used as defined in [RFC4447] and [RFC4448].
在单个I-SID域中的PBB U-PEs的情况下，I-SID分配在所有MPLS接入网络中全局执行，因此不需要I-SID转换。此场景支持I-SID绑定模式，并且假设I-SID到网桥域（例如，B-VLAN）的映射在所有参与的PE设备上是一致的。在I-SID绑定模式的情况下，网桥域（例如B-VLAN）映射到VPLS实例，并使用[RFC4447]和[RFC4448]中定义的现有以太网原始模式（0x0005）或标记模式（0x0004）PW类型。
I-SID mode can be considered to be a degenerate case of I-SID bundling where a single bridge domain is used per I-SID. However, that results in an increased number of bridge domains and PWs in the PEs. PBB flood containment (B-MAC multicast pruning) per I-SID can be used in conjunction with I-SID bundling mode to limit the scope of flooding per I-SID thus removing the need for I-SID mode.
I-SID mode can be considered to be a degenerate case of I-SID bundling where a single bridge domain is used per I-SID. However, that results in an increased number of bridge domains and PWs in the PEs. PBB flood containment (B-MAC multicast pruning) per I-SID can be used in conjunction with I-SID bundling mode to limit the scope of flooding per I-SID thus removing the need for I-SID mode.translate error, please retry
In this case, the PBB function is incorporated at the N-PE to improve the scalability of H-VPLS networks in terms of the numbers of MAC addresses and service instances that are supported.
在这种情况下，在N-PE处合并PBB功能，以提高H-VPLS网络在MAC地址和所支持的服务实例数量方面的可伸缩性。
Customer networks or hosts (CE) connect into the U-PE nodes using standard Ethernet interfaces [802.1D-REV], [802.1Q], or [802.1ad]. The U-PE is connected upstream to one or more VPLS N-PE nodes by MPLS PWs (per customer). These, in turn, are connected via a full mesh of PWs (per customer or group of customers) traversing the IP/MPLS core.
客户网络或主机（CE）使用标准以太网接口[802.1D-REV]、[802.1Q]或[802.1ad]连接到U-PE节点。U-PE通过MPLS PWs（每个客户）向上游连接到一个或多个VPLS N-PE节点。反过来，它们通过穿过IP/MPLS核心的完整PW网（每个客户或客户组）进行连接。
The U-PE still provides the same type of services toward its customers as before and they are:
U-PE仍然向其客户提供与以前相同类型的服务，他们是：
- Port mode (either 802.1D, 802.1Q, or 802.1ad) - VLAN mode (either 802.1Q or 802.1ad) - VLAN-bundling mode (either 802.1Q or 802.1ad)
- 端口模式（802.1D、802.1Q或802.1ad）-VLAN模式（802.1Q或802.1ad）-VLAN绑定模式（802.1Q或802.1ad）
The spoke PW from the U-PE to the N-PE is not service multiplexed because there is no PBB functionality on the U-PE, i.e., one service per PW.
从U-PE到N-PE的分支PW不是服务多路复用的，因为U-PE上没有PBB功能，即每个PW一个服务。
PBB PBB
BEB +----------+ BEB
| | | |
+-----------+ | | IP | | +-----------+
| MPLS | V | MPLS | V | MPLS |
| Access +----+ | Core | +----+ Access |
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| | | | | |
+-----------+ +----------+ +-----------+
PBB PBB
BEB +----------+ BEB
| | | |
+-----------+ | | IP | | +-----------+
| MPLS | V | MPLS | V | MPLS |
| Access +----+ | Core | +----+ Access |
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| | | | | |
+-----------+ +----------+ +-----------+
Figure 8: H-VPLS with MPLS Access Network and PBB N-PE
图8：具有MPLS接入网络和PBB N-PE的H-VPLS
By incorporating a PBB function, the N-PE maps each of these services (for a given customer) onto a single I-SID based on the configuration at the N-PE. Many I-SIDs can be multiplexed within a single bridge domain (e.g., B-VLAN). The N-PE can, then, either map a single I-SID into a VPLS instance or map a bridge domain (e.g., B-VLAN) onto a VPLS instance, according to its configuration. Next, the encapsulated frames are sent over the set of PWs associated with that VPLS instance.
通过合并PBB功能，N-PE根据N-PE上的配置将这些服务中的每一项（针对给定客户）映射到单个I-SID上。许多I-SID可以在单个网桥域（例如，B-VLAN）内多路复用。然后，N-PE可以根据其配置将单个I-SID映射到VPLS实例，或者将网桥域（例如，B-VLAN）映射到VPLS实例。接下来，通过与该VPLS实例关联的PW集发送封装的帧。
In the case of PBB N-PEs in a single I-SID Domain, I-SID assignment is performed globally across all MPLS access networks and therefore there is no need for I-SID translation. This scenario supports I-SID bundling mode, and it is assumed that the mapping of the I-SIDs to the bridge domain (e.g., B-VLAN) is consistent across all the participating PE devices. In the case of the I-SID bundling mode, a bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and an existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type as defined in [RFC4447] and [RFC4448], can be used.
在单个I-SID域中的PBB N-PEs的情况下，I-SID分配在所有MPLS接入网络中全局执行，因此不需要I-SID转换。此场景支持I-SID绑定模式，并且假设I-SID到网桥域（例如，B-VLAN）的映射在所有参与的PE设备上是一致的。在I-SID绑定模式的情况下，网桥域（例如B-VLAN）映射到VPLS实例，并且可以使用[RFC4447]和[RFC4448]中定义的现有以太网原始模式（0x0005）或标记模式（0x0004）PW类型。
I-SID mode can be considered to be a degenerate case of I-SID bundling where a single bridge domain is used per I-SID. However, that results in an increased number of bridge domains and PWs in the PE. PBB flood containment (B-MAC multicast pruning) per I-SID can be used in conjunction with I-SID bundling mode to limit the scope of flooding per I-SID thus removing the need for I-SID mode.
可以将I-SID模式视为I-SID绑定的退化情况，其中每个I-SID使用一个网桥域。然而，这导致PE中桥域和PW的数量增加。每个I-SID的PBB泛洪遏制（B-MAC多播修剪）可与I-SID绑定模式结合使用，以限制每个I-SID的泛洪范围，从而消除对I-SID模式的需要。
Operators and service providers that have deployed H-VPLS with either MPLS or Ethernet are unlikely to migrate to PBB technology over night because of obvious cost implications. Thus, it is imperative to outline migration strategies that will allow operators to protect investments in their installed base while still taking advantage of the scalability benefits of PBB technology.
由于明显的成本影响，使用MPLS或以太网部署H-VPL的运营商和服务提供商不太可能在夜间迁移到PBB技术。因此，有必要概述迁移策略，使运营商能够保护对其安装基础的投资，同时仍能利用PBB技术的可扩展性优势。
In the following subsections, we explore three different migration scenarios that allow a mix of existing H-VPLS access networks to coexist with newer PBB-based access networks. The scenarios differ in whether or not the Ethernet service frames passing over the VPLS core are PBB-encapsulated. The first scenario, in Section 7.1, involves passing only frames that are not PBB-encapsulated over the core. The second scenario, in Section 7.2, stipulates passing only PBB-encapsulated frames over the core. Whereas, the final scenario, in Section 7.3, depicts a core that supports a mix of PBB-encapsulated and non-PBB-encapsulated frames. The advantages and disadvantages of each scenario will be discussed in the respective sections.
在下面的小节中，我们将探讨三种不同的迁移场景，它们允许现有的H-VPLS接入网络与新的基于PBB的接入网络共存。场景的不同之处在于通过VPLS核心的以太网服务帧是否是PBB封装的。第7.1节中的第一个场景涉及仅传递未在核心上封装PBB的帧。第二种情况，在第7.2节中，规定只在核心上传递PBB封装的帧。然而，第7.3节中的最终场景描述了支持PBB封装和非PBB封装帧混合的核心。每种方案的优缺点将在各自的章节中讨论。
In this scenario, existing access networks are left unchanged. All N-PEs would forward frames based on C-MACs. In other words, Ethernet frames that are traversing the VPLS core (within PWs) would use the 802.1ad frame format, as in current VPLS. Hence, the N-PEs in existing access networks do not require any modification. For new MPLS access networks that have PBB functions on the U-PE, the corresponding N-PE must incorporate built-in IB-BEB functions in order to terminate the PBB encapsulation before the frames enter the core. A key point here is that while both the U-PE and N-PE nodes implement PBB IB-BEB functionality, the former has the I-component facing the customer (CE) and the B-component facing the core; whereas the latter has the I-component facing the core and the B-component facing the customer (i.e., access network).
在这种情况下，现有的接入网络保持不变。所有N-PE将基于C-MAC转发帧。换句话说，在当前VPLS中，穿过VPLS核心（在PWs内）的以太网帧将使用802.1ad帧格式。因此，现有接入网络中的N-PEs不需要任何修改。对于在U-PE上具有PBB功能的新MPLS接入网络，相应的N-PE必须包含内置IB-BEB功能，以便在帧进入核心之前终止PBB封装。这里的一个关键点是，虽然U-PE和N-PE节点都实现PBB IB-BEB功能，但前者具有面向客户（CE）的I组件和面向核心的B组件；后者的I组件面向核心，B组件面向客户（即接入网络）。
PBB PBB
+----------+ IB-BEB IB-BEB
| | | |
+-----------+ | IP | | +-----------+ |
| MPLS | | MPLS | V | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
PBB PBB
+----------+ IB-BEB IB-BEB
| | | |
+-----------+ | IP | | +-----------+ |
| MPLS | | MPLS | V | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
Figure 9: Migration with 802.1ad Service Frames over VPLS Core
图9:VPLS核心上802.1ad服务帧的迁移
The main advantage of this approach is that it requires no change to existing access networks or existing VPLS N-PEs. The main disadvantage is that these N-PEs will not leverage the advantages of PBB in terms of MAC address and PW scalability. It is worth noting that this migration scenario is an optimal option for an H-VPLS deployment with a single PBB-capable access network. When multiple PBB-capable access networks are required, then the scenario in Section 7.3 is preferred, as it provides a more scalable and optimal interconnect amongst the PBB-capable networks.
这种方法的主要优点是不需要更改现有的接入网络或现有的VPLS N-PEs。主要缺点是，这些N-PE将无法利用PBB在MAC地址和PW可伸缩性方面的优势。值得注意的是，此迁移场景是使用单个支持PBB的接入网络部署H-VPLS的最佳选择。当需要多个支持PBB的接入网络时，则首选第7.3节中的场景，因为它在支持PBB的网络之间提供了更可扩展和最佳的互连。
This scenario requires that the VPLS N-PE connecting to existing MPLS access networks be upgraded to incorporate IB-BEB functions. All Ethernet service frames passing over the VPLS core would be PBB-encapsulated. The PBB over MPLS access networks would require no special requirements beyond what is captured in Section 6 of this document. In this case, both the U-PE and N-PE, which implement IB-BEB functionality, have the I-component facing the customer and the B-component facing the core.
此场景要求升级连接到现有MPLS接入网络的VPLS N-PE，以合并IB-BEB功能。通过VPLS核心的所有以太网服务帧都将被PBB封装。MPLS接入网络上的PBB不需要超出本文件第6节规定的特殊要求。在这种情况下，实现IB-BEB功能的U-PE和N-PE都具有面向客户的I组件和面向核心的B组件。
PBB PBB
IB-BEB +----------+ IB-BEB
| | | |
+-----------+ | | IP | +-----------+ |
| MPLS | V | MPLS | | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
PBB PBB
IB-BEB +----------+ IB-BEB
| | | |
+-----------+ | | IP | +-----------+ |
| MPLS | V | MPLS | | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
Figure 10: Migration with PBB Service Frames over VPLS Core
图10:VPLS核心上PBB服务帧的迁移
The main advantage of this approach is that it allows better scalability of the VPLS N-PEs in terms of MAC address and pseudowire counts. The disadvantage is that it requires upgrading the VPLS N-PEs of all existing MPLS access networks.
这种方法的主要优点是，它允许VPLS N-PEs在MAC地址和伪线计数方面具有更好的可伸缩性。缺点是它需要升级所有现有MPLS接入网络的VPLS N-PEs。
In this scenario, existing access networks are left unchanged, and they exchange Ethernet frames with 802.1ad format over the PWs in the core. The newly added access networks, which incorporate PBB functionality exchange Ethernet frames that are PBB-encapsulated amongst each other over core PWs. For service connectivity between existing access network (non-PBB-capable) and new access network (PBB based), the VPLS N-PE of the latter network employs IB-BEB functionality to decapsulate the PBB header from frames outbound to the core and encapsulate the PBB header for frames inbound from the core. As a result, a mix of PBB-encapsulated and 802.1ad Ethernet service frames are exchanged over the VPLS core.
在这种情况下，现有的接入网络保持不变，它们通过核心的PWs交换802.1ad格式的以太网帧。新添加的接入网络（包含PBB功能）交换通过核心PWs相互封装的PBB以太网帧。对于现有接入网络（不支持PBB）和新接入网络（基于PBB）之间的服务连接，后一个网络的VPLS N-PE使用IB-BEB功能将PBB报头从出站帧解压缩到核心，并将PBB报头封装到从核心入站帧。因此，通过VPLS核心交换PBB封装和802.1ad以太网服务帧的混合。
This mode of operation requires new functionality on the VPLS N-PE of the PBB-capable access network, so that the PE can send frames in 802.1ad format or PBB format, on a per PW basis, depending on the capability of the destination access network. Effectively, the PE would have to incorporate B-BEB as well as IB-BEB functions.
此操作模式要求在支持PBB的接入网络的VPLS N-PE上具有新的功能，以便PE可以根据目的地接入网络的能力，基于每个PW发送802.1ad格式或PBB格式的帧。实际上，PE必须结合B-BEB和IB-BEB功能。
A given PE needs to be aware of the capability of its remote peer in order to determine whether it connects to the right PW Forwarder. This can be achieved either via static configuration or by extending the VPLS control plane (BGP-based auto-discovery and LDP Signaling) discussed in [RFC6074]. The latter approach and the details of the extensions required are out of scope for this document.
给定的PE需要了解其远程对等方的能力，以确定其是否连接到正确的PW转发器。这可以通过静态配置或扩展[RFC6074]中讨论的VPLS控制平面（基于BGP的自动发现和LDP信令）来实现。后一种方法和所需扩展的细节不在本文件的范围内。
PBB
B-BEB PBB
+----------+ IB-BEB IB-BEB
| | | |
+-----------+ | IP | | +-----------+ |
| MPLS | | MPLS | V | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | |N-PE| |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
PBB
B-BEB PBB
+----------+ IB-BEB IB-BEB
| | | |
+-----------+ | IP | | +-----------+ |
| MPLS | | MPLS | V | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | |N-PE| |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
Figure 11: Migration with Mixed 802.1ad and PBB Service Frames over VPLS Core
图11:VPLS核心上混合802.1ad和PBB服务帧的迁移
The U-PE and N-PE of the PBB-capable access network both employ BEB functionality. The U-PE implements IB-BEB functionality where the I-component faces the customer (CE) and the B-component faces the core. The N-PE, on the other hand, implements IB-BEB functionality with the I-component facing the core and the B-component facing the customer (access network). In addition, the N-PE implements standalone B-BEB functionality.
支持PBB的接入网络的U-PE和N-PE均采用BEB功能。U-PE实现IB-BEB功能，其中I组件面向客户（CE），B组件面向核心。另一方面，N-PE实现IB-BEB功能，I组件面向核心，B组件面向客户（接入网络）。此外，N-PE实现了独立的B-BEB功能。
This scenario combines the advantages of both previous scenarios without any of their shortcomings, namely: it does not require any changes to existing access networks and it allows the N-PE to leverage the scalability benefits of 802.1ah for PBBN to PBBN connectivity. The disadvantage of this option is that it requires new functionality on the N-PE of the PBBN access. A second disadvantage is that this option requires two P2MP LSPs to be set up at the ingress N-PE: one for the N-PEs that support PBB encapsulation and another one for the N-PEs that don't support PBB encapsulation.
该方案结合了前两种方案的优点，但没有任何缺点，即：不需要对现有接入网络进行任何更改，并且允许N-PE利用802.1ah的可扩展性优势实现PBBN到PBBN的连接。此选项的缺点是它需要PBBN接入的N-PE上的新功能。第二个缺点是，此选项需要在入口N-PE设置两个P2MP LSP：一个用于支持PBB封装的N-PE，另一个用于不支持PBB封装的N-PE。
The authors would like to thank Chris Metz and Dinesh Mohan for their valuable feedback and contributions.
作者要感谢Chris Metz和Dinesh Mohan的宝贵反馈和贡献。
This document does not introduce any additional security aspects beyond those applicable to VPLS/H-VPLS. VPLS/H-VPLS security considerations are already covered in [RFC4111] and [RFC4762].
除适用于VPLS/H-VPLS的安全方面外，本文件不介绍任何其他安全方面。[RFC4111]和[RFC4762]中已经介绍了VPLS/H-VPLS安全注意事项。
[802.1ad] "IEEE Standard for and metropolitan area networks -- Virtual Bridged Local Area Networks -- Provider Bridges", 802.1ad-2005, August 2005.
[802.1ad]“IEEE标准和城域网——虚拟桥接局域网——提供商网桥”，802.1ad-2005，2005年8月。
[802.1ah] "IEEE Standard for Local and metropolitan area networks -- Virtual Bridged Local Area Networks Amendment 7: Provider Backbone Bridges", IEEE Std. 802.1ah-2008, August 2009.
[802.1ah]“IEEE局域网和城域网标准——虚拟桥接局域网修改件7：提供商主干网桥”，IEEE标准802.1ah-2008，2009年8月。
[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4447]Martini，L.，Ed.，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。
[RFC4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron, "Encapsulation Methods for Transport of Ethernet over MPLS Networks", RFC 4448, April 2006.
[RFC4448]Martini，L.，Ed.，Rosen，E.，El Aawar，N.，和G.Heron，“通过MPLS网络传输以太网的封装方法”，RFC 4448，2006年4月。
[RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007.
[RFC4762]Lasserre，M.，Ed.，和V.Kompella，Ed.，“使用标签分发协议（LDP）信令的虚拟专用LAN服务（VPLS）”，RFC 4762，2007年1月。
[RFC6074] Rosen, E., Davie, B., Radoaca, V., and W. Luo, "Provisioning, Auto-Discovery, and Signaling in Layer 2 Virtual Private Networks (L2VPNs)", RFC 6074, January 2011.
[RFC6074]Rosen，E.，Davie，B.，Radoaca，V.，和W.Luo，“第二层虚拟专用网络（L2VPN）中的资源调配、自动发现和信令”，RFC 6074，2011年1月。
[802.1Q] "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q(tm), 2012 Edition, October 2012.
[802.1Q]“局域网和城域网IEEE标准-媒体访问控制（MAC）网桥和虚拟桥接局域网”，IEEE标准802.1Q（tm），2012年版，2012年10月。
[802.1D-REV] "IEEE Standard for Local and metropolitan area networks Media Access Control (MAC) Bridges", IEEE Std. 802.1D, June 2004.
[802.1D-REV]“局域网和城域网媒体访问控制（MAC）网桥的IEEE标准”，IEEE标准802.1D，2004年6月。
[RFC6246] Sajassi, A., Ed., Brockners, F., Mohan, D., Ed., and Y. Serbest, "Virtual Private LAN Service (VPLS) Interoperability with Customer Edge (CE) Bridges", RFC 6246, June 2011.
[RFC6246]Sajassi，A.，Ed.，Brockners，F.，Mohan，D.，Ed.，和Y.Serbest，“虚拟专用局域网服务（VPLS）与客户边缘（CE）网桥的互操作性”，RFC 62462011年6月。
[RFC4111] Fang, L., Ed., "Security Framework for Provider-Provisioned Virtual Private Networks (PPVPNs)", RFC 4111, July 2005.
[RFC4111]Fang，L.，Ed.“提供商提供的虚拟专用网络（PPVPN）的安全框架”，RFC 4111，2005年7月。
Authors' Addresses
作者地址
Ali Sajassi Cisco EMail: sajassi@cisco.com
Ali Sajassi Cisco电子邮件：sajassi@cisco.com
Samer Salam Cisco EMail: ssalam@cisco.com
Samer Salam Cisco电子邮件：ssalam@cisco.com
Nabil Bitar Verizon Communications EMail : nabil.n.bitar@verizon.com
Nabil Bitar Verizon通信电子邮件：Nabil.n。bitar@verizon.com
Florin Balus Nuage Networks EMail: florin.balus@nuagenetworks.net
Florin Balus Nuage Networks电子邮件：Florin。balus@nuagenetworks.net