Extensions to VPLS PE model for Provider Backbone Bridging
draft-ietf-l2vpn-pbb-vpls-pe-model-06

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Document Type Active Internet-Draft (l2vpn WG)
Authors Florin Balus  , Ali Sajassi  , Nabil Bitar 
Last updated 2013-04-16 (latest revision 2012-10-22)
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Send notices to l2vpn-chairs@tools.ietf.org, draft-ietf-l2vpn-pbb-vpls-pe-model@tools.ietf.org
L2VPN Working Group                                    F. Balus (editor)
Internet Draft                                            Alcatel-Lucent
Intended Status: Informational                        
Expires: April 2013                                 Ali Sajassi (editor)
                                                                   Cisco
                                                    
                                                    Nabil Bitar (editor)
                                                                 Verizon
                                                                                
                                                        
                                                                         
 
 
                                                       October 22, 2012 
 
                                      
        Extensions to VPLS PE model for Provider Backbone Bridging 
                 draft-ietf-l2vpn-pbb-vpls-pe-model-06.txt

Status of this Memo 

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Abstract 

   IEEE 802.1ah standard [IEEE802.1ah], also known as Provider Backbone 
   Bridges (PBB) defines an architecture and bridge protocols for 
   interconnection of multiple Provider Bridge Networks (PBNs). PBB was 
   defined in IEEE as a connectionless technology based on multipoint 
   VLAN tunnels. MSTP is used as the core control plane for loop 
   avoidance and load balancing. As a result, the coverage of the 
   solution is limited by STP scale in the core of large service 
   provider networks. PBB on the other hand can be used to attain better 
   scalability in terms of number of customer MAC addresses and number 
   of service instances that can be supported.  

   Virtual Private LAN Service (VPLS) [RFC4664] provides a framework for 
   extending Ethernet LAN services, using MPLS tunneling capabilities, 
   through a routed MPLS backbone without running (M)STP across the 
   backbone. As a result, VPLS has been deployed on a large scale in 
   service provider networks.  

   This draft discusses extensions to the VPLS PE model required to 
   incorporate desirable PBB components while maintaining the Service 
   Provider fit of the initial model.  

   Table of Contents 

   1. Introduction...................................................3 
   2. General terminology............................................4 
   3. PE Reference Model.............................................5 
   4. Packet Walkthrough.............................................8 
   5. Control Plane.................................................10 
   6. Efficient Packet replication in PBB VPLS......................11 
   7. PBB VPLS OAM..................................................11 
   8. Security Considerations.......................................11 
   9. IANA Considerations...........................................11 
   10. References...................................................11 
      10.1. Normative References....................................11 
      10.2. Informative References..................................12 
   11. Contributors.................................................12 
   12. Acknowledgments..............................................12 

 
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1. Introduction 

   IEEE 802.1ah standard [IEEE802.1ah], also known as Provider Backbone 
   Bridges (PBB) defines an architecture and bridge protocols for 
   interconnection of multiple Provider Bridge Networks (PBNs). PBB 
   provides data plane hierarchy and new addressing designed to improve 
   the scalability of MAC addresses and service instances in Provider 
   Backbone Networks. MSTP is still used as the core control plane for 
   loop avoidance and load balancing. As a result, the coverage of the 
   solution is limited by STP scale in the core of large service 
   provider networks.  

   Virtual Private LAN Service (VPLS) provides a solution for extending 
   Ethernet LAN services, using MPLS tunneling capabilities, through a 
   routed MPLS backbone without requiring the use of (M)STP across the 
   backbone. VPLS use of the structured FEC 129 [RFC4762] also allows 
   for inter-domain, inter-provider connectivity and enables auto-
   discovery options across the network improving the service delivery 
   options.  

   A hierarchical solution for VPLS was introduced in [RFC4762] for the 
   purpose of improved scalability and to provide efficient handling of 
   packet replication. These improvements are achieved by reducing the 
   number of PE devices connected in a full-mesh topology through the 
   creation of two-tier PEs. A U-PE aggregates all the CE devices in a 
   lower-tier access network and then connects to the N-PE device(s) 
   deployed around the core domain. In VPLS, MAC address learning and 
   forwarding are done based on customer MAC addresses (C-MACs), which 
   poses scalability issues on the N-PE devices as the number of VPLS 
   instances (and thus customer MAC addresses) 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 (in terms of PW manageability and troubleshooting) as the 
   number of customer service instances grows.  

   This document describes how PBB can be integrated with VPLS to allow 
   for useful PBB capabilities while continuing to avoid the use of MSTP 
   in the backbone. The combined solution referred in this document as 
   PBB-VPLS results in better scalability in terms of number of service 
   instances, PWs and C-MACs that need to be handled in the VPLS PEs.  

   Section 2 gives a quick terminology reference. Section 3 covers the 
   reference model for PBB VPLS PE. Section 4 describes the packet 
   walkthrough. Section 5 to 7 discusses the PBB-VPLS usage of existing 
   VPLS mechanisms - control plane, efficient packet replication, OAM. 
 
 
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2. General terminology 

   Some general terminology is defined here; most of the terminology 
   used is from [IEEE802.1ah], [RFC4664] and [RFC4026]. Terminology 
   specific to this memo is introduced as needed in later sections.  

   802.1ad: IEEE specification for "QinQ" encapsulation and bridging of 
   Ethernet frames 
    
   802.1ah: IEEE specification for "MAC tunneling" encapsulation and 
   bridging of frames across a provider backbone bridged network. 
    
   B-BEB: A backbone edge bridge positioned at the edge of a provider 
   backbone bridged network. It contains a B-component that supports 
   bridging in the provider backbone based on B-MAC and B-TAG 
   information 
    
   B-MAC: The backbone source or destination MAC address fields defined 
   in the 802.1ah provider MAC encapsulation header.   
    
   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 I and B components. 

   B-component: A bridging component contained in backbone edge and 
   core bridges that bridges in the backbone space (B-MAC addresses,
   B-VLAN)  
 
   B-TAG:  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-Tagged Service Interface: This is the interface between a BEB and 
   BCB in a provider backbone bridged network. Frames passed through 
   this interface contain a B-TAG field. 
    
   B-VID: The specific VLAN identifier carried inside a B-TAG
 
   B-PW: The pseudowire used to interconnect B-component instances.
    
   I-component: A bridging component contained in a backbone edge bridge 
   that bridges in the customer space (customer MAC addresses, S-VLAN)  
    

    
 
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   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, service VLAN IDs) and a 
   B-component for bridging the provider's backbone space (B-MAC, B-
   TAG). 

   I-BEB: A backbone edge bridged positioned at the edge of a provider 
   backbone bridged network. It contains an I-component for bridging in 
   the customer space (customer MAC addresses, service VLAN IDs). 
    
   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-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-Tagged Service Interface: This the interface defined between the I 
   and B components inside an IB-BEB or between two B-BEB. Frames passed 
   through this interface contain an I-TAG field    
    
   PBB: Provider Backbone Bridge 
    
   PBBN: Provider Backbone Bridged Network 
    
   PBN: Provider Bridged Network. A network that employs 802.1ad (QinQ) 
   technology. 
    
   S-TAG: A field defined in the 802.1ad QinQ encapsulation header that 
   conveys the service VLAN identifier information (S-VLAN). 
    
   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-VLAN: The specific service VLAN identifier carried inside an S-TAG 
    
   

3. PE Reference Model 

   The following gives a short primer on PBB before describing the PE 
   reference model for PBB-VPLS. The internal components of a PBB bridge 
   module are depicted in Figure 1. 

 
 
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                   +-------------------------------+ 
                   |      802.1ah Bridge Model     |  
                   |                               | 
        +---+      |  +------+      +-----------+  | 
        |CE |---------|I-Comp|------|           |  | 
        +---+      |  |      |      |           |-------- 
                   |  +------+      |           |  | 
                   |     o          |   B-Comp  |  | 
                   |     o          |           |-------- 
                   |     o          |           |  | 
        +---+      |  +------+      |           |  | 
        |CE |---------|I-Comp|------|           |-------- 
        +---+  ^   |  |      |  ^   |           |  |   ^ 
               |   |  +------+  |   +-----------+  |   | 
               |   +------------|------------------+   | 
               |                |                      | 
               |                |                      | 
             S-tagged         I-tagged              B-tagged 
             Service I/F      Service I/F           Service I/F 
                
                        Figure 1: PBB Bridge Model 
                                      
   Provider Backbone Bridges (PBBs) [IEEE 802.1ah] offers a scalable 
   solution for service providers to build large bridged networks. The 
   focus of PBB is primarily on improving two main areas with provider 
   Ethernet bridged networks: 
    
     - MAC-address table scalability  
     - Service instance scalability 
    
   To obviate the above two limitations, PBB introduces a hierarchical 
   network architecture with associated new frame formats which extend 
   the work completed by Provider Bridges (IEEE 802.1ad). In the PBBN 
   architecture, customer networks (using IEEE 802.1Q or 802.1ad 
   bridging) are aggregated into Provider Backbone Bridge Networks 
   (PBBNs) which utilize the IEEE 802.1ah frame format. The frame 
   format employs a MAC tunneling encapsulation scheme for tunneling 
   customer Ethernet frames within provider Ethernet frames across the 
   PBBN. A VLAN identifier (B-VID) is used to segregate the backbone 
   into broadcast domains and a new 24-bit service identifier (I-SID) 
   is defined and used to associate a given customer MAC frame with a 
   provider service instance (also called the service delimiter). It 
   should be noted that in [802.1ah] there is a clear segregation 
   between provider service instances (represented by I-SIDs) and 
   provider VLANs (represented by B-VIDs) which was not the case for 
   802.1ad.  
 
 
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   As shown in the figure 1, a PBB bridge may consist of a single B-
   component and one or more I-components. In simple terms, the B-
   component provides bridging in provider space (B-MAC, B-VLAN) and the 
   I-component provides bridging in customer space (C-MAC, S-VLAN). The 
   customer frame is first encapsulated with the provider backbone 
   header (B-MAC, B-tag, I-tag); then, the bridging is performed in the 
   provider backbone space (B-MAC, B-VLAN) through the network till the 
   frame arrives at the destination BEB where it gets de-encapsulated 
   and passed to the CE. If a PBB bridge consists of both I & B 
   components, then it is called IB-BEB and if it only consists of 
   either B-component or I-component, then it is called B-BEB or I-BEB 
   respectively. The interface between an I-BEB or IB-BEB and a CE is 
   called S-tagged service interface and the interface between an I-BEB 
   and a B-BEB (or between two B-BEBs) is called I-tagged service 
   interface. The interface between a B-BEB or IB-BEB and a Backbone 
   Core Bridge (BCB) is called B-Tagged service interface.  

   To accommodate the PBB components the VPLS model defined in [RFC4664] 
   is extended as depicted in figure 1.  

    
        +----------------------------------------+ 
        |       PBB-VPLS-capable PE model        | 
        |   +---------------+          +------+  |   
        |   |               |          |VPLS-1|------------ 
        |   |               |==========|Fwdr  |------------ PWs 
   +--+ |   |     Bridge    ------------      |------------ 
   |CE|-|-- |               |          +------+  | 
   +--+ |   |     Module    |             o      | 
        |   |               |             o      | 
        |   |   (802.1ah    |             o      | 
        |   |    bridge)    |             o      | 
        |   |               |             o      | 
   +--+ |   |               |          +------+  | 
   |CE|-|-- |               ------------VPLS-n|------------- 
   +--+ |   |               |==========| Fwdr |------------- PWs 
        |   |               |     ^    |      |------------- 
        |   +---------------+     |    +------+  | 
        |                         |              | 
        +-------------------------|--------------+ 
                         LAN emulation Interface 
    
                    Figure 2: PBB-VPLS capable PE Model 
    

 
 
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   The PBB Module as defined in [IEEE802.1ah] specification is expanded 
   to interact with VPLS Forwarders. The VPLS Forwarders are used in 
   [RFC4762] to build a PW mesh or a set of spoke-PWs (HVPLS 
   topologies). The VPLS instances are represented externally in the 
   MPLS context by a L2FEC which binds related VPLS instances together. 
   VPLS Signaling advertises the mapping between the L2FEC and the PW 
   labels and implicitly associates the VPLS bridging instance to the 
   VPLS Forwarders [RFC4762]. 

   In the PBB-VPLS case the backbone service instance in the B-component 
   space(B-VID) is represented in the backbone MPLS network using a VPLS 
   instance. Same as for the regular VPLS case, existing signaling 
   procedures are used to generate through PW labels the linkage between 
   VPLS Forwarders and the backbone service instance.  

   Similarly with the regular HVPLS, another L2FEC may be used to 
   identify the customer service instance in the I-component space. This 
   will be useful for example to address the PBB-VPLS N-PE case where 
   HVPLS spokes are connecting the PBB-VPLS N-PE to a VPLS U-PE. 

   It is important to note that the PBB-VPLS solution inherits the PBB 
   service aggregation capability where multiple customer service 
   instances may be mapped to a backbone service instance. In the PBB-
   VPLS case this means multiple customer VPNs can be transported using 
   a single VPLS instance corresponding to the backbone service 
   instance, thus reducing substantially resource consumption in the 
   VPLS core. 

4. Packet Walkthrough 

   Since PBB bridge module inherently performs forwarding, the PE 
   reference model of Figure 2 can be expanded as the one shown in 
   Figure 3.  

   Furthermore, the B-component is connected via several virtual 
   interfaces to the PW Forwarder module. The function of PW Forwarder 
   is defined in [RFC3985]. In this context, the PW Forwarder simply 
   performs the mapping of the PWs to the Virtual Interface on the B-
   component without the need for any MAC lookup.  

   This simplified model takes full advantage of PBB bridge module where 
   all the [IEEE 802.1ah] procedures including the C-MAC/B-MAC 
   forwarding and PBB encapsulation/decapsulation takes place and thus 
   avoids specifying any of these functions in here.    

 
 
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   Because of text-based graphics, the Figure 3 only shows PWs on the 
   core-facing side; however, in case of MPLS access with spoke PWs, the 
   PE reference model is simply extended to include the same PW 
   Forwarder function on the access-facing side. To avoid cluttering the 
   figure, the access-side PW Forwarder is not depicted without loss of 
   any generality. 

       
        +------------------------------------------------+ 
        |               PBB-VPLS-capable PE model        | 
        |             +---------------+      +------+    |   
        |             |               |      |      |    | 
        |   +------+  |               ========      --------- 
   +--+ |   |      |  |               |      |      --------- PWs 
   |CE|-|-- | I-   ====               ========  PW  --------- 
   +--+ |   | comp |  |               |      | Fwdr | 
        |   +------+  |               |      |      --------- PWs 
        |             |    B-Comp     ========      ---------  
        |             |               |  ^   |      |    | 
        |   +------+  |               |  |   +------+    | 
   +--+ |   | I-   |  |               OOOOOOOOOOOOOOOOOOOOOOOO B-tag 
   |CE|-|-- | comp ====               |  |               |     I/Fs 
   +--+ |   |      |^ |               OOOOOOOOOOOOOOOOOOOOOOOO 
        |   +------+| |               |  |               | 
        |           | +---------------+  |               |   
        |           |                    |               | 
        +-----------|--------------------|---------------+ 
                    |                    |   
              Internal I-tag I/Fs   Virtual I/Fs 
    
    +----------+                                      +------------+ 
    |CMAC DA,SA|                                      | PSN header | 
    |----------|                                      |------------| 
    |SVID, CVID|                                      | PW Label   | 
    |----------|                                      |------------| 
    | Payload  |                                      | BMAC DA,SA | 
    +----------+                                      |------------| 
                                                      | PBB I-tag  | 
                                                      |------------| 
                                                      | CMAC DA,SA | 
                                                      |------------| 
                                                      | SVID, CVID | 
                                                      |------------| 
                                                      |  Payload   | 
                                                      +------------+ 
    
               Figure 3: Packet Walkthrough for PBB VPLS PE 
 
 
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   In order to better understand the data plane walkthrough let us 
   consider the example of a PBB packet arriving over a B-PW. The PSN 
   header is used to carry the PBB encapsulated frame over the backbone 
   while the PW Label will point to the related Backbone Service 
   Instance (B-SI), same as for regular VPLS. The PW Label has in this 
   case an equivalent role with the Backbone VLAN id on the PBB B-tagged 
   interface. 

   An example of the PBB packet for regular Ethernet PW is depicted in 
   Figure 3 on the right hand side. The MPLS packet from MPLS core 
   network is received by the PBB-VPLS PE. The PW Forwarder function of 
   the PE uses PW label to derive the virtual interface-id on the B-
   component and then after removing the PSN and PW encapsulation, it 
   passes the packet to the B-component. From there on, the processing 
   and forwarding is performed according to the [IEEE 802.1ah] where 
   bridging based on B-MAC DA is performed which result in one of the 
   three outcomes:   

     1. The packet is forwarded to a physical interface on the B-
       component. In this case, the 802.1ah Ethernet frame is forwarded 
       as is. 

     2. The packet is forwarded to a virtual interface on the B-
       component. This is not typically the case because of a single 
       split-horizon group within a VPLS instance; however, if there is 
       more than one split-horizon group, then such forwarding takes 
       place. In this case, the PW Forwarder module adds the PSN and PW 
       labels before sending the packet out.  

     3. The packet is forwarded toward the access side via one of the I-
       tagged service interfaces connected to the corresponding I-
       components. In this scenario, the I-component removes the B-MAC 
       header according to [IEEE 802.1ah] and bridges the packet using 
       C-MAC DA.  

     4. If the destination B-MAC is an unknown or a Group MAC address 
       (Multicast or Broadcast), then the B-component floods the 
       packet to one or more of the three destinations described above. 

5. Control Plane 

   The control plane procedures described in [RFC6074], [RFC4761] and 
   [RFC4762] can be re-used in a PBB-VPLS to setup the PW infrastructure 
   in the service provider and/or customer bridging space. This allows 
   porting the existing control plane procedures (e.g. BGP-AD, PW setup, 
   VPLS MAC Flush, PW OAM) for each domain.   
 
 
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6. Efficient Packet replication in PBB VPLS 

   The PBB VPLS architecture takes advantage of the existing VPLS 
   features addressing packet replication efficiency. HVPLS hierarchy 
   may be used in both customer and backbone service instances to reduce 
   the redundant distribution of packets over the core. IGMP and PIM 
   snooping may be applied on a per customer service instance to control 
   the distribution of the Multicast traffic to non-member sites.  

   [IEEE802.1ah] specifies also the use of MMRP protocol [IEEE802.1ak] 
   for flood containment in the backbone instances. The same solution 
   can be ported in the PBB-VPLS solution.  

   Further optimizations of the packet replication in PBB-VPLS are out 
   of the scope of this draft. 

7. PBB VPLS OAM 

   The existing VPLS, PW and MPLS OAM procedures may be used in each 
   customer or backbone service instance to verify the status of the 
   related connectivity components.  

   PBB OAM procedures make use of the IEEE 802.1ag and Y.1731 tools in 
   both I-component and B-component.  

   Both set of tools (PBB and VPLS) may be used for the combined PBB-
   VPLS solution. 

8. Security Considerations 

   No new security issues are introduced beyond those that are described 
   in [RFC4761] and [RFC4762]. 

9. IANA Considerations 

   IANA does not need to take any action for this draft. 

10. References 

10.1. Normative References 

   [RFC4761] Kompella, K. and Rekhter, Y. (Editors), "Virtual Private 
             LAN Service (VPLS) Using BGP for Auto-Discovery and 
             Signaling", RFC 4761, January 2007. 

 
 
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   [RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual Private 
             LAN Service (VPLS) Using Label Distribution Protocol (LDP) 
             Signaling", RFC 4762, January 2007. 

   [RFC6074] E. Rosen, et Al. "Provisioning, Autodiscovery and 
             Signaling in L2VPNs", RFC 6074, January 2011   

10.2. Informative References 

   [RFC3985] Bryant, S. and Pate, P. (Editors)," Pseudo Wire Emulation 
             Edge-to-Edge (PWE3) Architecture", RFC 3985, May 2005. 

   [RFC4664] Andersson, L. and Rosen, E. (Editors),"Framework for Layer 
             2 Virtual Private Networks (L2VPNs)", RFC 4664, Sept 2006 

   [IEEE802.1ah] IEEE 802.1ah "Virtual Bridged Local Area Networks, 
             Amendment 6: Provider Backbone Bridges", Approved Standard 
             June 12th, 2008  

   [IEEE802.1ak] IEEE Draft P802.1ak/D8.0 "Virtual Bridged Local Area 
             Networks, Amendment 7: Multiple Registration Protocol", 
             Work in Progress, November 29, 2006 

   [RFC4026] Andersson, L. et Al., "Provider Provisioned Virtual Private 
             Network (VPN) Terminology", RFC 4026, May 2005. 

11. Contributors     

   The following authors contributed to this document: John Hoffmans
   (KPN), Geraldine Calvignac (France Telecom), Olen Stokes (Extreme
   Networks), Raymond Zhang and Matthew Bocci (Alcatel-Lucent).

12. Acknowledgments 

   The authors would like to thank Wim Henderickx, Mustapha Aissaoui,
   Dimitri Papadimitriou, Pranjal Dutta, Jorge Rabadan and Maarten 
   Vissers for their insightful comments and probing questions. 

 
 
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Authors' Addresses 

   Ali Sajassi  
   Cisco  
   170 West Tasman Drive  
   San Jose, CA  95134, U.S.  
   Email: sajassi@cisco.com  
        
   Nabil Bitar 
   Verizon 
   40 Sylvan Road 
   Waltham, MA 02145 
   Email: nabil.bitar@verizon.com 
    
   Florin Balus 
   Alcatel-Lucent 
   701 E. Middlefield Road 
   Mountain View, CA, USA 94043   
   Email: florin.balus@alcatel-lucent.com 
    
   Matthew Bocci 
   Alcatel-Lucent, 
   Voyager Place 
   Shoppenhangers Road 
   Maidenhead 
   Berks, UK 
   e-mail: matthew.bocci@alcatel-lucent.co.uk 
    
   Raymond Zhang 
   BT 
   2160 E. Grand Ave. 
   El Segundo, CA 900245 USA 
   EMail: raymond.zhang@bt.com 
    
   Geraldine Calvignac 
   France Telecom 
   2, avenue Pierre-Marzin 
   22307 Lannion Cedex 
   France 
   Email: geraldine.calvignac@orange-ftgroup.com 
 
   John Hoffmans 
   KPN 
   Regulusweg 1 
   2516 AC Den Haag 
   Nederland 
   Email: john.hoffmans@kpn.com

Balus, et al.          Expires April 22, 2013                 [Page 13] 


Internet-Draft  Extensions to VPLS PE model for PBB   October 2012  
   
   Olen Stokes 
   Extreme Networks 
   PO Box 14129 
   RTP, NC 27709 
   USA 
   Email: ostokes@extremenetworks.com  

 
 
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