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Internet Engineering Task Force (IETF)                     F. Balus, Ed.Request for Comments: 7041                                Alcatel-LucentCategory: Informational                                  A. Sajassi, Ed.ISSN: 2070-1721                                                    Cisco                                                           N. Bitar, Ed.                                                                 Verizon                                                           November 2013Extensions to the Virtual Private LAN Service (VPLS)Provider Edge (PE) Model for Provider Backbone BridgingAbstract   The IEEE 802.1 Provider Backbone Bridges (PBBs) specification defines   an architecture and bridge protocols for interconnection of multiple   Provider Bridged Networks (PBNs).  Provider backbone bridging was   defined by IEEE as a connectionless technology based on multipoint   VLAN tunnels.  PBB can be used to attain better scalability than   Provider Bridges (PBs) in terms of the number of customer Media   Access Control addresses and the number of service instances that can   be supported.   The Virtual Private LAN Service (VPLS) provides a framework for   extending Ethernet LAN services, using MPLS tunneling capabilities,   through a routed MPLS backbone without running the Rapid Spanning   Tree Protocol (RSTP) or the Multiple Spanning Tree Protocol (MSTP)   across the backbone.  As a result, VPLS has been deployed on a large   scale in service provider networks.   This document discusses extensions to the VPLS Provider Edge (PE)   model required to incorporate desirable PBB components while   maintaining the service provider fit of the initial model.Balus, et al.                 Informational                     [Page 1]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7041.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Table of Contents1. Introduction ....................................................32. General Terminology .............................................43. PE Reference Model ..............................................64. Packet Walkthrough ..............................................95. Control Plane ..................................................116. Efficient Packet Replication in PBB VPLS .......................127. PBB VPLS OAM ...................................................128. Security Considerations ........................................129. References .....................................................139.1. Normative References ......................................139.2. Informative References ....................................1310. Contributors ..................................................1411. Acknowledgments ...............................................15Balus, et al.                 Informational                     [Page 2]

RFC 7041           Extensions to VPLS PE Model for PBB     November 20131.  Introduction   The IEEE 802.1 Provider Backbone Bridges specification [PBB] defines   an architecture and bridge protocols for interconnection of multiple   Provider Bridged Networks (PBNs).  PBB can be used to attain better   scalability than Provider Bridges [PB] in terms of the number of   customer Media Access Control (MAC) addresses and the number of   service instances that can be supported.  PBB provides a data-plane   hierarchy and new addressing designed to achieve such better   scalability in Provider Backbone Networks.  A number of Ethernet   control-plane protocols, such as the Rapid Spanning Tree Protocol   (RSTP), the Multiple Spanning Tree Protocol (MSTP), and Shortest Path   Bridging (SPB), could be deployed as the core control plane for loop   avoidance and load balancing for PBB.  The applicability of these   control protocols is out of scope for this document.   The 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 a native   Ethernet control-plane protocol 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 [RFC4761] and   [RFC4762] to provide improved scalability and efficient handling of   packet replication.  These improvements are achieved by reducing the   number of Provider Edge (PE) devices connected in a full-mesh   topology through the creation of two-tier PEs.  A User-facing PE   (U-PE) aggregates all the Customer Edge (CE) devices in a lower-tier   access network and then connects to the Network-facing PE (N-PE)   device(s) deployed around the core domain.  In VPLS, Media Access   Control (MAC) address learning and forwarding are done based on   Customer MAC addresses (C-MACs); this poses scalability issues on the   N-PE devices as the number of VPLS instances (and thus C-MACs)   increases.  Furthermore, since a set of pseudowires (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 to in this documentBalus, et al.                 Informational                     [Page 3]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   as PBB-VPLS results in better scalability in terms of the number of   service instances, PWs, and C-MACs that need to be handled in the   VPLS PEs.Section 2 provides a quick terminology reference.Section 3 covers   the reference model for PBB VPLS PEs.Section 4 describes the packet   walkthrough.  Sections5 through7 discuss the PBB-VPLS usage of   existing VPLS mechanisms -- the control plane; efficient packet   replication; and Operations, Administration, and Maintenance (OAM).2.  General Terminology   Some general terminology is defined here; most of the terminology   used is from [PBB], [PB], [RFC4664], and [RFC4026].  Terminology   specific to this memo is introduced as needed in later sections.   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 Backbone MAC (B-MAC)      and B-tag information.   B-component: A bridging component contained in backbone edge and core      bridges that bridges in the backbone space (B-MAC addresses,      B-VLAN).   B-MAC: The backbone source or destination MAC address fields defined      in the PBB provider MAC encapsulation header.   B-tag:  Field defined in the PBB 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: The interface between a BEB and a      Backbone Core Bridge (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-VLAN: The backbone VLAN associated with a B-component.   B-PW: The pseudowire used to interconnect B-component instances.   BEB: A backbone edge bridge positioned at the edge of a provider      backbone bridged network.  It can contain an I-component, a      B-component, or both I-components and B-components.   C-VID: The VLAN identifier in a customer VLAN.Balus, et al.                 Informational                     [Page 4]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   DA: Destination Address.   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, service VLAN IDs).   I-component: A bridging component contained in a backbone edge bridge      that bridges in the customer space (customer MAC addresses,      service VLAN identifier information (S-VLAN)).   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 PBB provider MAC encapsulation header      that conveys the service instance information (I-SID) associated      with the frame.   I-Tagged Service Interface: The interface defined between the      I-components and B-components inside an IB-BEB or between two      B-BEBs.  Frames passed through this interface contain an I-tag      field.   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).   PBs: Provider Bridges (IEEE amendment (802.1ad) to 802.1Q for "QinQ"      encapsulation and bridging of Ethernet frames [PB]).   PBBs: Provider Backbone Bridges (IEEE amendment (802.1ah) to 802.1Q      for "MAC tunneling" encapsulation and bridging of frames across a      provider network [PBB]).   PBBN: Provider Backbone Bridged Network.   PBN: Provider Bridged Network.  A network that employs 802.1ad (QinQ)      technology.   PSN: Packet-Switched Network.   S-tag: A field defined in the 802.1ad QinQ encapsulation header that      conveys the service VLAN identifier information (S-VLAN).Balus, et al.                 Informational                     [Page 5]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   S-Tagged Service Interface: 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.   SA: Source Address.   S-VID: The VLAN identifier in a service VLAN.   Tag: In Ethernet, a header immediately following the Source MAC      Address field of the frame.3.  PE Reference Model   The following gives a short primer on the Provider Backbone Bridge   (PBB) before describing the PE reference model for PBB-VPLS.  The   internal components of a PBB bridge module are depicted in Figure 1.              +-------------------------------+              |       PBB Bridge Model        |              |                               |   +---+      |  +------+      +-----------+  |   |CE |---------|I-Comp|------|           |  |   +---+      |  |      |      |           |--------              |  +------+      |           |  |              |     o          |   B-Comp  |  |              |     o          |           |--------              |     o          |           |  |   +---+      |  +------+      |           |  |   |CE |---------|I-Comp|------|           |--------   +---+  ^   |  |      |  ^   |           |  |   ^          |   |  +------+  |   +-----------+  |   |          |   +------------|------------------+   |          |                |                      |          |                |                      |     S-tagged            I-tagged             B-tagged     Service Interface   Service I/F          Service I/F     (I/F)                        Figure 1: PBB Bridge ModelBalus, et al.                 Informational                     [Page 6]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   Provider Backbone Bridges (PBBs) [PBB] offer 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 that extend   the work completed by Provider Bridges (PBs).  In the PBBN   architecture, customer networks (using PBs) are aggregated into   PBBNs, which utilize the IEEE PBB 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 [PBB] 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 PBs.   As shown in 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 the provider space (B-MAC, B-VLAN),   and the I-component provides bridging in the 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   decapsulated and passed to the CE.  If a PBB bridge consists of both   I-components and B-components, then it is called an IB-BEB, and if it   only consists of either B-components or I-components, then it is   called a B-BEB or an I-BEB, respectively.  The interface between an   I-BEB or IB-BEB and a CE is called an S-tagged service interface, and   the interface between an I-BEB and a B-BEB (or between two B-BEBs) is   called an I-tagged service interface.  The interface between a B-BEB   or IB-BEB and a Backbone Core Bridge (BCB) is called a B-tagged   service interface.Balus, et al.                 Informational                     [Page 7]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   To accommodate the PBB components, the VPLS model defined in   [RFC4664] is extended as depicted in Figure 2.        +----------------------------------------+        |       PBB-VPLS-Capable PE Model        |        |   +---------------+          +------+  |        |   |               |          |VPLS-1|------------        |   |               |==========|Fwdr  |------------ PWs   +--+ |   |     Bridge    ------------      |------------   |CE|-|-- |               |          +------+  |   +--+ |   |     Module    |             o      |        |   |               |             o      |        |   |    (PBB       |             o      |        |   |    bridge)    |             o      |        |   |               |             o      |   +--+ |   |               |          +------+  |   |CE|-|-- |               ------------VPLS-n|-------------   +--+ |   |               |==========| Fwdr |------------- PWs        |   |               |     ^    |      |-------------        |   +---------------+     |    +------+  |        |                         |              |        +-------------------------|--------------+                         LAN Emulation Interface                    Figure 2: PBB-VPLS-Capable PE Model   The PBB module as defined in the [PBB] 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 (Hierarchical VPLS   (H-VPLS) topologies).  The VPLS instances are represented externally   in the MPLS context by a Layer 2 Forwarding Equivalence Class (L2FEC)   that 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.  In the same way 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 H-VPLS, 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 H-VPLS spokes are connecting the PBB-VPLS N-PE to a VPLS U-PE.Balus, et al.                 Informational                     [Page 8]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   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 substantially reducing resource consumption in the   VPLS core.4.  Packet Walkthrough   Since the PBB bridge module inherently performs forwarding, the PE   reference model of Figure 2 can be expanded as shown in Figure 3.   Furthermore, the B-component is connected via several virtual   interfaces to the PW Forwarder module.  The function of the 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 the PBB module -- where   all the [PBB] procedures, including C-MAC/B-MAC forwarding and PBB   encapsulation/decapsulation, take place -- and thus avoids the need   to specify any of these functions in this document.   Because of text-based graphics, Figure 3 only shows PWs on the   core-facing side; however, in the 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, but without losing any generality, the access-side PW   Forwarder (Fwdr) is not depicted.Balus, et al.                 Informational                     [Page 9]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013        +------------------------------------------------+        |               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 Interfaces (I/Fs)    +---------------+                                +--------------+    | C-MAC DA,SA   |                                | PSN Header   |    |---------------|                                |--------------|    | S-VID, C-VID  |                                | PW Label     |    |---------------|                                |--------------|    |    Payload    |                                | B-MAC DA,SA  |    +---------------+                                |--------------|                                                     | PBB I-tag    |                                                     |--------------|                                                     | C-MAC DA,SA  |                                                     |--------------|                                                     | S-VID, C-VID |                                                     |--------------|                                                     |   Payload    |                                                     +--------------+                Figure 3: Packet Walkthrough for PBB VPLS PE   In order to better understand the data-plane walkthrough, let us   consider the example of a PBB packet arriving over a Backbone   pseudowire (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), in the same way as for   regular VPLS.  The PW label has in this case an equivalent role with   the backbone VLAN identifier on the PBB B-tagged interface.Balus, et al.                 Informational                    [Page 10]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   An example of the PBB packet for the regular Ethernet PW is depicted   on the right-hand side of Figure 3.  The MPLS packet from the MPLS   core network is received by the PBB-VPLS PE.  The PW Forwarder   function of the PE uses the 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 are performed according to   [PBB], where bridging based on the Backbone MAC (B-MAC) Destination   Address (DA) is performed.  This scenario results in one of the   following outcomes:   1. The packet is forwarded to a physical interface on the      B-component.  In this case, the PBB 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 case, the I-component removes the B-MAC      header according to [PBB] and bridges the packet using the      C-MAC DA.   If the destination B-MAC is an unknown MAC address 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 reused in a PBB-VPLS to set up the PW infrastructure   in the service provider and/or customer bridging space.  This allows   porting the existing control-plane procedures (e.g., BGP   Auto-Discovery (BGP-AD), PW setup, VPLS MAC flushing, PW OAM) for   each domain.Balus, et al.                 Informational                    [Page 11]

RFC 7041           Extensions to VPLS PE Model for PBB     November 20136.  Efficient Packet Replication in PBB VPLS   The PBB VPLS architecture takes advantage of the existing VPLS   features addressing packet replication efficiency.  The H-VPLS   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"   basis to control the distribution of the multicast traffic to   non-member sites.   [IEEE-802.1Q] specifies the use of the Multiple MAC Registration   Protocol (MMRP) 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 document.7.  PBB VPLS OAM   The existing VPLS, PW, and MPLS OAM procedures may be used in each   customer service instance or backbone service instance to verify the   status of the related connectivity components.   PBB OAM procedures make use of the IEEE Ethernet Connectivity Fault   Management [CFM] and ITU-T Y.1731 [Y.1731] tools in both I-components   and B-components.   Both sets 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 described in   [RFC4761] and [RFC4762].Balus, et al.                 Informational                    [Page 12]

RFC 7041           Extensions to VPLS PE Model for PBB     November 20139.  References9.1.  Normative References   [RFC4761] Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private             LAN Service (VPLS) Using BGP for Auto-Discovery and             Signaling",RFC 4761, January 2007.   [RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private             LAN Service (VPLS) Using Label Distribution Protocol (LDP)             Signaling",RFC 4762, January 2007.   [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 2011.9.2.  Informative References   [RFC3985] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation             Edge-to-Edge (PWE3) Architecture",RFC 3985, March 2005.   [RFC4664] Andersson, L., Ed., and E. Rosen, Ed., "Framework for             Layer 2 Virtual Private Networks (L2VPNs)",RFC 4664,             September 2006.   [PBB]     Clauses 25 and 26 of "IEEE Standard for Local and             metropolitan area networks - Media Access Control (MAC)             Bridges and Virtual Bridged Local Area Networks", IEEE             Std 802.1Q-REV, 2013.   [PB]      Clauses 15 and 16 of "IEEE Standard for Local and             metropolitan area networks - Media Access Control (MAC)             Bridges and Virtual Bridged Local Area Networks", IEEE             Std 802.1Q-REV, 2013.   [CFM]     CFM clauses of "IEEE Standard for Local and metropolitan             area networks - Media Access Control (MAC) Bridges and             Virtual Bridged Local Area Networks", IEEE Std 802.1Q-REV,             2013.   [IEEE-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-REV, 2013.Balus, et al.                 Informational                    [Page 13]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013   [Y.1731]  ITU-T Recommendation Y.1731, "OAM functions and mechanisms             for Ethernet based networks", July 2011.   [RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual             Private Network (VPN) Terminology",RFC 4026, March 2005.10.  Contributors   The following people made significant contributions to this document:      Matthew Bocci      Alcatel-Lucent      Voyager Place      Shoppenhangers Road      Maidenhead      Berks, UK      EMail: matthew.bocci@alcatel-lucent.com      Raymond Zhang      Alcatel-Lucent      EMail: raymond.zhang@alcatel.com      Geraldine Calvignac      Orange      2, avenue Pierre-Marzin      22307 Lannion Cedex      France      EMail: geraldine.calvignac@orange.com      John Hoffmans      KPN      Regulusweg 1      2516 AC Den Haag      The Netherlands      EMail: john.hoffmans@kpn.comBalus, et al.                 Informational                    [Page 14]

RFC 7041           Extensions to VPLS PE Model for PBB     November 2013      Olen Stokes      Extreme Networks      PO Box 14129      RTP, NC  27709      USA      EMail: ostokes@extremenetworks.com11.  Acknowledgments   The authors would like to thank Wim Henderickx, Mustapha Aissaoui,   Dimitri Papadimitriou, Pranjal Dutta, Jorge Rabadan, Maarten Vissers,   and Don Fedyk for their insightful comments and probing questions.Authors' Addresses   Florin Balus (editor)   Alcatel-Lucent   701 E. Middlefield Road   Mountain View, CA  94043   USA   EMail: florin.balus@alcatel-lucent.com   Ali Sajassi (editor)   Cisco   170 West Tasman Drive   San Jose, CA  95134   USA   EMail: sajassi@cisco.com   Nabil Bitar (editor)   Verizon   60 Sylvan Road   Waltham, MA  02145   USA   EMail: nabil.n.bitar@verizon.comBalus, et al.                 Informational                    [Page 15]