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Versions: 00 01 02 draft-ietf-l2vpn-vpms-frmwk-requirements

Network Working Group                                          Y. Kamite
Internet-Draft                                        NTT Communications
Intended status: Informational                                 F. Jounay
Expires: January 15, 2009                                 France Telecom
                                                        B. Niven-Jenkins
                                                                      BT
                                                           July 14, 2008


Framework and Requirements for Virtual Private Multicast Service (VPMS)
           draft-kamite-l2vpn-vpms-frmwk-requirements-01.txt

Status of this Memo

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   This Internet-Draft will expire on January 15, 2009.

Abstract

   This document provides a framework and service level requirements for
   Virtual Private Multicast Service (VPMS).  VPMS is defined as a Layer
   2 VPN service that provides point-to-multipoint connectivity for a
   variety of Layer 2 link layers across an IP or MPLS-enabled PSN.
   This document outlines architectural service models of VPMS and
   states generic and high level requirements.  This is intended to aid
   in developing protocols and mechanisms to support VPMS.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Problem Statement  . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Scope of This Document . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  Ethernet Use Case  . . . . . . . . . . . . . . . . . . . .  5
     4.2.  ATM-based Use Case . . . . . . . . . . . . . . . . . . . .  5
     4.3.  TDM-based Use Case . . . . . . . . . . . . . . . . . . . .  6
   5.  Reference Model  . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Customer Requirements  . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Service Topology . . . . . . . . . . . . . . . . . . . . .  9
       6.1.1.  Point-to-Multipoint Support  . . . . . . . . . . . . .  9
       6.1.2.  Multiple Source Support  . . . . . . . . . . . . . . .  9
       6.1.3.  Reverse Traffic Support  . . . . . . . . . . . . . . . 10
     6.2.  Transparency . . . . . . . . . . . . . . . . . . . . . . . 12
     6.3.  Quality of Service (QoS) . . . . . . . . . . . . . . . . . 13
     6.4.  Protection and Restoration . . . . . . . . . . . . . . . . 13
     6.5.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.6.  Reordering Prevention  . . . . . . . . . . . . . . . . . . 14
     6.7.  Failure reporting  . . . . . . . . . . . . . . . . . . . . 15
   7.  Service Provider Network Requirements  . . . . . . . . . . . . 15
     7.1.  Scalability  . . . . . . . . . . . . . . . . . . . . . . . 15
     7.2.  Pseudo Wire Signaling and PSN Tunneling  . . . . . . . . . 15
     7.3.  Discovering VPMS Related Information . . . . . . . . . . . 16
     7.4.  Activation and Deactivation  . . . . . . . . . . . . . . . 16
     7.5.  Inter-AS support . . . . . . . . . . . . . . . . . . . . . 18
     7.6.  Operation, Administration and Maintenance  . . . . . . . . 18
     7.7.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 19
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 19
     11.2. Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
   Intellectual Property and Copyright Statements . . . . . . . . . . 21











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1.  Introduction

1.1.  Problem Statement

   [RFC4664] describes different types of Provider Provisioned Layer 2
   VPNs (L2 PPVPNs, or L2VPNs); Some of them are widely deployed today,
   such as Virtual Private Wire Service (VPWS) and Virtual Private LAN
   Service (VPLS).  A VPWS is a VPN service that supplies a Layer 2 (L2)
   point-to-point service.  A VPLS is an L2 service that emulates
   Ethernet LAN service across a Wide Area Network (WAN).

   For some use cases described hereafter, there are P2MP (point-to-
   multipoint) type services for Layer 2 traffic.  However, there is no
   straightforward way to realize them based on the existing L2VPN
   specifications.

   In a VPWS, a SP can set up point-to-point connectivity per a pair of
   CEs but it is impossible to replicate traffic for point-to-multipoint
   services in the SP's network side.  Even though a SP can build
   multiple PWs independently and make the CEs to replicate traffic over
   them, it is considered an inconvenient way for the customer and a
   waste of bandwidth resources.

   In a VPLS, SPs can naturally offer multipoint connectivity across
   their backbone.  Although it is seemingly applicable for point-to-
   multipoint service as well, there remains extra work for SPs to
   filter unnecessary traffic between irrelevant sites (i.e., from a
   receiver PE to another receiver PE) because VPLS provides full-mesh
   multipoint-to-multipoint connectivity between CEs.  Moreover, VPLS's
   MAC-based learning/forwarding operation is considered unnecessary for
   some scenarios particularly if customers just want to have simple
   unidirectional point-to-multipoint service, or if they require non-
   Ethernet Layer 2 connectivity.

   Consequently, There is a real need for a solution that natively
   provides point-to-multipoint service in L2VPN.

1.2.  Scope of This Document

   VPMS is defined as a Layer 2 service that provides point-to-
   multipoint connectivity for a variety of Layer2 link layers across an
   IP or MPLS-enabled PSN.  VPMS is categorized as a form of provider-
   provisioned Layer 2 Virtual Private Networks (L2VPN).

   This document introduces a new service framework, reference model and
   functional requirements for VPMS within the context of L2VPN, on top
   of the existing framework [RFC4664] and requirements [RFC4665].  It
   is intended to show a proper reference to introduce VPMS and a



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   checklist of requirements that will provide a consistent way to
   evaluate how well each solution satisfies the requirements.

   The technical specifications are outside the scope of this document.
   There is no intent to specify solution-specific details.

   This document provides requirements from both the Service Provider's
   and the Customer's point of view.


2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] .


3.  Terminology

   The content of this document makes use of the terminology defined in
   [RFC4026].  For readability purposes, we list some of the terms here
   in addition to some specific terms used in this document.

3.1.  Acronyms

   P2P:  Point-to-Point

   P2MP:  Point-to-Multipoint

   PW:  Pseudowire

   VPMS:  Virtual Private Multicast Service

   PE/CE:  Provider/Customer Edge

   P: Provider Router

   AC:  Attachment Circuit

   PSN:  Packet Switched Network

   SP:  Service Provider


4.  Use Cases






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4.1.  Ethernet Use Case

   For multicast traffic delivery, there is a requirement to deliver a
   unidirectional P2MP service in addition to the existing P2P service.
   The demand is growing to provide private services which support
   Ethernet traffic duplication, for various applications such as IP-
   based delivery of TV broadcasting, content delivery networks, etc.
   Moreover, many digital audio/video devices (e.g., MPEG-TS, HD-SDI)
   that supports Ethernet interfaces are becoming available, which will
   make Ethernet P2MP service more common.  Also there are some
   applications that naturally suited to static transport of VPMS.  For
   example, MPEG-TS/IP/ Ethernet in DVB-H is typically static broadcast
   without any signaling in the upstream direction.  VPMS could be a
   possible solution to provide these kinds of networking connectivity
   over PSNs.

   Currently VPLS [RFC4761][RFC4762] is able to give P2MP-type
   replication for Ethernet traffic.  Native VPLS already supports this
   capability via a full mesh of PWs, and an extension to optimize
   replication is also proposed [I-D.ietf-l2vpn-vpls-mcast] as an
   additional feature.  However, VPLS by nature requires MAC-based
   learning and forwarding, which might not be needed in some cases by
   particular users.  Generally, video distribution applications use
   unidirectional P2MP traffic, but may not always require any added
   expense of MAC address management.  In addition, VPLS is a service
   that essentially provides any-to-any connectivity between all CEs in
   a L2VPN as it emulates a LAN service.  However, if only P2MP
   connectivity is required, the traffic between different receivers is
   not always needed, and traffic from receiver to sender is not always
   needed, either.  In these cases, VPMS is a service that provides much
   simpler operation.

   Note that VPMS provides single coverage of receiver membership; that
   is, there is no distinct differentiation about multiple multicast
   groups.  All traffic from a particular Attachment Circuit (AC) will
   flow toward the same remote receivers, even if the destination MAC
   address is changed.  Basically in VPMS, destination MAC addresses are
   not used for forwarding, which is significantly different from VPLS.
   If MAC-based forwarding is preferred (i.e., multicast/unicast
   differentiation of MAC address), VPLS should be chosen rather than
   VPMS.

4.2.  ATM-based Use Case

   A use case of ATM-based service in VPMS could be to offer the
   capability for service providers to support IP multicast wholesale
   services over ATM in case the wholesale customer relies on ATM
   infrastructure.  The P2MP support alleviates the constraint in terms



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   of replication for ATM to support IP multicast services.

   Another use case of VPMS for ATM is for audio/video stream
   applications.  Today many digital TV broadcasting networks adopt ATM-
   based distribution systems with point-to-multipoint PVPs/PVCs.  The
   transport network supports replicating ATM cells in transit nodes to
   efficiently deliver programs to multiple terminals.  For migrating
   such ATM-based networks onto IP/MPLS-based networks, VPMS is
   considered to be a candidate solution.

4.3.  TDM-based Use Case

   Today the existing VPWS already supports TDM emulation services
   (SAToP, CESoPSN or TDMoIP).  It is a Layer 1 service, not Layer 2
   service; however, a common architecture is being used since they are
   all packet-based emulations over a SP's network.  VPMS is also
   considered to be a solution for such TDM applications that require
   point-to-multipoint topology.

   In a PSN environment, the existing VPWS allows support for 2G/3G
   mobile backhauling (e.g.  TDM traffic for GSM's Abis interface, ATM
   traffic for Release 99 UMTS's Iub interface).  Currently, the Mobile
   backhauling architecture is always built as a star topology between
   the 2G/3G controller (e.g.  BSC or RNC) and the 2G/3G Base Stations
   (BTS or NodeB).  Therefore VPWSes (P2P services) are used between
   each Base Station and their corresponding controller and nothing more
   is required.

   As far as synchronization in a PSN environment is concerned,
   different mechanisms can be considered to provide frequency and phase
   clock required in the 2G/3G Mobile environment to guarantee mobile
   handover and strict QoS.  One of them consists of using Adaptive
   Clock Distribution and Recovery.  With this method a Master element
   distributes a reference clock at protocol level by regularly sending
   TDM PW packets (SAToP, CESoPSN or TDMoIP) to Slave elements.  This
   process is based on the fact that the volume of transmitted data
   arrival is considered as an indication of the source frequency that
   could be used by the Slave element to recover the source clock
   frequency.  Consequently, with the current methods, the PE connected
   to the Master must setup and maintain as many VPWS (P2P) as their are
   Slave elements, and the Master has to replicate the traffic.  A
   better solution to deliver the clock frequency would be to use a VPMS
   which supports P2MP traffic.  This may scale better than P2P services
   (VPWS) with regards to the forwarding plane at the Master since the
   traffic is no longer replicated to individual VPWSes (P2P) but only
   to the AC associated to the VPMS (P2MP).  It may ease the
   provisioning process since only one source endpoint must be
   configured at the Ingress PE.  This alleviated provisioning process



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   would simplify the introduction of new Base Stations.  The main gain
   would be to avoid replication on the Master and hence save bandwidth
   consumed by the synchronization traffic which typically requires the
   highest level of QoS.  This kind of traffic will be competing with
   equivalent QOS traffic like VoIP, which is why it is significant to
   save the slightest bandwidth.


5.  Reference Model

   The VPMS reference model is shown in Figure 1.



         +-----+ AC1                                  AC2    +-----+
         | CE1 |>---+     ------------------------      +--->| CE2 |
         +-----+    |    |                        |     |    +-----+
          VPMS A    |  +------+ VPMS A        +------+  |    VPMS A
          Sender    +->|......>...+.......... >......|>-+    Receiver
                       | VPMS |   .           | VPMS |
                       | PE1  |   .    VPMS B | PE2  |
                    +-<|......<.. . ....+.....<......|<-+
                    |  +------+   .     .     +------+  |
         +-----+    |    |        .     .         |     |   +-----+
         | CE4 |<---+    |Routed  .     .         |     +---| CE3 |
         +-----+ AC4     |Backbone.     .         |     AC3 +-----+
          VPMS B         |        .     .         |          VPMS B
          Receiver       |      +-v-----v-+       |          Sender
                          ------| .     . |-------
                                | . VPMS. |
                                | . PE3 . |
                                +---------+
                                  v     v
                                  |     |
                               AC5|     |AC6
                                  v     v
                             +-----+   +-----+
                             | CE5 |   | CE6 |
                             +-----+   +-----+
                             VPMS A     VPMS B
                             Receiver   Receiver

                       Figure 1: Reference Model for VPMS

   A single VPMS instance provides isolated service reachability domains
   to each customer.  One VPMS instance corresponds to a unique
   unidirectional point-to-multipoint service.  In Figure 1, there are
   two VPMS instances shown, VPMS A and VPMS B. In principle, there is



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   no traffic exchange allowed between these different instances.

   In a VPMS, a single CE-PE connection is used for transmitting frames
   for delivery to multiple remote CEs, with point-to-multipoint
   duplication.  The SP's network (PE as well as P) has a role to
   duplicate frames so that The traffic source does not need to send
   multiple frames to individual receivers.

   In a VPMS, there are two types of CE, senders and receivers.  A
   sender CE can send out traffic as a source into a VPMS instance.  A
   receiver CE can receive traffic from a sender site, but cannot
   receive from other receiver CEs.  A sender CE itself does not have
   capability of receiving traffic.

   Like VPWS, an Attachment Circuit (AC) is provided to accommodate CEs
   in a VPMS.  In a VPMS, an AC attached to a VPMS MUST be configured as
   "sender" or "receiver" not both.  That is, any AC is associated with
   the role of either sending side (Tx) or receiving side (Rx) from the
   view of the CE.  Thus every AC deals with unidirectional traffic
   flows.  In Figure 1, AC1 and AC3 are configured as senders while AC2,
   AC4, AC5 and AC6 are configured as receivers.  CE1 could send traffic
   to VPMS A via AC1, but it could also receive traffic from VPMS B if
   another AC is connected to CE1.

   Basically there is a one-to-one mapping between an attachment circuit
   and each customer's P2MP topology.  A unique VPMS instance
   corresponds to each topology.  For example, all traffic from CE1 to
   PE1 (thorough AC1) is mapped to VPMS A's topology (to CE2 and CE5).

   In the context of VPMS, one "VPN" is a specific set of sites that
   have been configured to allow communication, composed of one or more
   sets of VPMS instances.  The customer's administrative policies may
   allow sender and receiver CEs to be overlapped by multiple VPMS
   instances (for details, see Section 6.1. as an example).  A VPN will
   be finally defined by those VPMS instance sets.  In short, VPMS is
   defined as a common point-to-multipoint (P2MP) delivery topology, and
   the customer's administrative policy will determine the real VPN
   domain in the broad sense by picking up one or more VPMS instances.

   In a VPMS, PEs will be connected using PW technology which may
   include P2MP traffic optimization.  P2MP traffic optimization will
   provide the benefit of traffic replication for high bandwidth
   efficiency.  The sender CE has only to transmit one stream towards
   the PE, it does not have to replicate traffic.  The backbone side is
   a IP or MPLS-enabled routed PSN.

   VPMS can support various Layer 2 protocol services such as Ethernet,
   ATM, etc.



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6.  Customer Requirements

6.1.  Service Topology

6.1.1.  Point-to-Multipoint Support

   A solution MUST support unidirectional point-to-multipoint
   connectivity from a sender to multiple receivers.  A sender CE is
   assured to send traffic to one or more receiver CEs.  Receiver CEs
   include not only the CEs which are located at remote sites, but also
   the local CEs which are connected to the same sender-side PE.  If
   there is only one receiver in the instance, it is considered
   equivalent to unidirectional point-to-point traffic.

6.1.2.  Multiple Source Support

   A solution MUST support multiple sender topologies in one VPMS
   instance, where a common receiver group is reachable from two or more
   senders.  This means that a solution needs to support having multiple
   P2MP topologies in the backbone whose roots are located apart in a
   common service.  In other words, each P2MP topology MUST only have a
   single sender, however multiple P2MP topologies can be grouped
   together into a single VPMS instance.  For example, in Figure 2,
   traffic from sender CE1 and CE2 both reach receivers CE3 and CE4
   while CE1, CE2, CE3 and CE4 all are associated with a single service.
   This topology is useful for increasing service reliability by
   redundant sources.  Note that every receiver has only to have one AC
   connected to each PE to receive traffic. (in Figure 2, AC3 and AC4
   respectively).  Thus a solution will also need to support protection
   and restoration mechanism combining these multiple P2MP topologies.
   (See section 6.4 too).




















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     +-----+ AC1                                         AC2+-----+
     | CE1 |>-+      ----------------------------        +-<| CE2 |
     +-----+  |     |                            |       |  +-----+
      VPMS A  |  +------+                      +------+  |    VPMS A
     Sender   +->|......>..    .............+..<......|<-+    Sender
              Tx | VPMS | .    .            .  | VPMS | Tx
                 | PE 1 | .    .            .  | PE 2 |
                 |      | .    .            .  |      |
                 +------+ .    .            .  +------+
                    |     .    .            .    |
                    |     +..  .  ......    .    |
                    |     .    .       .    .    |
                    |     .    .       .    .    |
                    |   +-v----v-+   +-v----v-+  |
                     ---| .   .  |---| .   .  |---
                    VPMS|  . .   |   |  . .   |VPMS
                    PE 3|   .    |   |   .    |PE 4
                        +--------+   +--------+
                            v            v
                         AC3|            |AC4
                            v            v
                        +-----+       +-----+
                        | CE3 |       | CE4 |
                        +-----+       +-----+
                        VPMS A         VPMS A
                        Receiver       Receiver


                       Figure 2: Multiple source support

6.1.3.  Reverse Traffic Support

   There are cases where a reverse traffic flow is necessary.  A sender
   CE might sometimes want to receive traffic from a receiver CE.  There
   are some usage scenarios for this, such as stream monitoring through
   a loopback mechanism, control channels which need feedback
   communication etc.  The simplest way to accomplish this is to provide
   different VPMS instances for reverse traffic, i.e. a sender CE is a
   receiver of another VPMS instance.

   Figure 3 illustrates this kind of reverse traffic scenario, where CE1
   is configured as a sender in VPMS A and a receiver in VPMS B. VPMS B
   is used for reverse traffic.  Note that a closed single network here
   is composed of two VPMS instances.  In operational terms, CE1 and CE4
   belong to the same closed "VPN" by administrative policy (e.g., CE1,
   CE2, CE3 and CE4 are the devices in one enterprise's intranet
   network).




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   Such bi-directional instances can be easily created if two distinct
   ACs are provisioned for sending and receiving exclusively (e.g., if
   VLAN id in dot1Q tagged frame is a service delimiter, different VLAN
   ids are uniquely allocated for Tx and Rx).  This approach is
   acceptable if a receiver CE device can change Layer 2 interface
   appropriately in data transmitting and receiving.

   Meanwhile it is also true that this might be considered a limitation
   in some deployment scenarios.  If a CE is an IP router or Ethernet
   bridge, reverse traffic is normally expected to be received on the
   same interface as forward traffic on the receiver CE. (i.e., the same
   VLAN id is to be used for reverse traffic if the AC supports dot1Q
   tagged frames.)

   Therefore, in a VPMS solution, both of the two type of ACs, sending
   (Tx) and receiving (Rx), SHOULD be allowed to be placed in the same
   physical/virtual circuit.  In Figure 3, suppose AC5 of VPMS A is
   provisioned as {VLAN id = 100, direction= Rx}.  It is expected that
   operators can provision AC6 of VPMS B in the same physical port as
   {VLAN id = 100, direction = Tx} or as {VLAN id = 101, direction =
   Tx}.  That is, the combination between VLAN id and the flow direction
   is now considered to be a service delimiter.

   Note, in most implementations of VPWS today, every AC is always
   considered bidirectional and a unique Layer 2 header/circuit (ATM
   VPI/VCI, an Ethernet port, a VLAN etc.) is considered the service
   delimiter.  In contrast in VPMS, every AC is considered
   unidirectional and traffic direction is an additional element to
   identify a unique AC.






















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          +-----+   <-- Rx VPMS B
          + CE1 +<----------------+
          +-----+--------------+  |
    VPMS A Sender --> Tx VPMS A|  |
     VPMS B Receiver       AC1 v  ^ AC2
                             +----------+ VPMS
                             | .  .     | PE1
                             | .   ...  |
                      -------| .      . |--------
                     |       +-v------^-+        |
                     |         .      .          |
                     |         +      .          |
                   +------+  . . .    .        +------+
                +-<|......<..  .  ..  .  ......>..... |>-+
                |  | VPMS |    .      .        | VPMS |  |
             AC3|  | PE2  |    .      .        | PE3  |  |AC4
                |  +------+    .      .        +------+  |
      +-----+   |    |         .      .          |       |   +-----+
      | CE2 |<--+    | Routed  .      .          |       +-->| CE3 |
      +-----+ <--    | Backbone.      .          |       --> +-----+
     VPMS A     Rx   |       +-v------^-+        |        Rx VPMS A
     Receiver         -------| .      . |--------            Receiver
                             | .   ...  |
                             | .  .     | VPMS
                             +----------+ PE4
                            AC5v  ^AC6
                               |  |  <-- Tx VPMS B  +-----+
                               |  +----------------<| CE4 |
                               +------------------->+-----+
                                --> Rx VPMS A      VPMS A Receiver
                                                   VPMS B Sender

                       Figure 3: Reverse traffic support

6.2.  Transparency

   A solution is intended to provide Layer 2 protocol transparency.
   Transparency SHOULD be honoured per VPMS instance basis.  In other
   words, Layer 2 traffic can be transparently transported from a sender
   CE to receiver CEs in a given instance.  Note, however, if service
   delimiting fields (VLAN Id in Ethernet, VPI/VCI in ATM, DLCI in FR
   etc.) are assigned by SP, they are not transparent.  It depends on
   SP's choice if they are assigned at each AC.  Hence it could be that
   some of receiver CEs are getting traffic with different delimiting
   fields than the other receiver CEs.

   VPMS solution SHOULD NOT require any special packet processing by the
   end users (CEs).



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6.3.  Quality of Service (QoS)

   A customer may require that the VPMS service provide the guaranteed
   QoS.  In particular, for real time applications which are considered
   common in point-to-multipoint delivery, delay and loss sensitive
   traffic MUST be supported.  The solution SHOULD provide native QoS
   techniques for service class differentiation, such as IEEE 802.1p CoS
   for Ethernet.

   For bandwidth committed services (e.g., ATM CBR), a solution SHOULD
   guarantee end-to-end bandwidth.  It MAY provide flow admission
   control mechanisms to achieve that.

6.4.  Protection and Restoration

   A solution MUST provide protection and restoration mechanism for end-
   to-end services.

   A solution MUST allow dual-homed redundant access from a CE to
   multiple PEs.  Additionally, a solution SHOULD provide protection
   mechanism between the different PEs to which a CE is attached.  This
   is because when an ingress PE node fails whole traffic delivery will
   fail unless a backup sender PE is provided, even in case of dual-
   homed access.  Similarly, if an egress PE node fails, traffic toward
   that CE is never received unless a backup egress PE is provided.
   Figure 4 is an example for this access topology.

   When dual-homed access to sender PEs is provided, a sender CE MAY
   transmit just a single copy of the traffic to either one of the two
   sender PEs, or it MAY transmit a copy of the traffic to both the PEs
   simultaneously.  The latter scenario is usually applicable when a
   source device has only a simple forwarding capability without any
   switchover functionality.  Note that it consumes more resources at
   CE-PE than in the single copy case.  In the dual traffic case, the
   backup ingress PE SHOULD be able to filter unnecessary traffic under
   normal conditions.  Also in either case, single traffic or dual
   traffic, the protection mechanism of ingress PEs described in the
   previous paragraph will be necessary to handle the traffic
   appropriately.

   In the case of dual-homed access to receiver PEs, a receiver CE MAY
   receive a single copy of the traffic from either one of the two
   sender PEs, or receive a copy of the traffic from both PEs
   simultaneously.  It might be needed to support switchover mechanism
   between egress PEs in failure.  The dual traffic approach is
   applicable if CE has fast switchover capability as a receiver, but
   note that additional traffic resources are always consumed at PE-CE.




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              +-----+
              + CE1 +--------------+
              +-----+               \
        VPMS A  |                   |
        Sender  |                   v AC1
    (dual-homed)|                 +----+
                |            -----|VPMS|--------
                |           |     | PE1|        |
                \           |     +----+        |
                 \  AC2   +----+             +----+   AC4
                  +------>|VPMS|             |VPMS|------------+
                          | PE2|  Routed     | PE3|             \
                          +----+  Backbone   +----+\            |
                     AC3 /  |                   |   \ AC5       v
              +-----+   /   |                   |    \        +-----+
              + CE2 +<-+    |                   |     \       | CE3 |
              +-----+       |    +----+         |      \      +-----+
              VPMS A         ----|VPMS|---------        \     VPMS A
              Receiver           | PE4|                  |    Receiver
                                 +----+                  |
                                   |  AC6                v
                                    \                 +-----+
                                     +--------------->| CE4 |
                                                      +-----+
                                                      VPMS A
                                                      Receiver
                                                     (dual-homed)

                       Figure 4: Dual homing support

6.5.  Security

   The basic security requirement raised in Section 6.5 of [RFC4665]
   also applies to VPMS.

   In addition, a VPMS solution MAY have the mechanisms to activate the
   appropriate filtering capabilities (for example, MAC/VLAN filtering
   etc.), and it MAY be added with the filtering control mechanism
   between particular sender/receiver sites inside a VPMS instance.  For
   example, in Figure 1, filtering can be added such that traffic from
   CE1 to CE4 and CE5 is allowed but traffic from CE1 to CE6 is
   filtered.

6.6.  Reordering Prevention

   A solution SHOULD prevent Layer 2 frame reordering when delivering
   customer traffic under normal conditions.




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6.7.  Failure reporting

   A solution MAY provide information to the customer about failures.
   For example, if there is a loss of connectivity toward some of the
   receiver CEs, it is reported to the sender CE.


7.  Service Provider Network Requirements

7.1.  Scalability

   A VPMS solution MUST be designed to scale well with an increase in
   the number of any of the following metrics:

   -  the number of PEs (per VPMS instance and total in a SP network)
   -  the number of VPMS instances (per PE and total)
   -  the number of sender CEs (per PE, VPMS instance and total)
   -  the number of receiver CEs (per PE, VPMS instance and total)

   A VPMS solution SHALL document its scalability characteristics in
   quantitative terms.  A solution SHOULD quantify the amount of state
   that a PE and a P device has to support.

   The scalability characteristics SHOULD include:

   -  the processing resources required by the control plane in managing
      PWs (neighborhood or session maintenance messages, keepalives,
      timers, etc.)
   -  the processing resources required by the control plane in managing
      PSN tunnels
   -  the memory resources needed for the control plane
   -  other particular elements inherent to each solution that impact
      scalability

7.2.  Pseudo Wire Signaling and PSN Tunneling

   A VPMS solution SHOULD provide an efficient replication that can
   contribute to reducing the bandwidth resource required for VPMS in a
   SP's network.  For supporting optimized replication, it is expected
   to take advantage of PW mechanisms that are capable of P2MP traffic.
   However, the detailed discussion of this type of PW is out of scope
   of this document.  Specific requirements for such a PW extension is
   discussed in [I-D.jounay-pwe3-p2mp-pw-requirements].

   This document does not raise any specific requirements for particular
   PSN tunneling schemes (point-to-point, point-to-multipoint and
   multipoint-to-multipoint) that is applied only to VPMS.  Requirements
   for PSN tunnels used by P2MP PWs is discussed in



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   [I-D.jounay-pwe3-p2mp-pw-requirements].  The type of PSN tunnel used
   will be dependent on individual deployment scenarios (e.g., which PSN
   protocol is available now in the core and how much network resources
   operators will want to optimize).

7.3.  Discovering VPMS Related Information

   A solution SHOULD support auto-discovery methods that dynamically
   allow VPMS information to be discovered by the PEs to minimize the
   amount of configuration the SP must perform.

   All of the requirements on discovery described in Section 7.3 of
   [RFC4665] SHOULD be satisfied in VPMS as well.

   Auto-discovery will help operators' initial configuration of adding a
   new VPN (i.e., VPMS instance), adding/deleting new sender/receiver,
   and so on.

   The information related to remote sites will be as follows:

   -  Information to identify the VPMS instance
   -  PE router ID / IP address as location information
   -  Information to identify Attachment Circuits and their associated
      group information to compose a unique service (i.e., VPMS
      instance).
   -  CE role in each VPMS (Sender and/or Receiver)
   -  SP-related information (AS number, etc. for an inter-provider
      case)

   (Needs discussion, including showing example scenario.)

7.4.  Activation and Deactivation

   This section raises generic requirements for handling related
   information about remote sites after the initial provisioning to ease
   the total operation of VPMS.

   A solution SHOULD provide a way to activate/deactivate the
   administrative status of each CE/AC.  After initial provisioning, a
   SP might change connectivity configuration between particular CEs
   inside a single VPMS instance for operational reasons.  This feature
   will be beneficial to help such a scenario.

   For example, in Figure 5, CE1, CE3, CE4 and CE5 (and their ACs) are
   initially provisioned for VPMS A. CE2 is not provisioned for any
   VPMSes.  In VPMS A, CE1 is a sender and CE3, CE4 and CE5 are
   receivers.  Traffic will usually flow from CE1 to all receivers, CE3,
   CE4 and CE5.  However, for maintenance operation, application's



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   request (e.g., stream program has changed) or some other reasons, CE4
   needs to be set as administratively deactivated.  Then it becomes
   necessary to turn off traffic from PE4 to CE4.  This operation must
   be appropriately distinguished from failure cases.

   When deactivating a particular site, backbone PSN/PW resources (e.g.,
   admission control of PSN tunnel) MAY be released for that particular
   direction in order to provide that bandwidth to other services.  In
   Figure 5, CE3 is now administratively activated and receiving
   traffic.  However, if CE3 comes to be administratively deactivated,
   and if RSVP-TE (including P2P and/or P2MP) is used for backbone PSN,
   then TE reserved resources from PE1 to PE3 may be released.

   In addition, a solution SHOULD allow single-sided activation
   operation at a sender PE.  In some scenarios, operators prefer
   centralized operation.  This is often considered natural for one-way
   digital audio/video distribution applications: SPs often want to
   complete their service delivery by a single operation at one source
   PE, not by multiple operations at many receiver PEs.  Figure 5
   illustrates this scenario, where a SP only has to do single-sided
   operation at PE1 (source) to administratively activate/deactivate
   various connections from AC1 to AC3, AC4 and/or AC5.  It is not
   needed to perform operations on PE3 and PE4 directly.




























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              +-----+   AC1
              + CE1 +----------------+
              +-----+                |
        VPMS A Sender                |
              (sending now)          v
                                  +----+
                             -----|VPMS|--------
                            |     | PE1|        |
                            |     +----+        |
                          +----+             +----+
                          |VPMS|             |VPMS|
                          | PE2|  Routed     | PE3|
                          +----+  Backbone   +----+
                     AC2 /  |                   |  \ AC3
              +-----+   /   |                   |    \   +-----+
              + CE2 +<-+    |                   |     +->| CE3 |
              +-----+       |    +----+         |        +-----+
         (not provisioned)   ----|VPMS|---------    VPMS A Receiver
                                 | PE4|              (receiving now)
                                 +----+
                              AC5 /  \  AC4
              +-----+            /    \                  +-----+
              + CE5 +<----------+      +---------------->| CE4 |
              +-----+                                    +-----+
          VPMS A Receiver                            VPMS A Receiver
          (receiving now)                             (not receiving)

                               CE1/AC1: Administratively activated
                               CE2/AC2: No VPMS provisioned
                               CE3/AC3: Administratively activated
                               CE4/AC4: Administratively deactivated
                               CE5/AC5: Administratively activated

                       Figure 5: Site activation and deactivation

7.5.  Inter-AS support

   A solution SHOULD support inter-AS scenarios, where there is more
   than one provider providing a common VPMS instance and VPN.  More
   specifically, it is necessary to consider the case where some of the
   PEs that compose one VPMS belong to several different ASes.

7.6.  Operation, Administration and Maintenance

   TBD (for further study for next revision)






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7.7.  Security

   TBD (for further study for next revision)


8.  Security Considerations

   Security consideration will be covered by section 6.5. and section
   7.7.  (This is for further study for next revision.)


9.  IANA Considerations

   This document has no actions for IANA.


10.  Acknowledgments

   Many thanks to Ichiro Fukuda, Kazuhiro Fujihara, Ukyo Yamaguchi and
   Kensuke Shindome for their valuable review and feedback.


11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4026]  Andersson, L. and T. Madsen, "Provider Provisioned Virtual
              Private Network (VPN) Terminology", RFC 4026, March 2005.

11.2.  Informative References

   [I-D.ietf-l2vpn-vpls-mcast]
              Aggarwal, R., Kamite, Y., Fang, L., and Y. Rekhter,
              "Multicast in VPLS", draft-ietf-l2vpn-vpls-mcast-04 (work
              in progress), June 2008.

   [I-D.jounay-pwe3-p2mp-pw-requirements]
              JOUNAY, F., "Use Cases and signaling requirements for
              Point-to-Multipoint PW",
              draft-jounay-pwe3-p2mp-pw-requirements-01 (work in
              progress), November 2007.

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




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   [RFC4665]  Augustyn, W. and Y. Serbest, "Service Requirements for
              Layer 2 Provider-Provisioned Virtual Private Networks",
              RFC 4665, September 2006.

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

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


Authors' Addresses

   Yuji Kamite
   NTT Communications Corporation
   Tokyo Opera City Tower
   3-20-2 Nishi Shinjuku, Shinjuku-ku
   Tokyo  163-1421
   Japan

   Email: y.kamite@ntt.com


   Frederic Jounay
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   France

   Email: frederic.jounay@orange-ftgroup.com


   Ben Niven-Jenkins
   BT
   208 Callisto House, Adastral Park
   Ipswich, IP5 3RE
   UK

   Email: benjamin.niven-jenkins@bt.com










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