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   Internet-Draft                                  A. Sajassi (Editor)
   L2VPN Working Group                                          Cisco
   Category: Informational
                                                     D. Mohan (Editor)
   
   
   Expires: April 24, 2011                           October 24, 2010
   
   
   
                   L2VPN OAM Requirements and Framework
                   draft-ietf-l2vpn-oam-req-frmk-11.txt
   
   
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   10, 2008. The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.
   
   Abstract
   
   This draft provides framework and requirements for Layer 2 Virtual
   Private Networks (L2VPN) Operation, Administration and Maintenance
   (OAM). The OAM framework is intended to provide OAM layering across
   L2VPN services, Pseudo Wires (PWs) and Packet Switched Network (PSN)
   tunnels. The requirements are intended to identify OAM requirement
   for L2VPN services (i.e. VPLS, VPWS, and IPLS). Furthermore, if
   L2VPN services OAM requirements impose specific requirements on PW
   OAM and/or PSN OAM, those specific PW and/or PSN OAM requirements
   are also identified.
   
   
   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 RFC 2119.
   
   When these key words are used in consideration of RFC 2119, these
   key words are used in capitalized form as indicated above.
   
   
   
   Table of Contents
   
   Conventions used in this document.................................. 2
   1. Introduction.................................................... 4
   1.1 Relationship with Other OAM Work............................... 5
   1.2 Terminology.................................................... 6
   2. L2VPN Services & Networks....................................... 6
   3. L2VPN OAM Framework............................................. 7
   3.1. OAM Layering.................................................. 7
   3.2. OAM Domains................................................... 8
   3.3. MEPs and MIPs................................................. 9
   3.4. MEP and MIP Identifiers...................................... 10
   4. OAM Framework for VPLS......................................... 10
   4.1. VPLS as Service/Network...................................... 10
   4.1.1. VPLS as Bridged LAN Service................................ 10
   4.1.2. VPLS as a Network.......................................... 11
   4.1.3. VPLS as (V)LAN Emulation................................... 11
   
   
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   4.2. VPLS OAM..................................................... 11
   4.2.1. VPLS OAM Layering.......................................... 12
   4.2.2. VPLS OAM Domains........................................... 13
   4.2.3. VPLS MEPs & MIPs........................................... 13
   4.2.4. VPLS MEP and MIP Identifiers............................... 14
   5. OAM Framework for VPWS......................................... 14
   5.1. VPWS as Service.............................................. 15
   5.2. VPWS OAM..................................................... 15
   5.2.1. VPWS OAM Layering.......................................... 16
   5.2.2. VPWS OAM Domains........................................... 16
   5.2.3. VPWS MEPs & MIPs........................................... 18
   5.2.4. VPWS MEP and MIP Identifiers............................... 20
   6. VPLS Service OAM Requirements.................................. 20
   6.1. Discovery.................................................... 20
   6.2. Connectivity Fault Management................................ 20
   6.2.1. Connectivity Fault Detection............................... 21
   6.2.2. Connectivity Fault Verification............................ 21
   6.2.3. Connectivity Fault Localization............................ 21
   6.2.4. Connectivity Fault Notification and Alarm Suppression...... 21
   6.3. Frame Loss................................................... 21
   6.4. Frame Delay.................................................. 22
   6.5. Frame Delay Variation........................................ 22
   6.6. Availability................................................. 22
   6.7. Data Path Forwarding......................................... 23
   6.8. Scalability.................................................. 23
   6.9. Extensibility................................................ 23
   6.10. Security.................................................... 24
   6.11. Transport Independence...................................... 24
   6.12. Application Independence.................................... 24
   7. VPWS OAM Requirements.......................................... 25
   7.1. Discovery.................................................... 25
   7.2. Connectivity Fault Management................................ 25
   7.2.1. Connectivity Fault Detection............................... 25
   7.2.2. Connectivity Fault Verification............................ 26
   7.2.3. Connectivity Fault Localization............................ 26
   7.2.4. Connectivity Fault Notification and Alarm Suppression...... 26
   7.3. Frame Loss................................................... 27
   7.4. Frame Delay.................................................. 27
   7.5. Frame Delay Variation........................................ 27
   7.6. Availability................................................. 28
   7.7. Data Path Forwarding......................................... 28
   7.8. Scalability.................................................. 28
   7.9. Extensibility................................................ 28
   7.10. Security.................................................... 29
   7.11. Transport Independence...................................... 29
   7.12. Application Independence.................................... 30
   
   
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   7.13. Prioritization.............................................. 30
   8. VPLS (V)LAN Emulation OAM Requirements......................... 30
   8.1. Partial-mesh of PWs.......................................... 30
   8.2. PW Fault Recovery............................................ 31
   8.3. Connectivity Fault Notification and Alarm Suppression........ 31
   9. OAM Operational Scenarios...................................... 31
   9.1. VPLS OAM Operational Scenarios............................... 31
   10. Acknowledgments............................................... 33
   12. IANA Considerations........................................... 33
   11. Security Considerations....................................... 33
   13. References.................................................... 33
   13.1 Normative References......................................... 33
   13.2 Informative References....................................... 34
   A1. Appendix 1 - Alternate Management Models...................... 34
   A1.1. Alternate Model 1 (Minimal OAM)............................. 34
   A1.2. Alternate Model 2 (Segment OAM Interworking)................ 35
   Authors' Addresses................................................ 36
   
   
   1. Introduction
   
   This draft provides framework and requirements for Layer 2 Virtual
   Private Networks (L2VPN) Operation, Administration and Maintenance
   (OAM).
   
   The scope of OAM for any service and/or transport/network
   infrastructure technologies can be very broad in nature. OSI has
   defined the following five generic functional areas commonly
   abbreviated as "FCAPS" [NM-Standards]: a) Fault Management, b)
   Performance Management, c) Configuration Management, d) Accounting
   Management, and e) Security Management.
   
   This draft focuses on the Fault and Performance Management aspects.
   Other functional aspects of FCAPS are for further study.
   
   Fault Management can typically be viewed in terms of the following
   categories:
     - Fault Detection
     - Fault Verification
     - Fault Isolation
     - Fault Notification & Alarm Suppression
     - Fault Recovery
   
   Fault Detection deals with mechanism(s) that can detect both hard
   failures, such as link and device failures, and soft failures, such
   as software failure, memory corruption, mis-configuration, etc.
   Typically a lightweight protocol is desirable to detect the fault
   and thus it would be prudent to verify the fault via Fault
   
   
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   Verification mechanism before taking additional steps in isolating
   the fault. After verifying that a fault has occurred along the data
   path, it is important to be able to isolate the fault to the level
   of a given device or link. Therefore, a Fault Isolation mechanism is
   needed in Fault Management. Fault Notification mechanism can be used
   in conjunction with Fault Detection mechanism to notify the devices
   upstream and downstream to the fault detection point. For example,
   when there is a client/server relationship between two layered
   networks, Fault Detection at the server layer may result in the
   following Fault Notifications:
     - sending a forward Fault Notification from server layer to the
        client layer network(s) using the Fault Notification format
        appropriate to the client layer
     - sending a backward Fault Notification at server layer, if
        applicable, in the reverse direction
     - sending a backward Fault Notification at client layer, if
        applicable, in the reverse direction
   
   Finally, Fault Recovery deals with recovering from the detected
   failure by switching to an alternate available data path using
   alternate devices or links (e.g., device redundancy or link
   redundancy).
   
   Performance Management deals with mechanism(s) that allow
   determining and measuring the performance of network/services under
   consideration. Performance Management can be used to verify the
   compliance to both the service and network level metric
   objectives/specifications. Performance Management typically consists
   of measurement of performance metrics e.g. Frame Loss, Frame Delay,
   Frame Delay Variation (aka Jitter) etc. across managed entities when
   the managed entities are in available state. Performance Management
   is suspended across unavailable managed entities.
   
   [L2VPN-FRWK] specifies three different types of Layer 2 VPN
   services. These are VPWS, VPLS and IPLS.
   
   This document provides a reference model for OAM as it relates to
   L2VPN services and their associated Pseudo Wires (PWs) and Public
   Switched Network (PSN) tunnels. OAM requirement for L2VPN services
   (e.g. VPLS and VPWS) are also identified. Furthermore, if L2VPN
   services OAM requirements impose requirements for PW and/or PSN OAM,
   those specific PW and/or PSN OAM requirements are also identified.
   
   
   1.1 Relationship with Other OAM Work
   
   This document leverages protocols, mechanisms and concepts defined
   as part of other OAM work. More specifically:
   
   IEEE Std. 802.1ag-2007 [IEEE 802.1ag] specifies the Ethernet
   Connectivity Fault Management protocol, which defines the concepts
   of Maintenance Domains, Maintenance End-Points and Maintenance
   Intermediate Points. This standard also defines mechanisms and
   
   
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   procedures for proactive fault detection (Continuity Check), fault
   notification (Remote Defect Indication - RDI), fault verification
   (Loopback) and fault isolation (LinkTrace) in Ethernet networks.
   
   ITU-T Std. Y.1731 [Y.1731] builds upon and extends IEEE 802.1ag in
   the following areas: it defines fault notification and alarm
   suppression functions for Ethernet (via Alarm Indication Signal -
   AIS). It also specifies messages and procedures for Ethernet
   performance management, including loss, delay, jitter and throughput
   measurement.
   
   1.2 Terminology
   
   This document introduces and uses the following terms. Further, this
   document also uses the terms defined in [L2VPN-FRWK] and [L2VPN-
   TERM].
   
   AIS         Alarm Indication Signal
   FM          Fault Management
   IPLS        IP-only LAN Service
   ME          Maintenance Entity which is defined in a given OAM
                domain and represents an entity requiring monitoring
   MEG         Maintenance Entity Group which represents MEs belonging
                to the same service instance. MEG is also called as
                Maintenance Association (MA).
   MEP         Maintenance End Point is responsible for origination
                and termination of OAM frames for a given MEG
   MIP         Maintenance Intermediate Point is located between peer
                MEPs and can process OAM frames but does not initiate
                or terminate them
   OAM Domain  OAM Domain represents a region over which OAM frames
                can operate unobstructed
   PM          Performance Management
   RDI         Remote Defect Indication
   SLA         Service Level Agreement
   STP         Spanning Tree Protocols
   VPLS        Virtual Private LAN Service
   VPWS        Virtual Private Wire Service
   
   
   2. L2VPN Services & Networks
   
   As described in [L2VPN-REQ], following Figure 1 shows a L2VPN
   reference model. L2VPN A represents a point-to-point service while
   L2VPN B represents a bridged service.
   
   
   
   
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    +-----+                                   +-----+
    + CE1 +--+                             +--| CE2 |
    +-----+  |    .....................    |  +-----+
    L2VPN A  |  +----+             +----+  |  L2VPN A
             +--| PE |-- Service --| PE |--+
                +----+   Provider  +----+
               /  .      Backbone     .  \    --------_
    +-----+   /   .         |         .   \  /        \   +-----+
    + CE4 +--+    .         |         .    +-\ Access  \--| CE5 |
    +-----+       .       +----+      .      | Network |  +-----+
    L2VPN B       ........| PE |.......       \       /   L2VPN B
                          +----+   ^           -------
                            |      | logical
                            |      | switching
                         +-----+   | instance
                         | CE3 |
                         +-----+
                         L2VPN B
   
               Figure 1: L2VPN Reference Model
   
   
   [L2VPN-FRWK] specifies VPWS, VPLS and IPLS services. VPWS is a
   point-to-point service where CEs are presented with point-to-point
   virtual circuits. VPLS is a bridged LAN service provided to a set of
   CEs that are members of a VPN. CEs that are members of the same
   service instance communicate with each other as if they are
   connected via a bridged LAN. IPLS is a special VPLS which is used to
   carry only IP service packets.
   
   [L2VPN-REQ] assumes the availability of runtime monitoring protocols
   while defining requirements for management interfaces. This draft
   specifies the requirements and framework for operations,
   administration and maintenance (OAM) protocols between network
   devices.
   
   
   3. L2VPN OAM Framework
   3.1. OAM Layering
   
   The point-to-point or bridged LAN functionality is emulated by a
   network of PEs to which the CEs are connected. This network of PEs
   can belong to a single network operator or can span across multiple
   network operators. Furthermore, it can belong to a single service
   provider or can span across multiple service providers. A service
   provider is responsible for providing L2VPN services to its
   customers; whereas, a network operator (aka facility provider)
   provides the necessary facilities to the service provider(s) in
   support of their services.  A network operator and a service
   provider can be part of same administrative organization or they can
   be different administrative organizations.
   
   
   
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   Different layers involved in realizing L2VPNs include service layer
   and network layers. Network layers can be iterative. In context of
   L2VPNs, the service layers consists of VPLS, VPWS (e.g. Ethernet,
   ATM, FR, HDLC, SONET, etc. point-to-point emulation), and IPLS.
   Similarly in context of L2VPNs, network layers consist of MPLS/IP
   networks. The MPLS/IP networks can consist of networks links
   realized by different technologies e.g. SONET, Ethernet, ATM etc.
   
   Each layer is responsible for its own OAM. This document provides
   the OAM framework and requirements for L2VPN services and networks.
   
   
   3.2. OAM Domains
   
   When discussing OAM tools for L2VPNs it is important to provide OAM
   capabilities and functionality over each domain that a service
   provider or a network operator is responsible for. For these
   reasons, it is also important that OAM frames are not allowed to
   enter/exit other domains. We define an OAM domain as a network
   region over which OAM frames operate unobstructed as explained
   below.
   
   At the edge of an OAM domain, filtering constructs should prevent
   OAM frames from exiting and entering that domain. OAM domains can be
   nested but not overlapped. In other words, if there is a hierarchy
   of the OAM domains, the OAM frames of a higher-level domain pass
   transparently through the lower-level domains but the OAM frames of
   a lower-level domain get blocked/filtered at the edge of that
   domain.
   
   In order to facilitate the processing of OAM frames, each OAM domain
   can be associated with a level at which it operates. Higher level
   OAM domains can contain lower level OAM domains but the converse is
   not true. It may be noted that the higher level domain does not
   necessarily mean a higher numerical value of the level encoding in
   the OAM frame.
   
   A PE can be part of several OAM domains with each interface
   belonging to the same or a different OAM domain. A PE shall block
   outgoing OAM frames and filter out incoming OAM frames whose domain
   level is lower or same to the one configured on that interface and
   pass through the OAM frames whose domain level is higher than the
   one configured on that interface.
   
   Generically, L2VPNs can be viewed as consisting of customer OAM
   domain, service provider OAM domain, and network operator OAM domain
   as depicted in Figure 2.
   
   
   
   
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       ---                                                  ---
      /   \         ------     -------     -----           /   \
      |   CE--     /      \   /       \   /     \      --CE    |
      \   /   \   /        \ /         \ /       \    /    \   /
       ---     --PE         P           P         PE--      ---
                  \        / \         / \       /
                   \      /   \       /   \     /
                    ------     -------     -----
   
                       Customer OAM Domain
          |<-------------------------------------------->|
   
                    Service Provider OAM Domain
                 |<------------------------------>|
   
                   Operator   Operator   Operator
                 |<-------->|<--------->|<------->|
                   OAM Domain OAM Domain OAM Domain
   
   
                       Figure 2: OAM Domains
   
   
   The OAM Domains can be categorized as:
   
     8 Hierarchical OAM Domains: Hierarchical OAM Domains result from
        OAM Layering and imply a contractual agreement among the OAM
        Domain ownerships. In the above example, Customer OAM Domain,
        Service Provider OAM Domain and Operator OAM Domains are
        hierarchical.
     8 Adjacent OAM Domains: Adjacent OAM Domains are typically
        independent of each other and do not have any relationship
        among them. In the above example, the different Operator OAM
        Domains are independent of each other.
   
   
   3.3. MEPs and MIPs
   
   Maintenance End Points (MEPs) are responsible for origination and
   termination of OAM frames. MEPs are located at the edge of their
   corresponding OAM domains. Maintenance Intermediate Points (MIPs)
   are located within their corresponding OAM domains and they normally
   pass OAM frames but never initiate them. Since MEPs are located at
   the edge of their OAM domains, they are responsible for filtering
   outbound OAM frames from leaving the OAM domain or inbound OAM
   frames from entering the OAM domain.
   
   An OAM frame is generally associated with a Maintenance Entity (ME)
   or a Maintenance Entity Group (MEG), where a MEG consists of a set
   of MEs associated with the same service instance. A ME is a point-
   to-point association between a pair of MEPs and represents a
   monitored entity. For example, in a VPLS service which involves n
   CEs, all the MEs associated with the VPLS service in the customer
   
   
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   OAM domain (i.e. from CE to CE) can be considered to be part of a
   VPLS MEG, where the n-point MEG consists of a maximum of n(n-1)/2
   MEs. MEPs and MIPs correspond to a PE or more specifically to an
   interface of a PE. For example, an OAM frame can be said to
   originate from an ingress PE or more specifically an ingress
   interface of that PE. A MEP on a PE receives messages from n-1 other
   MEPs (some of them may reside on the same PE) for a given MEG.
   
   In Hierarchical OAM Domains, a MEP of lower-level OAM domain can
   correspond to a MIP or a MEP of a higher-level OAM domain.
   Furthermore, the MIPs of a lower-level OAM domain are always
   transparent to the higher-level OAM domain (e.g., OAM frames of a
   higher-level OAM domain are not seen by MIPs of a lower-level OAM
   domain and get passed through them transparently). Further, the MEs
   (or MEGs) are hierarchically organized in hierarchical OAM domains.
   For example, in a VPWS service, the VPWS ME in Customer OAM domain
   can coincide with the Attachment Circuit (AC) ME, PW ME and another
   AC ME in Service Provider OAM Domain. Similarly, the PW ME can
   coincide with different ME in Operator OAM Domains.
   
   
   3.4. MEP and MIP Identifiers
   
   As mentioned previously, OAM at each layer should be independent of
   other layers e.g. service layer OAM should be independent of
   underlying transport layer. MEPs and MIPs at each layer should be
   identified with layer specific identifiers.
   
   
   4. OAM Framework for VPLS
   
   Virtual Private LAN Service (VPLS) is used in different contexts. In
   general, VPLS is used in the following contexts: a) as a bridged LAN
   service over networks, some of which are MPLS/IP, b) as an MPLS/IP
   network supporting these bridged LAN services, and c) as (V)LAN
   emulation.
   
   
   4.1. VPLS as Service/Network
   
   4.1.1. VPLS as Bridged LAN Service
   
   The most common definition for VPLS is for bridged LAN service over
   an MPLS/IP network. The service coverage is considered end-to-end
   from UNI to UNI (or AC to AC) among the CE devices and it provides a
   virtual LAN service to the attached CEs belonging to that service
   instance. The reason it is called bridged LAN service is because the
   VPLS-capable PE providing this end-to-end virtual LAN service is
   performing bridging functions (either full or a subset) as described
   in the [L2VPN-FRWK]. This VPLS definition, as specified in [L2VPN-
   REQ], includes both bridge module and LAN emulation module (as
   specified in [L2VPN-FRWK]).
   
   
   
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   A VPLS service instance is also analogous to a VLAN provided by IEEE
   802.1Q networks since each VLAN provides a Virtual LAN service to
   its MAC users. Therefore, when a part of the service provider
   network is Ethernet based (such as H-VPLS with QinQ access network),
   there is a one-to-one correspondence between a VPLS service instance
   and its corresponding provider VLAN in the service provider Ethernet
   network. To check the end-to-end service integrity, the OAM
   mechanism needs to cover the end-to-end VPLS service as defined in
   [L2VPN-REQ] which is from AC to AC including bridge module, VPLS
   forwarder, and the associated PWs for this service. This draft
   specifies the framework and requirements for such OAM mechanism.
   
   
   4.1.2. VPLS as a Network
   
   Sometimes VPLS is also used to refer to the underlying network that
   supports bridged LAN services. This network can be an end-to-end
   MPLS/IP network as H-VPLS with MPLS/IP access or can be a hybrid
   network consisting of MPLS/IP core and Ethernet access network as in
   H-VPLS with QinQ access. In either case, the network consists of a
   set of VPLS-capable PE devices capable of performing bridging
   functions (either full or a subset). These VPLS-capable PE devices
   can be arranged in a certain topology such as hierarchical topology
   (H-VPLS) or distributed topology (D-VPLS) or some other topologies
   such as multi-tier or star topologies. To check the network
   integrity regardless of the network topology, network-level OAM
   mechanisms (such as OAM for MPLS/IP networks) are needed. The
   discussion of network-level OAM is outside of the scope of this
   draft.
   
   
   4.1.3. VPLS as (V)LAN Emulation
   
   Sometimes VPLS also refers to (V)LAN emulation. In such context,
   VPLS only refers to the full mesh of PWs with split horizon that
   emulates a LAN segment over MPLS/IP network for a given service
   instance and its associated VPLS forwarder. Since the emulated LAN
   segment is presented as a Virtual LAN (VLAN) to the bridge module of
   a VPLS-capable PE, the emulated segment is also referred to as an
   emulated VLAN. The OAM mechanisms in this context refer primarily to
   integrity check of VPLS forwarders and its associated full-mesh of
   PWs and the ability to detect and notify a partial mesh failure.
   This draft also covers the OAM framework and requirements for such
   OAM mechanism.
   
   
   4.2. VPLS OAM
   
   When discussing the OAM mechanisms for VPLS, it is important to
   consider that the end-to-end service can span across different types
   of L2VPN networks. As an example, in case of [VPLS-LDP], the access
   network on one side can be bridged network e.g. [IEEE 802.1ad], as
   described in section 11 of [VPLS-LDP]. The access network can also
   
   
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   be a [IEEE 802.1ah] based bridged network. The access network on
   other side can be MPLS based as described in section 10 of [VPLS-
   LDP]; and the core network connecting them can be IP, MPLS, ATM, or
   SONET. Similarly, the VPLS service instance can span across [VPLS-
   BGP], and distributed VPLS as described in [L2VPN-SIG].
   
   Therefore, it is important that the OAM mechanisms can be applied to
   all these network types. Each such network may be associated with a
   separate administrative domain and also multiple such networks may
   be associated with a single administrative domain. It is important
   to ensure that the OAM mechanisms are independent of the underlying
   transport mechanisms and solely rely on VPLS service, i.e. the
   transparency of OAM mechanisms must be ensured over underlying
   transport technologies such as MPLS, IP, etc.
   
   This proposal is aligned with the discussions in other standard
   bodies and groups such as ITU-T Q.5/13, IEEE 802.1, and MEF which
   address Ethernet network and service OAM.
   
   
   4.2.1. VPLS OAM Layering
   
   Figure 3 shows an example of a VPLS service (with two CE belonging
   to customer A) across a service provider network marked by UPE and
   NPE devices. More CE devices belonging to the same Customer A can be
   connected across different customer sites. Service provider network
   is segmented into core network and two types of access network.
   Figure 3(A) shows the bridged access network represented by its
   bridge components marked B, and the MPLS access and core network
   represented by MPLS components marked P. Figure 3(B) shows the
   service/network view at the Ethernet MAC layer marked by E.
   
   
           ---                                                   ---
          /   \         ------      -------      ----           /   \
          | A CE--     /      \    /       \    /    \       --CE A |
          \   /   \   /        \  /         \  /      \     /   \   /
           ---     --UPE       NPE          NPE        UPE--     ---
                      \        /  \         /  \      /
                       \      /    \       /    \    /
                        ------      -------      ----
   
       (A)    CE----UPE--B--B--NPE---P--P---NPE---P----UPE----CE
   
       (B)    E------E---E--E---E------------E----------E-----E
   
                  Figure 3: VPLS specific device view
   
   As shown in Figure 3(B), only the devices with Ethernet
   functionality are visible to OAM mechanisms operating at Ethernet
   MAC layer and the P devices are invisible. Therefore, the OAM along
   the path of P devices (e.g., between two PEs) is covered by
   transport layer and it is outside the scope of this document.
   
   
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   However, VPLS services may impose some specific requirements on PSN
   OAM. This document aims to identify such requirements.
   
   4.2.2. VPLS OAM Domains
   
   As described in the previous section, a VPLS service for a given
   customer can span across one or more service providers and network
   operators. Figure 4 depicts three OAM domains: (A) customer domain
   which is among the CEs of a given customer, (B) service provider
   domain which is among the edge PEs of the given service provider,
   and (C) network operator domain which is among the PEs of a given
   operator.
   
        ---                                                   ---
       /   \         ------      -------      ----           /   \
       |   CE--     /      \    /       \    /    \       --CE   |
       \   /   \   /        \  /         \  /      \     /   \   /
        ---     --UPE       NPE          NPE        UPE--     ---
                   \        /  \         /  \      /
                    \      /    \       /    \    /
                     ------      -------      ----
   
                          Customer OAM Domain
   (A)     |<----------------------------------------------->|
   
                          Provider OAM Domain
   (B)            |<---------------------------------->|
   
                    Operator     Operator     Operator
   (C)            |<--------->|<---------->|<-------->|
                    OAM Domain  OAM Domain   OAM Domain
   
                       Figure 4: VPLS OAM Domains
   
   
   4.2.3. VPLS MEPs & MIPs
   
   As shown in Figure 5, (C) represents those MEPs and MIPs that are
   visible within the customer domain. The MIP associated with (C) are
   expected to be implemented in the bridge module/VPLS forwarder of a
   PE device, as per the [L2VPN-FRWK]. (D) represents the MEPs and MIPs
   visible within the service provider domain. These MEPs and MIPs are
   expected to be implemented in the bridge module/VPLS forwarder of a
   PE device, as per the [L2VPN-FRWK]. (E) represents the MEPs and MIPs
   visible within each operator domain where MIPs only exist in an
   Ethernet access network (e.g., an MPLS access network doesn't have
   MIPs at the operator level). Further, (F) represents the MEPs and
   MIPs corresponding to the MPLS layer and may apply MPLS based
   mechanisms. The MPLS layer shown in Figure 5 is just an example and
   specific OAM mechanisms are outside the scope of this document.
   
   
   
   
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        ---                                                   ---
       /   \         ------      -------      ----           /   \
       | A CE--     /      \    /       \    /    \       --CE A |
       \   /   \   /        \  /         \  /      \     /   \   /
        ---     --UPE       NPE          NPE        UPE--     ---
                   \        /  \         /  \      /
                    \      /    \       /    \    /
                     ------      -------      ----
   
    (A)    CE----UPE--B-----NPE---P------NPE---P----UPE----CE
    (B)    E------E---E------E------------E----------E-----E
   
                            Customer OAM domain
    (C)    MEP---MIP--------------------------------MIP---MEP
   
                            Provider OAM domain
    (D)          MEP--------MIP-----------MIP-------MEP
   
                    Operator    Operator     Operator
    (E)          MEP-MIP--MEP|MEP-------MEP|MEP-----MEP
                   OAM domain   OAM domain   OAM domain
   
                                 MPLS OAM   MPLS OAM
    (F)                       MEP--MIP--MEP|MEP-MIP-MEP
                                  domain     domain
   
              Figure 5: VPLS OAM Domains, MEPs & MIPs
   
   
   4.2.4. VPLS MEP and MIP Identifiers
   
   In VPLS, for Ethernet MAC layer, the MEPs and MIPs should be
   identified with their Ethernet MAC addresses. As described in [VPLS-
   LDP], VPLS instance can be identified in an Ethernet domain (e.g.,
   802.1ad domain) using VLAN tag (service tag) while in an MPLS/IP
   network, PW-ids are used. Both PW-ids and VLAN tags for a given VPLS
   instance are associated with a Service Identifier (e.g., VPN
   identifier). MEPs and MIPs Identifiers, i.e. MEP Ids and MIP Ids,
   must be unique within their corresponding Service Identifiers within
   the OAM domains.
   
   For Ethernet services, e.g. VPLS, Ethernet frames are used for OAM
   frames and the source MAC address of the OAM frames represent the
   source MEP in that domain. For unicast Ethernet OAM frames, the
   destination MAC address represents the destination MEP in that
   domain. For multicast Ethernet OAM frames, the destination MAC
   addresses corresponds to all MEPs in that domain.
   
   
   5. OAM Framework for VPWS
   
   Figure 6 shows the VPWS reference model. VPWS is a point-to-point
   service where CEs are presented with point-to-point virtual
   
   
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   circuits. VPWS is realized by combining a pair of Attachment
   Circuits between the CEs and PEs and a PW between PEs.
   
   
        |<------------- VPWS1 <AC11,PW1,AC12> ------------>|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC11---|    |.......PW1........|    |--AC12----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   |    |---AC21---|    |.......PW2........|    |--AC22----|    |
   +----+          |    |==================|    |          +----+
        |          +----+     PSN Tunnel   +----+          |
        |                                                  |
        |<------------- VPWS2 <AC21,PW2,AC22> ------------>|
   
                Figure 6: VPWS Reference Model
   
   
   5.1. VPWS as Service
   
   VPWS service can be categorized as:
     8 VPWS with homogeneous ACs (where both ACs are same type)
     8 VPWS with heterogeneous ACs (where the ACs are of different
        Layer-2 encapsulation)
   
   Further, the VPWS can itself be classified as:
     8 Homogeneous VPWS (when two ACs and PW are of the same type)
     8 Heterogeneous VPWS (when at least one AC or PW is different
        type than the others)
   
   Based on the above classifications, the heterogeneous VPWS may have
   either homogeneous or heterogeneous ACs. On the other hand,
   homogeneous VPWS can have only homogeneous ACs.
   
   
   5.2. VPWS OAM
   
   When discussing the OAM mechanisms for VPWS, it is important to
   consider that the end-to-end service can span across different types
   of networks. As an example, the access network between CE and PE on
   one side can be Ethernet bridged network, ATM network, etc. In
   common scenarios, it could simply be a point-to-point interface such
   as Ethernet PHY.  The core network connecting PEs can be IP, MPLS,
   etc.
   
   Therefore, it is important that the OAM mechanisms can be applied to
   different network types some of which are mentioned above. Each such
   network may be associated with a separate administrative domain and
   also multiple such networks may be associated with a single
   administrative domain.
   
   
   
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   5.2.1. VPWS OAM Layering
   
   Figure 7 shows an example of a VPWS service (with two CE devices
   belonging to customer A) across a service provider network marked by
   PE devices. Service provider network can be considered to be
   segmented into a core network and two types of access network.
   
   In the most general case, a PE can be client service aware when it
   processes client service PDUs and is responsible for encapsulating
   and de-encapsulating client service PDUs onto PWs and ACs. This is
   particularly relevant for homogeneous VPWS. The service specific
   device view for such a deployment is highlighted by Figure 7(A) for
   these are the devices that are expected to be involved in end-to-end
   VPWS OAM.
   
   In other instances, a PE can be client service unaware when it does
   not process native service PDUs but instead encapsulates access
   technology PDUs over PWs. This may be relevant for VPWS with
   heterogeneous ACs. For example, if the service is Ethernet VPWS
   which is offered across an ATM AC, ATM PW and Ethernet AC. In this
   case, the PE which is attached to ATM AC and ATM PW may be
   transparent to the client Ethernet service PDUs. On the other hand,
   the PE which is attached to ATM PW and Ethernet AC is expected to be
   client Ethernet service aware. The service specific device view for
   such a deployment is highlighted by Figure 7(B) for these are the
   devices that are expected to be involved in end-to-end VPWS OAM,
   where PE1 is expected to be client service unaware.
   
   
        |<--------------- VPWS <AC1,PW,AC2> -------------->|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC1----|............PW..............|--AC2-----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   +----+          |    |==================|    |          +----+
                   +----+     PSN Tunnel   +----+
   
           access             core                 access
        |<---------->|<---------------------->|<------------>|
   
    (A).CE----------PE-----------------------PE-------------CE
   
    (B).CE-----------------------------------PE-------------CE
   
                Figure 7: VPWS specific device view
   
   
   
   
   5.2.2. VPWS OAM Domains
   
   
   
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   As described in the previous section, a VPWS service for a given
   customer can span across one or more network operators.
   
   Figure 8a and 8b depicts three OAM domains: (A) customer domain
   which is among the CEs of a given customer, (B) service provider
   domain which depends on the management model, and (C) network
   operator domain which is among the PEs of a given operator and could
   also be present in the access network if the ACs are provided by a
   different network operator. The core network operator may be
   responsible for managing the PSN Tunnel in these examples.
   
   For the first management model, as shown in Figure 8a, the CEs are
   expected to be managed by the customer and the customer is
   responsible for running end-to-end service OAM, if needed. The
   service provider is responsible for monitoring the PW ME and the
   monitoring of the AC is the shared responsibility of the customer
   and the service provider. In most simple cases, when the AC is
   realized across a physical interface that connects the CE to PE, the
   monitoring requirements across the AC ME are minimal.
   
   
   
        |<--------------- VPWS <AC1,PW,AC2> -------------->|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC1----|............PW..............|--AC2-----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   +----+          |    |==================|    |          +----+
                   +----+     PSN Tunnel   +----+
   
                        Customer OAM Domain
    (A).|<------------------------------------------------->|
   
                    Service Provider OAM Domain
    (B)            |<--------------------------->|
   
                        Operator OAM Domain
    (C)                 |<---------------->|
   
            Figure 8a: VPWS OAM Domains - Management Model 1
   
   
   Figure 8b highlights another management model, where the CEs are
   managed by the Service Provider and where CEs and PEs are connected
   via an access network. The access network between the CEs and PEs
   may or may not be provided by a distinct network operator. In this
   model, the VPWS service ME spans between the CEs in the Service
   Provider OAM Domain, as shown by Figure 8b(B). The Service Provider
   OAM Domain may additionally monitor the AC MEs and PW MEs
   individually, as shown by Figure 8b(C). The network operators may be
   responsible for managing the access service MEs (e.g. access
   tunnels) and core PSN Tunnel MEs, as shown by Figure 8b(D). The
   
   
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   distinction between Figure 8b-(C) and 8(b)-D) is that in (C), MEs
   have MEPs at CEs and at PEs, and have no MIPs. While in (D) MEs have
   MEPs at CEs and at PEs and furthermore, MIPs may be present in
   between the MEPs; thereby, providing visibility of the network to
   the operator.
   
   
        |<--------------- VPWS <AC1,PW,AC2> -------------->|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC1----|............PW..............|--AC2-----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   +----+          |    |==================|    |          +----+
                   +----+     PSN Tunnel   +----+
   
                        Customer OAM Domain
   (A) |<-------------------------------------------------->|
   
                   Service Provider (SP) OAM Domain
   (B)  |<------------------------------------------------>|
   
           SP OAM             SP OAM             SP OAM
   (C)  |<--------->|<----------------------->|<---------->|
           Domain              Domain             Domain
   
          Operator            Operator          Operator
   (D)  |<--------->|<----------------------->|<---------->|
         OAM Domain          OAM Domain         OAM Domain
   
            Figure 8b: VPWS OAM Domains - Management Model 2
   
   
   Note: It may be noted that unlike VPLS OAM Domain in Figure 4, where
   multiple operator domains may occur between the U-PE devices, VPWS
   OAM domain in Figure 8a and 8b highlight a single Operator domain
   between PE devices. This is since unlike the distributed VPLS PE
   case (H-VPLS) where VPLS service aware U-PEs and N-PEs may be used
   to realize a distributed PE, the VPWS has no such distributed PE
   model. If the PSN involves multiple Operator domains, resulting in a
   Multi-segment PW [Ms-PW Arch], VPWS OAM Domains remain unchanged
   since S-PEs are typically not aware of native service.
   
   
   5.2.3. VPWS MEPs & MIPs
   
   The location of MEPs and MIPs can be based upon the management model
   used in the VPWS scenarios. The interest remains in being able to
   monitor end-to-end service and also support segment monitoring in
   the network to allow isolation of faults to specific areas within
   the network.
   
   
   
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   The end-to-end service monitoring is provided by end-to-end ME and
   additional segment OAM monitoring is provided by segment MEs, all in
   the Service Provider OAM Domain. The end-to-end MEs and segment MEs
   are hierarchically organized as mentioned earlier for hierarchical
   OAM domains. This is shown in Figure 8b (B) and (C).
   
   The CE interfaces support MEPs at the end-to-end Service Provider
   OAM level for VPWS as an end-to-end service as shown in Figure 9
   (B1) and (B2). In addition, PE interfaces may support MIPs at end-
   to-end Service Provider OAM level when PEs are client service aware,
   as shown in Figure 9 (B2). As an example, if one considers an end-
   to-end Ethernet line service offered to a subscriber between CE1 and
   CE2 which is realized via ATM type AC1 and AC2 and PW which
   encapsulates ATM over MPLS, the PEs can be considered as Ethernet
   service unaware, and therefore cannot support any Ethernet MIPs.
   Figure 9 (B1) represents this particular situation. Of course,
   another view of the end-to-end service can be ATM, in which case PE1
   and PE2 can be considered to be service aware, and therefore support
   ATM MIPs. Figure 9 (B2) represents this particular situation.
   
   In addition, CEs and PE interfaces support MEPs at a segment (lower
   level) Service Provider OAM level for AC and PW MEs and no MIPs are
   involved at this segment Service Provider OAM Level, as shown in
   Figure 9 (C). Operators may also run segment OAM by having MEPs at
   Network Operator OAM level, as shown in Figure 9 (D).
   
   The advantage of having layered OAM is that end-to-end and segment
   OAM can be carried out in an independent manner. It is also possible
   to carry out some optimizations, e.g. when proactive segment OAM
   monitoring is performed, proactive end-to-end monitoring may not be
   needed since client layer end-to-end ME could simply use fault
   notifications from the server layer segment MEs.
   
   Although many different OAM layers are possible, as shown in Figure
   9, not all may be realized. For example, Figure (B2) and (D) may be
   adequate in some cases.
   
   
        |<--------------- VPWS <AC1,PW,AC2> -------------->|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC1----|............PW..............|--AC2-----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   +----+          |    |==================|    |          +----+
                   +----+     PSN Tunnel   +----+
   
   
   (B1) MEP-----------------------------------------------MEP
   (B2) MEP----------MIP---------------------MIP----------MEP
   (C)  MEP-------MEP|MEP------------------MEP|MEP--------MEP
   (D)  MEP-------MEP|MEP------------------MEP|MEP--------MEP
   
   
   
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                  Figure 9: VPWS MEPs & MIPs
   
   
   5.2.4. VPWS MEP and MIP Identifiers
   
   In VPWS, the MEPs and MIPs should be identified with their native
   addressing schemes. MEPs and MIPs Identifiers, i.e. MEP Ids and MIP
   Ids, must be unique within their corresponding OAM domains and must
   also be unique to the VPWS service instance.
   
   
   6. VPLS Service OAM Requirements
   
   These requirements are applicable to VPLS PE offering VPLS as an
   Ethernet Bridged LAN service, as described in Section 4.1.1.
   Further, the performance metrics used in requirements are based on
   [MEF10.1] and [RFC2544].
   
   It is noted that OAM solutions that meet the following requirements
   may make use of existing OAM mechanisms e.g. Ethernet OAM, VCCV,
   etc. however must not break these existing OAM mechanisms. If
   extensions are required to existing OAM mechanisms, these should be
   coordinated with relevant groups responsible for these OAM
   mechanisms.
   
   
   6.1. Discovery
   
   Discovery allows a VPLS service aware device to learn about other
   devices that support the same VPLS service instance within a given
   domain.
   
   Discovery also allows a VPLS service aware device to learn
   sufficient information (e.g. IP addresses, MAC addressed etc.) from
   other VPLS service aware devices such that VPLS OAM frames can be
   exchanged among the service aware devices.
   
   (R1) VPLS OAM MUST allow a VPLS service aware device to discover
   other devices that share the same VPLS service instance(s) within a
   given OAM domain.
   
   
   6.2. Connectivity Fault Management
   
   VPLS service is realized by exchanging service frames/packets
   between devices that support the same VPLS service instance. To
   allow the exchange of service frames, connectivity between these
   service aware devices is required.
   
   
   
   
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   6.2.1. Connectivity Fault Detection
   
   To ensure service, pro-active connectivity monitoring is required.
   Connectivity monitoring facilitates connectivity fault detection.
   
   (R2a) VPLS OAM MUST allow pro-active connectivity monitoring between
   two VPLS service aware devices that support the same VPLS service
   instance within a given OAM domain.
   
   
   6.2.2. Connectivity Fault Verification
   
   Once a connectivity fault is detected, connectivity fault
   verification may be performed.
   
   (R2b) VPLS OAM MUST allow connectivity fault verification between
   two VPLS service aware devices that support the same VPLS service
   instance within a given OAM domain.
   
   
   6.2.3. Connectivity Fault Localization
   
   Further, localization of connectivity fault may be carried out.
   
   (R2c) VPLS OAM MUST allow connectivity fault localization between
   two VPLS service aware devices that support the same VPLS service
   instance within a given OAM domain.
   
   
   6.2.4. Connectivity Fault Notification and Alarm Suppression
   
   Typically, when connectivity fault is detected and optionally
   verified, VPLS service device may notify the NMS (Network Management
   System) via alarms.
   
   However, a single transport/network fault may cause multiple
   services to fail simultaneously causing multiple service alarms.
   Therefore, VPLS OAM must allow service level fault notification to
   be triggered at the client layer as a result of transport/network
   faults in the service layer. This fault notification should be used
   for the suppression of service level alarms at the client layer.
   
   (R2d) VPLS OAM MUST support fault notification to be triggered as a
   result of transport/network faults. This fault notification SHOULD
   be used for the suppression of redundant service level alarms.
   
   
   6.3. Frame Loss
   
   A VPLS service may be considered degraded if service-layer
   frames/packets are lost during transit between the VPLS service
   aware devices. To determine if a VPLS service is degraded due to
   frame/packet loss, measurement of frame/packet loss is required.
   
   
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   (R3) VPLS OAM MUST support measurement of per-service frame/packet
   loss between two VPLS service aware devices that support the same
   VPLS service instance within a given OAM domain.
   
   
   6.4. Frame Delay
   
   A VPLS service may be sensitive to delay experienced by the VPLS
   frames/packets during transit between the VPLS service aware
   devices. To determine if a VPLS service is degraded due to
   frame/packet delay, measurement of frame/packet delay is required.
   
   VPLS frame/packet delay measurement can be of two types:
   
   One-way delay
   One-way delay is used to characterize certain applications like
   multicast and broadcast applications. The measurement for one-way
   delay usually requires clock synchronization between two devices in
   question.
   
   Two-way delay
   Two-way delay or round-trip delay does not require clock
   synchronization between two devices involved in measurement and is
   usually sufficient to determine the frame/packet delay being
   experienced.
   
   (R4a) VPLS OAM MUST support measurement of per-service two-way
   frame/packet delay between two VPLS service aware devices that
   support the same VPLS service instance within a given OAM domain.
   
   (R4b) VPLS OAM SHOULD support measurement of per-service one-way
   frame/packet delay between two VPLS service aware devices that
   support the same VPLS service instance within a given OAM domain.
   
   
   6.5. Frame Delay Variation
   
   A VPLS service may be sensitive to delay variation experienced by
   the VPLS frames/packets during transit between the VPLS service
   aware devices. To determine if a VPLS service is degraded due to
   frame/packet delay variation, measurement of frame/packet delay
   variation is required. For frame/packet delay variation
   measurements, one-way mechanisms are considered to be sufficient.
   
   (R5) VPLS OAM MUST support measurement of per-service frame/packet
   delay variation between two VPLS service aware devices that support
   the same VPLS service instance within a given OAM domain.
   
   
   6.6. Availability
   
   
   
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   A service may be considered unavailable if the service
   frames/packets do not reach their intended destination (e.g.
   connectivity is down or frame/packet loss is occurring) or the
   service is degraded (e.g. frame/packet delay and/or delay variation
   threshold is exceeded).
   
   Entry and exit conditions may be defined for unavailable state.
   Availability itself may be defined in context of service type.
   
   Since availability measurement may be associated with connectivity,
   frame/packet loss, frame/packet delay and frame/packet delay
   variation measurements, no additional requirements are specified
   currently.
   
   
   6.7. Data Path Forwarding
   
   If the VPLS OAM frames flow across a different path than the one
   used by VPLS service frames/packets, accurate measurement and/or
   determination of service state may not be made. Therefore data path,
   i.e. the one being taken by VPLS service frames/packets, must be
   used for the VPLS OAM.
   
   (R6) VPLS OAM frames MUST be forwarded along the same path (i.e.
   links and nodes) as the VPLS service/data frames.
   
   
   6.8. Scalability
   
   Mechanisms developed for VPLS OAM need to be such that per-service
   OAM can be supported even though the OAM may only be used for
   limited VPLS service instances, e.g. premium VPLS service instances,
   and may not be used for best-effort VPLS services.
   
    (R7) VPLS OAM MUST be scalable such that a service aware device can
   support OAM for each VPLS service that is supported by the device.
   
   
   6.9. Extensibility
   
   Extensibility is intended to allow introduction of additional OAM
   functionality in future such that backward compatibility can be
   maintained when interoperating with older version devices. In such a
   case, VPLS OAM with reduced functionality should still be possible.
   Further, VPLS Service OAM should be defined such that OAM incapable
   devices in the middle of the OAM domain should be able to forward
   the VPLS OAM frames similar to the regular VPLS service/data
   frames/packets.
   
   (R8a) VPLS OAM MUST be extensible such that new functionality and
   information elements related to this functionality can be introduced
   in future.
   
   
   
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   (R8b) VPLS OAM MUST be defined such that devices not supporting the
   OAM are able to forward the OAM frames in a similar fashion as the
   regular VPLS service/data frames/packets.
   
   
   6.10. Security
   
   VPLS OAM frames belonging to an OAM domain originate and terminate
   within that OAM domain. Security implies that an OAM domain must be
   capable of filtering OAM frames. The filtering is such that the OAM
   frames are prevented from leaking outside their domain. Also, OAM
   frames from outside the OAM domains should be either discarded (when
   such OAM frames belong to same or lower-level OAM domain) or
   transparently passed (when such OAM frames belong to a higher-level
   OAM domain).
   
   (R9a) VPLS OAM frames MUST be prevented from leaking outside their
   OAM domain.
   
   (R9b) VPLS OAM frames from outside an OAM domain MUST be prevented
   from entering the OAM domain when such OAM frames belong to the same
   level or lower-level OAM domain.
   
   (R9c) VPLS OAM frames from outside an OAM domain MUST be transported
   transparently inside the OAM domain when such OAM frames belong to
   the higher-level OAM domain.
   
   
   6.11. Transport Independence
   
   VPLS service frame/packets delivery is carried out across transport
   infrastructure, also called network infrastructure. Though specific
   transport/network technologies may provide their own OAM
   capabilities, VPLS OAM must be independently supported as many
   different transport/network technologies can be used to carry
   service frame/packets.
   
   (R10a) VPLS OAM MUST be independent of the underlying
   transport/network technologies and specific transport/network OAM
   capabilities.
   
   (R10b) VPLS OAM MAY allow adaptation/interworking with specific
   transport/network OAM functions. For example, this would be useful
   to allow Fault Notifications from transport/network layer(s) to be
   sent to the VPLS service layer.
   
   
   6.12. Application Independence
   
   VPLS service itself may be used to carry application frame/packets.
   The application may use its own OAM; service OAM must not be
   dependent on application OAM. As an example, a VPLS service may be
   
   
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   used to carry IP traffic; however, VPLS OAM should not assume IP or
   rely on the use of IP level OAM functions.
   
   (R11a) VPLS OAM MUST be independent of the application technologies
   and specific application OAM capabilities.
   
   
   
   7. VPWS OAM Requirements
   
   These requirements are applicable to VPWS PE. The performance
   metrics used in requirements are based on [MEF10.1] and [RFC2544],
   which are applicable to Ethernet Services.
   
   It is noted that OAM solutions that meet the following requirements
   may make use of existing OAM mechanisms e.g. Ethernet OAM, VCCV,
   etc. however must not break these existing OAM mechanisms. If
   extensions are required to existing OAM mechanisms, these should be
   coordinated with relevant groups responsible for these OAM
   mechanisms.
   
   
   7.1. Discovery
   
   Discovery allows a VPWS service aware device to learn about other
   devices that support the same VPWS service instance within a given
   domain. Discovery also allows a VPWS service aware device to learn
   sufficient information (e.g. IP addresses, MAC addresses etc.) from
   other VPWS service aware devices such that OAM frames can be
   exchanged among the VPWS service aware devices.
   
   (R12) VPWS OAM MUST allow a VPWS service aware device to discover
   other devices that share the same VPWS service instance(s) within a
   given OAM domain.
   
   
   7.2. Connectivity Fault Management
   
   VPWS Service is realized by exchanging service frames/packets
   between devices that support the same VPWS service instance. To
   allow the exchange of service frames, connectivity between these
   service aware devices is required.
   
   7.2.1. Connectivity Fault Detection
   
   To ensure service, pro-active connectivity monitoring is required.
   Connectivity monitoring facilitates connectivity fault detection.
   
   (R13a) VPWS OAM MUST allow pro-active connectivity monitoring
   between two VPWS service aware devices that support the same VPWS
   service instance within a given OAM domain.
   
   
   
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   (R13b) VPWS OAM mechanism SHOULD allow detection of misbranching or
   misconnections.
   
   
   7.2.2. Connectivity Fault Verification
   
   Once a connectivity fault is detected, connectivity fault
   verification may be performed.
   
   (R13c) VPWS OAM MUST allow connectivity fault verification between
   two VPWS service aware devices that support the same VPWS service
   instance within a given OAM domain.
   
   
   7.2.3. Connectivity Fault Localization
   
   Further, localization of connectivity fault may be carried out. This
   may amount to identifying the specific AC and/or PW that is
   resulting in the VPWS connectivity fault.
   
   (R13d) VPWS OAM MUST allow connectivity fault localization between
   two VPWS service aware devices that support the same VPWS service
   instance within a given OAM domain.
   
   
   7.2.4. Connectivity Fault Notification and Alarm Suppression
   
   Typically, when connectivity fault is detected and optionally
   verified, service device may notify the NMS (Network Management
   System) via alarms.
   
   However, a single transport/network fault may cause multiple
   services to fail simultaneously causing multiple service alarms.
   Therefore, OAM must allow service level fault notification to be
   triggered at the client layer as a result of transport/network
   faults in the service layer. This fault notification should be used
   for the suppression of service level alarms at the client layer.
   
   For example, if an AC fails, both local CE and local PE which are
   connected via AC may detect the connectivity failure. The local CE
   must notify the remote CE about the failure while the local PE must
   notify the remote PE about the failure.
   
   (R13e) VPWS OAM MUST MUST support fault notification to be triggered
   as a result of transport/network faults. This fault notification
   SHOULD be used for the suppression of redundant service level
   alarms.
   
   
   (R13f) VPWS OAM SHOULD support fault notification in backward
   direction, to be triggered as a result of transport/network faults.
   This fault notification SHOULD be used for the suppression of
   redundant service level alarms.
   
   
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   7.3. Frame Loss
   
   A VPWS service may be considered degraded if service-layer
   frames/packets are lost during transit between the VPWS service
   aware devices. To determine if a VPWS service is degraded due to
   frame/packet loss, measurement of frame/packet loss is required.
   
   (R14) VPWS OAM MUST support measurement of per-service frame/packet
   loss between two VPWS service aware devices that support the same
   VPWS service instance within a given OAM domain.
   
   
   7.4. Frame Delay
   
   A VPWS service may be sensitive to delay experienced by the VPWS
   service frames/packets during transit between the VPWS service aware
   devices. To determine if a VPWS service is degraded due to
   frame/packet delay, measurement of frame/packet delay is required.
   
   VPWS frame/packet delay measurement can be of two types:
   - One-way delay
   One-way delay is used to characterize certain applications like
   multicast and broadcast applications. The measurement for one-way
   delay usually requires clock synchronization between two devices in
   question.
   - Two-way delay
   Two-way delay or round-trip delay does not require clock
   synchronization between two devices involved in measurement and is
   usually sufficient to determine the frame/packet delay being
   experienced.
   
   (R15a) VPWS OAM MUST support measurement of per-service two-way
   frame/packet delay between two VPWS service aware devices that
   support the same VPWS service instance within a given OAM domain.
   
   (R15b) VPWS OAM SHOULD support measurement of per-service one-way
   frame/packet delay between two VPWS service aware devices that
   support the same VPWS service instance within a given OAM domain.
   
   
   7.5. Frame Delay Variation
   
   A VPWS service may be sensitive to delay variation experienced by
   the VPWS frames/packets during transit between the VPWS service
   aware devices. To determine if a VPWS service is degraded due to
   frame/packet delay variation, measurement of frame/packet delay
   variation is required. For frame/packet delay variation
   measurements, one-way mechanisms are considered to be sufficient.
   
   
   
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   (R16) VPWS OAM MUST support measurement of per-service frame/packet
   delay variation between two VPWS service aware devices that support
   the same VPWS service instance within a given OAM domain.
   
   
   7.6. Availability
   
   A service may be considered unavailable if the service
   frames/packets do not reach their intended destination (e.g.
   connectivity is down or frame/packet loss is occurring) or the
   service is degraded (e.g. frame/packet delay and/or delay variation
   threshold is exceeded).
   
   Entry and exit conditions may be defined for unavailable state.
   Availability itself may be defined in context of service type.
   Since availability measurement may be associated with connectivity,
   frame/packet loss, frame/packet delay and frame/packet delay
   variation measurements, no additional requirements are specified
   currently.
   
   
   7.7. Data Path Forwarding
   
   If the VPWS OAM frames flow across a different path than the one
   used by VPWS service frames/packets, accurate measurement and/or
   determination of service state may not be made. Therefore data path,
   i.e. the one being taken by VPWS service frames/packets, must be
   used for the VPWS OAM.
   
   (R17a) VPWS OAM frames MUST be forwarded along the same path as the
   VPWS service/data frames.
   
   (R17b) VPWS OAM MUST be forwarded using the transfer plane (data
   plane) as regular VPWS service/data frames/packets and must not rely
   on control plane messages.
   
   
   7.8. Scalability
   
   Mechanisms developed for VPWS OAM need to be such that per-service
   OAM can be supported even though the OAM may only be used for
   limited VPWS service instances, e.g. premium VPWS service instance,
   and may not be used for best-effort services.
   
   (R18) VPWS OAM MUST be scalable such that a service aware device can
   support OAM for each VPWS service that is supported by the device.
   
   
   7.9. Extensibility
   
   Extensibility is intended to allow introduction of additional OAM
   functionality in future such that backward compatibility can be
   maintained when interoperating with older version devices. In such a
   
   
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   case, VPWS service OAM with reduced functionality should still be
   possible. Further, VPWS service OAM should be such that OAM
   incapable devices in the middle of the OAM domain should be able to
   forward the VPWS OAM frames similar to the regular VPWS service/data
   frames/packets.
   
   (R19a) VPWS OAM MUST be extensible such that new functionality and
   information elements related to this functionality can be introduced
   in future.
   
   (R19b) VPWS OAM MUST be defined such that devices not supporting the
   OAM are able to forward the VPWS OAM frames in a similar fashion as
   the regular VPWS service/data frames/packets.
   
   
   7.10. Security
   
   VPWS OAM frames belonging to an OAM domain originate and terminate
   within that OAM domain. Security implies that an OAM domain must be
   capable of filtering OAM frames. The filtering is such that the VPWS
   OAM frames are prevented from leaking outside their domain. Also,
   VPWS OAM frames from outside the OAM domains should be either
   discarded (when such OAM frames belong to same or lower-level OAM
   domain) or transparently passed (when such OAM frames belong to a
   higher-level OAM domain).
   
   (R20a) VPWS OAM frames MUST be prevented from leaking outside their
   OAM domain.
   
   (R20b) VPWS OAM frames from outside an OAM domain MUST be prevented
   from entering the OAM domain when such OAM frames belong to the same
   level or lower-level OAM domain.
   
   (R20c) VPWS OAM frames from outside an OAM domain MUST be
   transported transparently inside the OAM domain when such OAM frames
   belong to the higher-level OAM domain.
   
   
   7.11. Transport Independence
   
   VPWS service frame/packets delivery is carried out across transport
   infrastructure, also called network infrastructure. Though specific
   transport/network technologies may provide their own OAM
   capabilities, VPWS OAM must be independently supported as many
   different transport/network technologies can be used to carry
   service frame/packets.
   
   (R21a) VPWS OAM MUST be independent of the underlying
   transport/network technologies and specific transport/network OAM
   capabilities.
   
   (R21b) VPWS OAM MAY allow adaptation/interworking with specific
   transport/network OAM functions. For example, this would be useful
   
   
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   to allow Fault Notifications from transport/network layer(s) to be
   sent to the VPWS service layer.
   
   
   7.12. Application Independence
   
   VPWS service itself may be used to carry application frame/packets.
   The application may use its own OAM; VPWS OAM must not be dependent
   on application OAM. As an example, a VPWS service may be used to
   carry IP traffic; however, VPWS OAM should not assume IP or rely on
   the use of IP level OAM functions.
   
   (R22a) OAM MUST be independent of the application technologies and
   specific application OAM capabilities.
   
   
   
   7.13. Prioritization
   
   VPWS service could be composed of several data flows each related to
   a given usage/application with specific requirements in term of
   connectivity and/or performances. Dedicated VPWS OAM should be
   applicable to these flows.
   
   (R23) VPWS OAM SHOULD support configurable prioritization for OAM
   packet/frames to be compatible with associated VPWS service
   packets/frames.
   
   
   8. VPLS (V)LAN Emulation OAM Requirements
   
   8.1. Partial-mesh of PWs
   
   As indicated in [BRIDGE-INTEROP], VPLS service OAM relies upon
   bidirectional Ethernet links or (V)LAN segments and failure in one
   direction or link results in failure of the whole link or (V)LAN
   segment. Therefore, when partial-mesh failure occurs in (V)LAN
   emulation, either the entire PW mesh should be shutdown when only an
   entire VPLS service is acceptable or a subset of PWs should be
   shutdown such that the remaining PWs have full connectivity among
   them, when partial VPLS service is acceptable.
   
   (R13a) PW OAM for PWs related to a (V)LAN emulation MUST allow
   detection of partial-mesh failure condition.
   
   (R13b) PW OAM for PWs related to a (V)LAN emulation MUST allow the
   entire mesh of PWs to be shutdown upon detection of a partial-mesh
   failure condition.
   
   (R13c) PW OAM for PWs related to a (V)LAN emulation MUST allow the
   subset of PWs to be shutdown upon detection of a partial-mesh
   failure condition in a manner such that full mesh is present across
   the remaining subset.
   
   
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   Note: Shutdown action in R13b and R13c may not necessarily involve
   withdrawal of labels etc.
   
   
   8.2. PW Fault Recovery
   
   As indicated in [BRIDGE-INTEROP], VPLS service OAM fault detection
   and recovery relies upon (V)LAN emulation recovery such that fault
   detection and recovery time in (V)LAN emulation should be less than
   the VPLS service fault detection and recovery time to prevent
   unnecessary switch-over and temporary flooding/loop within customer
   OAM domain that is dual-homed to provider OAM domain.
   
   (R14a) PW OAM for PWs related to a (V)LAN emulation MUST support a
   fault detection time in the provider OAM domain faster than the VPLS
   fault detection time in the customer OAM domain.
   
   (R14b) PW OAM for PWs related to a (V)LAN emulation MUST support a
   fault recovery time in the provider OAM domain faster than the VPLS
   fault recovery time in the customer OAM domain.
   
   8.3. Connectivity Fault Notification and Alarm Suppression
   
   When connectivity fault is detected in (V)LAN emulation, PE devices
   may notify the NMS (Network Management System) via alarms. However,
   a single (V)LAN emulation fault may result in CE devices or U-PE
   devices detecting connectivity fault in VPLS service and therefore
   also notifying the NMS. To prevent multiple alarms for the same
   fault, (V)LAN emulation OAM must provide alarm suppression
   capability in the VPLS service OAM.
   
   (R15) PW OAM for PWs related to a (V)LAN emulation MUST support
   interworking with VPLS service OAM to trigger fault notification and
   allow alarm suppression in the VPLS service upon fault detection in
   (V)LAN emulation.
   
   
   9. OAM Operational Scenarios
   
   This section highlights how the different OAM mechanisms can be
   applied as per the OAM framework for different L2VPN services.
   
   9.1. VPLS OAM Operational Scenarios
        ---                                                   ---
       /   \         ------      -------      ----           /   \
       | A CE--     /      \    /       \    /    \       --CE A |
       \   /   \   /        \  /         \  /      \     /   \   /
        ---     --UPE       NPE          NPE        UPE--     ---
                   \        /  \         /  \      /
                    \      /    \       /    \    /
                     ------      -------      ----
   
   
   
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                            Customer OAM domain
    (C)    MEP---MIP--------------------------------MIP---MEP
   
                     Service Provider(SP) OAM domain
    (D)          MEP--------MIP-----------MIP-------MEP
   
                    SP OAM       SP OAM       SP OAM
    (D1)         MEP-MIP--MEP|MEP-------MEP|MEP-----MEP
                    domain       domain       domain
   
                    Operator    Operator     Operator
    (E)          MEP-MIP--MEP|MEP-------MEP|MEP-----MEP
                   OAM domain   OAM domain   OAM domain
   
                                 MPLS OAM   MPLS OAM
    (F)                      MEP--MIP-----MEP--MIP--MEP
                                  domain      domain
   
              Figure 10: VPLS OAM Domains, MEPs & MIPs
   
   
   Among the different MEs identified in Figure 5, for VPLS OAM in
   Customer OAM domain, [IEEE 802.1ag] and [Y.1731] Ethernet OAM
   mechanisms can be applied, to meet various requirements identified
   in Section 6. The mechanisms can be applied across Figure 10 (C)
   MEs.
   
   Similarly, inside the Service Provider OAM domain, [IEEE 802.1ag]
   and [Y.1731] Ethernet OAM mechanisms can be applied across Figure 10
   (D) MEs to meet functional requirements identified in Section 6.
   
   It may be noted that in the interim, when [IEEE 802.1ag] and
   [Y.1731] capabilities are not available across the PE devices, the
   fault management option using segment OAM introduced in Section
   5.2.3 can be applied, with the limitations cited below. In this
   option, the Service Provider can run segment OAM across the Figure
   10 (D1) MEs. The OAM mechanisms across the Figure 10 (D1) MEs can be
   non-Ethernet e.g. VCCV, or BFD when network technology is MPLS. The
   Service Provider can monitor each sub-network segment ME using the
   native technology OAM and by performing interworking across the
   segment MEs, attempt to realize end-to-end monitoring between a pair
   of VPLS end-points. However, such mechanisms do not fully utilize
   the data plane forwarding as experienced by native (i.e. Ethernet)
   service PDUs and therefore monitoring is severely limited in the
   sense that monitoring at Figure 10 (D1) and interworking across them
   could lead to an indication that the ME between VPLS end-points is
   functional while the customer may be experiencing end-to-end
   connectivity issues in the data plane.
   
   Inside the Network Operator OAM domain, [IEEE 802.1ag] and [Y.1731]
   Ethernet OAM mechanisms can also be applied across Figure 10 (E) MEs
   to meet functional requirements identified in Section 6. In
   addition, the network operator could decide to use native OAM
   
   
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   mechanisms e.g. VCCV or BFD across Figure 10 (F) MEs for additional
   monitoring or as an alternative to monitoring across Figure 10 (E)
   MEs.
   
   
   10. Acknowledgments
   
   The authors would like to thank Deborah Brungard, Vasile Radoaca,
   Lei Zhu, Yuichi Ikejiri, Yuichiro Wada, and Kenji Kumaki for their
   reviews and comments.
   
   Authors would also like to thank Shahram Davari, Norm Finn, Dave
   Allan, Thomas Nadeau, Monique Morrow, Yoav Cohen, Marc Holness,
   Malcolm Betts, Paul Bottorff, Hamid-ould Brahim, Lior Shabtay, and
   Dan Cauchy for their feedback.
   
   
   12. IANA Considerations
   
   This document has no actions for IANA.
   
   
   11. Security Considerations
   
   This document takes into account the security considerations and
   imposes requirements on solutions to prevent OAM messages from
   leaking outside an OAM domain and for OAM domains to be transparent
   to OAM frames from higher OAM domains, as specified in Section 6.10
   and 7.10.
   
   For additional levels of security, the solutions may be required to
   encrypt and/or authenticate OAM frames inside an OAM domain however
   solutions are out of the scope of this draft.
   
   
   13. References
   
   13.1 Normative References
   
   [IEEE 802.1ad] "IEEE Standard for Local and metropolitan area
   networks - virtual Bridged Local Area Networks, Amendment 4:
   Provider Bridges", 2005
   
   [IEEE 802.1ag] "IEEE Standard for Local and metropolitan area
   networks - virtual Bridged Local Area Networks, Amendment 5:
   Connectivity Fault Management", 2007
   
   [IEEE 802.1ah] "IEEE Standard for Local and metropolitan area
   networks - virtual Bridged Local Area Networks, Amendment 6:
   Provider Backbone Bridges", 2008
   
   [Y.1731] "ITU-T Recommendation Y.1731 (02/08) - OAM functions and
   mechanisms for Ethernet based networks", February 2008
   
   
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   [L2VPN-FRWK] "Framework for Layer 2 Virtual Private Networks
   (L2VPNs)", RFC 4664
   
   [L2VPN-REQ] "Service Requirements for Layer-2 Provider Provisioned
   Virtual Private Networks", RFC 4665
   
   [L2VPN-TERM] "Provider Provisioned Virtual Private Network (VPN)
   Terminology", RFC 4026
   
   [MEF10.1] "Ethernet Services Attributes: Phase 2", MEF 10.1, 2006
   
   [NM-Standards] "TMN Management Functions", M.3400, February 2000
   
   [VPLS-BGP] "Virtual Private LAN Service", RFC 4761, Jan 2007
   
   [VPLS-LDP] "Virtual Private LAN Services over MPLS", RFC 4762, Jan
   2007
   
   
   13.2 Informative References
   
   [BRIDGE-INTEROP] "VPLS Interoperability with CE Bridges", draft-
   ietf-l2vpn-vpls-bridge-interop-05.txt, Work in progress, March 2010
   
   [L2VPN-SIG] "Provisioning, Autodiscovery, and Signaling in L2VPNs",
   draft-ietf-l2vpn-signaling-08.txt, Work in progress, May 2006
   
   [MS-PW Arch] "An Architecture for Multi-segment Pseudowire Emulation
   Edge-to-Edge", draft-ietf-pwe3-ms-pw-arch-04.txt, Work in progress,
   June 2008
   
   [RFC2544] "Benchmarking Methodology for Network Interconnect
   Devices", RFC 2544, 1999
   
   
   A1. Appendix 1 - Alternate Management Models
   
   In consideration of the management models that can be deployed
   besides the hierarchical models elaborated in this document, this
   section highlights some alternate models that are not recommended
   due to their limitations, as pointed out below. These alternatives
   have been highlighted as potential interim models while the network
   equipments are upgraded to support full functionality and meet the
   requirements set forward by this document.
   
   
   A1.1. Alternate Model 1 (Minimal OAM)
   
   In this model, the end-to-end service monitoring is provided by
   applying CE to CE ME in the Service Provider OAM Domain.
   
   
   
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   A MEP is located at each CE interface that is part of the VPWS
   service, as shown in Figure A1.1 (B). The network operators can
   carry out segment (e.g. PSN Tunnel ME, etc.) monitoring independent
   of the VPWS end-to-end service monitoring, as shown in Figure A1.1
   (D).
   
   The advantage of this option is that VPWS service monitoring is
   limited to CEs. The limitation of this option is that the
   localization of faults at the VPWS Service level.
   
   
        |<--------------- VPWS <AC1,PW,AC2> -------------->|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC1----|............PW..............|--AC2-----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   +----+          |    |==================|    |          +----+
                   +----+     PSN Tunnel   +----+
   
   
   (B)  MEP-----------------------------------------------MEP
   (D)  MEP-------MEP|MEP------------------MEP|MEP--------MEP
   
            Figure A1.1: VPWS MEPs & MIPs - Minimal OAM
   
   
   A1.2. Alternate Model 2 (Segment OAM Interworking)
   
   In this model, the end-to-end service monitoring is provided by
   interworking OAM across each segment. Typical segments involved in
   this case include two AC MEs and PW ME, as shown in Figure A1.2 (C).
   These segments are expected in the Service Provider OAM Domain. An
   interworking function is required to transfer the OAM information
   flows across the OAM segments for the purposes of end-to-end
   monitoring. Depending on whether homogenous VPWS is deployed or
   heterogeneous VPWS is deployed, the interworking function could be
   straightforward or more involved.
   
   In this option, the CE and PE interfaces support MEPs for AC and PW
   MEs and no MIPs are involved at the Service Provider OAM Level, as
   shown in Figure A1.2 (C). The network operators may run segment OAM
   by having MEPs at Network Operator OAM level, as shown in Figure
   A1.2 (D).
   
   The limitations of this model are that it requires interworking
   across the OAM segments and does not conform to the OAM layering
   principles, where each OAM layer ought to be independent of the
   other. For end-to-end OAM determinations, the end-to-end service
   frame path is not necessarily exercised. Further, it requires
   interworking function implementation for all possible technologies
   across access and core that may be used to realize end-to-end
   services.
   
   
   Sajassi & Mohan      Expires: January 2011               [Page 35]
   

   Internet Draft   draft-ietf-l2vpn-oam-req-frmk-11.txt     July 2010
   
   
        |<--------------- VPWS <AC1,PW,AC2> -------------->|
        |                                                  |
        |          +----+                  +----+          |
   +----+          |    |==================|    |          +----+
   |    |---AC1----|............PW..............|--AC2-----|    |
   | CE1|          |PE1 |                  | PE2|          |CE2 |
   +----+          |    |==================|    |          +----+
                   +----+     PSN Tunnel   +----+
   
   
   (C)  MEP-------MEP|MEP------------------MEP|MEP--------MEP
   (D)  MEP-------MEP|MEP------------------MEP|MEP--------MEP
   
       Figure A1.2: VPWS MEPs & MIPs - Segment OAM Interworking
   
   
   Authors' Addresses
   
   Ali Sajassi
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   Email: sajassi@cisco.com
   
   Dinesh Mohan
   Nortel
   3500 Carling Ave
   Ottawa, ON K2H8E9
   Email: mohand@nortel.com
   
   Simon Delord
   Uecomm
   658 Church St
   Richmond, VIC, 3121, Australia
   E-mail: sdelord@uecomm.com.au
   
   Philippe Niger
   France Telecom
   2 av. Pierre Marzin
   22300 LANNION, France
   E-mail: philippe.niger@francetelecom.com
   
   Samer Salam
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   Email: ssalam@cisco.com
   
   
   Sajassi & Mohan      Expires: January 2011               [Page 36]
   

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