One document matched: draft-ouldbrahim-l2vpn-service-mediation-01.txt

Differences from draft-ouldbrahim-l2vpn-service-mediation-00.txt



        L2VPN WG                                        Hamid Ould-Brahim 
        Internet Draft                                   Jeffrey Sugimoto 
        Expiration Date: April 2005                       Elizabeth Hache 
                                                               Greg Wright 
                                                          Nortel Networks 
                                                  
                                                            Himanshu Shah 
                                                           Ciena Networks 
                                                  
                                                         Peter Busschbach 
                                                                    Lucent 
                                                   
                                                              October 2004 
                                               
         
      
         
                           Service Mediation between  
                        Layer-2 and PWE3/L2VPN Networks 
         
                draft-ouldbrahim-l2vpn-service-mediation-01.txt 
      
      
         
     Status of this Memo 
          
        By submitting this Internet-Draft, I certify that any 
        applicable patent or other IPR claims of which I am aware have 
        been disclosed, or will be disclosed, and any of which I become 
        aware will be disclosed, in accordance with RFC 3668. 
         
        This document is an Internet-Draft and is in full conformance 
        with all provisions of Section 10 of RFC2026 [RFC-2026].   
      
        Internet-Drafts are working documents of the Internet 
        Engineering Task Force (IETF), its areas, and its working 
        groups. Note that other groups may also distribute working 
        documents as Internet-Drafts.  
         
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        documents at any time. It is inappropriate to use Internet- 
        Drafts as reference material or to cite them other than as 
        "work in progress."  
         
        The list of current Internet-Drafts can be accessed at 
        http://www.ietf.org/ietf/1id-abstracts.txt  
        The list of Internet-Draft Shadow Directories can be accessed 
        at http://www.ietf.org/shadow.html. 
      
         
     Abstract 
             
     Ould-Brahim, et. al                                                  1 

      draft-ouldbrahim-l2vpn-service-mediation-01.txt       October 2004 

        [SWALLOW-IW] describes an approach for interworking a native 
        ATM SPVC segment with an ATM/FR-based pseudowire. The approach 
        requires that an ATM edge device to encode the remote MPLS 
        provider edge IP address within the NSAP destination address 
        per call-basis, and covers mostly ATM and FRF.8 specifications. 
        This draft covers other scenarios where a) the native layer-2 
        edge doesnÆt have a priori knowledge of the remote PE IP 
        addresses, b) the Layer-2 Provider Edge and the layer-2 network 
        can be native Frame Relay (FR) using native layer-2 signaling 
        protocols, c) the native layer-2 network can use not only NSAP 
        addressing but as well E.164, X.121, or any preferred native 
        addressing scheme, and d) the interface between the MPLS/IP 
        network and native layer-2 network can be FRF.10/X.76 
        interface. We refer to the above problem space as "Service 
        Mediation" to indicate that the native layer-2 signaling is 
        terminated at the MPLS/IP device attached to the layer-2 
        network and the "mediated" service is an end-to-end connection 
        built from two segments: one segment is in its native layer-2 
        form which we denote as Native Wire (NW) established using 
        native layer-2 signaling protocols and the other segment is a 
        pseudowire (PW) established using PWE3/L2VPN signaling 
        protocols. 
      
         
     Acronyms 
                 
           AGI              Attachment Group Identifier 
           AII              Attachment Individual Identifier 
           GID              Generalized ID FEC  
           L2PE             Layer-2 Provider Edge 
           L2E              Layer-2 Edge Device 
           MPE              MPLS Provider Edge 
           MME              MPLS Mediation Edge 
           MI               Mediation Interface 
           MF               Mediation Function 
           NW               Native Wire 
           PSN              Packet Switched Network (MPLS/IP network) 
           SAII             Source Attachment Individual Identifier 
           TAII             Target Attachment Individual Identifier         
         
     1. Introduction 
         
        [SWALLOW-IW] describes an approach for interworking a native 
        ATM SPVC segment with an ATM/FR-based pseudowire. The approach 
        requires that an ATM edge device to encode the remote MPLS 
        provider edge IP address within the NSAP destination address 
        per call-basis, and covers mostly ATM and FRF.8 specifications. 
        This draft covers other scenarios where a) the native layer-2 
        edge doesnÆt have a priori knowledge of the remote PE IP 
        addresses, b) the Layer-2 Provider Edge and the layer-2 network 
        can be native Frame Relay (FR) using native layer-2 signaling 
        protocols, c) the native layer-2 network can use not only NSAP 
      
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        addressing but as well E.164, X.121, or any preferred native 
        addressing scheme, and d) the interface between the MPLS/IP 
        network and native layer-2 network can be FRF.10/X.76 
        interface. We refer to the above problem space as "Service 
        Mediation" to indicate that the native layer-2 signaling is 
        terminated at the MPLS/IP device attached to the layer-2 
        network and the "mediated" service is an end-to-end connection 
        built from two segments: one segment is in its native layer-2 
        form which we denote as Native Wire (NW) established using 
        native layer-2 signaling protocols and the other segment is a 
        pseudowire (PW) established using PWE3/L2VPN signaling 
        protocols. 
      
        Figure 1 describes the network reference diagram for Service 
        Mediation. The service provider network consists of one or 
        multiple native layer-2 networks attached to an MPLS network. 
        Examples of layer-2 networks are Frame Relay and ATM networks. 
        The MPLS network is composed of Provider edge devices and 
        internal provider devices. For the purpose of service 
        mediation, we partition the MPLS provider edge devices into 
        ôMPLS Provider Edge devicesö denoted as MPE and MPLS Mediation 
        Edge referred as MME devices (in the context of this document 
        weÆll refer to these devices as just ôMPEö and ôMMEö).  MPE 
        connects customer sites that are attached to the MPLS network, 
        and MME interconnects layer-2 networks to MPLS network. Note 
        that MPE could as well be an MME.  
         
        Similarly, we partition the layer-2 network devices into Layer-
        2 Provider Edge devices (L2PE) and Layer-2 Edge devices (L2E). 
        L2PE are layer-2 switches attaching customer sites and L2E are 
        layer-2 devices that are attached to MME via an Interface 
        referred as a Mediation Interface (MI). Examples of mediation 
        interfaces are FRF.10/X.76, PNNI, AINI, etc.  Note that an L2E 
        can as well be an L2PE. 
         
                         
        +---+  +----+            +---+      +---+           +---+ +---+ 
        |CE1|--|L2PE|-( layer-2)-|L2E|-<MI>-|MME|(Backbone)-|MPE|-|CE2| 
        +---+  +----+ ( network) +---+      +---+    MPLS   +---+ +---+ 
                          
         
                       {MI:   Mediation Interface    } 
                       {MME:  MPLS Mediation Edge    }  
                       {L2PE: Layer-2 Provider Edge  } 
                       {L2E:  Layer-2 Edge           } 
                       {MPE: MPLS Provider Edge      } 
                       {CE:  Customer Edge           } 
            
                 Figure 1: Service Mediation Network Reference 
                  
        We propose to model the native layer-2 network as a layer-2 VPN 
        which is assigned a globally unique identifier within the MPLS 
      
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        network (i.e., VPN-ID, AGI, etc). The MPLS network is modeled 
        as a layer-2 host with one or multiple layer-2-based addresses.  
         
         
     2. Requirements 
         
        The following list represents the minimum set of requirements 
        for supporting service mediation. Note that some of the 
        requirements of this list are taken from [SM-SCOPE-REQ].  
      
          . Single solution that supports both native Ethernet, Frame 
             Relay and ATM layer-2 networks where an L2PE and MPE 
             Attachment circuits can be FR, ATM, or Ethernet. 
      
          . Should be flexible to support multiple layer-2 network 
             deployment scenarios with no impact on customer layer-2 
             signaling and routing protocols. Examples of scenarios are 
             Frame Relay running on top of an ATM network using FRF.8, 
             Frame relay network with X.76/FRF.10 network interfaces 
             and using E.164 or X.121 addressing plans, ATM PNNI 
             networks attaching to MPLS core network, ATM networks 
             attaching through an AINI interface, etc.  
              
          . Ability to establish dynamic end-to-end mediated  
             connection from a layer-2 network to the MPLS network and 
             from the MPLS network to the layer-2 network. 
           
          . Does not require per call configuration at the MME and L2E 
             levels. 
           
          . Accommodates (though not limited to) the case where the 
             provider encodes the remote MPE IP address within the 
             native layer-2 destination address per call-basis as 
             described in [SWALLOW-IW] (this case applies to layer-2 
             connections established using ATM NSAP addresses). 
           
          . Should provide as an option the ability for the MME to 
             discover dynamically the set of endpoints to be mediated 
             across the MPLS network.   (i.e., the architecture should 
             support single-sided provisioning model with discovery).  
      
          . It is proposed that "vanilla" [PWE3-CONTROL] and IETF 
             L2VPN protocols can be used as the base protocols for 
             service mediation on the MPLS network side.  
      
          . It is proposed that PWE3 encapsulation methods can be used 
             for service mediation (with no changes to existing PWE3 
             standards). 
           
          . Does not require L2E, L2PE, MPEs and internal MPLS core 
             nodes to be aware of the Mediation Function (i.e., only 
             the MME implements the Mediation Function).  
      
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          . Supports resiliency under multiple failure conditions 
             requiring no operator intervention (e.g., allows the 
             layer-2 network to select dynamically a different MME in 
             case the primary MI/MME/L2E fails, or the MPLS and/or the 
             layer-2 networks experience a network failure, etc). 
      
          . Supports scenarios where the layer-2 connection is 
             established between disparate service endpoint types such 
             as FR or ATM to Ethernet endpoints on the MPLS network. 
             The dataplane encapsulation should be based on 
             "Multiservice Interworking IAs".  
      
          . Must be scalable so that it can support large networks with 
             very large numbers of connections. 
      
          . The MPE and MME should agree on an encapsulation method 
             either through signaling (as in negotiation) or through 
             manual configuration. 
      
          . Should meet the QoS requirements of the mediated native 
             layer-2 connection. 
         
     1.2 Network Reachability and Planning 
         
        In order for the layer-2 signaling to reach the set of MMEs, 
        the MPLS network needs to be reachable from the layer-2 
        network. This is accomplished by provisioning layer-2 prefix 
        addresses routable within the layer-2 network. For ATM, NSAP 
        summary addresses are configured at the edge device (L2E in the 
        case of AINI/UNI, MPLS Mediation Edge ûMME, in the case of 
        PNNI). The layer-2 network (L2PE) has a view of which MME node 
        it can reach. The prefix address could represent the entire 
        MPLS domain, or distinct network regions or specific nodes 
        (MPEs).  
         
        In the case of Frame Relay (besides the use of FRF.8), 
        destination nodes, distinct network regions, or even the entire 
        MPLS network can be assigned standard layer-2 addresses of 
        X.121 or E.164 addressing plans. The prefix address relates to 
        the FRF.10 interface point (when such interface is used). A 
        possible mechanism for routing Frame Relay calls to the MMEs 
        within the Frame Relay network is to use hunt group servers. 
        Hunt group servers are actually assigned the appropriate prefix 
        address for the MPLS region to which they will direct the 
        calls. As a result when the frame relay call is initiated in 
        the layer-2 network the call is routed to the hunt group 
        servers which will pass it along to one of the FRF.10 
        interfaces (MME). 
         
        In the case of calls originating from the MPLS network, the set 
        of MMEs need to be reachable from the MPLS network and more 
        precisely from the set of MPEs. The MPEs can be configured  (or 
      
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        auto-discovered) with a list of potential MME IP addresses to 
        use. An MPE that intends to place a call (in this case an LSP 
        through sending the Label Mapping) will select a particular MME 
        given a local policy. 
      
         
     2. Endpoint Identification and Association 
         
         
        Since the endpoints of a mediated service are in most cases 
        different, we propose in this architecture to use the 
        Generalized ID style signaling to setup the pseudowire within 
        the MPLS network as described in [PWE-CONTROL] and [L2VPN-SIG].  
         
        The forwarder identifier on the MPE is known as Attachment 
        Individual Identifier (AII), and the signaling protocol carries 
        both a "Source Attachment Individual Identifier" (SAII) 
        representing the identifier of the local forwarder and a Target 
        Attachment Individual Identifier (TAII) identifying the target 
        forwarder and a common part represented by the Attachment Group 
        Identifier (AGI).  
         
        The AGI uniquely identifies the native layer-2 network (or 
        region thereof) within the MPLS network. One can built the AGI 
        from a VPN-ID format taken from RFC2685 or from other 
        mechanisms such as RFC2547 that guarantees its uniqueness 
        within the MPLS network. The network operator may choose to 
        associate a unique AGI per layer-2 network type, or per layer-2 
        network region. The AGI must represent unique layer-2 network 
        (or region thereof). 
         
        To setup a mediated service, the signaling protocols and the 
        mediation function must be able to associate the Forwarder at 
        one endpoint (i.e., L2PE) with the Forwarder at the other 
        endpoint (i.e., MPE). This association can be accomplished as 
        follows: On one end of the spectrum, layer-2 calls originating 
        from the layer-2 network will encode information that exactly 
        identifies the target forwarder and the destination MPE in the 
        MPLS network. In this scenario the forwarder located on the MPE 
        side will be identified using layer-2 related information (such 
        as port number VPI.VCI, DLCI values) and the called layer-2 
        address on layer-2 network must contain the IP address of the 
        destination MPE. We refer to this scenario as the "unmapped 
        mode". This model is described in detail in [SWALLOW-IW]. 
              
        On the other end of the spectrum, the layer-2 calls will carry 
        information that maps to one or many target forwarder 
        identifiers with their associated MPE addresses. These 
        identifiers may have no relationship to the layer-2 network. We 
        refer to this model as the "mapped mode" to indicate that a 
        mapping function is required at the MME to resolve the actual 
        destination endpoints during the signaling phase.  
           
      
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     3. Unmapped Mode 
         
        The unmapped mode describes a function on the MME that derives 
        the TAII and the destination IP address exclusively from the 
        layer 2 signaling information. 
         
        The Unmapped mode, proposed and described in details in 
        [SWALLOW-IW], requires that the forwarder identifiers at the 
        MPE and the IP address of the MPE are taken exclusively from 
        the layer-2 information carried within the native layer-2 call 
        originated from the layer-2 network. In this model, the source 
        attachment identifiers (SAII) on the MPE must represent 
        information relevant to the layer-2 network being mediated.  
         
        In this mode, the native layer-2 address represented by the 
        Called Party Number (in this case the ATM NSAP address) encodes 
        the IP address of the destination MPE and is assigned a 
        specific address format code that indicates that this address 
        contains an IP address. 
          
        During the signaling phase the mediation function will screen 
        the Called Party Information Elements and extracts the IP 
        address of the destination MPE, the port number and the VPI.VCI 
        values. [SWALLOW-IW] suggests the use of an AFI (Address Format 
        Indicator) of 35 and an ICP (Internet Code Point) of 0002. The 
        MME screens the AFI and ICP from the received call, extracts 
        the IP address representing the loopback address of the 
        destination MPE and establishes a pseudowire to that MPE. The 
        TAII is exclusively constructed from the information carried 
        within the NSAP address (in this case the ESI ûEnd System 
        Identifier) and the SPVC IE (VPI.VCI/DLCI values). 
         
        Since the unmapped mode requires that the L2PE and more 
        precisely the called address to have prior knowledge of the IP 
        address of the destination MPE, it results that with the 
        unmapped mode an auto-discovery mechanism is not needed. Since 
        as well the information carried within the Called Party 
        information elements is enough to construct both the IP address 
        of the destination MPE and the TAII, no lookup is necessary at 
        the MME to build the signaling information destined to MPE. 
              
        However, in the unmapped mode any changes to MPE addressing 
        require reconfiguration of all L2PE having layer-2 connections 
        destined to that MPE. It is not as well possible for this mode 
        to support address mobility where forwarder identifiers on the 
        MPE need to be moved from one port to another, one MPE to 
        another without reconfiguring all the L2PEs having layer-2 
        connections destined to that MPE.                
         
     4. Mapped Mode 
         
        The mapped mode does not require the L2PE and the native layer-
        2 destination address to encode and to have prior knowledge of 
      
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        the IP address of the MPE. This is accomplished by maintaining 
        at the MME level, a mapping function that resolves the 
        association between the information carried within the call 
        such as called party number and VPI.VCI/DLCI values to <SAII, 
        MPE-IP address> values (and vice versa). Such mapping can be 
        manually provisioned at the MME or dynamically discovered. This 
        mode can support layer-2 calls carrying a variety of addressing 
        plans (such as E.164, NSAP, X.121, etc.). 
         
        It results that in the mapped mode, the layer-2 connection can 
        use any available addressing plan without encoding an IP 
        address in the destination native address. The forwarder 
        identifiers on the MPE can be identified using any bit string 
        values that may have no relationship to the layer-2 network. An 
        example of forwarder identifier in the mapped mode is "Sally's 
        Bakery", or "NSAP123456789" or "VPI10.VCI100", "E.164/234567", 
        etc. 
         
        Prior to establishing a layer-2 connection that is to be 
        mediated across an MPLS network, an auto-discovery mechanism 
        can be used to reduce the information provisioned on the MME 
        (i.e., an auto-discovery eliminates the need for the MME to be 
        configured with a list of MPEs that have. attachment circuit 
        identifiers intended to be used for mediation purposes). The 
        use of an auto-discovery mechanism in the proposed architecture 
        allows the following key network values to be supported:  
          
             a) Any configuration changes to MPE IP addressing does not  
             require configuration changes to the layer 2 network 
             connections.  
              
             b) The Provider to support service endpoint mobility of 
             the layer-2 endpoints residing on the MPLS core network 
             (as long as the forwarder identifiers remains unchanged).  
              
             c) The MME to dynamically learn the set of remote 
             endpoints with their MPE IP addresses. 
         
        An example of an auto-discovery that can be used is described 
        in [VPN-AUTO-DISCOVERY].  In this mechanism, the auto-discovery 
        proceeds by having each MPE distributing its set of AII tuples 
        with itself as the BGP next hop and with a set of export route 
        target values. In most common scenarios the MMEs and MPEs will 
        be clients of a set of BGP route reflectors which will 
        distribute L2VPN information to them. The MMEs are configured 
        with an import policy that imports NLRIs containing attachment 
        identifiers that are intended to be mediated. Once the 
        information is received, each MME will record the actual IP 
        address of the remote MPE and its related set of attachment 
        circuits. 
         
        It may happen that the MPE would want to advertise to the MME a 
        pool of attachment identifiers instead of advertising each 
        individual attachment identifier. In this scenario, the auto-
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        discovery will carry pool identifiers representing a grouping 
        of attachment identifiers that are intended to be mediated. 
        Depending on the service being mediated, the pool identifier 
        can be a bit string value representing an NSAP prefix (for the 
        case of ATM), an E-164/X.121 prefix (for the case of Farme 
        Relay), or just any bit string value. The pool id MUST be 
        unique within the layer-2 network. 
      
        An L2PE that intends to establish a mediated layer-2 connection 
        will initiate a layer-2 connection SETUP (using native layer-2 
        signaling protocol) destined to the remote attachment circuit 
        (or remote MPE). Note that no special knowledge is required at 
        the L2PE regarding the mediated nature of the service.  
         
        The call is then routed to the L2E and subsequently to the MPLS 
        Mediation device (MME) which will screen the layer-2 
        information carried within the SETUP message and performs 
        normal layer-2 functions (e.g., CAC, QoS, etc) at the MI.  
         
        If these functions fail the call is cleared. If not the MME 
        will screen for ATM calls the Called Party Number and 
        particularly the AFI and ICP values. If the AFI and ICP values 
        indicate values of "35" and "0002" then the called party number 
        encodes the IP address of the destination MPE. The mediation 
        function will then operate using the unmapped mode. The MME 
        extract the ESI value and combines it with information from the 
        SPVC IE to construct the TAII (see [SWALLOW-IW]). 
         
        For calls that do not encode an IP address in their Called 
        Party Number, the mapping function is based on the Called Party 
        information which must correspond one to one to the target 
        attachment identifier (or pool identifier). In this case, the 
        operator will need to associate for each forwarder identifier 
        on the MPE (SAII) its corresponding called layer-2 destination 
        address and its associated VPI.VCI/DLCI values. The MME is 
        provided (through configuration or through the use of an auto-
        discovery mechanism) with the SAII and MPE IP address (and in 
        the case of pool style advertisement, the MME is provided with 
        a pool identifier and MPE IP address). 
         
        During call processing, the MME will screen the called party 
        number and SPVC information element and performs a best match 
        with the SAII (or pool identifier) and locate the destination 
        MPE IP address. If an entry is found, then the MME extracts the 
        <SAII (or POOL_ID), MPE_IP address> from the mapping table and 
        establishes a targeted LDP session to the remote MPE if one 
        does not already exist. If the MME is given a priori (through 
        configuration or other means) a specific TAII to use during 
        signaling in the MPLS network, then that TAII will be used in 
        the Label mapping message.  
         
        Once the reverse label mapping is received from the MPE, the 
        MME will format a native layer-2 connect/accept message 
      
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        destined to the remote L2PE and the end to end layer-2 
        connection is established. 
         
         
     4.1 Alternative Signaling and Endpoint Association: Special Case 
         
        In most cases and scenarios, the MPE is given only the SAII, 
        and the L2PE is given the "calling" and "called" information in 
        their native form. That information is enough to establish the 
        end-to-end mediated service.  
         
        If the forwarder identifier on the MPE is structured based on 
        called party information (such as the approached described in 
        the previous section), then the mapping function will screen 
        the called party, match it to the SAII and locate the 
        destination MPE IP address in order to process the call to the 
        MPLS network.  
         
        In the case where the forwarder identifier on the MPE has no 
        relation to the called address such as a bit string like 
        "Sally's bakery", the MME would have to associate the called 
        address to the actual SAII. This approach requires a 
        configuration of an additional specific layer-2 called party 
        information (be it an address, or an address with its 
        VPI.VCI/DLCI values) per each forwarder identifier on the MPE. 
         
        During signaling the MME will screen the called party 
        information, and match it to the stored called party 
        information, if an entry is found, then the MME extracts the 
        <SAII, MPE_IP address> from the mapping table. 
         
        It may happen that the MPE is given the TAII and the SAII where 
        the TAII is structured according to native Calling Party 
        information. In that case, it is possible to use the TAII to 
        perform the association between the native call and the 
        destination MPE. Note that this is special case of deployment.  
        
        In this case, when the layer-2 call reaches the MME, the MME 
        extracts the Calling Party and use it to look up the mapping 
        table in order to identify the destination <TAII, IP address to 
        use>. If a match is found, the MME will establish a pseudowire 
        to the destination MPE with a TAII equals to the SAII 
        attachment identifier configured on or distributed by MPE.  
         
        This approach keeps the relevancy of layer-2 related 
        information such as called party number including the 
        VPI.VCI/DLCI values, only to the layer-2 network, and it 
        decouples the actual called party information from the set of 
        MPE forwarder information on the MPLS network. The Called Party 
        information is only required to represent information about 
        reaching the MPLS network through a given set of MMEs. It is 
        possible (though not required) that all mediated connection 
        from a given layer 2 network (or layer-2 network region) to 
      
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        have the same Called Party information, all what is required is 
        the L2PE to have distinct Calling Party information. 
         
         
     5. Resiliency 
         
         
        In case of failure of the MI, L2E, or MME, the call is cleared 
        and a new call is rerouted to an alternate MME, which will 
        process the call according to steps described in the signaling 
        section.  
         
        In the case of ATM, automatic rerouting of connections upon 
        network failures can be achieved by PNNI with the primary and 
        secondary MME configured with the same NSAP summary address. As 
        long as a suitable path exists between the calling PNNI node 
        and the alternate MME node, PNNI can recover from any link or 
        node failure in order to complete the call to the MME.  
        In the case of AINI, similar rerouting mechanism can be used. 
        If AINI link fails then the summary address provisioned against 
        the AINI link is withdrawn from the PNNI network. Alternate 
        MMEs can be provisioned with summary addresses to provide 
        redundancy capabilities.  
         
        In the case of Frame Relay, the layer-2 network will have to 
        select an alternate FRF.10 interface. If hunt group servers are 
        used within the layer-2 network and in the scenario that a 
        particular FRF.10 interface (to the MME) becomes unavailable, 
        the hunt group server will be notified of the failure and a new 
        call will be routed to an alternate MME. 
         
        For calls originating from the MPLS network, a failure of the 
        MME will cause a global repair of the mediated connection. In 
        this case, the initial layer-2 call is cleared and the service 
        label is released. The MPE will then selects an alternate MME 
        based on some internal policy such as the proximity (select the 
        closest MME), or availability (selects the one that is 
        available), or in rotary mode, or based on some predefined MME 
        preferences, etc.  
               
     5.1 Service Resiliency 
         
      
        In the context of service resiliency, a primary attachment 
        circuit can be associated with one or many backup attachment 
        circuits. The backup attachment circuits can be on the same or 
        different MPE than the primary. The primary and backup 
        attachment circuit identifiers are unique within the AGI.  
         
        The MME will build a mapping table of <primary AII, {Backup 
        AIIs}>. That association can be made through configuration at 
        the MME or through a discovery mechanism. This table can be 

      
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      draft-ouldbrahim-l2vpn-service-mediation-01.txt       October 2004 

        populated from the auto-discovery mechanism or can be locally 
        configured.  
         
        The mapping table with backups can be used in failure 
        situations. For example, the MME may have a local policy that 
        indicates that upon receiving a status from the remote MPE that 
        indicates failure of the primary attachment circuit, the MME 
        initiates a new pseudowire to the backup attachment circuit. 
         
        The approach allows service resiliency with multiple backup 
        attachment circuits. A primary attachment circuit may be 
        associated with a number of backup attachment circuits. If for 
        example a primary fails and a first backup is activated, a 
        failure of the first backup may trigger another pseudowire to 
        be established to the second backup, and so on. Note as well 
        that when the primary attachment circuit recovers, the MME may 
        decide to terminate the backup connection and reestablishes the 
        mediated connection back to the primary with no operator 
        intervention (if desired). 
         
        Note that there is no restriction on the type of backup 
        identifier to be used or the service type of the backup. An ATM 
        VC port can be backed up by an Ethernet VLAN or an Ethernet 
        port.  
         
        How the MME selects which backup to use can be a local policy 
        at the MME or can be guided by information advertised by each 
        backup MPE. For example each backup attachment circuit will 
        indicate its preference level.  
         
        Upon failure of the primary attachment circuit (or the primary 
        MPE) the MME may decide to clear the layer-2 call and 
        subsequent calls will be directed to the backup attachment 
        circuit (we refer to this scenario as global repair approach). 
        Another option is the MME decides to perform a local repair and 
        establishes a pseudowire to the backup attachment circuit 
        without impacting the layer-2 connection established on the 
        layer-2 network.  
         
     6. Security Considerations 
         
        This draft does not introduce any new security considerations 
        to [L2VPN-SIG] or [PWE3-CONTROL]. 
                
     7. References 
         
        [SWALLOW-IW] Swallow draft ôSoft Permanent Virtual Circuit 
        Interworking between PWE3 and ATMö, draft-swallow-pwe3-spvc-iw-
        00.txt draft-swallow-pwe3-spvc-iw-00.txt 
         
        [PWE3-CONTROL] Martini, L., et al., ôPseudowire Setup and 
        Maintenance using LDPö, draft-ietf-pwe3-control-protocol-
        05.txt, December 2003 
      
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      draft-ouldbrahim-l2vpn-service-mediation-01.txt       October 2004 

         
        [L2VPN-SIG] Rosen, E., Radoaca, V., ôProvisioning Models and 
        Endpoint Identifiers in L2VPN Signalingö, draft-ietf-l2vpn-
        signaling-00.txt 
         
        [VPN-AUTO-DISCOVERY] Ould-Brahim, H., Rosen, E., Rekhter, Y., 
        ôUsing BGP as an Auto-Discovery Mechanism for Provider-
        Provisioned VPNsö, draft-ietf-l3vpn-bgpvpn-auto-00.txt . 
         
        [SM-SCOPE-REQ] "Service Mediation scope and requirements",  
        mpls forum baseline text, 2004. 
         
        [SHAH-QOS] Shah, H., Ould-Brahim, H., Metz, C., "QoS Signalling 
        for PWE3", draft-shah-pwe3-pw-qos-signaling-00.txt, work in 
        progress. 
      
         
     8. Author's Addresses 
         
            
        Hamid Ould-Brahim 
        Nortel Networks  
        P O Box 3511 Station C 
        Ottawa ON K1Y 4H7 Canada                       
        Phone: +1 (613) 765 3418                   
        Email: hbrahim@nortelnetworks.com 
         
        Jeffrey Sugimoto 
        Nortel Networks    
        P O Box 3511 Station C 
        Ottawa ON K1Y 4H7 Canada                       
         
        Email: sugimoto@nortelnetworks.com 
         
        Elizabeth Hache 
        Nortel Networks  
        P O Box 3511 Station C 
        Ottawa ON K1Y 4H7 Canada                       
         
        Email: hache@nortelnetworks.com 
               
         
        Greg Wright 
        Nortel Networks  
        P O Box 3511 Station C 
        Ottawa ON K1Y 4H7 Canada                       
         
        Email: gwright@nortelnetworks.com 
            
        Himanshu Shah  
        35 Nagog Park,  
        Acton, MA 01720  
      
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           draft-ouldbrahim-l2vpn-service-mediation-01.txt     October 2004 
      
      
        Email: hshah@ciena.com 
         
        Peter Busschbach 
        Lucent Technologies 
        67 Whippany Rd 
        Whippany, NJ 07981 
        Phone: 973-386-8244 
        email: busschbach@lucent.com 
         










































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