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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 4448

Network Working Group                                       Luca Martini
Internet Draft                                           Nasser El-Aawar
Expiration Date: February 2003              Level 3 Communications, LLC.

Giles Heron                                                Eric C. Rosen
PacketExchange Ltd.                                  Cisco Systems, Inc.




                                                             August 2002


Encapsulation Methods for Transport of Ethernet Frames Over IP/MPLS Networks


                 draft-ietf-pwe3-ethernet-encap-00.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other 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

   An Ethernet PW allows Ethernet/802.3 Protocol Data Units (PDUs) to be
   carried over Packet Switched Networks (PSNs) using MPLS transport.
   This enables Service Providers to leverage their existing PSN to
   offer Ethernet services.

   This document describes methods for encapsulating Ethernet/802.3 PDUs
   for transport over an MPLS or IP network.




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Table of Contents

    1      Specification of Requirements  ..........................   2
    2      Introduction  ...........................................   3
    3      Requirements for Ethernet Pseudo-Wire Emulation  ........   5
    3.1    Packet Processing  ......................................   6
    3.1.1  Encapsulation  ..........................................   6
    3.1.2  MTU Management  .........................................   6
    3.1.3  Frame Ordering  .........................................   6
    3.1.4  Frame Error Processing  .................................   6
    3.1.5  IEEE 802.3x Flow Control Interworking  ..................   7
    3.2    Maintenance  ............................................   7
    3.3    Management  .............................................   7
    3.4    QoS Considerations  .....................................   8
    3.5    Security Considerations  ................................   8
    4      General encapsulation method  ...........................   9
    4.1    The Control Word  .......................................   9
    4.1.1  Setting the sequence number  ............................  10
    4.1.2  Processing the sequence number  .........................  10
    4.2    MTU Requirements  .......................................  11
    4.3    Tagged Mode  ............................................  12
    4.4    Raw Mode  ...............................................  12
    5      Using an MPLS Label as the Demultiplexer Field  .........  12
    5.1    MPLS Shim EXP Bit Values  ...............................  12
    5.2    MPLS Shim S Bit Value  ..................................  12
    5.3    MPLS Shim TTL Values  ...................................  13
    6      Security Considerations  ................................  13
    7      Intellectual Property Disclaimer  .......................  13
    8      References  .............................................  13
    9      Author Information  .....................................  14
           Appendix A - Interoperability Guidelines  ...............  17
           Appendix B - QoS Details  ...............................  19





1. Specification of Requirements

   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







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2. Introduction

   In an MPLS or IP network, it is possible to use control protocols
   such as those specified in [PWE3-CRTL] to set up "Pseudo Wires" (PW)
   that carry the the Protocol Data Units of layer 2 protocols across
   the network.  A number of these PWs may be carried in a single
   tunnel.  This requires of course that the layer 2 Packet data Units
   (PDUs) be encapsulated.  We can Three layers of this encapsulation
   can be distinguished:

     - the "tunnel header", which contains the information needed to
       transport the PDU across the IP or MPLS network; this is header
       belongs to the tunneling protocol, e.g., MPLS, GRE, L2TP.

     - the "demultiplexer field", which is used to distinguish
       individual emulated virtual circuits within a single tunnel; this
       field must be understood by the tunneling protocol as well; it
       may be, e.g., an MPLS label or a GRE key field.

     - the "PW  encapsulation", which contains the information about the
       enclosed layer 2 PDU which is necessary in order to properly
       emulate the corresponding layer 2 protocol.

   This document specifies the PW  encapsulation for the ethernet
   protocols. Although different layer 2 protocols require different
   information to be carried in this encapsulation, an attempt has been
   made to make the encapsulation as common as possible for all layer 2
   protocols. Other layer 2 protocols are described in separate
   documents.  [PWE3-ATM] [PWE3-FRAME]

   This document also specifies the way in which the demultiplexer field
   is added to the PW encapsulation when an MPLS label is used as the
   demultiplexer field.

   The scope of this document also includes:

     - Pseudo-wire (PW) requirements for emulating Ethernet trunking and
       switching behavior.

     - PE-bound and CE-bound packet processing of Ethernet PDUs

     - QoS and security considerations

     - Inter-domain transport considerations for Ethernet PE

   The following two figures describe the reference models which are
   derived from [PWE3-FRAME] [PWE3-REQ] to support the Ethernet PW
   emulated services.



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           Native    |<----- Pseudo Wire ---->|  Native
          Ethernet   |                        |  Ethernet
             or      |  |<-- PSN Tunnel -->|  |    or
           VLAN      V  V                  V  V   VLAN
          Service  +----+                  +----+ Service
   +----+    |     | PE1|==================| PE2|     |    +----+
   |    |----------|............PW1.............|----------|    |
   | CE1|    |     |    |                  |    |     |    |CE2 |
   |    |----------|............PW2.............|----------|    |
   +----+    |     |    |==================|    |     |    +----+
        ^          +----+                  +----+     |    ^
        |      Provider Edge 1         Provider Edge 2     |
        |                                                  |
        |<-------------- Emulated Service ---------------->|

      Figure 1: PWE3 Ethernet/VLAN Interface Reference Configuration
    +-------------+                                +-------------+
    |  Emulated   |                                |  Emulated   |
    |  Ethernet   |                                |  Ethernet   |
    | (including  |         Emulated Service       | (including  |
    |  VLAN)      |<==============================>|  VLAN)      |
    |  Services   |                                |  Services   |
    +-------------+           Pseudo Wire          +-------------+
    |Demultiplexer|<==============================>|Demultiplexor|
    +-------------+                                +-------------+
    |    PSN      |            PSN Tunnel          |    PSN      |
    | MPLS or IP  |<==============================>| MPLS or IP  |
    +-------------+                                +-------------+
    |  Physical   |                                |  Physical   |
    +-----+-------+                                +-----+-------+
          |                                              |
          |                MPLS or IP Network            |
          |             ____     ___       ____          |
          |           _/    ___/       _/    __       |
          |          /               __/         _     |
          |         /                                   |
          +========/                                 |===+
                                                    /
                                                   /
                        ___      ___     __      _/
                      _/   ____/   ___/  ____/

       Figure 2: Ethernet PWE3 Protocol Stack Reference Model

   For the purpose of this document R1 will be defined as the ingress
   router, and R2 as the egress router. A layer 2 PDU will be received
   at R1, encapsulated at R1, transported, decapsulated at R2, and
   transmitted out of R2.



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3. Requirements for Ethernet Pseudo-Wire Emulation

   An Ethernet PW emulates a single Ethernet link between exactly two
   endpoints.  The following reference model describes the termination
   point of each end of the PW within the PE:
              +-----------------------------------+
              |                PE                 |
      +---+   +-+  +-----+  +------+  +------+  +-+
      |   |   |P|  |     |  |PW ter|  | PSN  |  |P|
      |   |<==|h|<=| NSP |<=|minati|<=|Tunnel|<=|h|<== From PSN
      |   |   |y|  |     |  |on    |  |      |  |y|
      | C |   +-+  +-----+  +------+  +------+  +-+
      | E |   |                                   |
      |   |   +-+  +-----+  +------+  +------+  +-+
      |   |   |P|  |     |  |PW ter|  | PSN  |  |P|
      |   |==>|h|=>| NSP |=>|minati|=>|Tunnel|=>|h|==> To PSN
      |   |   |y|  |     |  |on    |  |      |  |y|
      +---+   +-+  +-----+  +------+  +------+  +-+
              |                                   |
              +-----------------------------------+
                          ^        ^
                          |        |
                          A        B

              Figure 3: PW reference diagram

   The PW terminates at a logical port within the PE, defined at point A
   in the above diagram. This port provides an Ethernet MAC service that
   will deliver each Ethernet packet that is received at point A,
   unaltered, to the point A in the corresponding PE at the other end of
   the PW.

   The "NSP" function includes packet processing needed to translate the
   Ethernet packets that arrive at the CE-PE interface to/from the
   Ethernet packets that are applied to the PW termination point. Such
   functions may include stripping, overwriting or adding VLAN tags,
   physical port multiplexing and demultiplexing, PW-PW bridging, L2
   encapsulation, shaping, policing, etc.

   The points to the left of A, including the physical layer between the
   CE and PE, and any adaptation (NSP) functions between it and the PW
   terminations, are outside of the scope of PWE3 and are not defined
   here.

   "PW Termination", between A and B, represents the operations for
   setting up and maintaining the PW, and for encapsulating and
   decapsulating the Ethernet packets according to the PSN type in use.
   This document defines these operations, and the services offered and



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   required at points A and B.

   "PSN Tunnel" denotes the PSN tunneling technology that is being used:
   MPLS or GRE/IP.

   A pseudo wire can be one of the two types: raw or tagged. This is a
   property of the emulated Ethernet link and indicates whether the
   pseudo wire MUST contain an 802.1Q VLAN tag (i.e. tagged mode) or MAY
   contain a tag (i.e. raw mode).


3.1. Packet Processing

3.1.1. Encapsulation

   The entire Ethernet frame without any preamble or FCS is transported
   as a single packet.  A VC label is prepended to this and the packet
   is forwarded through a PSN tunnel (either MPLS or GRE/IP).


3.1.2. MTU Management

   Ingress and egress PWESs MUST agree on their maximum MTU size to be
   transported over the PSN.


3.1.3. Frame Ordering

   In general, applications running over Ethernet do not require strict
   frame ordering. However the IEEE definition of 802.3 [802.3] requires
   that frames from the same conversation are delivered in sequence.
   Moreover, the PSN cannot (in the general case) be assumed to provide
   or to guarantee frame ordering.  Therefore if strict frame ordering
   is required, the control word defined below MUST be utilized and its
   sequence number processing enabled.


3.1.4. Frame Error Processing

   An encapsulated Ethernet frame traversing a psuedo-wire may be
   dropped, corrupted or delivered out-of-order. Per [PWE3-REQ],
   packet-loss, corruption, and out-of-order delivery is considered to
   be a "generalized bit error" of the psuedo-wire. Therefore, the
   native Ethernet frame error processing mechanisms MUST be extended to
   the corresponding psuedo-wire service. Therefore, if a PE device
   receives an Ethernet frame containing hardware level CRC errors,
   framing errors, or a runt condition, the frame MUST be discarded on
   input.  Note that this processing is part of the NSP function and is



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   outside the scope of this draft.


3.1.5. IEEE 802.3x Flow Control Interworking

   In a standard Ethernet network, the flow control mechanism is
   optional and typically configured between the two nodes on a point-
   to-point link (e.g.  between the CE and the PE). IEEE 802.3x PAUSE
   frames MUST NOT be carried across the PW. See Appendix A for notes on
   CE-PE flow control.


3.2. Maintenance

   It is desirable to have a signaling mechanism for establishing
   Ethernet PWs and for detecting failure of an Ethernet PW.  It is
   recommended that the procedures defined in [PWE3-CRTL] be used for
   this purpose.


3.3. Management

   The PW management model of Ethernet PW follows the general management
   guidelines for PW management as appear in [PW-MIB] and defined in
   [PWE3-REQ], [PWE3-FRAME].  It is composed of 3 components.  [PW-MIB]
   defines the parameters common to all types of PW and PSNs, for
   example common counters, error handling, some maintenance protocol
   parameters etc.  For each type of PSN there is a separate module that
   defines the association of the PW to the PSN tunnel, see example in
   [PW-MPLS-MIB] for the MPLS PSN.  For Ethernet PW, an additional MIB
   module [PW-ENET-MIB] defines the Ethernet specific parameters
   required to be configured or monitored.

   The above modules enable both manual configuration and the use of
   maintenance procedures to set up the Ethernet PW and monitor PW state
   where applicable.

   As specified in [PWE3-REQ] and [PWE3-FRAME], an implementation SHOULD
   support the relevant PW MIB modules for PW set-up and monitoring.
   Other mechanisms for PW set up (command line interface for example)
   MAY be supported.










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3.4. QoS Considerations

   The ingress PE MAY consider the user priority (PRI) field [802.1Q] of
   the VLAN tag header when determining the value to be placed in the
   Quality of Service field of the encapsulating protocol (e.g., the EXP
   fields of the MPLS label stack).  In a similar way, the egress PE MAY
   consider the Quality of Service field of the encapsulating protocol
   when queuing the packet for CE-bound.

   A PE MUST support the ability to carry the Ethernet PW as a best
   effort service over the PSN.  Transparency of PRI bits (if sent from
   CE to PE) between CE devices, regardless of the COS support of the
   PSN.  Where the 802.1Q VLAN field is added at the PE, a default PRI
   setting of zero MUST be supported, a configured default value is
   recommended.

   A PE may support additional QOS support by means of one or more of
   the following methods:

        -i. One COS per PW End Service (PWES), mapped to a single COS PW
            at the PSN.
       -ii. Multiple COS per PWES mapped to a single PW with multiple
            COS at the PSN.
      -iii. Multiple COS per PWES mapped to multiple PWs at the PSN.

            Examples of the cases above and details of the service
            mapping considerations are described in Appendix B.

            The PW guaranteed rate at the PSN level is PW provider
            policy based on agreement with the customer, and may be
            different from the Ethernet physical port rate.
            Consideration of Ethernet flow control was discussed above.


3.5. Security Considerations

   This document specifies the security consideration regarding the
   encapsulation for the PW.  In terms of encapsulation, security of the
   encapsulated packets depends on the nature of the protocol that is
   carried by these packets, while the encapsulation itself shall not
   affect the related security issues.

   Nevertheless, the security limitations of the PE and/or the PW MUST
   not restrict the security implementation choices of the user of the
   PWE3 (i.e.  users should be able to implement IPSEC or any other
   appropriate security mechanism in addition to the security inherent
   in the PW)".




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   It is required that PEs will have user separation between different
   PW and different virtual ports that the PWs are connected to.  For
   example: if two PWs are connected to the same physical port and
   associated to different virtual ports (i.e. VLANs), it is required
   that packets from one VC will not be forwarded to the VLAN that is
   associated to the second VCs.

   A received packet is associated with a PW by means of the VC label.
   However this mechanism provides no guarantee that the packet was sent
   by the peer PE.  Further checks may be useful to protect against
   mis-configuration and connection hijacking.

   The PE must be able to be protected from malformed, or maliciously
   altered, customer traffic. This includes, but is not limited to,
   illegal VLAN use, short packets, long packets, etc.

   Security achieved by access control of MAC addresses is out of scope
   of this document.

   Additional security requirements related to the use of PW in a
   switching (virtual bridging) environment are not discussed here as
   they are not within the scope of this draft.

   In the case of a PW crossing from one autonomous system to another,
   through a private interconnection, security considerations are much
   the same as in the intra-domain case. However in some cases the PW
   may travel through a third-party autonomous system, or across a
   public interconnection point. In these cases there may be a
   requirement to encrypt the user data using a method appropriate to
   the PSN tunneling mechanism.


4. General encapsulation method

4.1. The Control Word

   When carrying Ethernet over an IP or MPLS backbone sequentiality may
   need to be preserved.  The OPTIONAL control word defined here
   addresses this requirement.  Implementations MUST support sending no
   control word, and MAY support sending a control word.

   In all cases the egress router must be aware of whether the ingress
   router will send a control word over a specific virtual circuit.
   This may be achieved by configuration of the routers, or by
   signaling, for example as defined in [PWE3-CRTL].

   The control word is defined as follows:




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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Reserved            |       Sequence Number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   In the above diagram the first 16 bits are reserved for future use.
   They MUST be set to 0 when transmitting, and MUST be ignored upon
   receipt.

   The next 16 bits provide a sequence number that can be used to
   guarantee ordered packet delivery. The processing of the sequence
   number field is OPTIONAL.

   The sequence number space is a 16 bit, unsigned circular space. The
   sequence number value 0 is used to indicate an unsequenced packet.


4.1.1. Setting the sequence number

   For a given emulated VC, and a pair of routers R1 and R2, if R1
   supports packet sequencing then the following procedures should be
   used:

     - the initial packet transmitted on the emulated VC MUST use
       sequence number 1
     - subsequent packets MUST increment the sequence number by one for
       each packet
     - when the transmit sequence number reaches the maximum 16 bit
       value (65535) the sequence number MUST wrap to 1

   If the transmitting router R1 does not support sequence number
   processing, then the sequence number field in the control word MUST
   be set to 0.


4.1.2. Processing the sequence number

   If a router R2 supports receive sequence number processing, then the
   following procedures should be used:

   When an emulated VC is initially set up, the "expected sequence
   number" associated with it MUST be initialized to 1.

   When a packet is received on that emulated VC, the sequence number
   should be processed as follows:





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     - if the sequence number on the packet is 0, then the packet passes
       the sequence number check

     - otherwise if the packet sequence number >= the expected sequence
       number and the packet sequence number - the expected sequence
       number < 32768, then the packet is in order.

     - otherwise if the packet sequence number < the expected sequence
       number and the expected sequence number - the packet sequence
       number >= 32768, then the packet is in order.

     - otherwise the packet is out of order.

   If a packet passes the sequence number check, or is in order then, it
   can be delivered immediately. If the packet is in order, then the
   expected sequence number should be set using the algorithm:

   expected_sequence_number := packet_sequence_number + 1 mod 2**16
   if (expected_sequence_number = 0) then expected_sequence_number := 1;

   Packets which are received out of order MAY be dropped or reordered
   at the discretion of the receiver.

   If a router R2 does not support receive sequence number processing,
   then the sequence number field MAY be ignored.


4.2. MTU Requirements

   The network MUST be configured with an MTU that is sufficient to
   transport the largest encapsulation frames.  If MPLS is used as the
   tunneling protocol, for example, this is likely to be 8 or more bytes
   greater than the largest frame size.  Other tunneling protocols may
   have longer headers and require larger MTUs.  If the ingress router
   determines that an encapsulated layer 2 PDU exceeds the MTU of the
   tunnel through which it must be sent, the PDU MUST be dropped. If an
   egress router receives an encapsulated layer 2 PDU whose payload
   length (i.e., the length of the PDU itself without any of the
   encapsulation headers), exceeds the MTU of the destination layer 2
   interface, the PDU MUST be dropped.











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4.3. Tagged Mode

   In this mode each frame MUST include an 802.1Q field.  All frames in
   a PW MUST have the same 802.1Q tag value.  Note that the tag may be
   overwritten by the NSP function at ingress or at egress.

   Note that when using the signaling procedures defined in [PWE3-CRTL],
   such a PW should be signaled as being of type "Ethernet VLAN".


4.4. Raw Mode

   In this mode each frame SHOULD NOT include an 802.1Q field.

   Note that when using the signaling procedures defined in [PWE3-CRTL],
   such a PW should be signaled as being of type "Ethernet".


5. Using an MPLS Label as the Demultiplexer Field

   To use an MPLS label as the demultiplexer field, a 32-bit label stack
   entry [MPLS-LABEL] is simply prepended to the emulated VC
   encapsulation, and hence will appear as the bottom label of an MPLS
   label stack.  This label may be called the "VC label".  The
   particular emulated VC identified by a particular label value must be
   agreed by the ingress and egress LSRs, either by signaling (e.g, via
   the methods of [PWE3-CRTL]) or by configuration. Other fields of the
   label stack entry are set as follows.


5.1. MPLS Shim EXP Bit Values

   If it is desired to carry Quality of Service information, the Quality
   of Service information SHOULD be represented in the EXP field of the
   VC label.  If more than one MPLS label is imposed by the ingress LSR,
   the EXP field of any labels higher in the stack SHOULD also carry the
   same value.


5.2. MPLS Shim S Bit Value

   The ingress LSR, R1, MUST set the S bit of the VC label to a value of
   1 to denote that the VC label is at the bottom of the stack.








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5.3. MPLS Shim TTL Values

   The ingress LSR, R1, SHOULD set the TTL field of the VC label to a
   value of 255.


6. Security Considerations

   This document specifies only encapsulations, and not the protocols
   used to carry the encapsulated packets across the network.  Each such
   protocol may have its own set of security issues, but those issues
   are not affected by the encapsulations specified herein.

   Specific security issues related to encapsulation are addressed in
   the requirements section above.


7. Intellectual Property Disclaimer

   This document is being submitted for use in IETF standards
   discussions.


8. References

   [PWE3-CRTL] "Transport of Layer 2 Frames Over MPLS",
        Martini, L., et al., draft-ietf-pwe3-control-protocol-00.txt,
        ( work in progress ), February 2003.

   [PWE3-ATM] "Encapsulation Methods for Transport of ATM Cells/Frame
        Over IP and MPLS Networks", Martini L., et al.,
        draft-ietf-pwe3-atm-encap-00.txt, ( work in progress ),
        February 2003.

   [PWE3-FRAME] "Encapsulation Methods for Transport of Frame-Relay
        Over IP and MPLS Networks", Kawa, C., et al.,
        draft-ietf-pwe3-frame-encap-00.txt, ( work in progress ),
        June 2002.

   [PWE3-REQ] "Requirements for Pseudo Wire Emulation Edge-to-Edge
        (PWE3)", Xiao, X., McPherson, D., Pate, P., White, C.,
        Kompella, K., Gill, V., Nadeau, T.,
        draft-pwe3-requirements-03.txt, ( work in progress ), June 2002.

   [PWE3-FRAME] "Framework for Pseudo Wire Emulation Edge-to-Edge
        (PWE3)", Pate, P., Xiao, X., So, T., Malis, A., Nadeau, T.,
        White, C., Kompella, K., Johnson, T., Bryant, S.,
        draft-pate-pwe3-framework-03.txt, ( work in progress ),



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        June 2002.

   [PW-MIB] "Pseudo Wire (PW) Management Information Base using SMIv2",
        Zelig, D., Mantin, S., Nadeau, T., Danenberg, D.,
        draft-zelig-pw-mib-02.txt, ( work in progress), February 2002.

   [PW-MPLS-MIB] "Pseudo Wire (PW) over MPLS PSN Management Information
        Base", Zelig D., Mantin, S., Nadeau, T., Danenberg, D.,
        Malis, A., draft-zelig-pw-mpls-mib-01.txt, ( work in progress ),
        February 2002.

   [PW-ENET-MIB] "Ethernet Pseudo Wire (PW) Management Information
        Base", Zelig, D., Nadeau, T., draft-zelig-pw-enet-mib-00.txt,
        ( work in progress ) February 2002.

   [802.3] IEEE, ISO/IEC 8802-3: 2000 (E), "IEEE Standard for
        Information technology -- Telecommunications and information
        exchange between systems -- Local and metropolitan area networks
        -- Specific requirements -- Part 3: Carrier Sense Multiple
        Access with Collision Detection (CSMA/CD) Access Method and
        Physical Layer Specifications", 2000.

   [802.1Q] ANSI/IEEE Standard 802.1Q, "IEEE Standards for Local and
        Metropolitan Area Networks: Virtual Bridged Local Area
        Networks", 1998.

   [MPLS-LABEL] "MPLS Label Stack Encoding", Rosen, E., Rekhter, E.,
        Tappan, D., Fedorkow, G., Farinacci, D., Li, T., Conta, A.,
        RFC 3032.


9. Author Information


   Luca Martini
   Level 3 Communications, LLC.
   1025 Eldorado Blvd.
   Broomfield, CO, 80021
   e-mail: luca@level3.net


   Nasser El-Aawar
   Level 3 Communications, LLC.
   1025 Eldorado Blvd.
   Broomfield, CO, 80021
   e-mail: nna@level3.net





Martini, et al.                                                [Page 14]

Internet Draft   draft-ietf-pwe3-ethernet-encap-00.txt      August 2002



   Giles Heron
   PacketExchange Ltd.
   The Truman Brewery
   91 Brick Lane
   LONDON E1 6QL
   United Kingdom
   e-mail: giles@packetexchange.net


   Dan Tappan
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA, 01824
   e-mail: tappan@cisco.com


   Eric Rosen
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA, 01824
   e-mail: erosen@cisco.com


   Steve Vogelsang
   Laurel Networks, Inc.
   Omega Corporate Center
   1300 Omega Drive
   Pittsburgh, PA 15205
   e-mail: sjv@laurelnetworks.com


   Andrew G. Malis
   Vivace Networks, Inc.
   2730 Orchard Parkway
   San Jose, CA 95134
   e-mail: Andy.Malis@vivacenetworks.com


   Vinai Sirkay
   Vivace Networks, Inc.
   2730 Orchard Parkway
   San Jose, CA 95134
   e-mail: sirkay@technologist.com







Martini, et al.                                                [Page 15]

Internet Draft   draft-ietf-pwe3-ethernet-encap-00.txt      August 2002



   Vasile Radoaca
   Nortel Networks
   600  Technology Park
   Billerica MA 01821
   e-mail: vasile@nortelnetworks.com


   Chris Liljenstolpe
   Cable & Wireless
   11700 Plaza America Drive
   Reston, VA 20190
   e-mail: chris@cw.net


   Kireeti Kompella
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA 94089
   e-mail: kireeti@juniper.net


   Tricci So
   e-mail: tricciso@yahoo.ca


   XiPeng Xiao
   Redback Networks
   300 Holger Way,
   San Jose, CA 95134
   e-mail: xipeng@redback.com


   Chris Flores
   Austin, Texas
   e-mail: chris_flores@hotmail.com


   David Zelig
   Corrigent Systems
   126, Yigal Alon St.
   Tel Aviv, ISRAEL
   e-mail: davidz@corrigent.com








Martini, et al.                                                [Page 16]

Internet Draft   draft-ietf-pwe3-ethernet-encap-00.txt      August 2002



   Raj Sharma
   Luminous Netwokrs, Inc.
   10460 Bubb Road
   Cupertino, CA 95014
   e-mail: raj@luminous.com


   Nick Tingle
   TiMetra Networks
   274 Ferguson Drive
   Mountain View, CA 94043
   e-mail: nick@timetra.com


   Sunil Khandekar
   TiMetra Networks
   274 Ferguson Drive
   Mountain View, CA 94043
   email: sunil@timetra.com


   Loa Andersson
   Utfors
   P.O. Box 525,
   SE-169 29 Solna, Sweden
   e-mail: loa.andersson@utfors.se



Appendix A - Interoperability Guidelines

Configuration Options

   The following is a list of the configuration options for a point-to-
   point Ethernet PW based on the reference points of Figure 3:















Martini, et al.                                                [Page 17]

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   --------------|---------------|---------------|------------------
   Service and   |  Encap on C   |Operation at B | Remarks
   Encap on A    |               |ingress/egress |
   --------------|---------------|---------------|------------------
   1) Raw        | Raw - Same as |               |
                 | A             |               |
                 |               |               |
   --------------|---------------|---------------|------------------
   2) Tag1       | Tag2          |Optional change| VLAN can be
                 |               |of VLAN value  | 0-4095
                 |               |               | Change allowed in
                 |               |               | both directions
   --------------|---------------|---------------|------------------
   3) No Tag     | Tag           |Add/remove Tag | Tag can be
                 |               |field          | 0-4095
                 |               |               | (note i)
                 |               |               |
   --------------|---------------|---------------|------------------
   4) Tag        | No Tag        |Remove/add Tag | (note ii)
                 |               |field          |
                 |               |               |
                 |               |               |
   --------------|---------------|---------------|------------------

                Figure 4: Configuration Options

   Allowed combinations:

   Raw and other services are not allowed on the same physical port (A).
   All other combinations are allowed, except that conflicting VLANs on
   (A) are not allowed.

   Notes:

        -i. Mode #3 MAY be limited to adding VLAN NULL only, since
            change of VLAN or association to specific VLAN can be done
            at the PW CE-bound side.

       -ii. Mode #4 exists in layer 2 switches, but is not recommended
            when operating with PW since it may not preserve the user's
            PRI bits.  If there is a need to remove the VLAN tag (for
            TLS at the other end of the PW) it is recommended to use
            mode #2 with tag2=0 (NULL VLAN) on the PW and use mode #3 at
            the other end of the PW.







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IEEE 802.3x Flow Control Considerations

   If the receiving node becomes congested, it can send a special frame,
   called the PAUSE frame, to the source node at the opposite end of the
   connection. The implementation MUST provide a mechanism for
   terminating PAUSE frames locally (i.e. at the local PE). It MUST
   operate as follows:

   PAUSE frames received on a local Ethernet port SHOULD cause the PE
   device to buffer, or to discard, further Ethernet frames for that
   port until the PAUSE condition is cleared.  Optionally the PE MAY
   simply discard PAUSE frames.

   If the PE device wishes to pause data received on a local Ethernet
   port (perhaps because its own buffers are filling up or because it
   has received notification of congestion within the PSN) then it MAY
   issue a PAUSE frame on the local Ethernet port, but MUST clear this
   condition when willing to receive more data.


Appendix B - QoS Details

   Section 3.7 describes various modes for supporting PW QOS over the
   PSN.  Examples of the above for a point to point VLAN service are:

     - The classification to the PW is based on VLAN field only,
       regardless of the user PRI bits.  The PW is assigned a specific
       COS (marking, scheduling, etc.)  at the tunnel level.

     - The classification to the PW is based on VLAN field, but the PRI
       bits of the user is mapped to different COS marking (and network
       behavior) at the PW level.  Examples are DiffServ coding in case
       of IP PSN, and E-LSP in MPLS PSN.

     - The classification to the PW is based on VLAN field and the PRI
       bits, and packets with different PRI bits are mapped to different
       PWs.  An example is to map a PWES to different L-LSPs in MPLS PSN
       in order to support multiple COS service over an L-LSP capable
       network.

       The specific value to be assigned at the PSN for various COS is
       not specified and is application specific.









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Adaptation of 802.1Q COS to PSN COS

   It is not required that the PSN will have the same COS definition of
   COS as defined in [802.1Q], and the mapping of 802.1Q COS to PSN QOS
   is application specific and depends on the agreement between the
   customer and the PW provider.  However, the following principles
   adopted from 802.1Q table 8-2 MUST be met when applying set of PSN
   COS based on user's PRI bits.
                ----------------------------------
                |#of available classes of service|
   -------------||---|---|---|---|---|---|---|---|
   User         || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
   Priority     ||   |   |   |   |   |   |   |   |
   ===============================================
   0 Best Effort|| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 2 |
   (Default)    ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   1 Background || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
                ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   2 Spare      || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
                ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   3 Excellent  || 0 | 0 | 0 | 1 | 1 | 2 | 2 | 3 |
   Effort       ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   4 Controlled || 0 | 1 | 1 | 2 | 2 | 3 | 3 | 4 |
   Load         ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   5 Interactive|| 0 | 1 | 1 | 2 | 3 | 4 | 4 | 5 |
   Multimedia   ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   6 Interactive|| 0 | 1 | 2 | 3 | 4 | 5 | 5 | 6 |
   Voice        ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|
   7 Network    || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
   Control      ||   |   |   |   |   |   |   |   |
   ------------ ||---|---|---|---|---|---|---|---|

                Figure 5: IEEE 802.1Q COS Service Mapping


Drop precedence

   The 802.1P standard does not support drop precedence, therefore from
   the PW PE-bound point of view there is no mapping required.  It is
   however possible to mark different drop precedence for different PW
   packets based on the operator policy and required network behavior.



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Internet Draft   draft-ietf-pwe3-ethernet-encap-00.txt      August 2002


   This functionality is not discussed further here.


PSN COS labels interaction with VC label COS marking

   Marking of COS bits at the VC level is not required if the PSN tunnel
   is PE to PE based, since only the PSN COS marking is visible to the
   PSN network. In cases where the VC multiplexing field is carried
   without an external tunnel (for example directly connected PEs with
   PHP, or PEs connected using GRE/IP), the rules stated above for
   tunnel COS marking apply also for the VC level.

   In summary, the rules for COS marking shall be as follows:

     - If there is only a VC label then, it shall contain the
       appropriate CoS value (e.g. MPLS between PEs which are directly
       adjacent to each other).

     - If the VC label and PSN tunnel labels are both being used, then
       the CoS marking on the PSN header shall be marked with the
       correct CoS value.

     - If the PSN marking is stripped at a node before the PE, the PSN
       marking MUST be copied to the VC label. An example is MPLS PSN
       with the use of PHP.

       PSN QOS support and signaling of QOS is out of scope of this
       document.























Martini, et al.                                                [Page 21]


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