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rfc:rfc4618

Network Working Group L. Martini Request for Comments: 4618 E. Rosen Category: Standards Track Cisco Systems, Inc.

                                                              G. Heron
                                                              A. Malis
                                                               Tellabs
                                                        September 2006
              Encapsulation Methods for Transport of
     PPP/High-Level Data Link Control (HDLC) over MPLS Networks

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 A pseudowire (PW) can be used to carry Point to Point Protocol (PPP)
 or High-Level Data Link Control (HDLC) Protocol Data Units over a
 Multiprotocol Label Switching (MPLS) network without terminating the
 PPP/HDLC protocol.  This enables service providers to offer
 "emulated" HDLC, or PPP link services over existing MPLS networks.
 This document specifies the encapsulation of PPP/HDLC Packet Data
 Units (PDUs) within a pseudowire.

Martini, et al. Standards Track [Page 1] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

Table of Contents

 1. Introduction ....................................................2
 2. Specification of Requirements ...................................2
 3. Applicability Statement .........................................5
 4. General Encapsulation Method ....................................6
    4.1. The Control Word ...........................................6
    4.2. MTU Requirements ...........................................8
 5. Protocol-Specific Details .......................................9
    5.1. HDLC .......................................................9
    5.2. Frame Relay Port Mode ......................................9
    5.3. PPP .......................................................10
 6. Using an MPLS Label as the Demultiplexer Field .................11
    6.1. MPLS Shim EXP Bit Values ..................................11
    6.2. MPLS Shim S Bit Value .....................................11
 7. Congestion Control .............................................12
 8. IANA Considerations ............................................12
 9. Security Considerations ........................................12
 10. Normative References ..........................................13
 11. Informative References ........................................13

1. Introduction

 A PPP/HDLC pseudowire (PW) allows PPP/HDLC Protocol Data Units (PDUs)
 to be carried over an MPLS network.  In addressing the issues
 associated with carrying a PPP/HDLC PDU over an MPLS network, this
 document assumes that a PW has been set up by some means outside the
 scope of this document.  This may be via manual configuration, or
 using a signaling protocol such as that defined in [RFC4447].
 The following figure describes the reference models that are derived
 from [RFC3985] to support the HDLC/PPP PW emulated services.  The
 reader is also assumed to be familiar with the content of the
 [RFC3985] document.

2. 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 [RFC2119].

Martini, et al. Standards Track [Page 2] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

        |<-------------- Emulated Service ---------------->|
        |                                                  |
        |          |<------- Pseudowire ------->|          |
        |          |                            |          |
        |          |    |<-- PSN Tunnel -->|    |          |
        |          V    V                  V    V          |
        V   AC     +----+                  +----+    AC    V
  +-----+    |     | PE1|==================| PE2|     |    +-----+
  |     |----------|............PW1.............|----------|     |
  | CE1 |    |     |    |                  |    |     |    | CE2 |
  |     |----------|............PW2.............|----------|     |
  +-----+  ^ |     |    |==================|    |     | ^  +-----+
        ^  |       +----+                  +----+     | |  ^
        |  |   Provider Edge 1         Provider Edge 2  |  |
        |  |                                            |  |
  Customer |                                            | Customer
  Edge 1   |                                            | Edge 2
           |                                            |
           |                                            |
     native HDLC/PPP service                   native HDLC/PPP service
     Figure 1.  PWE3 HDLC/PPP interface reference configuration
 This document specifies the emulated PW encapsulation for PPP and
 HDLC; however, quality of service related issues are not discussed in
 this document.  For the purpose of the discussion in this document,
 PE1 will be defined as the ingress router and PE2 as the egress
 router.  A layer 2 PDU will be received at PE1, encapsulated at PE1,
 transported across the network, decapsulated at PE2, and transmitted
 out on an attachment circuit at PE2.

Martini, et al. Standards Track [Page 3] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

 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          C
                     Figure 2.  PW reference diagram
 The PW terminates at a logical port within the PE, defined at point B
 in the above diagram.  This port provides an HDLC Native Service
 Processing function that will deliver each PPP/HDLC packet that is
 received at point A, unaltered, to the point A in the corresponding
 PE at the other end of the PW.
 The Native Service Processing (NSP) function includes packet
 processing that is required for the PPP/HDLC packets that are
 forwarded to the PW termination point.  Such functions may include
 bit stuffing, PW-PW bridging, L2 encapsulation, shaping, and
 policing.  These functions are specific to the native packet
 technology and may not be required for the PW emulation service.
 The points to the left of B, 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 PPP/HDLC packets as necessary to transmit them
 across the MPLS network.

Martini, et al. Standards Track [Page 4] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

3. Applicability Statement

 PPP/HDLC transport over PW service is not intended to emulate the
 traditional PPP or HDLC service perfectly, but it can be used for
 some applications that require PPP or HDLC transport service.
 The applicability statements in [RFC4619] also apply to the Frame
 Relay port mode PW described in this document.
 The following are notable differences between traditional PPP/HDLC
 service, and the protocol described in this document:
  1. Packet ordering can be preserved using the OPTIONAL sequence field

in the control word; however, implementations are not required to

   support this feature.
  1. The Quality of Service model for traditional PPP/HDLC links can be

emulated, however this is outside the scope of this document.

  1. A Frame Relay Port mode PW, or HDLC PW, does not process any frame

relay status messages or alarms as described in [Q922] [Q933].

  1. The HDLC Flags are processed locally in the PE connected to the

attachment circuit.

 The HDLC mode is suitable for port-to-port transport of Frame Relay
 User Network Interface (UNI) or Network Node Interface (NNI) traffic.
 Since all packets are passed in a largely transparent manner over the
 HDLC PW, any protocol that has HDLC-like framing may use the HDLC PW
 mode, including PPP, Frame-Relay, and X.25.  Exceptions include cases
 where direct access to the HDLC interface is required, or modes that
 operate on the flags, Frame Check Sequence (FCS), or bit/byte
 unstuffing that is performed before sending the HDLC PDU over the PW.
 An example of this is PPP Asynchronous-Control-Character-Map (ACCM)
 negotiation.
 For PPP, since media-specific framing is not carried, the following
 options will not operate correctly if the PPP peers attempt to
 negotiate them:
  1. Frame Check Sequence (FCS) Alternatives
  1. Address-and-Control-Field-Compression (ACFC)
  1. Asynchronous-Control-Character-Map (ACCM)
 Note, also, that PW LSP Interface MTU negotiation, as specified in
 [RFC4447], is not affected by PPP Maximum Receive Unit (MRU)

Martini, et al. Standards Track [Page 5] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

 advertisement.  Thus, if a PPP peer sends a PDU with a length in
 excess of that negotiated for the PW tunnel, that PDU will be
 discarded by the ingress router.

4. General Encapsulation Method

 This section describes the general encapsulation format for PPP and
 HDLC packets over MPLS pseudowires.
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               PSN Transport Header (As Required)              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Pseudowire Header                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Control Word                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     PPP/HDLC Service Payload                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Figure 3.  General format for PPP/HDLC encapsulation over PSNs
 The PSN Transport Header depends on the particular tunneling
 technology in use.  This header is used to transport the encapsulated
 PPP/HDLC information through the packet-switched core.
 The Pseudowire Header identifies a particular PPP/HDLC service on a
 tunnel.  In case the of MPLS, the Pseudowire Header is the MPLS label
 at the bottom of the MPLS label stack.
 The Control Word is inserted before the PPP/HDLC service payload.  It
 may contain a length and sequence number.

4.1. The Control Word

 There are four requirements that may need to be satisfied when
 transporting layer 2 protocols over an MPLS PSN:
 i.    Sequentiality may need to be preserved.
 ii.   Small packets may need to be padded in order to be transmitted
       on a medium where the minimum transport unit is larger than the
       actual packet size.
 iii.  Control bits carried in the header of the layer 2 packet may
       need to be transported.

Martini, et al. Standards Track [Page 6] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

 iv.   Creating an in-band associated channel for operation and
       maintenance communications.
 The Control Word defined in this section is based on the Generic PW
 MPLS Control Word, as defined in [RFC4385].  It provides the ability
 to sequence individual packets on the PW and avoidance of equal-cost
 multiple-path load-balancing (ECMP) [RFC2992] and enables Operations
 and Management (OAM) mechanisms, including [VCCV].
 [RFC4385] states, "If a PW is sensitive to packet mis-ordering and is
 being carried over an MPLS PSN that uses the contents of the MPLS
 payload to select the ECMP path, it MUST employ a mechanism which
 prevents packet mis-ordering."  This is necessary because ECMP
 implementations may examine the first nibble after the MPLS label
 stack to determine whether the content of the labeled packet is IP.
 Thus, if the PPP protocol number of a PPP packet carried over the PW
 without a control word present begins with 0x4 or 0x6, it could be
 mistaken for an IPv4 or IPv6 packet.  This could, depending on the
 configuration and topology of the MPLS network, lead to a situation
 where all packets for a given PW do not follow the same path.  This
 may increase out-of-order packets on a given PW or cause OAM packets
 to follow a different path from that of actual traffic.
 The features that the control word provides may not be needed for a
 given PPP/HDLC PW.  For example, ECMP may not be present or active on
 a given MPLS network, and strict packet sequencing may not be
 required.  If this is the case, the control word provides little
 value and is therefore optional.  Early PPP/HDLC PW implementations
 have been deployed that do not include a control word or the ability
 to process one if present.  To aid in backwards compatibility, future
 implementations MUST be able to send and receive packets without the
 control word.
 In all cases, the egress PE MUST be aware of whether the ingress PE
 will send a control word over a specific PW.  This may be achieved by
 configuration of the PEs, or by signaling, as defined in [RFC4447].
 The control word is defined as follows:
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0 0 0 0|0 0 0 0|FRG|   Length  |     Sequence Number           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 Figure 4.  MPLS PWE3 control word

Martini, et al. Standards Track [Page 7] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

 In the above diagram, the first 4 bits are set to 0 in indicate a CW
 [RFC4385].
 The next 4 bits provide space for carrying protocol-specific flags.
 These are not used for HDLC/PPP, and they MUST be set to 0 for
 transmitting and MUST be ignored upon receipt.
 The next 2 bits are defined in [RFC4623].
 The next 6 bits provide a length field, which is used as follows: If
 the packet's length (defined as the length of the layer 2 payload
 plus the length of the control word) is less than 64 bytes, the
 length field MUST be set to the packet's length.  Otherwise, the
 length field MUST be set to zero.  The value of the length field, if
 not zero, is used to remove any padding that may have been added by
 the MPLS network.  If the control word is used and padding was added
 to the packet in transit on the MPLS network, then when the packet
 reaches the egress PE the padding MUST be removed before forwarding
 the packet.
 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.[RFC4385]
 The sequence number space is a 16-bit, unsigned circular space.  The
 sequence number value 0 is used to indicate an unsequenced
 packet.[RFC4385]
 The procedures described in Section 4 of [RFC4385] MUST be followed
 to process the sequence number field.

4.2. MTU Requirements

 The network MUST be configured with an MTU that is sufficient to
 transport the largest encapsulation packets.  When MPLS is used as
 the tunneling protocol, for example, this is likely to be 12 or more
 bytes greater than the largest packet size.  The methodology
 described in [RFC4623] MAY be used to fragment encapsulated packets
 that exceed the PSN MTU.  However, if [RFC4623] is not used, then if
 the ingress router determines that an encapsulated layer 2 PDU
 exceeds the MTU of the PSN tunnel through which it must be sent, the
 PDU MUST be dropped.
 If a packet is received on the attachment circuit that exceeds the
 interface MTU subTLV value [RFC4447], it MUST be dropped.  It is also
 RECOMMENDED that PPP devices be configured to not negotiate PPP MRUs
 larger than that of the AC MTU.

Martini, et al. Standards Track [Page 8] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

5. Protocol-Specific Details

5.1. HDLC

 HDLC mode provides port-to-port transport of HDLC-encapsulated
 traffic.  The HDLC PDU is transported in its entirety, including the
 HDLC address and control fields, but excluding HDLC flags and the
 FCS.  Bit/Byte stuffing is undone.  If the OPTIONAL control word is
 used, then the flag bits in the control word are not used and MUST be
 set to 0 for transmitting and MUST be ignored upon receipt.
 When the PE detects a status change in the attachment circuit status,
 such as an attachment circuit physical link failure, or if the AC is
 administratively disabled, the PE MUST send the appropriate PW status
 notification message that corresponds to the HDLC AC status.  In a
 similar manner, the local PW status MUST also be reflected in a
 respective PW status notification message, as described in [RFC4447].
 The PW of type 0x0006 "HDLC" will be used to transport HDLC packets.
 The IANA allocation registry of "Pseudowire Type" is defined in the
 IANA allocation document for PWs [RFC4446] along with initial
 allocated values.

5.2. Frame Relay Port Mode

 Figure 5 illustrates the concept of frame relay port mode or many-
 to-one mapping, which is an OPTIONAL capability.
 Figure 5a shows two frame relay devices physically connected with a
 frame relay UNI or NNI.  Between their two ports, P1 and P2, n frame
 relay Virtual Circuits (VCs) are configured.
 Figure 5b shows the replacement of the physical frame relay interface
 with a pair of PEs and a PW between them.  The interface between a
 Frame Relay (FR) device and a PE is either an FR UNI or an NNI.  All
 FR VCs carried over the interface are mapped into one HDLC PW.  The
 standard frame relay Link Management Interface (LMI) procedures
 happen directly between the CEs.  Thus with port mode, we have many-
 to-one mapping between FR VCs and a PW.

Martini, et al. Standards Track [Page 9] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

            +------+                          +-------+
            | FR   |                          |   FR  |
            |device|         FR UNI/NNI       | device|
            |    [P1]------------------------[P2]     |
            |      |      carrying n FR VCs   |       |
            +------+                          +-------+
               [Pn]: A port
                Figure 5a.  FR interface between two FR devices
                  |<---------------------------->|
                  |                              |
                   +----+                  +----+
 +------+          |    |     One PW       |    |         +------+
 |      |          |    |==================|    |         |      |
 |  FR  |    FR    | PE1| carrying n FR VCs| PE2|    FR   |  FR  |
 |device|----------|    |                  |    |---------|device|
 | CE1  | UNI/NNI  |    |                  |    | UNI/NNI | CE2  |
 +------+          +----+                  +----+         +------+
        |                                                 |
        |<----------------------------------------------->|
                                n FR VCs
         Figure 5b.  Pseudowires replacing the FR interface
 FR VCs are not visible individually to a PE; there is no
 configuration of individual FR VC in a PE.  A PE processes the set of
 FR VCs assigned to a port as an aggregate.
 FR port mode provides transport between two PEs of a complete FR
 frame using the same encapsulation as described above for HDLC mode.
 Although frame relay port mode shares the same encapsulation as HDLC
 mode, a different PW type is allocated in [RFC4446]: 0x000F Frame-
 Relay Port mode.
 All other aspects of this PW type are identical to the HDLC PW
 encapsulation described above.

5.3. PPP

 PPP mode provides point-to-point transport of PPP-encapsulated
 traffic, as specified in [RFC1661].  The PPP PDU is transported in
 its entirety, including the protocol field (whether compressed using
 Protocol Field Compression or not), but excluding any media-specific
 framing information, such as HDLC address and control fields or FCS.

Martini, et al. Standards Track [Page 10] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

 If the OPTIONAL control word is used, then the flag bits in the
 control word are not used and MUST be set to 0 for transmitting and
 MUST be ignored upon receipt.
 When the PE detects a status change in the attachment circuit (AC)
 status, such as an attachment circuit physical link failure, or if
 the AC is administratively disabled, the PE MUST send the appropriate
 PW status notification message that corresponds to the PPP AC status.
 Note that PPP negotiation status is transparent to the PW and MUST
 NOT be communicated to the remote MPLS PE.  In a similar manner, the
 local PW status MUST also be reflected in a respective PW status
 notification message, as described in [RFC4447].
 A PW of type 0x0007 "PPP" will be used to transport PPP packets.
 The IANA allocation registry of "Pseudowire Type" is defined in the
 IANA allocation document for PWs [RFC4446] along with initial
 allocated values.

6. Using an MPLS Label as the Demultiplexer Field

 To use an MPLS label as the demultiplexer field, a 32-bit label stack
 entry [RFC3032] is simply prepended to the emulated PW encapsulation
 and thus appears as the bottom label of an MPLS label stack.  This
 label may be called the "PW label".  The particular emulated PW
 identified by a particular label value must be agreed by the ingress
 and egress LSRs, either by signaling (e.g., via the methods of
 [RFC4447]) or by configuration.  Other fields of the label stack
 entry are set as described below.

6.1. 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
 PW label.  If more than one MPLS label is imposed by the ingress LSR,
 the EXP field of any labels higher in the stack MUST also carry the
 same value.

6.2. MPLS Shim S Bit Value

 The ingress LSR, PE1, MUST set the S bit of the PW label to a value
 of 1 to denote that the PW label is at the bottom of the stack.

Martini, et al. Standards Track [Page 11] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

7. Congestion Control

 As explained in [RFC3985], the PSN carrying the PW may be subject to
 congestion, the characteristics of which are dependent upon PSN type,
 network architecture, configuration, and loading.  During congestion,
 the PSN may exhibit packet loss that will impact the service carried
 by the PPP/HLDC PW.  In addition, since PPP/HDLC PWs carry an
 unspecified type of services across the PSN, they cannot behave in a
 TCP-friendly manner prescribed by [RFC2914].  In the presence of
 services that reduce transmission rate, PPP/HDLC PWs will thus
 consume more than their fair share and SHOULD be halted.
 Whenever possible, PPP/HDLC PWs should be run over traffic-engineered
 PSNs providing bandwidth allocation and admission control mechanisms.
 IntServ-enabled domains providing the Guaranteed Service (GS) or
 DiffServ-enabled domains using EF (expedited forwarding) are examples
 of traffic-engineered PSNs.  Such PSNs will minimize loss and delay
 while providing some degree of isolation of the PPP/HDLC PW's effects
 from neighboring streams.
 The PEs SHOULD monitor for congestion (by using explicit congestion
 notification, [VCCV], or by measuring packet loss) in order to ensure
 that the service using the PPP/HDLC PW may be maintained.  When
 significant congestion is detected, the PPP/HDLC PW SHOULD be
 administratively disabled.  If the PW has been set up using the
 protocol defined in [RFC4447], then procedures specified in [RFC4447]
 for status notification can be used to disable packet transmission on
 the ingress PE from the egress PE.  The PW may be restarted by manual
 intervention, or by automatic means after an appropriate waiting
 time.

8. IANA Considerations

 This document has no new IANA Actions.  All necessary IANA actions
 have already been included in [RFC4446].

9. Security Considerations

 The PPP and HDLC pseudowire type is subject to all the general
 security considerations discussed in [RFC3985][RFC4447].  This
 document specifies only encapsulations, and not the protocols that
 may be used to carry the encapsulated packets across the MPLS
 network.  Each such protocol may have its own set of security issues,
 but those issues are not affected by the encapsulations specified
 herein.

Martini, et al. Standards Track [Page 12] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

10. Normative References

 [RFC1661]    Simpson, W., "The Point-to-Point Protocol (PPP)", STD
              51, RFC 1661, July 1994.
 [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3032]    Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, January 2001.
 [RFC4385]    Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word
              for Use over an MPLS PSN", RFC 4385, February 2006.
 [RFC4446]    Martini, L., "IANA Allocations for Pseudowire Edge to
              Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
 [RFC4447]    Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
              Heron, "Pseudowire Setup and Maintenance Using the Label
              Distribution Protocol (LDP)", RFC 4447, April 2006.
 [RFC4619]    Martini, L., Ed., Kawa, C., Ed., and A. Malis, Ed.,
              "Encapsulation Methods for Transport of Frame Relay over
              Multiprotocol Label Switching (MPLS) Networks", RFC
              4619, September 2006.
 [RFC4623]    Malis, A. and M. Townsley, "Pseudowire Emulation Edge-
              to-Edge (PWE3) Fragmentation and Reassembly", RFC 4623,
              August 2006.

11. Informative References

 [Q922]       ITU-T Recommendation Q.922 Specification for Frame Mode
              Basic call control, ITU Geneva 1995.
 [Q933]       ITU-T Recommendation Q.933 Specification for Frame Mode
              Basic call control, ITU Geneva 2003.
 [RFC2914]    Floyd, S., "Congestion Control Principles", BCP 41, RFC
              2914, September 2000.
 [RFC2992]    Hopps, C., "Analysis of an Equal-Cost Multi-Path
              Algorithm", RFC 2992, November 2000.
 [RFC3985]    Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.

Martini, et al. Standards Track [Page 13] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

 [VCCV]       Nadeau, T., et al., "Pseudo Wire Virtual Circuit
              Connection Verification (VCCV)", Work in Progress,
              October 2005.

Contributing Author Information

 Yeongil Seo
 463-1 KT Technology Lab
 Jeonmin-dong Yusung-gu
 Daegeon, Korea
 EMail: syi1@kt.co.kr
 Toby Smith
 Laurel Networks, Inc.
 Omega Corporate Center
 1300 Omega Drive
 Pittsburgh, PA 15205
 EMail: tob@laurelnetworks.com

Martini, et al. Standards Track [Page 14] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

Authors' Addresses

 Luca Martini
 Cisco Systems, Inc.
 9155 East Nichols Avenue, Suite 400
 Englewood, CO, 80112
 EMail: lmartini@cisco.com
 Giles Heron
 Tellabs
 Abbey Place
 24-28 Easton Street
 High Wycombe
 Bucks
 HP11 1NT
 UK
 EMail: giles.heron@tellabs.com
 Eric C. Rosen
 Cisco Systems, Inc.
 1414 Massachusetts Avenue
 Boxborough, MA 01719
 EMail: erosen@cisco.com
 Andrew G. Malis
 Tellabs
 1415 West Diehl Road
 Naperville, IL  60563
 EMail: Andy.Malis@tellabs.com

Martini, et al. Standards Track [Page 15] RFC 4618 Transport of PPP/HDLC over MPLS September 2006

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 contained in BCP 78, and except as set forth therein, the authors
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Martini, et al. Standards Track [Page 16]

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