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rfc:rfc4816

Network Working Group A. Malis Request for Comments: 4816 Verizon Category: Standards Track L. Martini

                                                        Cisco Systems
                                                           J. Brayley
                                                          ECI Telecom
                                                             T. Walsh
                                                     Juniper Networks
                                                        February 2007
             Pseudowire Emulation Edge-to-Edge (PWE3)
Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service

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 IETF Trust (2007).

Abstract

 The document describes a transparent cell transport service that
 makes use of the "N-to-one" cell relay mode for Pseudowire Emulation
 Edge-to-Edge (PWE3) Asynchronous Transfer-Mode (ATM) cell
 encapsulation.

1. Introduction

 This transparent cell transport service allows migration of ATM
 services to a PSN without having to provision the ATM subscriber or
 customer edge (CE) devices.  The ATM CEs will view the ATM
 transparent cell transport service as if they were directly connected
 via a Time Division Multiplexer (TDM) leased line.  This service is
 most likely to be used as an internal function in an ATM service
 provider's network as a way to connect existing ATM switches via a
 higher-speed PSN, or to provide ATM "backhaul" services for remote
 access to existing ATM networks.

Malis, et al. Standards Track [Page 1] RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007

1.1. 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 [1].

2. Transparent Cell Transport Definition

 The transparent port service is a natural application of the "N-to-
 one" Virtual Circuit Connection (VCC) cell transport mode for PWE3
 ATM encapsulation described in [2], and MUST be used with pseudowires
 of type 0x0003, "ATM transparent cell transport" [4].
 The ATM transparent port service emulates connectivity between two
 remote ATM ports.  This service is useful when one desires to connect
 two CEs without processing or switching at the Virtual Path
 Connection (VPC) or VCC layer.  The ingress PE discards any
 idle/unassigned cells received from the ingress ATM port, and maps
 all other received cells to a single pseudowire.
 The egress PE does not change the Virtual Path Identifier (VPI),
 Virtual Circuit Identifier (VCI), Payload Type Identifier (PTI), or
 Cell Loss Priority (CLP) bits when it sends these cells on the egress
 ATM port.  Therefore, the transparent port service appears to emulate
 an ATM transmission convergence layer connection between two ports.
 However, since the ingress PE discards idle/unassigned cells, this
 service benefits from statistical multiplexing bandwidth savings.
 In accordance with [2], cell concatenation MAY be used for
 transparent cell-relay transport in order to save the PSN bandwidth.
 If used, it MUST be agreed between the ingress and egress PEs.  In
 particular, if the Pseudo Wire has been set up using the PWE3 control
 protocol [3], the ingress PE MUST NOT exceed the value of the
 "Maximum Number of concatenated ATM cells" Pseudowire Interface
 Parameter Sub-TLV (Interface Parameter ID = 0x02 [4]) received in the
 Label Mapping message for the Pseudo Wire, and MUST NOT use cell
 concatenation if this parameter has been omitted by the egress PE.
 ATM Operations and Management (OAM) cells MUST be transported
 transparently, and the PEs do not act on them.  If the PEs detect a
 PSN or pseudowire failure between them, they do not generate any OAM
 cells, but rather bring down the ATM interfaces to the CEs (e.g.,
 generating LOS on the ATM port), just as if it were a transmission
 layer failure.

Malis, et al. Standards Track [Page 2] RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007

 Similarly, ATM Integrated Local Management Interface (ILMI) signaling
 from the CEs, if any, MUST be transported transparently, and the PEs
 do not act on it.  However, the PEs must act on physical interface
 failure by either withdrawing the PW labels or by using pseudowire
 status signaling to indicate the interface failure.  The procedures
 for both alternatives are described in [3].

3. Security Considerations

 This document does not introduce any new security considerations
 beyond those in [2] and [3].  This document defines an application
 that utilizes the encapsulation specified in [2], and does not
 specify the protocols used to carry the encapsulated packets across
 the PSN.  Each such protocol may have its own set of security issues,
 but those issues are not affected by the application specified
 herein.  Note that the security of the transported ATM service will
 only be as good as the security of the PSN.  This level of security
 might be less rigorous than a native ATM service.

4. Congestion Control

 Since this document discusses an application of the "N-to-one" VCC
 cell transport mode for PWE3 ATM encapsulation described in [2], the
 congestion control considerations are identical to those discussed in
 section 15 of [2].  The PWE3 Working Group is also undertaking
 additional work on ATM-related congestion issues, and implementers
 should anticipate that an RFC will be published describing additional
 congestion control techniques that should be applied to ATM emulation
 over pseudowires.

5. Normative References

 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.
 [2] Martini, L., Jayakumar, J., Bocci, M., El-Aawar, N., Brayley, J.,
     and G. Koleyni, "Encapsulation Methods for Transport of
     Asynchronous Transfer Mode (ATM) over MPLS Networks", RFC 4717,
     December 2006.
 [3] 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.
 [4] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
     Emulation (PWE3)", BCP 116, RFC 4446, April 2006.

Malis, et al. Standards Track [Page 3] RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007

Acknowledgments

 The authors would like to thank the members of the PWE3 working group
 for their assistance on this document, and Sasha Vainshtein of Axerra
 in particular for his comments and suggestions.

Author's Addresses

 Andrew G. Malis
 Verizon Communications
 40 Sylvan Road
 Waltham, MA
 EMail: andrew.g.malis@verizon.com
 Luca Martini
 Cisco Systems, Inc.
 9155 East Nichols Avenue, Suite 400
 Englewood, CO, 80112
 EMail: lmartini@cisco.com
 Jeremy Brayley
 ECI Telecom
 Omega Corporate Center
 1300 Omega Drive
 Pittsburgh, PA 15205
 EMail: jeremy.brayley@ecitele.com
 Tom Walsh
 Juniper Networks
 1194 N Mathilda Ave
 Sunnyvale, CA 94089
 EMail: twalsh@juniper.net

Malis, et al. Standards Track [Page 4] RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007

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 contained in BCP 78, and except as set forth therein, the authors
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Malis, et al. Standards Track [Page 5]

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