Tech-invite3GPPspaceIETF RFCsSIP
93929190898887868584838281807978777675747372717069686766656463626160595857565554535251504948474645444342414039383736353433323130292827262524232221201918171615141312111009080706050403020100
in Index   Prev   Next

RFC 4816

Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service

Pages: 5
Proposed Standard

ToP   noToC   RFC4816 - Page 1
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.
ToP   noToC   RFC4816 - Page 2

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.
ToP   noToC   RFC4816 - Page 3
   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.
ToP   noToC   RFC4816 - Page 4
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
ToP   noToC   RFC4816 - Page 5
Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

Acknowledgement

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