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Network Working Group                                          A. MalisRequest for Comments: 4816                                      VerizonCategory: Standards Track                                    L. Martini                                                          Cisco Systems                                                             J. Brayley                                                            ECI Telecom                                                               T. Walsh                                                       Juniper Networks                                                          February 2007Pseudowire Emulation Edge-to-Edge (PWE3)Asynchronous Transfer Mode (ATM) Transparent Cell Transport ServiceStatus 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 20071.1.  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 inRFC 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 2007Acknowledgments   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.netMalis, et al.               Standards Track                     [Page 4]

RFC 4816      PWE3 ATM Transparent Cell Transport Service  February 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 inBCP 78 andBCP 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 athttp://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.Malis, et al.               Standards Track                     [Page 5]