Transport Working Group Ghassem Koleyni Internet Draft Nortel Networks Expiration Date: September 2002 Matthew Bocci Alcatel April 2002 Applicability Statement for ATM Cell Encapsulation over PSN (the basic mode) Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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. 1. Abstract This document discusses the applicability of ATM Cell encapsulation over PNS (Packet Switched Networks, e.g., MPLS). It discusses possible network applications. This document is a prerequisite for advancing ATM-MPLS Cell interworking on the standards track. The PSN (e.g., MPLS) is used to transport ATM layer services such as those defined by ITU-T as ATM transfer capabilities [2] and ATM Forum as ATM service categories [3]. The basic requirement is to transparently transport the ATM VCC or VPC service related information (e.g., traffic parameters, QoS, OAM, etc.) over the Koleyni, et al. Expires September 2002 [Page 1] Internet Draft draft-koleyni-pwe3-app-cell-over-PSN-00.txt April 2002 interworking LSP, also called Pseudo Wire (PW), over the packet network. Table of contents 1. Abstract 1 2. Introduction 2 3. Terminology 2 4. Applicability 2 5. Implementation and deployment considerations 3 6. Limitations 3 7. Security Considerations 3 8. References 4 9. Acknowledgement 4 10. Author's Addresses 4 2. Introduction Many service providers have multiple service networks and the Operational Support System capabilities needed to support these existing service offerings. Packet Switched Networks (PSNs) have the potential to reduce the complexity of a service provider's infrastructure by allowing virtually any existing digital service to be supported over a single networking infrastructure. 3. Terminology CTD Cell Transfer Delay MTU Maximum Transfer Unit OAM Operations, Administration, and Maintenance. PVC Permanent Virtual Connection. An ATM connection that is provisioning via a network management interface. The connection is not signalled. VCC Virtual Circuit Connection. An ATM connection that is switched based on the cell header's VCI. VPC Virtual Path Connection. An ATM connection that is switched based on the cell header's VPI. 4. Applicability The primary application supported by ATM cell encapsulation over MPLS is to enable the seamless transport of the currently defined ATM layer services (i.e., those identified as transfer capabilities by ITU-T [2] and those identified as service category by ATM Forum [3]) over an MPLS network. To provide this, the basic requirement of the ATM-MPLS interworking function is to map the ATM cells belonging to either VCC or VPC, together with any related OAM and protocol control information into, an interworking LSP that is set up over the MPLS network. Koleyni, et al. Expires September 2002 [Page 2] Internet Draft draft-koleyni-pwe3-app-cell-over-PSN-00.txt April 2002 The interworking LSPs corresponding to any VCC or VPC may be multiplexed into a transport LSP using conventional MPLS label stacking to achieve multiplexing gain and bandwidth efficiency. To provide support for ATM-MPLS interworking, the interworking function can multiplex multiple ATM connections (i.e. VPCs and/or VCCs) into a single MPLS LSP. The encapsulation method provides end users with the same quality of service on any given VPC or VCC as per corresponding SLA, traffic contracts and the QoS commitments for that connection. One important consideration to make when interworking is to allow OAM information to be treated as in the original network. The interworking function allows this transparency while performing cell encapsulation. Resource management cells are used extensively in certain service categories like ABR. Encapsulating ATM cells to MPLS packets allows this capability to be kept. Cell Loss priority (CLP) is used to provide discard information and Payload Type Indicator (PTI) provides information regarding the payload being transported. Information on both of these is obtained from the ATM cell header. CLP and PTI are both part of the service specific information fields. Concatenation of ATM cells belonging to a VCC or a VPC provides added bandwidth efficiency while preserving discard eligibility of each cell. 5. Implementation and deployment considerations Although the Single ATM cell encapsulation provides the simplest way for encapsulating ATM cells within a single MPLS packet, it lacks bandwidth efficiency. This can be improved substantially if the procedures enabling cells from any given VCC or VPC to be concatenated within the interworking LSP. 6. Limitations Cell encapsulation only supports point-to-point LSPs. Multi- point- to-point and point-to-multi-point are for further study (FFS). To have bi-directional connectivity, as required in ATM, two LSPs should be configured, one for each direction (ATM-to-MPLS and MPLS- to-ATM) of the ATM connection. Number of concatenated ATM cells is limited by the MTU (Maximum Transfer Unit) size and the cell transfer delay (CTD)objectives. 7. Security Considerations Koleyni, et al. Expires September 2002 [Page 3] Internet Draft draft-koleyni-pwe3-app-cell-over-PSN-00.txt April 2002 No additional security issues are introduced in this document. As ATM encapsulation to MPLS packet is related to MPLS, Cell encapsulation shares the security concerns associated with MPLS. 8. References [1} Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] ITU-T Recommendation I.371 (2000), Traffic control and congestion control in B-ISDN. [3] ATM Forum Specification af-tm-0121.000 (1999), Traffic Management Specification Version 4.1. 9. Acknowledgement The authors like to acknowledge the contribution to this work by: TBD 10. Author's Addresses Ghassem Koleyni Nortel Networks P O Box 3511, Station C Ottawa, Ontario, K1Y 4H7 Canada Email: ghassem@nortelnetworks.com Matthew Bocci Alcatel Telecom Ltd. Voyager Place, Shoppenhangers Rd Maidenhead, Berks, UK SL6 2PJ Email: Matthew.bocci@alcatel.com Koleyni, et al. Expires September 2002 [Page 4] Internet Draft draft-koleyni-pwe3-app-cell-over-PSN-00.txt April 2002 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into Koleyni, et al. Expires September 2002 [Page 5]