Network transport service providers and their users are seeking to rationalize their networks by migrating their existing services and platforms onto IP or MPLS enabled IP packet switched networks (PSN). This migration requires communications services that can emulate the essential properties of traditional communications links over a PSN. Some service providers wish to use MPLS technology to replace existing transport network infrastructure, relying upon pseudowire technology is an integral component of these network convergence architectures.
Pseudowire Emulation Edge to Edge (PWE3) will specify the encapsulation, transport, control, management, interworking and security of services emulated over IETF-specified PSNs.
A pseudowire emulates a point-to-point or point-to-multipoint link, and provides a single service which is perceived by its user as an unshared link or circuit of the chosen service. It is not intended that an emulated service will be indistinguishable from the service that is being emulated. The emulation need only be sufficient for the satisfactory operation of the service. Emulation necessarily involves a degree of cost-performance trade-off. In some cases it may be necessary to design more than one emulation mechanism in order to resolve these design conflicts. All emulated service definitions must include an applicability statement describing the faithfulness of the emulation.
Switching, multiplexing, modification or other operation on the traditional service, unless required as part of the emulation, is out of the scope of the PWE3 WG.
PWE3 will make use of existing IETF-specified mechanisms unless there are technical reasons why the existing mechanisms are insufficient or unnecessary.
PWE3 operates "edge to edge" and will not exert control on the underlying PSN, other than to use any existing QoS or path control mechanism to provide the required connectivity between the endpoints of the PW.
PWE3 will co-ordinate this with the AVT and TICTOC WGs. Where AVT or TICTOC require extensions to PWs to support time or frequency transfer this work will be undertaken by the PWE3 WG in co-ordination with the these WGs.
A PW operating over a shared PSN does not necessarily have the same intrinsic security as a dedicated, purpose built, network. In some cases this is satisfactory, while in other cases it will be necessary to enhance the security of the PW to emulate the intrinsic security of the emulated service. PW specifications MUST include a description of how they are to be operated over a shared PSN with adequate security. PWE3 will work with the MPLS, L2VPN and other relevant WGs for definitions of common solutions for the secure operation of pseudowires.
Whilst a service provider may traffic engineer their network in such a way that PW traffic will not cause significant congestion, a PW deployed by an end-user may cause congestion of the underlying PSN. Suitable congestion avoidance mechanisms are therefore needed to protect the Internet from the unconstrained deployment of PWs. Congestion avoidance may be more difficult with P2MP pseudowires than P2P pseudowires. The WG will consider both cases.
PWE3 will work closely with the L2VPN WG to ensure a clear demarcation is defined for where PWE3 stops and L2VPN starts, in particular in defining point-multipoint (P2MP) PWs.
PWE3 will work with MPLS and L2VPN to enhance the OAM suite for transport applications. PWE3 will coordinate very closely with any WG that is responsible for protocols which PWE3 intends to extend (e.g., the MPLS WG for LDP), as well as foster interaction with WGs that intend to extend PWE3 protocols.
The IETF PWE3 WG is the design authority for pseudo-wire over IP/MPLS PSN technology. An entity or individual that wishes to propose extensions or changes to this technology must bring the corresponding proposals to the PWE3 WG that would treat them via a process similar to one described in RFC 4929 for the MPLS/GMPLS change process.
Specify the following PW types:
Most of the initial specific PW types have been specified (e.g., Frame Realy, Ethernet, ATM). Investigation into and specification of a "generic PW" type and/or MPLS PW should be undertaken.
PWE3 will specify a PW type for the special case where the access service payloads at both ends are known to consist entirely of IP packets. PWE3 will not specify mechanisms by which a PW connects two different access services unless the Network Layer protocol is IP or MPLS.
Specify the control and management functions of chartered PW types, to include PW setup, configuration, maintenance and tear-down. The PWE3 WG will do this in its entirety for MPLS PSNs, and the L2TPEXT WG will develop the L2TP specifics for L2TPv3-based PWs.
Specify Operations and Management (OAM) mechanisms for all PW types, suitable for operation over both IP/L2TPv3 and MPLS PSNs, and capable of providing the necessary interworking with the OAM mechanisms of the emulated service.
Define requirements for and mechanisms to provide interconnection of PWs (to include inter-domain PWs).
Define requirements for and mechanisms to provide protection and restoration of PWs.
Publish document outlining PW-specific congestion avoidance and response guidelines.
Specify requirements and mechanisms for P2MP functionality for PWs. This work will be coordinated with the L2VPN and MPLS working groups.
Publish requirements and specification for PW to take advantage of multiple PSN paths that exist between PEs.
Publish requirements and specification for enhanced OAM.
Include extensions to the PWE3 protocols and RFCs necessary to create an MPLS Transport Profile (MPLS-TP). The work on the MPLS TP needs to be coordinated between three primary working groups (MPLS, PWE3, L2VPN and CCAMP) that are chartered to do MPLS TP work.
PWE3 WG started, organize editing teams.
Hold interim meeting, including discussion of priority of service-specific documents and consider pruning some deliverables
Accept drafts of service-specific documents as WG items