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Virtual Private Wire Services (VPWS) Or Pseudo Wire Emulation Edge To Edge (PWE3)

Virtual Private Wire Services (VPWS) or Pseudo Wire Emulation Edge to Edge (PWE3) provide point-to-point connectivity between customer sites, where the service provider network emulates a set of wires between the customer's sites over the underlying MPLS tunnel.

This is particularly useful in the case where a customer is currently using a set of ATM or Frame Relay connections between their different sites, as the VPWS can emulate the existing links. The customer can keep the same layer 2 connections to the service provider, but instead of data being carried natively over an ATM or Frame Relay service, the traffic is encapsulated and routed over the provider's MPLS backbone.

A widely deployed mechanism was first described in draft-Martini, and is still referred to by this name. In this mechanism, each virtual circuit (or virtual private wire) is signaled using extensions to the LDP protocol. A variety of circuit types have been defined to allow the transport of different Layer 2 services, including ATM, Frame Relay and Ethernet.

An alternative scheme has been proposed to automate the provisioning of multiple virtual circuits, for example the case of a multi-site enterprise that requires a full mesh of connections between all its sites. Rather than use LDP, this uses BGP to broadcast the VPN membership information between PE routers so that they can provision the necessary circuits without manual intervention. These BGP flows also carry MPLS labels that are used to signal the LSPs that carry the data. The resulting service is similar to that provided by a BGP/MPLS VPN, although layer 2, not layer 3, switching is used.

DC-MPLS provides full VPWS support using DC-LDP, which includes a comprehensive implementation of LDP and its VPWS extensions, including draft-ietf-pwe3-control-protocol. DC-MPLS can also be used to signal the underlying tunnels using DC-LDP and DC-RSVP.