Understand Pseudowires, VPWS and VPLS.

A pseudowire is an encapsualtion of a service for transmission over a packet switched network. A number of different types of pseudowires have been implemented, but the IETF Pseudowire Emulation End-to-End (PWE3) for transport of Ethernet packets over MPLS is probably the most widely known.

PWE3 allows Ethernet packets to be transparently transported across a network of routers. A point-to-point connection of this type would be considered a Virtual Private Wire Service (VPWS) and can be used, for example, to connect an IP-DSLAM to a BRAS function across an IP/MPLS network.

Virtual Private LAN Service (VPLS) uses pseudowires to establish a multipoint-to-multipoint LAN service across an IP/MPLS network. An integral part of this solution is the use of Virtual Switches for forwarding of traffic in the "hub" of the solution. These Virtual Switch Instances (VSI) use VLAN Ethernet forwarding mechanisms rather than routing to forward data to the right locations. VPLS is thus a layer 2 LAN solution as opposed to a 2547bis VPN service based on MPLS.

For more information on Pseudowires and VPLS. see:

http://en.wikipedia.org/wiki/Pseudowire

http://en.wikipedia.org/wiki/VPLS