Before we get into VPLS, let us take a quick look at MPLS Layer 2 VPNs, also referred to as point-to-point services. A point-to-point L2VPN circuit, as defined by the PWE3 working group, is a provider service that offers a point-to-point service infrastructure over an IP/MPLS packet switched network. The PWE3 working group of the IETF describes mechanisms on how to deliver L2 VPN services across a packet switched IP/MPLS network. The basic reference model is outlined in the picture below. A pseudo-wire (PW) is a connection between two provider edge (PE) devices, which connects two attachment circuits (ACs). An AC can be a Frame Relay DLCI, an ATM VPI/VCI, an Ethernet port, a VLAN, an HDLC, a PPP connection on a physical interface, a PPP session from an L2TP tunnel, an MPLS LSP, etc. During the setup of a PW, the two PE routers will be configured or will automatically exchange information about.