Figure 1 shows an application of a Frame Relay VLL. The Fpipe provides a point-to-point Frame Relay service between users connected to 7750 SR nodes on the IP/MPLS network. Users are connected to the 7750 SR.
PE nodes using Frame Relay PVCs PE1, PE2, and PE3 receive a standard Q.922 Core frame on the Frame Relay SAP and encapsulate it into a pseudowire packet according to the 1-to-1 Frame Relay encapsulation mode in RFC 4619, Encapsulation Methods for Transport of Frame Relay Over MPLS Networks. The 7750 SR Fpipe feature supports local cross-connecting when the users are attached to the same 7750 SR PE node.
The FR pseudowire is initiated using T-LDP signaling as specified in RFC 4447, Pseudo-wire Setup and Maintenance using LDP. The SDP can be an MPLS or a GRE type.