http://www.rfc-editor.org/rfc/rfc4618.txt
RFC 4618: Encapsulation Methods for Transport of PPP/High-Level Data Link Control (HDLC) over MPLS Networks, L. Martini, E. Rosen, G. Heron, A. Malis2006-09-01T23:00:00-00:00A pseudowire (PW) can be used to carry Point to Point Protocol (PPP) or High-Level Data Link Control (HDLC) Protocol Data Units over a Multiprotocol Label Switching (MPLS) network without terminating the PPP/HDLC protocol. This enables service providers to offer "emulated" HDLC, or PPP link services over existing MPLS networks. This document specifies the encapsulation of PPP/HDLC Packet Data Units (PDUs) within a pseudowire. [STANDARDS-TRACK]