http://www.rfc-editor.org/rfc/rfc1331.txt
RFC 1331: The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-to-Point Links, W. Simpson1992-05-01T23:00:00-00:00This document defines the PPP encapsulation scheme, together with the PPP Link Control Protocol (LCP), an extensible option negotiation protocol which is able to negotiate a rich assortment of configuration parameters and provides additional management functions. [STANDARDS-TRACK]