http://www.rfc-editor.org/rfc/rfc2153.txt
RFC 2153: PPP Vendor Extensions, W. Simpson1997-05-01T23:00:00-00:00The Point-to-Point Protocol (PPP) provides a standard method for transporting multi-protocol datagrams over point-to-point links. PPP defines an extensible Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection; and a family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols. This document provides information for the Internet community. It does not specify an Internet standard of any kind.