Link Control Protocol (LCP

A Link Control Protocol for establishing, configuring, and testing the data-link connection.

In order to be sufficiently versatile to be portable to a wide variety of environments, PPP provides a Link Control Protocol. The LCP is used to automatically agree upon the encapsulation format options, handle varying limits on sizes of packets, detect a looped-back link and other common misconfiguration errors, and terminate the link. Other optional facilities provided are authentication of the identity of its peer on the link, and determination when a link is functioning properly and when it is failing.

RFC 1661