When the Point to Point Protocol (PPP) is mentioned, most people think of asynchronous, dial-up networking. In fact, PPP is used whenever there are only two endpoints to a link. This means that all point to point links over dedicated lines, such as T1 or fractional T1 use PPP (assuming that the T1 line is not being used for Frame Relay), in addition to asynchronous links.
PPP incorporates LCP, Link Control Protocol, which is a handshaking mechanism that allows the two endpoints to negotiate elements of the link configuration, such as the MTU, and compression. LCP can also be used as a "heartbeat", much as LMI is used in a Frame Relay connection.
Once the link is established, it can be authenticated using PAP (Password Authentication Protocol) or CHAP (Challenge Handshake Authentication Protocol). PAP is a one-time authentication, while CHAP can occur more than once, such as in the middle of a session.
Since there are only two endpoints, there is no concept of routing in a PPP connection.
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