Phase 1: PPP Link Establishment
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8/28/2008
PPP uses the Link Control Protocol (LCP) to establish, maintain, and end the physical connection. Before information can be sent on a link, each of the two computers that make up the connection must test the link and agree on a set of parameters under which the link will operate.
During the initial phase of the Link Control Protocol, each computer in a given link must specify the desired parameters for a PPP connection in a Configure-Request and submit the request to its peer. If one of the two computers in a link fails to acknowledge the parameters received from its peer, the other computer must resubmit a packet that contains a set of alternate parameters. During the link authentication phase, the two peers also select which authentication protocol will be used during the user authentication phase. The two computers also decide whether they will negotiate the use of compression and/or encryption. The actual choice of compression/encryption algorithms and other details occurs during Phase 3.