PPP

(Point-to-Point Protocol) The most popular method for transporting IP packets over a serial link between the user and the ISP. Developed in 1994 by the IETF and superseding the SLIP protocol, PPP establishes the session between the user's computer and the ISP using its own Link Control Protocol (LCP). PPP supports PAP and CHAP authentication, as well as EAP, which is a conduit for numerous other authentication methods (see PAP, CHAP and EAP).

Any Full-Duplex Link

PPP can run on any full-duplex link from POTS to ISDN to T1, etc. On dial-up connections, PPP can hang up a low-quality call and redial. Using Multilink PPP (MPPP), two modems and phone lines can be bonded together to increase speed.

PPP Encapsulates the Packets

PPP encapsulates high-level protocol packets in HDLC-based frames; for example, IP over PPP (IPCP) for the Internet and IPX over PPP (IPXCP) for NetWare networks, and it can multiplex different protocols over the same circuit. PPP also supports ATM and Ethernet frames for DSL and cable modem hookups (see PPPoA and PPPoE). See PPTP and SLIP.

PPP and L2TP Together

PPP and its counterpart, the Layer 2 Tunneling Protocol (L2TP), are used together to extend a PPP session across the Internet for remote users.

The PPP Stack

PPP resides at the data link layer in the stack. Its typical use is accessing the Internet via TCP/IP over an analog modem (RS-232), ISDN or a T1 line. However, PPP can also simultaneously multiplex other transport protocols such as IPX, Appletalk and DECnet.

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