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PPP 403
PPP
PPP (Point-to-Point Protocol) is by far the most popular remote connectivity protocol because
it supports authentication with Challenge Handshake Authentication Protocol (CHAP) and
Password Authentication Protocol (PAP).
PPP was created as a solution to remote access connectivity problems. It was not the first
method for transmitting datagrams over serial point-to-point links, though--that was SLIP
(Serial Line Internet Protocol). SLIP has many shortcomings that PPP addresses. PPP provides
router-to-router and host-to-network connections over both synchronous and asynchronous
circuits. Other PPP duties include assignment and network protocol multiplexing, link
configuration, link quality testing, error detection, data compression, and address negotiation.
PPP also supports IPX and DECnet, whereas SLIP supports only IP packets.
The only absolute requirement imposed by PPP is the provision of a duplex circuit that can
operate in either asynchronous or synchronous bit-serial mode. PPP physical connections
operate across any DTE/DCE interface.
PPP transmits datagrams over serial point-to-point links. There are three components--LCP,
HDLC, and network control protocols:
·
LCP (Link Control Protocol)--LCP initiates and performs a handshake function that
establishes the connection, as shown in Figure 11-14.
Figure 11-14
Link Control Protocol
·
HDLC (High-Level Data Link Control)--PPP uses HDLC to encapsulate datagrams
over a point-to-point link.
·
Network Control Protocols--These initiate and perform a handshake function at Layer
3, configuring the link for different network protocols, as shown in Figure 11-15.
1. LCP: Hey Router B, are
you ready to bring the link up?
2. LCP: Yes, I am ready to
bring the link up!
Router A
Router B
3. Okay, let's do it!
87200333.book Page 403 Wednesday, August 22, 2001 2:53 PM