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Chapter 10
Wide Area Networking Protocols
F I G U R E 1 0 . 3
Point-to-point protocol stack
PPP contains four main components:
EIA/TIA-232-C
A Physical layer international standard for serial
communication.
HDLC
A method for encapsulating datagrams over serial links.
LCP
A method of establishing, configuring, maintaining, and terminat-
ing the point-to-point connection.
NCP
A method of establishing and configuring different Network layer
protocols. PPP is designed to allow the simultaneous use of multiple Net-
work layer protocols. Some examples of protocols here are IPCP (Internet
Protocol Control Protocol) and IPXCP (Internetwork Packet Exchange
Control Protocol).
It is important to understand that the PPP protocol stack is specified at the
Physical and Data Link layers only. NCP is used to allow communication of
multiple Network layer protocols by encapsulating the protocols across a
PPP data link.
Remember that if you have a Cisco router and a non-Cisco router connected
with a serial connection, you must configure PPP or another encapsulation
method, like Frame Relay, because the default of HDLC will not work!
Upper-layer Protocols
(such as IP, IPX, AppleTalk)
Physical layer
(such as EIA/TIA-232, V.24, V.35, ISDN)
Network Control Protocol (NCP)
(specific to each Network-layer protocol)
Link Control Protocol (LCP)
High-Level Data Link Control Protocol (HDLC)
OSI layer
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