TCP/IP Explained
An easy to understand, comprehensive, and high-level introduction to TCP/IP.
TABLE OF CONTENTS TCP/IP Explained
Section 22.3: The Point-to-Point Protocol (PPP)
22.3 The Point-to-Point Protocol (PPP)
The major motivation behind the development of PPP was the desire to be able to transport datagrams of different protocols over Point-to-Point links. Unlike SLIP, PPP provides mechanisms to identify the protocol carried in any packet, to test the link itself, and to negotiate a variety of options. PPP then is composed of three parts as described by RFC 1661:
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A method of encapsulating Multi-Protocol datagrams. PPP can handle different protocols since it has a protocol identifier field. Thus, IP, IPX, DECnet, AppleTalk and many others can be carried over a single link. Each separate packet however must contain only one protocol.
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A Link Control Protocol (LCP) capable of establishing, configuring, and testing the link.
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A whole family of Network Control Protocols (NCPs) that are used to configure the link for the various network layer protocols that will use it. This configuration includes addressing and other protocol specific issues. The table below lists a number of NCPs together with the associated RFCs in which they are defined and the protocol ID used. For example, PPP uses the Protocol ID 8021 16 to indicate that the IP Control Protocol is being carried during link configuration.
Table 22-1: PPP Network Control Protocols (NCPs)
| Protocol Description | PPP Protocol ID | Protocol | RFC |
|---|---|---|---|
| Internet Protocol Control Protocol | 8021 | IPCP | 1332 |
| OSI Network Layer Control Protocol | 8023 | OSINLCP | 1377 |
| AppleTalk Control Protocol | 8029 | ATCP | 1378 |
| Internetwork Packet Exchange Control Protocol | 802B | IPXCP | 1552 |
| Bridge Control Protocol | 8031 | BCP | 1638 |
| DecNet... |
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