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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Network Interface Layer (OSI Data Link Layer) Protocols
           9  TCP/IP Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP)

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Serial Line Internet Protocol (SLIP)
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PPP Fundamentals and Operation
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Point-to-Point Protocol (PPP)

Even as SLIP was being documented as a “nonstandard” in RFC 1055, work was underway for a newer protocol to provide full-featured IP transmission over direct links between pairs of devices. The result is the Point-to-Point Protocol (PPP), which defines a complete method for robust data link connectivity between units using serial lines or other physical layers. It includes numerous capabilities and features, including error detection, compression, authentication, encryption and much more.

Even though PPP is called a “protocol”, and even though it is considered part of TCP/IP—depending on whom you ask—it is really more a protocol suite than a particular protocol. The operation of PPP is based on procedures defined in many individual protocols, as we will see in this section. Thus, PPP can be considered a “protocol suite within a protocol suite”. Alternately, its components can be viewed as “subprotocols” within PPP.

In this section I provide a comprehensive look at the operation of the Point-to-Point Protocol, in four subsections. The first describes the fundamentals of PPP, including its history, standards and an overview of its general operation. The second explains the “core” protocols that are responsible for setting up PPP links and basic operation. The third covers the protocols used to implement various special features in PPP, such as compression and encryption. The last subsection provides detailed information on the various frame formats used by PPP protocols.

Note: The component protocols of PPP are normally just called “protocols” and not “subprotocols”. This is confusing, so watch out for it in networking literature. I try to be consistent in this section in referring to PPP as a suite, but remember that it really is often just collectively called a “protocol”.


Note: As we will see in this section, PPP can be used to carry the frames of many protocols operating at layers three and above. It is, however, best known for its use with IP, and that is the assumption for the descriptions in this section, unless otherwise specified.


Related Information: PPP is related to the High-Level Data Link Control (HDLC) protocol, which is in turn part of the Synchronous Data Link Control (SDLC) family of protocols. I have avoided reliance on the SDLC protocols in explaining PPP since PPP is important and widely used enough that I think it warrants independent description.


Quick navigation to subsections and regular topics in this section



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Serial Line Internet Protocol (SLIP)
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PPP Fundamentals and Operation
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