Please Whitelist This Site? I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :) If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads. If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK. Thanks for your understanding! Sincerely, Charles Kozierok Author and Publisher, The TCP/IP Guide

NOTE: Using software to mass-download the site degrades the server and is prohibited. If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

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)                 9  Point-to-Point Protocol (PPP)                      9  PPP Fundamentals and Operation

PPP Fundamentals and Operation 1 2 3 PPP Components and General Operation

Albert Einstein is credited with the following quote: “Everything should be made as simple as possible — but no simpler”. The Serial Line Internet Protocol (SLIP) is a good example of this maxim. It provides basic layer two framing for IP, but it is just too simple for many uses. Since all it does is frame the end of each datagram, it doesn't provide many of the features that we really need for reliable, secure and high-performance operation over serial links. This is especially true today when most serial connections are not short LAN cables but dial-up WAN connections over relatively long distances.

SLIP was basically a “hack” to fill a specific need: bridging the gap between IP at layer three and a serial link at layer one. It “gets the job done” but doesn't provide any of the features we really want in a robust protocol for direct links between devices. PPP was developed to be a complete protocol suite that would enable fully-functional layer two connectivity to support not just IP but the transmission of other network layer protocols as well.

The history of PPP goes back to the late 1980s, when SLIP was the de facto standard for serial IP implementations. The first formal IETF document related to PPP was RFC 1134, published in 1989. This RFC is not the standard itself but a proposal for what would eventually be defined as the first main PPP standard, RFC 1171, in 1990. This early document has been revised several times and several other documents added that define the various protocols that comprise the entire PPP suite. PPP standards are described later in this section.

The IETF is always smart about not reinventing the wheel. Rather than try to develop PPP from scratch, the decision was made to base it on the ISO High-Level Data Link Control (HDLC) protocol, which was initially developed by IBM. HDLC is a derivative of the Synchronous Data Link Control (SDLC) protocol. PPP's developers adapted its framing structure and some of its general operation from the HDLC protocol.

PPP Fundamentals and Operation 1 2 3 PPP Components and General Operation