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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

PPP Advantages and Benefits

A list of PPP's strengths reads very much like a list of SLIP's weaknesses, which I explained in detail in the topic on SLIP. Some of the specific benefits of PPP compared to SLIP include:

• A more comprehensive framing mechanism, compared to the single END character in SLIP.
  
  
• Specification of the encapsulated protocol, to allow multiple layer three protocols to be multiplexed on a single link.
  
  
• Error detection for each transmitted frame through the use of a CRC code in each frame header.
  
  
• A robust mechanism for negotiating link parameters, including the maximum frame size permitted.
  
  
• A method for testing links before datagram transmission takes place, and monitoring link quality.
  
  
• Support for authentication of the connection using multiple authentication protocols.
  
  
• Support for additional optional features, including compression, encryption and link aggregation (allowing two devices to use multiple physical links as if they were a single, higher-performance link).

The proliferation of serial links, especially for dial-up Internet access, has led to widespread use of PPP. It is now one of the most popular layer two WAN technologies in the networking world, and has replaced SLIP as the standard for serial connections on all but legacy implementations. While most often associated with dial-up modem use, PPP can run across any similar type of physical layer link. For example, it is often used to provide layer two functionality on ISDN B channels.

A key advantage of PPP is that it is an extensible protocol suite. Over the years new protocols have been added to the suite, to provide additional features or capabilities. For example, PPP is designed not to use just a single authentication protocol, but to allow a choice of which protocol is used for this purpose.

PPP's success has even led to the development of derivative protocols like PPP over Ethernet (PPPoE) and PPP over ATM (PPPoA). These actually layer PPP over existing data link layer technologies, which shows you how valued PPP's features are—even when a layer two technology is already in use, applying PPP on top provides authentication and management benefits for services like DSL.

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