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Header Compression CPPP/CSLIP

The Internet protocols introduce heavy overhead for some common types of network traffic. Probably the most extreme case is an interactive session with a user typing on a keyboard. With each keystroke, a packet is sent to the remote host and a reply is returned. Even though only a single byte of data is being sent, the addition of a TCP header (20 bytes) and an IP header (another 20 bytes) expand the resulting packet to at least 41 bytes. This represents 4000% overhead!

These problems are not apparent on Ethernet media, which enforces a 64-byte minimum size on all packets at the Data Link Layer. Other media may also be fast enough to disguise the problem, but dial-up modems can't tolerate such inefficiencies. RFC 1144 documents Van Jacobson compression, a popular technique for compressing TCP/IP headers. Van Jacobson compression can reduce packet header overhead from 4000% to 300%, enough to yield acceptable interactive performance at 2400 bps. This is often used in conjunction with SLIP or PPP, and referred to as CSLIP or CPPP.






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