Serial Line Internet Protocol (SLIP)

The Serial Line Internet Protocol (also SLIP) is an older industry encapsulation standard of the Internet Protocol designed to work over serial ports and modem connections. On Windows, SLIP is part of remote access client to ensure interoperability with other remote access software. The Serial Line Internet Protocol is documented in RFC 1055. On personal computers, SLIP has been largely replaced by the Point-to-Point Protocol (PPP), which is better engineered, has more features and does not require its IP address configuration to be set before it is established. On micro-controllers, however, SLIP is still the preferred way of encapsulating IP packets due to its very small overhead. Some people refer to the successful and widely used RFC 1055 Serial Line Internet Protocol as "Rick Adams' SLIP", to avoid confusion with other proposed protocols named "SLIP". Those other protocols include the much more complicated RFC 914 appendix D Serial Line Interface Protocol. SLIP modifies a standard TCP/IP datagram by:

• appending a special "END" byte to it, which distinguishes datagram boundaries in the byte stream,
• if the END byte occurs in the data to be sent, the two byte sequence ESC, ESC_END is sent instead,
• if the ESC byte occurs in the data, the two byte sequence ESC, ESC_ESC is sent.
• variants of the protocol may begin, as well as end, packets with END.

SLIP requires a serial port configuration of 8 data bits, no parity, and either EIA hardware flow control, or CLOCAL mode (3-wire null-modem) UART operation settings. SLIP does not provide error detection, being reliant on upper layer protocols for this. Therefore SLIP on its own is not satisfactory over an error-prone dial-up connection. It is however still useful for testing operating systems' response capabilities under load (by looking at flood-ping statistics).