The Serial Line Internet Protocol (SLIP) is an encapsulation

Encapsulation (networking)

In computer networking, encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects....

 of the Internet Protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 designed to work over serial port

Serial port

In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...

s and modem

Modem

A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...

 connections. It is documented in RFC 1055. On personal computers, SLIP has been largely replaced by the Point-to-Point Protocol

Point-to-Point Protocol

In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...

 (PPP), which is better engineered, has more features and does not require its IP address configuration to be set before it is established. On microcontrollers, however, SLIP is still the preferred way of encapsulating IP packets due to its very small overhead.

SLIP modifies a standard TCP/IP datagram

Datagram

A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....

 by appending a special "SLIP END" character

Character (computing)

In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....

 to it, which distinguishes datagram boundaries in the byte stream. SLIP requires a serial port configuration

Computer configuration

In communications or computer systems, a configuration is an arrangement of functional units according to their nature, number, and chief characteristics. Often, configuration pertains to the choice of hardware, software, firmware, and documentation...

 of 8 data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

s, no parity

Parity bit

A parity bit is a bit that is added to ensure that the number of bits with the value one in a set of bits is even or odd. Parity bits are used as the simplest form of error detecting code....

, and either EIA

Electronic Industries Alliance

The Electronic Industries Alliance was a standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They developed standards to ensure the equipment of different manufacturers was compatible and interchangeable...

 hardware flow control

Flow control

In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...

, or CLOCAL mode (3-wire null-modem) UART operation settings.

SLIP does not provide error detection, being reliant on upper layer protocol

Upper layer protocol

In computer networking, the term upper layer protocol refers to a more abstract protocol when performing encapsulation, in particular it is often used to describe the protocols above the network layer....

s 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

Ping

Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol network and to measure the round-trip time for messages sent from the originating host to a destination computer...

 statistics).

SLIP is also currently used in the BlueCore Serial Protocol for communication between Bluetooth modules and host computers.

CSLIP

A version of SLIP with header

Header

Header may refer to: Computers and engineering* Header , supplemental data at the beginning of a data block** E-mail header** HTTP header* Header file, a text file used in computer programming...

 compression

Data compression

In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....

 is called Compressed SLIP (CSLIP). The compression algorithm used in CSLIP is known as Van Jacobson TCP/IP Header Compression

Van Jacobson TCP/IP Header Compression

Van Jacobson TCP/IP Header Compression is a data compression protocol described in RFC 1144, specifically designed by Van Jacobson to improve TCP/IP performance over slow serial links. Van Jacobson compression reduces the normal 40 byte TCP/IP packet headers down to 3-4 bytes for the average case...

. CSLIP has no effect on the data payload of a packet and is independent of any compression by the serial line modem used for transmission. It reduces the Transmission Control Protocol

Transmission Control Protocol

The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

 (TCP) header from 20 byte

Byte

The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...

s to seven bytes. CSLIP has no effect on User Datagram Protocol

User Datagram Protocol

The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...

 (UDP) datagrams.

External links

• RFC 1055, which documents the SLIP "standard"
• TCP/IP over null-modem by Stefan Ott
• Configuring SLIP under Windows XP
• [ftp://ftp.rfc-editor.org/in-notes/rfc1144.pdf RFC 1144], which introduced the Van Jacobson TCP/IP Header Compression
  Van Jacobson TCP/IP Header Compression
  Van Jacobson TCP/IP Header Compression is a data compression protocol described in RFC 1144, specifically designed by Van Jacobson to improve TCP/IP performance over slow serial links. Van Jacobson compression reduces the normal 40 byte TCP/IP packet headers down to 3-4 bytes for the average case...
  
  used by CSLIP