The Serial Line Internet Protocol (SLIP) is an
encapsulation of the
Internet Protocol
The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
IP h ...
designed to work over
serial port
In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. ...
s and
router connections. It is documented in . On personal computers, SLIP has largely been replaced by the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
microcontrollers
A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs ( processor cores) along with memory and programmabl ...
, 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 Serial Line Internet Protocol as "Rick Adams' SLIP",
[ : "Requirements for an Internet Standard Point-to-Point Protocol" ] to avoid confusion with other proposed protocols named "SLIP". Those other protocols include the much more complicated appendix D Serial Line Interface Protocol.
Description
SLIP modifies a standard
TCP/IP
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
datagram
A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The del ...
by:
* appending a special "END"
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
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
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted ...
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
s, no
parity, and either
EIA Eia or EIA may refer to:
Medicine
* Enzyme immunoassay
* Equine infectious anemia
* Exercise-induced anaphylaxis
* Exercise-induced asthma
* External iliac artery
Transport
* Edmonton International Airport, in Alberta, Canada
* Erbil Internation ...
hardware
flow control, or CLOCAL mode (3-wire
null-modem
Null modem is a communication method to directly connect two DTEs ( computer, terminal, printer, etc.) using an RS-232 serial cable. The name stems from the historical use of RS-232 cables to connect two teleprinter devices or two modems in ord ...
)
UART
A universal asynchronous receiver-transmitter (UART ) is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significan ...
operation settings.
SLIP does not provide
error detection
In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communi ...
, being reliant on
upper layer protocol
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 ...
s for this. Therefore, SLIP on its own is not satisfactory over an error-prone
dial-up
Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telepho ...
connection. It is however still useful for testing
operating systems
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also inc ...
' response capabilities under load (by looking at flood-
ping
Ping may refer to:
Arts and entertainment Fictional characters
* Ping, a domesticated Chinese duck in the illustrated book '' The Story about Ping'', first published in 1933
* Ping, a minor character in ''Seinfeld'', an NBC sitcom
* Ping, a c ...
statistics).
SLIP escape characters were also required on some modem connections to escape
Hayes command set
The Hayes command set (also known as the AT command set) is a specific command language originally developed by Dennis Hayes for the Hayes Smartmodem 300 baud modem in 1981.
The command set consists of a series of short text strings which can b ...
, allowing therefore to pass binary data through those modems that would recognize some characters as commands.
CSLIP
A version of SLIP with
header compression
Compression may refer to:
Physical science
*Compression (physics), size reduction due to forces
*Compression member, a structural element such as a column
*Compressibility, susceptibility to compression
* Gas compression
*Compression ratio, of a ...
is called Compressed SLIP (CSLIP).
The compression algorithm used in CSLIP is known as
Van Jacobson TCP/IP Header Compression. 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
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly ...
(TCP) header from twenty
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
s to seven bytes. CSLIP has no effect on
User Datagram Protocol
In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...
(UDP) datagrams.
See also
*
Parallel Line Internet Protocol The Parallel Line Internet Protocol (PLIP) is a computer networking protocol for direct computer-to-computer communications using the parallel port normally used for connections to a printer.
The Parallel Line Internet Protocol provides link layer ...
*
Slirp
Slirp (sometimes capitalized SLiRP) is a software program that emulates a PPP, SLIP, or CSLIP connection to the Internet using a text-based shell account. Its original purpose became largely obsolete as dedicated dial-up PPP connections and b ...
*
KA9Q KA9Q, also called KA9Q NOS or simply NOS, was a popular early implementation of TCP/IP and associated protocols for amateur packet radio systems and smaller personal computers connected via serial lines. It was named after the amateur radio calls ...
*
Direct cable connection
Direct Cable Connection (DCC) is a feature of Microsoft Windows that allows a computer to transfer and share files (or connected printers) with another computer, via a connection using either the serial port, parallel port or the infrared port ...
*
In-band signaling
In telecommunications, in-band signaling is the sending of control information within the same band or channel used for data such as voice or video. This is in contrast to out-of-band signaling which is sent over a different channel, or even ov ...
*
KISS (TNC) KISS (Keep It Simple, Stupid) is a protocol for communicating with a serial terminal node controller (TNC) device used for amateur radio. This allows the TNC to combine more features into a single device and standardizes communications. KISS was de ...
*
Consistent Overhead Byte Stuffing Consistent Overhead Byte Stuffing (COBS) is an algorithm for encoding data bytes that results in efficient, reliable, unambiguous packet framing regardless of packet content, thus making it easy for receiving applications to recover from malformed ...
References
External links
* RFC1055:
* RFC1144: — introduced the
Van Jacobson TCP/IP Header Compression used by CSLIP
{{Authority control
Internet protocols
Link protocols
Logical link control