Handshaking

Handshaking

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In information technology
Information technology
Information technology is the acquisition, processing, storage and dissemination of vocal, pictorial, textual and numerical information by a microelectronics-based combination of computing and telecommunications...

, telecommunications, and related fields, handshaking is an automated process of negotiation that dynamically sets parameters of a communications channel established between two entities before normal communication over the channel begins. It follows the physical establishment of the channel and precedes normal information transfer.

It is usually a process that takes place when a computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 is about to communicate with a foreign device to establish rules for communication. When a computer communicates with another device like a modem, printer, or network server, it needs to handshake with it to establish a connection.

Handshaking can be used to negotiate parameters that are acceptable to equipment and systems at both ends of the communication channel, including, but not limited to, information transfer rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

, coding alphabet
Alphabet
An alphabet is a standard set of letters—basic written symbols or graphemes—each of which represents a phoneme in a spoken language, either as it exists now or as it was in the past. There are other systems, such as logographies, in which each character represents a word, morpheme, or semantic...

, 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....

, interrupt
Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....

 procedure, and other protocol or hardware features.
Handshaking is technique of communication between two entities.

Handshaking makes it possible to connect relatively heterogeneous systems or equipment over a communication channel without the need for human intervention to set parameters. One classic example of handshaking is that of 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...

s, which typically negotiate communication parameters for a brief period when a connection is first established, and thereafter use those parameters to provide optimal information transfer over the channel as a function of its quality and capacity. The "squealing" (which is actually a sound that changes in pitch 100 times every second) noises made by some modems with speaker output immediately after a connection is established are in fact the sounds of modems at both ends engaging in a handshaking procedure; once the procedure is completed, the speaker might be silenced, depending on the settings of operating system or the application controlling the modem.

Examples


The TLS
Transport Layer Security
Transport Layer Security and its predecessor, Secure Sockets Layer , are cryptographic protocols that provide communication security over the Internet...

Handshake Protocol is used to negotiate the secure attributes of a session. (RFC 5246, p.37)