The process by which two devices initiate communications. Handshaking begins when one device sends a message to another device indicating that it wants to establish a communications channel. The two devices then send several messages back and forth that enable them to agree on a communications protocol |
All communications between devices require that the
devices agree on the format of the data. The set of rules defining a format is
called a protocol. At the very least, a
communications protocol must define the following:
In addition, protocols can include sophisticated techniques for detecting and recovering from transmission errors and for encoding and decoding data.
The table lists the most commonly used protocols for communications via modems. These protocols are almost always implemented in the hardware; that is, they are built into modems.
In addition to the standard protocols listed in
the table, there are a number of protocols that complement these standards by
adding additional functions such as file transfer capability, error detection
and recovery, and data compression. The best-known are Xmodem, Kermit,
MNP, and CCITT V.42 . These protocols can be implemented
either in hardware or software.
| protocol |
An agreed-upon format for transmitting data between two devices. The protocol determines the following:
There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others, some are more reliable, and some are faster.
From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. The protocol can be implemented either in hardware or in software.
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