handshaking

1. Predetermined hardware or software activity designed to

establish or maintain two machines or programs in

synchronisation. Handshaking often concerns the exchange of

messages or packets of data between two systems with limited

buffers. A simple handshaking protocol might only involve

the receiver sending a message meaning "I received your last

message and I am ready for you to send me another one." A

more complex handshaking protocol might allow the sender to

ask the receiver if he is ready to receive or for the receiver

to reply with a negative acknowledgement meaning "I did not

receive your last message correctly, please resend it" (e.g. if

the data was corrupted en route).

Hardware handshaking uses voltage levels or pulses on wires

to carry the handshaking signals whereas softwarehandshaking uses data units (e.g. ASCII characters) carried

by some underlying communication medium.

Flow control in bit-serial data transmission such as

EIA-232 may use either hardware or software handshaking.

2. The method used by two modems to establish contact with

each other and to agreee on baud rate, error correction

and compression protocols.

3. The exchange of predetermined signals between agents

connected by a communications channel to assure each that it

is connected to the other (and not to an imposter). This may

also include the use of passwords and codes by an operator.

[Jargon File]

(1995-01-13)