G
LOSSARY
142
V.42
An ITU-T standard for modem
communications that defines a two-stage
process of detection and negotiation for
LAPM error control.
V.42 bis
An extension of ITU-T V.42 that defines a
specific data compression scheme for use
during V.42 connections.
Xmodem
The first of a family of error control software
protocols used to transfer files between
modems. These protocols are in the public
domain and are available from many bulletin
board services.
XON/XOFF
Standard ASCII control characters used to
tell an intelligent device to stop/resume
transmitting data.
Ymodem
An error-checking protocol that can send
several files of data at a time in 1024-byte
(1K) blocks. This protocol can use either
checksums or CRC for error checking.
Ymodem G
Similar to Ymodem, except it includes no error
checking, which makes it faster.
Zmodem
Similar to Xmodem and Ymodem, except it
includes batch transfer, the ability to recover
from a partially complete transfer, an autostart
feature, and improved efficiency.