User`s guide

44 56K Message Modem
V.32 bis
An ITU-T standard that extends the V.32 connection range: 4800,
7200, 9600, 12,000, and 14,400 bps. V.32 bis modems fall back to the
next lower speed when line quality is impaired, fall back further as
necessary, and also fall forward (switch back up) when line conditions
improve.
See online fall back/fall forward.
V.34
An ITU-T standard that currently allows data rates as high as 33,600
and 28,800 bps.
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.