US Robotics 56K Series Manual page 60

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 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.42bis
An extension of ITU-T V.42 that
defines a specific data compression
scheme for use during V.42 connections.
V.90
54
The ITU-T standard for 56 Kbps
modem communications.
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