US Robotics Sportster Flash x2 User Manual page 46

V.42
A 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.
42 Sportster Flash x2 - User's Guide