US Robotics Sportster Operating Instructions Manual page 130

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.
126
G
LOSSARY
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.