User`s manual

U.S. Robotics I-modem Command Reference
Handshaking, Error Control, Data Compression, and Throughput • Page 11-19
¥ MNP5 compression is disabled for Þles that are already compressed and 8-bit binary
Þles that appear to the I-modem to be already compressed. Disable MNP5 compressing
by sending the I-modem &K3.
¥ The Þle transfer is not slowed down by a File
Transfer Protocol. Many non-text Þles
require a File Transfer Protocol, but the results vary.
Note For the best throughput on error-controlled connections with hardware ßow
control, we recommend the most current version of ZMODEM
.
For example, certain public domain File Transfer Protocols have the following effects:
Kermit Newer versions support packets up to 9K and a sliding window design to elimi-nate
turn-around delay. With earlier versions, how-ever, throughput may be severely
reduced due to short block lengths (possibly under 128 bytes) and acknowledg-ment
turn-around time.
XMODEM
Throughput may be reduced if your version uses short block lengths (128 bytes).
Some versions use larger blocks (1K blocks). Throughput is also reduced by over-
head (error-control protocol information).
YMODEM
There is an improvement over XMODEM due to larger block lengths (1K bytes), but
throughput is still reduced by the protocol's error control overhead.