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Advanced Modem Concepts
Error Control
Error control guarantees that data sent and received between
your modem and the remote modem arrives with 100%
accuracy. Your modem uses the CCITT standard V.42 and MNP
error control protocols. These protocols make sure that errors
are eliminated — even if it means retransmitting certain portions
of data. This process occurs between the modems and is
completely transparent to you.
The \N command (described on page 4-10) allows you to select
which error control mode will be used. These different modes
allow your modem to communicate with remote modems that
may or may not support error control and data compression.
NOTE:
If one modem is configured for error control and the other
modem is not, the non-error control modem's monitor may
display "garbage" characters immediately after connecting.
This is normal since the non-error control modem
interprets these characters as data instead of part of the
error control handshaking process.
Data Compression
Data compression minimizes the amount of data sent over the
telephone line by removing redundant information and
compressing the data it receives from the computer. To do this,
the modem uses the V.42bis or MNP 5 data compression
protocols. Once a file is compressed, it can be sent faster across
the telephone line since there is less data to send. Once the file
is received by the other modem, the file is decompressed to its
original form before being sent to its attached computer. The
amount of data compression achieved is dependent on the type
of file being transferred. The more repetitive the data, the more
compressible it is.
Data compression is useful when transferring uncompressed
files. However, if the MNP protocol is used and the file has
already been compressed by PC software (such as PKZIP
prior to transfer, then data compression should be turned off.
Use the %C command to turn data compression on or off.
Issue 2
May 1995
r
)
E-3
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