U-90E
Data/Fax
Modem
Error Control and Data Compression
9-1
Chapter 9
Error Control and Data Compression
In Synchronous data communication, data is checked and corrected in the host by the so-
called “link layer protocols” to ensure data integrity. Normally, no data checking is
provided in the host for the asynchronous data communication. However, file transfer
protocols that include error checking are available with asynchronous hosts.
Nowadays, intelligent modems incorporate error control protocols inside the
modems for asynchronous data communication. Your data/fax modem U-90E also
provides error control, data compression and flow control features.
9.1 Error
Control
Error control keeps the modem data link error-free by detecting and re-transmitting
erroneous data. The U-90E modems support both MNP and V.42 error control protocols.
MNP (Microcom Network Protocol) is a set of protocols developed and licensed by
Microcom, Inc., and later used by many modem manufacturers. V.42 is an error control
standard developed by CCITT (now called ITU-T) - the international telecommunications
standard making organization.
The U-90E modems support level 4 and 3 error control MNP protocols, commonly
denoted as MNP4 and MNP3. V.42 supports both LAPM (Link Access Procedure for
Modems) and MNP4. A V.42 handshaking will try an LAPM connection first, and if not
successful, it will try MNP4. The maximum data block size used in the U-90E modem is
256 bytes.
