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Chapter 5 - Error Correction, Data Compression, and Speed Conversion
5.1
Introduction
The MT2834MR6 has intelligent features beyond those of the AT command set described in Chapter 3. This
chapter describes high performance features and commands that provide error correction, data compression
and speed conversion capabilities. The remainder of this chapter describes these features and the
commands that implement them, as well as related commands.
The MT2834MR6's error correction complies with the ITU-T V.42 standard. V.42 actually uses two error
correction protocols: LAP-M and MNP Class 3 & 4. MNP Class 3 & 4 error correction emerged as the industry
standard among modem manufacturers over the past decade. It is now in the public domain, and has been
implemented in dozens of modem brands with world wide installations in the hundreds of thousands of units.
LAP-M error correction is similar to MNP Class 3 & 4.
The MT2834MR6 provides two types of data compression: ITU-T V.42bis and MNP Class 5. V.42bis data
compression is newer; it requires concurrent LAP-M error correction. V.42bis is a very efficient data
compression technique that can provide up to 4-to-1 compression, depending on the type of data being
transmitted. MNP Class 5 data compression requires concurrent MNP Class 3 & 4 error correction. It is an
older and more established standard that offers data compression in the 2-to-1 range, which also depends
on the type of data being transmitted.
Speed conversion allows the modem to operate at one speed over the telephone lines and another speed at
the RS-232 serial port. This allows the computer or terminal to communicate with the modem at a fixed speed
of up to 115,200 bps, while the modem operates at various speeds up to 33,600 bps. Speed conversion is
vital if data compression is to be effective, since your terminal or computer must send data to the modem at a
higher speed than the modem is sending it over the phone line.
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