All rights reserved. Besides error control protocols, all current high-speed modems also support data compression protocols.
Some modems also use proprietary data compression protocols.
A modem cannot support data compression without utilizing an error control protocol, although it is possible to have a modem that only supports an error control protocol but not any data compression protocol. A MNP-5 modem requires MNP 4 error control protocol and a V.42bis modem requires V.42 error control protocol. That is to say, a 9600 bps MNP-5 modem can transfer data up to 19200 bps. That is why all those V.32 modem manufacturers claim that their modems provide throughput up to 38400 bps. Don't be fooled by the claim.