Data Communication

When modems talk back and forth they communicate over what is called a "carrier signal", then they put other wave forms over this. There are four major ways of doing the other communication.

V.34 - This is the protocol used for 28.8k and 33.6k communications. There were other protocols before V34 for lower speeds, but they will rarely need to be dealt with these days. All modems which are 28.8k or above can communicate with this protocol.

K56Flex - This is the 56k protocol created by Lucent and Rockwell. K56Flex is more reliable than the other 56k protocols.

X2 - This is the 56k protocol created by U.S. Robotics (3com). X2 tends to be a less reliable protocol than K56Flex or V.90.

V.90 - This is the International Standard for 56k modems. It is based primarily on the K56Flex protocol but also has some components from the X2 protocol. V.90 is often quicker than K56Flex, but is sometimes less reliable. All new 56k modems support V.90.

Error Correction

It is generally better to have error correction enabled on the modem otherwise you are likely to have problems. there are two protocols that are used to correct errors on a connection. They are :

V.42 (LAPM) - This is the International Standard for doing Error Correction and is usually the most reliable.

MNP - This is an old protocol that most modems support. Usually it is not as reliable as V.42, nut in some rare cases it might be.

Compression

Compression helps to speed up transition of information. Compression is not required for modems to work, and since a lot of information is already compressed before it reaches the modem, often it does not help significantly. Turning off compression can make a connection more reliable sometimes as there is one less language for the modem to speak. For this reason it is worth turning it off if people are having troubles connecting or getting disconnected. There are two protocols for compression :

V.42bis - This is the International Standard for Compression. It only works with V.42 Error Correction and is generally the more reliable method.

MNP5 - this is an older protocol that most modems support which also does compression. This will only work with MNP Error Correction.