Common terms used when discussing modems

Baud Rate

The rate of transmission, in bits per second. Because of the transmission protocols, bits per second won't correspond directly to bytes. For a generic modem, you get a byte every 10 bits or so. For modems with compression, you can get more bytes for less bits. If you are buying a fax modem, make sure the baud rate given is for data transmission. There are many modems available that have 9600 baud fax capabilities, but only 2400 baud data capabilities.

Data Compression/Error Correction

Error correction allows two modems to notice an error in transmission, and either correct the error or ask for re-transmission. Data compressions lets the modems talk to each other using less bits, thereby effectively speeding up the connection.

Error correction and data compression protocols are generally given obscure references, like v.32. The most common set of protocols are the MNP classes. MNP stands for Microcom Networking Protocol. MNP classes one thru four are seldom referred to any more. MNP class 5 represents the first (significant) data compression protocol. Typically, 2400 baud modems come with MNP 5 (but make sure). This protocol can double throughput (effectively making a 2400 baud modem as fast as a 4800 baud modem).

MNP class 9 is the next likely class you will here of. This provides better error correction, better compression (three times as fast rather than twice), connection baud rate negotiation (your modem will adjust to the receiving modem's baud rate). This is equivalent to v.42bis.

Many modems are described with v.number designations. v.32, and v.42 are the current common designations. They are equivalent to the error correction of MNP class 5 and class 9 modems respectively. If "bis" appears, this indicates data compression capabilities. The newest standard being developed for modems is v.fast.

Hayes command set

Almost all modems today are controlled with a Hayes command set , or a superset of those commands. Most commercial software expects to deal with a modem using these commands.

FAX

Many modems now have FAX capabilities. By combining this with the proper software, you can send and receive faxes without killing any trees.

How much to spend

Check the time of the last update of this document (at the bottom) - prices may change. These are estimates by the author.
Used 300 baud
Free
Used 1200 baud
Five bucks
Used 2400 baud
Twenty bucks, with MNP 5.
New 2400 baud
Fifty dollars, with MNP 5. For $20 more, you can have FAX.
New 9600 baud
Prices vary widely, you can probably get in somewhere under $150. Make sure the baud rate is the data rate, not the FAX rate.
New 14400 baud
Generally only slightly more expensive than the 9600 baud modems. Worth the extra $20 bucks. Again prices vary widely, so shop around.

Last Update: 1/10/94 JGW

Original author: TAF