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