Transmission Rate

Modems

Signals

Computer to Computer: Modems

Two types of signals are used for data transmission:

Digital and Analog.

A digital signal is a stream of 0's and 1's. So this type is particularly appropriate for computers to use.
An analog signal uses variations (modulations) in a signal to convey information. It is particularly useful for wave data like sound waves. Analog signals are what your land-line phone and sound speakers use.

When communications between computers use the telephone system for at least part of the channel, a device is needed to translate between the analog phone line and the digital computer. Such a device is the modem, which comes from Mod ulate/ Dem odulate, which is what a modem does. It modulates a digital signal from the computer into an analog one to send data out over the phone line. Then for an incoming signal it demodulates the analog signal into a digital one.

Though rather small, modems are very complex devices. There are entirely too many commands, protocols, and configuration choices available. Once you get a modem set up and working right the first time, you probably won't have to tinker with it much afterwards. Hurrah!!

Confusion abounds when it comes to measuring the transmission rate of a modem. Throughput is the term for the entire process - how much data is moved during a certain amount of time. Since the modem is only part of the process of moving data, getting a faster modem may not speed up your data transfers.

There are two different parts of the data transfer to measure: the digital process and the analog process.

Digital

The rate of digital transmission is measured in bits per second (bps). Common rates for regular modems are 28.8 Kbps, 33.6 Kbps, and 56 Kbps where the K stands for thousand. Completely digital devices (discussed below) are much faster. Faster is better, of course. 2400 bps would send a 20-page single-spaced report in 5 min. (This is SLOW!!)

Дата добавления: 2014-12-23