Requires and additional electrical socket and cable and will need desk space. With an external modem, when it gets stuck getting it back to work is as easy as flipping a switch. It is important to make sure that your modem can send data accurately, without errors and rapidly. When you speak on the phone you can sometimes hear other noises, which can corrupt data transmission and cause problems. To get over this 'electrical noise' on the telephone line, modems should include error correction features.
Data compression is also an important consideration when buying a modem.
It compresses data as it is being transmitted. The most common form of data compression is V.42bits. This can quadruple the effective rate at which data is sent by the modem. The standard that allows data transmission rates as high as 9,600 bps. The standard for data transmission at 14,400 bps and several slower rates.