broadband modems

[glenis]

i understand the concept of phone socket / modem / pc .but what exactly is inside a modem and why do we need one ?once you subscribe to a isp why can't you just plug your pc into the phone socket and have broadband?

[wildwood]

A (dialup) modem is basically a telephone without a handset and dialing is done electronically. The dialup signal is transmitted as a phone transmission, thus you can not use the phone when online because your line will be 'busy' as if someone was talking on another phone in your house. A broadband modem is not that much different but it utilizes a different signal.

You need a line filter for ADSL broadband because the broadband signal is transmitted over the phone line. The line filter separates the DSL signal from the telephone signal. This enables you to talk on the phone at the same time as being online.

[fo3nix]

Just to add a bit to wildwood's answer: modem stands for modulator/demodulator. Your computer has digital signals, and the phone line is analogue. A dial-up modem just converted these for you so that everything worked.

Broadband modems aren't modems in the same sense, though they do re-process the data.