Modem The main reason to use a modem is that commercial grade telephone circuitry is limited to a bandwidth of 300-3,400 Hz which provides a bandwidth of 3.1 KHz which is not wide enough to transmit digital signals without introducing distortion. Therefore the digital signal must be converted into an analogue signal before being transmitted over the telephone network, this also applies to the distant end so the received analogue signal must be converted back to the original digital form. This process is carried out by a piece of equipment called a MODEM and for this to be done there needs to be a modem at each end of the circuit. The ITU-T refers to a modem as Data Communication Equipment (DCE), while the EIA calls it Circuit Terminating Equipment (CTE). You may also need a modem to establish, maintain, and terminate each connection you set up via your telephone network using a leased circuit or a dial-up connection via the PSTN. It is common to find modems that provide automatic dialing, answering, and can even recover from a communication failure by finding an alternate channel. Before two modems can exchange data, they must first set up their modems with each other. This sequence of events is called a handshake. An interface is the means by which a terminal is connected to the modem and ensures that both electrical and mechanical compatibility is achieved.The use of a home telephone via PSTN.Note 1. The use of a modem in a data circuit. A modem works by passing digital data from the terminal or computer to an encoder (unless it is FSK modems) where the bit stream is encoded in dibits, tribits or quabits. This encoded signal... middle of paper... distance between the two modems, if it is about 25km and has a continuous DC path, then a short range modem, A-line driver or modem eliminator can be used for using such devices would be significantly cheaper. Another important consideration is whether the modem is on a dedicated dedicated circuit or on a dial-up connection. For a large international company with the expected daily amount of data transfer, a leased circuit would be used as they cannot afford to waste time as they need to perform these data transfers as quickly and efficiently as possible. However someone who only needs to be "on line" with the Internet and would only use the Internet for short periods of time would not find it convenient to have a leased circuit and therefore a normal telephone connection via PSTN would be more favorable.