A Modem is what brings the internet into your home or business. A Modem establishes and maintains a dedicated connection to your Internet Service Provider (ISP) to give you access to the internet. Now the reason why you need to have a modem is because of the two types of signals used in a computer and the internet.
A modem is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information.
The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data.
A modem can be used with any means of transmitting analog signals, from light-emitting diodes to radio.
A common type of modem is one that turns the digital data of a computer into a modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.
Modems are classified by the maximum amount of data they can send in a given unit of time, usually expressed in bits per second (bps) or bytes per second (Bs).
Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal.
Many modems are used to connect to the internet through telephone service or cable television service. Slow telephone service is called dial-up. Faster telephone service is called DSL (Digital Subscriber Line) and is usually more than ten times faster.
The computer only reads digital signals, but the internet only reads analog signals.
Dial-Up Modems
The term Modem compose word that refers to the two functional entities that make up the device, which are;
The modulator is the changing of digital data from a computer to analog data to be sent over telephone lines.
The demodulator is the changing of analog data which is received over the telephone lines to digital data to be used by a computer.
As analog data comes in from the internet, the Modem demodulates incoming analog signals into a digital signal, so that the computer can understand it.
Also, Modem modulates outgoing signals into an analog signal as goes out into the internet.
The effective bandwidth of a telephone line being used for data transmission is 2400Hz, with a range from 600Hz to 3000Hz.
Traditional telephone lines can carry frequencies between 300Hz and 3300Hz, giving them a bandwidth of 3300Hz. All this range is used for transmitting voice.
However, today telephone lines are capable of handling greater bandwidth than traditional lines, but Modem design is still based on traditional capability.
Modem Standards
Today’s modems are based on the V-series standard published by ITU-T. These are V-series modem standards
V.32
A data stream is divided into 4bits streams. A petabyte (5bits pattern among 8 bits) is transmitted, and the extra bits are used for error detection.
V.32 with a baud rate of 2400=4x2400=9600 bps.
V.32bis
In V.32bis uses 7 bits/baud (6bits are transmitted), and 1 bit for error control. V.32bis calls with a baud rate of 2400=6x2400=14400 bps.
V.34bis
In V.34bis have a bit rate of 28800 bps.
V.90
In V.32 modems have limitations on data rate (max 33.6 Kbps), but in V.90 modems can be used up to 56 Kbps in digital signaling. Example through an Internet Service Provider (ISP). V.90 are asymmetric (downlink and uplink).
Downloading rate (from ISP to PC) has a 56 Kbps limitation, while for Uploading rate (from PC to ISP) has a 33.6 Kbps limitation.
V.92
In V.92 modems have a downloading rate of 56Kbps and an uploading rate of 48Kbps. The modem can interrupt the internet connection when there is an incoming call if the line has a call waiting for services.
NB:
Dial-Up is a connection that is established using a modem. Telephone networks were created to support voice communication only. With the advent of the internet came the need for high-speed downloading and uploading, DIAL-UP MODEM was too slow. The telephone companies added new technology known as Digital Subscriber Line (DSL). DSL provides much faster access to the internet.
Cable networks were created to provide access to TV programs for that subscriber who had no reception because of natural obstructions like mountains.
