What is Dial-Up Modem? Modem Standards

Introduction

A Modem is what brings internet into your home or business. A Modem establishes and maintains a dedicate connection to your Internet Service Provider (ISP) to give you access to the internet. Now the reason why you need to have a modem because of the two types of the signals used in a computer and the internet.

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;

  • Modulator (signal modulator) creates analog signal from binary data.
  • Demodulator (signal demodulator) recovers the binary data from the modulated signal.

As analog data comes in from the internet, Modem demodulates incoming analog signals into digital signal, so that 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 range from 600Hz to 3000Hz.

Traditional telephone lines can carry frequencies between 300Hz and 3300Hz, giving them bandwidth of 3300Hz. All this range 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 based on V-series standard published by ITU-T. These are V-series modem standards

  1. V.32
  2. V.32bis
  3. V.34bis
  4. V.90
  5. V.92

V.32

Data stream is divided into 4 bits stream. A pentabit (5 bits pattern among 8 bits) is transmitted, the extra bits 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 is 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 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 a 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 downloading rate of 56 Kbps and uploading rate of 48 Kbps. Modem can interrupt the internet connection when there is an incoming call if the line has call waiting services.

NOTE:

Dial-Up is a connection that is established using a modem. Telephone networks were original created to support voice communication only. With advent of 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 originally created to provide access to TV programs for those subscriber who had no reception because of natural obstructions like mountains.


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