Modems

Objectives :

  • Identify the features of a modem
  • Discuss the working of a modem
  • Explain the different types of modems
  • Discuss about the modem standards and protocols
  • Install and configure a modem
  • Test a modem
  • Troubleshoot a modem

Modem :

Is a short form for Modulator/Demodulator

The process of converting binary information into analog signals is called modulation and process of converting analog signal back to binary information is called demodulation

Enables a computer to transfer data over the telephone or cable lines

Features of a Modem :

Transmission speed – high data transmission rate can be achieved by compressing the data

Voice or Data communication

Data compression – if the modem is trying to compress data that is already compressed, the compression will be less efficient

Auto answering

Fax capability

Working of a Modem :

Software in computer activates modem, which listens for dial tone on phone line

Modem dials a specified number

Modem at receiving end answers call and sends out a signal

Modem at sending end converts digital signals to analog signals

Modem at receiving end converts analog signals back to digital signals

Basic Types of Modems :

Internal - A modem card that you can plug into an expansion slot on the motherboard. It is advisable to remove the telephone line when not used

Internal-Modem

External - Connected to the PC through a cable, which is plugged into serial port on the back of the system unit.

External-Modem

Types of Modems :

X2 Modem – US robotics developed X2 technology to transmit data at the speed of 56 Kbps over plian old telephone service (POTS). Limitations: DTR is 40kbps from your computer to dial up server and ISP modem must support V.90 standard

V.90 Modem - Built with an assumption that one end of a modem session has a pure digital connection to the telephone line and DTR is 56 kbps

ISDN Modem - Enables to send data, voice, and video over digital telephone lines or over an ordinary telephone wire. DTR is 64 kbps and requires ISDN adapter to perform conversion between digital and analog signal

DSL Modem - Carries both voice and data at the same time. It’s a high speed connection that allows the phone wires to transmit modulated digital content at high speed

Cable Modem – Transfers data much faster than the regular telephone modems, ISDN modems, and DSL modems. External cable modem is connected to either Ethernet card or USB port on the computer. Communicates with a Cable Modem Termination System (CMTS) at the local cable TV company office

Modem Standards :

Two modems communicating with each other must support same modulation standards

Modem-Standards

Modem Protocols :

Modem-Protocols

Best practices and Precautions while installing a Modem :

Best Practices

  • Read the modem documentation before installing a modem

Precautions

  • Wear an anti-static wristband
  • Ensure the computer is switched off and unplug the power cord from the wall socket
  • Disconnect all the peripheral devices attached to the computer

Troubleshooting Modems :

To solve the problems that might arise due to modem itself or due to communication software such as auto dialer or dial up connection