Telephone Networks (PSTN)

Public switched telephone networks (PSTN) is a worldwide telephone system that manages telephone calls.

PSTN use one of the following technique to establish a communication link

  • Fiber optic
  • Telephone lines
  • Satellite communication
  • Microwave transmission links
  • Cellular networks

It is also used in computer communications through the internet by using dial-up lines or dedicated lines.

Dial-up lines

  • It uses the PSTN to establish a connection to the internet by dialing a number over the mobile phone.
  • It requires some time to establish the telephone connection (depending on location)
  • Configure the protocols before data transfer.
  • Slower communication can’t be used for media streaming. The data transfer rate is in Kbps.
  • The connection of dial-up lines is explained below

Dedicated lines

  • It is a connection that is always established between two communication devices.
  • These lines may be analog or digital. But the speed of digital is higher than that of analog.
  • They are used to connect home and business users to network all over the world.

Types of dedicated lines

1. ISDN Lines

  • ISDN stands for integrated service digital networks.
  • It uses ISDN modems for Data transmission over the telephone line.
  • ISDN modem must be present at both ends within the range of 3.5 miles for communication.
  • It provides a faster transfer rate than dial-up telephone lines for small businesses and home users. It provides a transfer rate of up to 1.54 Mbps.

2. DSL

  • DSL stands for digital subscriber line. It uses the telephone lines for digital data transmission.
  • Faster transfer rates (up to 10MBps) than ISDN.
  • It allows a user to use a phone and internet at a time.
  • In DSL, any computer that is close to the service provider’s office will work better.
  • It is better for small businesses and home users.
  • ADSL (asymmetric) is a type of DSL that provides a faster transfer speed.

The rate of receiving data from the internet is called the downstream rate, and sending data is called the upstream rate.

3. Cable

Cabling service also provides internet connection by transmitting data over television networks.

Faster transfer rates (up to 50MBps) than DSL.

  1. T-carrier lines
  2. A synchronous transfer mode.