Networks : ISDN

A terminal adaptor can be used to connect computers on a WAN together using an Integrated Services Digital Network (ISDN) channel.

ISDN channels are a more modern form of connection than the public switched telephone network. Data can be transmitted digitally over an ISDN channel, so faster transmission speeds can be achieved than when data is sent using a modem and an analogue telephone line. ISDN channels are not available in all countries.

A single ISDN channel transmits data continuously at 64KBps (kilobits per second). This compares to a maximum speed of 56.6KBps for a modem. More than one ISDN channel can be used at a time to send data between two computers. If two channels were used then a speed of 2*64=128KBps could be achieved. When very fast speeds are required, large numbers of channels (e.g. 32) can be used together or (if available) broadband could be used instead.

Advantages of
ISDN over Modem
  1. ISDN channels can transmit data faster than a modem can over a telephone line.
  2. ISDN channels establish a connection to another computer much more quickly than a modem does. The time it takes to connect to a WAN can be reduced to less than a second with ISDN compared to as long as a minute for a modem and telephone line.

GCSE ICT Companion 04 - (C) P Meakin 2004