Digital connections


An ISDN (Integrated Services Digital Network) capable phone line can provide connection speeds of up to 64 Kbps (single channel) or 128 Kbps (dual channel) using a terminal adapter often referred to as an ISDN modem. The terminal adaptor removes the need to convert digital signals to analogue signals before they’re sent down the telephone line, this results in a more reliable internet connection.


ADSL (Asymmetric Digital Subscriber Line) provides connection speeds of up to 24 Mbps and uses a telephone line to receive and transmit data.

Devices required to complete a digital connection to the internet

The speed that data can be transferred is dependent on a number of factors:

  • Phone lines were designed to carry voice signals - not data. Signal quality can vary between lines and whilst it doesn’t affect voice signals, it does affect data transmissions.
  • The distance between your house and the telephone exchange has an effect on the speed at which data is transferred. A distance of 4 km is considered the limit for ADSL technology, beyond which it may not work.

An ADSL modem/router is needed for broadband internet access over ADSL. This is usually provided by your ISP.

Phone calls can still be made whilst connected.


Cable companies do not use traditional telephone lines to provide broadband internet access. They have their own network, a combination of co-axial copper cable and fibre optic cable.

With their purposefully built infrastructure cable companies are able to provide speeds of up to 50 Mbps - considerably faster than the highest available ADSL speed (24 Mbps).

A cable modem/router is needed for broadband internet access over cable. This is usually provided by your ISP.

The making and receiving of phone calls is not affected because the telephone line is not used.