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Telrad Connegy IP Telephone system

Telrad LogoISDN Integrated Services Digital Network


ISDN stands for Integrated Services Digital Network and provides end-to-end digital connectivity over the telephone network.

Conventional telephone lines from a local exchange to your premises are analogue. These analogue lines severely limit the amount of information (either data or voice) that can be passed through them, because of this you are limited to one phone call per line, and modems must operate at a low speed to reduce the amount of error correction that is needed.

ISDN makes use of the fact that once a telephone line reaches the local exchange the analogue signal is converted into a digital signal and then transmitted at a rate of sixty-four thousand bits per second (64 kbps) on channels set up through the network. It is then converted at the remote exchange back to an analogue signal, which arrives at your phone. ISDN simply replaces the analogue path between you and the exchange with a fully digital service. As such, ISDN can provide an end to end (ie. all the way from one user in their premises, to another user in their premises) digital transmission path.

Basic Rate

This service provides two 64 kbit/s channels (Known as the B-channels) that can be used for communication and one 16 kbit/s channel (known as the D-channel) that is used for call setup and signalling, thus leaving the full bandwidth of the B-channels available for use. This service is supplied as ISDN 2e in the UK by British Telecom.

Primary Rate

This service provides anything from eight telephone lines or 'channels', upto thirty on one single cable. That is, one ISDN primary rate line installed in your premises can replace thirty existing analogue lines. Don't worry though if you don't need thirty telephone lines - because the channels are on one cable you could, for example, order a ten channel ISDN primary rate connection and then easily upgrade to a twenty or thirty channel connection as your business expands - all without the expense and disruption of the installation of a conventional analogue phone line. Primary Rate is supplied as ISDN 30 in the UK by British Telecom.

Telrad Unite IP systems support both Basic Rate and Primary Rate.