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Similar to PSTN (analogue lines) the ISDN is a network of digital lines. The idea behind ISDN is to provide one universal network for telephony, data, facimile, imaging and video. ISDN is sold by Telstra as OnRamp and with Optus it's Multiline.
Like the PSTN, ISDN has access methond to the network. Actually two types of network accesses are provided adn are referred to as PRA and BRA. These interfaces are the same regardless of the type of signal transmitted. All signals must be converted into a digital stream of ones' and zeros'.
ISDN is based on two main channel types, these are B channel and D channel. The B channel is a 64 Kbps channel that can handle voice, data imaging, video etc. The D channel is used for signalling. With the PSTN signalling was achieved by placing a loop on the line to let the exchange know you wish to make the call, and by the decadic or DTMF dialling to transfer the number you wish to be connect to.
The difference between the PSTN and ISDN is that the PSTN signalling and voice share the same channel however, with the ISDN the voice path is on B channel and all the signalling is on the D channel.
This page was last modified on 16 January 2010 and maybe out of date with regards to newer practices at the time of reading this article |
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