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Comparison between analogue and digital

Generally speaking analogue transmission can provide better quality video than digital. However against this is the higher cost of and inflexibility of analogue systems. Analogue systems need dedicated circuits whilst a high speed network such as SuperJANET can quite easily carry digital video and computer data by reserving a Permanent Virtual Circuit (PVC) to carry the video signal. There is potential for local campus networks which can be used to carry video without using all the bandwidth available.

Whilst it is possible to re-generate a digital signal which has been transmitted across a noisy link this is not possible for analogue signals. Digital transmission methods can also carry error protection information within the transmitted data so even if a signal is corrupted it can be corrected.

Since the cost of an ISDN call is directly proportional to the data rate a call at 384kbps will cost three times as much as one at 128kbps and a ISDN 30 call will cost fifteen times as much. Thus it is possible to choose the quality of a digital circuit as a function of its cost. See Appendix A for more details.

There is a choice to be made between permanent leased lines and the use of dial up facilities. The rental cost of leased lines are high, BT charges 16000 per annum for rental of the LIVE-NET 2 lines, but there is no hourly usage rate. However since leased lines only provide point to point links they are less flexible than dial up.

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