<- Virtual Exhibitions in Informatics

Telephone

The fixed-line telephone systems remain analogue and, although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting signals to digital before, if necessary, coverting them back to analogue for reception. Mobile phones have had a dramatic impact on telephone service providers. Mobile phone subscriptions now outnumber fixed line subscriptions in many markets.

The telephone run throw drastic changes. Starting with the operation of TAT-8 in 1988, the 1990's saw the widespread adoption of systems based around optic fibres. The benefit of communicating with optic fibres is that they offer a drastic increase in data capacity. TAT-8 itself was able to carry to carry 10 times as many telephone calls as the last copper cable laid at that time and today's optic fibre cables are able to carry 25 times as many telephone calls as TAT-8. This rapid increase in data capacity is due to several factors. Firstly, optic fibres are physically much smaller than competing technologies. Secondly, they do not suffer from crosstalk which means several hundred of them can be easily bundled together in a single cable. Lastly, improvements in multiplexing have lead to an exponential growth in the data capacity of a single fibre. This is due to technologies such as dense wavelength-division multiplexing, which at its most basic level is building multiple channels based upon frequency as discussed in the Technical foundations section.