Modern operation on Telephone

In a conventional telephone system, the caller is connected to the person they want to talk
to by the switches at various exchanges. The switches form an electrical connection
between the two users and the setting of these switches is determined electronically when
the caller dials the number based upon either pulses or tones made by the caller’s
telephone. Once the connection is made, the caller’s voice is transformed to an electrical
signal using a small microphone in the telephone’s receiver. This electrical signal is then
sent through various switches in the network to the user at the other end where it
transformed back into sound waves by a speaker for that person to hear. This person also
has a separate electrical connection between him and the caller which allows him to talk
back.

Today, the fixed-line telephone systems in most residential homes are analogue that is the speaker’s voice directly determines the amplitude of the signal’s voltage.However although short-distance calls may be handled from end-to-end as analoguesignals, increasingly telephone service providers are transparently converting signals todigital before converting them back to analogue for reception.Mobile phones have had a dramatic impact on telephone service providers. Mobile phonesubscriptions now outnumber fixed line subscriptions in many markets. Sales of mobilephones in 2005 totalled 816.6 million with that figure being almost equally sharedamongst the markets of Asia/Pacific (204 m), Western Europe (164 m), CEMEA (Central
Europe, the Middle East and Africa) (153.5 m), North America (148 m) and Latin
America (102 m).

In terms of new subscriptions over the five years from 1999, Africa has
outpaced other markets with 58.2% growth compared to the next largest market, Asia,
which boasted 34.3% growth. Increasingly these phones are being serviced by digital
systems such as GSM or W-CDMA with many markets choosing to depreciate analogue
systems such as AMPS. By digital it is meant the handsets themselves transmit digital
not analogue signals.However there have been equally drastic changes in telephone communication behind thescenes. Starting with the operation of TAT-8 in 1988, the 1990s saw the widespreadadoption of systems based upon optic fibres. The benefit of communicating with opticfibres is that they offer a drastic increase in data capacity. TAT-8 itself was able 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
drastic increase in data capacity is due to several factors.

First, optic fibres are physically
much smaller than competing technologies. Second, 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. However despite theadvances of technologies such as dense wavelength-division multiplexing, technologiesbased around building multiple channels based upon time division such as synchronousoptical networking and synchronous digital hierarchy remain dominant.Assisting communication across these networks is a protocol known as AsynchronousTransfer Mode (ATM).