In an analog telephone network, the caller is connected to the person he wants to talk to by switches at various telephone 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. Once the connection is made, the caller's voice is transformed to an electrical signal using a small microphone in the caller's handset. This electrical signal is then sent through the network to the user at the other end where it is transformed back into sound by a small speaker in that person's handset. There is a separate electrical connection that works in reverse, allowing the users to converse.
The fixed-line telephones in most residential homes are analog — that is, the speaker's voice directly determines the signal's voltage. Although short-distance calls may be handled from end-to-end as analog signals, increasingly telephone service providers are transparently converting the signals to digital for transmission before converting them back to analog for reception. The advantage of this is that digitized voice data can travel side-by-side with data from the Internet and can be perfectly reproduced in long distance communication (as opposed to analog signals that are inevitably impacted by noise).
Mobile phones have had a significant impact on telephone networks. Mobile phone subscriptions now outnumber fixed-line subscriptions in many markets. Sales of mobile phones in 2005 totalled 816.6 million with that figure being almost equally shared amongst 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. Increasingly these phones are being serviced by systems where the voice content is transmitted digitally such as GSM or W-CDMA with many markets choosing to depreciate analog systems such as AMPS.
There have also been dramatic changes in telephone communication behind the scenes. Starting with the operation of TAT-8 in 1988, the 1990s saw the widespread adoption of systems based on optic fibres. The benefit of communicating with optic fibers 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 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 led to an exponential growth in the data capacity of a single fibre.
Assisting communication across many modern optic fibre networks is a protocol known as Asynchronous Transfer Mode (ATM). The ATM protocol allows for the side-by-side data transmission mentioned in the second paragraph. It is suitable for public telephone networks because it establishes a pathway for data through the network and associates a traffic contract with that pathway. The traffic contract is essentially an agreement between the client and the network about how the network is to handle the data; if the network cannot meet the conditions of the traffic contract it does not accept the connection. This is important because telephone calls can negotiate a contract so as to guarantee themselves a constant bit rate, something that will ensure a caller's voice is not delayed in parts or cut-off completely. There are competitors to ATM, such as Multiprotocol Label Switching (MPLS), that perform a similar task and are expected to supplant ATM in the future.
Other articles related to "telephone":
... The Bell Telephone Hour (also known as The Telephone Hour) is a long-run concert series which began April 29, 1940 on NBC Radio and was heard on NBC ... Sponsored by Bell Telephone as the name assumes, it showcased the best in classical and Broadway music, reaching eight to nine million listeners each week ...
... List of Canadian telephone companies Australia Telstra, Optus, Vodafone, Hutchison Telecom(3G network), AAPT, Primus Telecom, Nextgen Networks, Agile ...
... US 174,465 -- Telegraphy (Bell's first telephone patent) -- Alexander Graham Bell US 186,787 -- Electric Telegraphy (permanent magnet receiver) -- Alexander Graham Bell US 474,230 -- Speaking Telegraph (graphite ... System—Amos Edward Joel (Bell Labs) US 3,906,166 -- Radio Telephone System (DynaTAC cell phone) -- Martin Cooper et al ...
... NBTel was founded as the New Brunswick Telephone Company in 1888 after Bell Telephone Company of Canada's attempt to establish telephone service in the Maritime provinces failed ... NBTel purchased the last independent telephone operator in New Brunswick, giving it a monopoly for the telephone service ...
... often erroneously referred to as RJ9, RJ10, and RJ22) 6P2C for RJ11 single telephone line 6P4C for RJ14 two telephone lines 6P6C for RJ25 three telephone lines ...
Famous quotes containing the word telephone:
“Men will not give up their privilege of helplessness without a struggle. The average man has a carefully cultivated ignorance about household mattersfrom what to do with the crumbs to the grocers telephone numbera sort of cheerful inefficiency which protects him better than the reputation for having a violent temper.”
—Crystal Eastman (18811928)
“The press and politicians. A delicate relationship. Too close, and danger ensues. Too far apart and democracy itself cannot function without the essential exchange of information. Creative leaks, a discreet lunch, interchange in the Lobby, the art of the unattributable telephone call, late at night.”
—Howard Brenton (b. 1942)
“But even in a telephone booth
evil can seep out of the receiver
and we must cover it with a mattress,
and then tear it from its roots
and bury it,
—Anne Sexton (19281974)