电子通信专业 外文翻译 外文文献 英文文献 电信现代运营.doc

毕业设计 （外文翻译材料） Telecommunication Modern Operation Telephone In an analogue 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 callers voice is transformed to an electrical signal using a small microphone in the callers handset. This electrical signal is then sent through the network to the user at the other end where it transformed back into sound by a small speaker in that persons 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 analogue — that is, the speakers voice directly determines the signals voltage. Although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting the signals to digital for transmission before converting them back to analogue 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 analogue 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 conte