Note for Wireless Communication - WC by harsh pittroda

Topics ( 4 )

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Telephony Background By Vaishali Kulkarni

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Background • World's largest machine; extends to all countries • Huge economic and social importance • Specialized in voice transmission • Other applications have been created: fax, data etc. • Basic service: full-duplex voice transmission • Small end-to-end delays, small delay variation (more than 150ms delay disturbs discussion --note satellites!) • Call admission control, and accepted calls will complete • Grows all the time, now mostly growth of mobile networks • Although most traffic in the telecom networks is now data, most of the money comes from voice 8/28/2017 Digital Voice Communication 2

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Background • Telephones are addressed by telephone numbers, that are unique • There are special numbers or area codes that need translation • The network formed by the end systems (telephones, faxes, modems etc.) and the hierarchic switching and transmission systems is called Public Switched Telephone Network (PSTN) or informally as Plain Old Telephone System (POTS). 8/28/2017 Digital Voice Communication 3

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FOUR WIRE TO TWO WIRE CONVERSION • In order to provide bidirectional telephony service between two persons 8 wires (4 pairs) are required. • Any reduction in the number of wires required will result in enormous cost economy. 4w to 2w conversion Time sharing of functions 4