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Telecommunications Long distance communication May or may not involve computers
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Components Phone lines Cable Satellites
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Applications: Distributed processing Strategic alliances EDI Bulletin boards Fax machines Cell phones
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Applications: EFT – electronic fund transfers Telecommuting Teleconferencing Videoconferencing Office automation Groupware – allows tracking of information by several people
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Because we are using phone lines we need to be able to communicate with the telephone system. Done by a specific type of hardware called a MODEM.
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MODEMS Modulate/demodulate
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MODEMS Modulate/demodulate Translates digital signals to analogue (modulate) and back again (demodulate) Internal/External modems
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Two types of signals: analogue 1.Voice grade 2.Used by telephones digital 1.Descreet states 2.Used by computers
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Three types of modulation: analogue Amplitude – soft/loud characteristics (height) AM – changes the amplitude while keeping the frequency fixed. Frequency – pitch; how often does it change FM – changes the frequency while keeping the amplitude fixed Phase – amount of time when there is no change
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Three types of media speeds: Narrowband – 45-150 bps (bits per second) Voice Grade -300-9,600 bps Wideband -19,200-500,000
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Three types of media modes: Simplex – one way Half-duplex -two way but one way at a time Full Duplex -two way simultaneously
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Two types of transmission: Asynchronous – sends a single character at a time has a special start/stop signal Synchronous -sends a group of characters requires synchronized sending and receiving devices has error check bits to determine if message is correct
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