Telecommunications Long distance communication May or may not involve computers

Components Phone lines Cable Satellites

Applications: Distributed processing Strategic alliances EDI Bulletin boards Fax machines Cell phones

Applications: EFT – electronic fund transfers Telecommuting Teleconferencing Videoconferencing Office automation Groupware – allows tracking of information by several people

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.

MODEMS Modulate/demodulate

MODEMS Modulate/demodulate Translates digital signals to analogue (modulate) and back again (demodulate) Internal/External modems

Two types of signals: analogue 1.Voice grade 2.Used by telephones digital 1.Descreet states 2.Used by computers

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

Three types of media speeds: Narrowband – bps (bits per second) Voice Grade ,600 bps Wideband -19, ,000

Three types of media modes: Simplex – one way Half-duplex -two way but one way at a time Full Duplex -two way simultaneously

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