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Telecommunications
Long distance communicationMay or may not involve
computers
Components
Phone linesCableSatellites
Applications:
Distributed processingStrategic alliances
EDI
Bulletin boardsFax machinesCell phones
Applications:
EFT – electronic fund transfersTelecommutingTeleconferencingVideoconferencingOffice 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/demodulateTranslates 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 – 45-150 bps (bits per second)
Voice Grade - 300-9,600 bps
Wideband - 19,200-500,000
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