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