WANs

Wide Area Networks are spread over longer distances. Communication can be over leased telephone lines and via satellite. The communication links can be high speed or low speed.

Packet switching can be used in WANs. The data needs to be organised to be sent or received in a packet by a packet assembler and disassembler (PAD).

The transmission media can be :

·        Twisted pair consists of insulated copper wire eg house telephones

·        Coaxial cable is a stiff cable that has an outer metal shield eg television aerial

·        Fibre optic cable transmits light and not electricity eg 1970's lamps

·        Antennae or line of sight transmitters sends radio waves.

·        Satellite systems send high frequency radio waves. Satellites are generally placed 35000km above the earth in a geosynchronous orbit.

A network consists of

·        A user workstation

·        Protocol control to allow data to be sent through the network

·        An interface

·        Physical transmission medium

Network topologies can be

·        Ring topology eg token ring consists of stations in a closed loop. It does not require a main computer. A token or pattern of bits is passed around the ring. When the station has this token it is allowed to transmit.

·        Bus topology is an open ended ring. Expansion or adding extra computers is easier.

·        Star topology has a central station through which all the other computers must communicate. If it fails then the system hangs. The central station is called a hub.

·        Mixed topology can combine all three topologies.

Terms

MODEM         PCMIASLOT ADDRESS    PARITY                       CABLING                   TCONNECTOR

TOKEN           PARALLEL    TERMINAL     TOPOLOGY   CSMA/CD                 SERIAL

INTERFACE CARD             POLLING                   FILE SERVER          JAMMING SIGNAL

TWISTED WIRE PAIR          MICROWAVE LINKS                       SATELLITE   POINT TO POINT

CO-AXIAL CABLE               MULTI-DROP                                    STD LINK                   FIBRE OPTICS

LEASED LINE                                  MULTIPLEXER                                 ASYNCHRONOUS COMMUNICATION

INTERNET                             GATEWAY                             ETHERNET

Theory Exercises
P286 Q1 to Q6
P292 Q1 to Q3
P300 Q1 to Q4