Knowledge Society
Lecture 5
Telecommunications
In the latter half of the 20th century, computer and telecommunication
technology have rapidly merged
Today, a large number of computers are linked to some form of networks
A network allows individuals to access shared resources easily and productively
The ‘stand alone’ computer is quickly becoming a thing of the past
Another trend is that of wireless networking where you can access resources
from anywhere
Digital and Analogue
o Conversion from analogue based technology to digital technology (e.g.
mobile phones, TVs and sound systems)
o Digital refers to communication signals that are represented in a two
state (or binary) way
o Modern computers process binary data using electrical switches that
can either be on (1) or off (2)
Computer networks
o A system of interconnected computers and telecommunications
equipment so that applications, data and peripherals can be shared
o Organisations that have set of computers have them networked
o Many homes also have their own networks
Network types
o PAN =
A personal area network wirelessly connects devices that are
used by individuals
Bluetooth is often used to enable PANs
o LAN =
A local area network connects computers and devices in a
limited geographical area
A router directs communications messages between different
networks
Used to connect a LAN to the internet
A bridge is an interface between two networks of he same
types
A gateway is an interface that connects two dissimilar
networks
E.g. a gateway could be used to connect to LANs that run
different NOSs (network Operating Systems)
There are two types of LANs
1. Client-server – consists of clients (typically PCs) that
request services from computers called servers
2. Peer-to-peer – consists of computers that can directly
communicate with one another, no servers
o 25 computers is the limit of this type of network
o MANs
A Metropolitan Area Network is a commnuications network
covering a city
An example of this is a mobile network
o WANs
Wide Area Network covers a wide geographical area
The ultimate WAN is th internet
Communication channles and bandwidth
o A communication channel is the physical medium over which dadta
travels in a communication
o Data is transmitted via electromagnetic waves
o Waves differ because of their frequency (waves per second)
o The higher the frequency the faster the transmission
o A range of frequencies is called a band or bandwidth
o For digital signals this measured in bps (bits per second)
o The higher the bandwidth the faster the transmission of the signal
o Broadband connections are very high speed connections
Wired communications
o Twisted pair
Telephone cabling
Consists of 2 shielded copper wires twisted around one
another
o Coaxial cable
Better insulation than twisted pair and has a higher
transmission rate
o Fibre Optic
Strands of class that transmit light
They have a low error rate and many major under sea data
cables are now fibre optic
Harder to tap/intercept that other wires, which provides greater
security
o Infrared
Infrared signals are usually effective for a few meters
Requires unobstructed view between transmitter and receiver
Mobile devices such as PDAs often transmit infrared
o Broadcast Radio
Normal AM and FM radio
o Microwave Transmitter
o Transmits voice and data through the air as microwaves
o Like infrared, line of sight technology
o Often used by telephone and pay TV companies
o Used if it is difficult to install a cable and line of sight is available (like
a desert)
Satellites
o Use microwave technology in order to relay signals around earth
o Uplink = transmit data from the ground to the satellite
o Downlink is the opposite
o Three types of satellites occupy different orbits of the earth
1. GEO
2. MEO
3. LEO
Short Range Wireless Communications
o Pagers
Restaurants are using these devices so that customers can
‘page’ a waiter
o Global Positioning System (GPS)
Uses satellites to locate objects on Earth
Available for vehicles in order to navigate
Also used to locate lost or stolen items
Intranets and Extranets
o Intranet
Organisation’s internal private network that is ‘contained’
internet
Connecting intranets together to form a virtual private network
(VPN)
o Extranet
Extension of an intranet
Allows certain trusted people/organisations access to intranet
Firewalls
o System of hardware and software that blocks unauthorised internal and
external users from accessing the intranet and sensitive data
o E.g. Bond has a firewall that prohibits people outside the campus
logging onto machines with the university
