Introduction to information systems T. Cornford, M. Shaikh is1 060 2013

4.6.1 Wide area networks and local area networks
The basis of most wide area networking was, in the past, the old landline 
telephone system. Simple telephone connections were once used to 
transmit data with the aid of modems. But, since telephone networks were 
built to transmit voices in analogue form, not computer data in a digital 
form, they are not really suitable for high volumes and high-speed data 
transmission. The result was the establishment of special-purpose data 
communications networks that are able to provide far better performance 
characteristics – although they may use the telephone wires for the final 
link to the house or office – the ‘last mile’. Today in most countries we 
expect to receive such data at speeds of, say, 5 to 20 megabits per second – 
maybe more if we are lucky and live in a big city. 
But things have changed more fundamentally. Once it was a question of 
forcing data onto an essentially voice-oriented telephone network. Now we 
see the opposite. The most general network available to us is the digital 
network – the internet – and voice traffic can now be easily integrated into 
this. Thus we see a huge growth in Voice over IP technology (VOIP). The 
most common example is the service of Skype (www.skype.com), but there 
are many other VOIP providers and 4G mobile phones all work using VOIP. 
Of course, traditional telephone companies do not like their business being 
hijacked by new start-up internet companies that can offer international 
calls at zero cost. 
Local area networks (LANs) are used to link computers within a 
restricted geographical range. A LAN will typically connect computers in 
one building or one city block. They use special cabling – often based on 
fibre optics – and can transfer data at speeds in excess of 100 megabits per 
second. (100 megabits per second may be a conservative figure – whatever 
figure we write here is bound to be exceeded before this subject guide is 
revised again!) If a dedicated computer is attached to a local area network 
to provide services, it is called a server. For example, a college computer 
system may have 20 microcomputers in a room connected by a 100 Mb/
sec network to one print server and one file server. The file server would 
allow the sharing of data and programs among a class of students. Today 
such a network may well not be based on wired connections, but might 
use a wireless technology (WiFi) although probably slower than 100 Mb/
sec, to allow machines to communicate.
We should also note that networks are usually described in terms of raw 
speed of transmission in terms of bits per second (MB/sec). But quantities 
of data are expressed in bytes (megabytes or kilobytes). So, if we need 
to answer a question about how long it would take to transmit a file 
measured in megabytes across a network whose speed is expressed in 
megabits per second, we need to multiply the file size by 8 – to convert 
bytes into bits – before dividing by the network speed. 
Even then we may not have a very accurate answer.
First, because the raw capacity of a network may be being shared by many 
users – we don’t have the full capacity available to us. 
Second, because there are plenty of ‘housekeeping’ and control overheads 
that also need to be taken into account. In particular, assuming we are 
using the main network protocols of the internet – TCP/IP – we will have 
to add considerably more data to the total to transmit as the data is split 

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Chapter 4: Contemporary trends in information and communication technologies
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up into separate packages; each one is numbered, and the destination 
address is added to each. What is more, a network may not be very 
reliable; we have to expect some packets of data will be lost, and we will 
need to identify these (through the packet numbers), and ensure that they 
are resent.