Office Technologies

F7J9 34

Outcome 1

Communication Networks

April 2023

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Communications networks

Office TechnologiesF7J9 34 Business & Management

A local area network (LAN) is a collection of computers within a single office or building that connect to a common electronic connection – commonly known as a network backbone. A LAN can be connected to other networks either directly or through a WAN.

A WAN normally connects networks over a large physical areas, such as in different buildings, towns or even countries. Figure 1 shows four local area networks : LAN A, LAN B, LAN C and LAN D, some of which are connected by the WAN.

Figure 1

A modem connects a LAN to a WAN when the WAN connection is an analogue line. For a digital connection a gateway connects one type of LAN to another LAN or WAN, and a bridge connects the same type of LAN to another.

The public switched telecommunications network (PSTN) provides long distance analogue lines. These public telephone lines can connect one network to another using circuit switching. A modem is used to transmit digital signals over the PSTN and converts digital data into a transmittable form for the transmission line. Figure 2 shows the connection of computers to a PSTN.

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Figure 2

A public switched data network (PSDN) allows the direct connection of digital equipment to a digital network. This has the advantage of not requiring the conversion of digital data into an analogue form.

The integrated services digital network (ISDN) allows the transmission of many types of digital data into a truly global digital network. Data types include digitized video, digitized speech and computer data. Since the switching and transmission are digital, fast access times and relative high bit-rates are possible. All connections to the ISDN require network termination equipment.

LOCAL AREA NETWORKS

Why network

Local area networks allow the orderly flow of information between connected nodes. Their main advantages are that:

it is easier to set up new users and equipment it allows the sharing of resources it is easier to administer users it is easier to administer software licences it allows electronic mail to be sent between users it allows the connection of different types of computers which can

communicate with each other.

Figure 3 illustrates typical resources that can be set up with shared resources.

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Figure 3

Maintaining a Network

A major advantage of LANs is their ability to share information over a network. Normally, it is easier to store application programs at a single locate and make them available to users rather than having copies individually installed on each computer (unless the application program requires special configurations or there are special licensing agreements.) This saves on expensive disk space and increases the availability of common data and configurations. This disadvantage of this is that it increases the traffic on a network.

Most networks have a network manager, or a network group, who manage the users and peripherals on a network. On a well-maintained network the network manager will:

control the users on the network, that is who can and cannot log in

control which of the users are allowed to use which facilities control which of the users are allowed to run which application

programs control the use of software packages by limited users to license

agreements standardise the set up of application programs to a single source back-up important files on a regular basis onto a mass back-up

system set up simple-to-use procedures to access programs such as

icons, menus etc possibly control PC viruses by running automatic scanning

programs update application programs by modifying them at a single

source

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Sharing resources

Computers not connected to a network may require extra peripherals such as printers, fax machines, modems, plotters and so on. This may be resource inefficient, as other users cannot get access to them unless they are physically disconnected and connected to their own computer. Normally, it is more efficient to share resources over a network.

Access to networked peripherals is also likely to be simpler as the system manager can standardise configurations. Peripherals that are relatively difficult to set up such as plotters, fax machines and modems are set up once and their configurations stored. The network manager can also bar certain users from using certain peripherals.

There is normally a trade off between the usage of a peripheral and the number required. For example a single laser printer in a busy office may not be able to cope with the demand. A good network copes with this by segmentation, so that printers are assigned to different areas or users. The network may also allow for re-direction of printer data if a printer was to fail or become busy.

Sharing Disk Resources (network file servers)

Many computer systems require access to a great deal of information and to run many application programs such as word processors, spreadsheets, presentation packages computer-aided design (CAD) packages and so on. Most local hard-disks could not store all the required data and application programs. A network allows users to access files and application programs on remote disks.

Multi-tasking operating systems allow all hard-disks on a network to be electronically inked as a single file system. Most PCs operating systems are not multi-tasking and normally networked to a single file server computer. In this case the network server normally has a local drive that is available to all users on the network.

Disadvantages and potential pitfalls of networks

The main disadvantage of networks is that users become dependent upon them. For example, if a network file server develops a fault then many users may not be able to run application programs and get access to shared data. On many sites a back-up server can be switched into action when the main server fails. A fault on the network may allow stop users from being able to access peripherals such as printers and plotters. To minimise this a network is

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Office TechnologiesF7J9 34 Business & Management

normally segmented so that a failure in one part of it does not affect any other parts.

Another major problem with networks is that efficiency is very dependent on the skill of the system manager. A badly managed network may operate less efficiently than non-networked machines. Also, a badly run network may allow external users into it with little protection against them causing damage. Novices causing problems such as deleting important files could cause damage.

The main disadvantages are summarised below:

if network file server develops a fault then users may not be able to run application programs

a fault on the network can cause users to lose data if the network stops operating then may not be possible to

access various resources User work-throughput becomes dependent upon network and the

skill of the system manager. it is difficult to make the system secure from hackers, novices or

industrial espionage decisions on resource planning tend to become centralised, eg

what word processor is used, what printers are bought networks that have grown with little thought can be inefficient in

the long term as traffic increases on a network the performance degrades

unless it is designed properly resources may be located too far away from some users the larger the network becomes the more difficult it is to

manage.

Source: Applied Data Communications and Networks, W Buchanan, Chapman & Hall 1996

Other References:

Information Systems for Business Management, Martin R. Combs, Pitman Publishing 1995

Management Information Systems: Conceptual Foundations, Structure and Development, 2nd Edition, Gordon B Davis and Margrethe H Olson McGraw-Hill Book Inc 1984

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