Page 93 - DCAP309_INFORMATION_SECURITY_AND_PRIVACY

Unit 7: Network Security

7.2 Network Types Notes

7.2.1 Local Area Networks (LANs)

Networks that connect computers lying within a small distance (such as a room, or within a
building) from each other are called Local Area Networks (LANs). A Local Area Network (LAN)
is a group of computers and associated devices that share a common communications line or
wireless link and share the resources of a single processor or server within a small geographic
area usually within an office building. Usually, the server has applications and data storage that
are shared in common by multiple computer users. A local area network may serve as few as
two or three users (for example, in a home network) or as many as thousands of users.

Example: An FDDI network
LANs have become commonplace in many organizations for providing telecommunications
network capabilities that link end users in offices, departments, and other work groups.

Ethernet is by far the most commonly used LAN technology. A number of corporations use the
Token Ring technology. FDDI is sometimes used as a backbone LAN interconnecting Ethernet
or Token Ring LANs. Another LAN technology, ARCNET, once the most commonly installed
LAN technology, is still used in the industrial automation industry. In some situations, a wireless
LAN may be preferable to a wired LAN because it is cheaper to install and maintain.
A suite of application programmes can be kept on the LAN server. Users who need an application
frequently can download it once and then run it from their local hard disk. Users can order
printing and other services as needed through applications run on the LAN server. A user can
share files with others at the LAN server; read and write access is maintained by a LAN
administrator. A LAN server may also be used as a Web server if safeguards are taken to secure
internal applications and data from outside access.

LAN provides access to more computing power, data, and resources than would be practical if
each user needed an individual copy of everything.
LAN provides the benefits of personal computing. One is not forced to do personal work through
a central computer that may not be able to respond to the users’ requests when many of them
share its capacity.

LAN can link multiple workstations to one laser printer, fax machine, or modem. This makes a
single piece of equipment available to multiple users and avoids unnecessary equipment
purchases.
LAN users can select personal files that they want co-workers to see, such as engineering drawings,
department plans, contracts, or drafts of memos. Co-workers can look at these files without
delays for printing paper copies.
LAN can be used to transmit and manage electronic mail and messages.
LAN also provides access to shared databases. Figure 7.1 shows a LAN system that is set up for
this purpose because it contains a file server for retrieving data requested by the workstations.
The file server is linked to a disk that contains shared databases, such as the firm’s customer list
and telephone directory. When a workstation needs data in a shared database, it sends a request
message to the file server, which performs the retrieval from the disk and sends the data to the
requesting workstation. This arrangement avoids maintaining redundant copies of data.

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