What is a LAN ?

Overview

In it's most basic form;

A LAN is a data communication facility providing high speed switched connections between processors, peripherals, and terminals within a single building, site or workgroup.

Historically, LAN's have evolved from the data processing or office processing industry where;

Economics suggest relatively expensive storage devices and printers should be shared by multiple computers.

LANs benefit from old technology. For example;

Redundant computers (or duplicated components)
Mirror hard disks
Expandability
Heterogeneous - should work with other network types (Inter-network ability)

Thus, LAN's have evolved partly in response to the emergence of Low Cost computing, and it's need for high cost peripherals.

Characteristics

In the Business, or Office context, a LAN has the following characteristics:

Two or more computers connected via short-range, high speed data path. eg : Ethernet
Each computer on LAN referred to as 'node'. They are generally PC's, though network computers (NC's) are becoming popular..
The Computer that manages the database is called the 'server'.

LAN Server

The Computer that manages the database is called the 'server'.
The Server is usually a Powerful PC such as a Pentium CPU, 32MB or more of RAM, and a 2GB or more Hard Disk.

The Server provides ;

Message processing, to transfer messages between nodes.
For the sharing of peripherals such as Printers.
For the sharing of Databases (Locking).

Resource sharing

A LAN is;

Any group of desktop computers that are connected for the purposes of sharing resources.

For Example;

Hard Disks
Laser Printers
High Speed Printers
Plotters
Colour printers
High speed modem

[Star network]

Average size = 5 users

Local Area Network definition

A LAN is

A set of FUNCTIONS

Allows people to share and communicate more effectively.
Spans a single office, site or workgroup. (In that it doesn't use an external/public organisation for its connectivity).
Includes hardware and software

Practical implications and problems

Heterogeneous systems (eg. Apple, IBM)
Cabling requirements
Sharing - Drives, Files, Printers, Modems
Contingency planning
- Backup of shared devices
- Shared device maintenance
- Servers down (acceptable recovery times?)
Positioning of devices
- Printers near stations?
- Server centrally placed in a star network ?