Local Area Network (LAN)
A network of computers which covers relatively small area (as compared to the Wide Area Network) is called Local Area Network (LAN). A LAN provides networking ability to a group of computers in close proximity to each other, for example, in an office, an organisation, a school or a home.
Each individual computer on a LAN has its own CPU and with the help of this CPU the computer carries out the programs but simultaneously it is also able to access the data on other computers on LAN and the devices on LAN such as laser printers. A LAN consequently, can be connected to other LANs and to internet or any other Wide Area Network (WAN).
When two or more LANs are connected to each-other over any distance (ranging from small distance to large geographical area) through telephone lines and radio waves, such a system of LANs is called Wide Area Network (WAN).
The data can be transmitted at a very fast rate within LANs, even faster than the data transfer over a telephone line, but there is a limit to the distance that can be covered and also there is a limit on the number of computers (devices) which can be connected to a single LAN.
LANs are usually assembled with reasonably priced hardware such as Ethernet cables, network adapters and hubs. However, it is important to note that wireless LAN and other more advanced LAN hardware options also exist these days.
Types of LANs
There are different types of LANs and the following characteristics differentiate between different types of LANs:
It refers to the geometric arrangement of the devices on the network. It refers to the shape of a local area network (LAN) or other communication system.
There are four main topologies;
Here, all the devices are connected to a central cable called Bus or Backbone. Such networks are easy to install and economical for small networks. Ethernet systems utilise this bus topology.
In ring topology, all the devices are connected to each other in the shape of a close loop and consequently, each device is directly connected to two other devices (one on either side of it).
Here, the messages travel around the ring and each device reads the messages addressed to it. Such networks can cover larger distances than other types of networks because each device regenerates the messages as they pass through it. Such assemblies are expensive and difficult to install they provide high bandwidth.
Here, all the devices are connected to a central hub. Such networks are easy to install and they can be managed easily. However, since all the data passes through the central hub, the bottlenecks can occur, as a hub repeats all the information it receives and forwards the information to all the devices attached to it. For more information please refer the article on Network Hub.
This arrangement is combination of the bus topology and the star topology. Here the groups of devices arranged in star topology are connected to a linear bus (backbone) cable. In such cases, usually high bandwidth bus connects a collections of slower bandwidth star segments.
Figure-1 below depicts various topologies;
Figure-1: LAN Topologies - Various Types
[The figure above, available online at http://www.webopedia.com/TERM/T/topology.html]
Protocols are agreed-upon arrangements for transmitting the data between two devices. They form rules and encoding specifications for sending data. They determine the following;
• The type of error checking to be used
• How the sending device is going to indicate that it has finished sending a message
• How the receiving device is going to indicate that it has received a message
• Whether the network uses a peer-to-peer or client/server architecture for the data transfer
The programmers can choose the protocols from a number of different standard protocols. The computer or device must support the appropriate protocols in order to communicate with other computers/devices.
This refers to various media utilised to physically link the devices on the network such as twisted-pair wire (which is normal electrical wire), coaxial cable (type of cable used for cable television) or fiber optic (cables made out of glass-fiber). However, some networks perform without connecting the physical media at all, instead, they communicate through radio waves.
1. Network Hub
3. OSI Model