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Sunday, July 12, 2009

Quick Tech Explanation: Local Area Networks - LANs

Local Area networks, generally called LANs, are privately owned networks within a single building or campus of up to a few kilometers in size. Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist as a part of modern LANs.
The most common type of local area network is an Ethernet LAN. If you look at size of LAN's, the smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many of the larger LANs are divided into logical groups called subnets.

LANs are distinguished from other kinds of networks by three characteristics:
1. Size: LANs have a size limit and cannot expand beyond this size, essentially meaning that it is possible to plan and design for the worst case transmission time.
2. Topology: This is the geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line. In a bus network, one machine is master and is allowed to transmit. An arbitration mechanism is needed to resolve conflicts when two or more machines want to transmit simultaneously.
In ring network, each bit propgates around on its own, not waiting for the rest of the packet to which it belongs.
3. Protocols: The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.
4. Media: Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves.

Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

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