Local+Area+Network

=Local Area Network (LAN)=

A local area network (LAN) is a computer network or a group of associated devices that are linked together by a common communications line or a wireless link that operate in a nearby server. WLAN (Wireless Lan) or LAWN (Local Area Wireless Network) connects to a series of wired cables that sends out signals to the user. LAN generally covers a much smaller area compared to WAN (Wide Area Network) but provides much faster data transmission compared to a wider network service shared by millions.

The major technologies that LAN use are:

Ethernet ARCNET (Attached Resource Computer NET) Token Ring FDDI (Fiber Distributed Data Interface)

Ethernet
Robert M. Metcalfe originally named Ethernet in regards to the substance of ether (a passive light-transmitting substance) because the network itself was designed as a passive medium that could transmit data anywhere throughout the network. Ethernet’s generally use coaxial cable (copper protected cable used by many cable TV companies) as it’s transmitters. The standards used are called 10BASE-T that provide 10 megabytes per second (mps) but there are also faster Ethernets that can do 100mps, 1gps or even 10gps.

ARCNET
ARCNET are more popular among the automation industries and require either coaxial cable or fiber optic lines to run on. It generally has more expansion options and runs on a token-bus system where the LAN server always circulates empty messages on a bus and when someone uses LAN then it’ll insert a token and hence inserts a message. Once this is done it’ll automatically restart to 0.

Token Ring
In brief, the LAN runs in a circular ring or star topology:

1. Empty information frames are continuously circulated on the ring.

2. When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.

3. The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0.

4. When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.

5. The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send.

FDDI
A data transmission system that runs on fiber optic lines, FDDI use a Token Ring protocol to operate in a large geographical area (up to 200km) that could support thousands of users. FDDI are primary backbones for WAN and have two supporting rings that can each transfer at 100mps and the secondary serves as a backup in case the first ring fails.

Sources:

[|local area network], accessed on Feb. 20, 2006.

Metcalfe, Robert and Boggs. David. [|Ethernet: Distributed Packet Switching for Local Computer Networks], Accessed on Feb 20, 2006.