A data communications system designed to link computers and peripheral devices such as printers and
modems. LAN cabling has a limited usable distance of up to 6 miles and 10 Km and is best used within a
building or campus environment. The advantages of using a LAN is that users can share peripheral devices
connected to the LAN instead of having those devices attached to each computer. Network users can also
share information stored in the network server(s) such as databases and programs.In addition, network users
can communicate with each other via messaging or e-mail.

A local area network used to connect computers and peripheral devices (printers, modems, etc.) so they can be shared by users of the network. Originally developed by Xerox, DEC, and Intel to run at 10Mbps, Ethernet networks can now run at 100Mbps. Named after the invisible substance thought by some to fill all space and transmit electromagnetic waves, Ethernet is the most widely used networking system in the world.

Ethernet can use twisted pair, coaxial, or fiber optic cabling and BNC, RJ45, or fiber optic connectors.

The IEEE (Institute of Electrical and Electronic Engineers) created the 802.3 standard for the operation of 10 Mbps networks. There are different versions of 802.3, depending on the type of cabling used. The IEEE

standard for Thick Ethernet is 10Base5 and for Thin Ethernet is 10Base2. The standard for twisted pair Ethernet is 10BaseT and the standard for fiber optics is 10BaseFL.

Ethernet accesses data using CSMA/CD - Carrier Sense Multiple Access with Collision Detection. This method allows multiple users to access the network through a common cable. All devices attached to the network check for transmissions in progress (signals are checked not only at the start of transmission but also during transmission). If no signals are present the transmission is sent. If a signal is detected then transmission is delayed. Collision detection is applied when two or more devices transmit at the same time. In this case each device stops transmission and attempts to retransmit after waiting a certain amount of time (different for each device and determined by an algorithm). The same occurs in the event of a collision. A device knows if a collision occurred when it does not receive its own transmission back.

There are two topologies used with an Ethernet network and they are bus and star. Bus topology is used
by 10 Base5 and 10 Base2. It consists of a shared common cable with a 50ohm terminator connected to each end. Devices can be attached anywhere on the cable with the use of a T-connector. Transmission signals
are sent throughout the entire cable, however, only the device with the proper address receives the signal.
Bus topology's disadvantage is that if a break occurs anywhere in the cable the entire network connected
to it goes down. Star topology is used by 10 BaseT & 10 BaseFL and 100 BaseTX, 100 BaseT4, &
100 BaseFX. It connects workstations to a central hub via individual cables directly wired to the hub. Thus,
a break in the cable only affects the individual device connected to the hub. However, if the central hub
breaks down, then the entire network is down.

Benefits of Using Ethernet
Fast & Accurate Transmission of Data with Speeds of up to 100Mbps
Varied Cable Types - Coax, Thin Coax, UTP, and Fiber Optic
2 Topologies - Bus and Star
Compatible with more LAN devices than any other standard.

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