LOCAL AREA NETWORK (LAN)
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. |
Ethernet
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.
TOPOLOGIES
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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