Basic Network Topology
Networks are made up of 2 basic components. Computers (servers, workstations) that want to share
resources between each other, and the medium (cable or wireless) that allows communication.
Network topology refers to the physical layout of computers, cable, wireless cells, and other network
equipment. Many networks use a combination of different topologies.
There are 5 basic network topologies
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Bus
Star
Mesh
Ring
wireless
Bus Topology
A Bus topology uses a single linear cable to connect multiple computers. The cable is also often called a
backbone, segment, or trunk. Mostly T-connectors are used to connect computers to the cable segment.
Commonly coaxial cable is used in a bus topology. One computer at a time can transmit but all
computers listen to all traffic on the cable, only accepting packets addressed to them. Broadcast Packets
however are accepted by all computers on the segment. A packet sent by a computer travels in both
directions on the cable, until the destination PC accepts the packet. Until the destination computer
accepts the packet the network is occupied and no other computer can send. A bus topology needs
terminators at both ends of the cable. Without these, signals will bounce up and down the cable and the
network will crash.
Bus Topology
A bus topology is a passive topology, computers on the network do not resend or regenerate data. This
means if one computer fails the entire network doesn't fail. A bus topology uses less cabling than a star
or mesh topology making it cheaper. An important feature is if 1 computer fails the network does not
fail. A bus topology is difficult to troubleshoot, normally a break in the cable, in large networks this can
be difficult to isolate. The heavier the traffic on a bus the slower the network.
A bus topology with a break in the cable.
Star Topology
In a star topology, all computers will connect through a central hub or switch. A star topology is the
most common topology and is commonly used for ethernet networks. The centralised cabling of a star
topology makes it very easy to manage. If one link in a hub goes down its very easy to isolate the
problem. If a cable breaks only the computer connected to that cable is affected. Of course if a hub or
switch completely fails then the whole network is affected, but again is easy to isolate the problem. A
star topology is easy to add or change configurations because all connections are in a central location. A
star topology is more expensive than a bus because of the additional cabling to the central location.
There is no need for termination. Only one computer can communicate at a time on a star topology.
This is the easiest solution for the home and small office network, providing fast network speeds and
easy setup. The cost of cabling has decreased over the last few years making it an attractive option.
Mesh Topology
A mesh topology provides a connection to every computer/device on the network. More comonly used
in something like a national telephone network. The mesh topology is fault tolerant becuse of the
multiple connections. If there is a break in the cable the data always has another route to take, unless of
course all the cables break at once, but not very likely. A mesh topology is very expensive because of all
the cabling involved.
Ring Topology
A ring topology is exactly that, a ring. The wire loops around all computers/devices on the network with
no beginning or end. There is no need for termination. the signal travels in 1 direction on a ring being
passed from computer to computer. Each computer checks the packet for its destination and passes it
on much like a repeater would, because of this signal degeneration is very low. Each computer has equal
communication access on a ring, providing good performance for each computer. If one computer fails
or a cable link is broken the whole network goes down (this is not the case with some newer
technologies). Trouble shooting can be difficult as isolating a problem is not always easy. Changing a
cable will disrupt the entire network.
Wireless Topology
A wireless topology uses few cable (if any) to connect systems. A wireless network is made up of
transmitters that broadcast packets using radio frequencies. The transmitter (cell) extends the radio
sphere around itself. Network devices and computers have transmitter/receiver that recieves
broadcasts from the cell and transmits back to the cell. A cell is also called a wireless access point (WAP).
The WAP is often connected to a wired network, which might be your ADSL connection. A antenna can
also be used on or near buildings. Bluetooth and infrared can be considered wireless connections but
are better suited to temporary connections such as mobile phones etc. A wireless network obviously
does not need much cabling, and troubleshooting failed components is very easy. Other devices and
structures can cause interference and blockages.