Network topology are the
physical layout of the network that the locations of
the computers and how the cable is run between them.
It is important to use the right topology. Each topology
has its own strengths and weakness.
A bus topology connects computers along a single or
more cable to connect linearly as figure
1. A network
that uses a bus topology is referred to as a "bus
network" which was the original form of Ethernet
networks. Ethernet 10Base2 (also known as thinnet) is
used for bus topology.
Figure 1: Bus Topology.
Bus topology is the cheapest way of connecting computers
to form a workgroup or departmental LAN, but it has
the disadvantage that a single loose connection or cable
break can bring down the entire LAN
Termination is important issue in bus networks. The
electrical signal from a transmitting computer is free
to travel the entire length of the cable. Without the
termination, when the signal reaches the end of the
wire, it bounces back and travels back up the wire.
When a signal echoes back and forth along an unterminated
bus, it is called ringing. The terminators absorb the
electrical energy and stop the reflections.
Advantages of the bus
Bus is easy
to use and understand and
inexpensive simple network
It is easy to extend a network by adding cable with
a repeater that boosts the signal and allows it to travel
a longer distance.
Disadvantages are following:
A bus topology becomes slow by heavy network traffic
with a lot of computer because networks do not coordinate
with each other to reserve times to transmit.
It is difficult
to troubleshoot a bus because a cable break or loose
connector will cause reflections and bring down the
A star topology links the computers by individual cables
to a central unit,
usually a hub as in figure
2. When a computer or other networking
component transmits a signal to the network, the signal
travels to the hub. Then, the hub forwards the signal
simultaneously to all other components connected to
the hub. Ethernet 10BaseT
is a network based on the star topology. Star topology
is the most popular
way to connect computers in a workgroup or departmental
Figure 2: Star topology
Advantages of star
topology are such as:
The failure of a single computer or cable doesn't
bring down the entire network.
The centralized networking equipment can reduce costs
in the long run by making network management much easier.
It allows several cable types in same network with a
hub that can accommodate multiple
Disadvantages of star
topology are such as:
Failure of the central hub causes the whole network
It is slightly more expensive than using bus topology.
A ring topology connects the computers along a single
path whose ends are joined to form a circle as figure
3. The circle might be logical only
but the physical arrangement of the cabling might be
similar to star topology, with a hub or concentrator
at the center. The ring topology is commonly used in
token ring networks that the ring of a token ring network
is concentrated inside a device called a Multistation
Access Unit (MAU) and Fiber
Distributed Data Interface (FDDI) networks
that the ring in this case is both a physical and logical
ring and usually runs around a campus or collection
of buildings to form a high-speed backbone network.
Figure 3: Ring topology
One computer cannot monopolize the network.
It continue to function after capacity is exceeded but
the speed will be slow.
Failure of one computer can affect the whole network.
It is difficult to troubleshoot.
Adding and removing computers disrupts the network.
|Daniel L. Grigore
Computer Software Engineer
Programmer at Lahitech.com