Transcript Network Topoogies

Information Technology
Lecture No 3
By: Khurram Shahid
Network Topology
The way in which a number of computers are connected
together in a network is called network topology. It is the
physical layout or arrangement of computer in a network.
There five basic topologies for connecting computer in a
network.
These are:
• Bus Topology
• Ring topology
• Star topology
• Tree topology
• Mesh topology
 Bus Topology
In bus topology, the computer or network nodes are
connected to a common communication medium, called
the backbone. A special type of central wire is used as
the backbone. This central wire is called the bus. The
computers are connected to the bus. The ends of the bus
are closed with terminators. These terminators are used
to absorb signals. Bus topology is commonly used for
small and networks.
Working of Bus Topology
The sending computer attaches the address of the
destination computer with the data. It then sends this
data to the bus. All computers connected to the bus
receive the data but only that computer accepts the data
whose address matches the address attached with the
data. In this topology only one computer can send data
at a time. Therefore, the speed of a network reduces as
the number of computer attached to the bus increase.
Advantages
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It is simply and reliable for very small networks.
It is easy to install.
It requires minimum length of communication cable.
It is easy to extend as extra cable can be connected to
make a longer bus.
 A repeat can also be used to extend the length of the bus.
 If a node is out of order, it does not affect the rest of the
network.
Disadvantages
 It can support only a small number of computers. As the
number of computer increases, the network gets slower.
 It is difficult to troubleshoot a bus. A cable-break, fault in
any one computer or a loose connection may cause
breakdown of the whole network.
 Star topology
In star topology, all computers or nodes are directly
connected to a central device. The device that connects
the nodes is called hub.
Working of Star Topology
Each computer on a star network communication with
the central hub. The hub then sends data to the
destination computer or computers.
Advantages
 It is easy to modify a star network. New
computers can be added to the central hub or
any computer can be removed without affecting
the network.
 It is usually easy to troubleshoot a star network.
 If any computer in the star topology breaks
down, the network is not affected.
 Since the data rate between the central hub and
a node is relatively low, low specification twisted
pair can be used to connect the nodes to the
central hub.
Disadvantage
 If the central hub fails, the whole network breaks down.
 Star topology requires more communication cable than
any other topology.
 Star topology is very costly
 Ring topology
In ring topology, each computer or node is connected to
the next computer and the last computer is connected to
the first. Thus, a ring of computers is formed.
Working of Ring Topology
Every computer receives message from the previous
computer and transmits it to the next computer receives
the message. Since each computer re-transmits what it
receives, signal-loss does not occur.
Advantages
 All computers on the ring have equal access to the
network.
Disadvantages
 Failure of one computer can affect the whole network.
 It is difficult to troubleshoot a ring network.
 Adding or removing a computer affects the whole
network.
 Tree Topology
A tree topology combines characteristics of linear bus
and star topologies. It consists of group of starconfigured workstations connected to a linear bus. The
bus works as the backbone cable for the network.
Advantage
 Point-to-point wiring for individual segments.
 Supported by several hardware and software
manufacturers.
Disadvantage
 Overall length of each segment is limited by the type of
cabling used.
 If the backbone breaks down, the entire network goes
down.
 It is more difficult to configure and wire than other
topologies.
 Mesh Topology
In mesh topology, each device is physically
connected to every other device on the network.
Thus messages sent on a mesh network can
take any of several possible paths from source
of destination. Each device is physically
connected to every other device on the network.
This increases performance and reliability.
However the complexity and difficulty of creating
a mesh network increase as number of nodes
on the network increases.