Topology is physical or logical arrangement of computer. The
physical topology of a network refers to the configuration of
cables, computers, and other peripherals.
Physical topology should not be confused with logical topology
which is the method used to pass information between
It is the geometric representation of the relationship of all the
links and linking devices i.e. nodes to each other. Depending on
the need of an organization different arrangements of
computers are available.
In mesh topology each node is
connected to every other node by direct links.
For n nodes , there would be n(n-1)/2 physical
To accommodate that many links,
every device on the network must have n-1
Every device has dedicated point to point link to
every other device.
• The use of dedicated links will increase the
number of input/output ports.
• Installation and reconfiguration are difficult in
• The hardware required to connect each other can
be prohibitively expensive.
• The cable length is much more in this topology
comparing to other.
• The use of dedicated links guaranteed that each connection can
carry its own data.
• The Mesh topology does not have traffic congestion problems.
• Point to point links make fault identification and fault isolation easy
in this topology.
• It is also robust in nature. Of one link is down, all the rest of the
network can still continue.
• When every message sent travels along dedicated line, only
intended recipient sees it. Physical boundaries prevent other users
from gaining access to messages, so we can say that there is data
• As we know that mesh topology have major drawback of
cabling that has been overcome here in star topology with a
special network device that is HUB.
• In star topology, each device has a dedicated point to point
link hub. The devices are not directly linked to each other.
• A star topology does not allow direct traffic between devices.
There devices can only communicate via the hub.
• It is less expensive than mesh topology.
• Each device needs only one link and one input port to connect it to any
number of other.
• It is easy to install and reconfigure.
• Less cabling is required.
• Moves and deletion involves only connection between the device and the
• Robustness i.e. if one link fails, only that link is affected and so helps in
easy fault identification and fault isolation.
• Hub is used to monitor link problems and by pass defective links.
• Two terminals/devices can’t interact directly
i.e. they have to go via central controller hub.
This leads to no privacy in the network.
• The network’s dependence on the main
computer is more i.e. if the central computer
(HUB) breaks down the entire network stops
• The tree topology is a variation of a star. The tree topology
requires the computer to be linked in a hierarchical way.
• Nodes in a tree are linked to a central hub that controls the
traffic to the network.
• Not every device plugs directly into the central hub. the
majority of devices connect to a secondary hub that in turn
is connected to the central hub.
• A central hub in the tree is an active hub. An active hub
contains a repeater.
• Repeater is a hardware device that regenerates the
received bit patterns before sending them out.
• The secondary hubs may be active or passive hubs.
• A passive hub provides a simple physical connection
between the attached devices.
• The packets carrying the addresses of the destination
nodes should have the complete address i.e. all the
nodes above in the hierarchy must also have to be
• Point to point wiring for individual segments.
• Supported by several hardware and software
• Overall length of each segment is limited by
the type of cabling used.
• Id the backbone line breaks, the entire
segment goes down.
• More difficult to configure and wire than
• A linear bus topology consists of a main run of cable
with a terminator at each end.
• All nodes are connected to the linear cable.
• Ethernet and Local Talk Networks use a linear bus
• This topology is a multipoint configuration. One long
cable acts as backbone to link all the devices in the
network. All nodes are connected to bus that runs
through the network.
• Drop line is a connection running between the device an
the main cable.
• A tap is a connector that either splices into the main cable.
• As a signal travels along the backbone, some of its energy is
transformed into heat.
• Signal becomes weaker and weaker when farther it has to
• There is a limit on the number of taps a bus can support
depending on the distance between those taps.
• Easy to install. Easy to connect a computer or
peripheral to linear bus. Requires less cable
• Backbone cable can be laid along the most
efficient path, then connected to the nodes by
drop line of various length.
• Only the backbone cable stretches through the
entire facility. Each drop line has to reach only as
far as the nearest point on the backbone.
• Entire network shuts down if there is a break in
the main cable.
• Terminators are required at both ends of the
• Difficult to identify the problem if the entire
network shuts down.
• Not meant to be used as a stand alone solution in
a large building.
• In a ring topology, each device has dedicated point to
point line configuration only with two devices on either
side or it.
• A signal is passed along the ring in one direction from
device to device until it reaches its destination.
• Each device in the ring incorporates a repeater. When a
device receives a signal intended for another device.
• To connect n devices in a ring topology we need n
• A ring is relatively easy to install and reconfigure, each
device is linked only to its immediate neighbours.
• To add or delete a device requires moving only two
connections. The only constraints are media and traffic
• Fault isolation is simplifies. In a ring a signal is
circulating at all times. If one device does not receive a
signal within a specified period. It can issue an alarm.
The alarm alerts the network operator of the problem
and its locations.
• Supports unidirectional traffic.
• In a simple ring, a break in the ring can disable
the entire network. This weakness can be
solved by using dual ring.