Network topology is the layout pattern (or structure)
of the interconnection of the various elements (software and hardware) of the
network.
There are two types of topologies
* The physical topology
* Logical Topology
In this
particular lesson, we will focus our attention on the physical topology
II-Physical Topology
I I-1 Definition
The physical topology refers to the physical design of
the network, its physical layout or the geometric arrangement of the nodes and
the links
There are five basic physical topologies:
*The bus topology
*
The star topology
*
The ring topology
* The mesh topology
*
The tree topology
a) The Bus topology
Diagram
As we can see from the diagram, here each node is
connected to a single cable which is the bus, also referred to as the backbone.
The T-connectors is used by computers to connect to
the main cable.
Explanation
In this network organization, any device which wants
to communicate sends the broadcast message to all the devices (through the main
cable), but only the intended receiver actually accepts and processes the
message. A terminator connected at each end of the main cable eliminates any
incoming signal to avoid the reverberation problem.
Advantages
·
It is topology
is not expensive
·
Easy to setup
Disadvantages
·
The entire
network shuts down if there is any break on the main cable
·
It is very difficult to diagnose a problem when the
network shuts down.
b) The Star Topology
Diagram
It is the most commonly used topology in the LAN. All the computers are connected at the
central point which can be a switch or a hub.
Explanation
In this network
organization, any device which wants to communicate sends the broadcast message
to the central point which will either forward it to the intended computer
(case of the switch) or to all the computers (case of hub).
Advantages
·
It very easy to setup
·
The adding, the removing or the malfunctioning of a
computer does not affect the rest of the network
·
It easy to diagnose and maintain
Disadvantages
·
If the central
point has a problem, all the computer are disconnected
·
It requires more cables and extra devices and is
therefore expensive
c) The tree topology
Diagram
This is the network pattern
that combines the characteristics of a bus and star topology.
Advantages
·
It allows for the expansion of an existing network
·
It is supported by several software and hardware
vendors
Disadvantages
·
If the backbone
line breaks, the entire segment goes down
·
It is difficult to configure and wire
d) The Ring topology
Diagram
This is a network topology whereby all devices are
connected to one another in the shape of closed loop (ring) so that each device
is directly connected to two others devices, one on either side.
Explanation
Messages flow in one direction. Since there is only
one path way between two nodes and the message is conveyed through a token
ring.
Advantages
·
The transfer of
data is fairly simple since it travels only in one direction.
·
No data collision
·
Very high transmission rates are possible
·
Extra computer can be added without any little
disturbance of the network, but it must shut down.
Disadvantages
·
If a single link fails, the entire network is
disrupted.
(This problem is solved by adding a second ring)
(This problem is solved by adding a second ring)
·
The downfall of a single node causes the downfall of
the whole network
·
Data must pass through every computer until it reaches
the destination
·
Difficult to troubleshoot
Line topology - This rare topology works
by connecting every host to the host located to the right of it. Most
networking professionals do not even regard this as an actual topology, as it
is very expensive (due to its cabling requirements) and due to the fact that it
is much more practical to connect the hosts on either end to form a ring
topology, which is much cheaper and more efficient.
Diagram
e) The Mesh topology
Diagram
It is view as
the combination of the above (bus, star, ring)
Advantages
·
If any cable fails, there are many other ways for two
nodes to communicate
·
Mesh topology are installed where fault tolerance is
important
Disadvantages
·
It is very expensive to wire up
·
It is difficult to install
