Not meant to be used as a
stand-alone solution in a large building.
STAR
TOPOLOGY
The star topology uses a separate cable for each work station as
shown in fig.The cable connects the work station to a central device typically
a HUB. The configuration provides a more reliable network that is easily
expended. With star there is no central point of failure in the cable .if there
is a problem with the cable only the station connected to that cable is a
effected .to add more work stations simply connect another HUB
WORKING
OF STAR TOPOLOGY
Each computer in a star network communicates with the central
hub that resents the messages either to all computers (in a broad cast network)
are only to destination computer (in a switch network).
Star network maybe designed to operate in a polled mode where
each user is asked in turn .if it has any information to transmit and in case,
if it has, the communication controller will either give full attention to that
device until it has no more information to send or it will allow the device to
send part of its information ,give another device a chance and then return back
to original device.
ADVANTAGES of STAR TOPOLOGY:
-
Easily expended and modified
-
Easy to troubleshoot
-
Multiple cable types supported by hub
DISADVANTAGES of STAR TOPOLOGY:
- If hub fails then entire network will fail
- Require more cables
- May require a device to rebroadcast signals across the network
RING
TOPOLOGY
STRUCTURE of RING TOPOLOGY
In ring topology each computer is connected to the next computer
and the last computer is connected to the first computer. Thus a ring of
computers is formed as shown in figure below.
WORKING of RING TOPOLOGY :
Every computer is connected to the next computer in the ring and
each transmits what it receives from the previous computer. The messages flow
around the ring in one direction.
Some ring network do ring token passing. A short message called
token (memory area)is passed around a ring until a computer wishes to send
information to other computers. That computer modifies token, adds an
electronic address and data and send it around the ring. Each computer in
sequence receives the token and next computer until either the electronic
address matches the address of a computer
Or the token return to its origin .The receiving computer
returns a message to the sender indicating that message has been received.
ADVANTAGES of RING TOPOLOGY:
- It provides an orderly network in which every device has
access to the token and can transmit.
- It performs well under a heavy load.
DISADVANTAGES of RING TOPOLOGY
- Failure of one computer can effect the whole network .
- Difficult to troubleshoot.
- Change mode with adding or removing a device effect the
entire network.
MESH
TOPOLOGY
STRUCTURE of MESH TOPOLOGY
Mesh
Topology involve the
concept of routes. Unlike each of the previous topologies, messages sent on a
mesh network can take any of several possible paths from source to destination.
(Recall that even in a ring, although two cable paths exist, messages can only
travel in one direction.) Some WANs, most notably the Internet, employ mesh
routing.
A
mesh network in which every device connects to every other is called a full
mesh. As shown in the illustration below, partial mesh networks also exist in
which some devices connect only indirectly to others.
WORKING of MESH TOPOLOGY
For sending messages, check the cable connected into two
devices. A message is send directly from sender to receiver because each one
has individual and separate connection.
ADVANTAGES of MESH TOPOLOGY :
- Enhance for error tolerance provided by redundant links.
- Easy to troubleshoot.
DISADVANTAGES of MESH TOPOLOGY:
- Difficult to install and maintain.
- Expensive.
Hybrid Topology
A
combination of any two or more network topologies. Note 1: Instances can occur
where two basic network topologies, when connected together, can still retain
the basic network character, and therefore not be a hybrid network. For
example, a tree network connected to a tree network is still a tree network.
Therefore, a hybrid network accrues only when two basic networks are connected
and the resulting network topology fails to meet one of the basic topology
definitions. For example, two star networks connected together exhibit hybrid
network topologies. Note 2: A hybrid topology always accrues when two different
basic network topologies are connected.
