In
communication networks, a topology is a usually schematic description of the
arrangement of a network, including its nodes and connecting lines.
There are two ways of defining network
geometry:-
The physical
topology and
The logical (or signal) topology.
Basic topologies are:-
·
Bus
·
Star
·
Ring or circular
·
Mesh
·
Tree
·
Hybrid
BUS:-
In local area
networks where bus topology is used, each node is connected to a single cable.
Each computer or server is connected to the single bus cable. A signal from the
source travels in both directions to all machines connected on the bus cable
until it finds the intended recipient.
· Advantages of Bus Topology:-
· Works well for small
networks
·
Relatively
inexpensive to implement
·
Easy to add
to it.
Disadvantages of Bus
Topology:-
•
Management
costs can be high
• Potential
for congestion with network traffic.
Star:-
In local
area networks with a star topology, each network host is connected to a central
hub with a point-to-point connection. In Star topology every node (computer
workstation or any other peripheral) is connected to central node called hub or
switch.
Advantage:-
•
Good option for modern networks
•
Low startup costs
•
Easy to manage
•
Offers opportunities for expansion
•
Most popular topology in use; wide variety of
equipment available.
Disadvantages:-
•
Hub is a single point of failure
• • Requires
more cable than the bus.
Ring:-
A network
topology that is set up in a circular fashion in which data travels around the
ring in one direction and each device on the ring acts as a repeater to keep
the signal strong as it travels. Each device incorporates a receiver for the
incoming signal and a transmitter to send the data on to the next device in the
ring. The network is dependent on the ability of the signal to travel around
the ring. When a device sends data, it must travel through each device on the
ring until it reaches its destination.
Advantages
of Ring Topology:-
•Easier
to manage; easier to locate a defective node or cable problem
•Well-suited
for transmitting signals over long distances on a LAN
•Handles
high-volume network traffic
•Enables
reliable communication.
Disadvantages
of Ring Topology:-
•Expensive
•Requires
more cable and network equipment at the start
•Not
used as widely as bus topology
–Fewer equipment options
–Fewer options for expansion to high-speed
communication
- Mesh:-
A fully connected
network is a communication network in which each of the nodes is
connected to each other. In graph theory it
known as a complete graph. A fully connected network doesn't need to use switching nor broadcasting. However, its major
disadvantage is that the number of connections grows quadratically with the
number of nodes, per the formula
-
and so it is extremely impractical for large networks. A two-node network is technically a fully connected network.
-
Tree:-
This particular type of network topology is based on a hierarchy of nodes. The highest level of any tree network consists of a single, 'root' node, this node connected either a single (or, more commonly, multiple) node(s) in the level below by (a) point-to-point link(s). These lower level nodes are also connected to a single or multiple nodes in the next level down.
Advantages:-
- It is scalable Secondary nodes allow more devices to be connected to a central node.
- Point to point connection of devices.
- Having different levels of the network makes it more manageable hence easier fault identification and isolation.
Disadvantages:-
- Maintenance of the network may be an issue when the network spans a great area.
- Since it is a variation of bus topology, if the backbone fails, the entire network is crippled.
NOTE:-
definition: Tree topology is a combination of Bus and Star topology.
An example of this network could be cable TV technology. Other examples are in dynamic tree based wireless networks for military, mining and otherwise mobile applications. The Naval Postgraduate School, Monterey CA, demonstrated such tree based wireless networks for border security. In a pilot system, aerial cameras kept aloft by balloons relayed real time high resolution video to ground personnel via a dynamic self healing tree based network.
Hybrid:-
Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network
- A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub.
- A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone).
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