A topology is a generalized geometric configuration of some class of objects that join together. Topologies are the architectural “drawings” that show the overall physical configuration for a given communications system.
The different types of topologies are discussed below:
STAR TOPOLOGY:
Features:
Each node is connected by a point to point link to a central point, called as hubs, concentrators or multipoint repeaters
These central points can be passive or active
The hub may have extra features like LEDs that indicate activity and errors on each port, making it even easier to isolate problems
Advantages:
Easy to install and wire
One malfunctioning node does not affect the rest of the network
It can accommodate different wiring
Easy to add new stations as each station has its own direct cable connection to the hub.
Stations can be disconnected from the hub one at a time.
Disadvantages:
If the hub or concentrator fail, nodes attached are disabled
Depending on where the hubs are located, star networks can acquire more cable length than a linear topology
More expensive than linear bus topologies
RING TOPOLOGY:
Features:
A “pure” ring topology is a collection of separate point to point links, arranged to make a ring.
Data flows only in one direction
To send a message, a node transmits new bits onto the ring
If a node receives a message that is not addressed to it, it repeats the message without copying it
Advantages:
All stations have equal access
Data packet travel at a greater speed
Faults tolerance builds into the design
Degrade nicely under high utilization
Disadvantages:
Expensive topology
Failure of one compute may impact others
It is complex to implement and to extend the network
Data clashes can also occur if two machines send messages at the same time
MESH TOPOLOGY:
Features:
Point to point links directly connect every site to every other site
Usually built over time as new sites are added to the overall network
Used for MAN or WAN networks
The number of point to point links increases sharply with the number of locations
Advantages:
Redundant links between devices
Good security
Reliability
Easy fault identification and isolation
Disadvantages:
Each node must have an interface for every other device
Bandwidth is wasted
Limited amount of I/O ports in a computer
BUS TOPOLOGY:
Features:
A bus is a single electrical circuit to which all devices in the network are connected
Cable is terminated at each end
Wiring is normally done point to point
A faulty cable will take entire LAN down
A bus topology is a broadcast network
Advantages:
Easy to connect a computer or peripheral to a linear bus
Requires less cable length than a star topology
Simple and easy to implement and extend
No central point of failure on a bus because there is no hub
Relatively easy to install
Disadvantages:
Entire network shut down if there is a break in the main cable
Terminators are required at both ends of the backbone cable
Difficult to identify the problem if the entire network shuts down
More expensive cabling
Not very fast
Higher error probability
Maintenance cost may be higher in long run
TREE TOPOLOGY:
Features:
Also known as ‘Hierarchical topology’
Combination of bus and star topologies
Very common in large networks
Advantages:
Point to point wiring for individual segments
Supported by several hardware and software vendors
Disadvantages:
More difficult to configure and wire than other topologies
Overall length of each segment is limited by the type of cabling used
If the backbone line breaks, the entire segment goes down