What is congestion?
Congestion is traffic.
Interference of two or more packets .
Reasons:- Sending packets the same time.
Definition: Congestion is a situation in which number of packets in network is greater than capacity of network or channel.
Total load > Capacity of channel ,
is the main reason of congestion
Effect of congestion :-
Two main factors are affected by congestion
1) Delay versus load.
2) Throughput versus load.
When load is less than network capacity delay is permission and vice versa .
Delay depends on propagation delay and transmission delay .
propagation time , transmission time, buffer time
Congestion is directly proportional to Delay
and
Congestion is directly proportional to Load
Throughput:-
Number of packets successfully delivered is called throughput .
Throughput is inversely proportional to congestion
When less congestion all packets will be successfully delivered means high throughput.
causes of congestion :
If number of packets are same .
If buffer capacity is less .
Insufficient memory buffer .
Slow processor .
Low bandwidth (capacity ) line if channel.
Failed router or processor .
If there is excess traffic to some specific host .
Congestion control:
It refers to technique and mechanism that can either defend congestion or remove congestion .
Two main types of congestion control :
1 ) Open loop ( prevention )
2 ) Closed loop ( removal ) the collision
1) Open loop :-
1. It is either handled by source or destination .
2. Retransmission property.
3. Use of sliding window protocol .example Selectivity.
4. Use of piggy bank acknowledgement .
5. Decision of discarding policy.
2. Closed loop congestion :-
Removal of congestion
1 by using CSMA policy
2 monitoring the system for congestion .
3 dynamically increase buffer capacity
4 if congestion detect at any point inform to all routers within that path
5 dynamically decides the router or path.
