What is CSMA ?

The CSMA (Carrier sense multiple Access) protocol operates on the principle of carrier sensing. In this protocol, a station (user) listens to see the presence of transmission (carrier) on the cable and decides to act accordingly

Type of CSMA

1. Non persistent CSMA :-
In this scheme , if a station wants to transmit a frame and it finds that the channel is busy then it has to wait for fixed interval of time. After this time, it again checks the status of the channel and if the channel is free then it transmits.



2. 1- Persistent CSMA :-
In this scheme,which want to transmit,continuously monitors the channel until it is idle and then transmit immediately. The disadvantage of this strategy is that if two stations transmit simultaneously a collision takes place.

3. P-Persistent CSMA :-
The possibility of such collision and retransmissions is reduced in the P-persistent CSMA. In t his scheme, all the waiting stations are not allowed to transmit simultaneously as soon as the channel becomes idle. A station is assumed to be transmitting with a probability p.

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