Behaviour of three persistance method in csma
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There Are Three Different Type of CSMA Protocols
(I) I-persistent CSMA
(ii) Non- Persistent CSMA
(iii) p-persistent CSMA
(i) I-persistent CSMA
• In this method, station that wants to transmit data continuously senses the channel to check whether the channel is idle or busy.
• If the channel is busy, the station waits until it becomes idle.
• When the station detects an idle-channel, it immediately transmits the frame with probability 1. Hence it is called I-persistent CSMA.
• This method has the highest chance of collision because two or more stations may find channel to be idle at the same time and transmit their frames.
• When the collision occurs, the stations wait a random amount of time and start allover again.
(ii) Non-persistent CSMA
• In this scheme, if a station wants to transmit a frame and it finds that the channel is busy (some other station is transmitting) then it will wait for fixed interval oftime.
• After this time, it again checks the status of the channel and if the channel is.free it will transmit.
• A station that has a frame to send senses the channel.
• If the channel is idle, it sends immediately.
• If the channel is busy, it waits a random amount of time and then senses the channel again.
• In non-persistent CSMA the station does not continuously sense the channel for the purpose of capturing it when it detects the end of previous transmission.
(iii) p-persistent CSMA
• This method is used when channel has time slots such that the time slot duration is equal to or greater than the maximum propagation delay time.
• Whenever a station becomes ready to send, it senses the channel.
• If channel is busy, station waits until next slot.
• If channel is idle, it transmits with a probability p.
• With the probability q=l-p, the station then waits for the beginning of the next time slot.
• If the next slot is also idle, it either transmits or waits again with probabilities p and q.
• This process is repeated till either frame has been transmitted or another station has begun transmitting.
• In case of the transmission by another station, the station acts as though a collision has occurred and it waits a random amount of time and starts again.
Hope it helps..... thanx
(I) I-persistent CSMA
(ii) Non- Persistent CSMA
(iii) p-persistent CSMA
(i) I-persistent CSMA
• In this method, station that wants to transmit data continuously senses the channel to check whether the channel is idle or busy.
• If the channel is busy, the station waits until it becomes idle.
• When the station detects an idle-channel, it immediately transmits the frame with probability 1. Hence it is called I-persistent CSMA.
• This method has the highest chance of collision because two or more stations may find channel to be idle at the same time and transmit their frames.
• When the collision occurs, the stations wait a random amount of time and start allover again.
(ii) Non-persistent CSMA
• In this scheme, if a station wants to transmit a frame and it finds that the channel is busy (some other station is transmitting) then it will wait for fixed interval oftime.
• After this time, it again checks the status of the channel and if the channel is.free it will transmit.
• A station that has a frame to send senses the channel.
• If the channel is idle, it sends immediately.
• If the channel is busy, it waits a random amount of time and then senses the channel again.
• In non-persistent CSMA the station does not continuously sense the channel for the purpose of capturing it when it detects the end of previous transmission.
(iii) p-persistent CSMA
• This method is used when channel has time slots such that the time slot duration is equal to or greater than the maximum propagation delay time.
• Whenever a station becomes ready to send, it senses the channel.
• If channel is busy, station waits until next slot.
• If channel is idle, it transmits with a probability p.
• With the probability q=l-p, the station then waits for the beginning of the next time slot.
• If the next slot is also idle, it either transmits or waits again with probabilities p and q.
• This process is repeated till either frame has been transmitted or another station has begun transmitting.
• In case of the transmission by another station, the station acts as though a collision has occurred and it waits a random amount of time and starts again.
Hope it helps..... thanx
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