CSMA IN COMPUTER NETWORK

Carrier sense multiple access , this is a mac layer protocal
in these slides all the points explained with flow chart for batter understanding.

1. CARRIER SENSE MULTIPLE ACCESS [CSMA] PREPARED BY : MUSKAN DHAWAN YOUTUBE CHANNEL : IT Hub by Muskan Dhawan E-MAIL ID : [email protected]

2. CSMA ( carrier sense multiple access ) CSMA is media access control (MAC) Protocol . Aim : avoid collision of signals during transmission. Working : it sense or listens whether the shared channel for transmission is busy or not, and transmits if the channel is not busy . Here single cable connects multiple nodes . W orking : when a station has frames to transmit , it attempt to detect presence of the carrier signal from the other nodes connected to shared channel. If a carrier signal is detect, it implies that a transmission is in progress . the transmission waits till the ongoing transmission executes to completion , and then initiates its own transmission. Since, the nodes detect for a transmission before sending their own frames, collision of frame is reduced . Worst case : if two nodes detect an idle channel at the same time , they may simultaneously initiate transmission and signals will collide .

3. Example Muskan dhawan

4. 1 –persistent Sense the channel _ if busy , keep listening to the channel nd transmit immediately when the channel becomes idle. _ if idle , transmit a packet immediately. if collision occures _ wait a random amount of time and start o ver again. This is an aggressive transmission algorithm. Here host transmit with a probability of 1. That’s why its called 1 persistent.

5. Non persistent Sense the channel _ if busy , wait a random amount of time and sense the channel again. _ if idle , transition a packet immediately. ° if collision occures Merits Better channel utilization longer delays
reduce chance of collision Reduce efficiency Muskan dhawan

6. condition If only B becomes ready in the middle of A’s transmission _ 1- persistent : B succeed as soon as A ends . _ non persistent : B may have to wait. if B and C becomes ready in the middle of A’s transmission _ 1 – persistent: B and C collide _ Non-persistent : B and C probably do not collide

7. P-persistent CSMA Hybrid Approach This approach is between 1-persistent and non-persistent CSMA access modes. When the transmitting node is ready to transmit data ,it sense the transmission medium for idle or busy . If idle then it transmits immediately. If busy then it sense the transmission medium continuously until it becomes idle., then transmits with probability ( p). If the node doesn’t transmit (the probability of the event is 1-p) it wait until the next available time slot. If the transmission medium is not busy it transmits again with the same probability [p]. This probabilistic hold-off repeats until the frame is finally transmitted or when the medium is F ound to become busy again ( some other node has already started transmitting) then whole logic cycle repeated. P – persistent CSMA used in wi-fi .

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