Algorithm for CSMA and Rules for CSMA/CD
Rules for CSMA/CD:
- If medium is idle, transmit, otherwise go to 2
- If the medium is busy, continue to listen until the channel is idle, then transmit immediately
- If collision is detected during transmission then transmit a brief jamming signal to assure that all station knows that there has been a collision so that stations can cease the transmission
- After transmitting the jamming signal wait for a random amount of time referred as back off then attempts transmit Again
Algorithm For CSMA:
Algorithm for CSMA are: Non-Persistent, 1-Persistent, and 2-Persistent. These are explained as following below.
(a) Non-Persistent CSMA:
If channel is not free then wait for random amount of time then sense the channel, if free then sends the data
- Transmit if medium is idle otherwise go to 2
- Wait for random amount of time and repeat (1) if medium is busy
(b) 1-Persistent CSMA:
Continuously sense the channel and when it sense that the channel is free, it transmit the data.
- If medium is idle transmit, otherwise go to 2
- Continuously keep sensing for the medium to become idle and repeat (1) if medium is busy
(c) 2-Persistent CSMA:
Sense the channel before sending the data.
- With probability “P”, the station sends its frame
- With probability 1-P, station waits for the beginning of the next time slot and check the line again:
- (i) If line is idle go to 1
- (ii) If line is busy, it act as a collision has occurred and uses the backoff algorithm
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