Question

On an Ethernet 802.3 network, if two or more devices should happen to send data at exactly the same time there will be a data collision. Explain in detail what happens if a data collision is detected.

Answer 1

In a case of data collision, CSMA/CD takes place. Following events takes place:

1. Collision is detected on the basis of voltage change in the medium.

2. If the medium is free it is said to be on a low voltage and if there is any transmission happening then there are standard voltage values.

3. If there is any data collision, abnormal voltages are produced in the medium and hence, the collision is detected.

To avoid the collision, the binary exponential backoff mechanism is used.

How Binary exponential backoff mechanism works:

This algorithm says at i^th column collision, the system should choose a random number between 0 to 2ⁱ - 1

1st collision 0 or 1

2nd collision 0 to 3, anyone

-> If the system chooses number "0", it means, after collision system will start sensing the cable immediately

->If 1, then it means after 1-time slot system will start sensing the cable and so on.