What is Binary Exponential Back-off Algorithm?
When two station A and B transmit data simultaneously there will be collision and when collision occurs both the stations waits for some time before retransmitting the data. The time for which they stop sending the data is called back-off time and to calculate the back-off time we use an algorithm knows as Binary Exponential Back-off Algorithm.
How Binary Exponential Back- off Algorithm(BEB) Work?
After undergoing the collision both the stations wait for random amount of time in the range of [0, (2^n)-1].
Value
of n is - the nth times they are undergoing
collision.
If a station chooses a time K which is in the range [0, (2^n)-1] then
Back-off time = K*time slot
Example 1 -
Collision occurs for 1st time then n=1 and range will be 0 to 1. Means K value will be between 0 to 1.
|
Station A |
Station B |
Remark |
|
K=0 |
K=0 |
A waits for 0 unit and B waits for 0 unit before transmitting data after collision |
|
K=0 |
K=1 |
A waits for 0 unit and B waits for 1 unit before transmitting data after collision |
|
K=1 |
K=0 |
A waits for 1 unit and B waits for 0 unit before transmitting data after collision |
|
K=1 |
K=1 |
A waits for 1 unit and B waits for 1 unit before transmitting data after collision |
Example 2 -
Collision occurs for 2nd time then n=2 and range will be 0 to 3.Means K value will be between 0 to 3.
|
Station A |
Station B |
Remark |
|
K=0 |
K=0 |
A waits for 0 unit and B waits for 0 unit before transmitting data after collision |
|
K=0 |
K=1 |
A waits for 0 unit and B waits for 1 unit before transmitting data after collision |
|
K=0 |
K=2 |
A waits for 0 unit and B waits for 2 unit before transmitting data after collision |
|
K=0 |
K=3 |
A waits for 0 unit and B waits for 3 unit before transmitting data after collision |
|
K=1 |
K=0 |
A waits for 1 unit and B waits for 0 unit before transmitting data after collision |
|
K=1 |
K=1 |
A waits for 1 unit and B waits for 1 unit before transmitting data after collision |
|
K=1 |
K=2 |
A waits for 1 unit and B waits for 2 unit before transmitting data after collision |
|
K=1 |
K=3 |
A waits for 1 unit and B waits for 3 unit before transmitting data after collision |
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