Understanding Aloha Protocols in Shared Networks
Aloha is like a free-for-all communication method used in Wi-Fi and other shared networks. With Aloha, multiple devices can send data whenever they want, kind of like people talking in a crowded room. However, because everyone can talk at the same time, sometimes their messages collide and become unreadable, like when two people speak over each other. This can cause data to get mixed up or lost.
Types:-
?Pure Aloha
Pure Aloha lets stations send data whenever they want. When they do, they wait for an acknowledgment. If they don't get it in time, they wait for a random period, called back-off time, before trying again. This randomness reduces the chances of collisions.
The best performance happens when all frames are the same length. When two frames collide, meaning they both try to use the channel at once, they mess each other up.
If a new frame starts just as another one finishes, both get ruined and need to be sent again.
The time when frames are most at risk is twice the length of a transmission frame.
The throughput, or efficiency, is highest when a certain number of stations try to transmit at once. This efficiency decreases as more stations try to transmit simultaneously. The maximum efficiency is about 0.184 when half the stations try to transmit at once.
Throughput =Gxe^-2G
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Slotted Aloha
Slotted Aloha was created to boost the effectiveness of Pure Aloha because Pure Aloha had a lot of collisions.
In Slotted Aloha, the channel time is split into specific time slots. Data can only be sent at the start of a slot. If a station misses its slot, it has to wait for the next one. This makes collisions less likely.
The vulnerable time now equals the time it takes to transmit a frame.
The throughput formula is slightly different, and the maximum efficiency occurs when the number of stations attempting to transmit simultaneously is 1. The highest efficiency achieved is around 0.368.
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