Differences between Pure and Slotted Aloha

Prerequisite – Computer Network | Multiple Access Protocols
Aloha is the type of Random access protocol, It have two types one is Pure Aloha and another is Slotted Aloha.
In Pure Aloha, Stations transmit whenever data is available at arbitrary times and Colliding frames are destroyed. While In Slotted aloha, A station is required to wait for the beginning of the next slot to transmit. vulnerable period is halved as opposed to pure Aloha.

Now, we shall see the difference between these Protocols:

S.NO Pure Aloha Slotted Aloha
1. In this aloha, any station can transmit the data at any time. In this, any station can transmit the data at the beginning of any time slot.
2. In this, The time is continuous and not globally synchronized. In this, The time is discrete and globally synchronized.
3. Vulnerable time for pure aloha
= 2 x Tt
Vulnerable time for Slotted aloha
= Tt
4. In Pure Aloha, Probability of successful transmission of data packet

= G x e-2G
In Slotted Aloha, Probability of successful transmission of data packet

= G x e-G
5. In pure aloha, Maximum efficiency

= 18.4%
In slotted aloha, Maximum efficiency

= 36.8%
6. Pure aloha doesn’t reduces the number of collisions to half. Slotted aloha reduces the number of collisions to half and doubles the efficiency of pure aloha.



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