Pure ALOHA vs. Slotted ALOHA: What's the Difference?

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Key Differences

The difference between Pure ALOHA and Slotted ALOHA is that in Pure ALOHA time is continuous whereas in slotted ALOHA time is discrete.

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Pure ALOHA vs. Slotted ALOHA

In a computer system, there are sub link layer, and pure ALOHA and slotted ALOHA are random access protocol that is implemented. In the system of network protocols, the purpose of both pure ALOHA and slotted ALOHA is same that is to determine the competing station must get the next chance of accessing the multi access channel. And that is done on MAC layer that is medium access control layer. There are types of ALOHA that are pure ALOHA, and slotted ALOHA and the main difference between pure ALOHA and slotted ALOHA is that in Pure ALOHA time is continuous whereas in time slotted ALOHA time is discrete. After the invention of Pure ALOHA in 1970 slotted ALOHA was introduced by Robert that was another method to improve the capacity of Pure ALOHA. Slotted ALOHA improves all the problems that were in Pure ALOHA. In slotted ALOHA time is divided into different time slots. This time slot corresponds to the length of frames. Pure ALOHA allows the transmit of data whenever the data to send whereas Slotted ALOHA does not allow the transmit of data.  The slotted ALOHA wait till the next time slot is free. It allow each frame to be achieved with the help of special frames. The formula of slotted ALOHA is S=S*e^-G and when the throughput is maximum, that is G=1 that is 37% of total transmitted data frames.

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In Pure ALOHA time is continuous, Pure ALOHA was introduced by Norman Abramson and Pure ALOHA was introduced in the association of the University of Hawaii in 1970. Pure ALOHA has data to be sent, and it allows every station to transmit data. There is a possibility of the collision of data frames so when every station transmits the data without checking whether the channel is free or not. If the frame is free then its ok to get the frame for the transmission of data whereas if there is no free frame, then data collide. This collision cause frame overloading and the frame are destroyed. When the frame is damaged the stations, have to wait for the random amount of type, and when the frame is free, the transmission is done successful. There is a waiting time of each frame and when the waiting time is transmitting data the size of the frame should be random.  Waiting time of frames should not be the same as it can case data collisions. When frame size is uniform the throughput of pure ALOHA is maximum. There is a formula to calculate the throughput that is S- = G*e^-2G.

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Comparison Chart

BasisPure ALOHA Slotted ALOHA
MeaningIn Pure ALOHA time is continuousIn slotted ALOHA time is discrete.
IntroducedPure ALOHA was introduced by Norman Abramson and Pure ALOHA was introduced in the association of the University of Hawaii in 1970Slotted ALOHA was introduced by Robert that was another method to improve the capacity of Pure ALOHA
Formula There is a formula to calculate the throughput that is S- = G*e^-2G.The formula of slotted ALOHA is S=S*e^-G
GlobalTime is globally synchronized in Pure ALOHATime is not globally synchronized in slotted ALOHA

 What is Pure ALOHA?

In Pure ALOHA time is continuous, Pure ALOHA was introduced by Norman Abramson and Pure ALOHA was introduced in the association of the University of Hawaii in 1970. Pure ALOHA has data to be sent, and it allows every station to transmit data. There is a possibility of the collision of data frames so when every station transmits the data without checking whether the channel is free or not. If the frame is free then its ok to get the frame for the transmission of data whereas if there is no free frame, then data collide. This collision cause frame overloading and the frame are destroyed. When the frame is damaged the stations, have to wait for the random amount of type, and when the frame is free, the transmission is done successful. There is a waiting time of each frame and when the waiting time is transmitting data the size of the frame should be random.  Waiting time of frames should not be the same as it can case data collisions. When frame size is uniform, the throughput of pure ALOHA is maximum. There is a formula to calculate the throughput that is S- = G*e^-2G.

What is Slotted ALOHA?

After the invention of Pure ALOHA in 1970 slotted ALOHA was introduced by Robert that was another method to improve the capacity of Pure ALOHA. Slotted ALOHA improves all the problems that were in Pure ALOHA. In slotted ALOHA time is divided into different time slots. This time slot corresponds to the length of frames. Pure ALOHA allows the transmit of data whenever the data to send whereas Slotted ALOHA does not allow the transmit of data.  The slotted ALOHA wait till the next time slot is free. It allow each frame to be achieved with the help of special frames. The formula of slotted ALOHA is S=S*e^-G, and when the throughput is maximum, that is G=1 that is 37% of total transmitted data frames.

Key Differences

  1. In Pure ALOHA time is continuous whereas in slotted ALOHA time is discrete.
  2. Pure ALOHA was introduced by Norman Abramson and Pure ALOHA was introduced in the association of the University of Hawaii in 1970 whereas Slotted ALOHA was introduced by Robert that was another method to improve the capacity of Pure ALOHA.
  3. There is a formula to calculate the throughput that is S- = G*e^-2G whereas the formula of slotted ALOHA is S=S*e^-G.
  4. Time is globally synchronized in Pure ALOHA whereas time is not globally synchronized in slotted ALOHA

Explanatory Video