What Is The Concept Of Pure Aloha And Slotted Aloha?


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raaga Profile
raaga answered
ALOHA is a medium access protocol that was originally designed for ground based radio broadcasting however it is applicable to any system in which uncoordinated users are competing for the use of a shared channel. Pure ALOHA and slotted ALOHA are the two versions of ALOHA.

Pure ALOHA uses a very simple idea that is to let users transmit whenever they have data to send. Pure ALOHA is featured with the feedback property that enables it to listen to the channel and finds out whether the frame was destroyed. Feedback is immediate in LANs but there is a delay of 270 msec in the satellite transmission. It requires acknowledgment if listening to the channel is not possible due to some reason. It can provide a channel utilization of 18 percent that is not appealing but it gives the advantage of transmitting any time.

Slotted ALOHA divides time into discrete intervals and each interval corresponds to a frame of data. It requires users to agree on slot boundaries. It does not allow a system to transmit any time. Instead the system has to wait for the beginning if the next slot.
Anonymous Profile
Anonymous answered
Pure Aloha is a Continuous time system whereas Slotted Aloha is discrete time  system.
Anonymous Profile
Anonymous answered
Pure ALOHA doesn't check whether the channel is busy before transmission.
Slotted ALOHA send the data at the beginning of timeslot.
Anonymous Profile
Anonymous answered
Pure aloha not divided in to time .
Slotted aloha divided in to time
Anonymous Profile
Anonymous answered
Pure Aloha
Basic idea :- let user transmit whenever they have data to be sent.
-Stations does not listen to channels before transmiting.
-There will be collisions
-colliding frame will be damaged
-Sender can always find out wheather its frame was destroyed by listening to the channel
-with  a LAN ,the feedback is immediate
-with a satellite,there is a delay of 270m sec before the sender knows if the transmission was sucessful
-if listening while transmitting is not possible :need acknowledgement.
If the frame was destroyed the sender waits a random amount of time and sends it again.

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