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.
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.
