ALOHA system is known as a system in computer networking which was developed back in 1971 at the University of Hawaii. And AlOHA coordinates for arbitrating access to a shared communication network channels.
In ALOHA one of the major thing needs to be remembered is the transmission of the data. Because whenever both sides or nodes transmits the data there will be data collision. This is a one-directional transmission, If node1 is transmitting the data then node2 should receive the data.
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There are two types of ALOHA’s
- Pure ALOHA.
- Slotted ALOHA.
- Applicable to any shared transmission medium.
- When a station has a frame it sends at any time
- The station then listens for an amount of time equal to the Maximum possible round-trip propagation delay on the network plus small fixed time in requirement.
- It receives ACK.
- If not re-transmit it.
- If no ACK after repeated transmission gives up.
- Slotted ALOHA was invented to improve the efficiency of pure aloha.
- Divide the time into slots of the frame time & force the station to send only at the beginning of the time slot.
Pure ALOHA vs. slotted ALOHA
- Pure ALOHA does not require time synchronization but slotted aloha does.
- Maximum channel utilization in pure aloha is 18% whereas 37% in the case of slotted aloha.