A multiple access protocol used for transmitting data through a shared network is called ALOHA. In open system interconnection abbreviated as OSI model it operates in the MAC layer. Several data streams originating from multiple nodes can be transmitted from a multi-point transmission channel.
In this case all the nodes or stations present start transmitting a frame without knowing the transmission channel is idle or busy. There will not be any problem if the channel is idle. But when two frames try to transmit a frame simultaneously then there is collision and the frames will be discarded. Now as the station tries to send the same frame multiple times until it reaches successfully.
Types of ALOHA
Pure ALOHA: In this type the transmission is done continuously. Then the station which has available frames send them. Due to this there are collisions. In case of collision the sender needs to wait and try for the next time until the transmission is successful.
Slotted ALOHA: To overcome the problem of collision this scheme is used. In this case the channel is divided in a number of small intervals which are called slots. Then the frames can be sent by each sender only at the beginning of the slot, this increases the capacity and reduces the number of collisions. If more than one channel tries to transmit at the same instance in the beginning of a slot collision can still occur.
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