What ALOHA and What are the Types of ALOHA in Networking?


ALOHA, the earliest random access protocol and was developed at the University of Hawi in early 1970. which is designed for a wireless LAN but it can be used in any shared medium. There is a potential collision because of the shared medium.
There are two types of ALOHA’s

  1. Pure ALOHA.
  2. 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

  • 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 case of slotted aloha.


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