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

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ALOHA

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.

Pure 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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