What is slotted ALOHA in computer networks?

Aloha is a packet switching system. The time interval required to transmit one packet is called a slot. Aloha is a random access technique.

There are two ALOHA protocols as follows −

  • Pure ALOHA
  • Slotted ALOHA

Now let us see what Slotted ALOHA is −

Slotted ALOHA

The slotted ALOHA is explained below in stepwise manner −

Step 1 − Slotted ALOHA was introduced to improve the efficiency of pure ALOHA, because in pure ALOHA there is a high chance of collision.

Step 2 − In this protocol, the time of the shared channel is divided into discrete intervals called as slots.

Step 3 − The stations can send a frame only at the beginning of the slot and only one frame is sent in each slot.

Step 4 − In slotted ALOHA, if any station is not able to place the frame onto the channel at the beginning of the slot i.e. it misses the time slot then the station has to wait until the beginning of the next time slot.

Step 5 − In slotted ALOHA, there is still a possibility of collision if two stations try to send at the beginning of the same time slot.

Step 6 − The users are restricted to transmit only from the instant corresponding to the slot boundary.

The vulnerable period is only one time slot. It is shown below −

The throughput of slotted ALOHA is given by,

The Vulnerable time period is ‘1’.

Smax = 1/e
    = 0.368

Therefore, in slotted ALOHA, the channel utilization is 36 percent.

Updated on: 11-Sep-2021

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