Pure ALOHA

In 1970 Norman Abramson devised the ALOHA network at the University of Hawaii.

Pure ALOHA uses a contention based protocol:

• Users transmit whenever they wish.
• Users detect their own collisions.
• After a collision, a user 'backs-off' for a random time period and then retransmits.

What are our expectations for throughput of this approach?

• Infinite number of users each thinking and sending.
• Generation of packets is a Poisson distribution, with mean S. Here, S = number of packets generated per packet time.

If S > 1 we have chaos.
If 0 < S < 1 we get acceptable throughput.

Analysis can show the best possible utilization of 18.38%.