ALOHA

1. The central features of the ALOHA network

The central features of the “pure” Aloha network are:

  • All stations use a common transfer channel. Each user transmits its packets over the common broadcast channel in a completely unsynchronized (from one user to another) manner.
  • Whenever packet transmissions overlap by any amount of time there are collisions.
  • Each packet is encoded with an error-detection code.
  • After sending a packet, the user waits for an acknowledgment (ACK) from the receiver.
  • If no ACK is received, the packet is assumed lost in a collision. It is transmitted again with a randomly selected delay.

If each individual user of a channel has a low duty cycle, the probability of a packet from one sender to interfering with a packet from another sender is small as long as the total number of users on the common channel is not too large. As the number of the users increases, the number of packet overlaps increases and the probability that a packet will be lost due to an overlap also increases.

You can continue reading of the lesson and go to the next page or you can simulate pure ALOHA network .