Overview#
ALOHA for our purposes is about the ALOHA Network ProtocolThe version of the protocol (now called "Pure ALOHA", and the one implemented in ALOHAnet
) was quite simple:
- If you have data to send, send the data
- If, while you are transmitting data, you receive any data from another station, there has been a message collision. All transmitting stations will need to try resending "later".
Note that the first step implies that Pure ALOHA does not check whether the channel is busy before transmitting. Since collisions can occur and data may have to be sent again, ALOHA cannot use 100% of the capacity of the communications Channel. How long a station waits until it transmits, and the likelihood a collision occurs are interrelated, and both affect how efficiently the channel can be used. This means that the concept of "transmit later" is a critical aspect: the quality of the backoff scheme chosen significantly influences the efficiency of the protocol, the ultimate channel capacity, and the predictability of its behavior.
To assess Pure ALOHA, there is a need to predict its throughput, the rate of (successful) transmission of Frames.