ALOHAnet

The ALOHANET was the first wireless computer network. It was based on the ALOHA protocol and joined the many islands around Hawaii with the University of Honolulu, Hawaii. Even if it is no longer in operation today, as one of the basic principles of the ALOHA protocol is based on the Ethernet.

Survey

As the ARPANET, the ALOHANET with funds from the DARPA funded. But while the ARPANET used leased telephone lines, used the ALOHANET Packet Radio. When a node ARPANET was with several other nodes via lines to communicate while the ALOHANET all the same radio frequency used, so it was necessary to identify and treat collisions on this communication medium.

ALOHANET the two radio channels are used: a broadcast channel ( 413 475 MHz) and a random access channel ( 407 350 MHz). The individual stations their data packages sent to the central computer on the latter. This confirmed the reception of each packet on the broadcast channel. Tried to send two stations at the same time, neither of the two messages came right. The host sent no confirmation, and the transmitter tried it independently after a period randomly chosen again. The chances that both transmitter again produced a collision at the next transmission attempt, were minimized.

History

The ALOHANET was developed in 1970 under the leadership of Norman Abramson at the University of Hawaii and taken in the same year in operation. It was pure research purposes.

It was the first local area network, the allowed access to a central computer via radio links. It had a data transfer rate of 9600 bit / s and joined the central computer on Oahu with seven locations on four islands. By using repeaters it was soon extended to other Hawaiian Islands. The ALOHA network has a star topology. The central computer was originally a 2100 mini computer from Hewlett -Packard, who served as a concentrator. This mini computer received the one hand, data from telex, data display terminals, other minicomputers, etc., on the other hand, he submitted this data to an IBM mainframe or on the connected data networks. Later extensions enabled, that not only the devices can access the mainframe, but also any device on the host computer to communicate with each other.

For the data transfer via radio called Terminal Control Units were developed that consisted of control logic and UHF radio.

1972, was connected via a satellite link as the first computer network to the ARPANET.