ALOHAnet

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

Overview

Like the ARPANET , the ALOHAnet was financed with funds from DARPA . But while the ARPANET was using rented phone lines, the ALOHAnet was using packet radio . With the ARPANET, one node could communicate with several other nodes via lines, while with the ALOHAnet they all used the same radio frequency, which made it necessary to detect and deal with collisions on this communication medium.

Two radio channels were used with ALOHAnet: a broadcast channel (413.475 MHz) and a random access channel (407.350 MHz). On the latter, the individual stations send their data packets to the central computer. This confirmed receipt of every packet on the broadcast channel. If two stations tried to send at the same time, neither of the two messages arrived correctly. The central computer did not send an acknowledgment and the senders tried again independently of one another after a randomly chosen period of time. This minimizes the chances of both transmitters generating a collision again the next time they attempt to transmit.

history

The ALOHAnet was developed in 1970 under the direction of Norman Abramson at the University of Hawaii and put into operation in the same year. It was used for research purposes only.

It was the first local network that made it possible to access a central computer via radio links. It had a data transfer rate of 9600 bit / s and connected the central computer on the island of Oahu with seven locations on four islands. It was soon expanded to other Hawaiian islands through the use of repeaters . The ALOHA network has a star-shaped topology. The central computer was originally a 2100 minicomputer from Hewlett-Packard , which as a concentrator acted. This mini-computer received the one hand, data of teleprinters , data display terminals , minicomputers, etc. other, on the other hand it transmitted the data to a mainframe of IBM or to the connected data networks. Later expansions made it possible not only for the end devices to access the mainframe, but also for any end devices to communicate with each other via the central computer.

So-called Terminal Control Units were developed for data transmission via radio, which consisted of control logic and UHF radio equipment.

In 1972 it was the first computer network to be connected to the ARPANET via a satellite link .

The ALOHAnet was operated until 1976.

Web links

Individual evidence

  1. ^ Franklin F. Kuo: Computer Networks - The ALOHA System. (PDF; 408 KB) In: nvlpubs.nist.gov. August 11, 1981, p. 5 , accessed February 12, 2016 .