ALOHANET – Das erste Funknetz für den drahtlosen Internetzugang
The First Radio Network for Wireless Internet Access
The name Internet is known to nearly everyone. Available worldwide, it is a data transmission network connected to numerous host and data base computers – in reality a worldwide digital library access network containing public and private data. At no cost, host and search engines can be used to search through and interlink the data base contents. Much of the data stored ist freely accessible. Well-known services of des Internet are:
the electronic message exchange by so-calles e-mails, which are sent from a workstation to a data base of an Internet service provider; the latter in turn informs the person addressed about the arrival of the e-mail to enable him to read it via Internet when he decides to do so;
the World Wide Web, which enables a user at a workstation to search through all the available data bases of the world for self-defined key-words with the help of easily applicable software and to display the search result on the user’s screen;
the transmission of large data files and software to romote computer systems, where they are processed.
Data transmission requires either a wired or a wireless transmission network. The roots of the packet switched wired data network of the APRA (Advanced Research Projects Agency) that later became known as Internet in the early eighties go back to the late sixties.
Together with his group, Norman Abramson found and published information about a possibility for local packet based wireless Internet access via a UHF radio channel with a muliplexing rate of 56 kbs. they developed and implemented the first operational system in 1970 – the ALOHA system, which is still (in improved form) in operation at the University of Hawaii in Honolulu, U.S.A. In the network, a host in Honolulu uses a radio channel to broadcast data packets containing user data related to such types of services as those listed above and addressed to different terminals. Each terminal copies the packets addressed to it in its local input butter and processes them as if they had arrived via wired Internet.
The reverse procedure is much more complicated to carry out since the various terminals intending to transmit to the central host in Honolulu are distributed over many islands of Hawaii and the times at which they transmit cannot be coordinated. Abramson’s invention is to share the radio channel in a time-muliplexed way between terminals and to allow the terminals to transmit data packets to the host an a random-access basis, without any coordination with each other. If two or more transmissions overlap in time, the host is unable to receive any packet corecctly – during such a time period thr radio channel is in the collision state and cannot be used for transmission until the collision ends. Whenever they do not receive an acknowledgement from the host for a packet in due time, the terminals assme their packet collided and repeat the transmission. This access protocol to the radio channel was named ALOHA (i. e. „hello“).
Abramson defined the traffic performance of the ALOHA radio channel mahtematically, derived its most important parameters and proved its suitability for wireless Internet access by implementing and operating the system. His theoretical work stimulated others to start research work on random access protocols; random access protocols for different applications have since then been introduced for many other purposes.
From 1973 on he developed this technology for commercial use with geostationary satellites and established the ALOHANET, the first modern radio data network. This network used the first packet sensor, the first packet relays, the first packet radio satellite system, and the first wireless access to the Internet in the world. Today, satellite networks based on ALOHA channels for wireless Internet access are in operation worldwide, e.g. the VSAT (Very Small Aperture Terminal) Network. ALOHA channels are part of every wireless and mobile radio network, so that it is probable that the ALOHA protocol is the most widely used access protocol in the world. The protocol also paved the way for the introduction of related access protocols, e.g. those that have captured a very large market segment in wired local area networks today.
In the late aithties Abramson successfully extended his invention to the application of spread spectrum ALOHA channels, which improved the traffic capacity of the radio channels substantially. His results have also found acceptance as a standard for the third generation mobile radio system UMTS, which will improve the performance of cellular radio systems considerably and will replace the present mobile radio system GSM from 2003 on.
In view of the central significance of the ALOHA protocol for the whole of modern communication technology, Professor Norman Abramson, Ph. D., Founder and Chairman of the Board of ALOHA Networks, Inc., Professor for Information and Computer Science (1968-1995), University of Hawaii, has been selected as the winner of the Eduard Rhein Technology Award of 2000.
Prof. Dr. Bernhard Walke
RWTH Aachen University of Technology