NORM ABRAMSON AND ALOHANET Norm Abr

NORM ABRAMSON AND ALOHANET

Norm Abramson, a PhD engineer, had a passion for surfing and an interest in packet switching. This combination of interests brought him to the University of Hawaii in
1969. Hawaii consists of many mountainous islands, making it difficult to install and operate land-based networks. When not surfing, Abramson thought about how to design a network that does packet switching over radio. The network he designed had one central host and several secondary nodes scattered over the Hawaiian Islands. The network had two channels, each using a different frequency band. The downlink channel broadcasted packets from the central host to the secondary hosts;
and the upstream channel sent packets from the secondary hosts to the central host. In addition to sending informational packets, the central host also sent on the down- stream channel an acknowledgment for each packet successfully received from the secondary hosts.
Because the secondary hosts transmitted packets in a decentralized fashion, colli- sions on the upstream channel inevitably occurred. This observation led Abramson to devise the pure ALOHA protocol, as described in this chapter. In 1970, with contin- ued funding from ARPA, Abramson connected his ALOHAnet to the ARPAnet. Abramson’s work is important not only because it was the first example of a radio packet network, but also because it inspired Bob Metcalfe. A few years later, Metcalfe modified the ALOHA protocol to create the CSMA/CD protocol and the
Ethernet LAN.