QUERY RETRIEVAL PROTOCOLS IN A BROADCAST ENVIRONMENT.

The problem of reliable and fast retrieval of responses from a duplicated database system is analyzed. A query originating at a transmitter is broadcast to all receiver sites over a satellite channel. Through time-division multiplexing the channel carries both the queries from the broadcasting transmitter and the responses to queries from the multiple receiver sites. Each receiver site has a copy of the database and is capable of responding to the broadcast queries. A family of four protocols were developed which have different performance characteristics and implementation requirements. Analytical models for all protocols, except one which is evaluated by simulation, are presented.