Patent US 4,071,908

Messages are collected by a central polling station from a plurality of remote terminal stations on a multiparty line. The central polling station is arranged to initially query stations in groups, probing successively smaller size subgroups of each group if a station in the group returns an acknowledgement that it has a message and eventually addressing individual stations to collect the messages. In heavily loaded periods, when a large quantity of messages are available at the terminals, the polling station initially queries a smaller size subgroup (or in the extreme, initially addresses individual stations) while in lightly loaded periods, when few or no messages are available, the polling station initially queries a larger size group (or in the extreme, initially broadcasts a query to all of the terminals). Loading of the system is determined by measuring the duration of time required for polling and collecting all the available messages.