Adaptive polling technique

#There are many applications in which it is desirable to collect data messages from a plurality of remote terminals. Illustrative applications include telemetering and alarm detection systems. Such applications require that a central collection station perform two basic tasks; first, determine when a remote terminal has a message to transmit and second, establish communications with that remote terminal in order to receive the transmitted message. Two general methods utilized in the prior art to accomplish the aforementioned tasks are a polling method and a probing method.

#The polling method requires the central station to address each remote terminal, collect the message if one is available thereat, and then move on to the next remote terminal. It is necessary for the central station to address every remote terminal including those who do not have any messages. Typically, the messages in the illustrative applications are very short and in lightly loaded periods, where very few or none of the stations have available messages to send, the time required for sending addresses to all the terminal stations tends to dominate the total available time.

#In the probing method, the polling station initially queries stations in groups, then probes subgroups of smaller and smaller sizes if positive acknowledgements are received from terminals in the group indicating that messages are stored thereat and eventually addresses individual terminal stations in the probed subgroups to collect the messages. In lightly loaded periods, the central station does not probe into those groups or subgroups of remote terminal stations which have no messages to send and thus sends only a limited number of queries. However, in heavily loaded periods where a substantial number of the stations have available messages to send, the polling staton sends both group and individual queries and the total polling time for both probing for acknowledgements and addressing individual terminals to collect the messages would exceed the polling time in a system using the polling method.

#In the drawings:

#FIG. 1 discloses, in block form, a multiple terminal station message collection system;

#FIGS. 2 and 3, when arranged as shown in FIG. 4, show in schematic form the various circuits which form a central polling station which polls the terminal stations in accordance with this invention; and

#The polling system shown in FIG. 1 comprises polling station 101 and a plurality of remote stations which, in this specific embodiment, number 16 and are identified by the binary numbers 0000 to 1111. Polling station 101 is interconnected with the remote stations by way of a two-way transmission line arranged to form a multiparty line. Transmission of data signals may be broadcast from polling station 101 to all the remote stations and may be transmitted from any remote station to polling station 101.

#The present invention is embodied in a message collection system wherein polling station 101 collects messages from the various remote stations as part of the collection process. Polling station 101 sends polling words to the remote stations, certain of the polling words being directed to groups of remote stations to simultaneously query these stations whether they have messages thereat. Other polling words are directed to individual remote stations to instruct the remote station to send a message thereat to the polling station.

#Each polling word comprises two portions, namely a polling level number and an address number. Each remote station is selected by an individual address number which comprises a binary number that advantageously may be identical to the identifying binary number of the remote station as seen in FIG. 1. In general, the level number of the polling word designates how many bits of the remote station address number starting with the most significant bit is to be examined by the selection apparatus at the remote station. This has the effect, as further described below, of dividing the remote stations into groups and subgroups of various sizes.