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Contention Reduction Technique in a Contention Response Terminal System

IP.com Disclosure Number: IPCOM000087758D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Brown, JR: AUTHOR [+2]

Abstract

A polling system for a central communications station, for example a police headquarters office, and a plurality of remote terminals communicating with the central office via radio link facilities can be constructed using presently available systems for two-way radio communication. In order to implement the orderly passage of data to and from the central and any remote terminal, for example, located in a mobile police car, it is necessary that the radio link traffic be managed to prevent interference with the passage of data. Polling techniques have been developed by which usage of the radio link by any remote terminal is controlled by access signals granted by the central station.

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Contention Reduction Technique in a Contention Response Terminal System

A polling system for a central communications station, for example a police headquarters office, and a plurality of remote terminals communicating with the central office via radio link facilities can be constructed using presently available systems for two-way radio communication. In order to implement the orderly passage of data to and from the central and any remote terminal, for example, located in a mobile police car, it is necessary that the radio link traffic be managed to prevent interference with the passage of data. Polling techniques have been developed by which usage of the radio link by any remote terminal is controlled by access signals granted by the central station. This technique is slow and cumbersome and results in potentially great delays when more than one remote terminal has traffic that it wishes to send or inquiries that it wishes to make of the central.

A polling technique has been developed in which a large segment of the population of possible terminals having traffic to send can be virtually simultaneously granted access to the radio link. If more than one such remote terminal has actual traffic to send, contention for the usage of the radio link, with inevitable garbling of the messages involved, will occur. However, there is a finite probability that contention will not occur so that the overlapped or simultaneous polling of numerous stations is an economical and viable technique for a large majority of cases. In those cases where contention actually occurs, it is necessary to have link management techniques to eliminate or reduce the occurrence of contention.

This article describes a technique that can reduce the likelihood of contention and improve the system response time in granting access and service to each individual station when an overlap, simultaneous polling method, as discussed above, is utilized.

Within a normal system comprising at least one central station and numerous remote stations, there will be stations which, because of their function or task, will have less input traffic than others. The present contention reduction technique takes advantage of this fact to eliminate direct contention of remote terminals that have been identified as heavy input traffic terminals and, thereby, to minimize the probability of contention.

Initially, all terminal addresses (TAs) are assigned to a single polling queue. This will be referred to as the B segment and will be polled by the central station in the overlap polling technique beginning with the start of this queue and proceeding in a sequential manner through the list of terminals in the queue. As terminals or remote stations respond with input to their poll address access granting signals, their TAs are removed from the B segment and placed in an active queue, which will be referred to as the A segment. A limit on the number of TAs that can reside within the A segment is d...