Browse Prior Art Database

Polling Method for Cable Television

IP.com Disclosure Number: IPCOM000050043D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Foglia, HR: AUTHOR

Abstract

In a cable television system a large number of subscribers may receive service from a central unit. The central unit polls the subscribers sequentially, and a subscriber may respond with a request for a particular service. The time delay for the polling message to travel from the central unit to a subscriber plus the time for the response of the subscriber to return to the central unit are significant, in terms of the number of message bits that the central unit could transmit during such a delay. However, the central unit can transmit additional polling messages during this delay period, only if the subscribers respond to their individual polling messages in a sequence that does not cause the responses to overlap at the central unit.

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Polling Method for Cable Television

In a cable television system a large number of subscribers may receive service from a central unit. The central unit polls the subscribers sequentially, and a subscriber may respond with a request for a particular service. The time delay for the polling message to travel from the central unit to a subscriber plus the time for the response of the subscriber to return to the central unit are significant, in terms of the number of message bits that the central unit could transmit during such a delay. However, the central unit can transmit additional polling messages during this delay period, only if the subscribers respond to their individual polling messages in a sequence that does not cause the responses to overlap at the central unit. If the subscribers were all located equally distant from the central unit, a sequence of polling messages having a total length equal to the length of the delay would produce a similar sequence of distinct response messages at the central unit, as the subscribers respond in turn. By contrast, the problem is substantially complicated in a system in which the subscribers are located at differing distances from the central unit. The drawing illustrates a polling operation that permits interleaving in such a system.

Fig. 1 shows a sequence of polling messages and a subsequent sequence of responses in a system, in which the polling signals and the polling responses are transmitted on the same line. In the upper waveform, a numbered block represents a multi-bit polling message addressed to the subscriber identified by the number. In the lower waveform of Fig. 1, the numbered blocks represent a multi-bit polling response from the identified subscriber. Thus, the spacing between the polling signal for a particular subscriber and the response for the same subscriber equals a round trip delay. In this example, subscriber 1 is the nearest subscriber, and this polling message and the associated response have a minimum spacin...