Browse Prior Art Database

Contention Resolution in an Overlap Poll Communication System

IP.com Disclosure Number: IPCOM000088107D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 5 page(s) / 71K

Publishing Venue

IBM

Related People

Callender, GS: AUTHOR

Abstract

This article sets forth a method of resolving contention that may occur between two or more remote terminals communicating with a central station in a communication system when those terminals have been polled and granted access to the communication system by means of an overlap polling technique. An overlap polling or simultaneous polling method is one in which a large number of remote terminals which may have traffic to send to the central station are polled to give them access to the communication system or authority to transmit. They are polled contiguously, one after another, and without waiting for each individual terminal which may have traffic to respond before polling the next terminal.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 24% of the total text.

Page 1 of 5

Contention Resolution in an Overlap Poll Communication System

This article sets forth a method of resolving contention that may occur between two or more remote terminals communicating with a central station in a communication system when those terminals have been polled and granted access to the communication system by means of an overlap polling technique. An overlap polling or simultaneous polling method is one in which a large number of remote terminals which may have traffic to send to the central station are polled to give them access to the communication system or authority to transmit. They are polled contiguously, one after another, and without waiting for each individual terminal which may have traffic to respond before polling the next terminal. With this type of polling technique, contention for the use of the input channel between two or more such terminals having input traffic invited may occur.

Several types of contention may occur. Contention may occur during the header sequence by which a sending terminal identifies itself as the source of a message; contention may occur during the text portion of an input message; and noise may occur on the inbound channel which acts like contention with an otherwise clean transmission from a single terminal.

The received data line into the central station is held in a hold condition so long as no incoming signal is received at the central. For purposes of this description, it will be assumed that a radio communication system is utilized, although hard wire, television or other types of electronic communication systems may utilize the overlap polling method described.

The central station has means which indicate to an operational microcoded program within the control unit at the central station whenever the first transition occurs on the incoming data line from a hold condition to a mark condition. This indicates the start of a signal reception by the central. The mark condition is interpreted as the beginning of a data transmission from a remote terminal responding to a poll signal previously sent by the central. Some method of resolving contention must exist, as is evident from the above description.

As the overlap polling sequence is initiated on the transmission channel outbound from the central station, it utilizes a stored microcode routine which contains the addresses of the consecutive terminals to be polled in a polling list. The overlap polling sequence microcode routine also activates a receiving microcode routine which acts in a manner subservient to the transmission routine at the central during the first part of the polling sequence. The poll transmitting sequence routine constructs a list in memory of each terminal address as it is polled. Each terminal address in the list remains there so long as it is in contention with other terminal addresses polled. The transmission microcode routine also maintains two pointers to various lists constructed during the poll sequ...