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Adaptive Token Bus System

IP.com Disclosure Number: IPCOM000040771D
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Corr, FP: AUTHOR

Abstract

A token-bus system passes a token from station to station to give permission for data to be transmitted. This token-bus system has poor performance when only one of a large number of stations is active for significant periods of time as seen in curve a, Fig. 1. Only one packet at a time is sent and then the token is passed. This article proposes that an active one or few stations send more than one packet at a time if there is little or no activity from the other stations on the bus. In effect, each station adapts its number of packets per permission on the basis of bus activity. The IEEE Draft C, Project 802 Local Network Standards, May 17, 1982, describes a variable packet permission concept on page II-3-1. The methods proposed here are different from the 802 method. The IEEE method uses only a timer to detect activity.

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Adaptive Token Bus System

A token-bus system passes a token from station to station to give permission for data to be transmitted. This token-bus system has poor performance when only one of a large number of stations is active for significant periods of time as seen in curve a, Fig. 1.

Only one packet at a time is sent and then the token is passed. This article proposes that an active one or few stations send more than one packet at a time if there is little or no activity from the other stations on the bus. In effect, each station adapts its number of packets per permission on the basis of bus activity. The IEEE Draft C, Project 802 Local Network Standards, May 17, 1982, describes a variable packet permission concept on page II-3-1. The methods proposed here are different from the 802 method. The IEEE method uses only a timer to detect activity. The decision on how many packets to transmit is made separately per token round trip (that is, with only one active station, the IEEE approach has no way to increase the packets per permission on successive token round trips) and the IEEE method generally cannot allow a high maximum number of packets per permission because it could create long waiting times when many stations are active. In its simplest version, this article requires each station to put a unique mark (i.e., a number from 1 to 100) on the free token when it is passed after a data packet is sent by that station. If the token returns to the station with the mark unmodified, the station knows it is the only one sending data. It is now allowed to send N packets before passing the token (curve b, Fig. 1). If it again receives the token back with unmodified mark, the station can now send M packets where M is greater than N, curve c). Thus, if no other station has data to send, the sending station can send more and more data on each successive token pass. If the token returns with the number of another station, then the station r...