Browse Prior Art Database

A TOKEN-BASED METHOD FOR OVERLOAD CONTROL OF A DISPATCH CONTROLLER

IP.com Disclosure Number: IPCOM000007830D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-29
Document File: 2 page(s) / 118K

Publishing Venue

Motorola

Related People

Arieh Cimet: AUTHOR [+3]

Abstract

A dispatch controller (DAP) provides mobility management and call control for dispatch services. In general, a DAP is designed to operate at a point where a certain rate of location changes, call initia- tions, and push-to-talks can be sustained indefinitely, This is called the normal operating point (see Fig- ure 1). Unexpected events and natural variations in trahic create rates that push the DAP operating point beyond the normal point. Usually, there is a capac- ity reserve to account for these momentary traffic peaks and the DAP is able to operate up to a peak operating point (see Figure 1). However, if the traf- fic load increases beyond this peak operating point, the capacity starts degrading because the DAP can- not keep up with load and it starts losing messages.

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Mo7vRoLA Technical Developments

8

A TOKEN-BASED METHOD FOR OVERLOAD CONTROL OF A DISPATCH CONTROLLER

by Arieh Cimet, Andy Klotnia and John Vittallo

  A dispatch controller (DAP) provides mobility management and call control for dispatch services. In general, a DAP is designed to operate at a point where a certain rate of location changes, call initia- tions, and push-to-talks can be sustained indefinitely, This is called the normal operating point (see Fig- ure 1). Unexpected events and natural variations in trahic create rates that push the DAP operating point

beyond the normal point. Usually, there is a capac- ity reserve to account for these momentary traffic peaks and the DAP is able to operate up to a peak operating point (see Figure 1). However, if the traf- fic load increases beyond this peak operating point, the capacity starts degrading because the DAP can- not keep up with load and it starts losing messages.

Peak

b Traffic Load

Fig. 1 DAP operating points

  An overload control method is intended to maintain a system functioning below the peak oper- ating point under any traffic load. In the prior art, telephony switching systems have relied on two fea- tures: (a) the average system utilization can be measured or estimated, and (b) two overload con- trol levels. This overload control method works as follows. The system has a moving average estimate (AVG-UTIL) that is calculated based on utiliza- tion measurements. When AVG-UTIL approaches the peak operating point, the overload control method is triggered and the system starts rejecting all new

calls while maintaining existing calls. This control is kept in effect until the AVG-UTIL is under the normal operating point. At that point, the overload control is disengaged and new calls can be started again.

  In contrast with a telephone switch that is involved only in the call setup and teardown, a dis- patch controller is involved in call setup and tear- down and also in every push-to-talk (PTT). This implies that the typical two-level overload control method may not be adequate because the PTTs of

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170 August 1996

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Technical Developments

existing calls may still push the operating point beyond the peak. Another complication is that a mov- ing average would have to have a shorter sampling period because dispatch calls are usually much shorter than telephone calls. The result is that the overload control method would be triggered too late and after the system is alre...