BibTeX
@MISC{Perry13overloadcontrol,
author = {Ohad Perry and Ward Whitt},
title = {Overload Control for a System in Time-Varying Environment},
year = {2013}
}
Share
 |
 |
 |
 |
||
OpenURL
Abstract
In recent papers we considered how two large service systems that are primarily designed to operate independently, can help each other in face of unexpected overloads, due to a sudden change in the arrival rates. We proposed an overload control, which we named fixed-queue-ratio with thresholds (FQR-T), whose aim was to prevent any sharing of customers, i.e., sending customers from one class to be served in the other class ’ pool, during normal loads, and to initiate sharing automatically once a threshold is crossed, in which case the corresponding pool is considered overloaded. The goal is to keep the relation between the two queues fixed at a certain ratio, which is optimal in a deterministic “fluid” approximation, assuming a holding cost is incurred on the two queues. To avoid harmful sharing our control includes the one-way sharing rule, stipulating that sharing is allowed in only one direction at any time. In this paper we consider a more complex time-varying environment, in which the arrival rates and staffing levels are time dependent, so that the system may fluctuate between periods of various loads, with overloads possible in either direction. We show that FQR-T needs to be modified to account for these more complex settings, since it may be slow to react to the changing environment, and may even cause sever fluctuations once the arrival rates return to normal after an overload incident. Our new control, FQR with activation-and-release thresholds (FQR-ART) is designed to automatically respond to changes in the environment by initiating sharing in the right direction quickly, if that is needed, while avoiding harmful phenomenons, such as congestion collapse and severe oscillations during normal loads. A novel fluid approximation, described implicitly via an ordinary-differential equation (ODE) is developed, as well as an efficient algorithm to solve that ODE. 1
Keyphrases
overload control arrival rate time-varying environment normal load congestion collapse sudden change complex setting sever fluctuation large service system one-way sharing rule novel fluid approximation corresponding pool overload incident various load deterministic fluid approximation staffing level new control severe oscillation efficient algorithm activation-and-release threshold right direction class pool ordinary-differential equation certain ratio recent paper unexpected overload complex time-varying environment harmful phenomenon
