Stochastic Systems
- Stoch. Syst.
- Volume 6, Number 1 (2016), 132-210.
Chattering and congestion collapse in an overload switching control
Ohad Perry and Ward Whitt
Abstract
Routing mechanisms for stochastic networks are often designed to produce state space collapse (SSC) in a heavy-traffic limit, i.e., to confine the limiting process to a lower-dimensional subset of its full state space. In a fluid limit, a control producing asymptotic SSC corresponds to an ideal sliding mode control that forces the fluid trajectories to a lower-dimensional sliding manifold. Within deterministic dynamical systems theory, it is well known that sliding-mode controls can cause the system to chatter back and forth along the sliding manifold due to delays in activation of the control. For the prelimit stochastic system, chattering implies fluid-scaled fluctuations that are larger than typical stochastic fluctuations.
In this paper we show that chattering can occur in the fluid limit of a controlled stochastic network when inappropriate control parameters are used. The model has two large service pools operating under the fixed-queue-ratio with activation and release thresholds (FQR-ART) overload control which we proposed in a recent paper. The FQR-ART control is designed to produce asymptotic SSC by automatically activating sharing (sending some customers from one class to the other service pool) once an overload occurs. We have previously shown that this control is effective and robust, even if the service rates are less for the other shared customers, when the control parameters are chosen properly. We now show that, if the control parameters are not chosen properly, then delays in activating and releasing the control can cause chattering with large oscillations in the fluid limit. In turn, these fluid-scaled fluctuations lead to severe congestion, even when the arrival rates are smaller than the potential total service rate in the system, a phenomenon referred to as congestion collapse. We show that the fluid limit can be a bi-stable switching system possessing a unique nontrivial periodic equilibrium, in addition to a unique stationary point.
Article information
Source
Stoch. Syst., Volume 6, Number 1 (2016), 132-210.
Dates
Received: July 2015
First available in Project Euclid: 16 November 2016
Permanent link to this document
https://projecteuclid.org/euclid.ssy/1479287407
Digital Object Identifier
doi:10.1214/15-SSY187
Mathematical Reviews number (MathSciNet)
MR3580999
Zentralblatt MATH identifier
1356.60155
Subjects
Primary: 60K25: Queueing theory [See also 68M20, 90B22] 34C25: Periodic solutions 34C55: Hysteresis
Secondary: 60F1f7 37G15: Bifurcations of limit cycles and periodic orbits
Keywords
Stochastic networks fluid models overload control congestion collapse switching dynamical systems bi-stability periodicity
Citation
Perry, Ohad; Whitt, Ward. Chattering and congestion collapse in an overload switching control. Stoch. Syst. 6 (2016), no. 1, 132--210. doi:10.1214/15-SSY187. https://projecteuclid.org/euclid.ssy/1479287407
