UMTS Load Control with Access Class Barring

Disasters can cause extraordinary service demand by the public, while concurrently causing outages that reduce network capacity to serve the surging demand. It is imperative that services supporting disaster response management perform with minimal degradation during such events. In order to provide adequate service to special users like first responders, priority treatment mechanisms have to be developed. The 2G CDMA and GSM technologies have been augmented with priority treatment mechanisms and provide good priority service, but these benefits will be lost in the sunset of 2G technologies in the next few years. Consequently, other priority mechanisms have to be established on UMTS/3G. One of the proposed priority-treatment concepts is Access Class Barring (ACB), which is a new feature being rolled out by carriers that sheds voice and data traffic in response to extreme overloads. However, the degree to which ACB would improve voice call completion is unknown. Whether ACB would adequately improve priority service call completion probability is the topic of this study. A discrete-event simulation was performed to model extreme overload situations and predict the performance of ACB under various configurations. The simulation study found that ACB could drastically improve priority call completion probability from 12% to 69% in the most extreme overloads while allowing carriers to almost fully utilize their bandwidth with public traffic under extreme overloads.