Path switching and call protection for reliable IP Telephony

Application-layer path switching systems ensure the performance and reliability of real-time applications (such as IP Telephony) by exploiting inherent redundancies in the underlying IP network. These systems monitor quality throughout an IP Telephony call, rapidly detect performance problems and, if necessary, re-direct calls around problems and congestion in the network. Under normal network load conditions, these systems can easily find a feasible alternate path and restore call quality within sub-second timeframes. However, at high network load, finding alternate paths is challenging due to inherent inaccuracies in the techniques that attempt to measure an end-to-end path's ability to accommodate additional calls. These inaccuracies may adversely impact established calls on the path and some of the calls may even oscillate back and forth between various alternate paths. In this paper, we propose some novel techniques that address these problems and ensure system stability and performance at high network load. We introduce the concept of Spatial Slow Start, which allows rapid selection of a feasible path from a large possible set. In addition, we help protect a path's established calls from other switching calls by using intelligent back-off and probationary admission control techniques. We conducted extensive simulation studies to evaluate the performance of the proposed techniques. The results indicate that our techniques significantly reduce the number of oscillations and the amount of time that calls experience poor quality.