Configuring IP QoS mechanisms for graceful degradation of real-time services
Pitts,Jonathan
Queen Mary, University of London
Schormans,John
Queen Mary, University of London
Classical queueing theory tells us that mean delays are inversely proportional to unused capacity. For real-time traffic, this means congested network resources can cause most packets to go "out of contract". With delay and jitter bounds exceeded, delivered content is of no use to the application, resulting in sudden, catastrophic service degradation. Current QoS approaches in IP aim to prevent congestion by limiting load and using priority scheduling. In environments with heterogeneous QoS requirements, multiple application priority levels, and time varying resource capacities, such an approach is not easily scalable. This paper presents an overview of the theory to support a totally new perspective on congested shared resources. The new approach maintains both delay and jitter performance under congestion, while packet loss is gracefully degraded. We call this the BOUnded Delay IP CoS/QoS Configuration Architecture (BOUDICCA). BOUDICCA makes use of existing widely deployed IP QoS mechanisms to deliver graceful degradation for real-time services. We present analytical results for a DiffServ scenario under homogeneous and heterogeneous service congestion, and when link capacity is degraded. We quantify the performance improvements by using the ITU-T E-model to assess VoIP quality. The key benefit is that service quality can be maintained both up to and beyond normal fully loaded conditions on congested bottlenecks.
Professor Jonathan Pitts holds a Ph.D. and M.Eng. in Communications Engineering, both from Queen Mary, University of London, in the UK. Since 1994 he has been a member of academic staff in the Department of Electronic Engineering at Queen Mary, and as a full professor since 2001. In 1998 he was awarded a Royal Academy of Engineering Industrial Secondment to work with Cable & Wireless Communications, and in 2006 a short term research fellowship with British Telecom. His research interests focus on the study, and effective modelling, of communications network behaviour, and how to exploit that understanding to provide both network and service assurance. He has published over 100 papers on subjects ranging from multi-scale traffic modelling based on chaotic maps, to accelerated simulation techniques, and excess-rate queueing theory. He has also published a textbook (now in its second edition) with co-author Dr John Schormans on the subject of IP and ATM design and performance.