Configuring IP QoS Mechanisms for Graceful Degradation of Real-Time Services

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