Severe congestion handling approaches in NSIS RMD domains with bi-directional reservations

Real time applications usually impose strict QoS requirements on communication networks. Several QoS frameworks have been developed and standardized to satisfy these QoS requirements. Among them is the NSIS QoS framework that is currently being standardized by the NSIS (Next Steps In Signaling) working group within IETF. Each communication node or a domain on the path that supports the NSIS QoS framework is expected to support a QoS Model (QOSM) appropriate to the characteristics of its underlying technology. One of these QOSMs is the Resource Management in Diffserv QOSM (RMD-QOSM). RMD-QOSM is based on the reduced-state QoS concept meaning that RMD-QOSM aware interior nodes maintain per Diffserv-class reservation states instead of per flow reservation states. The reduced-state operation has many advantages, among which are scalability and flexibility, but it also results in complex handling of severe congestion situations. A severe congestion may occur when a router or link fails and the traffic is rerouted through another router or link which may become severely overloaded. This paper focuses on the investigation and evaluation of severe congestion handling solutions applied in a RMD-QOSM aware domain which supports bidirectional reservations initiated and maintained by preemption aware services.