Guaranteeing Enterprise VoIP QoS with Novel Approach to DiffServ AF Configuration

To satisfy the low delay, low jitter performance requirements of real-time traffic such as VoIP, DiffServ EF class using priority scheduling is normally recommended. This requires limits on admissible load, configured to meet the most stringent QoS in the real-time traffic mix. To handle multiple realtime service types with heterogeneous QoS, we propose a novel alternative: DiffServ AF classes with RED queue management. Recent queue theoretic advances have demonstrated RED´s ability to control the delay distribution of inelastic traffic under congested conditions. This significantly reduces late delivery of packets at the cost of (probabilistically) dropping a greater proportion in the network. We investigated the load-quality trade-off in a DiffServ domain with both hop-based and link weight optimized OSPF routing. End-to-end delay, jitter and loss were measured for two AF classes carrying VoIP across all source-destination paths in order to compare the effects of tail- drop and RED queue management. We used the ITU-T E-model to express how these performance measures affect voice quality; results demonstrate that our novel AF configuration enables the network to carry more traffic for a given quality level, and to degrade more gracefully under severe congestion.