Key Management Mechanisms Of QoS For VoIP

Internet has been one of social communication infrastructures. IP applications grow more rapidly, real-time applications such as VoIP and Video Conference will be one of new and important incentive points. Compared to traditional resource-dedicated PSTN, IP network is resource-shared. IP-based VoIP applications are cost-efficient. Extendable service is another adanvantage of VoIP. The service of IP network is usually a best effort one which is insufficient for VoIP. VoIP has distinct traffic characteristics and behavior model, and stringent QoS requirements. So, the current IP network architecture must be enhanced by QoS management mechanisms.This dissertation reviews VoIP implementation, VoIP performance metrics and voice quality measurement firstly. Then it presents a survey on management mechanisms used for ensuring QoS for Voice-over-IP applications, and discusses mechanisms respectively in data plane and control plane. Considering the key roles of packet forwarding and admission control, it proposes a new scheduling algorithm of advisedly dropping packets for VoIP queues, and a RED-based admission control algorithm. By colligating our researches, a prototype system for VoIP QoS management called QNet is designed and implemented.The main creativities of this dissertation are explained as follows:1. A new scheduling algorithm for VoIP queues called VASA algorithm is proposed. Network congestions severely influence on the quality of VoIP. Unfortunately the current queue management mechanisms could not guarantee QoS of VoIP efficiently when the VoIP traffic is congested. VASA algorithm can advisedly drop packets during network congestions in order to reduce the delay of VoIP packet and change the model of dropping packet. By coordinating with RED, it could enable some improvement of the performance of packet forwarding effectively during network congestions as compared with RED and the FIFO scheduling. They could indirectly increase network resources by 10%. VoIP quality measurements verify its feasibility and effectiveness.2. A RED-based admission control algorithm is proposed. The connection-oriented...