QoS provisioning for VoIP over wireless local area networks

Abstract

With proliferation of the IEEE 802.11 WLAN and the emerging 802.11n standard, the WLAN is poised as a promising ubiquitous networking technology to support VoIP services, which is gaining popularity due to their high cost efficiency. However, the 802.11 WLAN is not designed to support delay sensitive traffic such as VoIP. This problem is magnified during a handover as user roam the WLAN network resulting in excessive handover latency and consequently packet loss. In addition, a 802.11 WLAN handover process is predominantly based on the physical layer detection without QoS considerations. This often causes overloading of access points and consequently all its associated connections would suffer from high delay, resulting in unacceptable QoS for the VoIP services. The former can be resolved by reducing handover latency to achieve seamless handover and the latter can be mitigated by employing link layer detection in the 802.11 WLAN handover process and having an appropriate admission control scheme. In this paper, we proposed an integrated load balancing scheme incorporating (i) QoS-based fast handover to support seamless handover by eliminating both detection and scanning phases from the 802.11 WLAN handover process; and (ii) soft admission control to protect QoS of existing voice connections when resources are low. This synergy guarantees service QoS during and after handover respectively. Simulations showed that our proposed integrated load balancing scheme is capable of providing seamless handover and QoS enhancements in terms of increased throughput, reduced packet loss and bounded delay when considering heterogeneous voice traffic of different packetization intervals. Particularly, our proposed scheme effectuate QoS balance of both delay and throughput which jointly optimize overall system utilization.