Integrating SIP and IEEE 802.11e to support handoff and multi-grade QoS for VoIP-over-WLAN applications

With the increasing popularity of WLANs and the growing demand for VoIP services, there is a need to guarantee QoS for VoIP calls while support as many calls as possible. Prior efforts focus on call admission control (CAC), but did not address the important handoff and physical rate adaptation issues caused by mobility and wireless channel variation. Assuming that VoIP calls can be supported by multi-grade QoS levels and that handoff and rate adaptation are possible, we show how to conduct CAC and resource management by integrating SIP and the QoS mechanisms of IEEE 802.11e together. When wireless resource is stringent, our resource management can dynamically adjust the resource distribution among existing calls by controlling their supporting codecs and packetization intervals. This not only takes care of calls in bad channel conditions, but also can accept more calls. Thus multi-grade QoS is achieved with decreased blocking rate for new calls and less dropping rate for handoff calls. In addition, we also show how to achieve early resumption of resources for handoff calls. Both analytical and simulation results are presented to evaluate the performance of the proposed schemes.