整合SIP與IEEE 802.11e支援換手及提供多重品質等級的VoIP應用

Abstract

隨著無線網路技術蓬勃發展，在無線網路環境下支援網路電話的需求也隨之成長，當我們希望在有限頻寬下支援越多通話的同時，如何保障網路電話的服務品質成為一項重要的需求。 在本論文中我們探討在IEEE 802.11e無線區域網路下換手及網路電話服務品質的議題。 同時在本文中我們假設網路電話可支援多種品質等級，我們展示了如何藉由整合通話初始協定以及IEEE 802.11e下的服務品質機制來達成通話允許控制及換手的目標。我們所提出的方法依據網路的狀況對目前進行的通話做動態資源配置。其中多種品質等級是藉由改變編碼方式跟封裝的時間間隔 (PI) 來達成。結果顯示我們提出的方法有較好的頻寬使用率，降低對新進通話的阻塞率，同時也能減少換手後的通話被丟棄的機率。除此之外，我們也提出了當使用者離開無線網路基地台時，如何將原本所佔用的資源快速回收利用的方法。最後我們藉由分析及模擬的結果來驗證我們提出方法的成效。

With the increasing popularity of wireless networks and the growing demand for VoIP services, there is a need to guarantee QoS for VoIP calls while supporting as many calls as possible. This paper considers the handoff and QoS issues of VoIP calls under IEEE 802.11e WLANs. Assuming that VoIP calls can be supported by multiple levels of QoS, we show how to conduct call admission control and handoff by integrating SIP and QoS mechanisms of IEEE 802.11e. The proposed scheme is designed to dynamically adjust the resource distribution among existing calls according to the network condition. Multi-level QoS is achieved by adjusting codecs and packetization intervals of calls. The result shows better utilization of bandwidth, 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 as calls leave a QAP. Both analytical and simulation results are presented to evaluate the performance of the proposed schemes.