無線網路電話之動態負載均衡方案

Abstract

一般而言，無線網路擷取點的訊號涵蓋範圍通常會相互覆蓋，因此一無線網路用戶可能會偵測到多個無線網路擷取點並且選擇其中一個來連線以進入無線網路熱點。實驗結果顯示一個無線網路用戶通常會和訊號最強的擷取點聯繫並向其要求頻寬以便建立網路連線，然而，這種以用戶為中心的聯繫以及頻寬要求策略可能會導致擷取點間的負載不均，以致無線網路擷取點中擷取點的頻寬資源效用無法完全發揮。對於商業上部建無線網路電話系統這類必須在保證通話品質下最大化共同通話數目之無線網路電話系統而言，此一負載不均的問題將會是一個重要的議題。 本論文針對無線網路電話系統提出了一個之動態負載平衡方案，一開始網路協助的聯繫機制會建議一個用戶向負載最輕的擷取點來要求建立無線網路電話之通話。假使此用戶所有偵測到的擷取點皆負荷過載時，則本論文所提出的負載平衡方案將會啟動來進一步重新規劃正在通話的無線網路電話用戶和擷取點間的連線情形以便能騰出足夠的資源來提供新的通話要求。模擬結果說明了藉著本論文所提出的方案，無線網路電話系統通話服務要求被拒絕建立通話的機率將可大幅度地降低。

Coverage areas of WLAN access points (APs) are usually overlapped so a WLAN station (STA) might be able to find several APs to attach in a WLAN hotspot. Experimental results indicate that a WLAN STA normally associates with an AP with the maximal signal strength and requests the bandwidth of the AP for establishing network connections. However, this kind of STA-centric association and bandwidth request policy may introduce unbalance loads of APs, and the bandwidths of APs in a WLAN hotspot cannot be fully utilized. This unbalance load problem is a critical issue for the commercial deployment of voice over IP (VoIP) over WLAN (VoWLAN) service which has to maximize the number of concurrent VoWLAN sessions with Quality of Service (QoS) guarantees. In this paper, a novel dynamic load balancing scheme is proposed for a VoWLAN system. The network-assisted association policy first advices an STA to request a VoWLAN session through an AP with the minimal load. In case of the APs which the STA can attach are all overloaded, the proposed load balancing scheme further rearranges the serving VoWLAN STAs between APs in order to spare enough resources for accommodating that new request. Simulation results demonstrate that the reject rate of service requests for a VoWLAN system can be considerably reduced by employing the proposed scheme.