在無線區域網路上VoIP允入控制與服務品質管理之研究

由於IEEE 802.11無線區域網路在近幾年快速發展，使用802.11 無線區域網路存取各式各樣的網際網路服務也已相當普遍。然而無線區域網路有限之頻寬以及其傳輸特性，容易因為過多使用者分享有限的傳輸速度，而造成服務品質不佳。若要在無線區域網路中提供即時性訊務，如網路電話以及多媒體串流等服務，如何管理與控制使用者的使用網路的目的與數量，提供良好的網路服務品質，是一值得探討的重要議題。本論文提出一個在無線區域網路上使用網路電話的允入控制機制，並且使用支援SNMP 網管功能的802.11無線網路基地台實現此機制。對基地台上之無線用戶端進行連線目的與數量控制，同時蒐集基地台中的網管資訊，提供網管人員即時的用戶端封包傳送數、重試次數、錯誤率等資料。此機制讓基地台專為網路電話用途，只有網路電話服務的使用者能被允許使用無線網路基地台的資源，避免其他網路服務使用者的訊務量影響網路電話服務品質。此機制也同時控制通話人數，以確保能提供網路電話使用者良好的服務品質。

關鍵字

無線區域網路；網路電話；服務品質；簡單網路管理協定；允入控制；網路管理

並列摘要

In the recent years, IEEE 802.11 Wireless LANs are widely deployed. It is popular for users to access a variety of Internet services over WLANs. Due to the limited bandwidth and wireless communication characteristic of WLANs, heavy bandwidth usage shared by many users will lead to QoS degradation, which may significantly affect real time communication services, such as IP telephony and multimedia streaming services. Therefore, it is an important issue how to provide acceptable QoS in WLANs via limiting the number of current users and controlling the usage of bandwidth. In this thesis, a call admission control scheme for VoIP (Voice over IP) over WLANs is proposed. The proposed scheme can be implemented via the SNMP support in WLAN access points (APs). Through the monitoring of associations via SNMP, the proposed scheme can realize the number of current users at an AP and can limit the number of users such that the bandwidth shared by each user is sufficient for VoIP traffic. The scheme also collects the statistics data of each VoIP call, including the number of packets delivered, packets retransmitted, and errors. For better QoS control, the proposed scheme is also designed to disallow non-VoIP applications over the specific AP providing only VoIP services, such that the QoS of the VoIP services can be guaranteed.