IEEE 802.11 無線區域網路品質保證之柔性允入控制機制

Abstract

隨著科技的演進，無線網路傳輸速率亦逐漸成長。因此，無線多媒體溝通的需求也隨之增加。IEEE 802.11媒體存取控制機制是目前用於無線區域網路相當常見的方式。但是，此方法對於多媒體通訊並不提供訊務之品質保證(例如：音訊傳輸)。另一方面，允入控制機制也是另一種重要的方法。允入控制主要用於維持已連通知多媒體連結之品質，避免新進入之連結破壞原有的保證。在此，我們希望結合媒體存取控制與允入控制機制兩種概念，建立出一套整合性的演算法Soft-Guarantee-Based Call Admission Control (SCAC)，以提供柔性允入控制。此演算法主要著眼於提供音訊連結品質上的保證並提高整體無線空間的使用率。SCAC包含三個主要的元件：QoS-enabled Call Admission Control (Q-CAC)，Efficient Contention Control Algorithm (ECCA)，and Resource Management Database (RMDB)。以舊有連結的品質要求為基礎， Q-CAC搜尋事先建立好的資料庫(RMDB)，計算出對應的參數用以限制參與競爭的MT數量，並保證原有連結的品質需求。ECCA採用兩階段之演算法已提供音訊較佳之競入控制。透過模擬實驗結果，我們可以證明SCAC能夠提供系統事先定義之柔性保證程度(例如：99%品質保證)於音訊連結，同時提供較佳的競入控制機制給緊急的訊務。

With the advent of new broadband technologies providing higher user data rate, the wireless communication is clearly poised for rapid growth. IEEE 802.11 MAC protocol is the most common method used in Wireless LANs (WLANs) with poor QoS guarantee for higher priority traffic such as voice signaling requests. On the other way, call admission control (CAC) method is also important for maintaining the QoS guarantees of communications in AP’s polling table. In this paper, we combine the concepts of CAC and MAC to construct a complete algorithm called Soft-Guarantee-Based Call Admission Control (SCAC) method. This method focuses on supporting QoS guarantee for voice traffic. SCAC has three major components: QoS-enabled Call Admission Control (Q-CAC), Efficient Contention Control Algorithm (ECCA), and Resource Management Database (RMDB). Based on demands of MTs in AP’s polling table, Q-CAC limits the contending MTs with voice signaling requests for maintaining QoS of voice connections in AP’s polling table by searching pre-constructed RMDB. ECCA adopts two phases algorithm by improving Contention Control (CC) concept to provide better contention resolution mechanism for high priority traffic. Simulation results demonstrate that SCAC can support pre-defined soft QoS guarantee (ex: 99% QoS guarantee) for voice traffic and provide lower contending time for high priority traffic such as voice signaling traffic.