IEEE 802.16j無線網路中TCP之動態頻寬分配研究

Abstract

TCP應用是目前互聯網最廣為流傳的。IEEE 802.16 制定了不同應用的排序服務，但沒有TCP應用。 雖然TCP應用一般被歸類為盡全力傳送服務(best-effort)，但TCP效能非常受延遲和封包的遺失影響。因此，如何在IEEE 802.16j無線網路中作頻寬分配顯得十分重要。本論文探討不當頻寬分配對TCP的影響，並利用asymmetry ratio和IEEE 802.16j無線網路的特性提出一個動態頻寬分配的方法。這個方法會按照目前的網路狀況調整頻寬。我們利用ns2模擬其效能，結果顯示我們提出的方法，比其他固定頻寬分配，提供較高的網路吞吐量和公平性。

TCP based applications are the most popular Internet applications. IEEE 802.16 has specified the scheduling service for real-time and variable rate applications but not TCP based best-effort applications. Although such TCP applications are typically classified as ‘best-effort’, TCP performance is indeed very sensitive to delay and packet loss. Therefore, bandwidth allocation for enhancing TCP applications performance in IEEE 802.16j networks with relay stations is particularly interesting. We investigate the impact of improper bandwidth allocation on the performance of TCP. By considering the asymmetry ratio for TCP and the characteristics of IEEE 802.16j network, we propose an adaptive bandwidth allocation scheme which adjusts the bandwidth allocation according to the current traffic profile. The performance of our scheme is validated via ns-2 simulations. The results show that our scheme outperforms static allocation in terms of higher aggregate throughput and reasonable fairness among individual flows.