在IEEE802.16 WiMAX 網路中要求頻寬機制對Best Effort 連線的影響

Abstract

異質網路的排程是一個越來越流行的議題，我們可以發現有越來越多的相關文獻被提出，而在這些文獻中，作者們大多都是使用選擇傳送時間最短的路徑來做排程的動作。但是這些作者們都忽略了不同的要求頻寬機制(bandwidth request mechanism)會造成的影響。要求頻寬機制會影響上行鏈路(uplink)的頻寬分配(bandwidth allocation)，然而這些作者們僅考慮了不同網路介面的資料速率(data rate)，而沒考量要求頻寬機制的影響，如此一來，使用他們的方法並無法正確估算封包在IEEE 802.16 WiMAX網路中的傳輸時間。因此，我們研究了在IEEE 802.16 WiMAX網路中要求頻寬機制對Best Effort連線造成的影響。在此篇論文中，我們會討論在Best Effort連線上不同的要求頻寬機制，且有額外討論兩種都是以競爭(contention)為基礎的要求頻寬機制及兩種都是以揹負式(piggyback)為基礎的要求頻寬機制。從模擬的結果中，我們可以得知在網路流量大時，可使用輪詢(polling)的機制來要求頻寬；而在網路流量小時，可使用競爭(contention)機制或揹負式(piggyback)機制來要求頻寬。我們的研究結論可以幫助IEEE 802.16 WiMAX媒體存取控制(MAC)層排程機制的設計者設計出更有效率獲得頻寬的排程方式來增進系統的效能。

Heterogeneous network scheduling becomes more and more popular. There are some papers do the research of heterogeneous network scheduling, and they use the concept that choosing the interface with the shortest transmission time. However, in those papers, they didn’t consider the impact of bandwidth request mechanisms. In uplink, bandwidth request mechanisms affect the bandwidth allocation, and in those papers, they cannot use their methods to estimate the delivery time in IEEE 802.16 WiMAX networks, because they just consider the data rates of different interfaces, they didn’t consider the effects of the bandwidth request mechanisms. So we study the impacts of bandwidth request mechanisms for Best Effort (BE) traffic in IEEE 802.16 WiMAX networks. In this thesis, we discuss the different bandwidth request mechanisms on Best Effort connections, and discuss two different contention-based mechanisms and two different piggyback-based mechanisms additionally. From the simulation results, we can know the conclusion that in heavy traffic load, we should use polling mechanism; in light traffic load, we should use contention mechanism and piggyback mechanism. By our study, the conclusion may help the IEEE 802.16 WiMAX MAC layer scheduler designers to design a more efficient scheduler for requesting bandwidth to increase the system performance.