提供IEEE 802.11e無線區域網路服務品質保證的動態頻寬配置方法

A Dynamic Bandwidth Allocation Scheme for Supporting QoS Guarantees in IEEE 802.11e Wireless LANs

吳政翰(Jheng-Han Wu)

指導教授 ： 黃依賢 ； 黃毅然

元智大學/資訊學院/資訊工程學系/碩士(2004年)

摘要

本論文是在無線區域網路IEEE 802.11e EDCA的架構之下，針對媒體傳輸控制層提出一個動態配置頻寬的方式。在本論文中MAC層中定義兩個佇列，分別是即時性佇列及非即時性佇列。除此之外，在傳輸時定義一個Scheduled Duration，其中包含了Dedicated Period及Shared Period。在Dedicated Period中，只有即時性的資料可以存取傳輸媒介；在Shared Period中，則是即時性的資料和非即時性的資料共同競爭傳輸媒介。我們利用Queueing Theory分析我們建立的系統，數學模擬並分析即時性以及非即時性佇列間狀態的轉換情形，再根據目前狀態機率以及其狀態的轉移機率推出即時性佇列以及非即時性佇列的平均等待時間和資料遺失率。然後針對不同的網路傳輸量來動態調整Shared Period及Dedicated Period的長度以提供服務品質的需求。期望所提出之架構能夠滿足即時性資料的服務品質之需求，還能夠顧慮到非即時性資料的傳輸。最後則是在不同的Dedicated Period以及Shared Period之下，針對平均等待時間以及資料遺失率來分析網路的效能，並利用模擬來驗證所提出之數學model。

關鍵字

媒介存取控制層 ； IEEE 802.11e ； 無線區域網路 ； 排隊理論 ； 服務品質

並列摘要

This paper proposes a dynamic bandwidth allocation scheme for medium access control (MAC) layer queues for IEEE 802.11e EDCA. Two queues are defined in MAC layer: one is for real-time traffic and the other is for non real-time traffic. The transmission time is slotted and each time slot is defined as a Scheduled Duration, which includes two periods with Dedicated Period and Shared Period. The transmission medium is reserved only for real-time traffic in the Dedicated Period, and the transmission medium is shared by real-time traffic and non real-time traffic in the Shared Period. The analytical model is developed based on queueing theory to derive the state probabilities of real-time queue and non real-time queue and their transition probabilities, and the mean waiting time and loss probability of those two queues can be obtained, accordingly. The lengths of Dedicated Period and Shared Period will be dynamically adjusted based on traffic load to support QoS requirements. It is expected that our scheme not only provide the QoS of real-time traffic but also not sacrifice the non real-time traffic. The network performance of the queueing model is validated and compared by simulation in terms of mean waiting time and loss probability for different lengths of Dedicated Period and Shared Period.

並列關鍵字

MAC layer ； IEEE 802.11e ； WLANs ； Queueing theory ； QoS

參考文獻

[1] IEEE standard 802.11, ``Wireless LAN medium access control (MAC) and physical layer (PHY) specifications,'' 1999.

[6] Q. Ni et al., ``QoS issues and enhancements for IEEE 802.11 Wireless LAN," in INRIA Research Report, No. 4612, Nov. 2002.

[7] I. Aad and C. Castelluccia, ``Differentiation mechanisms for IEEE 802.11,'' in Proc. of IEEE Computer and Communications Societies, 2001.

[9] K. Kim et al., ``A wireless multimedia LAN architecture using DCF with shortened contention window for QoS provisioning,'' IEEE Communication Letter, 7(2), pp. 1291--1296, 2003.

[11] L. Romdhani et al., ``AEDCF: enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks,'' in Proc. of IEEE Wireless Communications and Networking, 2003.