ATM網路以虛擬計時為基礎的擁塞控制

Abstract

由於硬體技術的快速發展，使得我們可以整合許多原本由特定網路所提供 的服務，並進而支援日益普遍的多媒體服務。寬頻整體服務數位網路可以 提供使用者一個共通的網路界面並降低網路的建構成本。然而，多媒體服 務的訊務特性差異非常大，同時又必須滿足及時的要求，因此如何有效率 地滿足使用者所要求的服務品質並提高網路的使用量是目前ATM網路擁塞 控制的主要目標。最近有許多已發表的研究提出有關ATM網路擁塞控制的 方法，但是其中大部分不是沒有提出實用的演算法就是缺乏效率與彈性。 在本論文中，我們提出一個以虛擬計時為基礎的擁塞控制，除了保存了虛 擬計時演算法所具有的效率與彈性等特點之外，針對其無法確保延遲時間 上限的缺點，我們也提出了解決的方法。經由實際的模擬結果顯示出此一 擁塞控制法能有效地確保延遲時間的上限，並且在訊息包遺失率、佇列長 度、流通量等也能有預期的表現。 Owing to the rapid development of hardware, we are able to integrate services which are provided by dedicated networks at the old days and to provide the more popular multimedia services. In Broadband Integrate Service Digital Network (B- ISDN), a universal network interface can be provided to users. In this the construction cost of networks can be reduced. However, the traffic characteristics of multimedia services vary dramastically. Besides, the real time constraint of services has to be met. It has been the main goal of efficient congestion control for Asynchronous Transfer Mode (ATM) network to satisfy the Quality of Service (QOS) requested by users and maximize the utilization of network. A number of works on congestion control for ATM network have been published recently. However, they are either without practical algorithm or lack of flexibility and efficiency. In this thesis, we propose a virtual clock based congestion control. In addition to reserving the features of virtual clock algorithm such as efficiency and flexibility, we propose a method to solve the unbounded delay problem. It is shown by simulation that our scheme is able to bound the end-to-end delay and to perform as expected at other aspects like cell loss rate, queue length, throughput.