時槽式光叢集交換環中波長分配與訊務控制

Abstract

光叢集交換(Optical Burst Switching)環主要是設計應用於高速的都會型區域網路，並希望能支援的多種類型的服務。在光叢集交換環中，頻寬利用率、公平性、和穩定性都是很重要的議題。在本篇論文中，我們提出了一個波長分配與訊務控制(WATC)的方案來達成上述的考量。系統採用了預約的機制來避免時槽式系統中資料的碰撞，而且為了減少光電之間的轉換，每個節點中都沒有過境緩衝器。首先，排程器會依據入口緩衝器中佇列的權重來分配頻寬，然後由波長分配器(WA)決定適合的位置。波長分配器會適時地調整將要產生的資料叢集的大小，藉此有效利用空隙並提升頻寬利用率。另一方面，為了減輕一個下游節點可能遭受到頻寬挨餓的問題，一個乏晰保護性預約產生器(FPRG)會參考過境訊務的情況，動態地預留一些頻寬給入境的聲音與影像訊務。然後，公平流速產生器(FRG)再根據剩餘的頻寬產生一個評估過的公平流速，並由訊務控制器(TC)決定出最終宣傳的公平流速來規範上游的節點。模擬的結果顯示所提出的方案在波長分配的表現上有較高的頻寬利用率。在訊務控制方面，它也能使頻寬的使用達到公平。由於觀察窗口的應用，收斂時間可以比DBA縮短許多。波長分配與訊務控制的方案在各種不同的網路情景下都能展現出它穩定性。因此，它不失為一個可用在光叢集交換環的不錯方案。

The optical burst switching (OBS) ring network is mainly designed for high-speed metropolitan area network, which is expected to support many kinds of services. In the OBS rings, the issues of bandwidth utilization, service differentiation, fairness, and stability are important. In this thesis, the wavelength assignment and traffic control (WATC) scheme is proposed to achieve these considerations. The reservation mechanism is adopted to avoid burst collisions in the time-slot based system, and no transit buffers are deployed at each node for the reason of bypassing the traffic directly. The wavelength assigner (WA) cooperates with the scheduler to generate and then transmit data at the determined position, thereby increasing the bandwidth utilization and supporting service differentiation. In order to alleviate the bandwidth starvation problem a downstream node may suffer from, a fuzzy protective reservation generator (FPRG) preserves some bandwidth for ingress voice and video traffic referring to the network conditions. Afterwards, the fair rate generator (FRG) produces an estimated fair rate, and the traffic controller (TC) determines the advertised fair rate which regulates the upstream node. Since the observation window is applied, the convergence time is reduced. Besides, the WATC scheme shows stability in different kinds of network scenarios. The simulation results also show that the bandwidth utilization is high. Consequently, it is concluded that the WATC scheme is promising for the OBS rings.