同步頻寬計時器對FDDI網路效能的影響

Abstract

光纖分散式資料介面(Fiber Distributed Data Interface)是一使用環型 光纖為傳輸媒介，速率可達100 Mbps的高速區域網路。它使用計時環繞權 杖協定(timed token rotation protocol) 。光纖分散式資料介面的媒體 傳輸層(Media Access Control Layer, MAC Layer)提供兩種訊號流量( traffic) 傳輸模式：同步與非同步傳輸。非同步傳輸又依照傳輸的優先 權細分為八個層次。光纖分散式資料介面的效能與其作業環境的參數，例 如環型網路上的節點數、傳輸框架(frame)大小、目的權杖環繞時間( Target Token Rotation Time, TTRT)及同步頻寬計時器(ST)等有密切關 連。本論文主要是以模擬的方式，建構一個M/G/1 的等候模式，針對光纖 分散式資料介面網路的延遲(delay)及灌輸量(throughput)等效能測度作 探討。模擬的參數選定依環型網路的節點數可區分為四十五及一百兩大類 。每大類又依三種不同的 TTRT做實驗模擬。經由模擬結果的分析，我們 提出設定ST計時器的幾個參考原則(Guidelines)。最後，本研究提出一個 預測延遲時間的方法，配合ST計時器的設定參考原則，能提供網路管理者 一個有效的管理工具來調整光纖分散式資料介面的參數以提昇網路的效能 。 The Fiber Distributed Data Interface (FDDI) is a high speed local area network (HSLAN) operated at 100 Mbps using the fiber optic ring transmission medium. It uses a timed token rotation protocol. The FDDI medium access control (MAC) priority mechanism supports two classes of traffic : synchronous and asynchronous. The asynchronous class makes provision for up to eight different priority levels. The performance of FDDI is closely related to its operational parameters, such as the number of stations on the ring, the frame size, the Target Token Rotation Time (TTRT), and the Synchronous Bandwidth Timer (ST). The purpose of this paper is to analyze the delay time and throughput of the FDDI MAC protocol while both the synchronous and eight asynchronous traffic are presenting. We focus out attention on the rela- tionship between the FDDI performance and ST. A simulation model, which is based on the M/ G/1 cyclic queue service discipline, is developed. Two configurations, with 45 and 100 stations each, have been studied. From the simulation results obtained, we are able to propose several operational guidelines for setting ST. We conclude this thesis with a delay prediction procedure. This procedure, which is developed by incorporating Lagrange's form of the interpolating polynomial, can predict the mean frame delay within 1.5 percent of the simulation value. The prediction procedure in conjunction with operational guidelines provides an effect tools for tunig the FDDI network.