在ATM網路上訊務管理方法之設計

Abstract

國際電信協會(ITU-T)已經選擇非同步傳輸模式(ATM)技術來實施寬頻整合服務數位網路(B-ISDN)。 ATM網路能夠提供即時(real time)以及非即時(non-reral time)的服務給各式各樣的傳輸應用。這些應用十分廣泛，可能從有著嚴格品質需求的傳統語音服務，到簡單的電子郵件傳輸。而能否有效解決訊務管理(traffic management)上的問題，是ATM網路能否成功地被廣泛使用的一個重要議題。訊務管理所希望達成的目標包括：有效率的利用網路資源，例如頻寬(bandwidth)和緩衝區空間(buffer space)，以及提供使用者服務品質(QoS)的保證。在本論文中，我們將提出訊務排程(traffic scheduling)和緩衝區管理(buffer management)的方法，用以解決即時和非即時訊務傳輸的問題。 為了充分利用網路資源，同時提供滿意的服務品質給所有的網路使用者，必須將使用者的訊務依照其延遲(delay)及遺失(loss)的需求，分配到不同的服務類別。在本論文中，我們提出了Earliest Expected Due-time First (EEDF)排程法以及其實際硬體製作的架構來處理各個服務類別的延遲需求。此外，我們提出了藉由在訊務傳輸中即時監測封包遺失的情形來動態調整緩衝區配置的方法來處理各個服務類別的遺失需求。為了提供每一個資料流(flow)擁有延遲保證(guaranteed delay)以及傳輸量的公平性(throughput fairness)，利用per-VC queueing的架構搭配一個有效率的排程方法是必要的。我們提出了Frame-based Priority Scheduling (FBPS)排程演算法，FBPS雖然是以細胞(cell)為傳輸的基本單位，然而主要的焦點是在整個封包(packet)的執行效率。藉由有系統的分析，我們證明出FBPS演算法在延遲、所需的緩衝區空間以及傳輸公平性的界限。同時FBPS在製作上十分簡單。ATM保證框架速率服務(GFR service)，是希望能用來在ATM網路上支援TCP/IP的應用。GFR的服務是期望藉由single queue來支援所有的GFR VCs。針對GFR服務，我們提出一個Virtual Buffering Strategy (VBS)緩衝區管理方法。VBS能夠藉由有效率的分配緩衝區空間以及選擇性地丟掉封包來達到最小頻寬保證和公平分配多餘頻寬給各個GFR VC。 本篇論文中所提出的實驗數據以及結果分析將有助於能更深刻的了解我們所提出訊務管理的方法。

The International Telecommunications Union (ITU-T) has chosen ATM as the technology to implement Broadband Integrated services Digital Networks (B-ISDN). ATM networks have been designed to provide both real time and non-real time services to various applications. These applications vary from those having stringent service requirements like conversational voice, to those with simple reliability requirements like data transfer in email. The problem of traffic management has been widely recognized as critical to the development of ATM networks. The goals of traffic management are to efficiently allocate network resources including buffer space and bandwidth, and to provide the negotiated QoS guarantees to users. The main focuses of this research include scheduling and buffer management approaches in ATM networks for handling both real time and non-real time traffic. To fully utilize network resources while still providing satisfactory QoS to all network users,assigning the user's traffic into a service class with both delay and loss requirement becomes necessary. In this dissertation, the Earliest Expected Due-time First (EEDF) scheduling discipline with a feasible implementation architecture is proposed to handle the delay requirements of different service classes. Besides, a dynamic buffer allocation scheme with in-service monitoring and pushout-based cell discarding is also proposed to handle the loss requirements of various classes. In order to provide each flow with guaranteed delay and throughput fairness, a per-VC queueing architecture and an efficient scheduling algorithm become necessary. We propose a so-called Frame-based Priority Scheduling (FBPS) algorithm, which focuses on the packet-level performance while transmitting based on cells. The bounds on delay, backlog and fairness of FBPS are derived through systematic analyses. The most attractive feature of FBPS is its simplicity. The ATM GFR service is expected to be useful for TCP/IP based applications. A desirable implementation of GFR is to use a single queue for all GFR VCs. This research proposes the Virtual Buffering Strategy (VBS) for the GFR service. VBS provides minimum rate guarantees and fair sharing to VCs carrying TCP traffic by allocating buffers based on the guaranteed rate and selectively dropping packets. The simulation results and analysis in this research provide valuable insight into the proposed traffic management solutions for ATM networks.