All-IP 網路上服務品質及TCP 效能之研究

Abstract

整合型All-IP網路將以一個單一傳輸平台提供固定網路及行動網路上所有服務，包括語音、多媒體、資料等各類服務。此種革命性網路不但可以降低建置成本與營運管理成本，更可以提供一個新的服務平台，供營運者建置跨網路的應用服務。但，欲達到整合型網路的理想之前，我們仍須克服許多困難，其中最關鍵的問題之一即是品質問題。All-IP 網路承襲 packet switched 網路原有的特性，有三大品質問題有待克服： long delay time, ar jitter 以及 high packet loss rate。這些品質問題對某些諸如語音或多媒體等應用服務有關鍵性的影響。此外，由於未來的網路係由特性差異極大的異質性網路所組成，而欲在此種網路上支援品質要求差異極大的多樣應用服務，其品質管理變得異常複雜，難以引用現有的品質管理方案。本計畫旨在探討整合型All-IP網路之品質管理各項問題， 並提出適當的管理機制。我們提出Budget-Based QoS架構，以簡化管理、追求效率、不增加管理複雜度為原則，利用預算分配和預先資源分配規劃，來達成end-to-end的網路服務品質保證，根據此簡化管理原則，我們提供一套服務品質的管理工具，採用分層分權的方式將QoS管理權責以預算的方式分散至每個網路元件，如此可以避免繁複的折衝協調和即興式(real time on demand)的資源管理。此套管理工具，可供網路營運業者依其需要調整，在有限資源下追求使用者之整體最大滿意度。本年度所完成之項目為「選擇性保證封包送達之通訊協定設計」，「適用於無線隨意式網路之逐節點TCP傳輸協定」以及「有助於提高服務品質的前瞻式封包排程機制」。

All-IP network uses a single packet-switched network to carry most services such as voice, video, and data, that were supported by today`s separated circuit-switched and packet-switched networks. This revolutionary network not only reduces deployment and operation costs, but also facilitates the creation of new services that can be executed across circuit-switched and packet-switched networks. Among many challenges that need to be addressed in order to make All-IP networks possible, the QoS problem is a critical one. Long delay time, large jitter, and high packet loss rate are inherent QoS problems in a packet switched network. Time sensitive services such as voice and video may severely suffer from these QoS problems. Furthermore, future All-IP networks may be composed of many heterogeneous subnetworks which may diversify in many different aspects such as bandwidth, response time, and loading characteristics. To maintain a high satisfactory level for diversified services on these heterogeneous networks becomes a great challenge to network operators. This project is aiming to design a QoS management system as well as associated software facilities for All-IP networks. With the assistant from BBQ system, network operators can choose their QoS policies and tune their networks to maximize their satisfactory level in offering services to their users. Assuming that each network component is able to maintain its commitment to the quality budget, BBQ (Budget Based QoS) system allocates QoS quality to network components based on a systematic resource planning aiming to provide a high level confidence in maintaining end-to-end QoS commitments. Resource planning tools developed in this project will facilitate operators to maximize their satisfactory level under the resource availability constraints. The accomplishments of this year are (1) proposed Partial-Reliable TCP to guarantee the delivery of designated packets selectively (2) designed an Hop-by-hop TCP for MANET where packet loss rate are high, and (3) designed a QoS-aware forward-looking scheduling mechanism to enhance the .satisfactibility of overall service quality.