無線網狀網路中提供內容配送服務的探討

Abstract

隨著網路的頻寬日益增大，對多媒體資料傳輸的需求也逐漸成長。不過一旦觀眾人數增加，加上多媒體資料本身所佔的頻寬較大，傳輸品質經常會受到嚴重的影響。Akamai是一個內容配送(Content distribution)服務的提供者，她不但解決了上述問題，大幅改善多媒體資料在網際網路傳輸的效率，也獲得企業廣泛的使用，如CNN、美國職棒大聯盟等。 近年來，無線網狀網路(Wireless mesh network, WMN)因為具有覆蓋範圍廣大以及佈建成本低的優點，對於公司、校園、甚至是整個都市，都相當適合作為最後一哩(Last mile)的解決方案。可以預期的是，將會有更多樣的服務透過這種網路架構來傳遞。但根據有線及無線網路特性的不同，我們無法直接套用有線網路上CDN的實做方式，必須針對無線環境中的限制設計出一個適合的架構以提供Content distribution服務。 本篇論文針對即時影音節目(Live event broadcasting)設計了一個適用於無線網狀網路的架構來提供良好的傳輸效能，並達到有效率的網路資源使用。我們從Akamai的實作方式得到啟發，並仿效Internet的骨幹網路，提出結合Overlay backbone與資源保留的兩階段資料遞送概念，除了大幅改善Throughput以及Delay jitter的表現，還支援動態使用者管理，提供符合Service level agreement(SLA)的品質保證。

With the increasing bandwidth of networks, we can demand more for multimedia services. But due to the huge consumption of resources, transmission quality will be degraded when user population grows. Akamai is a content distribution service provider, it not only solves problems mentioned before, but also improves the efficiency of multimedia transmission. Wireless mesh network(WMN) is an architecture that allows accessing Internet through multihop transmission. It becomes popular because of its low cost and wide coverage. Thus, for a city, institute, or company, it is an excellent 'last-mile' solution. We can expect that many multimedia services will be provided on this network architecture. But compared with wired networks, there are many constraints on wireless communication, such as low bandwidth and interference. So we should not directly apply CDN architecture on the Internet. It is needed to take the characteristics of wireless mesh network into consideration and come up with a new architecture to handle content distribution in this environment. In this paper, we focus on live event broadcasting services and design a suitable architecture for transmitting multimedia packets in wireless mesh networks. We are motivated by Akamai and the concept of Internet backbone. We propose a “two-stage” content distribution scheme that combines overlay backbone and virtual circuit to improve throughput, delay jitter, and also support dynamic user management.