基於OpenFlow下實現車載內容傳遞網路

Abstract

在本篇論文中我們提出基於OpenFlow協定來實作適用於移動車載上的內容傳遞網路並使用Http live streaming（HSL）的技術達到多媒體影音串流播放。傳統的內容傳遞網路架構下，需要額外負擔龐大的資料蒐集並從中分析計算出適合的代理伺服器再經由HTTP伺服器輔助封包重新繞送。而在軟體定義網路架構中，我們透過OpenFlow提供的Vendor訊息蒐集路側單元所儲存的街道影片之Metadata，藉此找出擁有影像內容的伺服器，並利用控制器提供的頻寬資訊選擇適合的原始伺服器，再將影片片段預先佈署至車輛行駛的路側單元上，同時動態的在路側單元的路由表上加入新的繞送規則，當車輛經過時則不需重新導向封包。另外針對車載網路的特性，我們提出了影片切割的方法並經由HLS協定傳遞影像。最後我們使用一個結合mininet與ns3無線模組的OpenNet模擬器做為效能評估環境，進行影片的影像峰值訊噪比、影音串流初始延遲時間與影片連續播放程度的分析，透過上述數據證明我們提出的系統架構能夠有效地提升影片播放品質。

In this thesis, we propose a Software-Defined Network (SDN) architecture to sup-port a vehicular mobile Content Delivery Network (CDN). Traditional CDN needs to pay the cost of huge content data location, nodes’ bandwidth and network topology collection and analyzing to find a surrogate server closer to user. In a vehicular mobile CDN, it even more difficult to find a closer surrogate server, since most users are travelling in high speed. In our SDN mobile CDN architecture, we assume each Road-Side Unit （RSU）combines with a SDN switch and a content server. The SDN controller will collect the street videos’ metadata which is stored on a RSU using the vendor specific message of OpenFlow protocol, thereby identifying the server which has video content which a user needs. In order to support the mobile user, multiple surrogate servers (RSUs) on the target vehicle travelling path need to be de-termined by the SDN controller. Then a pre-cache mechanism implemented in the controller will decide video segment size and cache the video on each surrogate RSU. Finally the SDN controller will install a dynamic routing rule in each surrogate RSU’s flow table to redirect a HTTP request to the surrogate server.. In addition, we employ an popular Http Live Streaming (HLS) technology to deliver the video. In this thesis, we use the OpenNet simulator which unites mininet and ns-3 wireless module to ana-lyze our system’s performance. The performance metrics include Peak Signal to Noise Ratio (PSNR), Start Up Delay, and Playout Continue Index（PCI）. The simulation results show that our SDN based vehicular mobile CDN can increase about 33% PSNR in average.