內容傳遞網路中重導向機制之設計

The Design of Redirection Mechanisms on the Content Delivery Network

吳孟寰(Meng-Huan Wu)

指導教授 ： 吳和庭

國立臺北科技大學/電資學院/資訊工程系研究所/碩士(2012年)

摘要

內容傳遞網路(Content Delivery Network, CDN)，是將使用者的請求分散至各處的代理緩存伺服器(Surrogate server)，以減輕原始伺服器(Origin server)的負擔，並避開網路中的瓶頸（Bottleneck）和壅塞部分，增加傳輸速度以減少回應時間，進而提高整體網路的效能。CDN以重新導向讓使用者連線導向至較佳代理緩存伺服器，代理伺服器提供使用者能以較短時間取得內容，且能降低長距離傳輸內容而導致封包遺失、封包延遲的情況。但目前所提出的重新導向機制在設計上不夠完善，目前所提出的重新導向只能在使用者新建連線時才作重新導向，但可能因此導致新建連線時使用者的最佳代理緩存伺服器滿載，使得使用者被導向至次佳代理緩存伺服器；當原先滿載的代理緩存伺服器有空閒時，卻無法將較差代理緩存伺服器導向至較佳代理緩存伺服器。
本論文所設計的重新導向演算法使用內容管理器(Content manager)監控代理緩存伺服器的負載狀況，並且記錄沒能取得最佳代理緩存伺服器的使用者，有機會將使用者再次重新導向到較佳的代理緩存伺服器，使得能更即時取得內容。本論文透過模擬的結果，分析重新導向演算法為終端用戶所帶來的效益。

關鍵字

內容傳遞網路 ； 重新導向 ； 代理緩存伺服器 ； OMNeT++

並列摘要

Content Delivery Networks (CDN) are composed of multiple surrogate servers located at different geographic locations which redirection user requests for the goal of mitigating the load of the origin Server, avoiding busy transmission paths, and increasing the data transfer rate to lower response time, in the end improving overall network performance. CDN uses methods of redirection that forward the user connections to the suitable surrogate servers that offer a lower response time for accessing data, in the meantime reducing the packet losses and delays possible in long transmission paths. However, the current mechanisms for redirection are flawed, as they can only perform redirection when a user connection is established. This may cause the target surrogate server to become overloaded during a newly created connection, as a result redirecting the user to a less suitable surrogate server. A previously overloaded surrogate server may also become idle, yet unable to redirect a user to a more suitable surrogate server from a less suitable surrogate server.
This thesis provides a redirection algorithm that uses a content manager to monitor the work load of surrogate servers, and maintains a record of the users that did not obtain the optimal suitable surrogate servers. This allows users to be redirected repeatedly until a more suitable surrogate server is found and allows a more instantaneous access of content. This thesis analyzes the performance improvements of terminal users applying the algorithm through simulation results.

並列關鍵字

Content Delivery Network ； Redirection ； Surrogate server ； OMNeT++

參考文獻

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