隨著網路頻寬的增加，影音多媒體串流的傳遞也隨之增加，由於影音多媒體串流的資料量大、頻寬需求高、持續時間長、需要通過廣域網路(WAN)並且需要保障原始內容提供者(origin content provider)的智慧財產權。因此常見的做法是使用內容傳遞網路(CDN)，使用者的請求必須先到原始內容提供者報到後再由內容傳遞網路轉向(redirect)到離使用者最接近的內容快取伺服器(replica/cache server)來分擔影片伺服器的負載、降低頻寬的使用量，並且可以保障原始內容提供者的智慧財產權。 另外有人提出使用點對點傳輸網路(Peer-to-Peer Network)傳遞影音多媒體的串流，因為點對點傳輸網路資料是由使用者間彼此分享，所以不會有單一伺服器過載的情況，並且系統可以有較佳的擴充性及容錯能力，但是當使用者彼此之間分享檔案的時候，無法確保原始內容提供者的智慧財產權。 利用複製可追查型 CDN-P2P 遞送網路架構，兼任伺服器功能的使用者快取(peer cache)可以提供服務給其他使用者，如同點對點傳輸網路分散內容快取伺服器的負載。並且在此架構下進行複製下載，如同內容傳遞網路都必須要取得原始內容提供者之複製許可才可以在最近的內容快取伺服器進行複製下載，以保障原始內容提供者的智慧財產權。 在複製可追查型 CDN-P2P 遞送網路架構下，有額外的使用者快取可以提供服務，與單純只有內容快取伺服器的環境不同，因此本文在假設(1)內容傳遞網路提供者於提供獎勵回饋機制給願意兼任快取的使用者情況下，使用者快取將承擔一定時間的快取服務工作(2)使用者在觀看完影片後才會離線以及(3)使用者向使用者快取請求複製下載時，會向抵達時間最接近的使用者快取請求複製下載的前提下，針對內容快取伺服器提出一個較佳的快取置換法。 文中分析與比較在有無額外使用者快取服務協助下的一般內容快取伺服器快取命中率改善情形，本文亦提出一個利用額外使用者快取的 HPLRU 快取替換法，文中亦模擬比較各種快取承擔時間、承擔意願機率以及影片熱門度等各種情況下之快取替換結果。在有額外使用者快取的情況下，HPLRU 皆顯示有更佳的快取命中率改善。 As the growth of bandwidth of Internet, the delivery of multimedia stream increases too. Because multimedia stream has huge amount of data, uses more bandwidth, be delivered through WAN and need to protect the copyrights of the origin content provider. So the common method is to use the Content Delivery Network (CDN), the peers must register to the origin content provider first, then the CDN will redirect the request of peers to the nearest replica/cache server to share the load of the video server, reduce the use of bandwidth and protect the copyrights of the origin content provider. Someone proposed Peer-to-Peer Network to transmit multimedia stream, because p2p network share data with each other, the overload will not happen to any video server. The system has better scalability and ability of fault tolerant. When the data shared with each other, the p2p network can not protect the copyrights of the origin content provider. Using the replication-aware CDN-P2P architecture, the external peer cache with server function can provide service to other peers to decrease the load of the replica/cache server like p2p network, peers must get the copy permission of the origin content provider to download contents from the nearest replica/cache server like CDN. Under the replication-aware CDN-P2P architecture, there is external peer cache can provide services, it is different with the environment only having replica/cache server. In this paper, we hypothesize that (1)CDN provider provides reward mechanism to the peers who are willing to be the peer cache (2)peers will be off line after finishing the video(3)peers request to download contents from peer cache which has the closest arrival time. We propose a better cache replacement scheme of replica/cache server. We analyze and compare the hit ratio of replica/cache server with and without external peer cache service and proposed a HPLRU scheme used external peer cache. We also simulate the result of cache replacement with variant peer cache service time, peer cache rate and video popularity. The HPLRU scheme shows the better cache hit ratio than other schemes under the consideration of added external peer cache.
