主動式網路輔助之應用層即時分層多播

Application-Level Layered Live Multicasting with Active service Assistance

林康司(Kang-Sze Lin)

指導教授 ： 鍾添曜

元智大學/資訊學院/資訊工程學系/碩士(2004年)

摘要

在資料網路中，路由器通常不提供多播的傳輸服務，導致ㄧ對多的多媒體服務需用多次的單播傳輸來達成多播傳輸;這會加重頻寬負荷，尤其加重在資料源的輸出頻寬需求。在現有的網路上建立一個P2P(Peer to Peer)多播網路，利用對等(Peer)節點來轉送多播資料，以分散資料源的網路負荷。但是對等節點的穩定性遠不如主從式架構中的伺服器，對等節點頻繁的上下線導致通訊拓樸與通訊品質不穩定;這也會造成P2P網路維護的成本。另外，應用層的傳輸是利用Peer節點間建立虛擬的通道(Tunnel)，節點與通道形成應用層的網路拓樸。在無法詳細的搜集網路拓樸架構的前提下，應用層拓樸與網路實體拓樸會不一致。當兩拓樸的差異性大時，在應用層資料繞送路徑，對於實體拓樸將不是最佳繞送路徑; 這會導致通訊資源的浪費。
本論文提出ALMA(Application-Level Layered Multicast with Active service Assistance)演算法，以主動式網路(Active Networks)的機制輔助，建構P2P的應用層即時多媒體分層多播服務(Application-Level Layered Multicast)。利用分層多播搭配主動式網路的方法克服使用者節點間環境的異質性(Heterogeneous)，解決傳統RLM(Receiver Driven Layered Multicast)所遭遇的問題，讓使用者節點可以依據其網路環境，觀賞符合其頻寬的影片品質。主要利用主動式網路動態佈建服務的功能與資源存取服務，提供類似於代理人模式的多媒體多播環境(Agent-based multicast)，以建立趨近於實體網路拓樸的應用層拓樸。所有對等(Peer)節點在加入服務時必須先丟出主動式封包，該封包在經過事前先佈建在網路上的主動式節點(Active Node)時，會被主動攔上並執行分析。透過此機制盡量讓來自相同自主系統(Autonomous System, AS)的對等節點能在同一個叢集(cluster)中取得資訊，並建立多媒體多播樹(Relay Tree)。

關鍵字

點對點網路 ； 多媒體多播樹 ； 主動式網路 ； 代理人模式多媒體多播 ； 分層式多播 ； 接收端驅動式分層多播

並列摘要

Although most of the newer routers and switches are configurable for supporting IP Multicast, many of them are, by default, not enabled. Unicast is used in cases in which IP Multicast is not available, which causes heavy load at servers. Recently, Peer-to-Peer (P2P) networking has been used to deliver streaming data for reducing source bandwidth requirement. But because of the unpredictable behavior of peers, a P2P system is usually not stable and reliable. Consequently, it usually delivers streaming data of low quality and requires expensive cost to maintain streaming topology. On top of that, P2P networking constructs a virtual link which is not physical topology aware between peers, and causes unnecessary routing penalty. If an application level topology is very different from the underneath physical topology, it will generate penalty of high delay latency and high bandwidth cost.
This thesis presents a new Algorithm called ALMA (Application-Level Layered Multicast with Active service Assistance). ALMA constructs a P2P Application-Level Layered Multicast to overcome the heterogeneous properties of a P2P System, to solve the problem of the former RLM (Receiver Driven Layered Multicast), and to let the peer enjoy right quality streaming video fit its environment. ALMA takes advantage of the dynamic deployment service and caching service of Active Networks to provide an environment resembling Agent-based multicast for constructing an application level topology which is highly physical topology aware. ALMA provides join, leave and tree management algorithm for conquering other past P2P multicast tree model. Additionally, ALMA takes use of Layered Multicasts and Active Networks’ characteristics to provide downgrade algorithm to highly decrease the occurrence of immediate interruption, and LAN broadcasting to reduce bandwidth requirement on the network. All peers must use an active packet for these services. When the active packet filtered by the pre-deployed Active Node, Active Node will collect the localized information to let the peers in the same AS (Autonomous System) could construct a sub-tree which is topology awareness.

並列關鍵字

Peer to Peer ； Relay Tree ； Active Networks ； Agent-based multicast ； Layered Multicast ； Receiver-Driven Layered Multicast

參考文獻

[2] D.J. Wetherall, J.V Guttag, D.L Tennenhouse, “ANTS: a toolkit for building and dynamically deploying network protocols”, IEEE OPENARCH’98, pp. 117-129, April 1998.

[3] R. Matei; A. Iamnitchi; P. Foster, “Mapping the Gnutella Network”, IEEE Internet Computing Journal, Vol. 6, pp. 50-57, 2002.

[4] Li Gong, “JXTA:A Network Programming Environment”, IEEE Internet Computing, Vol. 5, pp. 88-95, May 2001.

[7] S. Banerjee, B. Bhattacharjee, C. Kommareddy, “Scalable application layer multicast”, ACM SIGCOMM’02, 2002.

[9] A. Banchs, W. Effelsberg, C. Tschudin, V. Turau, “Multicasting Multimedia Streams with Active Networks”, IEEE Local Computer Networks, 1998. LCN '98, pp. 150-159, Oct. 1998.