The Design of Overlay Architecture for Live Media Streaming over Peer-to-Peer Networks

於同儕式網路上對即時多媒體串流重疊式架構設計之研究

臧意周(Yih-Jou Tzang)

指導教授 ： 黃能富

國立清華大學/電機資訊學院/資訊工程學系/博士(2010年)

摘要

即時多媒體串流的應用已越來越廣泛，這也是為什麼有許多重疊式網路架構被使用的原因。以對等同儕方式為基礎建構的多媒體串流雛型系統Live2006，提供了可擴充、穩健及高使用率的即時多媒體服務。基於網路應用層多重傳播的概念，以樹狀結構的設計來連接網路各個使用者，使每位使用者能分享所接收到的媒體串流，來降低網路間傳送所產生的流量。Live2006雛型系統不但可有效的減低媒體伺服器原有的負載，並且減少了建構提供大量使用之遠距教學服務所需的成本。此Live2006雛型系統也可使用在家庭或社區網路，並能有效降低網路下載頻寬的使用量，甚至在大量的使用者同時在觀看某一個教學節目(或球賽)時，均能夠提供使用者高品質的視訊服務。另Live2006雛型系統亦提供給在NAT之後，私有IP位址的使用者多媒體串流的服務。因此，使用者能夠藉由各自擁有的設備，在任何時間、任何地點（有網路的環境下），不受限制輕易的收取雛型系統提供的各種節目與資料，當然也包含一些部份資源有限的手持式設備。此外，因為Live2006雛型系統提供的是一個多媒體資料傳送架構平台，它僅需一些改變及調整就可以整合目前現有存在的多媒體遠距教學服務系統。Live2006雛型系統不只可在IPv4環境下運作，並且也可以執行在IPv6網路上，而IPv6的一些特點，如IPv6提供手持式設備的使用服務有較佳的行動力及經由任意傳播服務的能力來提供較好的系統效能，更強化了Live2006雛型系統的功能。
在傳送多媒體資料的方面，雖然網路應用層多重傳播已受到大家的關注與重視，但它仍有一些蠻嚴重的問題尚待解決：多重傳播樹是脆弱的，當某個點（使用者）故障將造成多重傳播樹的裂解，本篇的另一成果就是在對等同儕的即時多媒體串流環境下，提出一個嶄新的階層式環形樹的架構，此架構結合了環狀及樹狀的結構特色，具有穩健的、可靠的、能迅速回復的及可擴充的結構，並且能夠實際被使用作為網路應用層多重傳播架構的型態。當某個點（使用者）進入或離開此系統，此架構能夠快速的回復，如此，即時多媒體串流可在極小的延遲下，非常平順的傳送。此提出的階層式環形樹架構的型態是以非常有效率的方式來建構與管控，並不會在多重傳播樹中有樹分離及合併樹的問題產生，我們藉由實際測試來驗證此架構及演算法的成效，實驗結果顯示儘管在高劇烈變動的對等同儕式網路下，傳送即時多媒體資料，仍然只有很小的延遲及封包遺失率。而在大量數目的網路端點（使用者）進入或離開此系統時，架構的管控不論是在模擬或實測結果，都能得到很低的相關overhead (join overhead, departure overhead and control overhead)，而且架構具備快速回復、提供較佳的多媒體串流服務品質及更為強健的系統結構，並優於ZIGZAG的方法。

關鍵字

即時多媒體串流 ； 重疊式網路架構 ； 應用層多重傳播 ； 對等同儕式網路 ； 環形樹為基礎的結構

並列摘要

The number of live multimedia streaming applications is increasing, explaining the use of many overlay network topologies. A P2P-based multimedia streaming system, called Live2006, provides a scalable, robust, and high available live streaming service. Based on the concept of Application Layer Multicast, a tree-based structure is designed to connect the peers, and the peers share the receiving streaming to reduce network traffic. Live2006 can not only efficiently reduce the loading of the streaming server, but also minimize the cost of constructing a complete distance education system to support large number of users. The proposed Live2006 system can also be established for home or community networks to reduce the usage of downloaded bandwidth. A high level quality of service is maintained even if a significant number of individuals are watching the same program. Live2006 also provides the streaming services for users using the private IP addresses behind an NAT (Network Address Translation). Thus, users can easily access the programs through their devices, including the resource limited handset devices, in anytime and anywhere without constraint. Additionally, since Live2006 is a multimedia data transmission framework, it is easy to integrate with existing distance education service systems with only a few changes. Live2006 not only operates under IPv4 environment, but also works in IPv6 network. Some IPv6 features, such as IPv6 mobility (provides handset users better service) and anycast (provides better system efficiency) even perfects the functionality of Live2006.
Although Application-Layer Multicast (ALM) has attracted much attention in transmitting multimedia, it has a serious problem: the multicast tree is fragile and a peer failure will cause tree partitions. This work presents a novel Hierarchical Ring Tree (HRT) architecture for Peer-to-Peer (P2P) live multimedia streaming. The proposed architecture combines ring-based and tree-based structures in a robust, scalable, reliable and resilient structure that can be used practically as an ALM topology. When peers enter or leave the system, the topology is recovered rapidly such that live multimedia stream can be delivered smoothly with a low latency. The proposed HRT topology is constructed and maintained efficiently without splitting or merging trees. The performance of the proposed architecture and algorithms is evaluated experimentally. Experimental results indicate that the proposed topology can be used in a high-churn P2P network with a small delay. Simulation and experiment results reveal that the proposed architecture has a lower overhead than the ZIGZAG approach when handling peers’ joining or leaving, exhibits faster recovery, better quality of service during streaming, and a more robust topology, even with an extremely large number of peers joining/leaving.

並列關鍵字

Live multimedia streaming ； Overlay network architecture ； Application-layer multicast (ALM) ； Peer-to-Peer (P2P) ； Ring-tree-based architecture

參考文獻

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