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Enabing Adaptive Video Streaming in P2P Systems

Enabing Adaptive Video Streaming in P2P Systems. Dan Jurca, Jacob Chakareski, Jean-Paul Wagner, and Pascal Frossard, Ecole Polytechnique Federale de Lausanne (EPFL) Director︰ 童曉儒 教授 Reporter ：第三組 陳盈君 M9656008 梁家國 M9656015 何政億 M9656019 蘇軍維 M9656027

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Enabing Adaptive Video Streaming in P2P Systems

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  1. Enabing Adaptive Video Streaming in P2P Systems Dan Jurca, Jacob Chakareski, Jean-Paul Wagner, and Pascal Frossard, Ecole Polytechnique Federale de Lausanne (EPFL) Director︰ 童曉儒 教授 Reporter：第三組 陳盈君 M9656008 梁家國 M9656015 何政億 M9656019 蘇軍維 M9656027 蔡翌潔 M9656034 陳建逸M9656036 IEEE Communications Magazine • June 2007

  2. OutLine • 簡介 • P2P架構 • P2P多媒體技術 • P2P系統的路徑與速率分配 • P2P網路電視架構 • P2P分散式傳送編碼 • 結論

  3. 介紹 P2P（peer to peer)利用點對點分散式網路架構傳輸型態進行網路資源分享，下載檔案的同時也提供他人下載檔案。即本身為伺服端及客服端。常見的p2p軟體如BT、Emule、Ezpeer、Kazza、eDonkey等 。

  4. P2P 軟體優勢 • 可傳送大量的資料 • 減少開發上的成本 • 為分散式網路架構 • 擴充性高 • 負載平衡 • 為多對多的傳送方式

  5. P2P網路安全 • P2P工具包可能會被惡意人員植入木馬後門程式或病毒 • P2P軟體上的漏洞,造成駭客入侵 • 使用P2P軟體時,可能會誤把資料夾打開分享 • 使用P2P下載相關版權軟體,造成侵權問題 • 使用P2P下載軟體,例電影,容易在工作上分心

  6. P2P軟體比較表

  7. 檔案切割法 • 利用Layered Encoding來作切割 • MDC (Multiple Description Coding)

  8. P2P架構 • 重疊網路(Overlay Network) ：是指我們刻意忽略網路的實體架構，將網路上的每個節點都視為一個單獨的節點，並且假設他們可以自由的互相連接。將這些單獨的節點採用某種特殊的結構來建置一個網路。 • 例如目前許多的P2P(pear-to-pear)架構，都是一種典型的重疊網路

  9. P2P架構 • P2P網路有多種分類方法，從網路結構到應用類型多種多樣，這是主要從網路集中化程度、網路結構和網路應用類型三個方面對P2P網路進行分類： • 分散式 • 集中式 • 混合式

  10. P2P架構 • 集中式P2P網路：集中式P2P模式中有一個中心伺服器來負責記錄共用資訊以及回答對這些資訊的查詢。

  11. P2P架構 • 分散式P2P網路 ：pear通過與相鄰pear之間的連接遍佈整個網路體系。

  12. P2P架構 • 半分散式P2P網路 ：在分散式模式基礎上，將pear按能力進行分類，使某些pear擔任特殊的任務。 • 用戶節點 • 超級節點

  13. P2P架構之比較 最主要的差異：peer發出request的方式，與server的存在 分散式：檔案的查詢及交換均在各點之間直接進行， 無伺服器介入 混合式：Server建立資料庫，供peer查詢 超節點：介於以上兩者之間，也有server， 但是不只一個

  14. P2P架構 • As a P2P system does not provide any guaranteed support to streaming services. • Two main types : • Tree-based overlay • Mesh overlay

  15. P2P架構 • Tree-based overlays organize the peers as a single or multiple tree overlay that connects the source of the media content to the clients.

  16. P2P架構 • Single tree have fundamentally limited by the following two factors: • The high rate of peers joining/leaving the system. • The received media quality is limited by the minimum upload bandwidth of the intermediate peers in the branch.

  17. P2P架構 • Multiple tree architectures address the aforementioned problems. • Multiple tree designing and maintaining such systems becomes less trivial. • Most importantly, the underlying physical topology must be carefully considered to achieve efficient content dissemination .

  18. P2P架構 • Mesh overlay architecture is based on self organization of nodes in a directed mesh that is used for media delivery to clients.

  19. P2P架構 The advantages of mesh overlay architecture ： • Low cost and simplicity of structural maintenance . • In the resilience of the topology to node failure or departure.

  20. P2P架構 • Streaming applications over such architectures faces important challenges. ： • Packet dissemination and data requests must follow closely the temporal ordering of the content at the source . • The limited look-ahead content availability.

  21. H.264/AVC ITU-T VCEG與ISO MPEG共同組成聯合視訊小組(Joint Video Term，JVT)來研訂新的視訊壓縮格式，此新格式在ITU-T組織中稱為H.264 首次將視訊編碼層(Video Coding Layer，VCL)與網路提取層(Network Abstraction Layer，NAL)的概念涵蓋進來

  22. H.264/AVC

  23. H.264/AVC 網路提取層 (Network Abstraction Layer，NAL) H.264/AVC標準的特色是將網路提取層的概念涵蓋進來。

  24. H.264/AVC

  25. H.264/AVC

  26. H.264/AVC 視訊編碼層 (Video Coding Layer，VCL) 視訊壓縮的原理是利用影像在時間與空間上存有相似性，這些相似的資料經過壓縮演算法處理之後，可以將人眼無法感知的部分抽離出來。

  27. H.264/AVC

  28. Scalable Video Coding(SVC) 可調性編碼器必須符合下列需求： SNR / temporal / spatial / complexity / region-of-interest / object-based以及 combined scalability、錯誤強韌性及 graceful degradation、base-layer 相容性、 低傳輸延遲、隨機存取功能、 良好的編碼效率、支援interlaced video等等。

  29. Scalable Video Coding(SVC) SVC會產生數層cumulated video streams，分別為Base Layer (BL)、Enhancement Layer 1 (EL1)、Enhancement Layer 2(EL2)…等等，而層數則由設計者自定。 Base Layer是提供給最低視訊收看品質給用戶，而用戶可依本身的網路環境來決定是否要訂閱Enhancement Layer1甚至到Enhancement Layer2來改良視訊收看的品質。

  30. Scalable Video Coding(SVC)

  31. Scalable Video Coding(SVC) • 針對傳統的群播架構，在異質性網路SVC擁有較好的網路可適性。

  32. MPE - FEC • MPE : Multi protocol Encapsulation • Container for upper layer protocols (IP,LLC/SNAP) • Optimized for IP over DVB • Associated with FEC in the DVB-H standard • FEC : Forward Error Correction • Extra layer added to provide error correction • Based on a Reed Solomon code RS (255,191)

  33. MPE - FEC

  34. MDC (Multiple Description Coding) Multiple Description Coding (MDC) is a coding technique which fragments a single media stream into n independent sub streams (n >= 2)

  35. MDC (Multiple Description Coding) • Multiple Description組成方式

  36. MULTI-PATH STREAMING IN MESH NETWORKS • 利用了P2P network 的multi-path特性,透過網路來源端總數來滿足media applications的頻寬要求。 • Multiple transmission paths傳遞優點 • Aggregated network bandwidth • Packet loss de-correlation • Delay reduction

  37. Client透過distinct network paths與其他的source node做連接。 Streaming application會在最佳的rate allocation下，去決定最好的subset of paths與possible sources • Available path bandwidth • Error rates • Media specific parameters

  38. 藉由正確的路徑選擇以及速率分配，讓接收端可以獲得最大的media quality • 在分散式方法下，必須 • source selection • media rate allocation • 所以在一個不穩定的拓樸環境之下，P2P系統應付channel與path的變化。 • path re-computation • adaptation of the media application

  39. RECEIVER-DRIVEN STREAMING SCENARIOS • 在Receiver-driven streaming例子，clinet端協調streaming程序中，可以了解Source peer selection與rate allocation。 • P2P系統中，Clinet端可以 • 存取位置資訊 • 透過candidate source nodes探查網路連結狀況

  40. 根據網路連結資訊與串流任務特性，接收端可以得知來源節點和網路傳輸路徑的選擇。根據網路連結資訊與串流任務特性，接收端可以得知來源節點和網路傳輸路徑的選擇。 • 在串流任務中，接收端透過RCTP reports獲得連結網路路徑的統計。 • construct a timely image of the available network topology • 接收端可以執行application adaptation，以反應在傳輸過程中觀察的改變。

  41. DISTRIBUTED PATH COMPUTATION • Receiver-driven scenarios最主要的問題點 • Requirement for full topology knowledge at a single peer (client) • 雖然Receiver知道完整的網路topology • Make an optimal decision • 但當網路規模越來越大，peer對end to end傳輸的監控會變得 • cumbersome • increasingly expensive or inefficient

  42. Augmenting the streaming scenario with intermediate peer functionality enables the maintenance of up-to-date information about network availability • The topology information is no longer relayed toward a single node • every intermediate peer makes an individual routing decision

  43. Distributed path computation會造成 • Sub-optimal streaming strategies • Heterogeneous network • 在每個中間peer做局部最佳的決策的結果或許與整個拓撲網路可達到的效能可能有很大的差異。

  44. 在網路狀態不穩定下，media application 可以獲得平均品質的衡量，透過 • flexibility and convergence time of the solution

  45. Routing of media packets in tree-based overlays • Straightforward • It is given directly by the structure of the multicast trees

  46. RATE-DISTORTION EFFICIENT SCHEDULING Packets of a media stream do not contribute to the video quality at a receiving peer, only if: • It arrives prior to its delivery deadline; • All the previous packets required for its correct decoding were received already.

  47. RATE-DISTORTION EFFICIENT SCHEDULING • video-on-demand(VoD) The benefit of each individual media packet can be computed and stored before the streaming session actually begins.

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