Peer-to-Peer Systems and Applications: A Comprehensive Overview

1. Peer-to-Peer 寛頻網路技術與應用 陳 志 玄

2. Outline • 簡介P2P • Definition • Inherent characteristics • P2P應用的分類 • Peer-to-Peer Content Distribution • P2P系統的模型 • P2P存在的問題 • 結論

3. Definition • Peer-to-peer systems are distributed systems consisting of • interconnected nodes able to selforganize into network topologies with the purpose of sharing resources • capable of adapting to failures • without requiring the intermediation or support of a global centralized server or authority.

4. Inherent characteristics • Scalability • Resistance to censorship and centralized control • Increased access to resources • Administration, maintenance, responsibility for the operation

5. Classification of Peer-to-Peer Applications • Communication and Collaboration • provide the infrastructure for using direct, usually real-time, communication and collaboration between peer computers. • Ex: chat and instant messaging applications • Distributed Computation • take advantage of the available peer computer processing power (CPU cycles). • divide the task into small work units and distributing them to different peer computers.

6. Classification of Peer-to-Peer Applications • Internet Service Support • Ex: peer-to-peer multicast systems • Database Systems • designing distributed database systems based on peer-to-peer infrastructures • Content Distribution • Share digital media and other data between users

7. Peer-to-Peer Content Distribution • Application: • Peer-to-peer “file exchange” These systems are targeted towards simple, one-off file exchanges between peers. • Peer-to-peer content publishing and storage systems These systems are targeted towards creating a distributed storage medium in—and through—which users will be able to publish, store, and distribute content in a secure and persistent manner.

8. Peer-to-Peer Content Distribution • Infrastructures • Routing and location Requests and messages must be routed with efficiency and fault tolerance. • Anonymity providing user anonymity. • Reputation management there is no central organization to maintain reputation information for users and their behavior.

9. P2P系統的網路模型 • Purest form peer-to-peer networks => supposed to be totally decentralized • But in practice this is not always true => according to degrees of centralization: • 集中目錄式網路模型 • 純P2P網路模型 • 混合式網絡模型

10. 一、集中目錄式網路模型 (1/3) • 最早出現的P2P應用模式 • 仍然具有中心化的特點也被稱為非純粹的P2P結構 • 類似於傳統的Client / Server模式 • 查詢 • 資料存放地 • 用於共享MP3音樂文件的Napster是其中最典型的代表

11. 集中目錄式網路模型 (2/3) -檔案取得的方式

12. 集中目錄式網路模型 (3/3) • Advantage: • simple to implement • locate files quickly and efficiently • Disadvantage: • If the central server failures, it is vulnerable to censorship, technical failure, or malicious attack. • These systems are considered inherently unscalable, as there are bound to be limitations to the size of the server database and its capacity to respond to queries.

13. 二、純P2P網路模型 • 純P2P模式也被稱作廣播式的P2P模型 • 沒有中央的server => 容錯性高、擴展性大 • Gnutella是現在應用最廣泛的純P2P非結構化網路模型 • 查詢方式：flooding / broadcast • The number of hops • TTL(time-to-live) • Loops • Unique message identifier

14. An example of the Gnutella search mechanism.

15. 三、混合式網路模型 (1/2) • Use the concept of supernodes => form many clusters • Kazaa是P2P混合模型的典型代表 • 查詢方式 • First, send a request to the supernode in the local cluster • If no result, other supernode and flooding

16. 混合式網路模型 (2/2) • Advantage: • Shorter discovery time • Better balanced load • Disadvantage: • If supernodes fail, the nodes in the cluster will be isolated. • Don’t form large-scale peer-to-peer system.

17. Problems • 為了要擺脫中央式的集中架構模式，又可能產生了一些非中央式架構的問題： • 安全性 • 匿名使用 • 名聲機制 • 資源管理

18. Conclusion • 技術層面 • 集中式 -> 完全分散 -> 混合式 • 網路管理層面 • 智慧財產權