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Advance Computer Networking bachelor of science in computer engineering
- 1. ADVANCED COMPUTER NETWORKS Peer-Peer(P2P) Networks 1
- 2. What is P2P? “the sharing of computer resources and services by direct exchange of information” 2
- 3. What is P2P? Various definitions seem to agree on sharing of resources direct communication between equals (peers) no centralized control 3
- 4. What is apeer? “…an entity with capabilities similar to other entities in the system.” 4
- 5. Client/Server Architecture Wellknown, powerful, reliable server is a data source Clients request data from server Very successful model WWW (HTTP), FTP, Web services, etc. Server Client Client Client Client Internet 5
- 6. Client/Server Limitations Scalabilityis hard to achieve Presents a single point of failure Requires administration P2P systems try to address these limitations 6
- 7. P2P Architecture Allnodes are both clients and servers Provide and consume data Any node can initiate a connection No centralized data source “The ultimate form of democracy on the Internet” “The ultimate threat to copy- right protection on the Internet” Node Node Node Node Node Internet 7
- 8. P2P Network Characteristics Clients are also servers and routers Nodes contribute content, storage, memory, CPU Nodes are autonomous (no administrative authority) Network is dynamic: nodes enter and leave the network “frequently” Nodes collaborate directly with each other (not through well- known servers) 8
- 9. P2P Applications Filesharing (BitTorrent, Napster, Kazaa) Multiplayer games (Counter Strike, Unreal Tournament, DOOM) Collaborative applications (ICQ, shared whiteboard) 9
- 10. Popular file sharingP2P Systems BitTorrent Large scale sharing of files. User A makes files (music, video, etc.) on their computer available to others User B connects to the network, searches for files and downloads files directly from user A Issues of copyright violation 10
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- 12. Structured original “Napster” design -when peer connects, it informs central server: IP address content 2) User B searches for file 3) User B requests file from User A centralized directory server peers User B User A 1 1 1 1 2 3 12
- 13. Centralized model A B D C filetransfer is decentralized, but locating content is highly centralized 13
- 14. Napster: how doesit work Four steps: Connect to Napster server Upload your list of files to server. Give server keywords to search the full list with. Select “best” of correct answers. 14
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- 19. Unstructured Fully distributed no central server Used by KaZaa Each peer indexes the files it makes available for sharing (and no other files) 19
- 20. KaZaa: Ping flooding Query QueryHit Query Query QueryHit Query Query QueryHit Filetransfer: HTTP Ping message sent over existing TCP connections peers forward ping message Pong sent over reverse path 20
- 21. KaZaa file dividedinto 256KB chunks. while downloading, peer uploads chunks to other peers. peers may come and go once peer has entire file, it may leave or remain 21
- 22. P2P : Skype Skypeclients (SC) Supernode (SN) 22
- 23. Issues with P2P Free Riding Downloading but not sharing any data On BitTorrent 15% of users contribute 94% of content 63% of users never responded to a query No ranking: what is a trusted source? 23