1. CS 414 - Spring 2012 CS 414 – Multimedia Systems Design Lecture 37 – Introduction to P2P (Part 1) Klara Nahrstedt

2. Administrative MP3 deadline Saturday April 28, 5pm  Demonstrations of MP3, April 30, 5-7pm Groups should sign up as follows:  5-6pm – 3 rd floor 3401 SC for groups that work with laptops and need wireless connectivity for MP3  6-7pm - 216 SC basement for groups who work with PCs and need wired connectivity for MP3 Top four groups will be decided Monday, April 30 at 7pm (via email, also posted on the newsgroup/classwebsite) - these groups will compete in front of the judges on Tuesday, May 1 CS 414 - Spring 2012

3. Administrative Competition of final four groups on Tuesday 5-7pm in 3401 SC/ 216 SC  ByteMobile Inc. company – judging competition (and TA/Instructor)  The top four groups should prepare 3-4 power-point slides to present Intro Slide – name of your system and your names (1 slide) Surveillance System Design – overall architecture (1 slide) Features of Your System - interface (1 slide) Features of Your System – other features (1 slide)

4. Administrative Homework 2 is posted  Deadline May 2, Wednesday midnight 11:59pm Peer Evaluations – due Friday, May 4, midnight  Peer Evaluation Form and Explanation - available on the class website  Submit your Peer Evaluation to klara@illinois.edu  Note: if you do not submit your peer evaluations, you get 0 for self-evaluation and 100% for your group mates. ¼ Unit projects – due Friday, May 4 midnight (if you need more time, arrange deadline with instructor) CS 414 - Spring 2012

5. Why P2P? People like to get together  Share things  Share information How can I find others to share? How can I find what they are sharing? CS 414 - Spring 2012

6. Why P2P? WWW to share?  Not everyone can set up and maintain a website  Might not have a good enough search engine rank Sharing on a social network?  Only possible if you created the content  People have to find you, instead of the content CS 414 - Spring 2012

7. Napster Created in 1999 to share music CS 414 - Spring 2012 Napster’s servers Store file directory (Filename/location) Clients/peers Store files Centralized Peer Management: Each Peer registers with the Napster server and Napster server(s) keep Peer List Centralized File Management: Searching for other peer file is central, i.e., Peers go to Napster servers which keep file list of files and which peer keeps what files

8. Napster- Search Operation CS 414 - Spring 2012 1. Query (keyword) 2. Servers search using ternary tree 3. Response 4. Ping candidates 5. Download

9. Napster’s drawbacks Asymmetric operation – servers vs. client peers  Centralized Peer Management and File Management  Scalability and congestion issues  Single point of failure Napster responsible for abetting users’ copyright violation CS 414 - Spring 2012

10. Contemporary P2P systems Symmetric operation – all nodes (peers) have the same functionality  System naturally scales with new peers Distributed Peer Management  Each peer when it comes online, advertises its own presence  Each peer keeps a peer list to whom it is connected Distributed File Management  Each peer keeps file list of files it keeps.  If a peer wants a file, it queries/searches for a file. CS 414 - Spring 2012

11. Contemporary P2P systems Basic operations  Insert file  Search file  Delete file  Maintain an overlay network CS 414 - Spring 2012 physical network Overlay P2P network

12. Contemporary P2P Systems (Classification) Usually classified depending on how peers connect to each-other  how the overlay network is created and maintained Unstructured – no particular connection pattern (e.g., randomly connected)  Gnutella  Fast Track Skype  BitTorrent, etc. CS 414 - Spring 2012

13. Contemporary P2P Systems (Classification) Structured – defines a distributed data structure (e.g., distributed hash table)  Chord  Pastry  CAN  Etc. CS 414 - Spring 2012

14. Gnutella – Example of Unstructured P2P CS 414 - Spring 2012 Servents (peers) Peer pointer Peers store: Their files Peer pointers (peer management)

15. Gnutella, searching for files CS 414 - Spring 2012 Query message: Query hit message: <id, QUERY HIT, ttl, hops, payload length, num hits, port, ip, speed, (fileindex, filename, filesize), servent id> “jazz”?? 1.Flood query ( ) 2.Ignore repeated messages 3.Answer if local match 4.Query hit sent using reverse path ( ) 5.Establish connection and fetch file ( ) “jazz”

16. Gnutella, maintaining overlay (peer management) CS 414 - Spring 2012 V X A Ping: Pong: Neighbor list: “A” “V” “X” 1.Periodically flood ping ( ) 2.Pong sent using reverse path( ) 3.Update neighbor list with received pongs Why periodically?

17. Gnutella, maintaining the overlay (peer management) CS 414 - Spring 2012 V X Peers can leave or fail at any time – P2P systems can have high churn rate!. Neighbor list: “A” “V” “X”

18. Gnutella: some issues Ping/Pong constitutes 50% of traffic Flooding causes excessive traffic Repeated searches with same keywords Large number of freeloaders (70% of users in 2000) CS 414 - Spring 2012

19. DHTs (Distributed Hash Tables) – Example of Structured P2P Hash table allows these operations on object identified by key:  Insert  Lookup  Delete Distributed Hash Table – same but in a distributed setting (object could be files) CS 414 - Spring 2012

20. DHT performance comparison MemoryLookup latencylookup overhead NapsterO(1) at client; O(N) at server O(1) GnutellaO(N) Chord (DHT)O(log(N)) CS 414 - Spring 2012

21. Conclusion P2P technology – very viable technology for multimedia distribution CS 414 - Spring 2012