1. Peer to peer INF 123 – Software Architecture tdebeauv@uci.edu 1

2. Outline Some theory Napster Gnutella/torrents Skype Sensor networks I won’t talk about – NAT punching/Firewall (ICE, STUN, TURN) – Distributed system algorithms/graph walks 2

3. SOME THEORY 3

4. Peer to peer Identical components running independently on different networked hosts Similar to distributed systems – The topology can change – Many paths from A to B Each peer is client and server to other peers Each peer provides resources: data, code, CPU, … 4

5. Peer 1 Peer 4Peer 2 Peer 3 Peer 4Peer 2 Peer 3 now later 5

6. Pros and cons Pros – Scaling: each node provides CPU and storage – Robust if one node fails Cons – Complex protocols for resource discovery – Security, trust management 6

7. Examples Skype Sensor networks (house, environment, …) DNS caching File sharing 7

8. NAPSTER: HYBRID CS AND P2P 8

9. Napster Open source Resource location – Client-server – Custom protocol on top of TCP Resource retrieval – P2P – HTTP GET 9

10. Communication diagram 10 Peer APeer B Content Directory 1) I have Gangnam Style 2) Who has Gangnam Style? 3) A has Gangnam Style 4) Give me Gangnam Style 5) Here is Gangnam Style

11. Behind Firewall? Sequence diagram 11

12. Protocol: I have a song “filename”, md5, size (B), bitrate (kbps), frequency (Hz), time (s) “C:\music\OMGPSY\gangnam.mp3” 9e107d9d372bb6826bd81d3542a419d6 1234567 128 44100 253 To class: why md5? 12

13. Protocol: Search query [FILENAME CONTAINS "artist name"] MAX_RESULTS [FILENAME CONTAINS "song"] [LINESPEED ] [BITRATE " "] [FREQ " "] [WMA-FILE] [LOCAL_ONLY] MAX_RESULTS 100 FILENAME CONTAINS “Gangnam Style” BITRATE “AT LEAST” “128” MAX_RESULTS 10000 # browse To class: query for songs from Psy? 13

14. Achilles’ heel Server = bottleneck Swamped with requests for the location of a popular song – Answer location requests slowly Heavy load if the only owner is behind a Firewall – Cap number of simultaneous transfers 14

15. Achilles’ heel #2 Server = single point of failure Without it, the peers are blind and useless Shutdown mandated by court order 15

16. GNUTELLA: FULL P2P 16

17. Gnutella Open source Resource retrieval – P2P – HTTP GET Resource location, peer discovery, … – P2P! – Custom over TCP Purely distributed/decentralized search engine Peer also called servent (server + client) 17

18. Flooding 18

19. Flood prevention Every message has a Time to Live flag (TTL) Decreased by 1 every hop When 0, don’t forward 19

20. Peer discovery Send ping When receiving ping – Send pong where it came from – And forward the ping to other nodes 20

21. Search query Query message payload Response: QueryHit message payload 21

22. Query hit 22

23. Seeds How do I find peers when I join for the first time? – Aka bootstrapping, seeding Need a reliable list of nodes/seeds – Same idea as web page seeds for web crawlers Ship the list in the software Also: IRC, mailing lists, websites with seeds 23

24. SKYPE: OVERLAY P2P 24

25. 25

26. Skype supernodes Promote “strong” peers to supernodes – Based on topology, bandwidth, … – Trade secret Directory distributed and replicated in supernodes – Robust and scalable directory 26

27. Privacy and security Calls relayed through supernodes – Proprietary protocol – Encrypted for privacy Closed-source client – Very hard to inspect the code – Even harder to hack it – Therefore: no malicious peers 27 http://recon.cx/en/f/vskype-part1.pdf http://www1.cs.columbia.edu/~salman/publications/skype1_4.pdf

28. SENSOR NETWORKS 28

29. Basic idea 29

30. Constraints Each node can – Sense – Compute – Communicate with its neighbors Non-functional properties – Low energy consumption – Fault-tolerance – Scalability – Low latency 30

31. Usage Home automation Army communication Forest fire, tsunami, or tornado detection Airport weather conditions … 31

32. London Heathrow Airport 32

33. 33 Base Station (aka sink or gateway) Analog-Digital Converter Deployment architecture System architecture

34. Communication: routing Flat Hierarchical (super nodes) Location-based Depends on network topology 34

35. Communication: protocol Multipath – Send data through multiple paths – Good fault-tolerance, but high energy cost Query-based – The gateway sends a query to the network – A node with the data answers the query Quality of Service-based – Balance energy consumption and data quality 35

36. Read more https://connect.innovateuk.org/web/network -of-sensors/article-view/-/blogs/advanced- sensor-networks-developed-for-heathrow- airport https://connect.innovateuk.org/web/network -of-sensors/article-view/-/blogs/advanced- sensor-networks-developed-for-heathrow- airport Routing Techniques in Wireless Sensor Networks: A Survey, Al-Karaki et al., 2004 36