1. ali@sics.se1 Peer-to-Peer System Ali Ghodsi Swedish Institute of Computer Science Royal Institute of Technology (KTH)

2. ali@sics.se2 Definition What is a distributed system? Leslie Lamport ”You know you have a distributed system when the crash of a computer you have never heard of stops you from getting any work done.” We counteract this definition!

3. ali@sics.se3 Distributed Systems Example of distributed systems: –File systems –Web servers –Mail servers –Databases Frequently, an organization stores all its files on a centralized distributed file server If it fails, no one can access their files Webb servers often become overloaded and fail The central mail server crashes, no one can read their email!

4. ali@sics.se4 Our effort Build on an 30-year old idea Arpanet, the precursor of Internet, was built for: –Military survivability If some part stops working, the rest should continue to function Internet has been quite successful so far… –No fail-stop yet But the effort stopped here…

5. ali@sics.se5 Peer-to-Peer System We want to build –Services –Servers –Applications That are self-managed Achieved by peer-to-peer techniques!

6. ali@sics.se6 Peer-to-Peer Middleware After several years of research –Built a middleware: DKS Provides: –Routing services –Directory services –Name-based messaging (multicast/publish/subscribe)

7. ali@sics.se7 Peer-to-Peer System DKS is self-managing Automatic managent: –Adding servers/resources –Removing servers/resources –Crash of servers/resources –Load balancing of data/nodes –Security

8. ali@sics.se8 Peer-to-Peer? How is it different from: –KaZaa –Napster –Gnutella –Skype These are so called unstructured p2p systems –Limited applicability (file sharing) –Inefficient (wastes bandwidth) Our focus is on structured p2p systems –Chord/CAN/Pastry (USA) –DKS/P-Grid (Europe)

9. ali@sics.se9 What can we do with DKS? Three concrete applications: –P2P Web server –P2P Backup –P2P File system

10. ali@sics.se10 P2P Web Works like an ordinary web server Differences: –It is distributed –Automatic data replication –Load-balancing of users Too much load –Add another server Publish your web pages Gets stored on the DKS 0 1 2 3 4 5 6 7 8 9 10 11 15 14 13 12 1 15 13 4 5 Store it here Store a new copy here Store a copy here

11. ali@sics.se11 P2P Backup Initialization –Install a client on your computer –Decide on amount of space to share –Choose files for backup Regular backup –Data is encrypted –Always accessible

12. ali@sics.se12 Conclusion Structured Peer-to-Peer system –Self-organizing Automatic fault-tolerance Automatic addition of nodes/resources Automatic removal of nodes/resources Automatic load-balancing Many interesting applications –File systems –Backup –Web –M.m. Cost-saving for companies –Save money on administration