Internet Resources Discovery (IRD)

1. Internet Resources Discovery (IRD) Peer-to-Peer (P2P) Technology (1) Thanks to Carmit Valit and Olga Gamayunov A. Frank

2. Content • Computer Networks • Client-Server Networks • Peer-to-Peer (P2P) Networks • Centralized Server • Distributed Service • P2P vs. SEs • P2P infrastructure • Some leading P2P Websites • Research Issuesfor future systems A. Frank

3. Computer Networks (1) Computer networks enable to: • Communicate. • Share files electronically. • Have an electronic mail system. • Have a networked storage area for backing up critical information. • Share expensive equipment such as laser printers and CD-ROM drives. A. Frank

4. Computer Networks (2) Computer networks come in two flavors: • Client-Server Networks • Peer-to-Peer Networking (P2P) • Centralized Server • Distributed Service A. Frank

5. CLIENT-SERVER Client Server A. Frank

6. Client-Server Networks (1) • A Client-Server network is a communication model which: • Has a central, dedicated computer, called a server. • Has a number of PCs, known as clients, connected to the server through the network. • The same machine can be both a server and a client. A. Frank

7. Client-Server Networks (2) • The server acts as a hub for: • Sharing printers • Doing global backup • Providing network security • Performing general management of the network • The server may also provide access to the company’s database, data files and E-mail messages. A. Frank

8. Advantages (1) • Software Consistency • All users use the same software version. • Upgrading software on the server affects all users. • Hardware Flexibility • The server alone is responsible for directing the network traffic. A. Frank

9. Advantages (2) • Centralized Storage • Data is not lost when a PC “crashes”. • Data is accessible to all relevant and authorized users (not just to the author). • Security • Data is accessible only to the relevant and authorized users. • Backup • Relevant data is backed up on the server. • Another server can backup the current active server. A. Frank

10. Disadvantages • Expensive • Difficult to set up • Difficult to maintain • The power of the clients is wasted • The clients are treated as dumb computers and their power is not being used. • Dependency on the server • If the server “falls”, this is a problem. A. Frank

11. What is P2P (Peer-to-Peer) • Every participating node acts as both a client and a server (“servent”). • Every node “pays” its participation by providing access to (some of) its resources. • Properties: • no central coordination and central database. • no peer has a global view of the system. • global behavior emerges from local interactions. • all existing data and services are accessible from any peer. • peers are autonomous. A. Frank

12. Types of P2P Systems • E-commerce systems: • eBay, B2B market places, B2B integration servers... • File sharing systems: • Napster, Gnutella, Groove, … • Distributed Databases: • Mariposa [Stonebraker96], … • Networks: • Internet • Mobile ad-hoc networks A. Frank

13. Peer-to-Peer Networking Peer-to-Peer networks come in 2 basic flavors: • Centralized Server - Servers direct the traffic. • Examples: Napster, Groove • Distributed Service - Server-free implementations that directly connect desktops over an IP network. • Example: Gnutella • Hierarchical model - Mix of centralized and decentralized model introduces of “super-peers”. • Example: FastTrack (?) A. Frank

14. CENTRALIZED SERVER Files and info move through the server and through each other Centralized Server A. Frank

15. Centralized Server P2P with a Centralized Server is derived from the Client-Server model. • The clients are connected to the server and to each other. • This enables the clients to communicate with each other without using an intermediate server. • The server doesn’t act as a hub for managing the network, but focuses on specific tasks to help the communication between the users, like: • Helps with the first “handshake” between the users (Napster). • Saves information temporarily (Groove). A. Frank

16. Advantages • All Client-Server advantages remain. • Using the power of the clients. • The clients are no longer dumb computers, and participate in managing the network. • The server has less responsibilities. • Which reduces the need for a powerful server or for several servers. A. Frank

17. Disadvantages • Low level of security • Allowing actions between clients without server supervision might spread viruses in the network. • Dependency on the server • Reduced, but still exists. A. Frank

18. Napster • Napster is an application and music indexing service from Napster, Inc., San Mateo, CA. • Provides an index to MP3 music files residing on other computers currently logged onto the Internet. • The digital music itself is not located on Napster servers, only the index service. A. Frank

19. Napster System Architecture • Central (virtual) database which holds an index of offered MP3/WMA files. • Clients connect to this server, identify themselves (account) and send a list of MP3/WMA files they are sharing (C/S). • Other clients can search the index and learn from which clients they can retrieve the file (P2P). • Combination of client/server and P2P approaches. • First time users must register an account. A. Frank

20. Napster Communication Model A. Frank

21. Napster Limitations (1) • Napster has a heavy cost in Internet traffic • MP3s are typically huge files (2-10 MB). • Napster turns every user into a server, tossing a huge amount of data out onto the networks. Result: Napster has high bandwidth demands. A. Frank

22. Napster Limitations (2) • “Transfer Error” • The available music depends on who is online at the time. • When a user goes offline, all the other users who started downloading from his hard drive get a transfer error. Result: Users need to continually check the Napster directory when downloading files. A. Frank

23. Napster Limitations (3) • Low level of security • The exchanging of files is done by the users without the supervision of a server. • There’s no protection from viruses that might have been built as MP3 files. Result: Users are more in need of a personal firewall than before. A. Frank

24. Groove (1) • Groove is software that enables small groups of users to quickly get together online to collaborate on projects. • The users can share all kinds of digital data. • Groove functions by creating a working space on each participating PC. A. Frank

25. Groove (2) • The work space includes tools to support collaboration: • Sharing Microsoft Office documents • Text chat • Live-voice chat • Photo viewing • Drawing pad • Browser • Only a Groove member, who was invited to a specific PC, can access its space. A. Frank

26. Groove (3) • When two or more users are online at the same time, they can work on the same document. • Any change made to a document is transmitted “live” over the Net to other users. • If the other users aren't online, the modifications are stored on a relay server. • As soon as a user plugs back in, his Groove space is updated. • Groove links users via their PCs without the assistance of a central server, but a server is in use. A. Frank

27. Groove Limitation • Only for small groups • The software is designed to work best for groups of 25 people or fewer. A. Frank