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

2 A. Frank 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 Issues for future systems

3 A. Frank 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. Computer Networks (1)

4 A. Frank Computer Networks (2) Computer networks come in two flavors: 1.Client-Server Networks 2.Peer-to-Peer Networking (P2P) –Centralized Server –Distributed Service

5 A. Frank Client Server

6 A. Frank 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.

7 A. Frank 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 messages.

8 A. Frank 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.

9 A. Frank 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.

10 A. Frank 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.

11 A. Frank 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. What is P2P (Peer-to-Peer)

12 A. Frank 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 Types of P2P Systems

13 A. Frank 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 (?)

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

15 A. Frank 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).

16 A. Frank 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.

17 A. Frank 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.

18 A. Frank 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.

19 A. Frank 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.

20 A. Frank Napster Communication Model

21 A. Frank 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.

22 A. Frank 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.

23 A. Frank 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.

24 A. Frank 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. Groove (1)

25 A. Frank 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. Groove (2)

26 A. Frank 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. Groove (3)

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