Internet Resources Discovery IRD PeertoPeer P 2 P

Internet Resources Discovery (IRD) Peer-to-Peer (P 2 P) Technology (1) Thanks to Carmit Valit and Olga Gamayunov 1 A. Frank

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

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. 3 A. Frank

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

Client Server 5 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. 6 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 E-mail messages. 7 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. 8 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. 9 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. 10 A. Frank

What is P 2 P (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. 11 A. Frank

Types of P 2 P Systems • E-commerce systems: – e. Bay, B 2 B market places, B 2 B integration servers. . . • File sharing systems: – Napster, Gnutella, Groove, … • Distributed Databases: – Mariposa [Stonebraker 96], … • Networks: – Internet – Mobile ad-hoc networks 12 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: Fast. Track (? ) 13 A. Frank

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

Centralized Server P 2 P 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). 15 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. 16 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. 17 A. Frank

Napster • Napster is an application and music indexing service from Napster, Inc. , San Mateo, CA. • Provides an index to MP 3 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. 18 A. Frank

Napster System Architecture • Central (virtual) database which holds an index of offered MP 3/WMA files. • Clients connect to this server, identify themselves (account) and send a list of MP 3/WMA files they are sharing (C/S). • Other clients can search the index and learn from which clients they can retrieve the file (P 2 P). • Combination of client/server and P 2 P approaches. • First time users must register an account. 19 A. Frank

Napster Communication Model 20 A. Frank

Napster Limitations (1) • Napster has a heavy cost in Internet traffic – MP 3 s 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. 21 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. 22 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 MP 3 files. Result: Users are more in need of a personal firewall than before. 23 A. Frank

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. 24 A. Frank

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

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. 26 • Groove links users via their PCs without the assistance of a central server, but a server is in use. A. Frank

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