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Internet Resources Discovery (IRD)

Peer-to-Peer (P2P) Technology (1)

Thanks to Carmit Valit and Olga Gamayunov

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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

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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)

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Computer Networks (2)

Computer networks come in two flavors:

1. Client-Server Networks

2. Peer-to-Peer Networking (P2P)– Centralized Server

– Distributed Service

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Client Server

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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.

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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.

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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.

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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.

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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.

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• 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)

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• 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

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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 (?)

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Centralized Server

Files and info move through the server and through each other

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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).

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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.

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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.

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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.

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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.

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Napster Communication Model

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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.

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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.

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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.

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• 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)

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• 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)

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• 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)

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Groove Limitation

• Only for small groups– The software is designed to work best for

groups of 25 people or fewer.