A. Frank Internet Resources Discovery (IRD) Peer-to-Peer (P2P) Technology (2) 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 Distributed Service

4 A. Frank Distributed Service P2P as a Distributed Service is a communication model in which: Each party has the same status (peer) in the network. Each party has the same capabilities and responsibilities. Either party can initiate a communication session. No party regulates network traffic or acts as a hub for managing the network.

5 A. Frank Advantages Inexpensive Easy to set up (relatively) Easy to maintain Easy to expand (within a limit) Uses the power of the clients No dependency on a server

6 A. Frank Disadvantages Low level of Security Decentralized Storage –If one PC “crashes”, all the data it contains won’t be available. Backup –Need to count on the user to back up his data.

7 A. Frank Gnutella is a peer-to-peer file-sharing program. It is designed for people to trade and share files across the Internet without using a centralized server. Gnutella (1)

8 A. Frank Gnutella functions by connecting each individual computer to several others, which in turn are connected to several others, and so on. The computers are connected with a limited domain of about 10,000 hosts. Gnutella has the capacity to transmit any type of file, not just music. Gnutella (2)

9 A. Frank Gnutella System Architecture No central server. Constrained broadcast. –Every peer sends packets it receives to all of its peers (typically 4). –Life-time of packets limited by time-to-live (typically set to 7). –Packets have unique IDs to detect loops. Hooking up to Gnutella systems requires that a new peer knows at least one Gnutella host.

10 A. Frank Gnutella Limitations (1) The more users – the less efficient: –With 56K-modems, users won’t be able to send multiple search requests quick enough to keep up with the amount of people online. –When too many people search simultaneously, traffic backs up. –Since 56k-modem users are also nodes connecting hundreds of other users, that network segment is essentially cut off.

11 A. Frank Gnutella Limitations (2) May cause a bottleneck: 1.User A makes a request for a file from user B. 2.User B is offline. 3.The Gnutella software sends a “push” packet broadcast to all the other users connected to user A, instead of routing it back to where it came from. 4.This lack of routing and pushing when the host is offline contributes to more then 50% of the total traffic on bad days.

12 A. Frank Problem of Free-riding: –24 hour sampling period: 70% of Gnutella users share no files. 50% of all responses returned by top 1% of sharing hosts. –A social problem not a technical one. –Problems: Degradation of system performance: collapse? Increase of system vulnerability. –Verified hypotheses: H1: A significant portion of Gnutella peers are free riders. H2: Free riders are distributed evenly across domains. H3: Often hosts share files nobody is interested in. Gnutella Limitations (3)

13 A. Frank PeerCast (1) Peercast is a peer-to-peer file-sharing program. It is designed for people to broadcast streaming media on the Internet without need for expensive servers or bandwidth.

14 A. Frank No central server, each user can be a client, server or broadcaster of streams. The client software uses the Gnutella 0.6 protocol, but is not connected to the Gnutella file share network. Instead of downloading files, the users download streams. PeerCast (2)

15 A. Frank PeerCast offers considerable savings: –for broadcasters: No need to provide bandwidth for all listeners. A single 56K modem can be used to broadcast to the entire network. –for companies: PeerCast offers broadcast directly to a single client and that provides the source for the entire network. PeerCast (3)

16 A. Frank Anonymous broadcasting: –clients do not tell each other if they are the source or just listening. Support for all popular media players (WinAmp, XMMS etc…). Full support for ICY-Metadata (MP3) and OGG comment headers for title/artist/song display. PeerCast (4)

17 A. Frank Sometimes the audio is jittery, or buffering is done often: –You may be getting relayed from someone who is having network problems. –Not enough bandwidth to relay to you. –A traffic slow down at their ISP. PeerCast Limitations (1)

18 A. Frank SEs vs. P2Ps? SEs operate under a centralized system. The problems: 1.It takes a lot of time to refresh a large index. 2.It is costly to maintain the hardware to gather up information from all over the Web. In P2P: 1.Refreshing the index is much faster. 2.Searching for relevant information is done via a Distributed Search.

19 A. Frank 1.Refreshing the Index In P2P, –When a user goes offline, his content disappears. –Coming back online, makes all his content visible again and indexed. For example: –It will take time with MP3 SEs to update their index, in case that a web site, which has indexed MP3 files, is closed. In contrast, Napster’s index is updated the minute a user goes offline/online.

20 A. Frank 2.Distributed Search (1) The idea: No need to operate from a centralized base. No need to send the crawlers all over the web and back to gather information. Users themselves will transmit the information they possess and will report it to the system.

21 A. Frank 2. Distributed Search (2) Examples: Napster distributes the query. –Napster’s users use a central index, but the information is taken from various sources, the users themselves, not from a central place. Gnutella distributes both the query and the index. –The query is sent out to all the computers in the network, and returns directly to the sending user with the findings. –The search is done from PC to PC, and not over an index, so Gnutella’s index is actually the whole network.

22 A. Frank More Advantages of P2P over SEs Anonymous. No ads, banners and advertising. Works on any OS. –No need to consider the OS or the Browser of the user in order to make a query.

23 A. Frank What do you need for P2P? At least 2 PCs Network Interface Cards (NICs) for each PC Cable between NICs A Network OS that supports P2P

24 A. Frank P2P for reliable E-Commerce: –Dynamic business models –Trust establishment –Peer-to-peer transactions –Decision making Quality of Service (QoS): –Improved fault tolerance –Quality guarantees Research Issues for future systems (1)

25 A. Frank Richer data model: –Relational XML –Metadata model –Improved search Multimedia Message-based applications: –Scalability –Improved search capabilities Mobility Research Issues for future systems (2)

26 A. Frank Some Leading P2P Websites (1) Centralized server applications : –ICQ A user-friendly Internet tool that informs you who's on- line at any time and enables you to contact them at will. –WorldStreet A website in the financial industry field. It connects securities market participants in a unified environment in which information and ideas are shared between interested and entitled parties. –MyCio A distribution of anti-virus and software updates. MyCio is designed for McAfee anti-virus and PC firewall programs but extensible to support other applications.

27 A. Frank Some Leading P2P Websites (2) Distributed services to share files of all types: –FreeNet freenet.sourceforge.netfreenet.sourceforge.net –Aimster –Alpine –iMesh

28 A. Frank Some more P2P sites MyNapster OpenNap Scour Exchange Gnumm FileNavigator Napigator Riffshare