This document discusses peer-to-peer (P2P) file sharing networks. It describes how early systems like Napster and Kazaa worked, comparing their centralized index models to the decentralized BitTorrent protocol. BitTorrent uses a tracker to coordinate file downloads between seeds (peers with the full file) and leeches, allowing transfers from multiple locations simultaneously for high speeds. While efficient, P2P networks face challenges around free-riding and availability of unpopular content.

1. Join the swarm!
PRASHANTH S
1CR11EC076

2.  Peer to peer
 More users, better it is
 Large amounts of data transfer
 Encourages peers to upload
 > a quarter of a billion monthly users*

3.  Client-server architecture
 Conventional method used for years
 Direct connection between server & client
 Large no. of dedicated servers

4.  Download data at high speeds
 Reach high transfer rates very quickly
 No loss of files once uploaded
 File availability does not depend on popularity

5.  Single point of failure
 Maintenance of servers
 Servers require large bandwidth
 Website crash eg: VTU website

6.  Decentralized communications model
 Nodes(peers) are interconnected
 Content not on a central server
 Content present on peer’s computer
 No need of server for data transfer
 Peers->provide and consume resources

7.  Designed as P2P MP3 sharing service
 Song downloaded from other peer
 Server only used to connect peers
 Redefined the internet

8.  Peers run Napster utility
 Central Index Server(CIS)
 Peers connect to CIS
 Peers inform CIS about files on their directory
 When the user wants a file, he queries the CIS
 CIS directs them to the computer that has it
 Connection is established between peers
 Transfer is initiated

10.  Transfer takes place from a single source
 Speed limited to upload capacity of source
 Requires only a subset of users to share
 Encourage free-riding
 Exerts too much load on original sources
 Napster was shutdown in its original form

11.  No CIS like the one used in Napster
 Made use of FastTrack protocol
 Super nodes and ordinary nodes
 1 super node serves 60 to 150 ordinary nodes

12.  Software comes with a list of super nodes
 The client connects to one of the super nodes
 A file request in passed through super node
 Super node passes the query super nodes
 The other super nodes pass it to ordinary nodes
 The ordinary nodes ask other ordinary nodes
 7 levels deep
 If a file is found, transfer takes place
 Super nodes do not take part in the transfer

15.  Super node has to handle lot of traffic
 Transfer happens between only 2 peers
 Bandwidth available to receiver not utilised
 Encourages free-riding

16. Similarities with Napster:
 Users share their files with everyone else
 Users run a software to connect to network
Differences with Napster:
 No central database like Napster
 Machines inform other machines about files
 Achieved using distributed query approach

17.  User types in the name of the required file
 This machine requests other known machines
 These machines search their directory
 If not found, forward the request
 This process may go 7 levels deep
 A single search may cover 8000 machines

19.  The 8000 machines may not contain the file
 Takes time for search results to appear
 Bandwidth to handle requests from other users
 Bandwidth available to receiver not utilised

20.  Seeder

21.  Seeder
 Leecher

22.  Seeder
 Leecher
 Torrent file

23.  Seeder
 Leecher
 Torrent file
 Swarm

24.  Seeder
 Leecher
 Torrent file
 Swarm
 Tracker

25.  Create a torrent
◦ Select files
◦ Choose a tracker
◦ Select saving directory
◦ Select piece size(better left untouched)
◦ Start seeding!!

26.  Downloading files
◦ Download torrent file
◦ Client software communicates with a tracker to find
 Other computers that have the complete file (seeds)
 Those with a portion of the file
◦ Peers communicate with each other
◦ Download/upload starts from/to different peers

27.  .torrent file
◦ Metadata about the required file
 The URL of the tracker
 Pieces <hash1, hash 2,…, hash n>
 Piece length
 Name of the file
 Length of the file

28.  Tit for tat approach
 Optimistic unchoking
 Random first piece
 Rarest first
 Endgame mode

29.  Pollution attack
 Bandwidth shaping

30.  Open source
 Share large amount of data quickly
 Discourages free-riding
 More users, the better it is
 Download takes place from multiple locations
 Reduces burden on original distributors
 Easy to download expensive software, movies
 Organisations distribute legitimate software

31.  Leechers may leave swarm after download
 Unpopular content has no seeds
 Takes time to reach high download speeds
 No streaming playback