Peer-to-Peer (p2p) Computing

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Peer-to-Peer (p2p) Computing

• CS-328

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In the beginning...

• was the Internet, and the only host computers on
  the Internet were UNIX
• and all was peaceful and calm (and peer-to-peer,
  by the way)
• and the UNIX weenies ruled supreme
• until the Web browser and Web server were
  invented and the Internet became the the
  playground of the masses

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so where did Client/Server come from ?

• it was a revenue model developed by networking
  companies (Microsoft, Novell, etc) at the
  insistence of Corporate America
• easier to manage centralized data centers
• client/server model fit business applications
• replace expensive mainframe computers with cheap
  desktop PCs accessing databases on cheap
  (relatively) PCs
• clients and servers

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(more)

• As C/S developed most of the big projects failed
  
• databases werent fast enough or scaleable enough
• solution move the database servers to UNIX (its
  faster) UNIXs networking environment was based
  on TCP/IP so the desktop clients were given a
  TCP/IP stack (enter winsock.dll, Novells DOS
  based stack )
• the intranet becomes heterogeneous

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(more)

• The web browser becomes the GUI of choice for
  corporate America (and elsewhere)
• cheap
• on every desktop
• easy to develop applications with

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(more...)

• The Internet and intranets grow like wildfire and
  the Client/Server model becomes the predominate
  application model
• Corporate America loves it
• resembles the old data center model
• centralized data and control over data
• big servers and server farms

UNTIL.
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(more)

• Someone decides they want to be in charge of
  their own data, and exchange it with whoever they
  want to.
• By the way, this could be done on the original
  Internet because all of the UNIX hosts had FTP
  clients and servers.
• Enter Peer-to-peer
• Napster, Gnutella and FreeNet to name a few

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What is it...

• Peer-to-peer computing is the sharing of computer
  resources and services by direct exchange between
  systems.
• These resources and services include the exchange
  of information, processing cycles, cache storage,
  and disk storage for files.
• Peer-to-peer computing takes advantage of
  existing desktop computing power and networking
  connectivity, allowing economical clients to
  leverage their collective power to benefit the
  entire enterprise.
• In a peer-to-peer architecture, computers that
  have traditionally been used solely as clients
  communicate directly among themselves and can act
  as both clients and servers, assuming whatever
  role is most efficient for the network.

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Is this really new?

• The Original Internet was all P2P
• Windows for Workgroups (W4W)
• late 1980s
• Corporate data centers hated W4W
• it was unmanageable
• users loved it they didnt need the data center
• they could share data with each other
• they could share their desktop printers
• IRC (Internet Relay Chat)
• users thought they were chatting with each other
  (P2P) but under the covers it was really C/S, but
  it helped instill the P2P mindset

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What is driving P2P?

• Reduced the load on servers
• allows them to perform specialized services
  (such as mail-list generation, billing, etc.)
  more effectively
• can reduce the need for IT organizations to grow
  parts of its infrastructure in order to support
  certain services, such as backup storage.
• inexpensive computing power
• unused mips on desktop computers
• bandwidth
• and storage.
• Unused storage on desktop

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P2P servents/clients of note

• Napster
• brokered
• uses a central server for users to find one
  another but straight P2P to exchange files
• Gnutella
• a technology not a specific client
• old store and forward
• uses HTTP
• Freenet
• anonymous file sharing
• no central control
• no easy way to delete a files from the system
• has its own protocol

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Gnutella

• How Gnutella exchanges data

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Gnutella
HTTP Client
HTTP Client
HTTP Client
HTTP Server
HTTP Server
HTTP Server
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FreeNet
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BitTorrent

• Similar to Gnutella in that files are transferred
  using HTTP or HTTPS
• Files must be prepared before serving
• a meta info file is created (.torrent file)
• .torrent files are always encrypted for transfer
  (insures privacy)
• contains hashing info for blocks of the file to
  be shared
• also contains a list of URLs for trackers
• .torrent is placed on web server and served as
  regular file
• need to have application/x-bittorrent .torrent
  added to mime types
• must also be regiatered in browser to kick of the
  BitTorrent client app.
• User must find .torrents via web searches
• user clicks on link to .torrent
• browser activates client
• client connects to tracker in .torrent file

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BitTorrent

• Tracker lets client know where other clients are
• Download starts with some arbitrary part of the
  file
• Once you have started downloading parts of the
  file the tracker gives your name out to others so
  that you will also be uploading parts of the file
  to your peers.
• Users are encouraged to stay connected to the
  system after their download is complete so as to
  not interfere with others downloads

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BitTorrent

• The web site is serving up static files as
  normal, but kicking off the BitTorrent helper app
  on the clients.
• The tracker is receiving information from all
  downloaders and giving them random lists of
  peers. This is done over HTTP or HTTPS.
• Downloaders are periodically checking in with the
  tracker to keep it informed of their progress,
  and are uploading to and downloading from each
  other via direct connections. These connections
  use the BitTorrent peer protocol, which operates
  over TCP.
• The origin is uploading but not downloading at
  all, since it has the entire file. The origin is
  necessary to get the entire file into the
  network. Often for popular downloads the origin
  can be taken down after a while since several
  downloads may have completed and been left
  running indefinitely.

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BitTorrent

• Client ports 6881 6889
• Server ports 80(HTTP) or 443(HTTPS)
• Home page http//bittorrent.com

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P2P with JINI

• JINI is Suns technology for Impromptu networks
• under the covers JINI is RMI
• when servant is started it bootstraps (registers)
  itself with the JINI lookup service (just like an
  RMI server)
• the lookup service stores remote references to
  the peers on the network
• peers then use RMI to connect directly to one
  another
• This is a brokered approach, similar to Napster
• main difference is Napsters brokering is done
  using a server and a database where this is using
  the RMI/JINI lookup service.
• If the registry drops off line the there is no
  service unless every servant can start up a
  registry if one cant be found.

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P2P with Multicast Sockets

• The main problem with the JINI/RMI implementation
  of P2P is the registry it is a single point of
  failure I.e. if the registry goes down then the
  P2P network is dead. No one can find a peer.
• Enter Multicast sockets
• similar to UDP (sends datagrams) but sends them
  multicast
• sender part of servant periodically broadcasts
  its presence
• receiver part of other servants receive the
  datagram and add the peer to their list of peers
  currently on line
• (this is like JINIs lease concept) if the
  receivers stop receiving the Im here message
  from a peer the assumption will be that the peer
  has left the network and the missing peer can be
  removed from the list of peers currently on line.
• Peers can communicate directly with one another
  using either TCP or UDP.

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P2P with JXTA

• Created by SUN in response to growing popularity
  of P2P
• Attempts to sole the following P2P problems
• Security/Authentication large p2p applications
  like AOL IMr and MSN IMr use central servers to
  bootstrap users onto the network. This helps
  insure that a particular user uses a particular
  online identity.
• Peer Discovery realizing the presence of your
  peers is difficult, multicast on the surface
  looks good but doesnt work well outside of the
  LAN environment
• Network Incompatibility currently each p2p
  product ends up with its own set of protocols
  thereby allowing no interoperability
• Platform Incompatibility developers must rewrith
  low level aspects of their p2p apps for each
  platform. Wireless and mobile devices have a very
  limited menu of p2p tools.

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JXTA (more)

• How do you do this?
• Standardize the low level protocols
• JXTA is designed to be a general infrastructure
• because all JXTA apps use the same low level
  protocols they will all be compatible
• JXTA networks consist of 3 basic entity types
• peer/peer groups
• any peer that uses JXTA protocols
• Peer Discovery
• Peer Resolver
• Peer Information
• Peer Membership
• Pipe Binding
• Endpoint Routing
• advertisements XML documents to replace the
  JINI Multicast function
• pipes/messages one-way communication channels

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JXTA (more)

• JXTA is still under development and is still
  resolving all of the problem areas.
• For more info
• http//www.jxta.com
• http//java.sun.com
• http//www.peerintelligence.com
• http//www.peertal.com