PowerPoint bemutat

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Introduction

• Widespread unstructured P2P network
• Currently between 200,000 300,000 hosts
• Ideal as a research test bed
• Large scale network demonstrates the need for
  scalable P2P protocols
  
• A Gnutella client has 4-10 TCP connections to
  other peers
  
• For signaling traffic UDP is used and to make use
  of the benefits of server based networks a
  ultra-peer state was created

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Introduction (Cont.)

• Ultra-peer status is self assigned by powerful
  peers and provides some extra functionality
  compared to ordinary nodes
  
• There exist many freely available Gnutella
  clients
  
• Some of the most popular are
• Limewire
• Bearshare
• Morpheus
• Shareaza
• It has the most increasing number of users
• It has a very pleasant GUI and connects also to
  eDonkey and BitTorrent

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Its Main Features

• This protocol underlies much of the current
  file-sharing activity on the Internet.
  
• It is based on TCP/IP and http!
• A file sharing network (fsn) is a bunch of
  machines that exchange files using gnutella.
  
• To connect to a gnutella network, you need the IP
  address of one single machine that is already
  part of the network.

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Gnutella

• Peer-to-peer indexing and searching service.
• Peer-to-peer point-to-point file downloading
  using HTTP.
  
• A gnutella node needs a server (or a set of
  servers) to start-up gnutellahosts.com
  provides a service with reliable initial
  connection points

But introduces a new single point of failure!
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Gnutella vs. Napster

• Like Napster, distributed file storage and
  transmission
  
• Added the ability to distribute file discovery
• Ask your direct peers who else they know
• Query those machines directly

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Concepts of Unstructured Services

• There are many interesting ideas being explored
• Breaking shared files into many parts to both
  increase bandwidth (parallel I/O) and increase
  security of content as no one site can access
  files without cooperation from its peers
• This type of technology makes censorship very
  hard.
  
• MojoNation has a load balancing and scheduling
  algorithm in the form of micro payments to reward
  those who contribute most to the community of
  peers.
• Gnutella - which is a family of related products
  -- is usually described as a P2P search engine as
  its interface is nearer that of a search engine
  than a Web file system

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Characteristics

• Gnutella is a distributed system for file
  sharing
  
• provide means for network discovery
• provide means for file searching and sharing
• Defines a network at the application level
• Employs the concept of peer-to-peer
• all hosts are equal (symmetry)
• there is no central point
• anonymous search, but reveal the IP addresses
  when downloading

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connection

• Once you establish connection to the first
  servent, you announce your presence.
  
• The first servent will pass on that message to
  all the servents that it is connected to, and so
  on.
  
• These servents all reply with data about
  themselves
  
• how many files it is sharing
• how many kilo bytes the files take up
• This already adds up to a lot of traffic!

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Gnutella File Sharing model

• Users register files with network neighbors
• Search across the network to find files to copy
• Does not require a centralized broker (as Napster)

Copying Final Fantasy 4
Bob
Carol
Where is Final Fantasy 4?
Carol has Final Fantasy 4
Where is Final Fantasy 4?
Alice
Ted
Carol has it
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Decentralized File-sharing Model
Resource Discovery

• Peers have same capability and responsibility
• The communication between peers is symmetric
• There is no central directory server Index on the
  metadata of shared files is stored locally among
  all peers
  
• Gnutella
• FreeServe
• MojoNation

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Decentralized (Cont.)
Resource Discovery

• every user acts as a client, a server or both
  (servent)
  
• User connects to framework and becomes a member
  of the community, allowing others to connect
  through him/her
  
• Users speak directly to other users with no
  intermediate or central authority
  
• No one entity controls the information that
  passes through the community

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Advantages and Disadvantages
Resource Discovery

• Advantages
• Inherent scalability
• Avoidance of single point of litigation
  problem
  
• Fault Tolerance
• Disadvantages
• Slow information discovery
• More query traffic on the network

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Unstructured Decentralized Services

• There some 200 available Napster clones to
  support this area http//www.ultimateresourcesite.
  com/napster/main.htm
  
• Currently the most popular is Imesh
  http//www.imesh.com, which has some 2 million
  users and can share any type of file.
  
• Some of the best known file sharing systems are
  
  
• MojoNation http//www.mojonation.net
• Freenet http//freenet.sourceforge.net/
• Gnutella http//gnutella.wego.com/
• These three are not server based like Napster but
  rather support waves of software agents
  expressing resource availability and interest
  propagating among an informal dynamic networks of
  peers

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DFS Variations

• DFS Distributed File Sharing

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P2P File Sharing Benefits

• Cost sharing
• Resource aggregation
• Improved scalability/reliability
• Anonymity/privacy
• Dynamism

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Management/Placement Challenges

• Per-node state
• Bandwidth usage
• Search time
• Fault tolerance/resiliency

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Gnutella in Details

• Share any type of files (not just music)
• Decentralized search unlike Napster
• You ask your neighbors for files of interest
• Neighbors ask their neighbors, and so on
• TTL field quenches messages after a number of
  hops
  
• Users with matching files reply to you

Figure from http//computer.howstuffworks.com/file
-sharing.htm
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The Gnutella protocol (v0.4)

• PING Notify a peer of your existence
• PONG Reply to a PING request
• QUERY Find a file in the network
• RESPONSE Give the location of a file
• PUSHREQUEST Request a server behind a firewall
  to push a file out to a client.

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Joining Gnutella Network
Gnutella Network

• The new node connects to a well known Anchor
  node.
  
• Then sends a PING message to discover other
  nodes.
  
• PONG messages are sent in reply from hosts
  offering new connections with the new node.
  
• Direct connections are then made to the newly
  discovered nodes.

New
PING
PING
PING
PONG
PING
PING
A
PING
PING
PONG
PING
PING
PING
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Properties of the Flooding

• Searching by flooding
• If you dont have the file you want, query 7 of
  your partners.
  
• If they dont have it, they contact 7 of their
  partners, for a maximum hop count of 10.
  
• Requests are flooded, but there is no tree
  structure.
  
• No looping but packets may be received twice

Note Play gnutella animation at
http//www.limewire.com/index.jsp/p2p
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Query flooding

• Gnutella
• no hierarchy
• use bootstrap node to learn about others
• join message

• Send query to neighbors
• Neighbors forward query to all attached neighbors
  (floods)
  
• If queried peer has object, it sends message back
  to querying peer

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More on query flooding

• Pros
• peers have similar responsibilities no group
  leaders
  
• highly decentralized
• no peer maintains directory info

• Cons
• excessive query traffic
• query radius may not have content when present
• bootstrap node still required
• maintenance of overlay network

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About the Flooding

• There is nothing that stops a servant flooding
  its network region with messages.
  
• Cost of maintaining Network
• Cost of searching file

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Breadth-First Search (BFS)
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Pros and Cons
Resource Discovery

• Benefits
• Peers speak directly with no central authority
• Nobody owns the Gnutella Network and nobody can
  shut it down
  
• No central point of failure
• Limited per-node state Isolated node failure can
  quickly and automatically be worked around
  
• Free loading
• Scalability
• Drawbacks
• Searches are less effective and can be slow
• Bandwidth intensive
• Gnutella network evolving to include controlled
  decentralization (limewire, bearshare, toadnode)

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Searching for a File
Gnutella Network

• A node broadcasts its QUERY to all its peers who
  in turn broadcast to their peers.
  
• Nodes route QUERYHITs along the QUERY path back
  to the sender containing file location details.
  
• To download files a direct connection is made
  using details of the host in the QUERYHIT
  messages.

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The Cooperation Spectrum
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Free Riding

• File sharing networks rely on users sharing data
• Two types of free riding
• Downloading but not sharing any data
• Not sharing any interesting data
• On Gnutella
• 15 of users contribute 94 of content
• 63 of users never responded to a query
• Didnt have interesting data
• Data from E. Adar and B.A. Huberman (2000), Free
  Riding on Gnutella

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Example GNUTELLA
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Summary of the Gnutellas Features

• Decentralized
• No single point of failure
• Not as susceptible to denial of service
• Cannot ensure correct results
• Flooding queries
• Search is now distributed but still not scalable

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Initials Problems and Fixes

• Freeloading WWW sites offering search/retrieval
  from Gnutella network without providing file
  sharing or query routing
  
• Block file-serving to browser-based
  non-file-sharing users
  
• Prematurely terminated downloads
• Software bugs
• long download times over modems
• modem users run gnutella peer only briefly
  (Napster problem also!) or any users becomes
  overloaded
  
• fix peer can reply I have it, but I am busy.
  Try again later

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Initials Problems and Fixes 2

• 2000 avg size of reachable network only 400-800
  hosts
  
• Why so small?
• modem users not enough bandwidth to provide
  search routing capabilities routing black holes
  
• Fix create peer hierarchy based on capabilities
• previously all peers identical, most modem
  blackholes
  
• connection preferencing
• favors routing to well-connected peers
• favors reply to clients that themselves serve
  large number of files prevent freeloading
  
• Limewire gateway functions as Napster-like
  central server on behalf of other peers
  
• for searching purposes

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Gnutella Enhancements

• Pings/Pongs can consume up to 50 of bandwidth
• Solutions
• Pong Limiting
• Pong Caching
• Ping Multiplexing
• http//www.limewire.com/index.jsp/pingpong

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Gnutella enhancements 2

• Cache query responses
• Results
• Evolving Protocol
• Gnutella Developer Forum
• UltraPeers
• Alternative query routing algorithms

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Can Heterogeneity Make GnutellaScale?

• Ideas
• Replace query flooding with multiple random
  walks
  
• Proactive replication
• replicas proportional to sqrt(request rate)
• Result Two orders of magnitude improvement in
  terms of query-time, per node load and message
  traffic
  

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Can Heterogeneity Make GnutellaScale? 2

• Gnutella assumption
• All peers are equal
• Not true! Heterogeneity among P2P peers (dial-up
  users vs. college users)
  
• Evolve topology to match node capacities
• Use random walks over this topology

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Can Heterogeneity Make GnutellaScale? 3

• Solution outline
• C_i, node capacity inj,i messages from j-i,
  outi,j messages i-j
  
• Init ini,jouti,j0, OutMaxi,jc_i/d_I
• Update according the messages received/sent
• Check if overloaded
• If so redirect high-input neighbor to neighbor
  with high OutMax (spare capacity)
  
• Intuitively, take yourself out of the loop
• If node cannot be found ask neighbor to throttle
  back
  
• Result Average query length reduces from 70 to
  2-9 hops
  
• depending on topology

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Measurement Results

• Who is sharing what?
• August 2000

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Problems With Gnutella

• Protocol scalability
• Message broadcast technique imposes limitations
  on the network size
  
• packets per message ?noPeersi
• In November 2000 dial-up bandwidth barrier
  reached
  
• Overlay network efficiency
• Random selection of peers results in inefficient
  use of the underlying network
  
• Redundant traffic generated on the Internet

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Heterogeneous connection qualities of the Gnutella

• 35 have upstream bottleneck bandwidth of at
  least 100Kbps
  
• only 8 have at least 10Mbps bandwidth
• 22 have bandwidth 100kbps or less

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Number of Shared Files
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Why Look at Gnutella

• Widespread unstructured P2P network
• Currently between 200,000 300,000 hosts
• 2006 still heavily in use by about 2 million
  users
  
• Gnutella clients (among others)
• LimeWire
• Morpheus
• BearShare
• OpenCola
• Shareaza
• It has the most increasing number of users
• It has a very pleasant GUI and connects also to
  eDonkey and BitTorrent
  
• Ideal as a research test bed
• Large scale network demonstrates the need for
  scalable P2P protocols

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Limewire Improvement on Gnutella

• Creation peer hierarchy based on capabilities
• previously all peers identical, most modem
  blackholes
  
• connection preferencing
• favors routing to well-connected peers
• favors reply to clients that themselves serve
  large number of files prevent freeloading
  
• Limewire gateway functions as Napster-like
  central server on behalf of other peers
  
• for searching purposes

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Limewire

• The Limewire P2P file sharing program connects to
  the Gnutella P2P network
  
• Limewire client software is widely recognized for
  its clean user interface that does not contain
  adware
  
• Sometimes billed as the fastest file sharing
  program
  
• Limewire claims to offer relatively good search
  and download performance
  
• Free Limewire software downloads are available
  for Windows, Linux and Macintosh operating
  systems
  
• Limewire Pro pay clients also exist

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BearShare

• The BearShare P2P file sharing program is a
  popular free software client for the Gnutella P2P
  network
  
• Both free and pay downloads of BearShare file
  sharing programs exist

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Shareaza

• Shareaza is an up-and-coming P2P file sharing
  program
  
• This client offers an extremely powerful search
  engine capable of connecting to multiple popular
  P2P networks including eDonkey, BitTorrent and
  Gnutella
• Shareaza file sharing software includes
  intelligence for detecting fake and/or corrupted
  files
  
• The free Shareaza download also contains no ads
  or spyware
  
• As the installed base of Shareaza client users
  grows
  
• expect Shareaza to become an even better P2P file
  sharing program

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Anonymous?

• The person you are getting the file from knows
  who you are
  
• Thats not anonymous.
• Other protocols exist where the owner of the
  files doesnt know the requester.
  
• Peer-to-peer anonymity exists

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Summary

• peer-to-peer networking applications connect to
  peer applications
  
• focus decentralized method of searching for
  files
  
• each application instance serves to
• store selected files
• route queries (file searches) from and to its
  neighboring peers
  
• respond to queries (serve file) if file stored
  locally
  
• Gnutella history
• 3/14/00 release by AOL, almost immediately
  withdrawn
  
• too late 23K users on Gnutella at 8 am this AM
• many iterations to fix poor initial design (poor
  design turned many people off)
  
• What we care about
• How much traffic does one query generate?
• how many hosts can it support at once?
• What is the latency associated with querying?
• Is there a bottleneck?