Seminar: Information Management in the Web

1
Seminar Information Management in the Web

• Gnutella, Freenet and more an overview of file
  sharing architectures
• Thomas Zahn

2
Peer-to-Peer - Introduction

• "opposite" of Client/Server
• no central servers ? information highly
  distributed
• every peer acts as a client AND server
• -gt can query, reply to queries and route messages
  at the same time
• every peer can directly "talk" to any other peer

3
Popular Peer-to-Peer Networks

• Napster
• Gnutella
• Freenet
• FastTrack (Kazaa)
• CHORD, CAN, PASTRY, TAPESTRY

4
Napster

• was used primarily for file sharing
• NOT a pure peer-to-peer network
• gt hybrid system
• peer turns to central DB for querying
  (client/server)
• peer downloads directly from other peer(s)
  (peer-to-peer)

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Napster
5
4
central DB
6
3
3. Download Request
2. Response
1. Query
4. File
1
2
Peer
6
Gnutella - overview

• pure peer-to-peer
• used for file sharing
• very popular gt practically proven ?
• very simple protocol
• no routing "intelligence"
• messages are always broadcast

7
Gnutella - PING/PONG
3
6
Ping 1
Ping 1
Pong 3
Pong 6
Pong 6,7,8
Pong 6,7,8
Ping 1
7
5
Pong 5
Pong 3,4,5
1
2
Pong 7
Ping 1
Ping 1
Ping 1
Pong 2
Known Hosts 2
Pong 8
8
Pong 4
Ping 1
3,4,5
6,7,8
Query/Response analogous
4
8
Gnutella - Pro Con

• VERY simple protocol gt easy to implement
• very little overhead
• practically proven functionality (?)
• message broadcasts flood network
• gtheavy network traffic
• gt bad, bad scalibility

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Gnutella Reachable Peers
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Gnutella Generated Traffic in Bytes (1)

• query message length 83 bytes
• simple query relaying (no responses)

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Gnutella Generated Traffic in Bytes (2)

• Mean percentage of users who typically share
  content 30
• Mean perctg. of users who typically have
  responses to search queries 40
• Mean number of search responses the typical
  respondent offers 10
• Mean length of search responses the typical
  respondent offers 60
• ? "Standard client settings yield a whopping 17MB
  generated in response to search query "

12
Freenet - Concepts

• peer-to-peer file storage retrieval system
• every document has a globally unique ID
• efficient (?) retrieval algorithm
• documents are retrieved with sublinear effort
• routing based on likelihood of answer capability
• focus on security

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Freenet Query Routing (1)

• every peer maintains routing table
• table contains known peers along with the IDs of
  the documents their are storing
• a request is routed to the peer most likely to
  have an answer (closest matching ID)
• responses are sent back upstream
• intermediate peers also store document and
  augment their routing tables

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Freenet Query Routing (2)
Routing Table B 14, 20 Doc Cache 19, 30
2. Forward to best match
C
Routing Table C 19, 30 D 45, 51 Doc Cache 14,20
Routing Table C 19, 30 D 17, 45, 51 Doc
Cache 14, 17, 20
Routing Table B 14, 20 X 47, 60 Doc Cache 5, 89
Routing Table B 14, 17, 20 X 47, 60 Doc
Cache 5, 17, 89
1. Query for doc 17
3. C has no match -gt backtrack
A
B
4. Forward query to 2nd best match
6. Route back response
Routing Table B 14, 20 Z 105, 110 Doc Cache 17,
45, 51, 102, 205
5. Send back doc 17
D
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Freenet Document Insert

• analogous to query routing
• insert is routed to the peer most likely to be
  interested in new doc (closest matching ID)
• intermediate peers cache document and augment
  routing tables
• until TTL is reached

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Freenet - Discussion

• efficient routing algorithm (compared to
  Gnutella)
• adequate security features/heuristics (the more
  popular a document, the more frequently it gets
  cached)
• no metasearch
• no updates, deletes possible
• worst case query routing DFS

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FUtella Concepts

• peer-to-peer platform for general knowledge
  sharing
• tries to model learning style of humans
• content-based routing
• combines and extends approaches from
• Gnutella (message format)
• JXTA (peer groups)
• JXTA Search (queryspaces and registrations)
• FreeNet (routing of registration discoveries)

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FUtella - Knowledge Groups
FUtella Net
Knowledge Group Queryspace "Computer
Architecture"
Group Head Peer E
Inserts Registration
E
. . .
Mi
M1
Members M1 - Mi
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FUtella - Knowledge Group Discovery 1
Routing Table "computer" -gt B "computer analysis"
-gt Y Registration Cache "computer" B "computer
analysis" Y
Routing Table "computer analysis" -gt C "computer
systems" -gt D "data base" -gt A Registration
Cache "computer analysis" Y "computer systems"
Z "data base" X
C
1. Discovery request "computer architecture"
2. Forward discovery request
3. C has no cached registration for "computer
architecture -gt backtrack
A
B
Routing Table "computer" -gt B "computer systems"
-gt Z "computer architecture" -gt E Registration
Cache "computer systems" Z "computer"
B "computer architecture" E
D
Routing Table "computer" -gt B "data base" -gt
X Registration Cache "computer" B "data base" X
4. Forward discovery request to 2nd best match
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FUtella - Knowledge Group Discovery 2
6. Forward discovery response
5. Discovery response
A
B
D
Containing registration "computer architecture" E
Routing Table "computer analysis" -gt C "computer
architecture" -gt D "computer systems" -gt D "data
base" -gt A Registration Cache "computer analysis"
Y "computer architecture" E "computer
systems" Z "data base" X
Routing Table "computer" -gt B "computer systems"
-gt Z "computer architecture" -gt E Registration
Cache "computer systems" Z "computer"
B "computer architecture" E
Routing Table "computer" -gt B "computer
architecture" -gt D "data base" -gt X Registration
Cache "computer" B "computer architecture"
E "data base" X
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Futella - Query Processing
1. Discovery request "computer architecture"
2. Forward discovery request
C
3. C has no cached registration for "computer
architecture -gt backtrack
A
B
4. Forward discovery request to 2nd best match
6. Forward discovery response
D
7. Send query
5. Discovery response containing cached
registration
8. Forward query to member
E
M1
9. Query response
8.Forward query to member
Knowledge group "computer architecture"
. . .
9. Query response
Mi
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Futella - Test Results (1)
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FUtella - Test Results (2)
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Conclusion

• first and second generation P2P systems still
  most widely used
• practically proven
• very flexible in terms of topology
• bad scalibility (Gnutella)
• no guaranteed lower bound on query effort
  (Freenet)
• (scientificly) far better approach DHTs (see
  next presentation)

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Questions ?

• ?