7DS: Node Cooperation in Mostly Disconnected Networks

1
7DS Node Cooperation in Mostly Disconnected
Networks

• Henning Schulzrinne
• (joint work with Arezu Moghadan, Maria
  Papadopouli, Suman Srinivasan and Andy Yuen)
• Dept. of Computer Science
• Columbia University

2
Problems with Wide Area Wireless

• 802.11 currently hard to deploy across city or
  large area
• 2.5G/3G wireless networks not suitable for large
  data volumes
• cost and network design
• Problem How can mobile devices / gadgets get and
  generate information?
• Examples
• PDAs and smartphones
• digital content such as news, maps, tourist
  information, entertainment
• digital still and video cameras ? MB of data
• Solution 7DS!

3
Concept

• Use local peer-to-peer wireless networks to
  exchange information
• Peers can get information they do not have from
  another peer
• Model core Internet data applications
• Internet ? mobile web access (retrieval)
• Mobile ? Internet email (messaging)
• Once wireless 7DS network set up, it could be
  used for any purpose
• Getting web pages from peers
• Sending e-mails
• File transfer to selected client

4
Illustration
In the absence of the Internet, nodes can
exchange information amongst themselves
Internet
5
Realization
6
System architecture
web browser
proxy search engine
Internet
email client
email queue
7
Design

• Peer-to-peer network set up using zeroconf
• Protocol enables devices to get IP address and
  communicate without a DHCP / other server
• Proxy server serves content
• If connected to Internet, functions normally
• If not connected, connects to peers to get
  information

8
Design

• Search engine
• Allows self / peers to search within the devices
  database for necessary information
• Multicast querying system
• Allows peers to query systems in peer-to-peer
  network
• Searches can be for files or keywords
• Transport System
• To forward e-mail

9
Design
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Connection Proxy Server

• Connection set up using zeroconf protocol
• Similar to AppleTalk, Microsoft NETBIOS, Novell
  IPX
• Uses link-local addressing, multicast DNS, DNS
  service discovery
• Proxy server
• Peers user client uses localhost proxy server by
  default
• Detects Internet connection availability
• If Internet, normal network operation
• No Internet, peer-to-peer data exchange

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Search Engine

• Provides ability to query self for results
• Searches the cache index using Swish-e library
• Presents results in any of three formats HTML,
  XML and plain text
• Similar in concept to Google Desktop

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Query multicast engine

• Used to actually exchange information among peers
• Requesting peer broadcasts a query to the network
• Responding peers reply if they have information
• Send encoded string with list of matching items
• Requesting peer retrieves suitable information

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Analytical work on 7DS

• Email upload application
• How to remove message replicas upon email
  delivery?
• Impact of a feedback channel?
• P2P file exchange
• Throughput related to content popularity model
• How to improve dissemination for unpopular
  content?
• Push based vs. Pull based data dissemination
• Bloom filter based vs. query based strategy
• Optimal design parameters for Bloom filter based
  algorithm

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Email Delivery App

• How to remove redundant message replicas upon
  email delivery?
• Time-based (TB) purge message upon TTL
  expiration TB(TTL)
• Hop-based (HB) purge message when dissemination
  tree reaches specific depth and breadth
  HB(breadth,depth)
• Feedback (FB) receive notification upon message
  delivery
• 4 Schemes TB, HB, TB/FB, HB/FB
• Storage cost (number of message replicas)

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Email Delivery App (Cont d)

• Hop-based scheme is superior, with smaller
  expected cost and variance
• Expedited (100sec) and reliable message delivery
  (Pd1) possible at small cost
• 50 replicas for HB(7,2)
• With feedback HB(7,2) has a cost of 18 replicas

Stopping time time when all message replicas are
purged Message delivery time time when email
message is delivered FB and NFB schemes have same
message delivery time statistically Stopping time
and message delivery time is the same for FB
schemes
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Conclusion

• 7DS promises to allow local connectivity
• Exchange of information within local network
• No user intervention unless absolutely necessary
• New step in practical, large-scale wireless
  networking with gadgets?
• Remains to be seen