Delay Tolerant Networks

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Delay Tolerant Networks

• Computer and Network Architectures
• Björn Grönvall

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History

• Idea from InterPlaNetary Internet Proj.
• Deep space communications
• Create a network of Internets
• Handle enormous propagation delays
• Intermittent connectivity
• Extend ideas to handle terrestrial comm
• Delay Tolerant Networks (DTNs)

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Todays Internet

• TCP/IP protocol suite assumes that
• Continuos, bi-directional end-to-end path exists
• Round trip times (delays) are small
• Error rates are small
• Not necessarily true in challenged networks

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Challanged Networks

• Intermittent reachability
• Asymmetry
• Signal conditions
• Radio silence
• High error rates (due to poor S/N)
• Long or variable delays

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New Architecture

• Not based on packet switching
• Borrows ideas from message switching
• Store-and-forward entire bundles
• Bundles are much larger than packets and are
  transferred towards the destination (think email)

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Bundles

• Bundles are transferred using opportunistic or
  scheduled contacts
• Fly by satellites
• Moving troops
• Bundles are held on persistent storage
• Requires storage in network

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Bundle Custody

• Retransmissions happen on a hop-by-hop basis
  rather than end-to-end
• After successful transmission custody is
  transferred across the hop
• Transfer of custody frees resources
• Reliable delivery needs more

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Class of Service/Reliability

• Custody Transfer
• Confirmation to sender
• Return Receipt
• Confirmation to original source
• Bundle-Forwarding Notification
• Notification of forwarding (to source)

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Research Problems

• How to perform optimal routing over DTNs
  (scheduled contacts)
• Automatic prediction/scheduling of communication
  opportunities based on past experiences
• Routing for resource poor terminals in sensor
  networks