Delay Tolerant Networking

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Delay Tolerant Networking

• Dave Wick
• RVS Group
• University of Berne

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Overview

• Motivating a Delay Tolerant Network
• DTN Framework
• Routing Ideas
• Real World Applikation Zebranet
• Summary Outlook

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Overview

• Motivating a Delay Tolerant Network
• DTN Framework
• Routing Ideas
• Real World Applikation Zebranet
• Summary Outlook

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Outer Space Network
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What is a DTN?

• Network with intermittent connectivity
• Long variable delays
• Asymmetric data rates
• High error rates
• Consists of heterogenious networks

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Why do we need DTN research?

• To cover regions with no infrastructure
• Networks with pedestrians
• Intelligent highways
• Military battlefield
• Challange for academic research
• First the technology, then the need

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Challenges of a DTN

• Naming addressing
• Routing
• Data transmission (retransmission, flow control)
• Application interface
• Security
• QoS (prioritisation)
• Timesynchronization

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Overview

• Motivating a Delay Tolerant Network
• DTN Framework
• Routing Ideas
• Real World Applikation Zebranet
• Summary Outlook

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The DTN framework

• Overlay architecture
• Network of regional networks
• Gateways, routers and hosts
• Delay tolerant between within regions
• Unique identifiers region id, host id

Gateway
Region B
Region A
Address region b, host x
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The DTN framework

• Bundle concept
• Bundlelayer between app- region specific layers
• Use of bundles instead of packets
• Bundle store forward-routing
• Custody transfer
• Security
• Prioritization
• No routing algorithm proposed

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Overview

• Motivating a Delay Tolerant Network
• DTN Framework
• Routing Ideas
• Real World Applikation Zebranet
• Summary Outlook

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Routing algorithms

• Epidemic routing
• CAR, Context Aware Routing
• DTC, Disconnected Transitive Communication
• MoVe, Motion Vector Routing

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Assumptions
Epi CAR DTC MoVe
Hosts cooperate for transmission x x x x
Single carrier x x x
Use of indirect connectivity (through underlying network) x x
History of recently connected host x x
Position-information required x
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Context Aware Routing

• Calculates delivery probability for every known
  host
• Broadcast information in cloud
• Using the underlying proactive routing protocol
• Every node maintains a table containing the
  probabilities
• Send message directly if destination is in cloud
• Else send message to host with highest
  probability
• If host is unknown, deliver to host with highest
  mobility

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Delivery probability

• Adaptive weighted utility function
• Change rate of connectivity
• Probability of colocation with destination-host
• Weights are adapted at runtime

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CAR roundup

• Assets drawbacks
• Low number of messages on propagation
• Lightweight algorithm
• Table setup required
• Learning phase required
• Doesnt scale well

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Disconnected Transitive Communication

• Based as well on calculation of a utility
• Extension with additional measures
• 3 phases to collect information and send data
• Utility calculation
• Most recently noticed
• Most frequently noticed
• Future plans
• Power
• Rediscovery interval
• Source defined utility function

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DTC roundup

• Assets drawbacks
• More independent measures
• Adaptive, individual utility function
• Capsuled utility calculation
• Heavy traffic on demand
• No implementation

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Motion Vector

• Routing based on actual movement of the node
• Needs location information of itself and
  destination
• Motionvector based on past locations
• Broadcast hello-message to neighbors
• Send to host with closest distance (cd)

cd
ß
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MoVe roundup

• Assets drawbacks
• No history, no learning needed
• Easy to implement algorithm
• Position data needed
• Performs very badly in real world

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Overview

• Motivating a Delay Tolerant Network
• DTN Framework
• Routing Ideas
• Real World Applikation Zebranet
• Summary Outlook

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Zebranet

• The goal is tracking of zebras in wildlife
• Position, direction, heart rate, body temperature
  etc.
• Constraints
• One year of operation
• Low weight (lt1 kg)
• Wide range (gt1000 km2)
• No fixed basestation
• High data delivery rate

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Zebranet implementation

• Collar design
• Low high range radio
• Solar panels, battery
• 4 mbit flash memory
• Routing
• Flooding
• History based

Zebras
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Overview

• Motivating a Delay Tolerant Network
• DTN Framework
• Routing Ideas
• Real World Applikation Zebranet
• Summary Outlook

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Summary Outlook

• Framework allows to implement new algorithms
  quite fast
• Routing performance depends strongly on chosen
  scenario
• Realworld applications are rare and have
  experimental character
• Focus on improvement of existing protocols
• Decrease chattyness
• Improve buffer allocation deletion
• Message duplication for more efficient delivery
• Refine routing algorithms
• Merging different routing approaches