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					Introduction to Delay Tolerant Networks




       Delay Tolerant Networking


       Dave Wick
       RVS Group
       University of Berne




       8. Juni 2010                       1
Introduction to Delay Tolerant Networks



       Overview



       >      Motivating a Delay Tolerant Network

       >      DTN Framework

       >      Routing Ideas

       >      Real World Applikation: Zebranet

       >      Summary & Outlook



       8. Juni 2010                                 2
Introduction to Delay Tolerant Networks



       Overview



       >      Motivating a Delay Tolerant Network

       >      DTN Framework

       >      Routing Ideas

       >      Real World Applikation: Zebranet

       >      Summary & Outlook



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Introduction to Delay Tolerant Networks



       Outer Space Network


              Mars                                              Jupiter


                                                  Mars



                                                         Mars




                                   b
                              u
                                          Earth



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Introduction to Delay Tolerant Networks



       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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Introduction to Delay Tolerant Networks



       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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Introduction to Delay Tolerant Networks



       Challenges of a DTN



       >      Naming & addressing

       >      Routing

       >      Data transmission (retransmission, flow control)

       >      Application interface

       >      Security

       >      QoS (prioritisation)

       >      Timesynchronization


       8. Juni 2010                                              7
Introduction to Delay Tolerant Networks



       Overview



       >      Motivating a Delay Tolerant Network

       >      DTN Framework

       >      Routing Ideas

       >      Real World Applikation: Zebranet

       >      Summary & Outlook



       8. Juni 2010                                 8
Introduction to Delay Tolerant Networks



       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}




       8. Juni 2010                                                                          9
Introduction to Delay Tolerant Networks



       The DTN framework

       >      Bundle concept
               —      Bundlelayer between app- & region specific layers
               —      Use of ‚bundles‘ instead of packets
               —      Bundle store & forward-routing
               —      Custody transfer
               —      Security
                                                Apps                       Apps
               —      Prioritization                      Bundle layer

                                              Region        Region        Region
                                              specific      specific      specific
                                              layers        layers        layers



       >      No routing algorithm proposed


       8. Juni 2010                                                                  10
Introduction to Delay Tolerant Networks



       Overview



       >      Motivating a Delay Tolerant Network

       >      DTN Framework

       >      Routing Ideas

       >      Real World Applikation: Zebranet

       >      Summary & Outlook



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Introduction to Delay Tolerant Networks



       Routing algorithms




       >      Epidemic routing

       >      CAR, Context Aware Routing

       >      DTC, Disconnected Transitive Communication

       >      MoVe, Motion Vector Routing




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Introduction to Delay Tolerant Networks



       Assumptions




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




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Introduction to Delay Tolerant Networks



       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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Introduction to Delay Tolerant Networks



       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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Introduction to Delay Tolerant Networks



       CAR roundup



       >      Assets & drawbacks

               + Low number of messages on propagation
               + Lightweight algorithm

               -      Table setup required
               -      Learning phase required
               -      Doesn‘t scale well




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Introduction to Delay Tolerant Networks



       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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Introduction to Delay Tolerant Networks



       DTC roundup



       >      Assets & drawbacks

               + More independent measures
               + Adaptive, individual utility function
               + Capsuled utility calculation

               -      Heavy traffic on demand
               -      No implementation




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Introduction to Delay Tolerant Networks



       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)


                                                                  Destination


                                                            cd


                   Source                   ß


                                   Node B


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Introduction to Delay Tolerant Networks



       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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Introduction to Delay Tolerant Networks



       Overview



       >      Motivating a Delay Tolerant Network

       >      DTN Framework

       >      Routing Ideas

       >      Real World Applikation: Zebranet

       >      Summary & Outlook



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Introduction to Delay Tolerant Networks



       Zebranet




       >      The goal is tracking of zebras in wildlife
               — Position, direction, heart rate, body temperature etc.


       >      Constraints
               —      One year of operation
               —      Low weight (<1 kg)
               —      Wide range (>1000 km2)
               —      No fixed basestation
               —      High data delivery rate



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Introduction to Delay Tolerant Networks



       Zebranet implementation


       >      Collar design
               — Low & high range radio
               — Solar panels, battery
               — 4 mbit flash memory


       >      Routing
               — Flooding                                Zebras
               — History based            Base station
                                          (mobile)




       8. Juni 2010                                               23
Introduction to Delay Tolerant Networks



       Overview



       >      Motivating a Delay Tolerant Network

       >      DTN Framework

       >      Routing Ideas

       >      Real World Applikation: Zebranet

       >      Summary & Outlook



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Introduction to Delay Tolerant Networks



       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

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