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Epidemic Routing and Oracle Based Routing. Group 3 Sandeep Chinni Arif Khan Venkat Rajiv. Delay Tolerant Networks. Path from source to destination is not present at any single point in time.

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epidemic routing and oracle based routing

Epidemic Routing and Oracle Based Routing

Group 3

Sandeep Chinni

Arif Khan

Venkat Rajiv

delay tolerant networks
Delay Tolerant Networks
  • Path from source to destination is not present at any single point in time.
  • Combining snapshots of the network at different times may result in the formation of a source-destination path.
protocols for dtn
Protocols for DTN
  • Prioritized Epidemic Routing for Opportunistic Networks
    • Ram Ramanathan, Regina Rosales-hain
      • ACM MobiOpp 2007
  • Oracle Based Routing
    • S. Jain, K. Fall, and R. Patra. Routing in a Delay Tolerant Network.
      • In Proc. ACM Sigcomm, pages 145–158, 2004
epidemic routing
Epidemic Routing
  • Goal is to deliver messages with high probability even when there is never a fully connected path.
epidemic routing1
Epidemic Routing
  • Goal is to deliver messages with high probability even when there is never a fully connected path.- Can we do better?
  • The overall goal of Epidemic Routing is to
    • maximize message delivery rate
    • minimize message delivery latency
    • minimizing the aggregate system resources consumed in message delivery
epidemic routing protocol
Epidemic Routing Protocol
  • Anti-Entropy sessions
message information
Message Information
  • Message ID – a unique ID for all the messages that will be transmitted.
  • Hop Count – The maximum hops that a message can take before reaching the destination.
  • Optional Ack request
hosts nodes
Hosts/Nodes
  • Nodes set a maximum buffer size to aid epidemic routing.
  • This setting will limit memory and network usage.
  • There is a trade off between resource consumption and message delivery rate/latency.
  • Simple buffer management strategies like FIFO can be used when there is contention for resources - not the best though.
prioritized epidemic routing prep
Prioritized Epidemic Routing(PREP)
  • Prioritizes the messages for transmission and deletion using a priority function.
  • Priority function is based on
    • Current cost to destination
    • Current cost from source
    • Expiry time
    • Generation time
  • Inter-node costs are computed with a metric called average availability.
features of prep
Features of PREP
  • PREP has two modules:
    • Topology awareness
      • Helps in calculating routing costs from a node to a destination.
    • Message drop and Transmit property
      • A priority scheme for deleting and transmitting message packets.
topology awareness
Topology Awareness
  • Each node runs a neighbor discovery algorithm to find out its neighbors.
  • Each link between two nodes has a metric called the Average Availability(AA).
  • The average availability is calculated based on a short history of node link availability information.
  • If a link is not available for a configured time, then it is forgotten.
  • Periodically or whenever sufficient new link information is available Link State Advertisements (LSA) are exchanged between nodes.
topology awareness1
Topology Awareness
  • This LSA exchange is called Topology Sync as the nodes learn from each other.
  • LSA exchange gives the nodes the knowledge of the network topology during the recent time period.
  • This “best effort” topology awareness is used to compute routing costs.
  • Formula : (1-AA)+0.01
    • AA-Average Availability
  • Dijkstra’s algorithm is used for lowest cost route.
message drop transmit priority
Message Drop & Transmit Priority
  • Each message has a drop priority(Pd) and transmit priority(Pt).
  • Pd of a packet is the lowest cost path from the current node to the destination.
  • Pt of a packet is based on the cost to the destination and time-to-expire of the packet.
  • When the buffer of a node crosses a threshold, it starts to drop packets based on Pd and stops only after a lower threshold is crossed.
simulation
Simulation
  • PREP compared with Epidemic routing and AODV and simulation done in NS-2.
  • Simulation Parameters
advantages of prep
Advantages of PREP
  • Successful, as long as the resources are not overloaded.
  • Does not rely on extrapolating previous contact information.
  • Improves performance of Epidemic routing at high loads.
disadvantages
Disadvantages
  • Very high resource utilization even when less number of messages are being transmitted.
  • Route cost calculation is not possible in all cases and Pd cannot be computed.
oracle based routing
Oracle Based Routing
  • Knowledge centers (Oracles) are used to make routing decisions.
  • Based on the amount of information and network resources available suitable Routing protocols can be used.
oracles
Oracles
  • Contacts Summary Oracle
    • can answer questions about time-invariant aggregate statistics or summary characteristics about contacts.
  • Contacts Oracle
    • can answer any question regarding contacts between two nodes at any point in time.
    • Can be used for admission control.
  • Queuing Oracle
    • gives information about instantaneous buffer occupancies (queuing) at any node at any time.
    • can be used to route around congested nodes.
  • Traffic Demand Oracle
    • Can answer any questions regarding present or future traffic demand.
components for path calculation
Components for Path Calculation
  • Queuing time:
    • Time until a contact becomes available.
  • Transmission delay:
    • Time to inject a message completely into an edge.
  • Propagation delay:
    • Time to deliver the message (includes any intermediate queuing delay).
  • Storage Capacity.
routing algorithm classes
Routing Algorithm Classes
  • No knowledge
    • They do not use any oracles and hence perform badly.
  • Complete Knowledge
    • They utilize contacts, traffic and queuing oracles.
  • Partial Knowledge
    • They find routes in the absence of traffic demand oracle and use other oracles.
advantages drawbacks
Advantages & Drawbacks
  • Advantages
    • Based on the oracles available we can choose an appropriate algorithm for route calculation.
  • Drawbacks
    • Creating and maintaining oracles is a significant distributed systems problem.
what have we taken out of these papers
What have we taken out of these papers?
  • Prioritized epidemic routing might be of interest in worst case scenarios for our DTN protocol.
references
References

[1] A. Vahdat and D. Becker. Epidemic routing for partially connected ad hoc networks, 2000.

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