Epidemic Routing and Oracle Based Routing

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Epidemic Routing and Oracle Based Routing

• Group 3
• Sandeep Chinni
• Arif Khan
• Venkat Rajiv

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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.

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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 145158, 2004

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Epidemic Routing

• Goal is to deliver messages with high probability
  even when there is never a fully connected path.

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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

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Epidemic Routing Protocol

• Anti-Entropy sessions

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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

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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.

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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.

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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.

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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.

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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
• Dijkstras algorithm is used for lowest cost
  route.

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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.

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Simulation

• PREP compared with Epidemic routing and AODV and
  simulation done in NS-2.
• Simulation Parameters

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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.

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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.

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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.

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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 bu?er
  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.

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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.

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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.

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Oracle Based Routing Algorithms

• Schemes

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Simulation with Bus Routes
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Average Delay
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Delivery Ratio
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Bandwidth Variation
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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.

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What have we taken out of these papers?

• Prioritized epidemic routing might be of interest
  in worst case scenarios for our DTN protocol.

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References

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