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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.