Epidemic Routing and Oracle Based Routing

1. Epidemic Routing and Oracle Based Routing Group 3 Sandeep Chinni Arif Khan Venkat Rajiv

2. 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.

3. 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

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

5. 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

6. Epidemic Routing Protocol • Anti-Entropy sessions

7. 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

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

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

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. Oracle Based Routing Algorithms • Schemes:

25. Simulation with Bus Routes

26. Average Delay

27. Delivery Ratio

28. Bandwidth Variation

29. 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.

30. What have we taken out of these papers? • Prioritized epidemic routing might be of interest in worst case scenarios for our DTN protocol.

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