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. Combining snapshots of the network at different times may result in the formation of a source-destination path.

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

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 Anti-Entropy sessions

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 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) 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 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 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 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 Each message has a drop priority(P d ) and transmit priority(P t ). P d of a packet is the lowest cost path from the current node to the destination. P t 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 P d and stops only after a lower threshold is crossed.

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

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 Very high resource utilization even when less number of messages are being transmitted. Route cost calculation is not possible in all cases and P d cannot be computed.

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 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 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 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.

Oracle Based Routing Algorithms Schemes:

Simulation with Bus Routes

Average Delay

Delivery Ratio

Bandwidth Variation

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

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