Opportunistic routing in delay tolerant networks (DTNs)

In the world of communication, there are environments where connection connectivity is not guaranteed due to challenges like sparse node distribution, mobility or unstable links. DTNs allow data to be transmitted even when a direct path between the source and the destination does not exist.

Opportunistic routing, a key technique in DTNs takes advantage of the mobility of nodes and the dynamic nature of these networks to forward data when an opportunity rises.

Opportunistic routing in DTNs leverages the inherent mobility and sporadic contacts between nodes to deliver data. Rather than relying in predefined routes, nodes opportunistically decide whether and when to forward a message based on available contact opportunities. The routing decision is dynamic and made based on the network’s current condition.

The core principle behind opportunistic routing is that nodes frequently come into and out of contact with each other, When the nodes meet, they exchange messages, allowing data to gradually hop toward s its destination. 

Opportunistic routing dynamically exploits available opportunities, which makes it well-suited to DTNs when contact patterns are unpredictable and erratic.

Opportunistic Routing Protocols

• Epidemic routing: it is one of the simplest routing strategies. It spreads messages throughout the network like a “viral infection”. When nodes encounter each other, they exchange the message buffers ensuring data is replicated across multiple nodes. While this maximizes the chances of delivering data, it results in high overload, significant resource consumption and potential congestion.

• MaxProp: Designed for vehicular DTNs, it prioritizes message forwarding based on the likelihood of delivery. It calculates the probability of successful delivery for each massage based on the known mobility patterns of vehicles.

• PRoPHET (probabilistic Routing Protocol using History of Encounters and Transivity): PRoPHET uses a probabilistic approach to determine the best forwarding nodes. It assigns a delivery probability to each node based on historical encounters and probability of future contacts. Nodes with a higher probability of reaching the destination are preferred for forwarding messages.

• Spray and wait: This protocol addresses the high overhead of epidemic routing by limiting the number of messages copied distributed throughout the network. A message is initially sprayed to a limited number of nodes and the nodes holding copies wait until the destination or nodes closer to the destination. Spray and Wait strikes a balance between delivery and resource usage.

Challenges of opportunistic routing

• Limited network resources: opportunistic routing protocols must efficiently manage limited resources such as node buffers, energy and bandwidth.

• Security concerns: The open and dynamic nature of DTNs make them vulnerable to security threats. OR protocols must account for potential attacks such as message spoofing, denial of service (DoS) and data privacy breaches.

• Node Mobility and Contact prediction; opportunistic routing heavily relies on node mobility and contact patterns which are often unpredictable. Protocols like PRoPHET attempt to mitigate this by using historical data, but prediction remains an imprecise science.

• Message delivery delays: Nodes may store messages for an extended period before finding a forwarding opportunity. In time sensitive application, these delays may be unacceptable requiring optimization of forwarding strategies.

Conclusion

Opportunistic routing is a vital component of delay tolerant networks , providing a means of communication in environments where conventional routing fails. While it presents challenges in terms of resource management, delay and security, it also offers innovative solutions for scenarios ranging from disaster recovery to rural communication. The importance of opportunistic routing in DTNs will continue to grow driving further research and development in this exciting field.