delaytolerant

Delay-tolerant networking refers to a design approach for communications systems that must operate across links with long or unpredictable delays, disruptions, or partitions. In delay-tolerant networks, continuous end-to-end connectivity may not exist, so data are carried opportunistically and stored for later transmission rather than relying on a constant path.

A central concept is the bundle in a store-and-forward model. Data are encapsulated into bundles and carried by network nodes (DTN nodes) until a contact with a forwarder becomes available, at which point the bundle is forwarded toward its destination. Custody transfer allows intermediate nodes to acknowledge responsibility for delivering a bundle, helping to ensure reliability in disrupted environments. The underlying transport layer can be diverse, including traditional Internet links, wireless links, or space links, with convergence layers adapting to the available medium.

DTN architecture is standardized around the Bundle Protocol, which defines how bundles are formed, stored, forwarded, and secured, and how endpoints are addressed. The approach is used in space missions, where deep-space delays are common, but it is also applied to terrestrial scenarios such as disaster areas, rural or underwater networks, maritime communications, and vehicular ad hoc networks.

Challenges include efficient routing under sparse contact patterns, memory and energy constraints for intermediate storage, security and data integrity across long delays, and congestion control when multiple bundles compete for limited contact opportunities. Benefits include robust data delivery in highly intermittent networks and the ability to decouple sending and receiving in time, improving resilience when continuous connectivity cannot be guaranteed.