Disconnection-resilient IP link-state routing for airborne networks

As evolving operational requirements compel forces to deploy sparsely there is a need to extend tactical network protocols to operate in the Disruption-Tolerant Networking (DTN) regime, in which frequent disconnections are the norm. In airborne networks¹, connectivity may be temporarily lost when aircraft use different paths to avoid terrain or other obstacles or to perform assigned tasks. In sensor networks, nodes may become disconnected due to environmental conditions or power management, but the set of proximal nodes may not change much over time, despite the intermittent connections. These scenarios challenge standard link-state approaches, both in terms of the protocol overhead and the ability to maintain awareness of all network nodes. Routing protocols designed for the DTN regime, however, cause extreme packet replication to cover the most general conditions conceivable, making them impractical in realistic scenarios. We propose modifications to a widely used link-state protocol, OSPF, to deal with significantly more disruptions to connectivity while retaining the efficiencies of the shortest path approach. We describe simple changes that enable OSPF to find routes through a stable set of neighbors that are only intermittently available. Our use of OSPF minimizes changes and implementation costs, and takes advantage of reliable, proven methods for network state information delivery. We have implemented DTN-extended OSPF within the quagga IP routing framework. Our simulation tests show that, with our modifications, OSPF maintains a global view of the entire network, including both reachable and unreachable nodes, so that messages can be held and routed to temporarily unavailable nodes. Using simulations as well as real packet traffic over an emulated network, we compare DTN-extended OSPF with standard OSPF, and we show that our methods permit messages to be delivered to remote nodes in cases where standard OSPF would discard most or all packets. We conclude by outlining additional methods to reduce DTN overhead traffic and increase DTN-extended OSPF's reliability.