Abstract:
Due to intermittent connectivity and lack of persistent end-to-end path in Delay Tolerant
Networks (DTNs), routing protocols adopt hop-by-hop store and forward mechanism to
forward bundles towards the destination. The responsibility of reliable transmission is
also delegated in a hop-by-hop fashion using custody transfer. A node accepting the
custody of a bundle carries the liability of delivering or delegating it to the next hop.
Therefore, the node is required to keep the bundles in a persistent storage. Due to
limited storage capacity in the DTN nodes, storage congestion occurs when too many
bundles are contending for this scarce resource. As a result, bundle loss increases and the
delivery ratio of the network suffers.
As a reactive congestion mitigation scheme, a congested node can migrate some of its
bundles to the uncongested neighbors in order to make room for the new bundles and pull
back the bundles in its own storage when the congestion disappears. This scheme fails
when the neighbors themselves are congested. As a proactive scheme, a node can decide
whether to accept or reject the custody of a new bundle based on its current storage
status.
There are many proactive schemes available in the literature. However, their performance
can be improved further by introducing new features. In this thesis, we propose
a novel proactive congestion control scheme for DTN. Our scheme ranks the incoming
bundles using their priority and TTL. When congestion occurs, a node accepts or rejects
the bundles based on their rank. We also introduce the concept of head of line blocking,
confidence level, and dropping probability of the bundles to facilitate better decision
making. Simulation results show that our scheme achieves 20% to 25% higher delivery
ratio than that of the existing schemes.
