Novel congestion control algorithm for delay tolerant networks

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.