Token Based Congestion Control for DTNs

Delay tolerant networks (DTN) are characterized by intermittent connectivity, long delays and often constrained bandwidth. We consider mobile networks where node mobility and covert operation cause frequent disconnections. Nodes will see each other frequently but due to their movement, end-to-end paths do not remain stable long enough to complete a data transfer or even a simple data exchange, much less allow current congestion control protocols to react to these highly dynamic environments. To address the challenge of congestion control in DTNs we have implemented a novel congestion control mechanism based on the use of tokens. Network nodes must possess a token in order to inject messages into the network. Tokens are initially uniformly distributed but thereafter move randomly throughout the network. Using a discrete event simulator we show Token Based Congestion Control (TBCC) results in a reduction in the amount of dropped messages due to network congestion. In cases where drops are not allowed we add a constraint to the forwarding algorithm and show that network transit times are reduced by as much as 40% and total transit times, defined as the time from message generation until delivery to the destination, are reduced by 20%. We also show 36% reduction in the amount of intermediate network storage required. These results are significant since they show a reduction in both space (network storage) and time.