Congestion Management in Delay Tolerant Networks

In delay tolerant networks, custody transfer can provide certain degree of reliability as a custodian node cannot discard a message unless its life time expires or the custody is transferred to another node after a commitment. This creates a challenging decision making problem at a node in determining whether to accept a custody transfer: on one hand, it is beneficial to accept a large number of messages as it can potentially advance the messages toward their ultimate destinations and network utilization can be maximized; on the other hand, if the receiving node over-commits itself by accepting too many messages, it may find itself setting aside an excessive amount of storage and thereby preventing itself from receiving further potentially important, high yield (in terms of network utilization) messages. To solve this problem, in this paper, we apply the concept of revenue management, and employ dynamic programming to develop a congestion management strategy for delay tolerant networks. For a class of network utility functions, we show that the optimal solution is completely distributed in nature where only the local information such as available storage space of a node is required. This is particularly important given the nature of delay tolerant networks where global information is often not available and the network is inherently dynamic. Our simulation results show that the proposed congestion management scheme is effective in avoiding congestion and balancing network load among the nodes.