A message acknowledgment based congestion control (MACC) for delay tolerant networks

Delay Tolerant Networks (DTNs) are vulnerable to intermittent connectivity due to opportunistic contacts between mobile nodes. Therefore, routing protocols designed for these networks rely on spreading multiple copies of data packets or messages in the network to achieve a better delivery ratio. Although, multiple copies of messages enhance the message delivery probability, but simultaneously these extra copies of messages occupy finite buffer space and scarce wireless bandwidth. Eventually, it results in message drops, delay in delivery and poor delivery ratio. This condition in DTNs is termed as network congestion. Further, this congestion is aggravated by the buffering of the delivered messages. Since destination based explicit acknowledgment packet generation is not feasible for such networks, therefore nodes have to buffer the delivered messages until their lifetime expires. Such messages significantly contribute in the congestion. To address the congestion occurred due to the buffering of delivered messages, we propose a node contact based message acknowledgment algorithm. In this algorithm, whenever nodes come into the contact with each other they exchange information about the delivered messages and update their relative message buffers. The proposed mechanism is routing protocol independent as well as it can be easily integrated with other congestion control mechanisms. Extensive simulations, with different mobility models, routing protocols and congestion control schemes, signify the improvement in message delivery ratio for the proposed mechanism.