Fairness issue in message delivery in delay- and Disruption-Tolerant Networks for disaster areas

Delay- and Disruption-Tolerant Network (DTN) is a promising solution which allows us to communicate to each other even in disaster areas where a large number of users lose network connectivity due to significant damages on network infrastructures by earthquakes, tsunami, tornadoes, and so on. In DTN where messages are transferred from source nodes to destination nodes through other nodes, the communication performance largely depends on the employed routing scheme which determines the feature of the message distribution over the network. A lot of researchers have dedicated their significant efforts to develop an advanced routing algorithm which is superior in terms of message delivery ratio, message deliver delay, and/or efficiency. However, they have not taken into account a criterion, i.e., the fairness in message delivery, which is much more important for users as a service in disaster areas, where DTN takes a role of the access network conveying messages from a huge number of users to a few base stations connected to external networks. In this paper, we first point out that the fairness issue is critical in disaster areas where many-to-one traffic flow exists; messages originating from users in DTN converge on the gateway. Then the performance of existing routing algorithms is evaluated through extensive computer simulations in terms of the fairness in message delivery as well as traditional criteria. The results of performance comparison show that no routing algorithm can achieve the fair message delivery ratio, and the development of advanced routing algorithm is now still an open issue.