Throwboxes in delay tolerant networks: A survey of placement strategies, buffering capacity, and mobility models

Throwboxes are small inexpensive wireless storage devices which act as relays, i.e., intermediate nodes between source and destination in wireless networks. A number of throwbox placement techniques are proposed in the literature for different networks like delay tolerant networks (DTNs). Data forwarding opportunities in DTNs are limited due to intermittent connectivity of nodes which reduces network performance. Throwbox deployment in DTNs can improve delivery ratio, delays, control overhead and thus lifetime of a network consisting of resource stringent mobile nodes. However, in order to maximize benefit of deploying throwboxes, a number of factors need to be carefully taken into account like their cardinality, placement criteria, buffer management, network topology, mobility characteristics of nodes, application requirements, and cooperation of throwboxes among themselves and with other nodes. In this paper, we present a comprehensive survey on throwbox placement in DTNs. First, we discuss various applications of DTNs. Then, we review throwbox placement techniques followed by the affect of buffer capacity on network performance. Next, we analyze the mobility aspect of throwboxes and discuss how it can influence performance. Furthermore, we review existing literature based on the number of throwboxes to be deployed. We then discuss how cooperation between throwboxes can enhance performance. Finally, we present issues, challenges and future research directions relevant to throwbox placement in DTNs.