Performance Comparison of Unicast Routing Schemes in DTNs Mooi Choo Chuah, Peng Yang, Brian D. Davison, Liang Cheng {chuah, pey204, davison, cheng}@cse.lehigh.edu Lehigh University Abstract—Delay and disruption tolerant networks have been proposed to address data communication challenges in network scenarios where an instantaneous end-to-end path between a source and destination may not exist, and the links between nodes may be opportunistic, predictably connectable, or periodically- (dis)connected. In this paper, we focus on comparing the performance of different unicast routing schemes proposed for intragroup communications. In particular, we conduct performance studies for different DTN scenarios, e.g., DTNs with different node densities, DTNs with different mobility models, networks with different percentage of nodes supporting DTN functionality, etc. In addition, we also study intergroup DTN routing scenarios where message ferries and backhaul links are used. Our results indicate that (a) the store-and-forward and custody transfer concepts have significantly improved the delivery ratio in a sparsely connected network, (b) in very sparse networks, message ferries are required to enable communications, (c) a high delivery ratio can be maintained even with only 50% of the nodes supporting DTN functionality, (d) the two-way delay in bidirectional flows only experience 10% more delay than one- way delay, and, (e) some routing schemes are optimized to perform well in certain mobility scenarios and thus a hybrid scheme will work best in all scenarios. Keywords-disruption tolerant networks; custody transfer; route discovery; message ferry I. INTRODUCTION Packet-switched network communication has been studied for decades. Important progress has been made in robustness and scalability in the TCP/IP protocol suite based primarily on principles of end-to- end protocols and services [9]. However, there are many scenarios in which an end-to-end connection is not guaranteed or even possible, and so an intermediary is needed, perhaps to translate between protocols or to provide temporary storage (e.g., in mail servers). In these cases, without such intermediaries, communication would fail. In other cases, communication may fail not because of a lack of instantaneous connection, but because the connection properties fall beyond the expected bounds (excessive round-trip-time or high packet loss probability). Solutions have been proposed to deal with some specific situations, e.g., using link layer retransmissions to deal with high packet loss probability in wireless environments [4] or using performance enhancing proxies [28]. However, these solutions still do not work in situations where there