DTP: Double-Pairwise Time Protocol for Disruption Tolerant Networks

Network time synchronization (NTS) is essential for any distributed systems, including disruption tolerant networks (DTNs). The feature of frequent contact disruptions and discontinuous network connections in DTNs raises a new challenge in providing the NTS service: synchronization operations may be interrupted for a long period of time when links between the time synchronization peers are opportunistic. To address this challenge, we propose double- pairwise time protocol (DTP) that can achieve better clock estimations and synchronization results in DTNs than NTP-Core, which models the major functionality of processing synchronization messages in network time protocol (NTP) that is the time-keeping standard in the Internet. The characteristics of DTP include: i) DTP achieves approximately half of the maximum time error achieved by NTP-Core; and ii) DTP only requires minor modifications to be implemented in the current architecture of NTP. Simulation results based on trace data collected from existing DTN testbeds validate such characteristics of DTP.