Nautical Predictive Routing Protocol (NPRP) for the Dynamic Ad-Hoc Nautical Network (DANN)

The Carrier Strike Group (CSG) and the Expeditionary Strike Group (ESG) are two common types of US Naval units consisting of multiple ships traveling as a group. All vessels within the CSG/ESG transmit and receive data via satellite, even when those vessels are within radio frequency line of sight (RFLOS). Within the CSG/ESG, satellite communications (SATCOM) are clearly necessary for vessels well forward of the main body, but could be augmented by RFLOS wireless communications for some members of the CSG/ESG. The goal of this research is to identify software technology that minimizes the barriers to employing affordable, commercially available technology (i.e., 802.11x) for ship-to-ship communications at sea. Some of the existing barriers to 802.11x communications at sea result from communication protocols that do not support the varying topologies or human network intervention one would expect to encounter within the CSG/ESG. This paper advances the concept for a predictive routing protocol that proactively addresses the topological and human issues unique to the DANN. Proactive routing will re-route the transmissions prior to interruptions, thus preventing interruption of open communication sessions. 1 CSG/ESG Communications Issues Currently, passing data from ship-to-ship requires four separate transmissions [1]. Delays associated with signal propagation over long distances, communications protocols, network prioritization, dropped packets and other overhead issues can produce excessive delays and are often inadequate for VTC or VOIP sessions. The challenges and risks associated with some ship-to-ship data communications can be mitigated with predictive routing that eliminates the requirements for SATCOM and associated processing by the remote network operations center (NOC). The challenge of establishing and maintaining RFLOS communications at sea, with an acceptable quality of service, is rather unique. This research uses the Washington State Ferries (WSF) Wireless Internet Project as a baseline and advances that work to address a fully ad-hoc mobile network at sea. WSF research demonstrated the feasibility of pushing 802.11a up to 20 miles over water, identifying 802.11a as the baseline backhaul evaluated for the DANN [2]. This work was supported in part by ARO under project 5NPGARO032 and by AFOSR under project F1ATA05192G001. F. Kordon and J. Sztipanovits (Eds.): Monterey Workshop 2005, LNCS 4322, pp. 106–120, 2007. c © Springer-Verlag Berlin Heidelberg 2007 NPRP for the DANN 107 1.1 Problem Modeling Nautical communication requirements are modeled as a time-dependent graph where each vertex represents a vessel within the CSG/ESG, and each arc represents a communications link. Some of the unique challenges facing the DANN are summarized below. 1.2 Topological Challenges Vertices move out of range: – Vessel may move out of range due to course, speed, currents and wind, or to avoid obstacles and localized weather patterns. This could sever a link between vertices or disconnect the entire network. – Vessels may move out of range in response to direction from the CSG/ESG commander. – The NPRP will predict when the arc between two vertices will break connectivity, calculate course and speed data needed for vessels to maintain connectivity and find an alternative route for use in case repositioning the vessels is not possible. Localized Weather Patterns: – Localized weather patterns and sea states on or near the arc linking two vertices may indicate that more complex routing would provide a higher quality of service. – The NPRP will calculate the best route around localized weather patterns. If an alternate route does not exist, the NPRP will calculate course and speed data needed for vessels to establish an alternate route.