Delay Tolerant Networking (DTN) has been proposed to provide efficient and autonomous store-carry-and-forward data transport in space networks. Since these networks relay on scheduled contact plans, Contact Graph Routing (CGR) can be used to optimize routing and data delivery performance. However, transient or permanent faults can occur in large space networks, thus introducing uncertainties on the original contact plan reducing CGR performance. In this work, we propose alternative CGR metrics and study a novel replication-based CGR formulation that improves data delivery when operating under uncertain contact plans. This proposal is analyzed by means of simulation and compared with other scheduled and opportunistic routing approaches. Results provide a baseline to develop more specialized probabilistic CGR routing strategies that could cope with unplanned and transient faults in future space DTN networks.

We describe DynAlloy Analyzer, a tool that extends Alloy Analyzer with support for dynamic elements in Alloy models. The tool builds upon Alloy Analyzer in a way that makes it fully compatible with Alloy models, and extends their syntax with a particular idiom, inspired in dynamic logic, for the description of dynamic behaviours, understood as sequences of states over standard Alloy models, in terms of programs. The syntax is broad enough to accommodate abstract dynamic behaviours, e.g., using nondeterministic choice and finite unbounded iteration, as well as more concrete ones, using standard sequential programming constructions. The analysis of DynAlloy models resorts to the analysis of Alloy models, through an optimized translation that often makes the analysis more efficient than that of typical ad-hoc constructions to capture dynamism in Alloy.