Summary The Delay‐/Disruption‐Tolerant Networking (DTN) architecture was designed to cope with challenges such as long delays and intermittent connectivity. To exploit the a priori knowledge of contacts, typical of space networks, NASA‐JPL designed and included in ION (its DTN protocol suite) the Contact Graph Routing (CGR) algorithm. This paper studies the latest version, recently standardized as Schedule‐Aware Bundle Routing (SABR) within the Consultative Committee for Space Data Systems (CCSDS). The first part of the paper is devoted to the algorithm analysis, which distinguishes three logical phases to examine sequentially. Following this comprehensive study, three enhancements are proposed, which aim to improve SABR accuracy and resistance against possible loops. They are studied on a simple but challenging DTN topology, implemented on a virtual GNU/Linux testbed. Tests are performed by running the latest version of ION and an independent implementation of SABR developed by the authors, Unibo‐CGR. The numerical results are then examined in detail to highlight both SABR mechanisms and the advantages offered by the proposed enhancements.

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This paper aims to investigate the potential advantages and also the limits of source routing when applied to delay-/disruption-tolerant networking (DTN) space networks. To this end, it uses a variant of contact graph routing (CGR) called moderate source routing (MSR), recently proposed by the authors and fully compatible with interplanetary overlay network (ION), the DTN suite developed by NASA-JPL. MSR differs from standard CGR as the route to destination is not recalculated from scratch at each node, but possibly reused, if still valid, by next nodes. For this purpose, the route is saved in a dedicated extension block of the forwarded bundle (the data unit of the bundle protocol, used in DTN). Performance of MSR versus CGR is assessed by considering a simple but very challenging space layout. Numerical results, obtained on a GNU/Linux testbed, show that MSR is effective at reducing the chances of loops, in particular when the source has full knowledge of the state of the network; otherwise, network instabilities are still possible. In this case, they can be neutralized by means of the combined use of source routing and anti-loop tools, as shown in the paper. A further advantage of MSR is that it is compatible with standard CGR, which would facilitate a gradual or partial deployment.