Robust communications for disconnected, intermittent, low-bandwidth (DIL) environments

Battlefield communications can be disrupted by a number of factors including environmental constraints, wireless dynamics and mobility, and both intentional and non-intentional interference. Robust, reliable, and efficient mechanisms are needed in such environments to ensure that critical data is delivered in the face of disruptions, intermittent connectivity, and low-bandwidth (DIL). In this paper, we examine a tiered approach to providing reliable communication in DIL environments. We model a tactical network scenario in which nodes in a low bandwidth loosely-connected ad-hoc network periodically send position/location information (PLI) messages to a shore base station. We utilize this scenario to quantify the differences in performance between a number of layered approaches that utilize mechanisms such as the Simplified Multicast Forwarding (SMF) protocol, the NACK-oriented Reliable Multicast (NORM), and Delay/Disruption Tolerant Networking (DTN) in mitigating the challenges of DIL environments. Our evaluation of the layered approaches considers metrics relevant to two broad classes of data: `ephemeral´ and `persistent´: ephemeral data (e.g. instantaneous position-location information of a node) has a relatively short lifetime and older data is obviated by newer data; by contrast, persistent data (e.g. exact mobility track of a node) has a longer useful lifetime and is not obviated by newer data. We examine the latency and staleness for ephemeral data and the message delivery ratio for persistent data. Our results show that SMF at the IP layer provides robust delivery to a single connected component of the network whereas NACKing and retransmission by NORM addresses short disruptions. For long-term disruptions, a DTN gossiping (i.e. anti-entropy) router can effectively bridge the gap between disconnected components. Our evaluation leverages the Common Open Research Emulator (CORE) tool and the mobility scripting tools from the Naval Research Laboratory (NRL).