Solicitation-based Forwarding for Sensor Networks

Delivering sufficient fidelity to sensor network applications is challenging because unpredictable wireless links, network dynamics, and the presence of transitional regions in sensor networks impact the delivery of packets (i.e., fidelity) to the sink. One of the major reasons for this problem is due to the non-responsive nature of forwarding mechanisms commonly implemented in experimental sensor networks. Existing routing protocols implemented in these networks typically base their forwarding decision-making on some form of statistical observations regarding past communications or the quality of past beacon signals received by communicating nodes. This approach fails, however, to capture the link conditions at the exact time of forwarding packets across the wireless link, limiting the aggregate forwarding capability of the network. In this paper, we argue that the forwarding decision of a sensor device should be based not on historical information but on the instantaneous link conditions at the exact time of packet communications, and propose, solicitation-based forwarding (SOFA), a highly-responsive hop-by-hop routing protocol that results in increased application fidelity. SOFA represents a cost-effective, on-demand scheme that makes use of simple solicitation-based handshakes between a sender and multiple potential receivers at each wireless hop to negotiate the best forwarding path to a target destination (i.e., sink) when events occur in the sensor field. We present the detailed design, implementation, and experimental evaluation of SOFA in a 36-node Mica2 testbed using TinyOS, and discuss its measured performance benefits in comparison to the TinyOS standard routing protocol widely used by the experimental sensor network community