End-to-end communication cost is used to alleviate congestion. When congestion occurs, communication cost increases with respect to packet loss. The sink uses the communication cost information to slow down the reporting rate of the appropriate source and increase the reporting rate of other sources that have lower communication cost since reliability must be maintained.
GARUDA: GARUDA [88] is a reliable downstream data delivery transport protocol for WSNs. It addresses the problem of reliable data transfer from the sink to the sensors. Reliability is defined in four categories: (1) guarantee delivery to the entire field, (2) guarantee delivery to a subregion of sensors, (3) guarantee delivery to a minimal set of sensors to cover the sensing region, and (4) guarantee delivery to a probabilistic subset of sensors.
GARUDA’s design is a loss-recovery core infrastructure and a two-stage NACK-based recovery process. The core infrastructure is constructed using the first packet delivery method. The first packet delivery method guarantees first packet delivery using a Wait-for-First-Packet (WFP) pulse. WFP pulse is a small finite series of short duration pulses sent periodically by the sink. Sensor nodes within the transmission range of the sink will receive this pulse and wait for the transmission of the first packet. The first packet delivery determines the hop-count from the sink to the node. Nodes along the path can become candidates for the core.