— Lightweight protocols that are both bandwidth and power thrifty are desirable for sensor networks. In addition, for many sensor network applications, timeliness of data delivery at a sink that collects and interprets raw sensor data is of great importance. In this work, we propose a lightweight framework for source-to-sink data transfer in a wireless sensor network that is geared towards achieving the above two objectives. Our integrated framework consists of three elements: 1) simple labels that eliminate complex addressing requirements, 2) implicit routing that provides an inherent robustness during sleep/wake schedules, and 3) MAC layer anycast to support routing. Our framework, in addition, facilitates the self-organization of sensor nodes into a network that efficiently relays information from the sources to the sink. The key idea of our framework is to associate each sensor node with a hierarchical level with respect to a sink and using MAC layer anycast to simply further pa...