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Supporting end-to-end real-time communication is important for wireless sensor networks (WSNs) to accomplish the collaborative sensing tasks with specific timing constraints. However, without considering the unique constraints for WSNs, many existing real-time communication protocols prove to be infeasible for low-cost WSNs. In this paper, we propose a novel real-time communication scheme (RCS) to provide service-differentiated soft real-time guarantees for end-to-end communication in WSNs. We use hop-based geographic grouping to enable location awareness for sensor nodes with extremely low control overhead.We use dynamic forwarding with load-balanced receiver contention to provide a light-weight, yet efficient, routing technique, which can be easily adapted for duty cycle design. We use polling contention period based real-time MAC support to improve the service-differentiation granularity with better bandwidth utilization. The performance evaluation shows that our scheme can achieve low end-to-end latency, high on-time delivery ratio, fine services-differentiation granularity with load-balance for real-time traffic in unsynchronized low-cost WSNs.