In Wireless Sensor Networks (WSNs) and Wireless Personal Area Networks (WPANs), IEEE 802.15.4 [1] has emerged to be one of promising radio specifications at the view of physical layer and medium access control. Without any help of infrastructure, the low rate and low power communication should be guaranteed. To utilize the collected information under WSNs, the data typically pass through gateways or sinks. Simultaneously, the control messages for sensor networks reach to each sensor node via gateways. However, both multi-destinations of sensing data and multi-devices of each sensor node make the design of gateways and application servers be challenging issues. In this paper, the practical system architecture of WSNs has been proposed with the respect to the gateways and service broker. Additionally, the real deployment of proposed WSN system architecture will be discussed in this paper.