A two-tier network based mobile node for maintaining the communication links is presented in this paper. The mobile node has sensing, computation, communication and locomotion components assembled by off-the-shelf modules. The proposed mobile node is able to merge IEEE 802.15.4 and IEEE 802.11b/g protocols so as to acquire multimedia signals as well as regular low bandwidth data. The assessment of communication link quality and a simple PID based control scheme are illustrated in this paper as well. Inspired by virtual force method, we exploit RSSI samples as a control feedback factor into locomotion. The experimental results testify the feasibility of proposed method and show that the mobile node is competent for maintaining communication links of wireless sensor networks.