In application scenarios where sensor data is temporarily stored within the WSN - instead of transferring the data directly to a base station - data availability is an important factor. Ubiquitous Wireless Sensor Networks (WSNs) consist of sensor nodes which may communicate with each other via unreliable communication links. Furthermore, the sensor nodes themselves may fail. Ubiquitous WSNs may be used in application scenarios where they autonomously monitor the environment and are only sporadically visited by the mobile user for harvesting the collected sensor data. Thus, high availability of the measured data is of paramount priority.