The advances in the area of mobile computing is likely to make it feasible to predict the availability of wireless networks and their application level Quality of Service (QoS) characteristics along the user mobility path. Such predictions are referred to as QoS predictions which are provided by the QoS Context Source (QoSCS) hosted in the fixed network. On the multi-homed mobile devices, the QoS Predictions could be used for the handover to the optimal wireless network which satisfies the QoS requirements of the mobile applications. However, to achieve this functionality, a middleware support is necessary to obtain and make use of QoS predictions in realtime. To this end, we present design, architecture and validation of the context-aware computing support for network-assisted seamless vertical handover that uses QoS predictions to take a handover decision. We evaluate the proposed solution, in a case where it is applied in the mobile health care applications. The obtained simulation results encourage us to conduct the real-time system validation by employing the proposed solution.