  Recently, IoT technologies have been progressed, and many sensors and
actuators are connected to networks. Previously, IoT services were developed by
vertical integration style. But now Open IoT concept has attracted attentions
which achieves various IoT services by integrating horizontal separated devices
and services. For Open IoT era, we have proposed the Tacit Computing technology
to discover the devices with necessary data for users on demand and use them
dynamically. We also implemented elemental technologies of Tacit Computing. In
this paper, we propose three layers optimizations to reduce operation cost and
improve performance of Tacit computing service, in order to make as a
continuous service of discovered devices by Tacit Computing. In optimization
process, appropriate function allocation or offloading specific functions are
calculated on device, network and cloud layer before full-scale operation.
