  The piling up storage and compute stacks in cloud data center are expected to
accommodate the majority of internet traffic in the future. However, as the
number of mobile devices significantly increases, getting massive data into and
out of the cloud wirelessly inflicts high pressure on the bandwidth, and
meanwhile induces unpredictable latency. Fog computing, which advocates
extending clouds to network edge, guarantees low latency and location-aware
service provisioning. In this article, we consider fog computing as an ideal
complement rather than a substitute of cloud computing, and we propose a
software defined networking (SDN) enabled framework for cloud-fog
interoperation, aiming at improving quality of experience and optimizing
network resource usage. Two case studies are provided to illuminate the
feasibility and advantage of the proposed framework. At last, potential
research issues are presented for further investigation.
