The emergence of multi-screen cloud social TV has the potential to transform TV experience, providing a unified media experience across a diverse set of devices at an affordable cost. One key technology to support unified media experience across multiple screens is to instantiate a virtual machine (VM) as a cloud clone of the user, to manage all his/her media outlets (e.g., TV and smartphone), as implemented in our Cloud-Centric Media Network (CCMN). In this case, as the user shifts his attention from one device to another, the cloud clone can migrate to another location for better quality of experience. In this paper, we investigates the problem of cloud-clone migration for the multi-screen social TV application, minimizing its monetary cost. This problem can be cast into the Markov Decision Process (MDP) framework, to balance a trade-off between the migration cost and the transmission cost. Under this framework, we first derive an upper and lower bound for the optimal monetary cost, by considering a fixed placement policy and an offline policy. We then follow up with an online policy using a dynamic programming approach. Our numerical results indicate, up to 10% monetary cost can be saved, by optimally migrating the cloud clone. Moreover, the cost reduction depends on the length of content-delivery path, the data size associated with VM migration, and the user behavior pattern. These insights would offer operational guidelines to deliver cost effective multi-screen social TV services over CCMN, potentially easing its adoption.
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