The energy consumption of the Internet is anticipated to be one of the main contributors to global energy consumption in the coming decades. As a result, renewed attention has been given to the energy efficient design and operation of network services. The video on demand (VoD) service is expected to be one of the most prominent services through the Internet in the near future. Due to the enormous energy consumption arising from storage and transport of movies, energy efficient design and operation of VoD systems are important considerations. In this paper, we formulate energy consumption models to analyze the energy consumption arising from storage and transport of movies in VoD systems. We consider five strategic content placement locations located at different levels of the video distribution network and we comparatively analyze the energy consumption of storage and transport when the movies are stored and delivered from these locations. Moreover, we derive thresholds for movie request arrival rates which determine whether replication of a movie in a given content placement location is energy efficient and whether turning ON a set of content storages located at a particular level of the network is energy efficient. By numerically analyzing the energy consumption models, we show that the energy efficiency of VoD services can be significantly improved by delivering movies from the most energy efficient content placement locations in the network. We show that this can be achieved by designing and operating VoD systems based on our derived thresholds which optimize the energy efficiency of VoD services for all user request arrival rates.
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