Content-based services are gaining tremendous popularity recently with the proliferation of a wide range of contents. Traditionally, hosting and distribution of these ubiquitous contents are accomplished using content distribution networks (CDNs). CDNs distribute contents in multiple hosting locations for load balancing, availability, and easy access. However, scalability and cost of CDNs are becoming major challenges due to the increase of content-based services. To combat these problems, peer-to-peer (P2P) systems are being considered in combination with CDN to complement each other in a hybrid system. Research works and practical deployments have shown that hybrid CDN–P2P systems are feasible, inexpensive, and scalable. However, P2P-based content distribution systems are known to consume more system-wide energy than traditional CDNs. Hence, energy efficiency of such a hybrid system must be taken into consideration before wider implementation. In our study, we analyze the energy consumption of a hybrid CDN–P2P system in an IP-over-WDM network and show that, due to its hybrid nature, it is possible to exploit the P2P system to significantly reduce load on the CDN and at the same time constrain—and in some cases reduce—energy consumption. We propose energy-aware as well as energy-unaware content source selection mechanisms to help service providers achieve this win–win situation. Using simulations, we show that, for example, in case of a moderately popular content the server load can be reduced by 30%–40% while reducing the system-wide energy consumption by 10%–20% when compared with a traditional CDN.
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