Energy Efficiency in Content Delivery Networks Niemah Izzeldin Osman Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Electronic and Electrical Engineering October 2014 The candidate confirms that the work submitted is her own, except where work which has formed part of jointly-authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. Chapter 4 is based on the work from: N. I. Osman, T. El-Gorashi, and J. M. H. Elmirghani, “Reduction of energy consumption of Video-on-Demand services using cache size optimization,” in 2011 Eighth International Conference on Wireless and Optical Communications Networks, 2011, pp. 1–5. And: N. I. Osman, T. El-Gorashi, and J. M. H. Elmirghani, “Caching in green IP over WDM networks,” J. High Speed Networks (Special Issue Green Netw. Comput., vol. 19, no. 1, pp. 33–53, 2013. These papers have been published jointly with my PhD supervisor Prof. Jaafar Elmirghani and my PhD advisor Dr Taisir El-Gorashi. Chapter 5 is based on the work from: N. I. Osman, T. El-Gorashi, and J. M. H. Elmirghani, “The impact of content popularity distribution on energy efficient caching,” in 2013 15th International Conference on Transparent Optical Networks (ICTON), 2013, pp. 1–6. This paper has been published jointly with my PhD supervisor Prof. Jaafar Elmirghani and my PhD advisor Dr Taisir El-Gorashi. Chapter 6 and 7 are based on the work from: N. I. Osman, T. El-Gorashi, L. Krug, and J. M. H. Elmirghani, “Energy- Efficient Future High-Definition TV,” J. Light. Technol., vol. 32, no. 13, pp. 2364–2381, 2014. This paper has been published jointly with my PhD supervisor Prof. Jaafar Elmirghani, Ms. Louise Krug, industrial collaborator and my PhD advisor Dr Taisir El-Gorashi. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. © 2014 The University of Leeds and Niemah I. Osman To my children, this PhD thesis is dedicated to you. Acknowledgements First and foremost, all praise to Almighty Allah, for life, for health and the countless blessings He gave me. I would like to acknowledge my supervisor, Professor Jaafar Elmirghani for his guidance and patience through my PhD journey. His insightful advice and constant encouragement is most appreciated. I am very grateful and thankful to the Islamic Development Bank (IDB) for fully funding my PhD. Without this scholarship, my dream of a PhD from UK would have never been possible. I also thank Sudan University of Science and Technology for their financial support. Many thanks and gratitude goes to my colleagues in the Communication Systems and Networks group in the School of Electronic and Electronic Engineering. It was a privilege to have known them. I thank them for their company, reassurance and fruitful discussions. I am also indebted to my special friends Salima and Nahla. Their friendship comforted me and helped me escape many hurdles. I will always cherish the wonderful time I spent with them. I would also like to thank Nigel and Caroline, who were there for me when I most needed them. My gratitude goes to the members of the IDB Scholars Association UK. I was very fortunate to have the opportunity to meet and collaborate with such exceptional role i models from around the world. I truly thank them for inspiration and for uplifting my spirit. A big thank you goes to the residents of the Unipol student accommodation in Shay Street/Holborn Terrace, all 56 flats. It was a delight to have known them. I will miss the picnics, tea parties and celebrations that we constantly enjoyed. I would like to especially thank Shilan and her family, for the friendship, the laughter and the joy they brought into my family’s life during our stay at Leeds. I would like to express my appreciation to my beloved family back home, my father, Professor Izzeldin Osman and my mother Dr Khadiga Karrar. I don’t have enough words to thank them for supporting me in all possible ways. They are the reason behind my life achievements and have always shown me by example that everything is doable. I hope I made them proud. I would also like to thank my sisters, Dr Rasha Osman and Dr Ala Osman for always looking out for me and for their care and friendship. Finally, all my thank-yous go to my young family. My children, the apple of my eye, little Malak and baby Izzeldin. Their smiles and innocent gazes have changed the definition of life for me. I thank them for making my life so fulfilled and rewarding and for making every day so special. I dedicate my final acknowledgements to the love of my life, my dear husband Hassan Daleel, without whose kindness, sacrifices, and patience I would not have been able to pursue my dreams. I truly appreciate him standing by my side and thank him for his love, support and attention. Niemah ii Abstract The increasing popularity of bandwidth-intensive video Internet services has positioned Content Distribution Networks (CDNs) in the limelight as the emerging provider platforms for video delivery. The goal of CDNs is to maximise the availability of content in the network while maintaining the quality of experience expected by users. This is a challenging task due to the scattered nature of video content sources and destinations. Furthermore, the high energy consumption associated with content distribution calls for developing energy-efficient solutions able to cater for the future Internet. This thesis addresses the problem of content placement and update while considering energy consumption in CDNs. First, this work contributed a new energy-efficient caching scheme that stores the most popular content at the edge of the core network and optimises the size of cached content to minimise energy usage. It takes into account the trend of daily traffic and recommends putting inactive segments of caches in sleep-mode during off-peak hours. Our results showed that power minimisation is achieved by deploying switch-off capable caches, and the trend of active cache segments over the time of day follows the trend of traffic. Second, the study explores different content popularity distributions and determines their influence on power consumption. The distribution of content popularity dictates the resultant cache hit ratio achieved by storing a certain number of videos. Therefore, it directly influences the power consumption of the cache. The evaluation results iii indicated that under video services where the popularity of content is very diverse, the optimum solution is to store the few most popular videos in caches. In contrast, when video popularities are similar, the most power efficient scheme is either to cache the whole library or to avoid caching completely depending on the size of the video library. Third, this thesis contributed an evaluation of the power consumption of the network under real world TV data and considering standard and high definition TV programmes. We proposed a cache replacement algorithm based on the predictable nature of TV viewings. The time-driven proactive cache replacement algorithm replaces cache contents several times a day to minimise power consumption. The algorithm achieves major power savings on top of the power reductions introduced by caching. CDNs are expected to continue to be the backbone for Internet video applications. This work has shown that storing the right amount of popular videos in core caches reduces from 42% to 72% of network power consumption considering a range of content popularity distributions. Maintaining up-to-date cache contents reduces up to 48% and 86% of power consumption considering fixed and sleep-mode capable caches, respectively. Reducing the energy consumption of CDNs provides a valuable contribution for future green video delivery. iv Table of Contents Energy Efficiency in Content Delivery Networks ................................................. 1 Acknowledgements ........................................................................................................ i Abstract ............................................................................................................... iii Table of Contents .......................................................................................................... v List of Figures ........................................................................................................... viii List of Tables .............................................................................................................. xiv Glossary of Terms ....................................................................................................... xv List of Symbols ........................................................................................................... xix Chapter 1 Introduction................................................................................................ 1 1.1 Research Objectives ......................................................................................................3 1.2 Original Contributions ..................................................................................................4 1.3 List of Publications .......................................................................................................7