Opportunistic Content Distribution Feasibility, Design and Performance Evaluation

Abstract: Originally, the main purpose of the wired Internet was to interconnect hosts on different networks in order to allow them to communicate. Although this is still an important service, the Internet has evolved and today its predominant application is to provide its users with access to contents. This evolution is also taking place in the wireless domain and is to a large extent being pushed by advances in mobile platforms which now commonly have advanced multimedia capabilities. Today, contents are therefore both being consumed and produced by users on the move which calls for efficient dissemination of information to and from the mobile devices. This thesis considers content-centric networking, particularly in the context of mobile wireless networks. The main focus is on opportunistic distribution of content where mobile nodes directly exchange content items when they are within communication range. This opportunistic communication mode allows for networking in the absence of fixed infrastructure and it has several other benefits in terms of scalability, network-neutrality, locality and more. The contributions of this thesis lie in three areas. Firstly we study the feasibility of opportunistic content distribution among mobile nodes in urban areas using both analytic models and simulations. Our findings show that if nodes cooperate by sharing, even in a limited manner, content can spread efficiently in a number of common case scenarios. Secondly we present our design of PodNet: a middleware architecture for a mobile peer-to-peer content distribution. On the Internet, PodNet uses single source multicast to implement scalable and efficient delivery of published content to subscribers over the current unchanged Internet architecture. In the wireless domain, PodNet uses a decentralized content solicitation scheme that allows the distribution of content between mobile devices without requiring Internet connectivity and infrastructure support. Key components of the design are the content structure, multicast distribution, solicitation protocol, service discovery and an API based on the publish/subscribe paradigm. Thirdly we perform a thorough system evaluation to dimension important system parameters and to assess system performance. Our evaluation uses both experimental connectivity traces and a detailed simulator implementation that utilizes a realistic mobility model of pedestrians in an urban area.