I. Introduction
The number of Internet users has grown drastically in the last two decades. In 1995, there were only 16 million Internet users, which corresponds to 0.4 percent of the world's population [1]. By the end of 2015, this number exploded to reach 3.3 billion users, constituting 45% of the world's population [2]. This brisk growth is mainly due to the abundance of services available on the Internet such as search engines (e.g. Google, Bing, etc.), social media (e.g. Facebook, twitter, etc.), e-commerce (e.g. Amazon, e-bay, etc.) and multimedia services (e.g. IPTV, VoIP, VoD, etc.). These latter have become common and represent currently a very active research area and a new telecommunications market sector where customers are in a strong position. Indeed, the customers or end users have a variety of offers to select from. Apart from similar pricing schemes, which are a useful decision aid for users, their choices are also affected by the expected and experienced quality. Hence, the service providers are giving a lot of interest as to how users perceive usability, reliability, quality and price-worthiness. As a result, the concept of Quality of Experience (QoE) has been introduced in order to help the service providers to take into account the user's perception and satisfaction [3].