9 by John Wiley & Sons Ltd. 1 Introduction to be considered globally. Today, citizens around the world rely on ICT to conduct their everyday activities in personal or business life, and that requires having certain quality of services (QoS). Therefore guaranteeing QoS in the socio-economic environment of users is becoming very important. For that purpose there is a need for technical mecha- nisms and functions for implementation of the QoS in networks and end-users' devices, and for its regulation in a harmonized and globally accepted approach. That will enable greater quality of services provided to users as customers or consumers or content gen- erators, irrespective of their location or service provider (the entity that provides access to telecommunications services), where the provider can be a telecom operator (on local or national levels) or global over-the-top (OTT) provider (e.g. Google, Amazon, etc.). The Telecommunications/ICT Sector in the Twenty-First Century The telecommunication/ICT world in the twenty-first century is characterized by two important developments: It is becoming fully based on Internet technologies, including all networks (with fixed and mobile access) and all services (including all applications working over the Internet). It is becoming broadband, which means that there are enough high bitrates in access networks (and also end-to-end) which provide all available applications/services to run smoothly and with satisfactory quality experienced by end-users (we will define what the quality means later in the chapter). So, the ICT world is becoming all-IP (Internet protocol) and broadband on a global scale (Figure 1.1) [1]). However, it is even more interesting to note that mobile com- munications are spreading at a faster pace than fixed communications regarding access Mobile broadband Internet access Fixed broadband Internet access 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Figure 1.1 Global telecommunication/ICT broadband developments. 1.1 Th