 for data transmission) as the main characteristic of the traditional telecom/ICT world, the transition to Internet networking principles (based on separation of underlying transport technologies from the networking protocol above them, as well as separation of networking protocols from the application on the top) provided the possibility for the realization of one network for all telecommunication/ICT services. So, Internet net- working and Internet technologies (standardized primarily by the Internet Engineering Task Force (IETF)) have become the main approach in the telecommunication world, and have become the telecommunications from the network layer up to the application layer. Thus the Internet is not something separate from the telecommunication world, as it was considered to be at the beginning (in the 1980s and even the 1990s), nowadays it is the main part of that world. With this convergence, certain issues have also arisen. One of the main such issues is the QoS. Why? Because the telecom world based on telephony and TV had strict specifications for QoS requirements for those services, and the telephone and TV net- works were designed to provide end-to-end QoS (we will define QoS later). For example, in circuit-switching, PSTNs typically are established two channels end-to-end (each 64 kbit/s), one per direction between the two users (talking to each other over the tele- phone), and such bitrate is dedicated to the given call for its duration regardless of whether there are voice signals (i.e. talk) to transport over the line or not (i.e. silence). The same approach is present in TV broadcast networks; however, the bandwidth (in bit/s) for TV (i.e. for video) is many times higher than the one needed for voice. On the other side, the native Internet was built on best-effort principles, which means that the network will make the best effort to carry each IP packet from its source to its destina- tion address; however, there are no strict guarantees that the packet will be delivered. So, the Internet in it