 telephony over IP, are based on P2P communication because in such a case both end-hosts have similar capabilities and functionalities. So, QoS-enabled VoIP as a replacement of PSTN (implemented by telecom operators) is in fact implemented with P2P architectures for transfer of voice data. 2.2.3 Basic Internet Network Architectures Basic Internet architecture consists of interconnected IP networks. In each such IP net- work, every Internet host and router must have implemented the IP on the network layer (in the OSs). According to the network size (number of hosts as well as distance between the hosts), terrestrial IP networks are typically classified into the following types [20]: Local area network (LAN). It connects several hosts to several hundreds of hosts via network switches which work on layers 1 and 2. It is connected to the public Internet via a router, typically called a gateway router. LANs are used everywhere for access to IP-based infrastructure, including home networks, corporate networks, or networks in public places (hotels, cafeterias, etc.). LANs are typically represented with Eth- ernet and WiFi as unified wired and wireless local access to the Internet network, respectively. Metropolitan area network (MAN). This refers to a network which provides access to hosts on a territory the size of a metropolitan area (e.g. a city) and may be used for direct connection of subscribers (e.g. WiMAX [20]) or for connections of different LANs between each other or with the Internet network. Wide area network (WAN). This refers to nationwide transport networks which are used to connect various core networks and/or access networks (e.g. LANs, MANs). Typically WANs are deployed through fiber links (due to highest capacity of the fiber and its longest reach). They are used for building Internet transport and transit net- works on national, regional, continental, or intercontinental levels. Radio access network (RAN). This type of access network refers to access of the mobile networks (2G, 3G, 4G, 5G, etc.). For