the service stratum provides originating and terminating calls/session between end peers (i.e. hosts, network nodes). It typically consists of servers, databases, and service functions on different network elements (e.g. routers, switches, gateways) and user devices. NGN transport stratum: It provides functions that transfer various user data. On the network's side, transport stratum provides functions that control and manage trans- port resources for carrying the data end-to-end. The related transferred data may carry user, management, and/or control information. This stratum typically includes network nodes such as routers and switches and links for their interconnections, with different sets of functions to provide the transfer of all kinds of information (user data, control data, or management data). Figure 3.2 shows the separation of NGN service and transport stratums. The sep- aration includes all planes in the telecommunication networks: the user plane (refers to data generated or received by the end-user device, such as voice, video, web pages, emails), the control plane (refers to call/session control, such as signaling), and the management plane (refers to communication between entities related to configuration, accounting, fault management, performance, and security management). Overall, both stratums consist of different types of functions. The main target of the NGN functional architecture is real-time services, including conversational multimedia (e.g. VoIP with video or multimedia telephony) and content delivery services (e.g. IPTV). The NGN functional architecture is shown in Figure 3.3. The central position in the NGN architecture for control functions is reserved for the network access control functions (NACFs). These interact with other functional entities in the transport stratum (resource and admission control functions (RACFs), mobility management control functions (MMCFs), and several transport functions), with the Figure 3.2 NGN transport and service Management plane stratums. Control plan