re consists of two main types of RACFs: Policy decision functional entity (PD-FE). It provides a single contact point to the SCF (i.e. the service stratum) and RACF hides all details of the transport infrastructure and transport functions. Transport resource control functional entity (TRC-FE). It deals with different trans- port technologies and at the same time provides the resource-based admission con- trol decision. The TRC-FE is service-independent. The RACF is connected via its PD-FE with the NACF. Only optionally, when QoS sup- port for mobile nodes is required (e.g. in mobile networks), the RACF is also connected with MMCF. 3.4 QoS Architectures for NGN When QoS is a matter of interest, as in the case of RACF, the performance measurements become crucial, with aim of following QoS provisioning by measuring the network performance of different network segments (e.g. access network, core net- work, transit network). For that purpose there is an umbrella standard for management for performance measurement (MPM) in NGN, which is also connected to the RACF. The PD-FE is connected to SCFs in the service stratum and to transport functions in the transport stratum, in particular to the policy enforcement functional entity (PE-FE). The PE-FE is packet-to-packet gateway located at the boundary of different networks, or between the core and access networks. The TRC-FE is used in the transport stratum only. It instructs the transport resource enforcement functional entity (TRE-FE) to enforce the transport resource policy rules, which are technology-dependent. Hence, the TRE-FE differs for different transport technologies, including access and core networks. 3.4.2 Ethernet QoS for NGN Ethernet has already become the dominant access technology in all corporate and resi- dential environments. Note also that WiFi is the wireless extension of Ethernet. However, Ethernet is developing even further, from the access to the core and trans- port networks (e.g. metro Ethernet or, in other words, carrier-grade Ethernet). In such c