, have defined an intermediate layer for the IMS architecture with the Resource and Admission Control Function (RACF). The RACF intermediate layer lies between
thetransport layer and the application layer
andallocates resources such as quality of service (QoS) and bandwidth to individual sessions. When a session is invoked, for example for Internet television
(IPTV), the application requests appropriate transmission resources from the RACF layer. The RACF function then checks whether the desired resources are available and can be provided. If the RACF function is implemented across the entire IMS network or a Next Generation Network (NGN), it can be used to provide each user with the optimum transmission conditions.