ng the QoS request. The AAA cloud (Figure 3.7) may also include business relations needed in cases of interconnections between network providers or between the given network operators and application providers as third parties. Generally, NGN uses the Diameter as the main protocol for AAA and user subscrip- tion management (i.e. it is the main protocol for communication with the HSS, the users' database in NGNs). Finally, SIP and Diameter are standardized by the IETF, and have become crucial ele- ments in the IMS developed by 3GPP and in NGN developed by the ITU. So, they can be noted as examples of the synergy between SDOs which started in the twenty-first cen- tury and is targeted at having unified standards on a global scale, especially important for the control plane in the telecommunication systems where SIP and Diameter belong. From the NGN perspective, both protocols belong in the service stratum, together with the IMS as their system umbrella. The control plane is crucial for end-to-end QoS provisioning because it is directly related to service profiles of users in the system and signaling in the control plane regarding resource allocation for a given call or session (or simply a flow, either treated individually or aggregated with the same class flows). Authorizing entity (diameter server) AAA cloud (diameter application) Network Network Diameter client element element (e.g. in a router) (e.g. router) (e.g. router) Diameter control flow AAA - Authentication, authorization and accounting Application data flow Figure 3.7 Diameter architecture for QoS AAA. 3 QoS in NGN and Future Networks 3.4 QoS Architectures for NGN How does NGN provide QoS? It has two stratums (service and transport), which perfectly corresponds to the Internet approach where applications/services are inde- pendent of the underlying transport infrastructure. With such an approach, QoS provision must be made via certain functions between the two stratums because the service stratum maintains QoS requirements from different services, while