Enabling Policy, Charging and Subscription in IMS Networks
 
The promise of converged networks with all-IP interconnectivity comes closer with the IP Multimedia Subsystem (IMS) reference architecture. Core network signaling has been transformed from SS7-based protocols to SIP, DIAMETER, MGCP, RTP and COPS. While SIP drives the control-plane all the way from the user terminal to the IMS core network, bringing in rich media services and presence, it is DIAMETER that truly enables some of the critical functions in the IMS core network.
 
DIAMETER provides the support for the essential functions of Subscription, Charging and Policy in the network. Subscriber-related data that defines all the service-related parameters resides in the Home Subscriber System (HSS). Access to this data from session controllers and application servers is made possible by DIAMETER. Mechanisms for both online and offline charging for multimedia services are provided by the Policy Server through the Gq interface.
 
Evolving from the RADIUS protocol providing AAA support, DIAMETER has provides the 3GPP-IMS network a more versatile and extensible mechanism to support these interfaces.