Mobile networks have evolved such that 3rd generation mobile networks offer many different services that include multimedia messaging, streaming video, parental control, and mobile phone advertisements. The IP Multimedia Subsystem (IMS) is an architectural framework for delivering internet protocol (IP) multimedia to mobile users. The 3GPP developed IMS to evolve mobile networks beyond GSM. IMS allows service providers to deliver Internet services over a variety of networks that include, but are not limited to, GPRS, Wireless LAN, CDMA2000, and fixed line.
To ease the integration with the Internet, IMS uses Internet protocols such as Session Initiation Protocol (SIP). The purpose of IMS is to aid access of multimedia and voice applications across wireless and wireline terminals. This is done by having a service plane and a bearer plane. The service plane provides different services to wireless terminals across wireless networks. Alternatively, the bearer plane allocates the physical network recourses (i.e. network bandwidth) necessary to provide the services provisioned by the service plane. Further, IMS has allowed Application Servers to apply policies for certain applications to the bearer plane via a functional element known as the Policy and Charging Rules Function (PCRF). The policy framework defined in IMS, for example, allows a subscriber to receive appropriate bandwidth and reductions in latency for viewing of a streaming video (service application). The IMS and MMD standards define how the PCRF is used by application servers (AS) to push or pull policy information about how a user is to use the resources provided by the bearer plane (RF and IP resources at the access network).