Policy control is described in 3GPP specifications as being part of the Packet Core network architecture. Actually, this feature interacts not only with Packet Core nodes, but also with SIP servers belonging to the IMS subsystem, such as the P-CSCF.
This section describes the main concepts and added value of Policy Control, as well as the evolution of this mechanism (together with the charging feature), from the early Release 5 UMTS implementation up to the Release 7 enhancements and Evolved Packet Core architecture.
Policy control has not been invented with UMTS. Lots of attention has been paid to this in IETF groups, as part of the activity related to the evolution an enhancement of IP networks. Practically speaking, what could be a fair definition of ‘Policy Control’? One possible answer can be found, for example, in IETF document RFC2753, ‘Framework for Policy-Based Admission Control’, stating that ‘Policy Control is the application of rules to determine resource access and usage’.
In early UMTS implementation (including the Release 5 of UMTS 3GPP specifications), Policy Control was user-terminal driven. Depending on the requested service (Web browsing, streaming, Push-To-Talk), the user terminal was requesting a PDP context (or Packet Data Protocol context) with Quality of Service attributes being set accordingly to the type of the service (real-time versus nonreal-time service, maximum and mean bit rate, delay requirements, ...