At IP-CAN bearer activation the user shall have access to either IP-CAN services without Policy and Charging Control, or IP-CAN services with Policy and Charging Control. It is operator choice whether to offer both or only one of these alternatives for accessing the IM Subsystem.
When using IP-CAN without Policy and Charging Control, IP-CAN bearers are established according to the user's subscription, local operator's IP bearer resource based policy, local operator's admission control function and roaming agreements.
When using IP-CAN with Policy and Charging Control, PCC decisions (e.g., authorization and control) are also applied to the IP-CAN bearer.
The description in this clause and the following clauses (clauses 220.127.116.11
- 18.104.22.168) is applicable for the case when Policy and Charging Control is employed.
The IP-Connectivity Access Network contains a Policy and Charging Enforcement Function (PCEF, in 5GS corresponding to the combination of SMF and UPF) that has the capability of policing packet flow into the IP network, and restricting the set of IP destinations that may be reached from/through an IP-CAN bearer according to a packet classifier.
This policy 'gate' function has an external control interface that allows it to be selectively 'opened' or 'closed' on the basis of IP destination address and port. When open, the gate allows packets to pass through (to the destination specified in the classifier) and when closed, no packets are allowed to pass through. The control is performed by a PCRF/PCF (the interface between the PCRF/PCF and the P-CSCF is the Rx interface standardised in TS 23.203
or the N5 interface (using the Npcf_PolicyAutorization
service), standardised in TS 23.503
and TS 29.514
There are eight interactions defined for Policy and Charging Control:
Authorize QoS Resources.
Enabling of media flows authorized in (1), e.g. 'open' the 'gate'.
Disabling of media flows authorized in (1), e.g. 'close' the 'gate'.
Revoke Authorization for IP-CAN and IP resources.
Indication of IP-CAN bearer release from the PCEF in the IP-Connectivity Access Network to the PCRF/PCF.
Authorization of IP-CAN bearer modification.
Indication of IP-CAN bearer modification from the PCEF in the IP-Connectivity Access Network to the PCRF/PCF.
These requirements and functional description of these interactions are explained further in the following clauses. The complete specification of the interface between the PCRF/PCF and the PCEF is contained in TS 23.203
and TS 23.503
The Policy and Charging Control can also be used to enable the P-CSCF to retrieve the user location and/or UE Time Zone information from the access network as specified in TS 23.203
and TS 23.503