7.1 General

29.2133GPPPolicy and charging control signalling flows and Quality of Service (QoS) parameter mappingRelease 17TS

The PCRF discovery procedures are needed where more than one PCRF is present in an operator’s network realm. Within such a deployment, an additional functional element, called DRA, is needed. PCRF discovery procedures include all the procedures that involve a DRA functional element.

Routing of Diameter messages from a network element towards the right Diameter realm in a PLMN is based on standard Diameter realm-based routing, as specified in IETF RFC 6733 [61] using the UE-NAI domain part. If PLMN is separated into multiple realms based on PDN information or IP address range (if applicable); the PDN information available in the Called-Station-Id AVP, or the UE’s Ipv4 address available in the Framed-IP-Address AVP or the UE’s Ipv6 address or prefix provided within the Framed-Ipv6-Prefix AVP may be used to assist routing PCC message to the appropriate Diameter realm.

The DRA keeps status of the assigned PCRF for a certain UE and IP-CAN session across all reference points, e.g. Gx, Gxx, S9, Rx and for unsolicited application reporting, the Sd interfaces.

The DRA shall support the functionality of a proxy agent and a redirect agent as defined in IETF RFC 6733 [61]. The mode in which it operates (i.e. proxy or redirect) shall be based on operator’s requirements.

Diameter clients of the DRA, i.e. AF, PCEF, BBERF, RCAF and PCRF in roaming scenarios shall support all procedures required to properly interoperate with the DRA in both the proxy and redirect modes.

NOTE: The proxy mode includes two variants:

PA1: Proxy agent based on the standard Diameter proxy agent functionality. All the messages need to go through the DRA.

PA2: Proxy agent based on the standard Diameter proxy agent functionality. Session establishment messages always go through the DRA. Gx, Gxx and S9 session termination messages always go through the DRA. All other messages bypass the DRA.