4 Gq interface

29.2093GPPPolicy control over Gq interfaceRelease 6TS

4.1 Overview

The Gq interface is used for the service-based policy set-up information exchange between the PDF and the AF, e.g. the P-CSCF. As defined in the stage 2 specifications (3GPP TS 23.207 [3]), this information is used by the PDF for the Service Based Local Policy (SBLP) decisions. The PDF exchanges the policy information with the GGSN as specified in 3GPP TS 29.207 [4].

The Gq interface may be an intra- or inter-domain interface. One PDF shall be able to serve more than one AF and one given AF may interact with a number of PDFs, although on an AF session basis, it shall interact with only a single PDF.

Signalling flows related to the Gq interface are specified in 3GPP TS 29.208 [5].

4.2 Gq reference model

The Gq interface is defined between the PDF and the AF. The Gq interface may be an intra- or inter-domain interface. The PDF is in the same PLMN as the GGSN.

The relationships between the different functional entities involved are depicted in figure 4.1.

NOTE: For clarity in the diagram, the network elements that are not involved in SBLP are not presented here (e.g. radio network elements, SGSN, etc).

Figure 4.1: Gq interface architecture model

4.3 Functional elements and capabilities

4.3.1 Policy Decision Function (PDF)

The PDF acts as a Policy Decision Point for service based local policy control. The PDF makes the policy decisions based on the session and media related information obtained from the AF via the Gq interface. The PDF shall exchange the decision information with the GGSN via the Go interface.

4.3.2 Application Function (AF)

The AF is an element offering applications that require the control of IP bearer resources (e.g. UMTS PS domain/GPRS domain resources). One example of an application function is the P-CSCF. The AF shall use the Gq interface to exchange service based policy information with the PDF.