4 Architecture considerations

32.2773GPPCharging managementProximity-based Services (ProSe) chargingRelease 17Telecommunication managementTS

4.1 High level ProSe architecture

Figure 4.1.1 shows the high level view of the non-roaming architecture for ProSe that is defined in TS 23.303 [238].
In this figure, UE A and UE B have subscriptions from the same PLMN.

Figure 4.1.1: Non-roaming reference architecture

Figure 4.1.2 shows the high level view of non-roaming inter-PLMN architecture for ProSe defined in TS 23.303 [238]. In this figure, PLMN A is the HPLMN of UE A, and PLMN B is the HPLMN of UE B.

Figure 4.1.2: Inter-PLMN reference architecture

Figure 4.1.3 shows the high level view of the roaming architecture for ProSe as defined in TS 23.303 [238]. In this figure, UE A uses a subscription of PLMN A and UE B uses a subscription of PLMN B; UE A is roaming in PLMN C while UE B is not roaming.

Figure 4.1.3: Roaming reference architecture

NOTE 1: For EPC-level ProSe discovery the roaming architecture is not specified in the present document.

In 5G system, the high level 5G ProSe architecture is as defined in TS 23.304 [241] clause 4.2.

NOTE 2: As defined in TS 23.303 [238], the ProSe Function consists of Direct Provisioning Function (DPF), Direct Discovery Name Management Function (DDNMF) and EPC-level Discovery Function. In 5GS, the 5G DDNMF takes the role of "ProSe Function", DPF is replaced by PCF, and EPC-level Discovery Function is not supported.

4.1a Void

4.2 ProSe offline charging architecture

For ProSe Direct Discovery and EPC-level Discovery services, as described in TS 32.240 [1], the CTF (an integrated component in each charging relevant ProSe Function) generates charging events and forwards them to the CDF. The CDF, in turn, generates CDRs which are then transferred to the CGF. Finally, the CGF creates CDR files and forwards them to the Billing Domain.

If the ProSe Function generating the charging information has an integrated CDF, then the ProSe Function can produce CDRs. The CGF may also be integrated in the ProSe Function, or it may exist as a physically separate entity. If the CGF is external to the ProSe Function, then the CDF forwards the CDRs to the CGF across the Ga interface.
In this case, the relationship between ProSe Function/CDF and CGF is m:1. If the CGF is integrated in the ProSe Function, then there is only an internal interface between the CDF and the CGF. In this case, the relationship between ProSe Function/CDF and CGF is 1:1.

If the CDF is external to the ProSe Function, the charging events are transferred from the ProSe Function to the CDF via the Rf interface specified in TS 32.299 [50]. In this case, the relationship between ProSe Function and CDF is m:1.

When an external CGF is used, this CGF may also be used by other, i.e. non-ProSe, network elements, according to network design and operator decision. It should be noted that the CGF may also be an integrated component of the BD – in this case, the Bx interface does not exist and is replaced by a proprietary solution internal to the BD.

Figure 4.2.1 depicts the architectural options described above.

Figure 4.2.1: ProSe offline charging architecture

For the ProSe Direction Communication Service, the CTF is divided into two functional blocks as described in Annex D of TS 32.240 [1]. The Accounting Metrics Collection (AMC) function block is in the UE. The AMC sends usage information collected to the Accounting Data Forwarding (ADF) function block of the CTF in the ProSe Function over the PC3 reference point defined in TS 23.303 [238]. The subset of PC3 specific to usage information collection for charging purposes is denoted as PC3ch in figure 4.2.2.

Figure 4.2.2: ProSe Direct Communication offline charging architecture

The PC3 protocol shall allow the following deployment options for the ProSe Function CTF (ADF) for ProSe Direct Communication depicted in figure 4.2.2:

– The ProSe Function CTF (ADF) for ProSe Direct Communication may be deployed in the same system as any combination of the ProSe Function components defined in clause 4.4.1 of TS 23.303 [238] (i.e. Direct Provisioning Function, Direct Discovery Name Management Function, EPC-level Discovery Function).

– The ProSe Function CTF (ADF) for ProSe Direct Communication may be deployed in a logically or physically separate system from the ProSe Function components defined in clause 4.4.1 of TS 23.303 [238]. To support this deployment scenario, the PC3ch subset of the protocol for usage information report delivery shall not require interaction with any other ProSe Function component for successful and complete processing.

The network ensures that the UE can have IP access to its HPLMN ProSe Function, in non-roaming and roaming case, as defined in TS 23.303 [238].

When the UE is out of coverage, PC3 reference point is not available. UE will store the logged information and upload to the ProSe Function once the PC3 becomes available and the reporting criteria are met. UE’s reporting of usage information is only visible to the ProSe Function.

It is mandatory to support at least one of the options Rf, Ga or Bx interfaces from the ProSe Function as described in the specification.

4.3 ProSe online charging architecture

ProSe online charging is based on ProSe function utilizing Ro interface and application towards the OCS as specified in TS 32.299 [50]. The Ro reference point covers all online charging functionality required for ProSe.

Figure 4.3.1: ProSe online charging architecture

4.4 5G ProSe converged charging architecture

The 5G ProSe converged charging architecture in service-based representation can be achieved under the alternatives:

– ProSe converged charging architecture (CTF), depicted in figure 4.4.1.

– ProSe converged charging architecture when using PC5 (Distributed CTF), depicted in figure 4.4.2.

– ProSe converged charging architecture (CEF), depicted in figure 4.4.3.

– ProSe converged charging architecture in reference point representation for non-roaming, depicted in figure 4.4.4.

Details on the interfaces and functions can be found in TS 32.240 [1] for the general architecture components. Ga is described in clause 5.4.4 and Bx in clause 5.4.5 of this document, and Nchf is described in TS 32.290 [55].

For the 5G ProSe Direct Discovery and 5G ProSe Direct Communication Service over PC5, the CTF is divided into two functional blocks as described in Annex D of TS 32.240 [1]. The Accounting Metrics Collection (AMC) function block is in the UE. The AMC sends usage information collected to the Accounting Data Forwarding (ADF) function block of the CTF in the 5G DDNMF over the PC3a reference point defined in TS 23.304 [241]. The subset of PC3a specific to usage information collection for charging purposes is denoted as PC3ach in figure 4.2.2.

Figure 4.4.1: ProSe converged charging architecture (CTF)

Figure 4.4.2: ProSe converged charging architecture when using over PC5 (Distributed CTF)

Figure 4.4.3: ProSe converged charging architecture (CEF)

Editor’s Note: The architecture figure should follow up the decision of the common CEF issues.

Editor’s Note: The details for charging information transfer in CEF-based charging architecture over PC5 are ffs.

Figure 4.4.4 depicts the 5G ProSe converged charging architecture in reference point representation for non-roaming:

Figure 4.4.4: 5G ProSe converged charging architecture non-roaming reference point representation