4 Architecture model and concepts

23.3043GPPProximity based Services (ProSe) in the 5G System (5GS)Release 17TS

4.1 General concept

Proximity based Services (ProSe) are services that can be provided by the 5GS based on UEs being in proximity to each other.

The 5GS enablers for ProSe include the following functions:

– 5G ProSe Direct Discovery;

– 5G ProSe Direct Communication;

– 5G ProSe UE-to-Network Relay.

4.2 Architectural reference model

4.2.1 Non-roaming reference architecture

Figure 4.2.1-1 shows the high-level view of the non-roaming 5G System architecture for Proximity-based Services (ProSe) with service-based interfaces within the Control Plane. In this figure, UE A and UE B use a subscription of the same PLMN.

Figure 4.2.1-1: Non-roaming 5G System architecture for Proximity-based Services

Figure 4.2.1-2 shows the high-level view of the non-roaming 5G System architecture for Proximity-based Services (ProSe) in reference point representation. In this figure, UE A and UE B use a subscription of the same PLMN.

Figure 4.2.1-2: Non-roaming 5G System architecture for Proximity-based Services in reference point representation

4.2.2 Roaming reference architecture

Figure 4.2.2-1 shows the high-level view of the roaming 5G System architecture for Proximity-based Services (ProSe) with service-based interfaces within the Control Plane. In the figure, UE A uses a subscription of HPLMN.

Figure 4.2.2-1: Roaming 5G System architecture for Proximity-based Services

4.2.3 Inter-PLMN reference architecture

The following figure 4.2.3-1 shows the high level view of the non-roaming inter-PLMN architecture with service-based interfaces within the Control Plane. In this figure, PLMN A is the HPLMN of UE A and PLMN B is the HPLMN of UE B.

Figure 4.2.3-1: Non-roaming Inter-PLMN 5G System architecture for Proximity-based Services

Figure 4.2.3-2 shows the high level view of the roaming architecture with service-based interfaces within the Control Plane. 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 4.2.3-2: Roaming Inter-PLMN 5G System architecture for Proximity-based Services

4.2.4 AF-based service parameter provisioning

The 5G System provides NEF services to enable communication between NFs in the PLMN and a ProSe Application Server. Figure 4.2.4-1 shows the high level view of AF-based service parameter provisioning for 5G ProSe communications. The ProSe Application Server may provide ProSe service parameters to the PLMN via NEF. The NEF stores the ProSe service parameters in the UDR.

Figure 4.2.4-1: 5G System architecture for AF-based service parameter provisioning for 5G ProSe communications

4.2.5 Reference points

PC1: The reference point between the ProSe application in the UE and in the ProSe Application Server. It is used to define application level signalling requirements. This reference point is not specified in this release of the specification.

PC3a: The reference point between the UE and the 5G DDNMF. PC3a relies on 5GC user plane for transport (i.e. an "over IP" reference point). It is used to authorise 5G ProSe Direct Discovery request, and perform allocation of ProSe Application Codes / ProSe Restricted Codes corresponding to ProSe Application Identities used for 5G ProSe Direct Discovery.

PC5: The reference point between ProSe-enabled UEs used for control and user plane for 5G ProSe Direct Discovery, 5G ProSe Direct Communication and 5G ProSe UE-to-Network Relay.

PC8: The reference point between the UE and the 5G ProSe Key Management Function (5G PKMF). The details are defined in TS 33.503 [29].

Npc2: The reference point between the ProSe Application Server and the 5G DDNMF. It is used to define the interaction between ProSe Application Server and 5G DDNMF for 5G ProSe Direct Discovery.

Npc4: The reference point between the UDM and 5G DDNMF. It is used to provide subscription information in order to authorise 5G ProSe Direct Discovery request.

Npc6: The reference point between the 5G DDNMF in the HPLMN and the 5G DDNMF in a Local PLMN (5G ProSe Direct Discovery). This reference point is used for HPLMN control of ProSe service authorization.

Npc7: The reference point between the 5G DDNMF in the HPLMN and the 5G DDNMF in the VPLMN. It is used for HPLMN control of ProSe service authorization.

Npc8: The reference point between the PCF and the 5G DDNMF. It is used to define the interactions between the 5G DDNMF and the PCF to e.g. get a PDUID from the PCF.

Npc9: The reference point between the 5G PKMF of the 5G ProSe Remote UE and the 5G PKMF of the 5G ProSe UE-to-Network Relay. The details are defined in TS 33.503 [29].

Npc10: The reference point between the 5G PKMF and UDM. The details are specified in TS 33.503 [29].

NOTE: Npc2, Npc4, Npc6, Npc7, Npc8, Npc9 and Npc10 show the interactions that exist between the NF services in the NFs. These reference points are realised by corresponding NF service-based interfaces and by specifying the identified consumer and producer NF service as well as their interaction in order to realize a particular system procedure.

4.2.6 Service-based interfaces

N5g-ddnmf: Services provided by 5G DDNMF to manage inter-PLMN 5G ProSe Direct Discovery operations.

Npkmf: Service provided by 5G PKMF to support inter-PLMN ProSe security management. The function of Npkmf is defined in TS 33.503 [29].

In addition to the relevant services defined in TS 23.501 [4] for the following service-based interfaces, in the case of ProSe Service, the services can be provided by corresponding NF are as follows:

Nudm: Services provided by UDM are used to get 5G ProSe Service related subscription information to the AMF during Initial Registration procedure or UE Configuration Update (UCU) procedure to inform the AMF the subscription information has changed, and to provide ProSe Service related subscription information to 5G DDNMF for the authorisation of 5G ProSe Direct Discovery requests. The subscription information is described in TS 23.502 [5]. Services provided by UDM may also be used by the 5G PKMF for relay service authorisation, see TS 33.503 [29].

Npcf: Services provided by H-PCF are used to provide 5G ProSe Service related parameters to V-PCF for the UE and NG-RAN in the roaming case, and to enable the 5G DDNMF to get a PDUID or be notified of PDUID change.

Nudr: Services provided by UDR are used to notify the PCF and the UDM of the update of the 5G ProSe Service related information as described in TS 23.502 [5].

Nnef: Services provided by NEF are used by the ProSe Application Server to update 5G ProSe Service related information of 5GC.

Namf: Services provided by AMF are consumed by PCF to provide the 5G ProSe Service related parameters for the UE and the NG-RAN to the AMF, and to enable the AMF create or update the UE context related to 5G ProSe service.

Nnrf: Services provided by NRF are used to discover the PCF that supports 5G ProSe service and for 5G DDNMF in HPLMN to discover other 5G DDNMFs in VPLMN or local PLMN.

Naf: Services provided by AF are consumed by the DDNMF to request authorization for Discovery Request. The AF may update the authorization information to revoke the Restricted ProSe Direct Discovery permission.

4.2.7 5G ProSe UE-to-Network Relay reference architecture

4.2.7.1 5G ProSe Layer-3 UE-to-Network Relay reference architecture

The following figure 4.2.7.1-1 shows the high level reference architecture for 5G ProSe Layer-3 UE-to-Network Relay. In this figure, the 5G ProSe Layer-3 UE-to-Network Relay may be in the HPLMN or a VPLMN.

Figure 4.2.7.1-1: Reference architecture for 5G ProSe Layer-3 UE-to-Network Relay

The following figure 4.2.7.1-2 shows the non-roaming reference architecture for 5G ProSe Layer-3 UE-to-Network Relay when N3IWF is supported. In this figure, the PLMN A and PLMN B may be the same or different. When the 5G ProSe Layer-3 Remote UE may connect to NG-RAN directly to access PLMN B, and in that case it would take the role of UE in the figure. The N3IWF may be connected to Relay UE UPF via a Data Network.

Figure 4.2.7.1-2: Non-roaming architecture model for 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support

The following figure 4.2.7.1-3 shows the roaming reference architecture for 5G ProSe Layer-3 UE-to-Network Relay. In this figure, the PLMN A and PLMN B may be the same or different and/or the PLMN A and PLMN C may be the same or different. The N3IWF may be connected to Relay UE UPF via a Data Network.

Figure 4.2.7.1-3: Roaming architecture model for 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support

4.2.7.2 5G ProSe Layer-2 UE-to-Network Relay reference architecture

Figure 4.2.7.2-1 shows the 5G ProSe Layer-2 UE-to-Network Relay reference architecture. The 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay may be served by the same or different PLMNs. If the serving PLMNs of the 5G ProSe Layer-2 Remote UE and the 5G ProSe Layer-2UE-to-Network Relay are different then NG-RAN is shared by the serving PLMNs, see the 5G MOCN architecture in clause 5.18 of TS 23.501 [4].

Figure 4.2.7.2-1: 5G ProSe Layer-2 UE-to-Network Relay reference architecture

NOTE 1: Uu between the 5G ProSe Layer-2 Remote UE and NG-RAN consists of RRC, SDAP and PDCP.

NOTE 2: The 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay are served by the same NG-RAN. The Core Network entities (e.g., AMF, SMF, UPF) serving the 5G ProSe Layer-2 Remote UE and the 5G ProSe Layer-2 UE-to-Network Relay can be the same or different.

4.3 Functional Entities

4.3.1 UE

Any 5G ProSe-enabled UE may support the following functions:

– Exchange of information for 5G ProSe Direct Discovery between 5G ProSe-enabled UE and the 5G DDNMF over PC3a reference point.

– Procedures for 5G ProSe Direct Discovery of other 5G ProSe-enabled UEs over PC5 reference point.

– Procedures for 5G ProSe Direct Communication over PC5 reference point, including Broadcast, Groupcast and Unicast mode 5G ProSe Direct Communication.

– Procedures to act as a 5G ProSe Layer-2 UE-to-Network Relay.

– Procedures to act as a 5G ProSe Layer-3 UE-to-Network Relay.

– Procedures to act as a 5G ProSe Layer-2 Remote UE.

– Procedures to act as a 5G ProSe Layer-3 Remote UE.

– Indicating 5G ProSe Policy Provisioning Request in UE Policy Container for Registration Request or UE triggered 5G ProSe Policy provisioning, which may request one or multiple types of policies/parameters as listed below:

– Policy/parameters for 5G ProSe Direct Discovery;

– Policy/parameters for 5G ProSe Direct Communication;

– Policy/parameters for 5G ProSe Layer-2 Remote UE;

– Policy/parameters for 5G ProSe Layer-3 Remote UE;

– Policy/parameters for 5G ProSe Layer-2 UE-to-Network Relay;

– Policy/parameters for 5G ProSe Layer-3 UE-to-Network Relay.

– Receiving the 5G ProSe Policy from 5GC over N1 reference point.

– Configuration of parameters for 5G ProSe Direct Discovery, 5G ProSe Direct Communication and 5G ProSe UE-to-Network Relay (e.g. including IP addresses, ProSe Layer-2 Group IDs, see clause 5.1). These parameters can be pre-configured in the UE, or, if in coverage, provisioned or updated by signalling over the N1 reference point from the PCF in the HPLMN or over PC1 reference point from the ProSe Application Server.

– Reporting the following capabilities to 5GC over the N1 reference point:

– 5G ProSe Capability.

4.3.2 5G DDNMF

4.3.2.1 General

The 5G DDNMF is the logical function handling network related actions required for dynamic 5G ProSe Direct Discovery. In this version of the specification, it is assumed that there is only one logical 5G DDNMF in each PLMN that supports 5G ProSe Direct Discovery service.

NOTE: If multiple 5G DDNMFs are deployed within the same PLMN (e.g., for load reasons), the method to locate the 5G DDNMF that has allocated a specific ProSe Application Code or ProSe Restricted Code (e.g. through a database lookup, etc.) is not defined in this version of the specification.

The 5G DDNMF interacts with the 5G ProSe-enabled UE using procedures over PC3a reference point defined in clause 6.3.1 to allocate and resolve the mapping of ProSe Applications IDs and ProSe Application Codes used in 5G ProSe Direct Discovery. It uses ProSe related subscriber data stored in UDM for the authorisation of each discovery request. It also provides the UE with the necessary security material in order to protect discovery messages transmitted over the air. In restricted 5G ProSe Direct Discovery, it also interacts with the Application Server via Npc2 reference points or with other 5G DDNMFs via Npc6/Npc7 reference points for the authorization of the discovery requests.

The 5G ProSe-enabled UE use procedure defined in clause 4.3.2.2 to discovery the 5G DDNMF in the HPLMN. Based on the UE Local Configuration or URSP as defined in TS 23.503 [9], an existing PDU session is selected or a new PDU session is established, to carry the control signalling between the UE and the 5G DDNMF in the HPLMN.

The 5G DDNMF provides the necessary charging functionality or charging information for the usage of 5G ProSe Direct Discovery and/or ProSe Direct Communication to interact with CHF or for the provision to CEF.

The 5G DDNMF in the HPLMN may interact with the 5G DDNMF in a VPLMN or Local PLMN in order to manage the 5G ProSe Direct Discovery service.

The 5G DDNMF gets the address of the PCF for the UE from the BSF.

The 5G DDNMF gets the PDUID from the PCF and subscribes to notifications on Change of PDUID.

4.3.2.2 5G DDNMF Discovery

The 5G DDNMF of HPLMN is discovered through interaction with the Domain Name Service function. The UE may have the 5G DDNMF address in the Home PLMN (either as a FQDN or an IP address) pre-configured or provisioned as specified in clause 5.1.2.1. If it is not pre-configured or provisioned then the UE self-constructs the FQDN for it using e.g. the PLMN ID of the HPLMN.

The 5G DDNMF in the HPLMN uses the NRF to discovery other 5G DDNMFs in a VPLMN or local PLMN.

4.3.3 PCF

In addition to the functions defined in TS 23.501 [4] and TS 23.503 [9], the PCF includes functions to provision the UE with necessary policies and parameters to use 5G ProSe services, as part of the UE ProSe Policy information as defined in TS 23.503 [9] clause 4.2.2, based on the policies/parameters requested by the UE listed in clause 4.3.1 in the 5G ProSe Policy Provisioning Request:

– PC5 usage reporting configuration.

– Authorization policy and parameters for 5G ProSe Direct Discovery and Communication.

– Authorization policy and parameters for 5G ProSe UE-to-Network Relay Discovery and Communication (i.e. as 5G ProSe Layer-2 Remote UE, as 5G ProSe Layer-3 Remote UE, as 5G ProSe Layer-2 UE-to-Network Relay, as 5G ProSe Layer-3 UE-to-Network Relay).

– PDUID allocation with its validity timer.

The PCF may update the 5G ProSe policy and parameters to the UE under certain conditions.

When receiving the 5G ProSe Capability in Npcf_UEPolicyControl_Create Request from the AMF or when receiving the updated subscription data from UDR, the PCF generates the PC5 QoS parameters used by NG-RAN corresponding to a UE as defined in clause 5.4.2 of TS 23.287 [2].

4.3.4 AMF

In addition to the functions defined in TS 23.501 [4], the AMF performs the following functions:

– Select a PCF supporting 5G ProSe Policy/Parameter provisioning based on indication of 5G ProSe Capability as part of the "5GMM capability" in the Registration Request.

– Store the 5G ProSe Capability.

– Forward the 5G ProSe Capability to PCF in Npcf_UEPolicyControl_Create Request.

– Obtain from UDM the subscription information related to 5G ProSe and store them as part of the UE context data.

– Obtain PC5 QoS parameters from the PCF and store them as part of the UE context data.

– Provision the NG-RAN with indication about the UE authorization status about 5G ProSe Direct Discovery and 5G ProSe Direct Communication (i.e. as 5G ProSe-enabled UE for ProSe Direct Discovery, as 5G ProSe-enabled UE for ProSe Direct Communication), 5G ProSe UE-to-Network Relay Discovery and Communication (i.e. as 5G ProSe Layer-2 Remote UE, as 5G ProSe Layer-2 UE-to-Network Relay, as 5G ProSe Layer-3 UE-to-Network Relay).

– Provision the NG-RAN with PC5 QoS parameters related to 5G ProSe Direct Communication.

– Optionally support security procedures over Control Plane for 5G ProSe UE-to-Network relaying as defined in TS 33.503 [29].

4.3.5 UDM

In addition to the functions defined in TS 23.501 [4], the UDM performs the following functions:

– Subscription management for 5G ProSe Direct Discovery and Communication.

– Subscription management for 5G ProSe UE-to-Network Relay Discovery and Communication.

4.3.6 UDR

In addition to the functions defined in TS 23.501 [4], the UDR performs the following functions:

– Stores a path preference for ProSe services provided by the AF.

– Stores ProSe service parameters.

4.3.7 NRF

In addition to the functions defined in TS 23.501 [4], the NRF performs the following functions:

– PCF discovery by considering 5G ProSe Capability.

– 5G DDNMF Discovery.

Similar procedure can be used for 5G DDNMF discovery across PLMNs as specified in clause 4.17.5 of TS 23.502 [5] with the difference as below:

– The serving PLMN is replaced by home PLMN and home PLMN is replaced by local PLMN or serving PLMN.

4.3.8 ProSe Application Server

The ProSe Application Server supports the following functionalities.

For 5G ProSe Direct Discovery:

– Maintains permission information for the restricted 5G ProSe Direct Discovery using RPAUIDs;

– Storage of ProSe Discovery UE IDs and metadata;

– Mapping of RPAUID and PDUID for restricted 5G ProSe Direct Discovery;

– Provisioning parameters for Group Member Discovery to UE.

– Interaction with 5G DDNMF for 5G ProSe Direct Discovery, including:

– Allocation of the ProSe Restricted Code Suffix pool, if restricted Direct Discovery with application-controlled extension is used;

– Allocation of the mask(s) for ProSe Restricted Code Suffix, if restricted Direct Discovery with application-controlled extension is used.

For 5G ProSe Direct Communication:

– Provisioning a path preference for 5G ProSe Services to UDR;

– Provisioning parameters for 5G ProSe Direct Communication to UE.

For 5G ProSe UE-to-Network Relay service:

– Provisioning parameters for 5G ProSe UE-to-Network Relay Discovery and 5G ProSe UE-to-Network Relay Communication to UDR.

4.3.9 5G ProSe UE-to-Network Relay

4.3.9.1 General

Both 5G ProSe Layer-2 and Layer-3 UE-to-Network Relay entity provides the relaying functionality to support connectivity to the network for 5G ProSe Remote UEs. It can be used for both public safety services and commercial services (e.g. interactive service).

Both 5G ProSe Layer-2 and Layer-3 UE-to-Network Relay supports the following functions to enable connectivity to the network:

– 5G ProSe UE-to-Network Relay Discovery service as defined in clause 6.3.2.3, to allow discovery by the 5G ProSe Remote UE;

– access the 5GS as a UE as defined in TS 23.501 [4] with the enhancements as specified in clauses 6.2 and 6.6;

– relays unicast traffic (uplink and downlink) between the 5G ProSe Remote UE and the network, supporting IP, Ethernet or Unstructured traffic type.

NOTE: Relaying MBS traffic to a 5G ProSe Remote UE by a 5G ProSe UE-to-Network Relay is not supported in this release of the specification.

4.3.9.2 5G ProSe Layer-3 UE-to-Network Relay

In addition to the common 5G ProSe UE-to-Network Relay functions defined in clause 4.3.9.1, 5G ProSe Layer-3 UE-to-Network Relay supports the following functions to enable connectivity to the network:

– 5G ProSe Direct Communication via 5G ProSe Layer-3 UE-to-Network Relay as specified in clause 6.5.1, for the communication with the 5G ProSe Layer-3 Remote UEs for the relay operations;

– end-to-end QoS treatment for the 5G ProSe Layer-3 Remote UE’s traffic without N3IWF as defined in clause 5.6.2.1 and when accessing via an N3IWF as defined in clause 5.6.2.2;

– IP address management for the 5G ProSe Layer-3 Remote UE as defined in clause 5.5.1.3 in case the 5G ProSe Layer-3 Remote UE uses IP traffic type.

4.3.9.3 5G ProSe Layer-2 UE-to-Network Relay

In addition to the common 5G ProSe UE-to-Network Relay functions defined in clause 4.3.9.1, 5G ProSe Layer-2 UE-to-Network Relay supports the following functions to enable connectivity to the network:

– 5G ProSe Direct Communication via 5G ProSe Layer-2 UE-to-Network Relay as specified in clause 6.5.2, for the communication with the 5G ProSe Layer-2 Remote UEs for the relay operations;

– QoS handling for 5G ProSe Layer-2 UE-to-Network Relay and end-to-end QoS treatment as defined in clause 5.6.2.3.

4.3.10 SMF

In addition to the functions defined in TS 23.501 [4], the SMF supports the following function:

– Receiving 5G ProSe Layer-3 Remote UE report and maintaining the information of 5G ProSe Layer-3 Remote UE(s) handled by a 5G ProSe Layer-3 UE-to-Network Relay in the 5G ProSe Layer-3 UE-to-Network Relay’s SM context for the PDU Session associated with the relay.

4.3.11 NEF

In addition to the functions defined in TS 23.501 [4], the NEF supports the following:

– To enable AFs to provide service specific information to the 3GPP network, the NEF supports additional service parameters for ProSe policy as specified in clause 6.2.5.