Content for  TS 23.304  Word version:  19.1.0

5G ProSe Direct Discovery is defined as the process that detects and identifies another UE in proximity via NR PC5 reference point. As defined in clause 5.3.1.1 in TS 23.303, 5G ProSe Direct Discovery can be open or restricted; it can be standalone or used for subsequent actions e.g. to initiate 5G ProSe Direct Communication. In the case of inter-PLMN ProSe discovery and communication over PC5 reference point, the PC5 parameters need to be configured in a consistent way among the UEs within a certain region. The architecture for the Inter-PLMN PC5 case is defined in clause 4.2.3. The UEs may use the PC5 DRX mechanism to perform 5G ProSe Direct Discovery and 5G ProSe UE-to-Network Relay Discovery over PC5 reference point as specified in clause 5.13.

There are two models for 5G ProSe Direct Discovery: Model A and Model B which are defined in clause 5.3.1.2 in TS 23.303.

For 5G ProSe UE-to-Network Relay discovery, both Model A and Model B discovery are supported:

• Model A uses a single discovery protocol message (Announcement).
• Model B uses two discovery protocol messages (Solicitation and Response).

For Relay Discovery Additional Information, only Model A discovery is used. The procedures for 5G ProSe UE-to-Network Relay discovery are defined in clause 6.3.2.3.

5G ProSe Direct Discovery over the PC5 reference point has the following characteristics:

• PC5 communication channel is used to carry the discovery message over PC5. The discovery message over PC5 is differentiated with other PC5 messages by AS layer.
• ProSe layer shall indicate to AS layer whether the signalling is discovery message or PC5-S message.

Group discovery/management to support on demand-based group communication for commercial services has the following characteristics:

• The group discovery/formation/management can be carried out in the Application layer in coordination with the Application Server.
• Application layer signalling between the UE and the Application Server is out of scope of this specification.

5G ProSe Direct Discovery with 5G DDNMF has the following characteristics:

• 5G DDNMF in the 5GS is used for 5G ProSe Discovery Direct Code management (including allocation and resolution). The 5G DDNMF gets the PDUID from the PCF and subscribes to notifications on Change of PDUID.
• 5G DDNMF is defined in clause 4.3.2 and the detail procedure for 5G ProSe Direct Discovery with 5G DDNMF is defined in clause 6.3.

Group discovery/management to support public safety has the following characteristics:

• Pre-configured or provisioned information can be used for the 5G ProSe Direct Discovery procedure as defined in clause 5.1.2.

The information elements included in the 5G ProSe Direct Discovery messages are described in clause 5.8.1 and clause 6.3.2.

For 5G ProSe UE-to-UE Relay Discovery, both Model A and Model B discovery are supported:

• Model A uses a single discovery protocol message (Announcement).
• Model B uses two discovery protocol messages (Solicitation and Response).

The procedures for 5G ProSe UE-to-UE Relay Discovery with Model A/Model B are defined in clause 6.3.2.4. 5G ProSe UE-to-UE Relay Communication with integrated Discovery is also supported as specified in clause 6.7.3.

For 5G ProSe multi-hop UE-to-Network Relay discovery, both Model A and Model B discovery are supported. The procedures for 5G ProSe multi-hop UE-to-Network Relay discovery Model A are defined in clause 6.3.2.5.2. The procedures for 5G ProSe multi-hop UE-to-Network Relay discovery Model B are defined in clause 6.3.2.5.3. For Additional parameters announcement procedure, only Model A discovery is used and is defined in clause 6.3.2.5.4.

For 5G ProSe Multi-hop UE-to-UE Relay discovery, both Model A and Model B discovery are supported:

• Model A uses a single discovery protocol message (Announcement).
• Model B uses two discovery protocol messages (Solicitation and Response).

Based on the RSC used for the discovery, the 5G ProSe Multi-hop UE-to-UE Relay discovery may use one of the two different types of discovery operations, i.e. discovery for IP PDU type, and discovery for non-IP PDU type. A 5G ProSe Multi-hop UE-to-UE Relay may support only one or both types of discovery operations. The procedures for 5G ProSe Multi-hop UE-to-UE Relay discovery Model A/B for IP PDU type are defined in clause 6.3.2.6.2. The procedures for 5G ProSe Multi-hop UE-to-UE Relay discovery Model A/B for non-IP PDUs (e.g. Ethernet or Unstructured) are defined in clause 6.3.2.6.3.