6.2.12 Direct discovery update procedure for restricted discovery

24.5543GPPProximity-services (ProSe) in 5G System (5GS) protocol aspectsRelease 17Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

6.2.12.1 General

The discovery update procedure is used to update the discovery filters and/or allocate a new ProSe restricted code as defined in 3GPP TS 23.304 [2]. The 5G DDNMF can at any time update/revoke a previously allocated ProSe restricted code, or discovery filters.

6.2.12.2 Revocation of restricted discovery filters

6.2.12.2.1 Restricted discovery filters revocation procedure initiation

The 5G DDNMF in the HPLMN shall initiate the restricted discovery filters revocation procedure by sending the DISCOVERY_UPDATE_REQUEST to the UE with:

a) a new DDNMF transaction ID not used in any other direct discovery procedures in PC3a interface;

b) the discovery entry ID set to the discovery entry ID of the corresponding discovery entry that contains the restricted discovery filter to be revoked; and

c) optionally update info containing the restricted discovery filters that replace the existing ones, if the 5G DDNMF decides to remove only certain filter(s) and not others.

NOTE: The 5G DDNMF can include one or multiple transactions in one DISCOVERY_UPDATE_REQUEST message for different Restricted discovery filters and receive corresponding <response-update> element or <response-reject> element in a DISCOVERY_UPDATE_RESPONSE message for each respective transaction. In the following description of the network initiated direct discovery update request procedure, only one transaction is included.

Figure 6.2.12.2.1 illustrates the interaction of the UE and the 5G DDNMF in the restricted discovery filters revocation procedure.

Figure 6.2.12.2.1.1: Restricted discovery filters revocation procedure

6.2.12.2.2 Restricted discovery filters revocation procedure accepted by the UE

Upon receiving a DISCOVERY_UPDATE_REQUEST message, the UE shall check if the discovery entry ID contained in the DISCOVERY_UPDATE_REQUEST message is valid. If the discovery entry ID is valid, the UE shall proceed with the following direct discovery update procedure.

The UE shall remove all the restricted discovery filters corresponding to the discovery entry ID if the Update info is not included in the DISCOVERY_UPDATE_REQUEST message or shall remove the old restricted discovery filters and store the restricted discovery filter included in the Update info in the DISCOVERY_UPDATE_REQUEST message. Then the UE shall send a DISCOVERY_UPDATE_RESPONSE message to the 5G DDNMF with the <response-update> element which contains:

a) the DDNMF transaction ID set to the value of the DDNMF transaction ID received in the DISCOVERY_UPDATE_REQUEST message; and

b) discovery entry ID set to the value of the discovery entry ID received in the DISCOVERY_UPDATE_REQUEST message.

6.2.12.2.3 Restricted discovery filters revocation procedure completion by the 5G DDNMF

Upon receipt of the DISCOVERY_UPDATE_ RESPONSE message by the 5G DDNMF, if the DDNMF transaction ID contained in the <response-update> element does not match the value sent by the 5G DDNMF in a DISCOVERY_UPDATE_REQUEST message, the 5G DDNMF shall discard the DISCOVERY_UPDATE_RESPONSE message. Upon receipt of the DISCOVERY_UPDATE_ RESPONSE message by the 5G DDNMF, if the DDNMF transaction ID contained in the <response-update> element matches the value sent by the 5G DDNMF in a DISCOVERY_UPDATE_REQUEST message, the restricted discovery filters revocation procedure is complete.

6.2.12.2.4 Restricted discovery filters revocation procedure not accepted by the UE

If the DISCOVERY_UPDATE_REQUEST message cannot be accepted by the UE, the UE sends a DISCOVERY_UPDATE_RESPONSE message containing a <response-reject> element to the 5G DDNMF including an appropriate PC3a control protocol cause value.

If the discovery entry ID contained in the DISCOVERY_UPDATE_REQUEST message is not found in the UE context, the UE shall send a DISCOVERY_UPDATE_RESPONSE message containing a <response-reject> element with PC3 control protocol cause value #10 "Unknown or Invalid discovery entry ID".

6.2.12.2.5 Abnormal cases

6.2.12.2.5.1 Abnormal cases in the 5G DDNMF

The following abnormal cases can be identified:

a) Indication from the transport layer of transmission failure of DISCOVERY_UPDATE_REQUEST message (e.g., after TCP retransmission timeout)

The 5G DDNMF shall close the existing secure connection to the UE.

b) No response from the UE after the DISCOVERY_UPDATE_REQUEST message has been successfully delivered (e.g., TCP ACK has been received for the DISCOVERY_UPDATE_REQUEST message)

The 5G DDNMF shall retransmit the DISCOVERY_UPDATE_REQUEST message.

NOTE: The timer to trigger retransmission and the maximum number of allowed retransmissions are 5G DDNMF implementation specific.

6.2.12.2.5.2 Abnormal cases in the UE

The following abnormal cases can be identified:

a) Indication from the lower layer of transmission failure of DISCOVERY_UPDATE_RESPONSE message.

After receiving an indication from lower layer that the DISCOVERY_UPDATE_RESPONSE message has not been successfully acknowledged (e.g., TCP ACK is not received), the UE shall abort the procedure.

6.2.12.3 Allocation of new ProSe restricted code

6.2.12.3.1 New ProSe restricted code allocation procedure initiation

The 5G DDNMF in the HPLMN shall initiate the ProSe restricted code allocation procedure by sending the DISCOVERY_UPDATE_REQUEST to the UE with:

a) a new DDNMF transaction ID not used in any other direct discovery procedures in PC3a interface;

b) the discovery entry ID set to the discovery entry ID of the corresponding discovery entry that contains the ProSe restricted code to be replaced; and

c) update info containing the ProSe restricted code set to the ProSe restricted code to be replaced and a validity timer T5062 set to the T5062 timer value assigned by the 5G DDNMF to the ProSe restricted code.

Figure 6.2.12.3.1.1 illustrates the interaction of the UE and the 5G DDNMF in the ProSe restricted code allocation procedure.

NOTE: The 5G DDNMF can include one or multiple transactions in one DISCOVERY_UPDATE_REQUEST message for different ProSe restricted codes and receive corresponding <response-update> element or <response-reject> element in a DISCOVERY_UPDATE_RESPONSE message for each respective transaction. In the following description of the network initiated direct discovery update request procedure, only one transaction is included.

Figure 6.2.12.3.1.1: New ProSe restricted code allocation procedure

6.2.12.3.2 ProSe restricted code allocation procedure accepted by the UE

The UE shall replace the ProSe restricted code corresponding to the discovery entry ID included in the DISCOVERY_UPDATE_REQUEST message. The UE shall stop the validity timer T5062 if running and start the validity timer T5062 with the received value. Then the UE shall send a DISCOVERY_UPDATE_RESPONSE message to the 5G DDNMF with the <response-update> element which contains:

a) the DDNMF transaction ID set to the value of the DDNMF transaction ID received in the DISCOVERY_UPDATE_REQUEST message; and

b) discovery entry ID set to the value of the discovery entry ID received in the DISCOVERY_UPDATE_REQUEST message.

6.2.12.3.3 ProSe restricted code allocation procedure completion by the 5G DDNMF

Upon receipt of the DISCOVERY_UPDATE_ RESPONSE message by the 5G DDNMF, if the DDNMF transaction ID contained in the <response-update> element does not match the value sent by the 5G DDNMF in a DISCOVERY_UPDATE_REQUEST message, the 5G DDNMF shall discard the DISCOVERY_UPDATE_RESPONSE message. Upon receipt of the DISCOVERY_UPDATE_ RESPONSE message by the 5G DDNMF, if the DDNMF transaction ID contained in the <response-update> element matches the value sent by the 5G DDNMF in a DISCOVERY_UPDATE_REQUEST message, the ProSe restricted code allocation procedure is complete.

6.2.12.3.4 ProSe restricted code allocation procedure not accepted by the UE

If the discovery entry ID contained in the DISCOVERY_UPDATE_REQUEST message is not found in the UE context, the UE shall send a DISCOVERY_UPDATE _RESPONSE message containing a <response-reject> element with PC3a control protocol cause value #10 "Unknown or invalid discovery entry ID".

6.2.12.3.5 Abnormal cases

6.2.12.3.5.1 Abnormal cases in the 5G DDNMF

The following abnormal cases can be identified:

a) Indication from the transport layer of transmission failure of DISCOVERY_UPDATE_REQUEST message (e.g., after TCP retransmission timeout)

The 5G DDNMF shall close the existing secure connection to the UE.

b) No response from the UE after the DISCOVERY_UPDATE_REQUEST message has been successfully delivered (e.g., TCP ACK has been received for the DISCOVERY_UPDATE_REQUEST message)

The 5G DDNMF shall retransmit the DISCOVERY_UPDATE_REQUEST message.

NOTE: The timer to trigger retransmission and the maximum number of allowed retransmissions are 5G DDNMF implementation specific.

6.2.12.3.5.2 Abnormal cases in the UE

The following abnormal cases can be identified:

a) Indication from the lower layer of transmission failure of DISCOVERY_UPDATE_RESPONSE message.

After receiving an indication from lower layer that the DISCOVERY_UPDATE_RESPONSE message has not been successfully acknowledged (e.g., TCP ACK is not received), the UE shall abort the procedure.