6.2.2A Announce request procedure for restricted ProSe direct discovery model A

24.3343GPPProximity-services (ProSe) User Equipment (UE) to ProSe function protocol aspectsRelease 17Stage 3TS

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

6.2.2A.1 General

The purpose of the announce request procedure for restricted ProSe direct discovery model A is for the UE:

– to obtain a ProSe Restricted Code corresponding to the Restricted ProSe Application User ID (RPAUID) to be announced over the PC5 interface, upon a request for announcing from upper layers (e.g., application client) as defined in 3GPP TS 23.303 [2]; or

– to inform the ProSe Function that the UE wants to stop announcing a ProSe Restricted Code as defined in 3GPP TS 23.303 [2].

Before initiating the announce request procedure, the UE shall be authorised for restricted ProSe direct discovery model A announcing in the registered PLMN or local PLMN based on the service authorisation procedure as specified in clause 5.

NOTE: The notion of "local PLMN" does not apply for WLAN-based ProSe direct discovery. The UE can engage in WLAN-based ProSe direct discovery as announcing UE regardless of the serving PLMN or other PLMNs that provide E-UTRAN coverage in the UE location.

The UE includes the ProSe Restricted Code obtained as a result of a successful announce request procedure in a PC5_DISCOVERY message and passes the PC5_DISCOVERY message to the lower layers for transmission over the PC5 interface.

6.2.2A.2 Announce request procedure initiation

Before initiating the announce request procedure, the user sets the permissions for the restricted discovery using application layer mechanisms. The application client in the UE retrieves the PDUID provisioned to the UE as part of the service authorisation procedure as specified in clause 5 and obtains an RPAUID associated with the UE’s PDUID from the ProSe Application Server. The UE may provide metadata to be associated with the RPAUID, and the ProSe Application Server stores the metadata. This step is performed using mechanisms that are out of scope of the present specification.

If the UE is authorised to perform E-UTRA-based restricted ProSe direct discovery model A announcing in the PLMN operating the radio resources signalled from the serving PLMN, or if the UE is authorised to perform WLAN-based retricted ProSe direct discovery model A, it shall initiate an announce request procedure:

a) when the UE is triggered by an upper layer application to announce an RPAUID and the UE has no valid corresponding ProSe Restricted Code for that RPAUID of the upper layer application;

b) when the validity timer T4007 assigned by the ProSe Function to a ProSe Restricted Code has expired and the request from upper layers to announce the RPAUID corresponding to that ProSe Restricted Code is still in place;

c) when the UE selects a new PLMN while announcing a ProSe Restricted Code and intends to announce in the new PLMN, and the UE is authorised for restricted ProSe direct discovery model A announcing in the new PLMN;

d) when, while announcing a RPAUID, the UE intends to switch the announcing PLMN to a different PLMN without performing PLMN selection, and the UE does not have a valid allocated ProSe Restricted Code for this new PLMN yet; or

e) when the UE needs to update a previously sent restricted ProSe direct discovery model A announcing request.

When the UE selects a new PLMN while announcing a ProSe Restricted Code and the UE is not yet authorised for restricted ProSe direct discovery model A announcing in the new PLMN, the UE shall initiate an announce request procedure only after the UE is authorised for restricted ProSe direct discovery model A announcing in the new PLMN.

NOTE 1: To ensure service continuity if the UE needs to keep announcing a ProSe Restricted Code corresponding to the same RPAUID, the UE can initiate the announce request procedure before the validity timer T4007 assigned by the ProSe Function for a ProSe Restricted Code expires.

The UE initiates the announce request procedure by sending a DISCOVERY_REQUEST message with:

– a new transaction ID not used in any other direct discovery procedures in PC3 interface;

– the RPAUID set to the RPAUID received from upper layers;

– the command set to "announce";

– the UE identity set to the UE’s IMSI;

– the Application Identity set to the Application Identity of the upper layer application that requested the announcing;

– the Discovery Type set to "Restricted discovery";

– the ACE Enabled Indicator set to "application-controlled extension enabled" if application-controlled extension is required by the upper layers or "normal" if application-controlled extension is not used;

– the announcing type set to "on demand" if on demand announcing is requested by upper layers and "normal" if on demand announcing is not requested by upper layers;

– optionally the Requested Timer set to the length of validity timer associated with the ProSe Restricted Code that the UE expects to receive from the ProSe Function;

– the Discovery Entry ID set to a 0 if the announcing request is a new request, and set to the Discovery Entry ID received from the ProSe Function if the announcing request is to update a previously sent announcing request;

– optionally in case of E-UTRA-based restricted ProSe direct discovery model A the Announcing PLMN ID set to the PLMN ID of the local PLMN operating the radio resources that the UE intends to use for announcing the RPAUID; and

– optionally the PC5_tech set to the PC5 radio technology that the UE wishes to use. PC5_tech may include more than one PC5 radio technology.

If restricted ProSe direct discovery model A with application-controlled extension is requested by upper layers, the DISCOVERY_REQUEST message shall also include the Application Level Container, which contains application-level data transparent to the 3GPP network, to be used by the ProSe Application Server e.g. to assign ProSe Restricted Code Suffix(es).

When the UE initiates the announce request procedure to inform the ProSe Function that the UE wants to stop announcing a ProSe Restricted Code before the associated valid timer expires, the UE shall set the Requested Timer to 0.

NOTE 2: A UE can include one or multiple transactions in one DISCOVERY_REQUEST message for different RPAUIDs, and receive corresponding <restricted-announce-response> element or <response-reject> element in a DISCOVERY_RESPONSE message for each respective transaction. In the following description of the announce request procedure, only one transaction is included.

Figure 6.2.2A.2.1 illustrates the interaction of the UE and the ProSe Function in the announce request procedure.

Figure 6.2.2A.2.1: Announce request procedure for restricted ProSe direct discovery model A

6.2.2A.3 Announce request procedure accepted by the ProSe Function

Upon receiving a DISCOVERY_REQUEST message with the command set to "announce" and the Discovery Type set to "Restricted discovery", if the Requested Timer is included in the DISCOVERY_REQUEST message and the Requested Timer is set to 0, the ProSe Function shall check whether there is an existing UE context containing the discovery entry identified by the Discovery Entry ID included in the DISCOVERY_REQUEST message. If the discovery entry exists in the UE context, the ProSe Function shall inform the ProSe Function in the announcing PLMN to remove the corresponding discovery entry as specified in 3GPP TS 29.345 [5] when the announcing PLMN is not the same as that of the PLMN to which the ProSe Function belongs and remove the discovery entry identified by the Discovery Entry ID from the UE’s context. Then the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <restricted-announce-response> element with:

– the transaction ID set to the value of the transaction ID received in the DISCOVERY_REQUEST message, and

– the Discovery Entry ID set to the identifier associated with the corresponding discovery entry.

Upon receiving a DISCOVERY_REQUEST message with the command set to "announce" and the Discovery Type set to "Restricted discovery", if the Requested Timer is not included in the DISCOVERY_REQUEST message or the Requested Timer included in the DISCOVERY_REQUEST message is not set to 0, the ProSe Function shall perform the following procedure.

The ProSe Function shall check that the application corresponding to the Application Identity contained in the DISCOVERY_REQUEST message is authorised for restricted ProSe direct discovery model A announcing. If the application is authorised for restricted ProSe direct discovery model A announcing, the ProSe Function shall check whether there is an existing context for the UE.

If there is no associated UE context, the ProSe Function checks with the HSS whether the UE is authorised for restricted ProSe direct discovery model A announcing as described in 3GPP TS 29.344 [3]. If the check indicates that the UE is authorised, the ProSe Function creates a UE context that contains the UE’s subscription parameters obtained from the HSS. The HSS also provides to the ProSe Function the PLMN ID of the PLMN in which the UE is currently registered. If the UE context exists, the ProSe Function shall then check whether the UE is authorised for restricted ProSe direct discovery model A announcing in the currently registered PLMN or in case of E-UTRA-based restricted ProSe direct discovery model A the local PLMN identified by the Announcing PLMN ID included in the DISCOVERY_REQUEST message.

If the UE is authorised and the Discovery Entry ID included in the DISCOVERY_REQUEST message is set to 0 then:

– the ProSe Function shall check whether the UE is authorised to announce the RPAUID contained in the DISCOVERY_REQUEST message. Optionally this can include checking with the ProSe Application Server as described in 3GPP TS 29.343 [31] to obtain the binding between the RPAUID and PDUID, and then verifying that the PDUID belongs to the requesting UE;

– if the UE is authorised to announce the RPAUID, the ACE Enabled Indicator is set to "application-controlled extension enabled", the Application Level Container is included in the DISCOVERY_REQUEST message and the requested application uses application-controlled extension, the ProSe Function shall check whether the UE is authorized to use ACE. If the UE is authorized for ACE, the ProSe Function shall invoke the procedure described in 3GPP TS 29.343 [31] to check whether the UE is authorised to announce the requested RPAUID with application-defined suffix(es), and obtain suffix-related information from the ProSe Application Server. The ProSe Function shall then allocate a ProSe Restricted Code Prefix and a value for validity timer T4007 to be used with the ProSe Restricted Code Suffix(es) obtained from the ProSe Application Server for the given RPAUID as specified in 3GPP TS 29.343 [31]. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message when allocating validity timer T4007;

– if the UE is authorised to announce the RPAUID, the ACE Enabled Indicator is set to "normal" in the DISCOVERY_REQUEST message and the requested application does not use application-controlled extension, the ProSe Function shall allocate the corresponding ProSe Restricted Code and a value for validity timer T4007. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message when allocating validity timer T4007;

– if the UE is authorised to announce the RPAUID, the ACE Enabled Indicator is set to "normal" in the DISCOVERY_REQUEST message, the Application Level Container is included in the DISCOVERY_REQUEST and the requested application only uses application-controlled extension, the ProSe Function shall check whether the UE is authorized to use ACE. If the UE is authorized for ACE, the ProSe Function shall invoke the procedure described in 3GPP TS 29.343 [31] to check whether the UE is authorised to announce the requested RPAUID with application-defined suffix(es), and obtain suffix-related information from the ProSe Application Server. The ProSe Function shall then allocate a ProSe Restricted Code Prefix and a value for validity timer T4007 to be used with the ProSe Restricted Code Suffix(es) obtained from the ProSe Application Server for the given RPAUID as specified in 3GPP TS 29.343 [31] The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message when allocating validity timer T4007.

– if the UE is authorised to announce the RPAUID, the ACE Enabled Indicator is set to "application-controlled-extension enabled" and the Application Level Container is included in the DISCOVERY_REQUEST message but the requested application does not use application-controlled extension, the ProSe Function shall allocate the corresponding ProSe Restricted Code and a value for validity timer T4007. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message when allocating validity timer T4007; and

– the ProSe Function associates the allocated ProSe Restricted Code or ProSe Restricted Code Prefix with a new discovery entry in the UE’s context, and starts timer T4008. The HSS also provides to the ProSe Function the PLMN ID of the PLMN in which the UE is currently registered. For a given ProSe Restricted Code, timer T4008 shall be longer than timer T4007. By default, the value of timer T4008 is 4 minutes greater than the value of timer T4007.

If the Discovery Entry ID included in the DISCOVERY_REQUEST message is not set to 0 and if there is an existing discovery entry for this Discovery Entry ID value in the UE’s context, the ProSe Function shall either update the discovery entry with a new validity timer T4007, or allocate a new ProSe Restricted Code or ProSe Restricted Code Prefix for the requested RPAUID with a new validity timer T4007, restart timer T4008, and clear any existing on demand announcing enabled indicator. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message when allocating validity timer T4007.

If the Discovery Entry ID contained in the DISCOVERY_REQUEST message is not found in the UE context or there is no UE context in the ProSe Function, the ProSe Function shall behave as if the Discovery Entry ID included in the DISCOVERY_REQUEST message was set to 0, and the ProSe Function shall allocate a new non-zero Discovery Entry ID for this entry.

If the announcing type is set to "on demand" in the DISCOVERY_REQUEST message, the ProSe Function shall check if "on demand" announcing is authorised and enabled based on the Application Identity and the operator’s policy. If "on demand" announcing is authorised and enabled, and there is no ongoing monitoring request for this RPAUID, then the ProSe Function shall set the on demand announcing enabled indicator to 1 for the corresponding discovery entry in the UE’s context.

If a new UE context was created or an existing UE context was updated, and the UE is currently roaming or the Announcing PLMN ID is included in the DISCOVERY_REQUEST message, and the on demand announcing enabled indicator is not set to 1 for this discovery entry in the UE’s context, the ProSe Function checks with the ProSe function of the VPLMN or in case of E-UTRA-based restricted ProSe direct discovery model A the local PLMN represented by the Announcing PLMN ID whether the UE is authorised for restricted ProSe direct discovery model A announcing as described in 3GPP TS 29.345 [5].

The ProSe Function shall then send a DISCOVERY_RESPONSE message containing a <restricted-announce-response> element with:

– the transaction ID set to the value of the transaction ID received in the DISCOVERY_REQUEST message from the UE;

– if the on demand announcing enabled indicator is not set to 1 in the UE’s context for this discovery entry, either the ProSe Restricted Code set to the ProSe Restricted Code or the ProSe Restricted Code Prefix allocated by the ProSe Function, and optionally one or more ProSe Restricted Code Suffix Ranges which contain the suffix(es) for the RPAUID received in the DISCOVERY_REQUEST message;

– a Validity Timer T4007 set to the T4007 timer value assigned by the ProSe Function to the ProSe Restricted Code;

– the ACE Enabled Indicator set to "application-controlled extension enabled" if application-controlled extension is used, or "normal" if application-controlled extension is not used;

– the Restricted Security set to a value containing the security-related information for restricted discovery provided by the ProSe Function;

– the On Demand Announcing Enabled Indicator indicating whether the on demand announcing is enabled or not for this discovery entry if the Announcing Type is set to "on demand" in the DISCOVERY_REQUEST message;

– the Discovery Entry ID set to the ID of the discovery entry associated with this announce request in the UE’s context; and

– optionally the PC5_tech set to the one or more PC5 radio technologies that are authorized to be used for the assigned ProSe Restricted Code or the assigned ProSe Restricted Code Prefix and the associated ProSe Restricted Code Suffix Ranges.

If timer T4008 expires, the ProSe Function shall remove the discovery entry associated with the corresponding RPAUID from the UE’s context.

6.2.2A.4 Announce request procedure completion by the UE

Upon receipt of the DISCOVERY_RESPONSE message, if only the transaction ID and the Discovery Entry ID are contained in the <restricted-announce-response> element and the transaction ID and the Discovery Entry ID match the corresponding values sent by the UE in a DISCOVERY_REQUEST message, the UE shall:

– stop the validity timer T4007 for the discovery entry corresponding to the Discovery Entry ID received in the DISCOVERY_RESPONSE message;

– remove the discovery entry identified by the Discovery Entry ID included; and

– instruct the lower layers to stop announcing.

Upon receipt of the DISCOVERY_RESPONSE message, if the transaction ID contained in the <restricted-announce-response> element matches the value sent by the UE in a DISCOVERY_REQUEST message with the command set to "announce", the UE shall create a new discovery entry or update an existing discovery entry with the received ProSe Restricted Code or ProSe Restricted Code Prefix and the PLMN ID of the intended announcing PLMN. For this discovery entry, the UE shall stop the validity timer T4007, if running, for the discovery entry corresponding to the Discovery Entry ID received in the DISCOVERY_RESPONSE message, and start the validity timer T4007 for this discovery entry with the received value in the DISCOVERY_RESPONSE message. Otherwise the UE shall discard the DISCOVERY_RESPONSE message and shall not perform the procedures below.

If the DISCOVERY_RESPONSE message includes new ProSe Restricted Code or ProSe Restricted Code Prefix to replace the existing ProSe Restricted Code being announced, the UE shall notify lower layer to stop announcing the old ProSe Restricted Code in PC5 interface.

If the DISCOVERY RESPONSE message contains an On Demand Announcing Enabled Indicator set to 1, the UE shall wait for an Announcing Alert Request message from the ProSe Function of the HPLMN before starting to perform restricted ProSe direct discovery model A announcing. Otherwise, the UE may perform restricted ProSe direct discovery model A announcing as described below.

The UE requests the parameters from the lower layers for restricted Prose direct discovery model A announcing (see 3GPP TS 36.331 [12]). In case of E-UTRA-based restricted ProSe direct discovery the UE shall perform restricted ProSe direct discovery model A announcing only if the lower layers indicate that ProSe direct discovery is supported by the network. In case of E-UTRA-based restricted ProSe direct discovery if the UE in EMM-IDLE mode has to request resources for ProSe direct discovery announcing as specified in 3GPP TS 36.331 [12], the UE shall perform a service request procedure or tracking area update procedure as specified in 3GPP TS 24.301 [11]. The UE shall obtain the UTC time for the next discovery transmission opportunity for ProSe direct discovery from the lower layers.

If a valid UTC time is obtained, the UE shall generate the UTC-based counter corresponding to this UTC time as specified in subclause 12.2.2.18. If the resulting UTC-based counter is within Max Offset of the time shown by the clock used for ProSe by the UE, the UE shall either use the ProSe Restricted Code received in the DISCOVERY_RESPONSE message, or select one ProSe Restricted Code based on the ProSe Restricted Code Prefix and ProSe Restricted Code Suffix Range(s) received in the DISCOVERY_RESPONSE message as announced ProSe Restricted Code, along with the eight least significant bits of the UTC-based counter, in order to construct a PC5_DISCOVERY message, according to the format defined in subclause 11.2.5.

NOTE: The UE can use different codes formed based on different ProSe Restricted Code Suffixes to announce, without having to send a new DISCOVERY_REQUEST message to the ProSe Function, as long as the validity timer T4007 of the ProSe Restricted Code Prefix has not expired.

The UE shall then apply one or more of the DUIK, DUSK or DUCK with the associated Encrypted Bitmask, whichever received in the Restricted Code Security Material parameter of the DISCOVERY_RESPONSE message, along with the UTC-based counter to the PC5_DISCOVERY message, to e.g. generate a MIC value, scramble the message contents or provide confidentiality protection, as specified in 3GPP TS 33.303 [6].

The UE then passes the resulting PC5_DISCOVERY message, along with the PLMN ID of the intended announcing PLMN, to the lower layers for transmission if:

– the UE is currently authorised to perform restricted ProSe direct discovery model A announcing in the registered PLMN or in case of E-UTRA-based restricted ProSe direct discovery model A the local PLMN operating the radio resources that the UE intends to use;

– the validity timer T4007 for the corresponding discovery entry allocated ProSe Restricted Code or ProSe Restricted Code Prefix has not expired; and

– a request from upper layers to announce the RPAUID associated with both the ProSe Restricted Code or ProSe Restricted Code Prefix, and the authorised Application Identity, is still in place.

The UE shall ensure that it keeps on passing PC5_DISCOVERY messages to the lower layers for transmission until the validity timer T4007 of the ProSe Restricted Code or ProSe Restricted Code Prefix expires. How this is achieved is left up to UE implementation.

During the announcing operation, if one of the above conditions is no longer met, the UE may instruct the lower layers to stop announcing. When the UE stops announcing, In case of E-UTRA-based restricted ProSe direct discovery model A if the lower layers indicate that the UE is required to send a discovery indication to the eNodeB and the UE is in EMM-CONNECTED mode, the UE shall trigger the corresponding procedure in lower layers as specified in 3GPP TS 36.331 [12].

6.2.2A.5 Announce request procedure not accepted by the ProSe Function

If the DISCOVERY_REQUEST message cannot be accepted by the ProSe Function, the ProSe Function sends a DISCOVERY_RESPONSE message containing a <response-reject> element to the UE including an appropriate PC3 Control Protocol cause value.

If the application corresponding to the Application Identity contained in the DISCOVERY_REQUEST message is not authorised for ProSe direct discovery announcing, the ProSe Function shall send the DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #1 "Invalid application".

If the RPAUID contained in the DISCOVERY_REQUEST message is unknown to the ProSe Function or ProSe Application Server, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #9 "Unknown RPAUID".

If the RPAUID contained in the DISCOVERY_REQUEST message does not match the stored RPAUID for the requested Discovery Entry ID, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #10 "Unknown or Invalid Discovery Entry ID".

If the UE is not authorised for restricted ProSe direct discovery model A announcing, the ProSe Function shall send the DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #3 "UE authorisation failure".

If the UE is not authorised for restricted "on demand" restricted ProSe direct discovery model A announcing, the ProSe Function shall send the DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #13 "UE unauthorised for on-demand announcing".

If the RPAUID contained in the DISCOVERY_REQUEST message is not associated with the PDUID belonging to the requesting UE, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #3 "UE authorisation Failure".

If the UE is not authorized to use ACE, but the DISCOVERY_REQUEST message contains the ACE Enabled Indicator set to "application-controlled extension enabled", the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #12 "UE unauthorised for discovery with Application-Controlled Extension".

If the DISCOVERY_REQUEST message contains the ACE Enabled Indicator set to "application-controlled extension enabled", but does not contain the Application Level Container parameter, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #14 "Missing Application Level Container".

If the ProSe Application Server indicates to the ProSe Function that the Application Level Container in the DISCOVERY REQUEST message contains invalid information, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #15 "Invalid Data in Application Level Container".

If the Discovery Entry ID contained in the DISCOVERY_REQUEST message is unknown to the ProSe Function and the Requested Timer is set to zero, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value # 10 "Unknown or invalid Discovery Entry ID".

6.2.2A.6 Abnormal cases

6.2.2A.6.1 Abnormal cases in the UE

The following abnormal cases can be identified:

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

The UE shall close the existing secure connection to the ProSe Function, establish a new secure connection and then restart the announce request procedure.

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

The UE shall retransmit the DISCOVERY_REQUEST message.

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

c) Indication from upper layers that the request to announce the RPAUID is no longer in place after sending the DISCOVERY_REQUEST message, but before the announce request procedure is completed

The UE shall acknowledge the DISCOVERY_RESPONSE message received from the ProSe Function but discard its contents and then abort the procedure.

d) Change of PLMN

If a PLMN change occurs before the announce request procedure is completed, the procedure shall be aborted. If the UE is authorized to announce in the new PLMN, the procedure shall be restarted once the UE is registered on the new PLMN.

6.2.2A.6.2 Abnormal cases in the ProSe Function

The following abnormal cases can be identified:

a) Indication from the lower layer of transmission failure of DISCOVERY_RESPONSE message

After receiving an indication from lower layer that the DISCOVERY_RESPONSE message has not been successfully acknowledged (e.g. TCP ACK is not received), the ProSe Function shall abort the procedure, and stop any associated timer(s) T4008, if running.