Content for  TS 23.303  Word version:  18.0.0

The UE is configured with the data structure of the ProSe Application IDs corresponding to PLMNs the UE is authorised to monitor. This step is performed using mechanisms that are out of scope of 3GPP.

If the UE is authorised to monitor in at least one PLMN, or if UE intends to use WLAN-based PC5 for monitoring and is interested to monitor certain ProSe Application ID(s), it shall establish a secure connection with ProSe Function in the HPLMN to which it shall then send a Discovery Request (ProSe Application ID(s), UE Identity, monitor command, Application ID, Discovery Entry ID, [Requested Timer], [PC5_tech]) message for monitoring. The ProSe Application ID(s) indicate what the UE is interested to monitor and they consist a subset of the data structure of the PLMN. The UE Identity is set to e.g. IMSI. The Application ID represents a unique identifier of the application that has triggered the transmission of the Discovery Request message. The Discovery Entry ID indicates whether this is a new request. The Requested Timer is an optional parameter. When the Requested Timer is set to zero, procedures in clause 5.3.6A.1.3 shall be followed. PC5_tech is an optional parameter that indicates the PC5 radio technology (e.g. E-UTRA, WLAN) that UE wishes to use for monitoring. PC5_tech may include more than one PC5 radio technology. When this parameter is omitted the intended PC5 radio technology is E-UTRA. This request is always sent to the ProSe Function in HPLMN. If application-controlled extension is used, the Application Level Container is included; it contains information corresponding to the ProSe Application Code Suffix.

The ProSe Function checks for the authorization of the application represented by the Application ID. If there is no associated UE context, the ProSe Function shall check with HSS the authorisation for discovery and create a new context for this UE that contains the subscription parameters for this UE. The HSS provides the MSISDN of the UE. The authorisation information also contains the PLMNs that this UE is allowed to perform discovery. When the Discovery Entry ID in the Discovery Request message does not contain a valid value for this UE, the ProSe Function will create a new discovery entry in the UE's context for this request, and will return the corresponding identifier in the Discovery Response message in step 5.

If the UE indicated that it desires application-controlled extension by the inclusion of the Application Level Container, the ProSe Function sends an Auth Request (ProSe Application ID, Request Type, Application Level Container) to the Application Server indicated by the Application ID. The Request Type is set to "open discovery with application controlled extension/monitor".

The ProSe Application Server returns an Auth Response (Response Type, mask(s) for the ProSe Application Code Suffix(es) corresponding to ProSe Application ID). The Response Type is set to "open discovery with application-controlled extension /monitor ack". If the Discovery Request is authorised, and the ProSe Application ID sent by the UE in step 1 indicates another Local PLMN then steps 3-6 are executed, otherwise (i.e. the ProSe Application ID indicates HPLMN) only steps 5-6 are executed:

When the ProSe Application ID has PLMN-specific scope then the ProSe Function in HPLMN shall contact if needed) other PLMNs that are indicated by the ProSe Application ID(s) sent by the UE, in order to resolve the corresponding ProSe Application ID Name(s) to ProSe Application Code(s) and/or a ProSe Application Mask. The request shall also include the UE identity information e.g. IMSI or MSISDN in order to allow the ProSe Function in Local PLMN to perform charging and the Discovery Entry ID. If the ProSe Function in other PLMN receives the same Discovery Entry ID in a subsequent Monitor Request message, it updates the monitoring UE's corresponding discovery entry with the received corresponding parameters. The request may also include the PC5_tech parameter if it was provided by the UE in step 1. When this parameter is omitted the intended PC5 radio technology is E-UTRA.

If the ProSe Function of the Local PLMN stores valid ProSe Application Code(s) corresponding to the requested ProSe Application ID Name(s) and the requested PC5 radio technology (as indicated in step 3), then the ProSe Function of the Local PLMN returns the related ProSe Application Code(s) and/or ProSe Application Mask(s) and the corresponding TTL for each. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for monitoring. When the parameter is omitted the intended PC5 radio technology is E-UTRA. If application-controlled extension is used, the ProSe Application Code is replaced by the ProSe Application Code Prefix.

The ProSe Function in the HPLMN shall respond with a Discovery Response (Discovery Filter(s), Discovery Entry ID, [PC5_tech]) message. The TTL(s) in the Discovery Filter(s) indicates for how long the Discovery Filter(s) is going to be valid. If application-controlled extension is used, the ProSe Application Code in the Discovery Filter is replaced by the ProSe Application Code Prefix. Besides the ProSe Application Code(s), the Discovery Filter may also contain the mask(s) for the ProSe Application Code Suffix, which is/are obtained in from ProSe Application Server in step 2b. The UE may add additional mask(s) and values for the Suffix part. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for the Discovery Filter(s). When the parameter is omitted the intended PC5 radio technology is E-UTRA.

The UE may start monitoring using the Discovery Filter(s) in the radio resources that are authorized and configured by the PLMN(s) to be used for ProSe as defined in RAN specifications or using WLAN, or both. If the TTL corresponding to a Discovery Filter expires (because the UE has not refreshed the corresponding Discovery Request within the duration of the TTL), then the ProSe Function removes the entry related to that Discovery Filter from the UE context.

In this step, the application client in the UE retrieves its own PDUID and provides it to the ProSe Application Server. The ProSe Application Server allocates a Restricted ProSe Application User ID (RPAUID) for that PDUID, stores the binding between the PDUID and the RPAUID and returns the RPAUID to the application client in the UE. The application client in the UE stores the binding between the PDUID and its own RPAUID. When the application client in the UE intends to discover the announcing UE of other users (e.g. friends in the application), it obtains the RPAUID of those users (Target RPAUID(s)) from the ProSe App Server and triggers the UE to perform the monitor procedure, providing its own RPAUID and the Target RPAUIDs. The Target RPAUIDs of the UEs to be monitored are passed in an Application Level Container.

If the UE is authorised to monitor in at least one PLMN, or if UE intends to use WLAN-based PC5 for monitoring and is triggered by the application client to monitor, it shall establish a secure connection with the ProSe Function in HPLMN and it shall send a Discovery Request message to get the Discovery Filter for monitoring (RPAUID, UE Identity, command=monitor, Discovery Type, Application ID, Application Level Container, Discovery Entry ID, Requested Discovery Timer, [PC5_tech]). The Application Level Container contains the Target RPAUIDs indicating what the UE is interested to monitor. The RPAUID indicates the identity the UE uses to obtain the permission to monitor. The UE Identity is set to IMSI. The Application ID represents a unique identifier of the application that has triggered the transmission of the Discovery Request message. Discovery Type is set to "restricted discovery". The Discovery Entry ID indicates whether this is a new request. The Requested Discovery Timer is an optional parameter. When the Requested Discovery Timer is set to zero, the ProSe Function shall delete the Discovery Filter(s) indicated by the Discovery Entry ID, and release the associated resources. If restricted Direct Discovery with application-controlled extension is used, the Application Level Container may also include some information corresponding to the ProSe Restricted Code Suffix, e.g. group or user-specific information. The Discovery Type is set to "restricted discovery with application-controlled extension". PC5_tech is an optional parameter that indicates the PC5 radio technology (e.g. E-UTRA, WLAN) that UE wishes to use for monitoring. PC5_tech may include more than one PC5 radio technology. When this parameter is omitted the intended PC5 radio technology is E-UTRA. If the Requested Discovery Timer is included in step 1 and the value is set to zero, step 2 to step 9 are skipped.

The ProSe Function checks for the authorization of the application represented by the Application ID. If there is no associated UE context, the ProSe Function shall check with HSS the authorisation for discovery and, if necessary, create a new context for this UE that contains the subscription parameters for this UE. The HSS provides also the PLMN ID where the UE is registered. The HSS provides the MSISDN of the UE. When the Discovery Entry ID in the Discovery Request message does not contain a valid value for this UE, the ProSe Function creates a new discovery entry in the UE's context for this request, and returns the corresponding identifier in the Discovery Response message in step 10.

The ProSe Function sends an Auth Request (RPAUID, Request Type, Application Level Container) to the Application Server indicated by the Application ID. The Request Type is set to "restricted discovery/monitor". If restricted Direct Discovery with application-controlled extension is used, the Request Type is set to "restricted discovery with application-controlled extension".

If, based on the permission setting, the RPAUID is allowed to discover at least one of the Target RPAUID(s) contained in the Application Level Container, the ProSe Application Server returns an Auth Response (PDUID, Response Type, N sets of Target PDUID - Target RPAUID - Metadata Indicator, Application Level Container). The Response Type is set to "restricted discovery/monitor ack". Each Target PDUID is returned with the corresponding Target RPAUID(s) that the RPAUID is allowed to discover. The ProSe Function verifies that the returned PDUID belongs to the requesting UE. The Application Level Container includes the successful authenticated Target RPAUID(s). The Metadata Indicator is optional and signals whether there is metadata associated with the RPAUID, and if so, whether update to the metadata is allowed. If restricted Direct Discovery with application-controlled extension is used, the Response Type is set to "Restricted discovery with application-controlled extension /monitor ack". The Auth Response may also include the mask(s) for the ProSe Restricted Code Suffix(es) corresponding to each of the Target Restricted ProSe App User ID(s).

If the PLMN ID in the Target PDUID indicates the HPLMN and at least one of received pair of Target PDUID - Target RPAUID corresponds to a valid ProSe Restricted Code including a valid PC5 radio technology match as indicated via the PC5_tech parameter in step 1, the ProSe Function in the HPLMN retrieves the ProSe Restricted Code corresponding to that Target PDUID, Application ID and Target RPAUID. The Prose Function in the HPLMN stores, in the context of the announcing UE, the PDUID of the monitoring UE. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix. If the Announcing Enabled indicator is stored in the UE context, the ProSe Function of HPLMN shall trigger the Announcing Alert procedure (see clause 5.3.5) to notify the announcing UE to perform announcing.

If the PLMN ID in the Target PDUID indicates a PLMN different from the HPLMN, the ProSe Function in the HPLMN contacts the ProSe Function in that PLMN to retrieve the corresponding ProSe Restricted Code with a Monitor Request (RPAUID, UE Identity, Target PDUID, Application ID, Target RPAUID, Discovery Entry ID, [PC5_tech]) message. The request shall include the UE identity information e.g. IMSI or MSISDN in order to allow the ProSe Function in that PLMN to perform charging. If the ProSe Function in other PLMN receives the same Discovery Entry ID in a subsequent Monitor Request message, it updates the monitoring UE's corresponding discovery entry with the received corresponding parameters. The request may also include the PC5_tech parameter if it was provided by the UE in step 1. When this parameter is omitted the intended PC5 radio technology is E-UTRA.

If the pair of Target PDUID - Target RPAUID received from the HPLMN ProSe Function corresponds to a valid ProSe Restricted Code including a valid PC5 radio technology match as indicated via the PC5_tech parameter in step 6, the ProSe Function in the other PLMN retrieves the ProSe Restricted Code corresponding to that Target PDUID, Application ID and Target RPAUID. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix. If the Announcing Enabled indicator is stored in the UE context at the ProSe Function in the other PLMN (announcing UE's HPLMN), then the ProSe Function in the other PLMN shall trigger the Announcing Alert procedure (see clause 5.3.5) to notify the announcing UE to perform announcing.

Optionally, the ProSe Function in the other PLMN sends an Auth Request (RPAUID , Request Type, Target RPAUID) to the Application Server indicated by the Application ID. The Request Type is set to "restricted discovery/permission".

If, based on the permission setting, the RPAUID is allowed to discover the Target RPAUID, the ProSe Application Server acknowledges the Auth Request with an Auth Response (Target PDUID, Response Type). The Response Type is set to "restricted discovery/permission ack". The ProSe Function in the other PLMN verifies that the returned Target PDUID corresponds to the UE to be monitored. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix.

The ProSe Function in the other PLMN returns to the ProSe Function in the HPLMN the ProSe Restricted Code and the corresponding residual validity timer with a Monitor Response (ProSe Restricted Code, validity timer, [PC5_tech]) message. The Prose Function in the other PLMN also stores, in the context of the announcing UE, the PDUID of the monitoring UE. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for monitoring. When the parameter is omitted the intended PC5 radio technology is E-UTRA.

For each pair of Target PDUID - Target RPAUID returned by the application server in step 4, if the ProSe Function in the HPLMN has retrieved a valid ProSe Restricted Code, it builds the binding between ProSe Restricted Code with validity timer, Application ID, Target RPAUID, Metadata Indicator and Target PDUID and stores it into the discovery entry in the user context of the monitoring UE. Based on the ProSe Restricted Code and the associated validity timer the ProSe Function in the HPLMN allocates a Discovery Filter with the corresponding TTL. The ProSe Function in the HPLMN returns a Discovery Response (Discovery Filter(s), Metadata Indicator, Discovery Entry ID, Application Level Container, [PC5_tech]) message to the UE. The Discovery Filter includes the ProSe Restricted Code to be monitored and the TTL that indicates for how long the related ProSe Restricted Code in the Discovery Filter is valid after it is received. If configured by the operator, the Target RPAUID(s) and metadata corresponding to the ProSe Restricted Code(s) may be included in the Discovery Response message. The ProSe Function stores in the user context all the parameters passed to the UE. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix. Besides the ProSe Restricted Code(s), the Discovery Filter may also contain the mask(s) for the ProSe Restricted Code Suffix, which is/are obtained in from ProSe Application Server in step 4. The UE may add additional mask(s) and values for the Suffix part. If the Requested Discovery Timer is included in step 1 and the value is set to zero, the TTL in the Discovery Response message is set to zero. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for the Discovery Filter(s). When the parameter is omitted the intended PC5 radio technology is E-UTRA.

The UE obtains the corresponding radio resources that are authorized and configured by the PLMN(s) to be used for ProSe as defined in RAN specifications or uses WLAN, or both and starts to monitor using the Discovery Filter. The UE provides the Application Level Container, which contains the successful authenticated Target RPAUID(s), to the application client.

The UE is configured with the data structure of the ProSe Application IDs corresponding to PLMNs the UE is authorised to monitor. This step is performed using mechanisms out of scope of 3GPP.

If the UE is authorised to monitor in at least one PLMN, or if UE intends to use WLAN-based PC5 for monitoring and is interested to monitor certain ProSe Application ID(s), it shall establish a secure connection with the ProSe Function in HPLMN and it shall send a Discovery Request (ProSe Application ID(s), UE Identity, monitor command, Application ID, Discovery Entry ID, [Requested Timer], [PC5_tech]) message for monitoring. The ProSe Application ID(s) indicate what the UE is interested to monitor and they consist of a subset of the data structure of the PLMN. The UE Identity is set to e.g. IMSI. The Application ID represents a unique identifier of the application that has triggered the transmission of the Discovery Request message. The Discovery Entry ID indicates whether this is a new request. The Requested Timer is an optional parameter. When the Requested Timer is set to zero, procedures in clause 5.3.6A.1.3 shall be followed. PC5_tech is an optional parameter that indicates the PC5 radio technology (e.g. E-UTRA, WLAN) that UE wishes to use for monitoring. PC5_tech may include more than one PC5 radio technology. When this parameter is omitted the intended PC5 radio technology is E-UTRA. This request is always sent to the ProSe Function in HPLMN. If application-controlled extension is used, the Application Level Container is included; it contains information corresponding to the ProSe Application Code Suffix.

The ProSe Function checks for the authorization of the application represented by the Application ID. If there is no associated UE context, the ProSe Function shall check with HSS the authorisation for discovery and, if necessary, create a new context for this UE that contains the subscription parameters for this UE. The authorisation information also contains the PLMNs that this UE is allowed to perform discovery. The HSS provides also the VPLMN ID where the UE is registered. The HSS provides the MSISDN of the UE. When the Discovery Entry ID in the Discovery Request message does not contain a valid value for this UE, the ProSe Function will create a new discovery entry in the UE's context for this request, and will return the corresponding identifier in the Discovery Response message in step 5.

If the UE indicated that it desires application-controlled extension by the inclusion of the Application Level Container, the ProSe Function sends an Auth Request (ProSe Application ID, Request Type, Application Level Container) to the Application Server indicated by the Application ID. The Request Type is set to "open discovery with application controlled extension/monitor".

The ProSe Application Server returns an Auth Response (Response Type, mask(s) for the ProSe Application Code Suffix(es) corresponding to ProSe Application ID). The Response Type is set to "open discovery with application-controlled extension /monitor ack".

When the ProSe Application ID has PLMN-specific scope then the ProSe Function in HPLMN shall contact (if needed) other PLMNs that are indicated by the ProSe Application ID(s) sent by the UE, in order to resolve the corresponding ProSe Application ID Name(s) to ProSe Application Code(s) and/or a ProSe Application Mask. The request shall also include the UE identity information e.g. IMSI or MSISDN, in order to allow the ProSe Function in Local/Visited PLMN to perform charging and the Discovery Entry ID. If the ProSe Function in other PLMN receives the same Discovery Entry ID in a subsequent Monitor Request message, it updates the monitoring UE's corresponding discovery entry with the received corresponding parameters. The request may also include the PC5_tech parameter if it was provided by the UE in step 1. When this parameter is omitted the intended PC5 radio technology is E-UTRA.

If the ProSe Function of the other PLMN stores valid ProSe Application Code(s) corresponding to the requested ProSe Application ID Name(s) and the requested PC5 radio technology (as indicated in step 3), then the ProSe Function of the VPLMN/Local PLMN returns the related ProSe Application Code(s) and/or ProSe Application Mask(s) and the corresponding TTL for each. Based on the UE context in the ProSe Function of the VPLMN/Local PLMN, it also includes the PLMN ID of the PLMN that the "announcing UE" is registered (if roaming) for the ProSe Function in HPLMN of the monitoring UE to store in the associated UE context. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for monitoring. When the parameter is omitted the intended PC5 radio technology is E-UTRA. If application-controlled extension is used, the ProSe Application Code is replaced by the ProSe Application Code Prefix.

The ProSe Function in the HPLMN responds with a Discovery Response (Discovery Filter(s), Discovery Entry ID, [PC5_tech]) message. The TTL(s) in the Discovery Filter(s) indicate for how long the Discovery Filter(s) are going to be valid. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for the Discovery Filter(s). When the parameter is omitted the intended PC5 radio technology is E-UTRA. If application-controlled extension is used, the ProSe Application Code in the Discovery Filter is replaced by the ProSe Application Code Prefix. Besides the ProSe Application Code(s), the Discovery Filter may also contain the mask(s) for the ProSe Application Code Suffix, which is/are obtained in from ProSe Application Server in step 2b. The UE may add additional mask(s) and values for the Suffix part.

The UE may start monitoring using the Discovery Filter(s) in the radio resources that are authorized and configured by the PLMN(s) to be used for ProSe as defined in RAN specifications or using WLAN, or both.

In this step, the application client in the UE retrieves its own PDUID and provides it to the ProSe Application Server. The ProSe Application Server allocates a Restricted ProSe Application User ID (RPAUID) for that PDUID, stores the binding between the PDUID and the RPAUID and returns the RPAUID to the application client in the UE. The application client in the UE stores the binding between the PDUID and its own RPAUID. When the application client in the UE intends to discover the announcing UE of other users (e.g. friends in the application), it obtains the RPAUID of those users (Target RPAUIDs) from the ProSe App Server and triggers the UE to perform the monitor procedure, providing its own RPAUID and the Target RPAUIDs. The Target RPAUIDs of the UEs to be monitored are passed in an Application Level Container.

If the UE is authorised to monitor in at least one PLMN, or if UE intends to use WLAN-based PC5 for monitoring and is triggered by the application client to monitor, it shall establish a secure connection with the ProSe Function in HPLMN and it shall send a Discovery Request message to get the Discovery Filter for monitoring (RPAUID, UE Identity, command=monitor, Discovery Type, Application ID, Application Level Container, Discovery Entry ID, Requested Discovery Timer, [PC5_tech]). The Application Level Container contains the Target RPAUIDs indicating what the UE is interested to monitor. The RPAUID indicates the identity the UE uses to obtain the permission to monitor. The UE Identity is set to IMSI. The Application ID represents a unique identifier of the application that has triggered the transmission of the Discovery Request message. Discovery Type is set to "restricted discovery". The Discovery Entry ID indicates whether this is a new request. The Requested Discovery Timer is an optional parameter. When the Requested Discovery Timer is set to zero, the ProSe Function shall delete the Discovery Filter(s) indicated by the Discovery Entry ID, and release the associated resources. If restricted Direct Discovery with application-controlled extension is used, the Application Level Container may also include some information corresponding to the ProSe Restricted Code Suffix, e.g. group or user-specific information. The Discovery Type is set to "restricted discovery with application-controlled extension". PC5_tech is an optional parameter that indicates the PC5 radio technology (e.g. E-UTRA, WLAN) that UE wishes to use for monitoring. PC5_tech may include more than one PC5 radio technology. When this parameter is omitted the intended PC5 radio technology is E-UTRA. If the Requested Discovery Timer is included in step 1 and the value is set to zero, step 2 to step 9 are skipped.

The ProSe Function checks for the authorization of the application represented by the Application ID. If there is no associated UE context, the ProSe Function shall check with HSS the authorisation for discovery and, if necessary, create a new context for this UE that contains the subscription parameters for this UE. The HSS provides also the PLMN ID where the UE is registered. The HSS provides the MSISDN of the UE. When the Discovery Entry ID in the Discovery Request message does not contain a valid value for this UE, the ProSe Function creates a new discovery entry in the UE's context for this request, and returns the corresponding identifier in the Discovery Response message in step 10.

The ProSe Function sends an Auth Request (RPAUID, Request Type, Application Level Container) to the Application Server indicated by the Application ID. The Request Type is set to "restricted discovery/monitor". If restricted Direct Discovery with application-controlled extension is used, the Request Type is set to "restricted discovery with application-controlled extension".

If, based on the permission setting, the RPAUID is allowed to discover at least one of the Target RPAUID(s) contained in the Application Level Container, the ProSe Application Server returns an Auth Response (PDUID, Response Type, N sets of Target PDUID - Target RPAUID - Metadata Indicator, Application Level Container). The Response Type is set to "restricted discovery/monitor ack". Each Target PDUID is returned with the corresponding Target RPAUID(s) that the RPAUID is allowed to discover. The ProSe Function verifies that the returned PDUID belongs to the requesting UE. The Application Level Container includes the successful authenticated Target RPAUID(s). The Metadata Indicator is optional and signals whether there is metadata associated with the RPAUID, and if so, whether update to the metadata is allowed. If restricted Direct Discovery with application-controlled extension is used, the Response Type is set to "Restricted discovery with application-controlled extension /monitor ack". The Auth Response may also include the mask(s) for the ProSe Restricted Code Suffix(es) corresponding to each of the Target Restricted ProSe App User ID(s).

If the PLMN ID in the Target PDUID indicates the HPLMN and at least one of received pair of Target PDUID - Target RPAUID corresponds to a valid ProSe Restricted Code including a valid PC5 radio technology match as indicated via the PC5_tech parameter in step 1, the ProSe Function in the HPLMN retrieves the ProSe Restricted Code corresponding to that Target PDUID, Application ID and Target RPAUID. The Prose Function in the HPLMN stores, in the context of the announcing UE, the PDUID of the monitoring UE and the allocated validity timer. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix. If the Announcing Enabled indicator is stored in the UE context, the ProSe Function of HPLMN shall trigger the Announcing Alert procedure (see clause 5.3.5) to notify the announcing UE to perform announcing.

If the PLMN ID in the Target ProSe Disc UE ID indicates a PLMN different from the HPLMN, the ProSe Function in the HPLMN contacts the ProSe Function in that PLMN to retrieve the corresponding ProSe Restricted Code with a Monitor Request (RPAUID, UE Identity, Target PDUID, Application ID, Target RPAUID, Discovery Entry ID, [PC5_tech]) message. The request shall include the UE identity information e.g. IMSI or MSISDN in order to allow the ProSe Function in that PLMN to perform charging. If the ProSe Function in other PLMN receives the same Discovery Entry ID in a subsequent Monitor Request message, it updates the monitoring UE's corresponding discovery entry with the received corresponding parameters. The request may also include the PC5_tech parameter if it was provided by the UE in step 1. When this parameter is omitted the intended PC5 radio technology is E-UTRA.

If the pair of Target PDUID - Target RPAUID received from the HPLMN ProSe Function corresponds to a valid ProSe Restricted Code including a valid PC5 radio technology match as indicated via the PC5_tech parameter in step 6, the ProSe Function in the other PLMN retrieves the ProSe Restricted Code corresponding to that Target PDUID, Application ID and Target RPAUID. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix. If the Announcing Enabled indicator is stored in the UE context, the ProSe Function of HPLMN shall trigger the Announcing Alert procedure (see clause 5.3.5) to notify the announcing UE to perform announcing.

Optionally, the ProSe Function in the other PLMN sends an Auth Request (RPAUID , Request Type, Target RPAUID) to the Application Server indicated by the Application ID. The Request Type is set to "restricted discovery/permission".

If, based on the permission setting, the RPAUID is allowed to discover the Target RPAUID, the ProSe Application Server acknowledges the Auth Request with an Auth Response (Target PDUID, Response Type). The Response Type is set to "restricted discovery/permission ack". The ProSe Function in the other PLMN verifies that the returned Target PDUID corresponds to the UE to be monitored. If the Requested Discovery Timer is included in step 1 and the value is set to zero, the TTL in the Discovery Response message is set to zero.

The ProSe Function in the other PLMN returns to the ProSe Function in the HPLMN the ProSe Restricted Code and the corresponding residual validity timer with a Monitor Response (ProSe Restricted Code, validity timer) message. The Prose Function in the other PLMN also stores, in the context of the announcing UE, the PDUID of the monitoring UE and the allocated validity timer. The response may also include the PC5_tech parameter if it was provided by the HPLMN ProSe Function in step 7. When this parameter is omitted the intended PC5 radio technology is E-UTRA.

For each pair of Target PDUID - Target RPAUID returned by the application server in step 4, if the ProSe Function in the HPLMN has retrieved a valid ProSe Restricted Code, it builds the binding between ProSe Restricted Code with validity timer, Application ID, Target RPAUID, Metadata Indicator and Target PDUID and stores it into the discovery entry in the user context of the monitoring UE. Based on the ProSe Restricted Code and the associated validity timer the ProSe Function in the HPLMN allocates a Discovery Filter with the corresponding TTL. The ProSe Function in the HPLMN returns a Discovery Response (Discovery Filter(s), Metadata Indicator, Discovery Entry ID, Application Level Container, [PC5_tech]) message to the UE. The Discovery Filter includes the ProSe Restricted Code to be monitored and the TTL that indicates for how long the related ProSe Restricted Code in the Discovery Filter is valid after it is received. If configured by the operator, the Target RPAUID(s) and metadata corresponding to the ProSe Restricted Code(s) may be included in the Discovery Response message. The ProSe Function stores in the user context all the parameters passed to the UE. If restricted Direct Discovery with application-controlled extension is used, the ProSe Restricted Code is replaced by the ProSe Restricted Code Prefix. Besides the ProSe Restricted Code(s), the Discovery Filter may also contain the mask(s) for the ProSe Restricted Code Suffix, which is/are obtained in from ProSe Application Server in step 4. The UE may add additional mask(s) and values for the Suffix part. The optional PC5_tech parameter indicates the PC5 radio technology that may be used for the Discovery Filter(s). When the parameter is omitted the intended PC5 radio technology is E-UTRA.

The UE obtains the corresponding radio resources that are authorized and configured by the PLMN(s) to be used for ProSe as defined in RAN specifications or uses WLAN, or both and starts to monitor using the Discovery Filter. The UE provides the Application Level Container, which contains the successful authenticated Target RPAUID(s), to the application client.