6.2.2 Announce request procedure for open ProSe direct discovery

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

6.2.2.1 General

The purpose of the announce request procedure for open ProSe direct discovery is for the UE:

– to obtain one or more ProSe Application Code(s) to be announced over the PC5 interface, upon a request for announcing from upper layers as defined in 3GPP TS 23.303 [2];

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

– to upload metadata associated with a ProSe Application ID to the ProSe Function as defined in 3GPP TS 23.303 [2].

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

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 one of the ProSe Application Code(s) obtained as a result of a successful announce request procedure per PC5_DISCOVERY message and passes the PC5_DISCOVERY messages to the lower layers for transmission over the PC5 interface.

6.2.2.2 Announce request procedure initiation

Before initiating the announce request procedure for open ProSe direct discovery, the UE is configured with the data structure of the ProSe Application IDs appropriate for its HPLMN. This step is performed using mechanisms out of scope of 3GPP.

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

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

b) when the validity timer T4000 assigned by the ProSe Function to a ProSe Application Code has expired and the request from upper layers to announce the ProSe Application ID corresponding to that ProSe Application Code is still in place;

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

d) when, while announcing a ProSe Application ID, 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 Application Code for this new PLMN yet;

e) when the UE needs to inform the ProSe Function that the UE wants to stop announcing a ProSe Application Code; or

f) when the UE needs to update metadata associated with a ProSe Application ID to the ProSe Function.

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

NOTE 1: To ensure service continuity if the UE needs to keep announcing a ProSe Application Code corresponding to the same ProSe Application ID, the UE can initiate the announce request procedure before the TTL timer T4000 assigned by the ProSe Function for a Prose Application Code expires.

The UE initiates the announce request procedure for open ProSe direct discovery by sending a DISCOVERY_REQUEST message with:

– a new transaction ID;

– the ProSe Application ID set to the ProSe Application ID received from upper layers;

– the command set to "metadata_update" if the UE has a valid ProSe Application Code corresponding to the ProSe Application ID and intends to update metadata associated with the ProSe Application ID to the ProSe Function, otherwise 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 Entry ID set to 0 when this is a new request or set to the Discovery Entry ID received from the ProSe Function if the announce request is to update a previously sent announce request;

– 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;

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

– optionally the Metadata set to the metadata received from upper layers associated with the ProSe Application ID;

– optionally in case of E-UTRA-based open ProSe direct discovery 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 this ProSe Application ID; 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 open ProSe direct discovery 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 Application 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 Application 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 ProSe Application IDs, and receive corresponding <response-announce> 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 6.2.2.2.1 illustrates the interaction of the UE and the ProSe Function in the announce request procedure.

Figure 6.2.2.2.1: Announce request procedure

6.2.2.3 Announce request procedure accepted by the ProSe Function

Upon receiving a DISCOVERY_REQUEST message with the command set to "announce", 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 <response-announce> 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", 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 open ProSe direct discovery announcing. If the application is authorised for open ProSe direct discovery announcing, the ProSe Function may also check whether the ProSe Application ID contained in the DISCOVERY_REQUEST message is known. If the ProSe Application ID is known or the ProSe Function skips the check of the ProSe Application ID, the ProSe Function shall check whether there is an existing context for the UE associated with the requested ProSe Application ID.

If there is no associated UE context, the ProSe Function checks with the HSS whether the UE is authorised for open ProSe direct discovery announcing as described in 3GPP TS 29.344 [3]. If the check indicates that the UE is authorised then:

– the ProSe Function shall check whether the UE is authorised to announce the ProSe Application ID contained in the DISCOVERY_REQUEST message;

– if the UE is authorised to announce the ProSe Application ID, the ACE Enabled Indicator is included and 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 authorised to use ACE. If the UE is authorised 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 ProSe Application ID with application-defined suffix(es), and obtain suffix-related information from the ProSe Application Server. The ProSe Function shall then allocate one ProSe Application Code Prefix and a value for validity timer T4000 to be used with the ProSe Application Code Suffix(es) obtained from the ProSe Application Server for the given ProSe Application ID 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;

– if the UE is authorised to announce the ProSe Application ID, the ACE Enabled Indicator is included and 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 Application Code(s) and a value for validity timer T4000. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message;

– if the UE is authorised to announce the ProSe Application ID, the ACE Enabled Indicator is set included and 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 authorised to use ACE. If the UE is authorised 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 ProSe Application ID with application-defined suffix(es), and obtain suffix-related information from the ProSe Application Server. The ProSe Function shall then allocate one ProSe Application Code Prefix and a value for validity timer T4000 to be used with the ProSe Application Code Suffix(es) obtained from the ProSe Application Server for the given ProSe Application ID 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;

– if the UE is authorised to announce the ProSe Application ID, the ACE Enabled Indicator is included and 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 Application Code(s) and a value for validity timer T4000. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message; and

– if the UE is authorised to announce the ProSe Application ID and the ACE Enabled Indicator is not included in the DISCOVERY_REQUEST message, the ProSe Function shall allocate the corresponding ProSe Application Code(s) and a value for validity timer T4000. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message.

NOTE 1: A UE implementing a previous release of the protocol will not include the ACE Enabled Indicator in the DISCOVERY_REQUEST message.

NOTE 2: The ProSe Function can allocate multiple ProSe Application Codes for a given ProSe Application ID for instance in the case when one or more labels in the ProSe Application ID Name are wild carded as described in subclause 24.2.2 of 3GPP TS 23.003 [4].

If the requested ProSe Application ID is country-specific or global as described in subclause 24.2 of 3GPP TS 23.003 [4], the ProSe Function shall allocate the corresponding ProSe Application Code(s) or ProSe Application Code Prefix according to subclause 24.3 of 3GPP TS 23.003 [4]. The temporary identity part of each ProSe Application Code or ProSe Application Code Prefix is taken from the data structure corresponding to the country-specific or global ProSe Application ID namespace according to subclause 24.3 of 3GPP TS 23.003 [4]. The ProSe Function shall use the MCC and MNC of the PLMN ID of this ProSe Function for the PLMN ID part of the ProSe Application Code or ProSe Application Code Prefix.

After the ProSe Application Code(s) or ProSe Application Code Prefix allocation, the ProSe Function then associates the ProSe Application Code(s) or ProSe Application Code Prefix with a new discovery entry identified by a non-zero value Discovery Entry ID in the new context for the UE that contains the UE’s subscription parameters obtained from the HSS, and starts timer T4001. The HSS also provides to the ProSe Function the PLMN ID of the PLMN in which the UE is currently registered. For a given set of ProSe Application Codes or the allocated ProSe Application Code Prefix, timer T4001 shall be longer than timer T4000. By default, the value of timer T4001 is 4 minutes greater than the value of timer T4000.

If there is an existing context for the UE that contains the UE’s subscription parameters obtained from the HSS, but no discovery entry identified by the Discovery Entry ID contained in the DISCOVERY_REQUEST message, 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 Metadata is included in the DISCOVERY_REQUEST message, the ProSe Function shall allocate the ProSe Application Code or ProSe Application Code Prefix including a Metadata Index to indicate the current version of the Metadata, and store the received metadata in the UE context.

Moreover, if the command is set to "metadata_update" in the DISCOVERY_REQUEST message and there is an existing UE context stored in the ProSe Function, the ProSe Function shall update the metadata in the UE context by using the received Medadata in the DISCOVERY_REQUEST message, and update the ProSe Application Code or ProSe Application Code Prefix in the UE context by changing the Metadata Index portion and keeping the rest unchanged.

After the ProSe Application Code(s) allocation, the ProSe Function then associates the ProSe Application Code(s) with a new discovery entry identified by a non-zero value Discovery Entry ID in the UE context, and starts timer T4001.

If there is an existing context for the UE and a discovery entry identified by the Discovery Entry ID contained in the DISCOVERY_REQUEST message associated with the requested ProSe Application ID, the ProSe Function shall either update the discovery entry with a new validity timer T4000, or allocate new ProSe Application Code(s) or ProSe Application Code Prefix for the requested ProSe Application ID with a new validity timer T4000, and restart timer T4001. The ProSe Function may take into account the Requested Timer if contained in the DISCOVERY_REQUEST message.

If a new discovery entry was created or an existing discovery entry was updated and the UE is currently roaming or the Announcing PLMN ID is included in the DISCOVERY_REQUEST message, the ProSe Function checks with the ProSe Function of the VPLMN or in case of E-UTRA-based open ProSe direct discovery the local PLMN identified by the Announcing PLMN ID whether the UE is authorised for open ProSe direct discovery announcing as described in 3GPP TS 29.345 [5].

If the check indicates that the UE is authorised then the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-announce> element with:

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

– either the ProSe Application Code(s) set to the ProSe Application Code(s) allocated by the ProSe Function, or the ProSe Application Code ACE parameter set to include the ProSe-Application Code- Prefix allocated by the ProSe Function, and one or more ProSe Application Code Suffix Ranges which contain the suffix(es) for the ProSe Application ID received in the DISCOVERY_REQUEST message from the UE;

– Validity Timer T4000 set to the T4000 timer value assigned by the ProSe Function to the ProSe Application Code(s):

– if the ACE Enabled Indicator was included by the UE in the DISCOVERY_REQUEST message, 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 Discovery Entry ID set to the identifier associated with the corresponding discovery entry;

– the Discovery Key set to a value provided by the ProSe Function; and

– optionally the PC5_tech set to the one or more PC5 radio technologies that are authorized to be used for the assigned ProSe Application Code(s) or the assigned ProSe-Application Code- Prefix and the ProSe Application Code Suffix Ranges.

If timer T4001 expires, the ProSe Function shall remove the discovery entry identified by the Discovery Entry ID from the UE’s context.

6.2.2.4 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 <response-announce> 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 T4000 corresponding to the ProSe Application Code(s) or ProSe Application Code Prefix in the discovery entry identified by the Discovery Entry ID;

– 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 <response-announce> 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 Application Code(s) and the PLMN ID of the intended announcing PLMN. For this discovery entry, the UE shall stop the validity timer T4000 if running and start the validity timer T4000 with the received value. Otherwise the UE shall discard the DISCOVERY_RESPONSE message and shall not perform the procedures below.

For any one of the received ProSe Application Codes or ProSe Application Code Prefix in this discovery entry, the UE may perform open ProSe direct discovery announcing as described below.

The UE requests the parameters from the lower layers for Prose direct discovery announcing (see 3GPP TS 36.331 [12]). In case of E-UTRA-based open ProSe direct discovery the UE shall perform direct discovery announcing only if the lower layers indicate that ProSe direct discovery is supported by the network. In case of E-UTRA-based open 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 use the UTC-based counter and the Discovery Key contained in the <response-announce> element of the DISCOVERY_RESPONSE message to compute the MIC field for the PC5_DISCOVERY message as described in 3GPP TS 33.303 [6].

The UE shall either use the ProSe Application Code received in the DISCOVERY_RESPONSE message, or select one ProSe Application Code based on the ProSe Application Code Prefix and ProSe Application Code Suffix Range(s) received in the DISCOVERY_RESPONSE message as announced ProSe Application Code, along with the MIC and the four 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 Application Code Suffixes to announce, without having to send a new DISCOVERY_REQUEST message to the ProSe Function, as long as the validity timer T4000 of the ProSe Application Code Prefix has not expired.

The UE then passes the 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 open direct discovery announcing in the registered PLMN or in case of E-UTRA-based open ProSe direct discovery the local PLMN operating the radio resources that the UE intends to use;

– the validity timer T4000 for the corresponding discovery entry allocated ProSe Application Code or ProSe Application Code Prefix has not expired; and

– a request from upper layers to announce the ProSe Application ID associated with both the ProSe Application Code or ProSe Application 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 T4000 of the ProSe Application Code or ProSe Application 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 open ProSe direct discovery 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].

6.2.2.5 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 open 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 ProSe Application ID contained in the DISCOVERY_REQUEST message is unknown to the ProSe Function, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #2 "Unknown ProSe Application ID".

If the UE is not authorised for open ProSe direct discovery 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 to use the ProSe Application ID contained in the DISCOVERY_REQUEST message, 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 requests a country-specific ProSe Application ID for a country that does not correspond to the country of its HPLMN, and the ProSe Function has not authorized the UE to announce in that country, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #8 "Scope Violation in Prose Application ID".

If the UE requests a country-specific ProSe Application ID for a country that does not correspond to the country of its HPLMN, and the ProSe Function has no agreement to access the country-wide ProSe Application ID database of that country, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #8 "Scope Violation in Prose Application ID".

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".

If the UE is not authorised 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_REQUEST message does not contain the ACE Enabled Indicator and the requested application only uses application-controlled extension, the ProSe Function shall send a DISCOVERY_RESPONSE message containing a <response-reject> element with PC3 Control Protocol cause value #1 "Invalid Application".

6.2.2.6 Abnormal cases

6.2.2.6.1 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 ProSe Application ID 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.

e) Absence of Discovery Entry ID parameter in a DISCOVERY_RESPONSE message received in response to a DISCOVERY_REQUEST message which contained a Discovery Entry ID parameter

If the DISCOVERY_REQUEST message:

– included a Requested Timer which is set to 0; or

– included an Announcing PLMN ID;

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

6.2.2.6.2 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) T4001, if running.