5 High level functionality and features

23.3043GPPProximity based Services (ProSe) in the 5G System (5GS)Release 17TS

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

5.1 Authorization and Provisioning for ProSe service

5.1.1 General

In 5GS, the parameters for 5G ProSe Direct Discovery, 5G ProSe Direct Communication, and 5G ProSe UE-to-Network Relay service may be made available to the UE in following ways:

– provisioned in the ME; or

– configured in the UICC; or

– provisioned in the ME and configured in the UICC; or

– provided or updated by the ProSe Application Server via PCF and/or PC1 reference point; or

– provided or updated by the PCF to the UE.

If the same parameters described in clauses 5.1.2.1, 5.1.3.1 and 5.1.4.1 are provided by different sources, the UE shall consider them in the following priority order:

– provided or updated by the PCF (including parameters determined by the PCF itself and parameters provided by the ProSe Application Server to the PCF as specified in clause 6.2.5);

– provided or updated by the ProSe Application Server via PC1 reference point;

– configured in the UICC;

– provisioned in the ME.

The parameters provided or updated by the ProSe Application Server via PC1 reference point may need to be complemented with configuration data from other sources listed above.

NOTE: The ProSe Application Server can provision the same ProSe parameters via 5GC as specified in clause 6.2.5 or directly to the UE via PC1 reference point, and can revoke (e.g. delete) the ProSe parameters via 5GC as specified in clause 6.2.5 in order for the provisioning via PC1 reference point to take effect.

The basic principles of service authorization and provisioning for 5G ProSe Direct Discovery, 5G ProSe Direct Communication, and 5G ProSe UE-to-Network Relay service are as follows:

– The PCF in the HPLMN may configure a list of PLMNs where the UE is authorized to use 5G ProSe Direct Discovery.

– The PCF in the HPLMN may configure a list of PLMNs where the UE is authorised to use 5G ProSe Direct Communication.

– The PCF in the HPLMN may configure a list of PLMNs where the UE is authorised to act as 5G ProSe UE-to-Network Relay. Authorisation for 5G ProSe Layer-2 UE-to-Network Relay and 5G ProSe Layer-3 UE-to-Network Relay are independent of each other.

– The PCF in the HPLMN may configure a list of PLMNs where the UE is authorised to access 5GC via 5G ProSe UE-to-Network Relay (i.e. to act as 5G ProSe Remote UE). Authorisation to access via 5G ProSe Layer-2 UE-to-Network Relay and via 5G ProSe Layer-3 UE-to-Network Relay are independent of each other.

– The PCF in the HPLMN merges authorization information from home and other PLMNs and provides the UE with the final authorization information.

– The PCF in the VPLMN or HPLMN may revoke the authorization (via H-PCF when roaming) at any time by using the UE Configuration Update procedure for transparent UE Policy delivery procedure defined in clause 4.2.4.3 of TS 23.502 [5].

– The ProSe Policy/parameters provisioning to UE is controlled by the PCF and may be triggered by UE. The PCF provisions one or more of the following ProSe Policy/parameters:

– ProSe Policy/parameters for 5G ProSe Direct Discovery as specified in clause 5.1.2.1;

– ProSe Policy/parameters for 5G ProSe Direct Communications as specified in clause 5.1.3.1;

– ProSe Policy/parameters for 5G ProSe Layer-2 and/or Layer-3 UE-to-Network Relay as specified in clause 5.1.4.1;

– ProSe Policy/parameters for 5G ProSe Layer-2 and/or Layer-3 Remote UE as specified in clause 5.1.4.1.

– The PCF includes the 5G ProSe Policy/parameters in a Policy Section identified by a Policy Section Identifier (PSI) as specified in clause 6.1.2.2.2 of TS 23.503 [9].

In addition to the above, ProSe usage reporting configuration and rules for charging can be (pre)configured in the UE or provided by the PCF.

In addition to the above, the path selection policy can be (pre)configured in the UE or provided by the PCF as defined in clause 5.11. A path preference for ProSe Services can be provided by ProSe Application Server to UDR, and may be used by PCF for path selection policy generation and update.

When a 5G ProSe Layer-3 Remote UE is using a 5G ProSe Layer-3 UE-to-Network Relay without involving N3IWF, the PCF based provisioning and update of 5G ProSe Policy/parameters to the 5G ProSe Layer-3 Remote UE are not supported.

5.1.2 Authorization and Provisioning for 5G ProSe Direct Discovery

5.1.2.1 Policy/Parameter provisioning for 5G ProSe Direct Discovery

The following sets of information for 5G ProSe Direct Discovery over PC5 reference point is provisioned to the UE:

1) Authorization policy for 5G ProSe Direct Discovery:

– When the UE is "served by NG-RAN":

– For open 5G ProSe Direct Discovery:

a) open 5G ProSe Direct Discovery Model A monitoring authorization policy:

– PLMNs in which the UE is authorised to perform 5G ProSe Direct Discovery monitoring.

b) open 5G ProSe Direct Discovery Model A announcing authorization policy:

– PLMNs in which the UE is authorized to perform announcing.

– For restricted 5G ProSe Direct Discovery:

a) restricted 5G ProSe Direct Discovery Model A monitoring authorization policy:

– PLMNs in which the UE is authorised to perform restricted 5G ProSe Direct Discovery Model A monitoring.

b) restricted 5G ProSe Direct Discovery Model A announcing authorization policy:

– PLMNs in which the UE is authorized to perform restricted 5G ProSe Direct Discovery Model A announcing.

c) restricted 5G ProSe Direct Discovery Model B Discoverer operation authorization policy:

– PLMNs in which the UE is authorized to perform Model B Discoverer operation.

d) restricted 5G ProSe Direct Discovery Model B Discoveree operation authorization policy:

– PLMNs in which the UE is authorized to perform Model B Discoveree operation.

NOTE 1: In this specification, [When the UE is "served by NG-RAN"] and [When the UE is "not served by NG-RAN"] are relevant to 5G ProSe Direct discovery/communications over NR PC5 reference point.

– When the UE is "not served by NG-RAN":

– Indicates whether the UE is authorized to perform 5G ProSe Direct Discovery for Model A and Model B when "not served by NG-RAN".

NOTE 2: If both Model A and Model B are authorized for 5G ProSe Direct Discovery, it is up to UE and application implementation to select a discovery model or perform both models simultaneously.

2) Parameters used for 5G ProSe Direct Discovery:

– The mapping of ProSe services (i.e. ProSe identifiers) to Destination Layer-2 ID(s) for sending/receiving initial signalling of discovery messages.

NOTE 3: The same Destination Layer-2 ID for 5G ProSe Direct Discovery can be mapped to more than one ProSe services.

NOTE 4: The values provisioned for the Destination Layer-2 ID(s) for 5G ProSe Direct Discovery, for Destination Layer-2 ID(s) for 5G ProSe Direct Communication, defined in clause 5.1.3.1 and for Destination Layer-2 ID(s) for 5G ProSe UE-to-Network Relay Discovery defined in clause 5.1.4.1, are different from each other.

– Application identifiers to be used for 5G ProSe Direct Discovery over PC5 interface.

NOTE 5: The Security parameters for 5G ProSe Direct Discovery can be provisioned by 5G DDNMF as defined in TS 33.503 [29].

3) Radio parameters when the UE is "not served by NG-RAN":

– Includes the radio parameters per NR PC5 with Geographical Area(s) and an indication of whether they are "operator managed" or "non-operator managed". The UE uses the radio parameters to perform 5G ProSe Direct Discovery over PC5 reference point when "not served by NG-RAN" only if the UE can reliably locate itself in the corresponding Geographical Area. Otherwise, the UE is not authorized to transmit.

NOTE 6: Whether a frequency band is "operator managed" or "non-operator managed" in a given Geographical Area is defined by local regulations.

– Default PC5 DRX configuration (see TS 38.331 [16]).

4) Restricted ProSe Discovery UE ID for Restricted Direct Discovery:

– ProSe Discovery UE ID.

5) Group Member Discovery parameters:

– For each discovery group that the UE belongs to include the following parameters that enable the UE to perform Group Member Discovery when provided by PCF or provisioned in the ME or configured in the UICC:

– Application Layer Group ID: Identifies an application layer group or a discovery group that the UE belongs to;

– Layer-2 Group ID: layer-2 ID for Application Layer Group ID;

– User Info ID: For Model A, this corresponds to the Announcer Info parameter when the UE is acting as an announcing UE. For Model B, this corresponds to the Discoverer Info in Solicitation messages and the Discoveree Info in Response messages, when the UE is acting as a discoverer or discoveree UE respectively.

NOTE 7: User Info ID is expected to be assigned uniquely to a user within the discovery group.

6) Optionally, the 5G DDNMF address (either FQDN or IP address) in the Home PLMN.

7) Validity timer indicating the expiration time of the Policy/Parameter for 5G ProSe Direct Discovery.

The above parameter sets bullet 2), bullet 3), bullet 5) and bullet 7) may be provided or updated to the UE by the ProSe Application Server, except for the Security parameters in bullet 2).

5.1.2.2 Principles for applying parameters for 5G ProSe Direct Discovery

For 5G ProSe Direct Discovery over PC5 reference point, the operator may pre-configure the UEs with the required provisioning parameters for 5G ProSe Direct Discovery, without the need for the UEs to connect to the 5GC to get this initial configuration. The following apply:

– The provisioning parameters for 5G ProSe Direct Discovery could be from different sources and their priorities are described in clause 5.1.1.

– The ME provisioning parameters shall not be erased when a USIM is deselected or replaced.

– The UE shall use radio resources for 5G ProSe Direct Discovery as follows:

– While a UE has a serving cell and is camped on a cell and the UE intends to use for 5G ProSe the radio resources (i.e. carrier frequency) operated by this cell, then the UE shall use the radio resource description indicated by this cell the UE is camped on and ignore any radio resource description of the same radio resource provisioned in the ME or the UICC. If the cell does not provide radio resources for ProSe, the UE shall not perform ProSe message transmission and reception on radio resources operated by this cell. The UE is allowed to perform 5G ProSe Direct Discovery with another UE not served by the same PLMN;

– If the UE intends to use "operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe that are not operated by the UE’s serving cell, as specified in clause 5.1.2.1, or if the UE is out of coverage, the UE shall search for a cell in any PLMN that is operating the provisioned radio resources (i.e. carrier frequency) as defined in TS 38.300 [12] and TS 38.304 [13]; and:

– If the UE finds such a cell in the registered PLMN or a PLMN equivalent to the registered PLMN, and authorization for 5G ProSe Direct Discovery to this PLMN is confirmed, the UE shall use the radio resource description indicated by that cell. If that cell does not provide radio resources for ProSe, the UE shall not perform ProSe message transmission and reception on those radio resources;

– If the UE finds such a cell but not in the registered PLMN or a PLMN equivalent to the registered PLMN, and that cell belongs to a PLMN authorized for 5G ProSe Direct Discovery and provides radio resources for ProSe then the UE shall perform PLMN selection triggered by 5G ProSe Direct Discovery as defined in TS 23.122 [14];

– If the UE finds such cell but not in a PLMN authorized for 5G ProSe Direct Discovery the UE shall not use 5G ProSe Direct Discovery;

– If the UE does not find any such cell in any PLMN, then the UE shall consider itself "not served by NG-RAN" and use radio resources provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe Direct Discovery, then the UE is not authorized to transmit;

– The UE is allowed to use "operator-managed" radio resources (i.e. carrier frequency) provisioned in the ME or the UICC for 5G ProSe Direct Discovery if the UICC indicates it is authorized;

– If the UE intends to use "non-operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe, according to TS 36.331 [15] or TS 38.331 [16] and as specified in clause 5.1.2.1, then the UE shall perform 5G ProSe Direct Discovery using resource provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe Direct Discovery, then the UE is not authorized to transmit;

NOTE 1: It is possible for operators to configure UEs (e.g. Public Safety UEs) to use only "operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe Direct Discovery when the UE is "not served by NG-RAN".

– The UE provisioning shall support setting Geographical Areas;

NOTE 2: It is possible for a UE to use other radio resources for 5G ProSe based on the Geographical Area instead of those operated by the serving NG-RAN cell, when provisioned in the UE, even if the UE’s serving cell offers normal service and the SIBs for NR sidelink communication defined in TS 38.331 [16] indicates that the service (5G ProSe Direct Discovery) is available. This is to cover the scenario when e.g. the radio resources used for 5G ProSe Direct Discovery are not owned by the serving network of the UE.

NOTE 3: When cross-carrier operation is supported, according to TS 36.331 [15] or TS 38.331 [16], a UE can be instructed by its serving cell to perform 5G ProSe Direct Discovery over a different carrier frequency. The UE is still considered as "served by NG-RAN" in this case.

NOTE 4: The scenario that a cell is detected and the cell does not provide support for 5G ProSe Direct Discovery when the UE attempts to use a carrier frequency configured for 5G ProSe Direct Discovery, is considered a configuration error. Therefore, the UE does not transmit on that frequency to avoid interference to the network.

– The 5G ProSe Direct Discovery is only specified for NR.

NOTE 5: It is out of scope of the present specification to define how the UE can locate itself in a specific Geographical Area. When the UE is in coverage of a 3GPP RAT, it can for example, use information derived from the serving PLMN. When the UE is not in coverage of a 3GPP RAT, it can use other techniques, e.g. Global Navigation Satellite System (GNSS). User provided location is not a valid input.

5.1.3 Authorization and Provisioning for 5G ProSe Direct Communication

5.1.3.1 Policy/Parameter provisioning for 5G ProSe Direct Communication

The following sets of information for 5G ProSe Direct Communications over PC5 reference point is provisioned to the UE:

1) Authorization policy:

– When the UE is "served by NG-RAN":

– PLMNs in which the UE is authorized to perform 5G ProSe Direct Communications over PC5 reference point when "served by NG-RAN".

– When the UE is "not served by NG-RAN":

– Indicates whether the UE is authorized to perform 5G ProSe Direct Communications over PC5 reference point when "not served by NG-RAN".

NOTE 1: In this specification, [When the UE is "served by NG-RAN"] and [When the UE is "not served by NG-RAN"] are relevant to 5G ProSe Direct Communications over NR PC5 reference point.

2) Groupcast mode 5G ProSe Direct Communication policy/parameters:

– For each application layer group supported include the parameters that enable the UE to perform Groupcast mode 5G ProSe Direct Communication when provided by PCF or provisioned in the ME or configured in the UICC:

– Application Layer Group ID: Identifies an application layer group that the UE belongs to.

– ProSe Layer-2 Group ID: Destination Layer-2 ID applicable only when the Application Layer Group ID is provided by the application layer

– ProSe Group IP multicast address

– Indication whether the UE should use IPv4 or IPv6 for that group

– For a specific Group configured to operate using IPv4, optionally an IPv4 address to be used by the UE as a source address. If none is provisioned, then the UE shall use Dynamic Configuration of IPv4 Link-Local Addresses RFC 3927 [18] to obtain a link local address for the Group.

3) Radio parameters when the UE is "not served by NG-RAN":

– Includes the radio parameters NR PC5 with Geographical Area(s) and an indication of whether they are "operator managed" or "non-operator managed". The UE uses the radio parameters to perform ProSe Direct Communications over PC5 reference point when "not served by NG-RAN" only if the UE can reliably locate itself in the corresponding Geographical Area. Otherwise, the UE is not authorized to transmit.

NOTE 2: Whether a frequency band is "operator managed" or "non-operator managed" in a given Geographical Area is defined by local regulations.

4) Policy/parameters related to privacy:

– The list of ProSe services (i.e. ProSe identifiers) with Geographical Area(s) that require privacy support.

– A privacy timer value indicating the duration after which the UE shall change each source Layer-2 ID self-assigned by the UE when privacy is required.

5) Policy/parameters when NR PC5 is selected:

– The mapping of ProSe services (i.e. ProSe identifiers) to radio frequencies with Geographical Area(s).

– The mapping of ProSe services (i.e. ProSe identifiers) to Destination Layer-2 ID(s) for broadcast.

– The mapping of ProSe services (i.e. ProSe identifiers) to Destination Layer-2 ID(s) for groupcast.

– The mapping of ProSe services (i.e. ProSe identifiers) to default Destination Layer-2 ID(s) for initial signalling to establish unicast connection.

NOTE 3: The same default Destination Layer-2 ID for unicast initial signalling can be mapped to more than one ProSe service. In the case where different ProSe services are mapped to distinct default Destination Layer-2 IDs, when the UE intends to establish a single unicast link that can be used for more than one ProSe service, the UE can select any of the default Destination Layer-2 IDs to use for the initial signalling.

NOTE 4: Security policies for Unicast mode 5G ProSe Direct Communication can be provisioned by PCF as defined in TS 33.503 [29].

– The mapping of ProSe services (i.e. ProSe identifiers) to PC5 QoS parameters defined in clause 5.6.1 (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.).

– The mapping of ProSe services (i.e. ProSe identifiers) to the corresponding NR Tx Profiles for broadcast and groupcast (see TS 38.300 [12] and TS 38.331 [16] for further information).

– AS layer configurations (see TS 38.331 [16]), i.e. the mapping of PC5 QoS profile(s) to radio bearer(s), when the UE is "not served by NG-RAN".

– The PC5 QoS profile contains PC5 QoS parameters described in clause 5.4.2 of TS 23.287 [2], and value for the QoS characteristics regarding Priority Level, Averaging Window, Maximum Data Burst Volume if default value is not used as defined in Table 5.4.4-1 of TS 23.287 [2] and in Table 5.6.1-1.

– For broadcast, groupcast and initial signalling to establish unicast connection, PC5 DRX configuration (see TS 38.331 [16]), e.g. the mapping of PC5 QoS profile(s) to PC5 DRX cycle(s), default PC5 DRX configuration, when the UE is "not served by NG-RAN".

6) Path selection policy:

– The mapping of ProSe services (i.e. ProSe identifiers) to path preference (i.e. PC5 preferred, Uu preferred, or no preference) as defined in clause 5.11.

NOTE 5: The path selection policy can be a one mapping for all ProSe services, i.e. same path preference for all ProSe services.

7) Validity time indicating the expiration time of the Policy/Parameter for 5G ProSe Direct Communication.

The above parameter sets from bullet 2) to 7) may be provided or updated to the UE by the ProSe Application Server.

5.1.3.2 Principles for applying parameters for 5G ProSe Direct Communication

For 5G ProSe Direct Communication over PC5 reference point, the operator may pre-configure the UEs with the required provisioning parameters for 5G ProSe Direct Communication, without the need for the UEs to connect to the 5GC to get this initial configuration. The following apply:

– The provisioning parameters for 5G ProSe Direct Communication could be from different sources and their priorities are described in clause 5.1.1.

– The ME provisioning parameters shall not be erased when a USIM is deselected or replaced.

– The UE shall use radio resources for 5G ProSe Direct Communication as follows:

– While a UE has a serving cell and is camped on a cell and the UE intends to use for 5G ProSe the radio resources (i.e. carrier frequency) operated by this cell, then the UE shall use the radio resource description indicated by this cell the UE is camped on and ignore any radio resource description of the same radio resource provisioned in the ME or the UICC. If the cell does not provide radio resources for 5G ProSe, the UE shall not perform ProSe message transmission and reception on radio resources operated by this cell.

– If the UE intends to use "operator-managed" radio resources (i.e. carrier frequency) for ProSe that are not operated by the UE’s serving cell, as specified in clause 5.1.3.1, or if the UE is out of coverage, the UE shall search for a cell in any PLMN that is operating the provisioned radio resources (i.e. carrier frequency) as defined in TS 38.300 [12] and TS 38.304 [13], and:

– If the UE finds such a cell in the registered PLMN or a PLMN equivalent to the registered PLMN, and authorization for 5G ProSe Direct Communication to this PLMN is confirmed, the UE shall use the radio resource description indicated by that cell. If that cell does not provide radio resources for 5G ProSe, the UE shall not perform 5G ProSe message transmission and reception on those radio resources.

– If the UE finds such a cell but not in the registered PLMN or a PLMN equivalent to the registered PLMN, and that cell belongs to a PLMN authorized for 5G ProSe Direct Communications and provides radio resources for 5G ProSe then the UE shall perform PLMN selection triggered by 5G ProSe Direct Communication as defined in TS 23.122 [14].

– If the UE finds such cell but not in a PLMN authorized for 5G ProSe Direct Communications the UE shall not use 5G ProSe Direct Communication.

– If the UE does not find any such cell in any PLMN, then the UE shall consider itself "not served by NG-RAN" and use radio resources provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe Direct Communication, then the UE is not authorized to transmit.

– The UE is allowed to use "operator-managed" radio resources (i.e. carrier frequency) provisioned in the ME or the UICC for 5G ProSe Direct Communication if the UICC indicates it is authorized.

– If the UE intends to use "non-operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe, according to TS 36.331 [15] or TS 38.331 [16] and as specified in clause 5.1.3.1, then the UE shall perform 5G ProSe Direct Communication using resource provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe Direct Communications, then the UE is not authorized to transmit.

NOTE 1: It is possible for operators to configure UEs (e.g. Public Safety UEs) to use only "operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe Direct Communication when the UE is "not served by NG-RAN.

– The UE provisioning shall support setting Geographical Areas.

NOTE 2: It is possible for a UE to use other radio resources for 5G ProSe based on the Geographical Area instead of those operated by the serving NG-RAN cell, when provisioned in the UE, even if the UE’s serving cell offers normal service and the SIBs for NR sidelink communication defined in TS 38.331 [16] indicates that the service (5G ProSe Direct Communication) is available. This is to cover the scenario when e.g. the radio resources used for 5G ProSe Direct Communication are not owned by the serving network of the UE.

NOTE 3: When cross-carrier operation is supported, according to TS 36.331 [15] or TS 38.331 [16], a UE can be instructed by its serving cell to perform 5G ProSe Direct Communication over a different carrier frequency. The UE is still considered as "served by NG-RAN" in this case.

NOTE 4: The scenario that a cell is detected and the cell does not provide support for 5G ProSe Direct Communication when the UE attempts to use a carrier frequency configured for 5G ProSe Direct Communications, is considered a configuration error. Therefore, the UE does not transmit on that frequency to avoid interference to the network.

– The 5G ProSe Direct Communication is only specified for NR.

5.1.4 Authorization and Provisioning for 5G ProSe UE-to-Network Relay

5.1.4.1 Policy/Parameter provisioning for 5G ProSe UE-to-Network Relay

The following information is provisioned in the UE in support of the UE assuming the role of a 5G ProSe UE-to-Network Relay:

1) Authorisation policy for acting as a 5G ProSe Layer-3 and/or Layer-2 UE-to-Network Relay when "served by NG-RAN":

– PLMNs in which the UE is authorized to relay traffic for 5G ProSe Layer-3 and/or Layer-2 Remote UEs.

The authorisation for a UE to act as a 5G ProSe UE-to-Network Relay also authorizes the use of 5G ProSe UE-to-Network Relay Discovery with Model A and Model B.

NOTE 1: It is up to UE and application implementation to select a discovery model or whether to perform both models simultaneously.

2) ProSe Relay Discovery policy/parameters for 5G ProSe UE-to-Network Relay:

– Includes the parameters that enable the UE to perform 5G ProSe UE-to-Network Relay Discovery when provided by PCF or provisioned in the ME or configured in the UICC:

– 5G ProSe UE-to-Network Relay Discovery parameters (User Info ID, Relay Service Code(s), UE-to-Network Relay Layer Indicator per RSC, optional Control Plane Security Indicator per RSC). The UE-to-Network Relay Layer Indicator indicates whether the associated RSC is offering 5G ProSe Layer-2 or Layer-3 UE-to-Network Relay service. If the Control Plane Security Indicator is provided for a RSC, then the Control Plane based security procedure as described in clause 5.1.4.3.2 is performed for UE-to-Network Relay Communication for that RSC, otherwise if it is not provided for a RSC, then the User Plane based security procedure as described in clause 5.1.4.3.3 is performed for that RSC.

– Default Destination Layer-2 ID(s) for sending Relay Discovery Announcement and Relay Discovery Additional Information messages and receiving Relay Discovery Solicitation messages;

– For 5G ProSe Layer-3 UE-to-Network Relay, the PDU Session parameters (PDU Session type, DNN, SSC Mode, S-NSSAI, Access Type Preference) to be used for the relayed traffic for each ProSe Relay Service Code;

– Includes security related content for 5G ProSe UE-to-Network Relay, see TS 33.503 [29].

NOTE 2: 5G ProSe Relay Discovery policy/parameters can be provided from ProSe Application Server to the 5G ProSe UE-to-Network Relay, except for the Security parameters in bullet 2).

3) For 5G ProSe Layer-3 UE-to-Network Relay, QoS mapping(s):

– Each QoS mapping entry includes:

– a mapping between a 5QI value and a PQI value;

– a PQI PDB adjustment factor, for the PC5 communication for the 5G ProSe Layer-3 UE-to-Network Relay operation;

– optional the Relay Service Code(s) associates with the QoS mapping entry.

4) For 5G ProSe Layer-3 UE-to-Network Relay to relay Ethernet or Unstructured traffic from 5G ProSe Layer-3 Remote UE by using IP type PDU Session:

– Mapping of ProSe Service(s) to ProSe Application Server address information (consisting of IP address/FQDN and transport layer port number).

5) Validity time indicating the expiration time of the Policy/Parameter for 5G ProSe UE-to-Network Relay discovery and communication.

The following information is provisioned in the UE in support of the UE assuming the role of a 5G ProSe Remote UE and thereby enabling the use of a 5G ProSe UE-to-Network Relay:

1) Authorisation policy for using a 5G ProSe Layer-3 and/or Layer-2 UE-to-Network Relay:

– For 5G ProSe Layer-3 Remote UE, indicates whether the UE is authorised to use a 5G ProSe Layer-3 UE-to-Network Relay.

– For 5G ProSe Layer-2 Remote UE, indicates the PLMNs in which the UE is authorized to use a 5G ProSe Layer-2 UE-to-Network Relay.

The authorisation for a UE to act as a 5G ProSe Remote UE also authorizes the use of 5G ProSe UE-to-Network Relay discovery with Model A and Model B.

NOTE 3: It is up to UE and application implementation to select a discovery model or whether to perform both models simultaneously.

2) Policy/parameters for 5G ProSe UE-to-Network Relay Discovery:

– Includes the parameters for 5G ProSe Relay Discovery and for enabling the UE to connect to the 5G ProSe UE-to-Network Relay after discovery when provided by PCF or provisioned in the ME or configured in the UICC:

– 5G ProSe UE-to-Network Relay Discovery parameters (User Info ID, Relay Service Code(s), UE-to-Network Relay Layer indicator per RSC, optional Control Plane Security Indicator per RSC). The UE-to-Network Relay Layer Indicator indicates whether the associated RSC is offering 5G ProSe Layer-2 or Layer-3 UE-to-Network Relay service. If the Control Plane Security Indicator is provided for a RSC, then the Control Plane based security procedures as described in clause 5.1.4.3.2 is performed for UE-to-Network Relay Communication for that RSC, otherwise if it is not provided for a RSC, then the User Plane based security procedures as described in clause 5.1.4.3.3 is performed for that RSC.

– Default Destination Layer-2 ID(s) for sending Relay Discovery Solicitation messages and receiving Relay Discovery Announcement and Relay Discovery Additional Information messages;

– For 5G ProSe Layer-3 UE-to-Network Relay, the PDU Session parameters (PDU Session type, DNN, SSC Mode, S-NSSAI, Access Type Preference) to be used for the relayed traffic without using N3IWF access, or an indication of N3IWF access, for each ProSe Relay Service Code;

– For 5G ProSe Layer-3 UE-to-Network Relay, optionally the ProSe application Traffic Descriptor(s) (as defined in TS 23.503 [9]) to be used for the relayed traffic for each ProSe Relay Service Code;

– Includes security related content for 5G ProSe UE-to-Network Relay, see TS 33.503 [29].

3) Policy/parameters for N3IWF selection for 5G ProSe Layer-3 Remote UE:

– N3IWF identifier configuration for 5G ProSe Layer-3 Remote UE (either FQDN or IP address) in the HPLMN.

– 5G ProSe Layer-3 UE-to-Network Relay access node selection information – a prioritized list of PLMNs for N3IWF selection. It also indicates if selection of an N3IWF in a PLMN should be based on Tracking Area Identity FQDN or on Operator Identifier FQDN.

NOTE 4: 5G ProSe Relay Discovery policy/parameters can be provided from ProSe Application Server to the 5G ProSe Remote UE, except for the Security parameters in bullet 2).

4) Validity time indicating the expiration time of the Policy/Parameter for 5G ProSe UE-to-Network Relay discovery and communication.

The following information is provisioned in the UE in support of the UE assuming the role of a 5G ProSe UE-to-Network Relay as well as in the UE in support of the UE assuming the role of a 5G ProSe Remote UE and thereby enabling the use of a 5G ProSe UE-to-Network Relay:

1) Radio parameters for 5G ProSe UE-to-Network Relay Discovery when the UE is not "served by NG-RAN":

– Includes the radio parameters NR PC5 with Geographical Area(s) and an indication of whether they are "operator managed" or "non-operator managed". The UE uses the radio parameters to perform 5G ProSe Direct Discovery over PC5 reference point when "not served by NG-RAN" only if the UE can reliably locate itself in the corresponding Geographical Area. Otherwise, the UE is not authorized to transmit.

– Default PC5 DRX configuration (see TS 38.331 [16]).

2) Radio parameters for 5G ProSe UE-to-Network Relay communication when the UE is not "served by NG-RAN":

– Includes the radio parameters NR PC5 with Geographical Area(s) and an indication of whether they are "operator managed" or "non-operator managed". The UE uses the radio parameters to perform 5G ProSe Direct Communication over PC5 reference point when "not served by NG-RAN" only if the UE can reliably locate itself in the corresponding Geographical Area. Otherwise, the UE is not authorized to transmit.

NOTE 5: The validity time of these radio parameters is the same as the validity time of the Policy/Parameter listed above for 5G ProSe UE-to-Network Relay or 5G ProSe Remote UE.

3) Policy/parameters related to privacy:

– A privacy timer value indicating the duration after which the UE shall change each source Layer-2 ID self-assigned by the UE when privacy is required.

5.1.4.2 Principles for applying parameters for 5G ProSe UE-to-Network Relay

5.1.4.2.1 Principles for applying parameters for ProSe UE-to-Network Relay discovery

For 5G ProSe UE-to-Network Relay discovery over PC5 reference point, the operator may pre-configure the UEs with the required provisioning parameters for 5G ProSe UE-to-Network Relay discovery, without the need for the UEs to connect to the 5GC to get this initial configuration. The following applies:

– The provisioning parameters for 5G ProSe UE-to-Network Relay discovery could be from different sources and their priorities are described in clause 5.1.1.

– The ME provisioning parameters shall not be erased when a USIM is deselected or replaced.

The UE shall use radio resources for 5G ProSe UE-to-Network Relay discovery as follows:

– While a UE has a serving cell and is camped on a cell and the UE intends to use for 5G ProSe UE-to-Network Relay discovery the radio resources (i.e. carrier frequency) operated by this cell, then the UE shall use the radio resource description indicated by this cell the UE is camped on and ignore any radio resource description of the same radio resource provisioned in the ME or the UICC. If the cell does not provide radio resources for 5G ProSe UE-to-Network Relay discovery, the UE shall not perform 5G ProSe UE-to-Network Relay discovery message transmission and reception on radio resources operated by this cell;

– If the UE intends to use "operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe UE-to-Network Relay discovery that are not operated by the UE’s serving cell, as specified in clause 5.1.4.1, or if the UE is out of coverage, the UE shall search for a cell in any PLMN that is operating the provisioned radio resources (i.e. carrier frequency) as defined in TS 38.300 [12] and TS 38.304 [13]; and:

– If the UE finds such a cell in the registered PLMN or a PLMN equivalent to the registered PLMN, and authorization for 5G ProSe UE-to-Network Relay discovery to this PLMN is confirmed, the UE shall use the radio resource description indicated by that cell. If that cell does not provide radio resources for 5G ProSe UE-to-Network Relay discovery, the UE shall not perform 5G ProSe UE-to-Network Relay discovery message transmission and reception on those radio resources;

– If the UE finds such a cell but not in the registered PLMN or a PLMN equivalent to the registered PLMN, and that cell belongs to a PLMN authorized for 5G ProSe UE-to-Network Relay discovery and provides radio resources for 5G ProSe UE-to-Network Relay discovery then the UE shall perform PLMN selection triggered by 5G ProSe UE-to-Network Relay discovery as defined in TS 23.122 [14];

– If the UE finds such cell but not in a PLMN authorized for 5G ProSe UE-to-Network Relay discovery the UE shall not use 5G ProSe UE-to-Network Relay discovery;

– If the UE does not find any such cell in any PLMN, then the UE shall consider itself "not served by NG-RAN" and use radio resources provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe UE-to-Network Relay discovery, then the UE is not authorized to transmit;

– The UE is allowed to use "operator-managed" radio resources (i.e. carrier frequency) provisioned in the ME or the UICC for 5G ProSe UE-to-Network Relay discovery if the UICC indicates it is authorized;

– If the UE intends to use "non-operator-managed" radio resources (i.e. carrier frequency) for ProSe UE-to-Network Relay discovery, according to TS 38.331 [16] and as specified in clause 5.1.4.1, then the UE shall perform 5G ProSe UE-to-Network Relay discovery using resource provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe UE-to-Network Relay discovery, then the UE is not authorized to transmit;

NOTE 1: It is possible for operators to configure UEs (e.g. Public Safety UEs) to use only "operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe UE-to-Network Relay discovery when the UE is "not served by NG-RAN".

– The UE provisioning shall support setting Geographical Areas;

NOTE 2: It is possible for a UE to use other radio resources for 5G ProSe UE-to-Network Relay discovery based on the Geographical Area instead of those operated by the serving NG-RAN cell, when provisioned in the UE, even if the UE’s serving cell offers normal service and the SIBs for NR sidelink communication defined in TS 38.331 [16] indicates that the service (5G ProSe UE-to-Network Relay discovery) is available. This is to cover the scenario when e.g. the radio resources used for 5G ProSe UE-to-Network Relay discovery are not owned by the serving network of the UE.

NOTE 3: When cross-carrier operation is supported, according to TS 38.331 [16], a UE can be instructed by its serving cell to perform 5G ProSe UE-to-Network Relay discovery over a different carrier frequency. The UE is still considered as "served by NG-RAN" in this case.

NOTE 4: The scenario that a cell is detected and the cell does not provide support for 5G ProSe UE-to-Network Relay discovery when the UE attempts to use a carrier frequency configured for 5G ProSe UE-to-Network Relay discovery, is considered a configuration error. Therefore, the UE does not transmit on that frequency to avoid interference to the network.

– The 5G ProSe UE-to-Network Relay discovery is only specified for NR.

5.1.4.2.2 Principles for applying parameters for 5G ProSe UE-to-Network Relay communication

For 5G ProSe UE-to-Network Relay communication over PC5 reference point, the operator may pre-configure the UEs with the required provisioning parameters for 5G ProSe UE-to-Network Relay communication, without the need for the UEs to connect to the 5GC to get this initial configuration. The following applies:

– The provisioning parameters for 5G ProSe UE-to-Network Relay communication could be from different sources and their priorities are described in clause 5.1.1.

– The ME provisioning parameters shall not be erased when a USIM is deselected or replaced.

The UE shall use radio resources for 5G ProSe UE-to-Network Relay communication as follows:

– While a UE has a serving cell and is camped on a cell and the UE intends to use for 5G ProSe UE-to-Network Relay communication the radio resources (i.e. carrier frequency) operated by this cell, then the UE shall use the radio resource description indicated by this cell the UE is camped on and ignore any radio resource description of the same radio resource provisioned in the ME or the UICC. If the cell does not provide radio resources for 5G ProSe UE-to-Network Relay communication, the UE shall not perform 5G ProSe UE-to-Network Relay communication message transmission and reception on radio resources operated by this cell;

– If the UE intends to use "operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe UE-to-Network Relay communication that are not operated by the UE’s serving cell, as specified in clause 5.1.4.1, or if the UE is out of coverage, the UE shall search for a cell in any PLMN that is operating the provisioned radio resources (i.e. carrier frequency) as defined in TS 38.300 [12] and TS 38.304 [13]; and:

– If the UE finds such a cell in the registered PLMN or a PLMN equivalent to the registered PLMN, and authorization for 5G ProSe UE-to-Network Relay communication to this PLMN is confirmed, the UE shall use the radio resource description indicated by that cell. If that cell does not provide radio resources for 5G ProSe UE-to-Network Relay communication, the UE shall not perform 5G ProSe UE-to-Network Relay communication message transmission and reception on those radio resources;

– If the UE finds such a cell but not in the registered PLMN or a PLMN equivalent to the registered PLMN, and that cell belongs to a PLMN authorized for 5G ProSe UE-to-Network Relay communication and provides radio resources for 5G ProSe UE-to-Network Relay communication then the UE shall perform PLMN selection triggered by 5G ProSe UE-to-Network Relay communication as defined in TS 23.122 [14];

– If the UE finds such cell but not in a PLMN authorized for 5G ProSe UE-to-Network Relay communication the UE shall not use 5G ProSe UE-to-Network Relay communication;

– If the UE does not find any such cell in any PLMN, then the UE shall consider itself "not served by NG-RAN" and use radio resources provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe UE-to-Network Relay communication, then the UE is not authorized to transmit;

– The UE is allowed to use "operator-managed" radio resources (i.e. carrier frequency) provisioned in the ME or the UICC for 5G ProSe UE-to-Network Relay communication if the UICC indicates it is authorized;

– If the UE intends to use "non-operator-managed" radio resources (i.e. carrier frequency) for 5G ProSe UE-to-Network Relay communication, according to TS 38.331 [16] and as specified in clause 5.1.4.1, then the UE shall perform 5G ProSe UE-to-Network Relay communication using resource provisioned in the ME or the UICC. If no such provision exists in the ME or the UICC or the provision does not authorize 5G ProSe UE-to-Network Relay communication, then the UE is not authorized to transmit;

– The UE provisioning shall support setting Geographical Areas;

NOTE 2: It is possible for a UE to use other radio resources for 5G ProSe UE-to-Network Relay communication based on the Geographical Area instead of those operated by the serving NG-RAN cell, when provisioned in the UE, even if the UE’s serving cell offers normal service and the SIBs for NR sidelink communication defined in TS 38.331 [16] indicates that the service (5G ProSe UE-to-Network Relay communication) is available. This is to cover the scenario when e.g. the radio resources used for 5G ProSe UE-to-Network Relay communication are not owned by the serving network of the UE.

NOTE 3: When cross-carrier operation is supported, according to TS 38.331 [16], a UE can be instructed by its serving cell to perform 5G ProSe UE-to-Network Relay communication over a different carrier frequency. The UE is still considered as "served by NG-RAN" in this case.

NOTE 4: The scenario that a cell is detected and the cell does not provide support for 5G ProSe UE-to-Network Relay communication when the UE attempts to use a carrier frequency configured for 5G ProSe UE-to-Network Relay communication, is considered a configuration error. Therefore, the UE does not transmit on that frequency to avoid interference to the network.

– The 5G ProSe UE-to-Network Relay communication is only specified for NR.

5.1.4.3 Network controlled security procedures for 5G ProSe UE-to-Network Relay

5.1.4.3.1 General

Security procedures over Control Plane and User Plane are specified for 5G ProSe UE-to-Network relaying in TS 33.503 [29].

5.1.4.3.2 Control Plane based security procedures for 5G ProSe UE-to-Network Relay

Control Plane-based security procedures for 5G ProSe UE-to-Network Relay call flow and procedure are defined in TS 33.503 [29], characterised by the following principles:

– 5G ProSe UE-to-Network Relay’s NAS signalling is used for the control plane based security procedure to authenticate and authorize a 5G ProSe Remote UE.

– A UE assuming the role of 5G ProSe UE-to-Network Relay can be configured to use a set of slices supporting Control Plane based security procedure. An AMF supporting Control Plane based security procedure for a 5G ProSe UE-to-Network Relay is selected as part of the slice. The 5G ProSe UE-to-Network Relay shall include in discovery messages the RSCs with the Control Plane Security Indicator set, as specified in clause 5.1.4.1, when the requested slice(s) corresponds to Control Plane based security procedure is(are) accepted. In addition, the 5G ProSe UE-to-Network Relay shall includes in discovery messages the RSCs without Control Plane Security Indicator as specified in clause 5.1.4.1.

– A 5G ProSe-enabled UE shall use Control Plane based security procedures if a RSC with Control Plane Security Indicator set is used by the Remote UE to establish the connection. Otherwise, if a RSC without Control Plane Security Indicator is used by the Remote UE to establish the connection, the 5G ProSe-enabled UEs shall use User Plane based security procedures as specified in clause 5.1.4.3.3.

– The AMF serving the 5G ProSe UE-to-Network Relay selects AUSF as specified in clause 6.3.4 of TS 23.501 [4] using the identification information the 5G ProSe Remote UE provided as specified in clause 6.3.3.3.2 of TS 33.503 [29].

– If the 5G ProSe Remote UE is configured by HPLMN to use control plane security procedure, the 5G ProSe Remote UE’s HPLMN AUSF shall support control plane based security procedure.

– If a network intends to use control plane security procedure then all the AMFs or the all AMFs within the network slices that the 5G ProSe UE-to-Network Relay uses shall support the control plane based security procedures.

NOTE: If the control plane security procedure is not supported, then the 5G ProSe Remote UE can select another 5G ProSe UE-to-Network Relay or user plane based security can be used.

5.1.4.3.3 User Plane based security procedures

User Plane-based security procedures for 5G ProSe UE-to-Network Relay are defined in TS 33.503 [29].

5.2 5G ProSe Direct Discovery

5.2.1 General

5G ProSe Direct Discovery is defined as the process that detects and identifies another UE in proximity via NR PC5 reference point. As defined in clause 5.3.3.1 in TS 23.303 [3], 5G ProSe Direct Discovery can be open or restricted; it can be standalone or used for subsequent actions e.g. to initiate 5G ProSe Direct Communication.

In the case of inter-PLMN ProSe discovery and communication over PC5 reference point, the PC5 parameters need to be configured in a consistent way among the UEs within a certain region. The architecture for the Inter-PLMN PC5 case is defined in clause 4.2.3.

The UEs may use the PC5 DRX mechanism to perform 5G ProSe Direct Discovery and 5G ProSe UE-to-Network Relay Discovery over PC5 reference point as specified in clause 5.13.

5.2.2 5G ProSe Direct Discovery Models

There are two models for 5G ProSe Direct Discovery: Model A and Model B which are defined in clause 5.3.1.2 in TS 23.303 [3].

5.2.3 5G ProSe UE-to-Network Relay Discovery

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

– Model A uses a single discovery protocol message (Announcement).

– Model B uses two discovery protocol messages (Solicitation and Response).

For Relay Discovery Additional Information, only Model A discovery is used.

The procedures for 5G ProSe UE-to-Network Relay discovery are defined in clause 6.3.2.3.

5.2.4 5G ProSe Direct Discovery Characteristics

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

– PC5 communication channel is used to carry the discovery message over PC5. The discovery message over PC5 is differentiated with other PC5 messages by AS layer.

– ProSe layer shall indicate to AS layer whether the signalling is discovery message or PC5-S signalling.

NOTE 1: The discovery message format is defined in stage 3.

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

– The group discovery/formation/management can be carried out in the Application layer in coordination with the Application Server.

– Application layer signalling between the UE and the Application Server is out of scope of this specification.

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

– 5G DDNMF in the 5GS is used for 5G ProSe Discovery Direct Code management (including allocation and resolution). The 5G DDNMF gets the PDUID from the PCF and subscribes to notifications on Change of PDUID.

– 5G DDNMF is defined in clause 4.3.2 and the detail procedure for 5G ProSe Direct Discovery with 5G DDNMF is defined in clause 6.3.

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

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

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

NOTE 2: Based on UE implementation, the application layer discovery messages are exchanged either as user traffic over PC5 or alternatively as part of metadata in PC5 Direct Discovery message as specified in clause 6.3.2.1 and clause 6.4.2. In the latter case, the PC5 Direct Discovery message can contain additional field carrying application layer metadata information, e.g., the Application layer discovery messages for group discovery. The format and contents of this additional field is out of scope of 3GPP. Performance of the PC5 Direct Discovery message including the application layer information will be affected if the resulted PC5 Direct Discovery message size is too big, e.g. longer delay and lower reliability.

5.3 5G ProSe Direct Communication

5.3.1 General

5G ProSe Direct Communication over PC5 reference point is supported when the UE is "served by NG-RAN" or when the UE is "not served by NG-RAN". A UE is authorized to perform 5G ProSe Direct Communication when it has valid authorization and configuration as specified in clause 5.1.3. 5G ProSe Direct Communication supports both the cases of public safety and commercial service.

5G ProSe Direct Communication over NR based PC5 reference point supports broadcast mode, groupcast mode, and unicast mode.

For broadcast and groupcast mode 5G ProSe Direct Communication, the following data unit types are supported: IPv4, IPv6, Ethernet, Unstructured, and Address Resolution Protocol (see RFC 826 [19]).

For unicast mode 5G ProSe Direct Communication, the following data unit types are supported: IPv4, IPv6, Ethernet, and Unstructured.

The identifiers used in the 5G ProSe Direct Communication over PC5 reference point are described in clause 5.8.2.

The QoS handling and procedures for the 5G ProSe Direct Communication over PC5 reference point are defined in clauses 5.6 and 6.4.

The UEs may use the PC5 DRX mechanism to perform 5G ProSe Direct Communication over PC5 reference point as specified in clause 5.13.

5.3.2 Broadcast mode 5G ProSe Direct Communication

Broadcast mode of 5G ProSe direct communication is supported over NR based PC5 reference point. The transmitting UE in broadcast communication determines the destination Layer-2 ID for broadcast as specified in clause 5.8.2 and assigns itself a source Layer-2 ID. The receiving UE determines the destination Layer-2 ID for broadcast reception as specified in clause 5.8.2. The transmitting UE determines the PC5 QoS parameters for this broadcast as specified in clause 5.6.1. The transmitting UE sends the service data using the source Layer-2 ID and the destination Layer-2 ID.

For IP type 5G ProSe direct communication over PC5 reference point, the mechanism for IP address allocation is described in clause 5.5.1.2.

5.3.3 Groupcast mode 5G ProSe Direct Communication

Groupcast mode of 5G ProSe direct communication is supported over NR based PC5 reference point. Group management is carried out by the application layer in coordination with Application Server and is out of scope of this specification. For commercial services, the Application Layer Group ID is provided by Application Server; and for public safety services, the pre-configured or provisioned Application Layer Group ID will be used for groupcast communication. The group size and member ID information could be used for groupcast control if it is provided by the application layer.

The transmitting UE in groupcast communication determines a source Layer-2 ID and a destination Layer-2 ID and the receiving UE determines destination Layer-2 ID, as specified in clause 5.8.2. The transmitting UE determines the PC5 QoS parameters for this groupcast as specified in clause 5.6.1. The transmitting UE sends the service data using the source Layer-2 ID and the destination Layer-2 ID.

For IP type 5G ProSe direct communication over PC5 reference point, the mechanism for IP address allocation is described in clause 5.5.1.2.

5.3.4 Unicast mode 5G ProSe Direct Communication

Unicast mode of 5G ProSe direct communication is supported over NR based PC5 reference point. A PC5 unicast link between two UEs is established for the 5G ProSe direct communication; and the PC5 unicast link could be maintained, modified, and released according to the application layer requests or communication requirements.

For the PC5 unicast link of the 5G ProSe direct communication, the principal for the PC5 unicast link of V2X communication described in TS 23.287 [2] clause 5.2.1.4 is reused with the following differences:

– V2X service is replaced by ProSe Application;

– V2X service type is replaced by ProSe identifier;

– New data unit types are supported (including IPv4, Ethernet and Unstructured).

For IP type 5G ProSe direct communication over PC5 reference point, the mechanism for IP address/prefix allocation is described in clause 5.5.1.1. The PC5 QoS handling for the unicast mode 5G ProSe direct communication is specified in clause 5.6.1.

5.4 5G ProSe UE-to-Network Relay

5.4.1 5G ProSe Layer-3 UE-to-Network Relay

5.4.1.1 General

The 5G ProSe Layer-3 UE-to-Network Relay shall provide generic function that can relay any IP, Ethernet or Unstructured traffic:

– For IP traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay uses IP type PDU Session towards 5GC.

– For Ethernet traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay can use Ethernet type PDU Session or IP type PDU Session towards 5GC.

– For Unstructured traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay can use Unstructured type PDU Session or IP type PDU Session (i.e. IP encapsulation/de-capsulation by 5G ProSe Layer-3 UE-to-Network Relay) towards 5GC.

The type of traffic supported over PC5 reference point is indicated by the 5G ProSe Layer-3 UE-to-Network Relay e.g. using the corresponding RSC. The 5G ProSe Layer-3 UE-to-Network Relay determines the PDU Session Type based on configuration of the mapping between PDU Session parameters and RSC, as specified in clause 5.1.4.1.

IP type PDU Session and Ethernet type PDU Session can be used to support more than one 5G ProSe Layer-3 Remote UEs while Unstructured type PDU Session can be used to support only one 5G ProSe Layer-3 Remote UE.

NOTE: The maximum number of PDU Sessions can affect the maximum number of 5G ProSe Layer-3 Remote UEs that the 5G ProSe UE-to-Network Relay can support.

The 5G ProSe Layer-3 Remote UE and 5G ProSe Layer-3 UE-to-Network Relay may use the PC5 DRX mechanism to perform 5G ProSe UE-to-Network Relay Communications over PC5 reference point as specified in clause 5.13.

5.4.1.2 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support

To support 5G ProSe Layer-3 Remote UE services with end-to-end confidentiality and IP address preservation requirements, the 5G ProSe Layer-3 UE-to-Network Relay with N3IWF shall provide access to the 5GC for the 5G ProSe Layer-3 Remote UE via N3IWF using the features defined in clause 4.2.8 of TS 23.501 [4].

5G ProSe Layer-3 UE-to-Network Relay is provisioned with RSC(s) and the corresponding PDU session parameters (e.g. S-NSSAI) to support N3IWF access as part of 5G ProSe Layer-3 UE-to-Network Relay Policy/parameters. When a 5G ProSe Layer-3 Remote UE connects with the corresponding RSC, the 5G ProSe Layer-3 UE-to-Network Relay determines the corresponding PDU session parameters based on the requested RSC.

NOTE: The 5G ProSe Layer-3 UE-to-Network Relay only includes a RSC in discovery message when the corresponding PDU session parameters (e.g. S-NSSAI) are authorized to be used in the accessed network.

The 5G ProSe Layer-3 Remote UE selects N3IWF as specified in clause 6.5.1.2.2. The selection of N3IWF follows the regulatory rules of the country where it is located, and when required by the regulations the 5G ProSe Layer-3 Remote UE only selects a N3IWF within the local country. QoS differentiation can be provided on per-IPsec Child Security Association basis and the details are provided in clause 5.6.2.2.

The 5GC to which the 5G ProSe Layer-3 UE-to-Network Relay registers and the 5GC to which the 5G ProSe Layer-3 Remote UE registers may be in the same PLMN or different PLMN.

5.4.1.3 Policy control and session binding to support 5G ProSe Layer-3 UE-to-Network Relay without N3IWF

To enable support for policy control for 5G ProSe Layer-3 Remote UEs accessing 5GC via a 5G ProSe Layer-3 UE-to-Network Relay without involving N3IWF, the policy control functionality specified in TS 23.503 [9] is applied with the following functionalities:

– The 5G ProSe Layer-3 UE-to-Network Relay, the SMF and PCF may be configured with a dedicated DNN for UE-to-Network Relay connectivity.

NOTE 1: If Local Breakout configuration is supported for relay connectivity, the dedicated DNN needs to be well-known DNN to allow seamless operation across various operators’ networks.

– The AF discovers the PCF serving the 5G ProSe Layer-3 UE-to-Network Relay PDU Session as specified in clause 6.1.1.2 of TS 23.503 [9].

– The PCF may validate any 5G ProSe Layer-3 Remote UE related service information from the AF based on roaming agreement and the dedicated DNN for UE-to-Network Relay functionality.

NOTE 2: For 5G ProSe Layer-3 UE-to-Network Relay connectivity, the UE identity that the SMF has provided (i.e. 5G ProSe Layer-3 UE-to-Network Relay Identity) and a UE identity provided by the AF (i.e. 5G ProSe Layer-3 Remote UE Identity) can be different, while the Session binding with the PDU Session is valid.

– The 5G ProSe Layer-3 Remote UEs may be assigned a /64 IPv6 Prefix from a shorter IPv6 prefix by the 5G ProSe Layer-3 UE-to-Network Relay.

– For a PDU Session to the dedicated DNN for 5G ProSe Layer-3 UE-to-Network Relay connectivity and using IPv6 prefix delegation (i.e. the assigned IPv6 network prefix is shorter than 64), the PCF shall perform session binding based on the IPv6 network prefix only. A successful session binding occurs whenever a longer prefix received from an AF matches the prefix value of the PDU Session. PCF shall not use the UE Identity for session binding for this PDU Session.

5.4.2 5G ProSe Layer-2 UE-to-Network Relay

The 5G ProSe Layer-2 UE-to-Network Relay provides forwarding functionality that can relay any type of traffic over the PC5 link.

The 5G ProSe Layer-2 UE-to-Network Relay provides the functionality to support connectivity to the 5GS for 5G ProSe Layer-2 Remote UEs. A UE is considered to be a 5G ProSe Layer-2 Remote UE if it has successfully established a PC5 link to the 5G ProSe Layer-2 UE-to-Network Relay. A 5G ProSe Layer-2 Remote UE can be located within NG-RAN coverage or outside of NG-RAN coverage.

For PLMN selection and relay selection in the 5G ProSe Layer-2 Remote UE:

– The 5G ProSe Layer-2 Remote UE checks whether the PLMN(s) within the RRC Container (see clause 5.8.3.3) obtained from the 5G ProSe Layer-2 UE-to-Network Relay(s) during 5G ProSe UE-to-Network Relay Discovery in clause 6.3.2.3 are authorized to be connected to via a 5G ProSe Layer-2 UE-to-Network Relay(s), and only the authorized PLMN(s) are then available PLMNs for NAS PLMN selection;

– The 5G ProSe Layer-2 Remote UE selects the 5G ProSe Layer-2 UE-to-Network Relay considering the selected PLMN by NAS layer.

The 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay may use the PC5 DRX mechanism to perform 5G ProSe UE-to-Network Relay Communications over PC5 reference point as specified in clause 5.13.

5.4.3 Mobility Restrictions for 5G ProSe UE-to-Network Relaying

The handling of Mobility Restrictions for 5G ProSe enabled UE follows the principles as specified in clause 5.3.4.1 of TS 23.501 [4] with the following additions and clarifications:

– Forbidden Area:

– In a Forbidden Area, a 5G ProSe enabled UE is not allowed to perform the Relay operation. If the 5G ProSe UE-to-Network Relay operates in a Forbidden Area of the 5G ProSe Remote UE, the 5G ProSe Remote UE is not allowed to access the network via this 5G ProSe UE-to-Network Relay.

– Service Area Restriction:

– Service Area Restriction is not applicable to 5G ProSe Layer-3 Remote UE.

– Service Area Restriction is not applicable to 5G ProSe enabled MCX-subscribed UEs as defined in clause 5.3.4.1 of TS 23.501 [4].

NOTE 1: It is expected that all 5G ProSe enabled Public Safety UEs are MCX-subscribed as defined in clause 5.16.6 of TS 23.501 [4].

– In a Non-Allowed Area, a 5G ProSe enabled UE follows the principles of a UE in limited service state as specified in clause 5.9. It cannot perform the Relay operation as 5G ProSe Layer-2 UE-to-Network Relay or 5G ProSe Layer-3 UE-to-Network Relay based on the conditions described in clause 5.9.

– In a Non-Allowed Area, a 5G ProSe Layer-2 Remote UE follows the principles as specified in clause 5.3.4.1 of TS 23.501 [4], for communication with the network via the 5G ProSe Layer-2 UE-to-Network Relay.

– Core Network type restriction, RAT type restriction:

In these cases, a 5G ProSe enabled UE is not able to register in the network and stays in limited service state, and the principles in clause 5.9 shall apply.

NOTE 2: Closed Access Group information is not specified for 5G ProSe.

NOTE 3: Principles of operation for emergency services (incl. exceptions from mobility restrictions) are not specified in Rel-17.

5.5 IP address allocation

5.5.1 General

5.5.1.1 IP address allocation for unicast mode of 5G ProSe direct communication

For unicast mode of 5G ProSe direct communication, the following mechanism for IP address/prefix allocation may be used:

a) DHCP-based IPv4 address allocation with one of the two UEs acting as a DHCP server.

b) IPv6 Stateless Address auto configuration specified in RFC 4862 [17] for assignment of IPv6 prefix, with one of the two UEs acting as IPv6 default router.

NOTE: Which UE acts as a DHCPv4 server or IPv6 default router is negotiated during secure layer-2 link establishment by exchanging the IP Address Configuration as described in clause 6.4.3.

c) IPv6 link-local addresses as defined in RFC 4862 [17] are formed by UEs locally. The IPv6 link-local addresses are exchanged during the establishment of a secure layer-2 link over PC5. The UEs shall disable duplicate address detection after the layer-2 link is established.

5.5.1.2 IP address allocation for broadcast and groupcast modes of 5G ProSe direct communication

For broadcast and groupcast modes of 5G ProSe direct communication, the following source IP address management applies:

a) the UE configures a link local IPv4 address to be used as the source IP address, as defined in clause 4.5.3 of TS 23.303 [3]. If it is not configured with an address, it uses Dynamic Configuration of IPv4 Link-Local Addresses RFC 3927 [18].

b) the UE configures a link local IPv6 address to be used as the source IP address, as defined in clause 4.5.3 of TS 23.303 [3]. The UE may use this IP address for direct communication without sending Neighbour Solicitation and Neighbour Advertisement message for Duplicate Address Detection.

NOTE: The destination IP address management for broadcast and groupcast modes of ProSe direct communication is left to UE implementation.

5.5.1.3 IP address allocation for communication with a 5G ProSe Layer-3 ProSe UE-to-Network Relay

For communication with a 5G ProSe Layer-3 UE-to-Network Relay, the following mechanism for IP address/prefix allocation applies:

– The PDU Session Type used for the relay traffic shall support the IP version used by the 5G ProSe Layer-3 Remote UE. If the 5G ProSe Layer-3 Remote UE initiates an allocation of IPv4 address or an IPv6 prefix when the requested IP version is not supported in the corresponding PDU Session then IP address/prefix allocation fails.

a) When the 5G ProSe Layer-3 Remote UE uses IPv4 to access the external DN:

a1) The IPv4 address allocation and IPv4 parameter configuration via DHCPv4 are performed according to RFC 2131 [24] and RFC 4039 [25] procedures. The IPv4 address provided to the 5G ProSe Layer-3 Remote UE from the 5G ProSe Layer-3 UE-to-Network Relay by DHCPv4 procedure shall correspond to a local IPv4 address range configured in the 5G ProSe Layer-3 UE-to-Network Relay.

a2) The DHCPv4 request from the 5G ProSe Layer-3 Remote UE is always sent subsequent to the establishment of the one-to-one 5G ProSe Direct Communication between the 5G ProSe Layer-3 Remote UE and the 5G ProSe Layer-3 UE-to-Network Relay, see details for the IPv4 address allocation in clause 5.4.4.3 of TS 23.303 [3] with the following difference:

– The ProSe Relay UE ID of the ProSe UE-to-Network Relay is replaced by the source Layer-2 ID of the 5G ProSe UE-to-Network Relay for PC5 unicast communication.

b) When the 5G ProSe Layer-3 Remote UE uses IPv6 to access the external DN:

b1) IPv6 network prefix allocation via IPv6 Stateless Address auto-configuration. Router solicitation from the 5G ProSe Layer-3 Remote UE is always sent subsequent to the establishment of the one-to-one ProSe Direct Communication between the 5G ProSe Layer-3 Remote UE and the 5G ProSe Layer-3 UE-to-Network Relay, see details for IPv6 prefix allocation in clause 5.4.4.2 of TS 23.303 [3] with the following differences:

– The 5G ProSe Layer-3 UE-to-Network Relay shall obtain the IPv6 prefix assigned to the 5G ProSe Layer-3 Remote UE via prefix delegation function from the network as defined in clause 5.5.2.

– The ProSe Relay UE ID of the ProSe UE-to-Network Relay is replaced by the source Layer-2 ID of the 5G ProSe UE-to-Network Relay for PC5 unicast communication.

– PDN connection is replaced by PDU Session.

b2) IPv6 parameter configuration via Stateless DHCPv6: The UE may use stateless DHCPv6 for additional parameter configuration.

b3) The 5G ProSe Layer-3 UE-to-Network Relay assigns IPv6 prefixes from IPv6 prefix range that have been assigned to the PDU Session used for the relay traffic via IPv6 prefix delegation.

5.5.2 IPv6 Prefix Delegation via DHCPv6 for 5G ProSe Layer-3 UE-to-Network Relay

Optionally a single network prefix shorter than the default /64 prefix may be assigned to a PDU Session. In this case, the /64 default prefix used for IPv6 stateless autoconfiguration will be allocated from this network prefix; the remaining address space from the network prefix can be delegated to the PDU Session using prefix delegation after the PDU Session establishment and IPv6 prefix allocation via IPv6 stateless address autoconfiguration as defined in clause 5.8.2.2.3 of TS 23.501 [4]. When PLMN based parameter configuration is used, the SMF provides the requested IPv6 prefix from a locally provisioned pool. When external DN based IPv6 prefix allocation is used, the SMF obtains the prefix from the external DN.

NOTE: Allocation of IPv6 prefixes with flexible prefix length can leverage e.g. local configuration on the SMF or interaction with the AAA server.

The address space provided is maintained as an IPv6 address space pool available to the PDU Session for DHCPv6 IPv6 prefix requests with the exclusion of the IPv6 prefix that is allocated to the PDU Session during PDU Session establishment as defined in clause 5.8.2.2.3 of TS 23.501 [4]. The total IPv6 address space available for the PDU Session (UE PDU Session prefix and UE PDU Session IPv6 address space pool) shall be possible to aggregate into one IPv6 prefix that will represent all IPv6 addresses that the UE may use. If the UE had indicated that it supports prefix exclusion and the prefix to be delegated to the UE includes the /64 prefix that was allocated to the PDU Session, the SMF shall utilise the prefix exclusion feature as specified for DHCPv6 Prefix Delegation in RFC 6603 [26].

The UE uses DHCPv6 to request additional IPv6 prefixes (i.e. prefixes in addition to the default prefix) from the SMF after completing stateless IPv6 address autoconfiguration procedures. The UE acts as a "Requesting Router" as described in RFC 8415 [27] and inserts one or more IA_PD option(s) into a DHCPv6 Solicit message sent from the UE to the SMF. The SMF acts as the DHCP server and fulfils the role of a "Delegating Router" according to RFC 8415 [27]. The UE optionally includes the RAPID_COMMIT option in the DHCPv6 Solicit message to trigger two-message DHCPv6 procedure instead of the four-message DHCPv6 procedure. The UE shall include OPTION_PD_EXCLUDE option code in an OPTION_ORO option to indicate support for prefix exclusion. In response to the DHCPv6 Solicit message, the UE receives a DHCPv6 Reply message with one or more IA_PD prefix(es) for every IA_PD option that it sent in the DHCPv6 Solicit message. The SMF delegates a prefix excluding the default prefix with help of OPTION_PD_EXCLUDE. Prefix exclusion procedures shall follow RFC 6603 [26].

5.6 QoS handling

5.6.1 QoS handling for 5G ProSe Direct Communication

In order to support QoS handling for 5G ProSe Direct Communication, the mechanism defined in clause 5.4 of TS 23.287 [2] is reused with the following differences:

– Only NR PC5 QoS model is used.

– PC5 Packet Filter Set supports three types of packet filters, i.e. the Prose IP Packet Filter Set, ProSe Ethernet Packet Filter Set, and the Prose Packet Filter Set. Each PC5 QoS Rule additionally contains the ProSe identifier when the ProSe identifier is not included in the PC5 Packet Filter Set.

– V2X IP Packet Filter Set is replaced by ProSe IP Packet Filter Set.

– V2X Packet Filter Set is replaced by ProSe Packet Filter Set. ProSe Packet Filter Set shall support Packet Filters based on at least any combination of:

– ProSe identifier;

– Source/Destination Layer-2 ID;

– Application Layer ID.

– ProSe Ethernet Packet Filter Set that has the same format as the Ethernet Packet Filter Set defined in clause 5.7.6.3 of TS 23.501 [4] is additionally defined.

– V2X application layer is replaced by ProSe application layer.

– V2X layer is replaced by ProSe layer.

– V2X service type is replaced by ProSe identifier.

– UE-PC5-AMBR is only applied for NR PC5.

– The PQI values are additionally defined. The one-to-one mapping of standardized PQI values that are additionally defined to PC5 QoS characteristics is specified in table 5.6.1-1.

Table 5.6.1-1: Standardized PQI values that are additionally defined to QoS characteristics mapping

PQI Value	Resource Type	Default Priority Level	Packet Delay Budget	Packet Error Rate	Default Maximum Data Burst Volume	Default Averaging Window	Example Services
24	GBR (NOTE 1)	1	150 ms	10^-2	N/A	2000 ms	Mission Critical user plane Push To Talk voice (e.g. MCPTT)
25		2	200 ms	10^-2	N/A	2000 ms	Non-Mission-Critical user plane Push To Talk voice
26		2	200 ms	10^-3	N/A	2000 ms	Mission Critical Video user plane
60	Non-GBR	1	120 ms	10^-6	N/A	N/A	Mission Critical delay sensitive signalling (e.g. MC-PTT signalling)
61		6	400 ms	10^-6	N/A	N/A	Mission Critical Data (e.g. example services are the same as 5QI 6/8/9 as specified in TS 23.501 [4])
92	Delay Critical GBR (NOTE 1)	5	5ms	10^-4	20000 bytes	2000 ms	Interactive service – consume VR content with high compression rate via tethered VR headset (See TS 22.261 [6])
93		6	10ms	10^-4	20000 bytes	2000 ms	interactive service – consume VR content with low compression rate via tethered VR headset; Gaming or Interactive Data Exchanging (See TS 22.261 [6])
NOTE 1: GBR and Delay Critical GBR PQIs can only be used for unicast PC5 communications.

5.6.2 QoS handling for 5G ProSe UE-to-Network Relay operations

5.6.2.1 QoS handling for 5G ProSe Layer-3 UE-to-Network Relay without N3IWF

For a 5G ProSe Layer-3 Remote UE accessing network via 5G ProSe Layer-3 UE-to-Network Relay without N3IWF, the QoS requirement of the relay traffic between 5G ProSe Layer-3 Remote UE and UPF can be satisfied by the corresponding QoS control for the PC5 link between 5G ProSe Layer-3 Remote UE and 5G ProSe Layer-3 UE-to-Network Relay (PC5 QoS control) and the QoS control for the PDU session established between 5G ProSe Layer-3 UE-to-Network Relay and UPF (i.e. Uu QoS control). The PC5 QoS is controlled with PC5 QoS rules and PC5 QoS parameters (e.g. PQI, GFBR, MFBR, PC5 LINK-AMBR) as specified in clause 5.4 of TS 23.287 [2]. The QoS for the PDU session established between the 5G ProSe Layer-3 UE-to-Network Relay and UPF (i.e. Uu QoS control) is controlled with QoS rules and 5G QoS parameters (e.g. 5QI, GFBR, MFBR) as specified in clause 5.7 of TS 23.501 [4].

As shown in figure 5.6.2.1-1 below, the end-to-end QoS can be met only when the QoS requirements are properly translated and satisfied over the two legs respectively.

Figure 5.6.2.1-1: End-to-End QoS translation for 5G ProSe Layer-3 UE-to-Network Relay operation

To achieve this, the QoS mapping can be pre-configured or provided to the 5G ProSe Layer-3 UE-to-Network Relay by the PCF using Prose Policy as specified in clause 5.1.4.1. The QoS mapping includes combinations of the 5QIs and PQIs mapping as entries. The PQI shall have standardized values as defined in Table 5.6.1-1 and in Table 5.4.4-1 of TS 23.287 [2]. The 5QI shall have standardized values as defined in TS 23.501 [4] clause 5.7.4. The QoS mapping also includes an adjustment factor for the PQI’s PDB, e.g. 1/5of the standardized PDB value in Table 5.6.1-1 and Table 5.4.4-1 of TS 23.287 [2].

If the QoS Flows setup are initiated by network, the SMF can base on the PCC rules or its local configuration to generates the QoS rules and QoS Flow level QoS parameters (e.g. 5QI, GFBR, MFBR) and signal to the 5G ProSe Layer-3 UE-to-Network Relay using PDU Session Establishment/Modification procedure. For the PDU sessions used for relaying, the SMF always provides the QoS Flow level QoS parameters to the 5G ProSe Layer-3 UE-to-Network Relay when establishes a QoS Flow. Then the 5G ProSe Layer-3 UE-to-Network Relay decides the PC5 QoS parameters for the corresponding PC5 QoS Flow by determining the PQI based the QoS mapping, and the GFBR and MFBR values for the PC5 GBR QoS Flow are set equal to the GFBR and MFBR values for the GBR QoS Flow respectively. The PCF differentiates the relay traffic based on either local configuration, e.g.by a dedicated DNN or S-NSSAI used for relay traffic or by the traffic filters.

NOTE: Separate QoS mappings can be configured for different RSCs.

If the 5G ProSe Layer-3 Remote UE initiates PC5 QoS Flows setup or modification during the Layer-2 link establishment or modification procedure, the 5G ProSe Layer-3 Remote UE provides the QoS Info as described in clause 6.4.3.6 to the 5G ProSe Layer-3 UE-to-Network Relay. The received PC5 QoS parameters of the QoS Info (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) are interpreted as the end-to-end QoS requirements by the 5G ProSe Layer-3 UE-to-Network Relay for the traffic transmission between 5G ProSe Layer-3 Remote UE and UPF. If the end-to-end QoS requirements can be supported by an entry in QoS mapping, the 5G ProSe Layer-3 UE-to-Network Relay uses the 5QI of the entry for the Uu QoS control, and uses the PQI of the entry for the PC5 QoS control. If the end-to-end QoS requirements cannot be supported by any entries in QoS mapping, the 5G ProSe Layer-3 UE-to-Network Relay, based on its implementation, decides the 5QI for the Uu QoS control and PQI for the PC5 QoS control. The 5G ProSe Layer-3 UE-to-Network Relay provides the QoS Info (including PQI value chosen by the 5G ProSe Layer-3 UE-to-Network Relay) as part of the Accept message to the 5G ProSe Layer-3 Remote UE. If the 5G ProSe Layer-3 Remote UE performs the Layer-2 link modification procedure to add new PC5 QoS Flow(s) or modify the existing PC5 QoS Flow(s) for IP traffic or Ethernet traffic over PC5 reference point, the 5G ProSe Layer-3 Remote UE may also provide the PC5 QoS Rule(s) for the PC5 QoS Flow(s) to be added or modified to the 5G ProSe Layer-3 UE-to-Network Relay. The 5G ProSe Layer-3 UE-to-Network Relay may generate the Packet Filters used over Uu reference point based on the received PC5 QoS Rule(s).

The 5G ProSe Layer-3 UE-to-Network Relay performs the UE requested PDU session Modification as defined in TS 23.502 [5], clause 4.3.3 for authorizing the requested QoS including the 5QI and the Packet Filters. If the PCF authorizes the requested QoS with a different 5QI value, the 5G ProSe Layer-3 UE-to-Network Relay may further update the PQI value based on the authorized 5QI value, and the 5G ProSe Layer-3 UE-to-Network Relay performs the Layer-2 link modification procedure as defined in clause 6.4.3.6 to update the corresponding PC5 QoS Flow with the updated PQI value.

Alternatively, reflective QoS control over Uu as defined in TS 23.501 [4], clause 5.6.5.3 can be leveraged for dynamic QoS handling of 5G ProSe Layer-3 Remote UE to save on signalling between SMF and 5G ProSe Layer-3 UE-to-Network Relay. Upon reception of a DL packet with RQI on the Uu for the 5G ProSe Layer-3 Remote UE, based on the indicated QFI, the 5G ProSe Layer-3 UE-to-Network Relay creates a new derived QoS rule or updates existing derived QoS rule corresponding to the remote UE, as defined in TS 23.501 [4]. The derived QoS rule is for UL packets from the 5G ProSe Layer-3 Remote UE at Uu interface.

Based on signalled QoS rules (via SMF) or derived QoS rules (Uplink Uu via reflective QoS), the 5G ProSe Layer-3 UE-to-Network Relay may generate the Packet Filters used over PC5 reference point and use the L2 Link Modification procedures as defined in clause 6.4.3.6 to either update existing PC5 QoS Flow(s) or to set up new PC5 QoS Flow(s) (when the QFI to PC5 QoS Flow mapping does not exist). The 5G ProSe Layer-3 UE-to-Network Relay may also provide the PC5 QoS Rule(s) for the PC5 QoS Flow(s) to be added or modified to the 5G ProSe Layer-3 Remote UE.

When the 5G ProSe Layer-3 UE-to-Network relay deletes the derived QoS rule e.g. after the RQ Timer expires, the 5G ProSe Layer-3 UE-to-Network Relay may perform L2 Link Modification procedures defined in clause 6.4.3.6 accordingly using the PQI mapped from the 5QI of the currently used QoS rule after the deletion of the derived QoS rule(s).

5.6.2.2 QoS handling for 5G ProSe Layer-3 UE-to-Network relay with N3IWF

When accessing 5GS via a 5G ProSe Layer-3 UE-to-Network Relay with N3IWF, the 5G ProSe Layer-3 Remote UE can request for PDU Session establishment or handover an existing PDU session to the N3IWF using UE requested PDU Session Establishment procedure defined in TS 23.502 [5] clause 4.12.5.

Figure 5.6.2.2-1: End-to-End QoS support via Layer-3 UE-to-Network Relay with N3IWF

For the 5G ProSe Layer-3 Remote UE’s PDU session(s) established via N3IWF, QoS differentiation can be provided on per-IPsec Child Security Association basis. N3IWF determines the IPsec child SAs as defined in TS 23.502 [5] clause 4.12. The N3IWF is preconfigured to allocate different IPsec child SAs for QoS Flows with different QoS profiles.

Based on configuration, the N3IWF can use one of the options below for QoS support in 5G ProSe Layer-3 UE-to-Network Relay UE’s serving PLMN:

– a static QoS mapping mechanism;

– a dynamic QoS signalling based mechanism.

For the static QoS mapping mechanism, a SLA is established to govern the QoS handling between the 5G ProSe Layer-3 Remote UE’s 5GC and the 5G ProSe Layer-3 UE-to-Network Relay UE’s 5GC, e.g. when the RSC is configured. The SLA can include the mapping between the DSCP markings for the IPsec child SAs with the Remote UE and the corresponding QoS, and N3IWF IP address(es). The non-alteration of the DSCP field between N3IWF and the 5G ProSe Layer-3 UE-to-Network Relay UE’s UPF is also assumed to be governed by an SLA and by transport-level arrangements that are outside of 3GPP scope. The packet detection filters at the 5G ProSe Layer-3 UE-to-Network Relay UE’s UPF can be based on the N3IWF IP address and the DSCP markings.

When the dynamic QoS signalling based mechanism is used by N3IWF, it works as follows:

– When the 5G ProSe Layer-3 Remote UE establishes or handovers a PDU session via the N3IWF as described in clause 4.12.5 of TS 23.502 [5], the PCF serving the PDU Session in the 5G ProSe Layer-3 Remote UE’s 5GC detects need for specific QoS and provides corresponding PCC rules to SMF in the 5G ProSe Layer-3 Remote UE’s 5GC. The resulted QoS information is provided to N3IWF in step 2b of clause 4.12.5 of TS 23.502 [5]. The N3IWF determines the IPSec Child SA(s) and signals to the 5G ProSe Layer-3 Remote UE, as in step 4 of clause 4.12.5 of TS 23.502 [5] via IKE signalling including the PDU Session ID, the QFI(s), optionally a DSCP value, and optionally the Additional QoS Information specified in clause 4.12.5 of TS 23.502 [5]. The PDU Session Establishment Accept message will be sent to the 5G ProSe Layer-3 Remote UE as in step 5 of clause 4.12.5 of TS 23.502 [5].

– Based on Additional QoS Information received from the N3IWF, the 5G ProSe Layer-3 Remote UE determines whether it is necessary to request for QoS session modification for the dedicated QoS Flows toward the 5G ProSe Layer-3 UE-to-Network Relay as described in clause 5.6.2.1. The 5G ProSe Layer-3 Remote UE also provides the N3IWF address, DSCP and the SPI as the traffic filter to enable filtering and mapping of DL traffic towards the right PDU Session/QoS Flow within the 5G ProSe Layer-3 UE-to-Network Relay UE’s 5GC.

NOTE: This mechanism allows to communicate GBR related parameters such as GFBR and MFBR from the PCF of the 5G ProSe Layer-3 Remote UE via the N3IWF and the 5G ProSe Layer-3 Remote UE to the 5G ProSe Layer-3 UE-to-Network Relay UE. The 5G ProSe Layer-3 UE-to-Network Relay UE would be able to request the GBR resources from its serving network using UE requested PDU session modification as in clause 4.3.3. of TS 23.502 [5].

– If the 5G ProSe Layer-3 UE-to-Network Relay performs the PDU Session Modification procedure, the PCF in the 5G ProSe Layer-3 UE-to-Network Relay UE’s 5GC authorizes the QoS parameters. If the PDU Session Modification procedure authorized the requested QoS parameters, the 5G ProSe Layer-3 UE-to-Network Relay acknowledges the 5G ProSe Layer-3 Remote UE over PC5. The 5G ProSe Layer-3 UE-to-Network Relay also provides the traffic filter provided by the 5G ProSe Layer-3 Remote UE to the SMF during the PDU Session Modification procedure, and the SMF updates the PSA UPF with DL Packet Detection Rules.

– The PSA UPF in the 5G ProSe Layer-3 UE-to-Network Relay UE’s 5GC maps the DL traffic from IPSec Child SA tunnel to appropriate PDU Session/QoS Flow considering SPI and N3IWF address (filters provided by the 5G ProSe Layer-3 Remote UE).

– The 5G ProSe Layer-3 Remote UE’s or the 5G ProSe Layer-3 Remote UE’s 5GC may initiated PDU Session Modification procedures as specified in clause 4.12.6 of TS 23.502 [5]. When the 5G ProSe Layer-3 Remote UE received QoS information from the N3IWF, the same interactions between the 5G ProSe Layer-3 Remote UE and 5G ProSe Layer-3 UE-to-Network Relay, and between the 5G ProSe Layer-3 UE-to-Network Relay and its 5GC as described above apply.

5.6.2.3 QoS handling for 5G ProSe Layer-2 UE-to-Network Relay

For a 5G ProSe Layer-2 Remote UE accessing network via 5G ProSe Layer-2 UE-to-Network Relay, the existing 5G QoS control is reused between the 5G ProSe Layer-2 Remote UE and the 5G ProSe Layer-2 Remote UE’s core network. The 5G ProSe Layer-2 Remote UE’s SMF provides QoS profiles to NG-RAN, how NG-RAN performs QoS enforcement for PC5 interface (between the 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay) and Uu interface (between the 5G ProSe Layer-2 UE-to-Network Relay and RAN) is specified in TS 38.300 [12].

5.7 Subscription to 5G ProSe

The subscription information in the UDM contains information to give the user permission to use 5G ProSe.

At any time, the operator can amend or remove the ProSe UE subscription rights from subscription information in the UDM, or to revoke the user’s permission to use 5G ProSe.

The following subscription information is defined for 5G ProSe:

– subscription for open 5G ProSe Direct Discovery for NR PC5:

– open 5G ProSe Direct Discovery Model A.

– subscription for restricted 5G ProSe Direct Discovery for NR PC5:

– restricted 5G ProSe Direct Discovery Model A;

– restricted 5G ProSe Direct Discovery Model A with application-controlled extension;

– restricted 5G ProSe Direct Discovery Model A with "on demand" announcing;

– restricted 5G ProSe Direct Discovery Model B.

– subscription for Broadcast, Groupcast and Unicast mode 5G ProSe Direct Communication for NR PC5.

– subscription for 5G ProSe UE acting as 5G ProSe Layer-2 UE-to-Network Relay.

– subscription for 5G ProSe UE acting as 5G ProSe Layer-3 UE-to-Network Relay.

– subscription for 5G ProSe Layer-2 Remote UE access via 5G ProSe Layer-2 UE-to-Network Relay

– subscription for 5G ProSe Layer-3 Remote UE access via 5G ProSe Layer-3 UE-to-Network Relay

– UE-PC5-AMBR for NR PC5.

– PC5 QoS parameters as defined in clause 5.6.1 used by NG-RAN.

– the list of the PLMNs authorized for 5G ProSe services, including:

– the list of the PLMNs where the UE is authorised for open 5G Direct Discovery Model A, i.e. to announce or monitor or both.

– the list of the PLMNs where the UE is authorised for restricted 5G ProSe Direct Discovery Model A, i.e. to announce or monitor or both.

– the list of the PLMNs where the UE is authorised for restricted 5G ProSe Direct Discovery Model B, i.e. to perform Discoverer operation or Discoveree operation or both.

– the list of the PLMNs where the UE is authorised to perform Broadcast, Groupcast and Unicast mode 5G ProSe Direct Communication for NR PC5.

– the list of the PLMNs where the UE is authorised to act as a 5G ProSe Layer-2 UE-to-Network Relay.

– the list of the PLMNs where the UE is authorised to act as a 5G ProSe Layer-3 UE-to-Network Relay.

– the list of the PLMNs where the UE is authorised to act as a 5G ProSe Layer-2 Remote UE.

5.8 Identifiers

5.8.1 Identifiers for 5G ProSe Direct Discovery

5.8.1.0 General

NOTE: The 5G DDNMF takes the role of "ProSe Function" if it exists in the following definitions in TS 23.303 [3].

5.8.1.1 ProSe Application ID

ProSe Application ID is defined in TS 23.303 [3].

5.8.1.2 Destination Layer-2 ID

Destination Layer-2 ID is defined in clause 5.6.1 of TS 23.287 [2].

The Destination Layer-2 ID for 5G ProSe Direct Discovery with Model A is selected based on the configuration as described in clause 5.1.2.1. The Destination Layer-2 ID for a Solicitation message for Model B is selected based on the configuration as described in clause 5.1.2.1.

For Group member discovery:

– If an Application Layer Group ID has a configured Layer-2 Group ID, which is provisioned as specified in clause 5.1.2.1, the UE uses this Layer-2 Group ID as the Destination Layer-2 ID,

– otherwise, the UE converts the Application Layer Group ID into a Destination Layer-2 ID.

NOTE: The mechanism for converting the application layer provided Application Layer Group ID to the Destination Layer-2 ID is defined in Stage 3.

5.8.1.3 Source Layer-2 ID

Source Layer-2 ID is defined in clause 5.6.1 of TS 23.287 [2].

The UE self-selects a Source Layer-2 ID for 5G ProSe Direct Discovery and Group member discovery.

NOTE: The UE implementation needs to ensure that when the UE self-selects Source Layer-2 IDs, the self-selected Source Layer-2 IDs are different between 5G ProSe Direct Discovery (including 5G ProSe UE-to-Network Relay Discovery) in clause 6.3.2 and 5G ProSe Direct Communication (including 5G ProSe UE-to-Network Relay Communication) in clause 6.4, and are different from any other provisioned Destination Layer-2 IDs as described in clause 5.1 and any other self-selected Source Layer-2 IDs used in a simultaneous 5G ProSe Direct Discovery (including 5G ProSe UE-to-Network Relay Discovery) with a different discovery model.

5.8.1.4 ProSe Application Code

ProSe Application Code is defined in TS 23.303 [3].

5.8.1.5 ProSe Restricted Code

ProSe Restricted Code is defined in TS 23.303 [3].

5.8.1.6 ProSe Query Code

ProSe Query Code is defined in TS 23.303 [3].

5.8.1.7 ProSe Response Code

ProSe Response Code is defined in TS 23.303 [3].

5.8.1.8 User Info ID

User Info ID (including Announcer Info, Discoverer Info, Discoveree Info) is defined in clause 3.1.

5.8.1.9 ProSe Discovery UE ID

ProSe Discovery UE ID is defined in TS 23.303 [3].

5.8.1.10 Restricted ProSe Application User ID

Restricted ProSe Application User ID is defined in TS 23.303 [3].

5.8.1.11 Announcing PLMN ID

Announcing PLMN ID is defined in TS 32.277 [22].

5.8.1.12 Announcer Info

Announcer Info is one of the uses of User Info ID as described in clause 5.8.1.8.

5.8.1.13 Discoverer Info

Discoverer Info is one of the uses of User Info ID as described in clause 5.8.1.8.

5.8.1.14 Target Info

Target Info provides information about the targeted discoveree in the Group Member Discovery Solicitation message specified in clause 6.3.2.2.3 and in the 5G ProSe UE-to-Network Relay Discovery Solicitation message specified in clause 6.3.2.3.3. The Target Info is the User Info ID of the discoveree.

5.8.1.15 Discoveree Info

Discoveree Info is one of the uses of User Info ID as described in clause 5.8.1.8.

5.8.1.16 Application Layer Group ID

Application Layer Group ID is defined in TS 23.303 [3].

5.8.2 Identifiers for 5G ProSe Direct Communication

5.8.2.1 General

Each UE has one or more Layer-2 IDs for 5G ProSe direct communication over PC5 reference point, consisting of:

– Source Layer-2 ID(s); and

– Destination Layer-2 ID(s).

Source and Destination Layer-2 IDs are included in layer-2 frames sent on the layer-2 link of the PC5 reference point identifying the layer-2 source and destination of these frames. Source Layer-2 IDs are always self-assigned by the UE originating the corresponding layer-2 frames.

The selection of the Source and Destination Layer-2 ID(s) by a UE depends on the communication mode of 5G ProSe direct communication over PC5 reference point for this layer-2 link, as described in clauses 5.8.2.2, 5.8.2.3, and 5.8.2.4. The Source Layer-2 IDs may differ between different communication modes.

5.8.2.2 Identifiers for broadcast mode 5G ProSe direct communication

For broadcast mode of 5G ProSe direct communication over PC5 reference point, the UE is configured with the Destination Layer-2 ID(s) to be used for ProSe applications. The Destination Layer-2 ID for a 5G ProSe direct communication is selected based on the configuration as described in clause 5.1.3.1.

The UE self-selects a Source Layer-2 ID.

5.8.2.3 Identifiers for groupcast mode 5G ProSe direct communication

For groupcast mode of 5G ProSe direct communication over PC5 reference point, the application layer may provide Application Layer Group ID.

The UE determines a Destination Layer-2 ID as below:

– When the Application Layer Group ID is provided by the application layer,

– and when ProSe Layer-2 Group ID is configured for the Application Layer Group ID provided by the application layer as specified in clause 5.1.3.1, the UE uses the ProSe Layer-2 Group ID as the Destination Layer-2 ID; or

– and when ProSe Layer-2 Group ID is not configured for the Application Layer Group ID provided by the application layer, the UE converts the Application Layer Group ID into a Destination Layer-2 ID.

– When the Application Layer Group ID is not provided by the application layer, the UE determines the Destination Layer-2 ID based on configuration of the mapping between ProSe Identifier and Layer-2 ID, as specified in clause 5.1.3.1.

NOTE: The mechanism for converting the application layer provided Application Layer Group ID to the Destination Layer-2 ID is defined in Stage 3.

The UE self-selects a Source Layer-2 ID.

5.8.2.4 Identifiers for unicast mode 5G ProSe direct communication

For unicast mode of 5G ProSe direct communication over PC5 reference point, the Destination Layer-2 ID used depends on the communication peer. The Layer-2 ID of the communication peer, identified by the peer’s Application Layer ID, may be discovered during the establishment of the PC5 unicast link, or known to the UE via prior ProSe direct communications, e.g. existing or prior unicast link to the same Application Layer ID, or obtained from 5G ProSe direct discovery process. The initial signalling for the establishment of the PC5 unicast link may use the known Layer-2 ID of the communication peer, or a default destination Layer-2 ID associated with the ProSe service (i.e. ProSe identifier) configured for PC5 unicast link establishment, as specified in clause 5.1.3.1. During the PC5 unicast link establishment procedure, Layer-2 IDs are exchanged, and should be used for future communication between the two UEs, as specified in clause 6.4.3.

The UE maintains a mapping between the Application Layer IDs and the source Layer-2 IDs used for the PC5 unicast links, as the ProSe application layer does not use the Layer-2 IDs. This allows the change of source Layer-2 ID without interrupting the ProSe applications.

When Application Layer IDs change, the source Layer-2 ID(s) of the PC5 unicast link(s) shall be changed if the link(s) was used for 5G ProSe communication with the changed Application Layer IDs.

Based on privacy configuration as specified in clause 5.1.3.1, the update of the new identifiers of a source UE to the peer UE for the established unicast link may cause the peer UE to change its Layer-2 ID and optionally IP address/prefix if IP communication is used as defined in clause 6.4.3.2.

5.8.3 Identifiers for 5G ProSe UE-to-Network Relay

5.8.3.1 Common identifiers for 5G ProSe UE-to-Network Relay

The following parameters are used for the 5G ProSe UE-to-Network Relay Discovery Announcement message (Model A), where Source Layer-2 ID and Destination Layer-2 ID are used for sending and receiving the message, and Announcer Info and Relay Service Code are contained in the message:

– Source Layer-2 ID: the 5G ProSe UE-to-Network Relay self-selects a Source Layer-2 ID for 5G ProSe UE-to-Network Relay Discovery.

– Destination Layer-2 ID: the Destination Layer-2 ID for 5G ProSe UE-to-Network Relay Discovery is selected based on the configuration as described in clause 5.1.4.1.

– Announcer Info: provides information (i.e. User Info ID) about the announcing user.

– Relay Service Code: parameter identifying a connectivity service the 5G ProSe UE-to-Network Relay provides to a 5G ProSe Remote UE. The Relay Service Codes are configured in a 5G ProSe UE-to-Network Relay for advertisement. Additionally, the Relay Service Code may also identifies authorized users the 5G ProSe UE-to-Network Relay would offer service to, and may be used to select the related security policies or information e.g. necessary for authentication and authorization between the 5G ProSe Remote UE and the 5G ProSe UE-to-Network Relay (e.g. a Relay Service Code for relays for police members only would be different than a Relay Service Code for relays for Fire Fighters only, even though potentially they provided connectivity to same DN e.g. to support Internet Access).

The following parameters are used for the 5G ProSe UE-to-Network Relay Discovery Solicitation message (Model B), where Source Layer-2 ID and Destination Layer-2 ID are used for sending and receiving the message, and Discoverer Info and Relay Service Code are contained in the message:

– Source Layer-2 ID: the 5G ProSe Remote-UE self-selects a Source Layer-2 ID for 5G ProSe UE-to-Network Relay Discovery.

– Destination Layer-2 ID: the Destination Layer-2 ID for 5G ProSe UE-to-Network Relay Discovery is selected based on the configuration as described in clause 5.1.4.1.

– Discoverer Info: provides information (i.e. User Info ID) about the discoverer user.

– Target Info: provides information (i.e. User Info ID) about the targeted discoveree user.

– Relay Service Code: information about connectivity that the discoverer UE is interested in. The Relay Service Codes are configured in the 5G ProSe Remote UEs interested in related connectivity services.

The following parameters are used in the 5G ProSe UE-to-Network Relay Discovery Response message (Model B), where Source Layer-2 ID and Destination Layer-2 ID are used for sending and receiving the message, and Discoveree Info and Relay Service Code are contained in the message:

– Source Layer-2 ID: the 5G ProSe UE-to-Network Relay self-selects a Source Layer-2 ID for 5G ProSe UE-to-Network Relay Discovery.

– Destination Layer-2 ID: set to the Source Layer-2 ID of the received 5G ProSe UE-to-Network Relay Discovery Solicitation message.

– Relay Service Code: identifies the connectivity service the 5G ProSe UE-to-Network Relay provides to 5G ProSe Remote UEs that matches the Relay Service Code from the corresponding Discovery Solicitation message.

– Discoveree Info: provides information (i.e. User Info ID) about the discoveree.

The following parameters may be used in the Relay Discovery Additional Information message (for Model A) based on the procedure defined in clause 6.5.1.3 for 5G ProSe UE-to-Network Relay where Source Layer-2 ID and Destination Layer-2 ID are used for sending and receiving the message, and the other parameters are contained in the message:

– Source Layer-2 ID: the 5G ProSe UE-to-Network Relay self-selects a Source Layer-2 ID to send the Relay Discovery Additional Information message.

– Destination Layer-2 ID: the Destination Layer-2 ID to send the Relay Discovery Additional Information message is selected based on the configuration as described in clause 5.1.4.1.

– Relay Service Code: the Relay Service Code associated with the message. The Relay Service Code is used to identify the security parameters needed by the receiving UE to process the discovery message.

– Announcer Info: provides information about the announcing user.

– Additional parameters: the additional parameters for 5G ProSe Layer-3 UE-to-Network Relay (when applicable) are defined in clause 5.8.3.2.

5.8.3.2 Identifiers for 5G ProSe Layer-3 UE-to-Network Relay

For 5G ProSe Layer-3 UE-to-Network relay, a Relay Service Code in the Announcement Message is associated with a set of PDU session parameters (e.g. PDU Session type, DNN, SSC Mode, S-NSSAI, Access Type Preference). The Relay Service Code may also represent if the relay UE can provide secure N3IWF connection.

For 5G ProSe Layer-3 Remote UE discovering 5G ProSe Layer-3 UE-to-Network relay, the Relay Service Code in the Solicitation Message represents the PDU session parameters that a PDU session of the relay should be able to support. The Relay Service Code may also represent if the remote UE requires secure N3IWF connection.

The following additional parameters may be used in the Relay Discovery Additional Information message (for Model A) for 5G ProSe Layer-3 UE-to-Network Relay:

– NCGI: indicates the NCGI of the serving cell of the 5G ProSe Layer-3 UE-to-Network Relay. This parameter may be requested by application running on 5G ProSe Layer-3 Remote UE.

– TAI: indicates the Tracking Area Identity of the serving cell of the 5G ProSe Layer-3 UE-to-Network Relay. This parameter may be used by 5G ProSe Layer-3 Remote UE to select a N3IWF.

5.8.3.3 Identifiers for 5G ProSe Layer-2 UE-to-Network Relay

The following parameters may be used in Announcement message (Model A) or Response message (Model B) in addition to the parameters as specified in clause 5.8.3.1:

– NCGI: indicates the NCGI of the serving cell of the 5G ProSe Layer-2 UE-to-Network Relay for 5G ProSe Layer-2 UE-to-Network Relay (re)selection.

– RRC Container: An RRC container, as defined in TS 38.331 [16], which includes the cell access related information for the serving cell of the 5G ProSe Layer-2 UE-to-Network Relay.

5.9 Support for 5G ProSe for UEs in limited service state

For UE in limited service state, as defined in TS 23.122 [14], 5G ProSe can be used over PC5 reference point with the following considerations.

UEs that are authorized to use 5G ProSe over PC5 reference point according to clause 5.1 shall be able to use the corresponding services following the principles defined in clause 5.1.2.2 for 5G ProSe Direct Discovery, clause 5.1.3.2 for 5G ProSe Direct Communication, and clause 5.1.4.2 for 5G ProSe UE-to-Network Relay when the UE enters in limited service state in 5GS:

– because UE cannot find a suitable cell of the selected PLMN as described in TS 23.122 [14]; or

– as the result of receiving one of the following reject reasons defined in TS 23.122 [14]:

– a "PLMN not allowed" response to a registration request or;

– a "5GS services not allowed" response to a registration request or service request.

A UE in limited service state shall only use the radio resources and procedure available in CM-IDLE mode for ProSe over PC5 reference point, for details see TS 36.300 [11] and TS 38.300 [12].

UEs shall not use 5G ProSe over PC5 reference point using the "operator-managed" radio resources, as specified in clauses 5.1.2.1, 5.1.3.1 and 5.1.4.1, if the UE has entered in limited service state due to all other situations (e.g. no SIM in the MS, an "illegal MS" or "illegal ME" response to a registration request, or an "IMSI unknown in HLR" response to a registration request) defined in TS 23.122 [14], where the UE is unable to obtain normal service from a PLMN. The UEs may use ProSe over PC5 reference point using the "non-operator-managed" radio resources, as specified in clauses 5.1.2.1, 5.1.3.1 and 5.1.4.1, according to the corresponding principles defined in clauses 5.1.2.2, 5.1.3.2 and 5.1.4.2.

5.10 PC5 operation in EPS for Public Safety UE

When the UE is in EPS, the UE shall use the valid ProSe policy and parameters provisioned by the ProSe Function in EPC for ProSe Direct Discovery and Prose Direct Communication. If the UE does not have valid ProSe policy and parameters, the UE shall request the network to provision the ProSe policy and parameters.

The UE that is authorized to perform ProSe Direct Discovery and/or ProSe Direct Communication in EPS can perform the authorized PC5 operation in EPS as specified in TS 23.303 [3].

5.11 Communication path selection between PC5 and Uu reference points

The "communication path selection between PC5 and Uu reference points" refers to the procedure on how a UE selects a communication path between PC5 reference point and Uu reference point before it communicates with another UE. The communication path over PC5 reference point means that the communication with another UE is performed by using 5G ProSe Direct Communication only. The communication path over Uu reference point means that the communication with another UE is performed via the network.

NOTE 1: The communication via 5G ProSe UE-to-Network Relay (Layer-2 or Layer-3) can be considered as the communication path over Uu reference point, as it involves communication via the network.

Path selection policy is provided to the UE to indicate which path(s) is preferred for all or specific ProSe services (i.e. PC5 preferred, Uu preferred or no preference indicated) as specified in clause 5.1.3.1.

The ProSe Application Server can provide a path preference for ProSe Services to UDR as specified in clause 6.2.5 and this may be used by PCF for path selection policy generation and update as specified in clause 6.2.2.

NOTE 2: ProSe Application Server can use QoS Sustainability analytics defined in TS 23.288 [8] to determine the path preference.

The UE may use the provisioned path selection policy to select the appropriate communication path for all or specific ProSe services.

UE operation related to the path selection for ProSe service is as follows:

– The UE evaluates the path selection policy in the policy and parameters for ProSe Direct Communication applicable to the ProSe service and selects the communication path as below:

– If PC5 preferred is indicated, the UE should prefer to use the PC5 for communication path for the ProSe service.

– If Uu preferred is indicated, the UE should prefer to use the Uu for communication path for the ProSe service.

– If no preference is indicated or no path selection policy is provisioned, the UE selects either a Uu or PC5 communication path based on its pre-configuration or implementation for the ProSe service.

NOTE 3: When either PC5 preferred or Uu preferred is indicated, the UE can still select the other non-preferred path, e.g. because the peer UE is not in proximity.

5.12 NAS level congestion control for 5G ProSe UE-to-Network Relay

The 5G ProSe UE-to-Network Relay may be subject to NAS level congestion control, as specified in clause 5.19.7 of TS 23.501 [4].

Both 5G ProSe Layer-2 UE-to-Network Relays and Layer-3 UE-to-Network Relays, when NAS Mobility Management congestion control as specified in clause 5.19.7.2 of TS 23.501 [4] is activated, i.e. the 5G ProSe UE-to-Network Relay receives a Mobility Management back-off timer from the AMF, the 5G ProSe UE-to-Network Relay is not able to serve the 5G ProSe Remote UE after the 5G ProSe UE-to-Network Relay enters CM_IDLE state. If the 5G ProSe UE-to-Network Relay has a Mobility Management back-off timer when it enters CM_IDLE state the 5G ProSe UE-to-Network Relay releases the PC5 connections with its 5G ProSe Remote UEs indicating it is temporarily not available, so the Remote UE can (re)select another 5G ProSe UE-to-Network Relay. The 5G ProSe UE-to-Network Relay does not perform UE-to-Network Relay Discovery as described in clause 6.3.2.3 and does not accept any PC5 connections for relaying until the back-off timer expires if the 5G ProSe UE-to-Network Relay is in CM_IDLE state.

A Remote UE may also be subject to NAS level congestion control as specified in TS 23.501 [4].

NOTE: The form of the temporarily not available indication will be determined by stage 3.

5.13 Support for PC5 DRX operations

5.13.1 General

PC5 DRX operations are supported to enable 5G ProSe-enabled UE power saving for the following functions:

– 5G ProSe Direct Discovery;

– Unicast, groupcast and broadcast mode 5G ProSe Direct Communication;

– 5G ProSe UE-to-Network Relay Discovery and 5G ProSe UE-to-Network Relay Communication.

Support for PC5 DRX operations in the AS layer is specified in TS 38.300 [12].

5.13.2 PC5 DRX operations for 5G ProSe Direct Discovery and 5G ProSe UE-to-Network Relay Discovery

For 5G ProSe Direct Discovery and 5G ProSe UE-to-Network Relay Discovery when the UE is "not served by NG-RAN", the UE uses the provisioned default PC5 DRX configuration for PC5 DRX operation as specified in clause 5.1.2.1 and clause 5.1.4.1, respectively.

5.13.3 PC5 DRX operations for 5G ProSe Direct Communication and 5G ProSe UE-to-Network Relay Communication

The ProSe layer determines the respective ProSe services (i.e. ProSe identifiers), and derives the corresponding PC5 QoS parameters based on either the mapping of ProSe services (i.e. ProSe identifiers) to PC5 QoS parameters, or the ProSe Application Requirements for the ProSe services (i.e. ProSe identifiers) provided by the application layer. For broadcast and groupcast, the ProSe layer also determines the NR Tx Profile based on the mapping of ProSe services (i.e. ProSe identifiers) to NR Tx Profiles as described in clause 5.1.3.1. The ProSe layer passes the PC5 QoS parameters and destination Layer-2 ID to the AS layer as specified in clauses 6.4.1, 6.4.2 and 6.4.3. The ProSe layer also passes the corresponding NR Tx Profile to the AS layer, if the ProSe layer has determined the corresponding NR Tx Profile.

NOTE: For broadcast and groupcast, the AS layer needs PC5 QoS parameters as well to determine the PC5 DRX parameter values for reception operation over PC5 reference point. Therefore, the ProSe layer determines the interested ProSe services (i.e. ProSe identifiers) and derives the PC5 QoS parameters based on its reception needs besides the transmission needs. How to derive the PC5 QoS parameters based on its reception needs (e.g. without establishing the PC5 QoS Flows) depends on UE implementation.

For broadcast or groupcast, the ProSe layer maintains a list of all ProSe services (i.e. ProSe identifiers), i.e. activated ProSe services and/or ProSe services that the UE is interested for reception, for a given destination Layer-2 ID and determines the NR Tx Profile to be mapped for the respective ProSe service based on the configuration described in clause 5.1.3.1. Whenever the list of the ProSe services for a given destination Layer-2 ID changes, the ProSe layer updates the AS layer for the NR Tx Profiles information by providing all the mapped NR Tx Profiles to the AS layer for the given destination Layer-2 ID, e.g. when providing other information such as the destination Layer-2 ID, PC5 QoS parameters.

For broadcast, the mapping from destination Layer-2 ID to NR Tx Profile is configured in the NG-RAN. The NG-RAN may derive the NR Tx Profile from the destination Layer-2 ID to perform the network scheduled operation mode, alignment of Uu DRX and PC5 DRX, etc.

When the PC5 DRX operation is needed, the AS layer determines the PC5 DRX parameter values for 5G ProSe Direct Communication or 5G ProSe UE-to-Network Relay Communication over PC5 reference point, taking into account, e.g., PC5 QoS parameters and/or destination Layer-2 ID provided by the ProSe layer.

For broadcast and groupcast, the UE enables the PC5 DRX based on the NR Tx Profile.

For unicast mode 5G ProSe Direct Communication and 5G ProSe UE-to-Network Relay Communication, two UEs may negotiate the PC5 DRX configuration in the AS layer, and the PC5 DRX parameter values can be configured per pair of source and destination Layer-2 IDs in the AS layer. For transmitting and receiving Direct Communication Request messages, a default PC5 DRX configuration may be used (see TS 38.300 [12]).

For broadcast and groupcast when the UE is "not served by NG-RAN", the UE uses the provisioned PC5 DRX configuration for PC5 DRX operation as specified in clause 5.1.3.1.