Content for  TS 24.501  Word version:  18.4.0

A 5GS can support time synchronization and TSC (see TS 23.501, TS 23.502, and TS 23.503). This subclause describes NAS-specific aspects of the 5GS features to support time synchronization and TSC. Interworking with EPS is not supported for a PDU session for time synchronization or TSC.

Two types of synchronization processes are supported by the 5GS: 5GS synchronization and (g)PTP domain synchronization (see TS 23.501). For 5GS synchronization, the lower layers provide the 5G internal system clock signalled via the NG-RAN (see TS 38.331) and the UE forwards the 5G internal system clock to the DS-TT(s). For (g)PTP domain synchronization, the UE supports forwarding (g)PTP messages (see TS 23.501, TS 23.502, and TS 24.535). For all (g)PTP domains associated with a PDU session:

1. if the UE receives (g)PTP message via the PDU session, the UE forwards the (g)PTP messages to the DS-TT associated with the PDU session; or
2. if the UE receives (g)PTP messages from the DS-TT associated with the PDU session, the UE forwards the (g)PTP messages via the PDU session.

Depending on the 5G access stratum-based time distribution or (g)PTP-based time distribution, the network timing synchronization status of the nodes involved in the operation (e.g., NG-RAN nodes, NW-TTs) may change. Using the 5GMM protocol, the network can request a supporting UE to reconnect to the network upon receiving an indication of a change in the RAN timing synchronization status.

A 5G system (5GS) can act as a user plane node of an external network (e.g. IEEE TSN bridge) or a 5GS can be independently used to enable TSC. For these purposes, information available at a UE is provided to the network and port management information containers are exchanged between a DS-TT and a TSN AF or a TSCTSF (see TS 24.539). During a UE-requested PDU session establishment procedure, if the UE supports transfer of port management information containers, then the UE indicates that transfer of port management information container is supported and the UE provides a DS-TT Ethernet port MAC address (if the PDU session type is Ethernet), port management information container, and a UE-DS-TT residence time (if available) to the network (see subclause 6.4.1.2). Once the UE has successfully established a PDU session and the UE has indicated that transfer of port management information container is supported during the UE-requested PDU session establishment procedure (see subclause 6.4.1.2), then port management information containers are exchanged via a UE-requested PDU session modification procedure and a network-requested PDU session modification procedure (see subclauses 6.3.2 and 6.4.2). The UE receiving a port management information container from the network shall forward the port management information container to the DS-TT. The SMF receiving a port management information container from the UE shall operate as described in TS 23.502.

A 5GS can support UAV identification, authentication, and authorization (see TS 23.256). This subclause describes NAS-specific aspects of the 5GS features to support UAV identification, authentication, authorization and C2 communication authorization. Before accessing 5GS for UAS services, the UE supporting UAS services must have an assigned CAA-level UAV ID. The UE can be registered to 5GS for UAS services if there is a valid aerial subscription in the UE's subscription.

The 5GS supports the USS UAV Authorization and Authentication (UUAA) procedure for a UE supporting UAS services. Depending on operator policy or regulatory requirements, the UUAA-MM procedure can be performed by the UE and the AMF at a registration procedure as specified in subclause 5.5.1.2 or the UUAA-SM procedure can be performed by the UE and the SMF at a PDU session establishment procedure as specified in subclause 6.4.1.2. The UE shall support UUAA-MM and UUAA-SM, and the network shall support UUAA-SM and may optionally support UUAA-MM. The UUAA procedure needs to be performed by 5GS with USS successfully before the connectivity for UAS services is established. During the registration procedure as described in subclause 5.5.1.2, the UE supporting UAS services provides CAA-level UAV ID to the AMF, and the AMF may trigger the UUAA-MM procedure. If the UE supporting UAS services does not provide CAA-level UAV ID to the AMF and the network is configured to perform UUAA-MM at registration procedure, the AMF may accept the registration request and shall mark in the UE's 5GMM context that the UE is not allowed to request UAS services. If the UE wants to use the UAS services by providing the CAA-Level UAV ID later on, the UE shall perform the registration procedure for mobility and periodic registration update. When a UE supporting UAS services requests to establish a PDU session as described in subclause 6.4.1.2 for USS communication, the UE provides CAA-level UAV ID to the network, and the SMF may trigger the UUAA-SM procedure based on the DNN and S-NSSAI combination for aerial services according to the user's subscription data and the CAA-level UAV ID provided by the UE. If the UE does not provide CAA-level UAV ID and the user's subscription data for the UE requires the UUAA-SM, the network rejects the UE-requested PDU session establishment procedure for the UAS services. The UE supporting UAS services shall not provide CAA-level UAV ID to the network over non-3GPP access, and the network shall not perform UUAA procedure for non-3GPP access and shall ensure that the UE is not allowed to access any aerial services in non-3GPP access. If provided by the upper layers, the UE supporting UAS services provides to the network the USS address during the registration procedure or PDU session establishment procedure so that the network uses the information to discover the USS. After successful UUAA procedure, either the AMF or the SMF may initiate re-authentication of the UAV when required by the USS. If UUAA-MM fails during a re-authentication and there are PDU sessions established using UAS services, the AMF shall request the SMF to perform the release of these PDU sessions and may trigger a network-initiated de-registration procedure based on operator policy. If UUAA-SM fails during a re-authentication, the SMF shall release the PDU session related to re-authentication. If the UUAA is revoked, the PDU session related to the UAS services shall be released by the SMF. Based on operator policy, the AMF may decide to keep the UE registered or trigger a de-registration procedure.

The 5GS supports USS authorization of C2 communication for pairing of UAV and UAV-C. The pairing of UAV and UAV-C needs to be authorized by USS successfully before the user plane connectivity for C2 communication (over Uu or over NR-PC5) is enabled. For C2 authorization procedure, the UE supporting UAS services provides to the network with CAA-level UAV ID. The USS authorization of UAV flight can also be performed during the C2 authorization procedure. The UE supporting UAS services provides the UAV flight authorization information to the network if provided by upper layers. The UE supporting UAS services can establish a PDU session for the C2 communication by providing the CAA-level UAV ID and the C2 authorization payload. The SMF upon reception of the UE's request for the PDU session establishment, determines that authorization is required based on the DNN and S-NSSAI combination of the PDU session is for aerial services according to user's subscription data and the CAA-level UAV ID included in the request. If a UE supporting UAS services uses a common PDU session for both USS communication and C2 communication, the C2 communication can be authorized using UUAA-SM procedure during the PDU session establishment procedure or during the PDU session modification procedure. If the pairing of UAV and UAV-C is revoked, the network shall disable C2 communication for the PDU session. The SMF upon reception of the UE's request for the PDU session establishment, determines that authorization is required based on the DNN and S-NSSAI combination of the PDU session is for aerial services according to user's subscription data and the CAA-level UAV ID included in the request. If a UE supporting UAS services uses separate PDU sessions for, respectively, USS communication and C2 communication, the C2 communication is authorized using UUAA-SM during the PDU session establishment procedure. If the pairing of UAV and UAV-C is revoked, the PDU session for C2 communication shall be released by the SMF. During the registration procedure for UAS services, direct C2 communication can be authorized as described in subclause 5.5.1.2. A UE supporting A2X over NR-PC5 can perform registration procedure for UAS services including a request for authorization of direct C2 communication by providing CAA-level UAV ID and C2 authorization payload.

A 5GS can support 3GPP satellite NG-RAN access technology (see TS 23.501). This subclause describes NAS-specific aspects of the 5GS features to support 3GPP satellite NG-RAN access technology.

For 3GPP satellite NG-RAN the UE shall store a list of "PLMNs not allowed to operate at the present UE location". Each entry consists of:

1. the current UE location is known, a geographical location is stored for the entry of this PLMN, and the distance to the current UE location is larger than a UE implementation specific value; or
2. the access is for emergency services (see TS 23.122 for further details).

Before storing a new entry in the list, the UE shall delete any existing entry with the same PLMN identity. Upon storing a new entry, the UE starts a timer instance associated with the entry with an implementation specific value that shall not be set to a value smaller than the timer value indicated by the network in the Lower bound timer value IE, if any. If the Lower bound timer value IE was not provided by the network, the value of the timer shall be set based on the UE implementation. The UE is allowed to attempt to access a PLMN via satellite NG-RAN access technology which is part of the list of "PLMNs not allowed to operate at the present UE location" only if:

1. the current UE location is known, a geographical location is stored for the entry of this PLMN, and the distance to the current UE location is larger than a UE implementation specific value.
2. the timer associated with the entry of this PLMN has expired; or
3. the access is for emergency services (see TS 23.122 for further details).

The list shall accommodate three or more entries. The maximum number of entries is an implementation decision. When the list is full and a new entry has to be inserted, the oldest entry shall be deleted. Each entry shall be removed if for the entry:

1. the UE successfully registers via satellite NG-RAN access technology to the PLMN stored in the entry except when the UE registers for emergency services; or
2. the timer instance associated with the entry expires.

The UE may delete the entry in the list, if the current UE location is known, a geographical location is stored for the entry of this PLMN, and the distance to the current UE location is larger than a UE implementation specific value. If the UE is in 5GMM-DEREGISTERED.LIMITED-SERVICE state and an entry from the list of "PLMNs not allowed to operate at the present UE location" is removed, the UE shall perform PLMN selection according to TS 23.122. When the UE is switched off, the UE shall keep the list of "PLMNs not allowed to operate at the present UE location" in its non-volatile memory. The UE shall delete the list of "PLMNs not allowed to operate at the present UE location" if the USIM is removed. If the UE is switched off when the timer instance associated with the entry in the list is running, the UE shall behave as follows when the UE is switched on and the USIM in the UE remains the same:

For 5GS mobility management via a satellite NG-RAN cell the UE shall apply the value of the applicable NAS timer indicated in Table 10.2.1 for access via a satellite NG-RAN cell. The NAS timer value obtained is used as described in the appropriate procedure subclause of this specification. The NAS timer value shall be calculated at start of a NAS procedure, and shall not be re-calculated until the NAS procedure is completed, restarted or aborted. The access via a satellite NG-RAN cell by a UE is indicated to the AMF by lower layers and shall be stored by the AMF. When an AMF that supports access via satellite NG-RAN cells performs NAS signalling with a UE via satellite NG-RAN cells, the AMF shall calculate the value of the applicable NAS timer indicated in Table 10.2.2 for access via a satellite NG-RAN cell. The NAS timer value obtained is used as described in the appropriate procedure subclause of this specification. The NAS timer value shall be calculated at start of a NAS procedure and shall not be re-calculated until the NAS procedure is completed, restarted or aborted.

For 5GS session management via a satellite NG-RAN cell the UE shall apply the value of the applicable NAS timer indicated in Table 10.2.1 for access via a satellite NG-RAN cell. The NAS timer value obtained is used as described in the appropriate procedure subclause of this specification. The NAS timer value shall be calculated at start of a NAS procedure, and shall not be re-calculated until the NAS procedure is completed, restarted or aborted. If the use of extended NAS timer for access via a satellite NG-RAN cell is indicated by the AMF (see TS 23.501 and TS 23.502), the SMF shall calculate the value of the applicable NAS timer indicated in Table 10.3.2 for access via a satellite NG-RAN cell. The NAS timer value obtained is used as described in the appropriate procedure subclause of this specification. The NAS timer value shall be calculated at start of a NAS procedure and shall not be re-calculated until the NAS procedure is completed, restarted or aborted.

When a UE camps on a satellite NG-RAN cell, the UE may receive multiple TACs from the lower layers. The UE shall construct TAIs from the multiple TACs (i.e. concatenate the identity of the current PLMN and each of the TACs) and select a TAI as follows:

1. if at least one TAI belongs to the current registration area of the UE, the UE shall select a TAI which belongs to the current registration area of the UE according to the followings.
   If there are multiple TAIs which belong to the current registration area of the UE, the UE shall select a TAI as follows:
   1. if there is a TAI which belongs to the list of "allowed tracking area" (if any) and does not belong to the list of "non-allowed tracking areas" (if any), the UE shall select a TAI which belongs to the list of "allowed tracking area" (if any) and does not belong to the list of "non-allowed tracking areas" (if any). In this case, if there are multiple TAIs which belong to the list of "allowed tracking area" (if any) and does not belong to the list of "non-allowed tracking areas" (if any), then the UE shall consider each of these TAIs equal and select a TAI in an implementation-specific way (e.g. taking into account LADN service area information). If these multiple TAIs contain the previous current TAI, the current TAI can be left unchanged.
   2. if there is no TAI which belongs to the list of "allowed tracking area" (if any) and does not belong to the list of "non-allowed tracking areas" (if any) or neither the list of "allowed tracking area" nor the list of "non-allowed tracking areas" is available, then the UE shall consider each of these TAIs equal and select a TAI in an implementation-specific way (e.g. taking into account LADN service area information). If these multiple TAIs contain the previous current TAI, the current TAI can be left unchanged.
2. if the current registration area is not available in the UE or no TAI belongs to the current registration area of the UE and:
   1. there is a TAI which belongs to neither the list of "5GS forbidden tracking areas for roaming" nor the list of "5GS forbidden tracking areas for regional provision of service", the UE shall select a TAI which belongs to neither the list of "5GS forbidden tracking areas for roaming" nor the list of "5GS forbidden tracking areas for regional provision of service". In this case, if there are multiple TAIs which belong to neither the list of "5GS forbidden tracking areas for roaming" nor the list of "5GS forbidden tracking areas for regional provision of service", then the UE shall consider each of these TAIs equal and select a TAI in an implementation-specific way.
   2. all TAIs belong to the list of "5GS forbidden tracking areas for roaming" or the list of "5GS forbidden tracking areas for regional provision of service", then the UE shall consider each of these TAIs equal and select a TAI in an implementation-specific way.

The UE shall consider the selected TAI as the current TAI. The UE shall select a TAI when:

1. the UE receives multiple TACs from the lower layers; or
2. the UE has received multiple TACs from the lower layers upon starting to camping on the current cell and the registration area, the list of "allowed tracking areas", the list of "non-allowed tracking areas", the list of "5GS forbidden tracking areas for roaming", or the list of "5GS forbidden tracking areas for regional provision of service" is updated.

Handling of the list of "5GS forbidden tracking areas for roaming" and the list of "5GS forbidden tracking areas for regional provision of service" is specified in clause 5.3.13.