Content for  TS 24.501  Word version:  17.5.0

A globally unique permanent identity, the 5G subscription permanent identifier (SUPI), is allocated to each subscriber for 5GS-based services. The IMSI, the network specific identifier, the GCI and the GLI are valid SUPI types. When the SUPI contains a network specific identifier, a GCI or a GLI, it shall take the form of a network access identifier (NAI). When the UE performs initial registration for onboarding services in SNPN or is registered for onboarding services in SNPN, the SUPI contains the onboarding SUPI derived from the default UE credentials. The UE derives the onboarding SUPI before or during the initial registration for onboarding services in SNPN and uses the derived onboarding SUPI in the initial registration for onboarding services in SNPN and while registered for onboarding services in SNPN. The structure of the SUPI and its derivatives are specified in TS 23.003. The UE provides the SUPI to the network in concealed form. The SUCI is a privacy preserving identifier containing the concealed SUPI. When the SUPI contains a network specific identifier, a GCI or a GLI, the SUCI shall take the form of a NAI as specified in TS 23.003. A UE supporting N1 mode includes a SUCI:

1. in the REGISTRATION REQUEST message when the UE is attempting initial registration procedure and a valid 5G-GUTI is not available;
2. in the IDENTITY RESPONSE message, if the SUCI is requested by the network during the identification procedure; and
3. in the DEREGISTRATION REQUEST message when the UE initiates a de-registration procedure and a valid 5G-GUTI is not available.

If the UE uses the "null-scheme" as specified in TS 33.501 to generate a SUCI, the SUCI contains the unconcealed SUPI. When:

• not operating in SNPN access operation mode; or
• operating in SNPN access operation mode but not performing initial registration for onboarding services and not registered for onboarding services;

the UE shall use the "null-scheme" if:

1. the home network has not provisioned the public key needed to generate a SUCI;
2. the home network has configured "null-scheme" to be used for the UE;
3. the UE needs to perform a registration procedure for emergency services after the failure of authentication procedure or after reception of a REGISTRATION REJECT message with the 5GMM cause #3 "Illegal UE", or to initiate a de-registration procedure before the registration procedure for emergency services was completed successfully, and the UE does not have a valid 5G-GUTI for the selected PLMN; or
4. the UE receives an identity request for SUCI during a registration procedure for emergency services or during a de-registration procedure that was initiated before the registration procedure for emergency services was completed successfully.

When operating in SNPN access operation mode and:

• performing initial registration for onboarding services; or
• registered for onboarding services;

the UE shall use the "null-scheme" if:

1. the public key needed to generate a SUCI is not configured as part of the default UE credentials; or
2. "null-scheme" usage is configured as part of the default UE credentials.

A W-AGF acting on behalf of an FN-RG shall use the "null-scheme" as specified in TS 33.501 to generate a SUCI. A W-AGF acting on behalf of an N5GC device shall use the "null-scheme" as specified in TS 33.501 to generate a SUCI. If a UE is a Multi-USIM UE, the UE shall contain and use a separate permanent equipment identifier (PEI) for each USIM the UE operates for accessing 5GS-based services; otherwise, a UE contains and uses a permanent equipment identifier (PEI) for accessing 5GS-based services. In this release of the specification, the IMEI, the IMEISV, the MAC address together with the MAC address usage restriction indication and the EUI-64 are the only PEI formats supported by 5GS. The structure of the PEI and its formats are specified in TS 23.003. Each UE supporting at least one 3GPP access technology (i.e. satellite NG-RAN, NG-RAN, E-UTRAN, UTRAN or GERAN) contains a PEI in the IMEI format and shall be able to provide an IMEI and an IMEISV upon request from the network. Each UE not supporting any 3GPP access technologies and supporting NAS over untrusted or trusted non-3GPP access shall have a PEI in the form of the Extended Unique Identifier EUI-64 [48] of the access technology the UE uses to connect to the 5GC. A UE supporting N1 mode includes a PEI:

1. when neither SUPI nor valid 5G-GUTI is available to use for emergency services in the REGISTRATION REQUEST message with 5GS registration type IE set to "emergency registration";
2. when the network requests the PEI by using the identification procedure, in the IDENTITY RESPONSE message; and
3. when the network requests the IMEISV by using the security mode control procedure, in the SECURITY MODE COMPLETE message.

Each 5G-RG supporting only wireline access and each FN-RG shall have a permanent MAC address configured by the manufacturer. For 5G-CRG, the permanent MAC address configured by the manufacturer shall be a cable modem MAC address. When the 5G-RG contains neither an IMEI nor an IMEISV, the 5G-RG shall use as a PEI the 5G-RG's permanent MAC address configured by the manufacturer and the MAC address usage restriction indication set to "no restrictions". The W-AGF acting on behalf of the FN-RG shall use as a PEI the MAC address provided by the FN-RG and if the MAC address provided by the FN-RG is not unique or does not correspond to the FN-RG's permanent MAC address according to W-AGF's configuration, the MAC address usage restriction indication set to "MAC address is not usable as an equipment identifier" otherwise the MAC address usage restriction indication set to "no restrictions". The 5G-RG containing neither an IMEI nor an IMEISV shall include the PEI containing the MAC address together with the MAC address usage restriction indication:

1. when neither SUPI nor valid 5G-GUTI is available to use for emergency services in the REGISTRATION REQUEST message with 5GS registration type IE set to "emergency registration";
2. when the network requests the PEI by using the identification procedure, in the IDENTIFICATION RESPONSE message; and
3. when the network requests the IMEISV by using the security mode control procedure, in the SECURITY MODE COMPLETE message.

The W-AGF acting on behalf of the FN-RG shall include the PEI containing the MAC address together with the MAC address usage restriction indication:

1. when the network requests the PEI by using the identification procedure, in the IDENTIFICATION RESPONSE message; and
2. when the network requests the IMEISV by using the security mode control procedure, in the SECURITY MODE COMPLETE message.

The W-AGF acting on behalf of the N5GC device shall use as a PEI the MAC address provided by the N5GC device and the MAC address usage restriction indication set to "no restrictions". Based on operator policy, the W-AGF acting on behalf of the N5GC device may encode the MAC address of the N5GC device using the EUI-64 format as specified in [48] and use as a PEI the derived EUI-64. The AMF can request the PEI at any time by using the identification procedure.

A temporary user identity for 5GS-based services, the 5G globally unique temporary identity (5G-GUTI), is used for identification within the signalling procedures. In case of PLMN the 5G-GUTI is globally unique and in case of SNPN the 5G-GUTI is unique within an SNPN. When the UE is registered to the same PLMN or SNPN over 3GPP and non-3GPP access, the UE and the AMF maintain one 5G-GUTI that is common to both 3GPP and non-3GPP access. When the UE is required to delete the 5G-GUTI according to a NAS procedure, the UE shall delete the 5G-GUTI only if it is not registered to the same PLMN or SNPN through other access. When the UE is registered to different PLMNs or SNPNs over 3GPP access and non-3GPP access, the UE maintains two 5G-GUTIs, a 5G-GUTI for the registration with a PLMN or SNPN over the 3GPP access and another 5G-GUTI for the registration with another PLMN or SNPN over the non-3GPP access. In the paging and service request procedures, a shortened form of the 5G-GUTI, the 5G S-temporary mobile subscriber identity (5G-S-TMSI), is used to enable more efficient radio signalling. The purpose of the 5G-GUTI and 5G-S-TMSI is to provide identity confidentiality, i.e., to protect a user from being identified and located by an intruder. The structure of the 5G-GUTI and its derivatives are specified in TS 23.003. The 5G-GUTI has two main components (see TS 23.501):

1. the GUAMI; and
2. the 5G-TMSI that provides an unambiguous identity of the UE within the AMF(s) identified by the GUAMI.

The 5G-S-TMSI has three main components:

1. the AMF set ID that uniquely identifies the AMF set within the AMF region;
2. the AMF pointer that identifies one or more AMFs within the AMF set; and
3. the 5G-TMSI.

A UE supporting N1 mode includes a valid 5G-GUTI, if any is available, in the REGISTRATION REQUEST and DEREGISTRATION REQUEST messages. In the SERVICE REQUEST message, the UE includes a valid 5G-S-TMSI as user identity. The AMF shall assign a new 5G-GUTI for a particular UE:

1. during a successful initial registration procedure;
2. during a successful registration procedure for mobility registration update;
3. after a successful service request procedure invoked as a response to a paging request from the network and before the:
   1. release of the N1 NAS signalling connection; or
   2. suspension of the N1 NAS signalling connection due to user plane CIoT 5GS optimization i.e. before the UE and the AMF enter 5GMM-IDLE mode with suspend indication;
   as specified in subclause 5.4.4.1; and
4. after the AMF receives an indication from the lower layers that the RRC connection has been resumed for a UE in 5GMM-IDLE mode with suspend indication and this resumption is a response to a paging request from the network, and before the:
   1. release of the N1 NAS signalling connection; or
   2. suspension of the N1 NAS signalling connection due to user plane CIoT 5GS optimization i.e. before the UE and the AMF enter 5GMM-IDLE mode with suspend indication;
   as specified in subclause 5.4.4.1.

The AMF should assign a new 5G-GUTI for a particular UE during a successful registration procedure for periodic registration update. The AMF may assign a new 5G-GUTI at any time for a particular UE by performing the generic UE configuration update procedure. If a new 5G-GUTI is assigned by the AMF, the UE and the AMF handle the 5G-GUTI as follows:

1. Upon receipt of a 5GMM message containing a new 5G-GUTI, the UE considers the new 5G-GUTI as valid and the old 5G-GUTI as invalid, stops timer T3519 if running, and deletes any stored SUCI. The new 5G-GUTI is stored in a non-volatile memory in the USIM if the corresponding file is present in the USIM, else in the non-volatile memory in the ME, as described in Annex C.
2. The AMF considers the old 5G-GUTI as invalid as soon as an acknowledgement for a registration or generic UE configuration update procedure is received.

Within the 5GS, the registration area is managed independently per access type, i.e., 3GPP access or non-3GPP access. The AMF assigns a registration area to the UE during the registration procedure. A registration area is defined as a set of tracking areas and each of these tracking areas consists of one or more cells that cover a geographical area. Within the 5GS, the concept of "registration to multiple tracking areas" applies:

1. A tracking area is identified by a TAI which is broadcast in the cells of the tracking area. The TAI is constructed from a TAC and a PLMN identity. In case of a shared network:
   1. one or more TACs; and
   2. any of the following:
      1. multiple PLMN identities;
      2. multiple SNPN identities; or
      3. one or more PLMN identities and one or more SNPN identities;
   are broadcast.
2. In order to reduce the tracking area update signalling within the 5GS, the AMF can assign several tracking areas to the UE. These tracking areas construct a list of tracking areas which is identified by a TAI list. When generating the TAI list, the AMF shall include only TAIs that are applicable on the access where the TAI list is sent. The AMF shall be able to allocate a TAI list over different NG-RAN access technologies. The AMF shall not allocate a TAI list containing both tracking areas in NB-N1 mode and tracking areas not in NB-N1 mode.
3. The UE considers itself registered to a list of tracking areas and does not need to trigger the registration procedure for mobility and periodic registration update used for mobility (i.e. the 5GS registration type IE set to "mobility registration updating" in the REGISTRATION REQUEST message) as long as the UE stays in one of the tracking areas of the list of tracking areas received from the AMF.
4. The UE will consider the TAI list as valid, until it receives a new TAI list in the next registration procedure for mobility and periodic registration update or generic UE configuration update procedure, or the UE is commanded by the network to delete the TAI list by a reject message or it is deregistered from the 5GS. If the registration request is accepted or the TAI list is reallocated by the AMF, the AMF shall provide at least one entry in the TAI list. If the new and the old TAI list are identical, the AMF does not need to provide the new TAI list to the UE during mobility registration update or periodic registration update.
5. The TAI list can be reallocated by the AMF.
6. When the UE is deregistered from the 5GS, the TAI list in the UE is invalid.
7. The UE includes the last visited registered TAI, if available, to the AMF. The last visited registered TAI is stored in a non-volatile memory in the USIM if the corresponding file is present in the USIM, else in the non-volatile memory in the ME, as described in Annex C.

The UE can request the use of mobile initiated connection only (MICO) mode during the registration procedure (see TS 23.501 and TS 23.502). The UE shall not request use of MICO mode over non-3GPP access. Furthermore, the UE in 3GPP access shall not request the use of MICO mode during:

1. a registration procedure for initial registration for emergency services (see subclause 5.5.1.2);
2. a registration procedure for initial registration for initiating an emergency PDU session (see subclause 5.5.1.2);
3. a registration procedure for mobility and periodic registration update (see subclause 5.5.1.3) for initiating an emergency PDU session if the UE is in the state 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE; or
4. a registration procedure for mobility and periodic registration update (see subclause 5.5.1.3) when the UE has an emergency PDU session established.

If the UE requests the use of MICO mode, the network can accept the use of MICO mode by providing a MICO indication when accepting the registration procedure. The UE may use MICO mode only if the network has provided the MICO indication IE during the last registration procedure. The UE may also request an active time value together with the MICO mode indication during the registration procedure. If the network accepts the use of MICO mode and does not include an active time value in T3324 IE to the UE, the AMF may include an "all PLMN registration area allocated" indication in the MICO indication IE to the UE. If the UE indicated the support for strictly periodic registration timer in the MICO indication IE to the network, the network may include a "strictly periodic registration timer supported" indication in the MICO indication IE to the UE. If the UE requested the use of active time by including an active time value and the network accepts the use of MICO mode and the use of active time, the AMF shall include an active time value in the T3324 IE to the UE. If the AMF indicates active time value to the UE, AMF should not indicate "all PLMN registration area allocated" indication in the MICO indication IE to the UE. Upon entering 5GMM-IDLE mode, AMF shall start the active timer with the active time value indicated to the UE and shall consider the UE is reachable for paging as long as the timer is running. If the UE enters 5GMM-CONNECTED mode over 3GPP access when the active timer is running, the AMF shall stop the active timer. If the network accepts the use of MICO mode, the UE may deactivate the AS layer and activate MICO mode by entering the state 5GMM-REGISTERED.NO-CELL-AVAILABLE if:

1. the UE is in 5GMM-IDLE mode over3GPP access;
2. the UE is in the 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE (as described in subclause 5.3.5.2) state for 3GPP access; and
3. no T3324 value is received from the network.

If the network accepts the use of MICO mode and indicates an active time value to the UE in a successful registration procedure, the UE shall start the timer T3324 with the value received from the network after entering 5GMM-IDLE mode over 3GPP access. At the expiry of the timer T3324, the UE may activate MICO mode by entering the state 5GMM-REGISTERED.NO-CELL-AVAILABLE if the UE is in the 5GMM-REGISTERED.NORMAL-SERVICE or 5GMM-REGISTERED.NON-ALLOWED-SERVICE (as described in subclause 5.3.5.2) state for 3GPP access. If the UE enters 5GMM-CONNECTED mode over 3GPP access when the timer T3324 is running, the UE shall stop the timer T3324. When MICO mode is activated, all NAS timers are stopped and associated procedures aborted except for timers T3512, T3346, T3447, T3396, T3584, T3585, any back-off timers, T3247, and the timer T controlling the periodic search for HPLMN or EHPLMN or higher prioritized PLMNs (see TS 23.122). The UE may deactivate MICO mode and activate the AS layer at any time. Upon deactivating MICO mode, the UE may initiate 5GMM procedures (e.g. for the transfer of mobile originated signalling or user data). When an emergency PDU session is successfully established after the MICO mode was enabled, the UE and the AMF shall locally disable MICO mode. The UE and the AMF shall not enable MICO mode until the AMF accepts the use of MICO mode in the next registration procedure. To enable an emergency call back, the UE should wait for a UE implementation-specific duration of time before requesting the use of MICO mode after the release of the emergency PDU session. If the AMF accepts the use of MICO mode and does not indicate "strictly periodic registration timer supported" in the MICO indication IE to the UE, the AMF starts the implicit de-registration timer for 3GPP access when entering 5GMM-IDLE mode for 3GPP access. If AMF accepts the use of MICO mode and indicates "strictly periodic registration timer supported" in the MICO indication IE to the UE, AMF shall start the strictly periodic monitoring timer with T3512 value indicated in the T3512 value IE after the registration procedure is completed. The AMF shall neither stop nor reset the strictly periodic monitoring timer when the NAS signalling connection is established or released for the UE. If the strictly periodic monitoring timer expires when NAS signalling connection is established for the UE, AMF shall restart the strictly periodic monitoring timer with the T3512 value, otherwise AMF shall start the implicit de-registration timer. When an emergency PDU session is successfully established and the MICO mode is disabled, the UE shall stop timer T3512 if running and the AMF shall stop strictly periodic monitoring timer if running. The UE and the AMF shall behave as if no "strictly periodic registration timer supported" indication was given to the UE in the last registration attempt. Upon successful completion of an attach procedure or tracking area updating procedure after inter-system change from N1 mode to S1 mode (see TS 24.301), the UE operating in single-registration mode shall locally disable MICO mode. After inter-system change from S1 mode to N1 mode, the UE operating in single-registration mode may re-negotiate MICO mode with the network during the registration procedure for mobility and periodic registration update.