Content for  TS 24.501  Word version:  18.5.0

If the initial registration request cannot be accepted by the network, the AMF shall send a REGISTRATION REJECT message to the UE including an appropriate 5GMM cause value. If the initial registration request is rejected due to general NAS level mobility management congestion control, the network shall set the 5GMM cause value to #22 "congestion" and assign a value for back-off timer T3346. In NB-N1 mode, if the registration request is rejected due to operator determined barring (see TS 29.503), the network shall set the 5GMM cause value to #22 "congestion" and assign a value for back-off timer T3346. If the REGISTRATION REJECT message with 5GMM cause #76 or #78 was received without integrity protection, then the UE shall discard the message. If the REGISTRATION REJECT message with 5GMM cause #62 was received without integrity protected, the behaviour of the UE is specified in subclause 5.3.20.2. Based on operator policy, if the initial registration request is rejected due to core network redirection for CIoT optimizations, the network shall set the 5GMM cause value to #31 "Redirection to EPC required". If the initial registration request is rejected because:

1. all the S-NSSAI(s) included in the requested NSSAI are rejected; and
2. the UE set the NSSAA bit in the 5GMM capability IE to:
   1. "Network slice-specific authentication and authorization supported" and:
      1. void;
      2. all default S-NSSAIs are not allowed; or
      3. network slice-specific authentication and authorization has failed or been revoked for all default S-NSSAIs and based on network local policy, the network decides not to initiate the network slice-specific re-authentication and re-authorization procedures for any default S-NSSAI requested by the UE; or
   2. "Network slice-specific authentication and authorization not supported" and all default S-NSSAIs are either not allowed or are subject to network slice-specific authentication and authorization;
      1. void
      2. void

the network shall set the 5GMM cause value of the REGISTRATION REJECT message to #62 "No network slices available". If the 5GMM cause value is set to #62 "No network slices available", the network shall include, in the rejected NSSAI of the REGISTRATION REJECT message, all the S-NSSAI(s) which were included in the requested NSSAI. If the UE has set the ER-NSSAI bit to "Extended rejected NSSAI supported" in the 5GMM capability IE of the REGISTRATION REQUEST message, the rejected S-NSSAI(s) shall be included in the Extended rejected NSSAI IE of the REGISTRATION REJECT message. Otherwise, the rejected S-NSSAI(s) shall be included in the Rejected NSSAI IE of the REGISTRATION REJECT message. In roaming scenarios, if the Extended rejected NSSAI IE is included in the REGISTRATION REJECT message, the AMF shall provide mapped S-NSSAI(s) for the rejected NSSAI. If the UE supports extended rejected NSSAI and the AMF determines that maximum number of UEs reached for one or more S-NSSAIs in the requested NSSAI as specified in subclause 4.6.2.5, the AMF shall include the rejected NSSAI containing one or more S-NSSAIs with the rejection cause "S-NSSAI not available due to maximum number of UEs reached" in the Extended rejected NSSAI IE in the REGISTRATION REJECT message. In addition, the AMF may include a back-off timer value for each S-NSSAI with the rejection cause "S-NSSAI not available due to maximum number of UEs reached" in the Extended rejected NSSAI IE of the REGISTRATION REJECT message. If the AMF receives the initial registration request along with the authenticated indication over N2 reference point on non-3GPP access and does not receive the indication that authentication by the home network is not required over N12 reference point, the network shall set the 5GMM cause value to #72 "Non-3GPP access to 5GCN not allowed". If the initial registration request from a UE supporting CAG is rejected due to CAG restrictions, the network shall set the 5GMM cause value to #76 "Not authorized for this CAG or authorized for CAG cells only" and should include the "CAG information list" in the CAG information list IE or the Extended CAG information list IE in the REGISTRATION REJECT message. If the UE does not support extended CAG information list, the CAG information list shall not be included in the Extended CAG information list IE. If the initial registration request from a UE not supporting CAG is rejected due to CAG restrictions, the network shall operate as described in bullet j) of subclause 5.5.1.2.8. If the UE's initial registration request is via a satellite NG-RAN cell and the network using the User Location Information provided by the NG-RAN, see TS 38.413, is able to determine that the UE is in a location where the network is not allowed to operate, the network shall set the 5GMM cause value in the REGISTRATION REJECT message to #78 "PLMN not allowed to operate at the present UE location". If the AMF receives the initial registration request including the service-level device ID set to the CAA-level UAV ID in the Service-level-AA container IE and the AMF determines that the UE is not allowed to use UAS services via 5GS based on the user's subscription data and the operator policy, the AMF shall return a REGISTRATION REJECT message with 5GMM cause #79 "UAS services not allowed". If the UE initiates the registration procedure for disaster roaming services and the AMF determines that it does not support providing disaster roaming services for the determined PLMN with disaster condition to the UE, then the AMF shall send a REGISTRATION REJECT message with 5GMM cause #80 "Disaster roaming for the determined PLMN with disaster condition not allowed". If the AMF receives the initial registration request over non-3GPP access and detects that the N3IWF used by the UE is not compatible with the allowed NSSAI and the UE has indicated its support for slice-based N3IWF selection in the REGISTRATION REQUEST message, the AMF may send a REGISTRATION REJECT message with 5GMM cause #81 "Selected N3IWF is not compatible with the allowed NSSAI" and may provide information for a suitable N3IWF in the REGISTRATION REJECT message indicating the suitable N3IWF that is compatible with the requested NSSAI. If the AMF receives the initial registration request over non-3GPP access and detects that the TNGF used by the UE is not compatible with the allowed NSSAI and the UE has indicated its support for slice-based TNGF selection in the REGISTRATION REQUEST message, the AMF may send a REGISTRATION REJECT message with 5GMM cause #82 "Selected TNGF is not compatible with the allowed NSSAI" and may provide information for a suitable TNAN in the TNAN information IE in the REGISTRATION REJECT message indicating the suitable TNGF that is compatible with the requested NSSAI. If the AMF received multiple TAIs from the satellite NG-RAN as described in TS 23.501, and determines that, by UE subscription and operator's preferences, all of the received TAIs are forbidden for roaming or for regional provision of service, the AMF shall include the TAI(s) in:

1. the Forbidden TAI(s) for the list of "5GS forbidden tracking areas for roaming" IE; or
2. the Forbidden TAI(s) for the list of "5GS forbidden tracking areas for regional provision of service" IE; or
3. both;

in the REGISTRATION REJECT message. Regardless of the 5GMM cause value received in the REGISTRATION REJECT message via satellite NG-RAN,

• if the UE receives the Forbidden TAI(s) for the list of "5GS forbidden tracking areas for roaming" IE in the REGISTRATION REJECT message, the UE shall store the TAI(s) belonging to the serving PLMN or equivalent PLMN(s) and ignore the TAI(s) which do not belong to the serving PLMN or equivalent PLMN(s) included in the IE, if not already stored, into the list of "5GS forbidden tracking areas for roaming"; and
• if the UE receives the Forbidden TAI(s) for the list of "5GS forbidden tracking areas for regional provision of service" IE in the REGISTRATION REJECT message, the UE shall store the TAI(s) belonging to the serving PLMN or equivalent PLMN(s) and ignore the TAI(s) which do not belong to the serving PLMN or equivalent PLMN(s) included in the IE, if not already stored, into the list of "5GS forbidden tracking areas for regional provision of service".

Furthermore, the UE shall take the following actions depending on the 5GMM cause value received in the REGISTRATION REJECT message. Other values are considered as abnormal cases. The behaviour of the UE in those cases is specified in subclause 5.5.1.2.7.

Upon receiving the REGISTRATION REJECT message including 5GMM cause #5 "PEI not accepted", the UE shall enter the state 5GMM-DEREGISTERED.NO-SUPI. If the REGISTRATION REJECT message is received,

• over 3GPP access; or
• over non-3GPP access and is integrity protected;

and the UE also supports the registration procedure over the other access, the UE shall in addition handle 5GMM parameters and 5GMM state for this access, as described for this 5GMM cause value. Upon receiving the REGISTRATION REJECT message including 5GMM cause value which is not #5 "PEI not accepted", the UE shall perform the actions as described in subclause 5.5.1.2.5 with the following addition: the UE shall inform the upper layers of the failure of the procedure. If the initial registration request for emergency services fails due to abnormal cases, the UE shall perform the actions as described in subclause 5.5.1.2.7 and inform the upper layers of the failure to access the network or the failure of the procedure. In a shared network, upon receiving the REGISTRATION REJECT message, the UE shall perform the actions as described in subclause 5.5.1.2.5, and shall:

1. inform the upper layers of the failure of the procedure; or
2. attempt to perform a PLMN or SNPN selection in the shared network and, if an initial registration for emergency services was not already attempted with the selected PLMN or SNPN and the REGISTRATION REQUEST message, for which the REGISTRATION REJECT message was received, is:
   • not for sending a PDU SESSION ESTABLISHMENT REQUEST message with request type set to "existing emergency PDU session", initiate an initial registration for emergency services with the selected PLMN or SNPN; or
   • for sending a PDU SESSION ESTABLISHMENT REQUEST message with request type set to "existing emergency PDU session", and:
     1. the selected PLMN is an equivalent PLMN or the selected SNPN is an equivalent SNPN, initiate an initial registration for emergency services with the selected PLMN or SNPN; and
     2. the selected PLMN is not an equivalent PLMN or the selected SNPN is not an equivalent SNPN, perform a PLMN or SNPN selection and initiate an initial registration for emergency services with the selected PLMN or SNPN if an initial registration for emergency services was not already attempted with the selected PLMN or SNPN.

In a shared network, if the initial registration request for emergency services fails due to abnormal cases, the UE shall perform the actions as described in subclause 5.5.1.2.7 and shall:

1. inform the upper layers of the failure of the procedure; or
2. attempt to perform a PLMN or SNPN selection in the shared network and, if an initial registration for emergency services was not already attempted with the selected PLMN or SNPN and the REGISTRATION REQUEST message is:
   • not for sending a PDU SESSION ESTABLISHMENT REQUEST message with request type set to "existing emergency PDU session", initiate an initial registration for emergency services with the selected PLMN or SNPN; or
   • for sending a PDU SESSION ESTABLISHMENT REQUEST message with request type set to "existing emergency PDU session", and:
     1. the selected PLMN is an equivalent PLMN or the selected SNPN is an equivalent SNPN, initiate an initial registration for emergency services with the selected PLMN or SNPN; and
     2. the selected PLMN is not an equivalent PLMN or the selected SNPN is not an equivalent SNPN, perform a PLMN or SNPN selection and initiate an initial registration for emergency services with the selected PLMN or SNPN if an initial registration for emergency services was not already attempted with the selected PLMN or SNPN.

If the network cannot accept an initial registration request with 5GS registration type IE set to "initial registration" and for sending a PDU SESSION ESTABLISHMENT REQUEST message with request type set to "initial emergency request", the UE shall perform the procedures as described in subclause 5.5.1.2.5. Then if the UE is in the same selected PLMN or SNPN where the last initial registration request was attempted, the UE shall:

1. inform the upper layers of the failure of the procedure; or
2. attempt initial registration for emergency services.

If the network cannot accept an initial registration request with 5GS registration type IE set to "initial registration", for establishing an emergency PDU session and the PDU session needs to be established due to handover of an existing PDN connection for emergency bearer services, the UE shall perform the procedures as described in subclause 5.5.1.2.5. Then if the UE is in the same selected PLMN or equivalent PLMN or the same selected SNPN or equivalent SNPN, where the last initial registration request was attempted, the UE shall attempt initial registration for emergency services. If the initial registration request, with 5GS registration type IE set to "initial registration" and for initiating an emergency PDU session, fails due to abnormal case b) in subclause 5.5.1.2.7, the UE shall perform the actions as described in subclause 5.5.1.2.7 and inform the upper layers of the failure to access the network. If the initial registration request, with 5GS registration type IE set to "initial registration" and for initiating an emergency PDU session, fails due to abnormal cases c), d) or e) in subclause 5.5.1.2.7, the UE shall perform the actions as described in subclause 5.5.1.2.7. Then if the UE is in:

1. the same selected PLMN or SNPN where the last initial registration request was attempted and the PDU session does not need to be established due to handover of an existing PDN connection for emergency bearer services, the UE shall:
   • inform the upper layers of the failure of the procedure; or
   • attempt initial registration for emergency services; or
2. the same selected PLMN or equivalent PLMN or the same selected SNPN or equivalent SNPN, where the last initial registration request was attempted and the PDU session needs to be established due to handover of an existing PDN connection for emergency bearer services, attempt initial registration for emergency services.

The following abnormal cases can be identified: For the cases c, d and e, the UE shall proceed as follows:

The following abnormal cases can be identified:

1. Lower layer failure
   If a lower layer failure occurs before the REGISTRATION COMPLETE message has been received from the UE and timer T3550 is running, the AMF shall locally abort the registration procedure for initial registration, enter state 5GMM-REGISTERED and shall not resend the REGISTRATION ACCEPT message. If a new 5G-GUTI was assigned to the UE in the registration procedure for initial registration, the AMF shall consider both the old and the new 5G-GUTI as valid until the old 5G-GUTI can be considered as invalid by the AMF or the 5GMM context which has been marked as deregistered in the AMF is released. If the old 5G-GUTI was allocated by an AMF other than the current AMF, the current AMF does not need to retain the old 5G-GUTI. During this period the network may use the identification procedure followed by a generic UE configuration update procedure if the old 5G-GUTI is used by the UE in a subsequent message.
2. Protocol error
   If the REGISTRATION REQUEST message is received with a protocol error, the AMF shall return a REGISTRATION REJECT message with one of the following 5GMM cause values:
   #96

   invalid mandatory information;

   #99

   information element non-existent or not implemented;

   #100

   conditional IE error; or

   #111

   protocol error, unspecified.
3. T3550 time-out
   On the first expiry of the timer, the AMF shall retransmit the REGISTRATION ACCEPT message and shall reset and restart timer T3550.
   This retransmission is repeated four times, i.e. on the fifth expiry of timer T3550, the registration procedure for initial registration shall be aborted and the AMF enters state 5GMM-REGISTERED. If a new 5G-GUTI was allocated in the REGISTRATION ACCEPT message, the AMF shall consider both the old and the new 5G-GUTIs as valid until the old 5G-GUTI can be considered as invalid by the AMF or the 5GMM context which has been marked as de-registered in the AMF is released. If the old 5G-GUTI was allocated by an AMF other than the current AMF, the current AMF does not need to retain the old 5G-GUTI. During this period, if the old 5G-GUTI is used by the UE in a subsequent message, the AMF acts as specified for case a) above.
4. REGISTRATION REQUEST message received after the REGISTRATION ACCEPT message has been sent and before the REGISTRATION COMPLETE message is received, if the REGISTRATION COMPLETE message is expected.
   1. If one or more of the information elements in the REGISTRATION REQUEST message differ from the ones received within the previous REGISTRATION REQUEST message, the previously initiated the registration procedure for initial registration shall be aborted if the REGISTRATION COMPLETE message has not been received and the new registration procedure for initial registration shall be progressed; or
   2. if the information elements do not differ, then the REGISTRATION ACCEPT message shall be resent and the timer T3550 shall be restarted. In that case, the retransmission counter related to T3550 is not incremented.
5. More than one REGISTRATION REQUEST message with 5GS registration type IE set to "initial registration" received and no REGISTRATION ACCEPT message or REGISTRATION REJECT message has been sent.
   1. If one or more of the information elements in the REGISTRATION REQUEST message with 5GS registration type IE set to "initial registration" differs from the ones received within the previous REGISTRATION REQUEST message with 5GS registration type IE set to "initial registration", the previously initiated the registration procedure for initial registration shall be aborted and the new the registration procedure for initial registration shall be executed;
   2. if the information elements do not differ, then the network shall continue with the previous the registration procedure for initial registration and shall ignore the second REGISTRATION REQUEST message.
6. REGISTRATION REQUEST message with 5GS registration type IE set to "initial registration" received in state 5GMM-REGISTERED.
   If a REGISTRATION REQUEST message with 5GS registration type IE set to "initial registration" is received in state 5GMM-REGISTERED the network may initiate the 5GMM common procedures; if it turned out that the REGISTRATION REQUEST message was sent by a genuine UE that has already been registered, the 5GMM context, if any, are deleted and the new REGISTRATION REQUEST is progressed, otherwise if network considers REGISTRATION REQUEST message was not sent by a genuine UE based on authentication procedure the network shall maintain the 5GMM-context, if any, unchanged.
7. REGISTRATION REQUEST message with 5GS registration type IE set to "mobility registration updating" or "periodic registration updating" received before REGISTRATION COMPLETE message, if the REGISTRATION COMPLETE message is expected.
   Timer T3550 shall be stopped. The allocated 5G-GUTI in the registration procedure for initial registration shall be considered as valid and the registration procedure for mobility and periodic registration update shall be progressed as described in subclause 5.5.1.3.
8. DEREGISTRATION REQUEST message received before REGISTRATION COMPLETE message, if the REGISTRATION COMPLETE message is expected.
   The AMF shall abort the registration procedure for initial registration and shall progress the de-registration procedure as described in subclause 5.5.2.2.
9. UE security capabilities invalid or unacceptable
   If the REGISTRATION REQUEST message is received with invalid or unacceptable UE security capabilities (e.g. no 5GS encryption algorithms (all bits zero), no 5GS integrity algorithms (all bits zero), mandatory 5GS encryption algorithms not supported or mandatory 5GS integrity algorithms not supported, etc.), the AMF shall return a REGISTRATION REJECT message.
10. Based on operator policy, if the initial registration request from a UE not supporting CAG is rejected due to CAG restrictions, the network shall reject the initial registration with a 5GMM cause value other than the 5GMM cause #76 (Not authorized for this CAG or authorized for CAG cells only).