School of Specs 24.501v20.0.0

3GPP 24.501 v20.0.0 — the document's own text

5.5.2.3.5 Abnormal cases in the network side

Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).

The following abnormal cases can be identified:

  • T3522 time-out

On the first expiry of the timer, the network shall retransmit the DEREGISTRATION REQUEST message and shall start timer T3522. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3522, the de-registration procedure shall be aborted. The network shall change to the state 5GMM-DEREGISTERED for the access type which the de-registration procedure is intended for.

  • Lower layer failure

The de-registration procedure is aborted. The network shall change to the state 5GMM-DEREGISTERED for the access type which the de-registration procedure is intended for.

  • De-registration procedure collision

If the network receives a DEREGISTRATION REQUEST message with "switch off" indication, before the network-initiated de-registration procedure has been completed:

    • If the access type included in the DEREGISTRATION REQUEST message sent by the UE is same as access type sent by the network, both procedures shall be considered completed; or
    • If the access type included in the DEREGISTRATION REQUEST message sent by the UE is not same as access type sent by the network, the network shall consder UE initiated de-registration completed. The network shall re-initiate the de-registration procedure, if required, for the access type not indicated in the DEREGISTRATION REQUEST message sent by the UE.

If the network receives a DEREGISTRATION REQUEST message without "switch off" indication, before the network-initiated de-registration procedure has been completed, the network shall send a DEREGISTRATION ACCEPT message to the UE.

  • De-registration and registration procedure for initial registration collision

If the network receives a REGISTRATION REQUEST message indicating either "initial registration" or "emergency registration" in the 5GS registration type IE before the network-initiated de-registration procedure has been completed, the network shall abort the de-registration procedure and the registration procedure shall be progressed after the PDU sessions associated with the access type the REGISTRATION REQUEST message is sent over have been deleted.

NOTE 1: The above collision case is valid if the DEREGISTRATION REQUEST message indicates the access type over which the initial registration procedure is attempted otherwise both the procedures are progressed.

  • De-registration and registration procedure for mobility and periodic registration update collision

If the network sent a DEREGISTRATION REQUEST message without 5GMM cause value #11, #12, #13, #15, #62, #74, #75 or #78 and the network receives a REGISTRATION REQUEST message indicating either "mobility registration updating" or "periodic registration updating" in the 5GS registration type IE before the network-initiated de-registration procedure has been completed, the de-registration procedure shall be progressed, i.e. the REGISTRATION REQUEST message shall be ignored.

If the network sent a DEREGISTRATION REQUEST message with 5GMM cause value #11, #12, #13, #15, #62, #74, #75 or #78 and the network receives a REGISTRATION REQUEST message indicating either "mobility registration updating" or "periodic registration updating" in the 5GS registration type IE before the network-initiated de-registration procedure has been completed, the de-registration procedure shall be aborted and the registration procedure shall be progressed.

NOTE 2: The above collision case is valid if the DEREGISTRATION REQUEST message indicates the access type over which the mobility and periodic registration procedure is attempted otherwise both the procedures are progressed.

  • De-registration and service request procedure collision

If the network receives a SERVICE REQUEST message or a CONTROL PLANE SERVICE REQUEST message before the network-initiated de-registration procedure has been completed (e.g. the DEREGISTRATION REQUEST message is pending to be sent to the UE), the network shall progress the de-registration procedure.

NOTE 3: The above collision case is valid if the DEREGISTRATION REQUEST message indicates the access type over which the service request procedure is attempted otherwise both the procedures are progressed.

  • De-registration requested for a UE not supporting CAG due to CAG restrictions

Based on operator policy, if the network-initiated de-registration procedure is triggered for a UE not supporting CAG due to CAG restrictions, the network shall send the DEREGISTRATION REQUEST message including a 5GMM cause value other than the 5GMM cause #76 (Not authorized for this CAG or authorized for CAG cells only).

NOTE 4: 5GMM cause #7 (5GS services not allowed), 5GMM cause #11 (PLMN not allowed), 5GMM cause #27 (N1 mode not allowed), 5GMM cause #73 (Serving network not authorized) can be used depending on the subscription of the UE and whether the UE roams or not.

  • Lower layers indication of non-delivered NAS PDU due to handover.

If the DEREGISTRATION REQUEST message could not be delivered due to an intra AMF handover and the target TA is included in the TAI list, then upon successful completion of the intra AMF handover the AMF shall retransmit the DEREGISTRATION REQUEST message. If a failure of handover procedure is reported by the lower layer and the N1 NAS signalling connection exists, the AMF shall retransmit the DEREGISTRATION REQUEST message.