Section: 5.5.2 Detach procedure 5.5.2.1 General
Content: The detach procedure is used: - by the UE to detach for EPS services only; - by the UE to disconnect from the last remaining PDN it is connected to if EMM-REGISTERED without PDN connection is not supported by the UE or the MME; - by the UE in CS/PS mode 1 or CS/PS mode 2 of operation to detach for both EPS services and non-EPS services or for non-EPS services only via a combined detach procedure; - by the network to inform the UE that it is detached for EPS services or non-EPS services or both; - by the network to disconnect the UE from the last remaining PDN to which it is connected if EMM-REGISTERED without PDN connection is not supported by the UE or the MME; and - by the network to inform the UE to re-attach to the network and re-establish all PDN connections. NOTE 1: After a successful completion of an inter-system change of the UE from S1 mode to non-3GPP access, if the non-3GPP network provides PDN connectivity to the same EPC and EMM-REGISTERED without PDN connection is not supported by the UE or the MME, the MME performs a local detach of the UE. NOTE 2: If EMM-REGISTERED without PDN connection is supported by the UE and the MME, the detach procedure is not triggered when disconnecting the UE from the last remaining PDN to which it is connected. The detach procedure also applies to the UE which is IMSI attached for "SMS only". The detach procedure with appropriate detach type shall be invoked by the UE if the UE is switched off, the USIM card is removed from the UE, the UE wishes to detach for EPS services, the UE wishes to detach for non-EPS services or as part of the eCall inactivity procedure defined in clause 5.5.4. If the detach procedure is triggered due to USIM removal, the UE shall indicate "switch off" in the detach type IE. When upper layers indicate that emergency bearer services are no longer required, the UE if still attached for emergency bearer services, may perform a detach followed by a re-attach to regain normal services, if the UE is in or moves to a suitable cell. If a detach is requested by the HSS for a UE that has bearers for emergency services, the MME shall not send a DETACH REQUEST message to the UE, and shall follow the procedures in clause 6.4.4.1 for a UE that has bearers for emergency services. If the detach procedure for EPS services is performed, the EPS bearer context(s), if any, for this particular UE are deactivated locally without peer-to-peer signalling between the UE and the MME. If the UE supports A/Gb mode or Iu mode or both, the UE shall store the TIN in the non-volatile memory in the ME, as described in annex C, for a subsequent attach procedure. The UE is allowed to initiate the detach procedure even if the timer T3346 is running. The network proceeds with the detach procedure even if NAS level mobility management congestion control is active.