In a detach procedure, the UE can notify the network that the UE does not continue to access the EPS network, or the network can instruct the UE that the UE is no longer allowed to continue to access the EPS network.
The detach procedure is used in the following scenarios:
A UE is detached from the EPS service.
The UE is disconnected from the last PDN connection.
The network instructs the UE that the UE cannot access the EPS network.
The UE is detached either explicitly or implicitly:
Explicit detach: The network or UE initiates a detach request and notifies the other side of the detach.
Implicit detach: The network detaches an UE and does not notify the UE of the detach. For example, the network considers the UE to be unreachable.
Detach types from Initiator point of view
a/ UE-initiated Detach
When a UE is powered off or is in the airplane mode, the UE initiates a detach procedure.
Switch Off: specifies whether the UE is detached from the network due to power-off. If the UE is detached from the network due to power-off, the MME does not send a Detach Accept message to the UE.
type-of-detach: specifies the detach procedure type.
- EPS-detach(1): The UE only deregisters from the EPC network.
- IMSI-detach(2): The UE only deregisters from the CS network.
- combined-EPS-detach(3): The UE deregisters from both the EPC network and CS network.
If multiple PDN connections are established, the bearer-specific parts of this procedure will be repeated for every PDN connection.
b/ MME-initiated Detach
If the UE does not communicate with the network for a long time, the MME initiates a detach procedure.
- The MME can initiate implicit or explicit detach. If the MME does not communicate with the UE for a long time, the implicit detach can be initiated. The MME does not send the Detach Request message to the UE during implicit detach.
- If the MME initiates an explicit detach procedure, the MME sends a Detach Request message to the UE. The message contains Detach Type.