1. The UE sends NAS message Deach Request to the CloudUSN.
2. The CloudUSN requests the CloudUGW to delete all bearers of the subscriber. When the CloudUGW deletes a dedicated bearer and PDN connection, the CloudUGW needs to notify the vPCRF through the Gx interface.
3. If the trunking service dedicated bearer initiated by the vTSN is deleted, the CloudUGW sends a Delete Trunk Bearer Notification message carrying the EPS Bearer IDs to the vTSN and sets the cause to PDN Disconnected. After receiving the trunking dedicated bearer deletion notification message and the release cause is PDN connection release, the vTSN releases the established trunking service session (including the trunking speaker and P2P call), but does not send trunking signaling to the terminal and waits for the trunking user detach message initiated by the CloudUSN.
Note:
If the CloudUGW does not receive a response from the vTSN or the response carries the failure cause value, go to step 4.
4. After releasing the user bearer information, the CloudUGW returns a response to the CloudUSN. In addition, the CloudUGW should trigger the IP-CAN session release procedure between the PCRFs. For details, please refer to the 3GPP 23.203.
5. If the trunking user successfully registers with the vTSN, the CloudUSN sends a Trunk User Detach Reqeust message to the vTSN to instruct the vTSN user to detach. After receiving the message, the vTSN proxies the UE to detach from the eMDC and returns a confirmation response to the CloudUSN.
6. If the CloudUSN does not receive a response from the vTSN or the response carries the failure cause value, go to step 6. The CloudUSN sends a Detach Accept message to the UE and releases the S1 signaling connection of the UE.
