UE IMS DRB Recovery After EPS Fallback Call Failure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In LTE and NR radio access networks, the lack of data radio bearers for International-protocol multimedia subsystem (IMS) signaling during evolution packet system fallback leads to delayed session initialization protocol signaling, causing call failures and missed urgent communications.
Innovation Solution
A user equipment (UE) method and system that determines the activation of PDU sessions and DRBs for IMS signaling, requesting base stations to reconfigure radio bearers when necessary, and executes RRC or RRE processes until the DRB is established, with process repetition and timing controls to ensure IMS signaling is available.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE returns to the NR RAN network after call completion, then the UE is in RRC connection state, but the UE cannot receive SIP signaling in time due to lack of DRB for IMS signaling
Solution Approach 1:
The UE proactively checks whether the PDU session is activated and whether DRB for IMS signaling exists before attempting to receive SIP signaling. This preliminary check allows the UE to detect the missing DRB condition early and trigger recovery procedures before the signaling timeout occurs, thereby reducing the time loss and improving call connection reliability
Solution Approach 2:
The UE implements a feedback mechanism by monitoring the presence of DRB for IMS signaling and comparing it with the PDU session activation state. When a mismatch is detected (PDU session activated but DRB missing), the UE triggers RRC process repetition or RRE to request reconfiguration. This closed-loop feedback ensures timely detection and correction of the configuration error, improving both response time and call success rate
2Reliability
If the gNB does not re-transmit radio bearer configuration information including DRB for IMS signaling, then the configuration remains incomplete, but repeated RRC or RRE processes increase signaling overhead
Solution Approach 1:
The UE autonomously detects the missing DRB configuration by checking its own PDU session activation state against the actual DRB presence. Instead of waiting for external detection or manual intervention, the UE self-identifies the configuration incompleteness and initiates recovery procedures, reducing the need for complex network-side detection mechanisms and minimizing unnecessary signaling
Solution Approach 2:
The UE repeats RRC or RRE processes only when specifically needed (when DRB is missing but PDU session is activated), rather than continuously or unnecessarily. This partial action approach applies the recovery procedure only to the specific missing configuration element, avoiding excessive signaling while ensuring the necessary DRB is established
Data Source
AI summary
A user equipment and a call recovery method executed by the user equipment are provided. The call recovery method executed by the user equipment includes: determining whether a protocol data unit PDU session is activated in the user equipment UE and an access mobility management function entity AMF based on PDU session information, and determining whether there is no data radio bearer DRB for bearing International protocol multimedia subsystem IMS signaling based on radio bearer configuration information; and requesting a base station gNB to re-transmit the radio bearer configuration information including the DRB for bearing the IMS signaling if the PDU session is activated in the UE and the AMF and there is no DRB for bearing the IMS signaling.