P-CSCF Bearer State Detection for IMS Call Continuity
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Solution Overview
Problem
In current 3GPP standards, when the IP-CAN Bearer is disconnected, mobile stations cannot receive terminating calls until re-registration is completed, leading to prolonged call rejection due to the P-CSCF's continuous transmission of rejection responses despite the mobile station being able to communicate through the IMS.
Innovation Solution
A communication control device and method that includes a bearer state detection unit to monitor the IP-CAN Bearer status and a terminating call control unit to cancel rejection responses upon detection of bearer re-establishment, triggered by specific signals from the mobile station related to originating calls, ensuring timely reactivation of terminating calls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the IP-CAN Bearer is removed during handover to UTRAN/GERAN, then the mobile station can perform handover to other networks, but the mobile station cannot receive terminating calls until re-registration is completed
Solution Approach 1:
The P-CSCF performs preliminary actions by detecting bearer re-establishment proactively and canceling rejection responses before terminating calls are attempted. The system monitors bearer state changes and prepares to restore service by canceling the rejection response state as soon as the bearer is re-established, rather than waiting for a failed call attempt.
2Measurement precision
If the P-CSCF transmits rejection responses when the IP-CAN Bearer is removed, then the system maintains accurate call routing information, but the mobile station is continuously rejected even after the bearer is re-established
Solution Approach 1:
The system implements feedback by continuously monitoring bearer state changes and using this information to dynamically adjust the rejection response transmission. When the bearer state changes from removed to re-established, the P-CSCF receives feedback about this change and automatically cancels the rejection response, ensuring that call routing decisions are always based on current bearer status.
3Stability of the object's composition
If the mobile station remains registered with IMS after IP-CAN Bearer removal, then the registration state is maintained, but the P-CSCF cannot distinguish between registered and bearer-available states
Solution Approach 1:
The P-CSCF acts as an intermediary that maintains separate tracking of registration state and bearer state. By introducing an additional bearer state detection mechanism independent of registration status, the system can distinguish between a mobile station that is registered versus one that has an available bearer, allowing for more nuanced call routing decisions without complicating the registration process itself.
Data Source
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AI summary
Provided are a communication control device by which a situation where a mobile station is disabled to receive a terminating call can be prevented from continuing for a long time, even when the IP-CAN bearer is removed for some reason. A P-CSCF 310 executes the steps of: detecting a state of the IP-CAN Bearer; transmitting a 503 Service Unavailable, rejecting a terminating call to an UE 100, to a source making the terminating call when loss of the IP-CAN Bearer which has been established is detected; and canceling the transmission of the rejection response when receiving a signal from the UE 100 in a situation where the loss of the IP-CAN bearer is detected, the signal being related to an originating call to the IP multimedia subsystem and being a signal other than registration to the IP multimedia subsystem.