Access Domain Selection for IMS Call Termination
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Solution Overview
Problem
In mobile communication systems, particularly in IMS centralized services, the existing access domain selection mechanisms are inadequate, leading to poor user experience due to unawareness of access network capabilities, resulting in failed session setups when users roam between different radio access technologies, especially in scenarios where the access network is not multiRAB or DTM capable.
Innovation Solution
The introduction of the Terminated Access Domain Selection function in the UE (TADS-UE) allows the terminal to analyze and inform the IMS network about the access network's capabilities, enabling informed selection of access domains for session control and media channels, thereby supporting the IMS in selecting the appropriate access domain for call termination and improving call setup success rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the IMS network selects access domain blindly without knowing access network capabilities, then the session control signaling can be established, but the call setup fails when roaming in non-DMT capable access networks
Solution Approach 1:
The terminal performs preliminary analysis of access network capabilities (DTM capability, PLMN information, radio access technology) before call establishment. This preliminary action enables the terminal to make informed access domain selection decisions before the actual call setup, preventing failures in non-DMT capable networks while maintaining PS domain usage where appropriate.
Solution Approach 2:
The terminal provides feedback information about access network capabilities to the IMS network through capability indication messages. This feedback mechanism enables the IMS network to adjust its access domain selection decisions based on actual network conditions, ensuring reliable call setup in roaming scenarios across different access technologies.
2Device complexity
If the same access domain is used for both session control signaling and media channels, then the signaling path is simplified, but the call cannot be established in non-DMT capable access networks
Solution Approach 1:
The invention segments the access domain selection into separate decisions for session control signaling and media channels. The terminal independently determines the appropriate access domain for each channel type based on network capabilities, allowing PS domain for signaling in capable networks and CS domain for media in non-DMT networks, thus maintaining simplicity while ensuring reliability.
Solution Approach 2:
The access domain selection becomes dynamic rather than static. The terminal and IMS network adaptively select different access domains for different channels based on real-time capability analysis, enabling flexible call establishment that works across diverse access network conditions without requiring a single fixed approach.
3Loss of time
If the terminal does not analyze access network capabilities, then the call setup process is faster, but the IMS network cannot make informed access domain selection
Solution Approach 1:
The terminal performs capability analysis as a preliminary action during the call setup process. By analyzing access network capabilities (DTM capability, PLMN, radio access technology) upfront, the terminal can quickly determine the appropriate access domain without delaying the overall call setup, as this information is gathered concurrently with other setup procedures.
Data Source
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AI summary
The present application discloses a system of at least a network element and at least a terminal. The system constituents are configured to provide assistance by the terminal to thenetwork element in terms ofaccess domain selectionfor at least one of the media channel and the session control channel of an incoming call to the terminal. In this regard, the terminalacquiresinformation about the capabilities of an access network inwhich the terminal is camping. Upon receiving, at the terminal, an invitation to participate in a call, the terminal analyzes the acquired information about the capabilities of the access network,and optionally or additionally of the IMS network. The terminal responds to the invitation, based on the result of the analyzing, with an indication that indicates a respective access domain to be used for at least one of the media channel and the session control channel of the incoming call.