CSFB Gateway MSC Handling Mobile Terminating Connection Attempts
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Solution Overview
Problem
The current CSFB procedure in 3GPP TS 23.272 faces challenges due to the lack of congruence between Tracking Areas (TAs) and Location Areas (LAs), leading to issues in call termination when a UE falls back from E-UTRAN to GERAN or UTRAN, requiring upgrades of all MSCs and complex vendor coordination, especially in large countries with international roaming.
Innovation Solution
A method is introduced to handle mobile terminating connection attempts by changing the association from a first routing node to a second routing node with CS fallback, using a CSFB Gateway (CSFB Gw-MSC) that handles the SGs interface with the MME, allowing for CS fallback without requiring all MSCs to support the SGs interface, thereby simplifying the deployment and reducing the need for widespread upgrades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If all MSCs are upgraded to support SGs interface for CSFB, then CSFB functionality is fully available, but device complexity and deployment cost increase significantly
Solution Approach 1:
The patent segments the CSFB functionality by introducing a dedicated CSFB Gateway MSC that handles SGs interface associations separately from other MSCs. This allows only specific MSCs to be upgraded with SGs interface support rather than requiring all MSCs to be upgraded, thereby reducing deployment complexity while maintaining full CSFB functionality.
Solution Approach 2:
The patent introduces a CSFB Gateway MSC as an intermediary node between the MME and the CS domain. This gateway MSC handles the SGs interface associations and coordinates with the target MSC during CSFB procedures, allowing legacy MSCs without SGs interface support to still participate in CSFB through this intermediary.
2Reliability
If CSFB is implemented with strict TA-LA congruence, then call termination reliability improves, but deployment flexibility and adaptability decrease
Solution Approach 1:
The patent implements dynamic handling of TA-LA congruence by allowing the CSFB Gateway MSC to determine target MSC identities dynamically during CSFB procedures rather than requiring static pre-configuration. The gateway can adapt to different scenarios including cases with and without TA-LA congruence, providing both reliability and deployment flexibility.
Solution Approach 2:
The patent changes the parameter of TA-LA congruence enforcement from a strict requirement to a flexible condition. The CSFB Gateway MSC can handle both congruent and non-congruent cases by dynamically determining target MSC identities, allowing the system to maintain call termination reliability while adapting to various deployment scenarios.
3Measurement precision
If international roaming coordination is required for CSFB, then call termination accuracy improves, but implementation time and complexity increase
Solution Approach 1:
The patent performs preliminary actions by having the CSFB Gateway MSC determine the target MSC identity and prepare the routing information before the actual CSFB execution. This preliminary determination of target MSC identity ensures call termination accuracy while reducing implementation time by avoiding last-minute coordination during international roaming scenarios.
Data Source
AI summary
A technique for handling mobile terminating connection attempts for a mobile terminal for which a change of an association from a first routing node to a second routing node is accompanied by a Circuit Switched (CS) fallback is described. In one exemplary embodiment, a method may be performed by a Circuit Switched Fallback Interworking Function (CSFB-IWF) for handling mobile terminating connection attempts for a mobile terminal for which a change of an association from the CSFB-IWF to a Mobile Switching Center (MSC) is accompanied by a Circuit Switched Fallback (CSFB). The method may include receiving a mobile terminating connection attempt to the mobile terminal. In response to receiving the mobile terminating connection attempt, the method may include paging the mobile terminal using a Mobility Management Entity (MME). In response to paging the mobile terminal, the method may include triggering the mobile terminal to initiate a CSFB procedure. Further, the method may include determining an identity of the MSC based on a message received by the CSFB-IWF from the MSC. Also, the method may include transmitting, to the MSC, a second mobile terminating connection attempt for a CS connection to the mobile terminal.