CS Fallback Mechanism for VoIP Call Routing in LTE Networks
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Solution Overview
Problem
Existing high-level signaling for preparing and executing fallback procedures for Mobile Originating (MO) and Mobile Terminating (MT) voice calls in wireless communications has unresolved issues, particularly in determining whether to route calls to the Packet Switched (PS) or Circuit Switched (CS) domain, and in handling call control, especially when IMS support is absent or incomplete.
Innovation Solution
The method involves determining CS fallback based on IMS registration status, sending a service request through the Non-Access Stratum (NAS) to the Access Stratum (AS), and using Radio Resource Control (RRC) messages to manage handovers between PS and CS domains, ensuring seamless call control transfer between VoIP and CS call clients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LTE network is deployed for high-speed PS services only, then spectral efficiency and data traffic performance are improved, but voice call capability is lost
Solution Approach 1:
The LTE network is enhanced to serve multiple functions: it continues to provide high-speed PS data services while also supporting voice calls through CS fallback mechanism. The network can route voice traffic to CS domain when needed, making the LTE network universal for both data and voice services.
Solution Approach 2:
The CS fallback mechanism acts as an intermediary between LTE PS domain and legacy CS domain. When voice calls are needed in LTE network, the system uses this intermediary mechanism to redirect calls to the CS domain, enabling voice capability without requiring full IMS deployment.
2Reliability
If IMS networks are deployed for voice call continuity, then voice service quality is improved, but network complexity and deployment cost increase
Solution Approach 1:
The patent extracts the essential voice call functionality from the complex IMS network and implements it through a simpler CS fallback mechanism. Instead of deploying full IMS for all voice services, the system uses this extracted approach to handle voice calls through basic CS domain redirection from LTE.
Solution Approach 2:
The CS fallback mechanism provides a cost-effective alternative to expensive IMS deployment. Operators can use their existing CS infrastructure (which is already deployed) to handle voice calls, avoiding the need to invest in new IMS networks while maintaining voice service quality.
3Ease of operation
If WTRU routes voice calls to PS domain using VoIP, then call setup flexibility is improved, but call control complexity increases
Solution Approach 1:
The call control system dynamically adapts its behavior based on network conditions and capabilities. The WTRU and network can dynamically decide whether to route voice calls through PS domain (VoIP) or redirect to CS domain through fallback mechanism, providing flexibility while managing complexity through dynamic adaptation rather than static configuration.
Data Source
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AI summary
A method and apparatus are used to perform a Circuit Switched (CS) fallback in wireless communications. The Non-Access Stratum (NAS) of the apparatus determines whether to perform a CS fallback based on an Internet Protocol (IP) Multimedia Subsystem (IMS) registration status, and sends a service request indicating a request to perform the CS fallback when the WTRU is attached to a CS domain. The apparatus also includes an Access Stratum (AS) that receives the CS service request from the NAS, sends an indication of the CS service request in a Radio Resource Control (RRC) message to an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), wherein the RRC message includes CS service information, and receives a handover conunand in response to the CS service request.