Circuit Switched Fallback Call Routing for Video Reliability
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Solution Overview
Problem
In 3GPP networks, circuit-switched fallback (CSFB) procedures often result in call drops for Unrestricted Digital Information (UDI) video calls when transferred to Global System for Mobile Communications (GSM) networks, as GSM does not support UDI video calls, while simple voice calls can be safely transferred to either GSM or Universal Mobile Telecommunications System (UMTS) CS domains.
Innovation Solution
Implementing a method where User Equipment (UE) indicates the call type to the LTE network, ensuring that CSFB procedures transfer calls to the appropriate CS domain; if the call is a UDI video call, it is only transferred to the UMTS network, which supports it, while simple voice calls can be transferred to either GSM or UMTS networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CSFB procedures transfer all calls to GSM network, then device complexity is reduced and ease of operation is improved, but call reliability deteriorates for UDI video calls
Solution Approach 1:
The system performs preliminary identification of call type (voice or UDI video) before initiating the CSFB procedure. The UE indicates the call type to the LTE network in advance, allowing the network to pre-determine the appropriate target network (GSM or UMTS) before the fallback occurs, ensuring reliable routing without adding complex real-time decision-making during the call transfer
Solution Approach 2:
The patent applies different routing policies based on call type: voice calls are routed to GSM network while UDI video calls are routed to UMTS network. This local differentiation in routing quality ensures each call type receives the appropriate network treatment, maintaining high reliability for both without requiring the entire system to be optimized for a single scenario
2Reliability
If CSFB procedures transfer calls to UMTS network only, then call reliability for UDI video calls is improved, but productivity decreases due to restricted routing options
Solution Approach 1:
The system implements call type-specific routing: UDI video calls are directed to UMTS network for reliable support, while voice calls are directed to GSM network for efficient handling. This localized quality assurance ensures each call type reaches the most appropriate network, maintaining both reliability and efficiency
Solution Approach 2:
The UE indicates the call type to the LTE network before the CSFB procedure begins, allowing the network to pre-determine the optimal routing path. This preliminary action eliminates the need for trial-and-error routing or call drops, thereby maintaining high call setup efficiency while ensuring reliable delivery
3Loss of information
If the system does not identify call type, then device complexity is reduced and ease of operation is improved, but loss of information occurs when UDI video calls are transferred to incompatible networks
Solution Approach 1:
The UE autonomously identifies its own call type (voice or UDI video) and indicates this information to the LTE network. This self-service approach allows the mobile device to provide the necessary service information without requiring complex network-side analysis or additional signaling infrastructure
Solution Approach 2:
The call type information is transmitted in advance during the service request phase, before the CSFB procedure begins. This preliminary transmission of information ensures the network has the necessary data to route the call appropriately, preventing information loss without adding complex real-time processing requirements
Data Source
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AI summary
Techniques described herein may enable a wireless cellular network to transfer a call from a packet-switched (PS) portion of the wireless cellular network to a circuit-switched (CS) portion of the wireless cellular network, in a manner that ensures that the CS network receiving the call can actually support the call. For instance, before the wireless cellular network selects RAT for the CS network for transferring a call, the wireless cellular network may identify a call type for the call (e.g., simple voice call, video call, etc.), identify a RAT for the CS network that can support the call type, and proceed to transfer the call to the CS portion of the wireless cellular network that can support the call type, thus ensuring that the call is not dropped as a result of the transfer.