Call Continuity Control During Subsystem Handoff
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Solution Overview
Problem
Existing communication systems face challenges in seamlessly transferring calls between circuit-switched and packet-based networks, such as cellular and WLAN, due to differences in technology and coverage gaps, leading to potential breaks in voice paths during handoffs, which inconvenience users.
Innovation Solution
A continuity control function (CCF) is implemented to anchor call control and signaling, allowing for smooth transfers between circuit-switched and multimedia subsystems by maintaining the call signaling leg and establishing a new bearer path, even during brief interruptions, using media gateways and resource functions to provide announcements to remote parties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If call transfer between circuit-switched and packet subsystems is implemented, then network coverage and mobility are improved, but call continuity and voice path stability deteriorate due to bearer path interruptions
Solution Approach 1:
The system performs preliminary actions by establishing the new bearer path in the target subsystem before releasing the old bearer path in the source subsystem. This ensures that the voice path is already available when the transition occurs, preventing call interruptions and maintaining call continuity during handoff between circuit-switched and packet subsystems.
Solution Approach 2:
The invention introduces an intermediary mechanism that coordinates the bearer path transition between subsystems. The intermediary manages the timing and sequencing of bearer path establishment and release, ensuring smooth transfer without breaking call continuity, thereby resolving the reliability issue during network adaptation.
2Adaptability or versatility
If simultaneous cellular and WLAN communications are supported in user element, then communication versatility is improved, but device complexity increases
Solution Approach 1:
The user element is designed with multi-functionality to support both cellular and WLAN communications through a single device. The system incorporates multiple communication interfaces and protocols that allow it to operate across different network types, achieving communication versatility without requiring separate devices for each network type.
Solution Approach 2:
The system dynamically switches between cellular and WLAN communication modes based on network availability, call state, and performance requirements. This dynamic adaptation allows the device to optimize its communication path in real-time, managing complexity through intelligent control rather than static hardware configurations.
3Reliability
If bearer path is maintained during subsystem transfer, then call continuity is improved, but transfer complexity increases due to coordination requirements
Solution Approach 1:
The system maintains continuous useful action by ensuring the bearer path remains active throughout the subsystem transfer process. The voice path is preserved by coordinating the establishment of the new bearer path before releasing the old one, eliminating gaps in communication and maintaining call continuity without requiring complex user-side intervention.
Solution Approach 2:
An intermediary control mechanism coordinates the complex bearer path transition process between subsystems. This intermediary manages the timing, signaling, and resource allocation required to maintain call continuity, thereby reducing the perceived complexity for end users while enabling reliable handoff between different network types.
Data Source
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Figure 3A
AI summary
The present invention maintains calls during transfers between different types of subsystems, even when there is a bearer path interruption at the user element due to the original connection from the transferring-out subsystem being dropped before the new connection in the transferring-in subsystem is established. The call signaling leg toward the remote endpoint of the remote party is held, while the call signaling leg toward the user element is moved from the transferring-out subsystem to the transferring-in subsystem and a new bearer path is established via the transferring-in subsystem. During transfers with a bearer path interruption, a portion of the bearer path leading to the remote endpoint may be connected to a media resource function, which will provide an announcement to the remote party. Once the user element is accessible in the transferring-in subsystem, the bearer path is further transferred to the user element via the transferring-in subsystem.