IMS Handover Control for Seamless CS to PS Bearer Transfer
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Solution Overview
Problem
Current mobile network technologies face challenges in seamless handover of real-time IP Multimedia Subsystem (IMS) calls between circuit switched (CS) and packet switched (PS) domains, particularly when users roam across cell boundaries or between different radio access networks, leading to potential service interruptions and reduced quality of service.
Innovation Solution
A method and apparatus for handover an ongoing real-time call from a circuit switched bearer to a packet switched bearer in a target cell, involving sending a handover instruction from the radio access network or mobile station to the IP Multimedia Subsystem, which establishes a packet switched bearer and transfers the call, utilizing knowledge of packet switched handover capabilities to select suitable target cells and manage the handover process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a real-time IMS call is handed over from circuit switched bearer to packet switched bearer during roaming, then service continuity and quality of service are maintained, but the handover complexity and signaling overhead increase
Solution Approach 1:
The system performs preliminary actions by establishing the packet switched bearer before releasing the circuit switched bearer during handover. The IP Multimedia Subsystem receives handover indication, establishes PS bearer with appropriate QoS parameters, and only then releases the CS bearer, ensuring service continuity without interruption
Solution Approach 2:
The IP Multimedia Subsystem acts as an intermediary between the radio access network and the core network during handover. It receives handover indication from the radio access network, coordinates with the packet switched domain to establish new bearers, and manages the transition from CS to PS domain, simplifying the overall handover complexity
2Speed
If packet switched handover is used in areas with limited PS network coverage, then faster handover is achieved, but service interruption occurs when PS resources are unavailable
Solution Approach 1:
The system dynamically adapts the handover mechanism based on available network resources. When PS resources are available, it performs fast PS handover; when PS resources are unavailable or coverage is limited, it maintains CS handover or delays PS bearer establishment until resources become available, ensuring service continuity without unnecessary interruptions
Solution Approach 2:
The system changes the handover parameters dynamically based on network conditions. It monitors PS network coverage and resource availability, adjusting the handover approach accordingly - using PS handover parameters when resources are available for fast handover, and switching to CS handover parameters when PS resources are unavailable to maintain service continuity
3Reliability
If circuit switched bearer is used for real-time calls in areas without PS handover support, then seamless handover is maintained, but quality of service and call efficiency are reduced
Solution Approach 1:
The system performs preliminary action by establishing packet switched bearers in advance in target cells before handover is triggered. This allows the handover to transition to the more efficient PS domain without interruption, improving call efficiency while maintaining seamless handover through pre-prepared PS resources
4Adaptability or versatility
If handover between different radio access networks is supported, then network versatility and user mobility are improved, but handover control and signaling complexity increase
Solution Approach 1:
The IP Multimedia Subsystem provides universal handover control functionality that works across different radio access networks (2G, 3G, LTE). It implements a unified handover mechanism that can handle intra-RAT and inter-RAT handovers, as well as transitions between CS and PS domains, through a single multi-functional architecture that simplifies control despite the diversity of networks
Data Source
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AI summary
A method of handing over an ongoing real-time call involving a mobile station, from a circuit switched bearer in a current cell of a radio access network to a packet switched bearer in a target cell of the same or a different radio access network, the ongoing call having been established using the services of an IP Multimedia Subsystem. The method comprises sending a handover instruction from the radio access network responsible for the current cell or from the mobile station to the IP Multimedia Subsystem, the instruction identifying the target cell, in response to receipt of said instruction at the IP Multimedia Subsystem, establishing a packet switched bearer in the target cell, and transferring the ongoing call from said circuit switched bearer to said packet switched bearer.