IMS Call Continuity During Network-Initiated CS Signaling

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Solution Overview

Problem

Existing methods for handling circuit switched signaling services in mobile networks often result in interruptions during calls established via the internet protocol domain, particularly when transitioning between packet switched and circuit switched access, as they fail to differentiate between voice calls and other signaling services like USSD, leading to unintended service fallbacks.

Innovation Solution

Implementing a method where a control node and terminal in a mobile network determine the status of ongoing calls via the internet protocol domain and packet switched access, allowing for the rejection of paging requests and initiation of call continuity procedures as needed, thereby avoiding interruptions during circuit switched signaling service terminations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the terminal performs CSFB procedure for network-initiated circuit switched signaling service, then the signaling service can be terminated, but the ongoing IMS voice call is interrupted

Engineering Contradiction:

Improvesignaling service terminationVSAvoidongoing call continuity

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent segments the handling of paging requests by type: MT-LR paging requests are handled differently from other circuit switched signaling service paging requests. When an IMS voice call is ongoing, MT-LR paging is rejected while other signaling services can proceed with CSFB, thus segmenting the problem to protect only voice calls while allowing other services to function normally

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary mechanism (the determination step) between receiving the paging request and executing CSFB. The control node determines whether the paging request is for MT-LR or other services, and this determination acts as an intermediary that prevents inappropriate CSFB execution during ongoing voice calls

Inventive Principle:

Principle #24Intermediary (Mediator)

2Duration of action of stationary object

If the terminal differentiates between MT-LR and other signaling services, then voice call continuity is protected, but the system complexity increases

Engineering Contradiction:

Improveongoing call continuityVSAvoidservice differentiation logic

Core Design Contradiction:

Duration of action of stationary objectVSDevice complexity

Solution Approach 1:

The existing paging rejection mechanism is made multi-functional: it serves both its original purpose of rejecting inappropriate paging during voice calls and the new purpose of protecting against CSFB-induced interruptions. The same determination logic handles both MT-LR differentiation and ongoing call protection, reducing the need for separate specialized mechanisms

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10805355B2Network initiated CS services during IMS call

Publication Date: 2020.10.13 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

An interruption of a call which is established or which is currently being established via an internet protocol domain of a mobile network may be avoided during a handling of a circuit switched signaling service to be terminated to a terminal and being different from a mobile terminating location request service.