CSFB Call Setup via New MSC Intermediary

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Solution Overview

Problem

The existing Circuit Switched Fallback (CSFB) technology faces challenges in efficiently setting up terminating calls due to the lack of congruence between Tracking Areas (TAs) and Location Areas (LAs), leading to issues where the 'old' Mobile Switching Center (MSC-S) cannot terminate calls when the User Equipment (UE) falls back to a Location Area not controlled by the established MSC-S, requiring costly upgrades and complex coordination across different network operators.

Innovation Solution

An enhanced Roaming Retry (RR) procedure is implemented, where the 'new' MSC derives the address of the 'old' MSC during a Location Update, allowing the 'new' MSC to trigger an enhanced RR procedure and forward necessary information to the 'old' MSC, enabling efficient call setup without requiring GMSC upgrades.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the UE falls back to a Location Area not controlled by the established MSC-S, then the UE can maintain connectivity, but the old MSC-S cannot terminate calls requiring costly upgrades and complex coordination

Engineering Contradiction:

Improvecall termination reliabilityVSAvoidnetwork coordination complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The new MSC-S performs a Location Update procedure with the UE before call termination, preliminarily establishing the correct MSC-S association. This preliminary action ensures that when a terminating call arrives, the UE is already registered with the appropriate MSC-S that controls its current Location Area, eliminating the need for costly GMSC upgrades and complex coordination procedures.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the GMSC is upgraded to support roaming retry procedures, then call setup success rate improves, but deployment cost and complexity increase significantly

Engineering Contradiction:

Improvecall setup success rateVSAvoiddeployment ease

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The new MSC-S acts as an intermediary between the UE and the old MSC-S. It intercepts incoming calls by performing a Location Update procedure, thereby redirecting call termination to itself without requiring modifications to the GMSC or old MSC-S. This intermediary approach achieves high call setup success rates while avoiding costly network-wide upgrades.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If the existing CSFB procedure is used without enhancement, then implementation is simple, but call setup delays occur when MSC-S mismatch happens

Engineering Contradiction:

Improvecall setup speedVSAvoidcall setup delay

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The Location Update procedure is performed as a preliminary action before call termination. This ensures that the UE is pre-registered with the correct MSC-S, eliminating the need for roaming retry procedures during call setup. The preliminary registration eliminates call setup delays while maintaining relatively simple implementation compared to full roaming retry support.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9538574B2Technique for terminating call set up in a CSFB situation

Publication Date: 2017.01.03 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A technique for controlling set up of a terminating call to a UE in a CSFB situation involving a first MSC paging the UE and a second MSC where the UE is performing a Location Update is described. A method implementation of this technique comprises receiving, from an HLR, a PRN message and forwarding information received in the PRN message to the second MSC.