CSFB IWF Eliminates SGs Interface Complexity

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Solution Overview

Problem

Current Circuit Switched Fallback (CSFB) processes in LTE systems require complex modifications and new interfaces, leading to increased call setup delays and costs due to the need for SGs interfaces and state machine changes in MSC and MME nodes, especially during roaming retries.

Innovation Solution

The introduction of a CSFB Internetworking Function (IWF) that connects to both CS and LTE networks through MAP interfaces, eliminating the need for SGs interfaces at the MSC, reducing roaming retry complexities, and allowing the CSFB IWF to operate independently without modifying existing MSCs, thereby simplifying the fallback process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If SGs interface is implemented between MME and MSC/VLR to enable CSFB, then voice call functionality is achieved, but device complexity and call setup delay increase

Engineering Contradiction:

Improvevoice call functionalityVSAvoidinterface complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent introduces an SGs Interface Function (SGs-IF) as an intermediary component that mediates between the MME and MSC/VLR. This separate functional entity handles the complex SGs interface signaling and state machine management, allowing the MME and MSC/VLR to remain relatively simple while still achieving full CSFB voice call functionality. The SGs-IF acts as a buffer and translator between the packet-switched and circuit-switched domains.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the CSFB functionality by separating the SGs interface handling into a distinct SGs-IF component rather than integrating it directly into the MME and MSC/VLR. This segmentation allows each node to have reduced complexity while the overall system achieves the required voice call adaptability through the coordinated interaction of multiple specialized components.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If SGs interface and state machine modifications are made in MSC and MME nodes, then CSFB is enabled, but call setup delay increases

Engineering Contradiction:

ImproveCSFB capabilityVSAvoidcall setup delay

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent implements preliminary action by pre-establishing the SGs interface signaling path and state machine configurations in the SGs-IF component before actual voice calls are initiated. The interface and its associated state machines are pre-configured and ready, allowing rapid call setup without the need for dynamic modifications during call establishment. This pre-preparation significantly reduces call setup delay while maintaining full CSFB capability.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If roaming retry procedures are implemented in MSC/HLR/GMSC, then MT call delivery is improved, but device complexity increases

Engineering Contradiction:

ImproveMT call deliveryVSAvoidnode modification complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent introduces the SGs-IF as an intermediary that centralizes the roaming retry logic and procedures. Instead of modifying multiple nodes (MSC, HLR, GMSC) to implement roaming retry, the SGs-IF handles all roaming-related signaling and retry operations in one place. This single-point management of roaming procedures improves MT call delivery reliability while minimizing the complexity changes required across the network, as only the SGs-IF needs substantial modifications.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10004003B2Internetworking for circuit switched fallback-network initiated USSD request/notification procedure mobile-terminated location request procedure provide subscriber information procedure

Publication Date: 2018.06.19 MAVENIR SYST INC

AI summary

A method for switch user equipment from a Long Term Evolution system to a Circuit Switched system when receiving a voice call is disclosed. The method may comprise: receiving, at an IWF (Internet Working Function) network node, a Mobility Application Part Unstructured Supplementary Service Data (MAP USSD) message identifying a User Equipment (UE) originated from a USSD application, the UE associated with a first Mobile Switching Center (MSC); initiating Circuit Switched Fallback (CSFB) by sending a paging request to the UE; receiving a Cancel Location message associated with the UE from a Home Location Register (HLR) indicative of the UE being associated with a second MSC; forwarding the MAP USSD message to the UE via the HLR and the second MSC; receiving a MAP USSD response message from the UE via the HLR; and forwarding the MAP USSD response message to the USSD application.