LTE VLR Presentation for Circuit Switched Fallback

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Solution Overview

Problem

Current Long Term Evolution (LTE) systems do not support voice calls, requiring Circuit Switched Fall Back (CSFB) for voice calls, which involves complex procedures and modifications to existing nodes, including the need for new interfaces and roaming retry mechanisms, complicating call setup and increasing costs.

Innovation Solution

A method that presents a network node as a Visited Location Resource (VLR) for User Equipment (UE) in an LTE system, using an SGs interface with the Mobile Management Entity (MME) and a MAP interface with the Mobile Switching Center (MSC), allowing for CSFB without requiring changes at the MSC or configuration changes, thereby eliminating the need for SGs interfaces and reducing call setup delays.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a new SGs interface is added between MSC and MME to enable CSFB, then voice call support is achieved, but device complexity and system complexity increase

Engineering Contradiction:

Improvevoice call supportVSAvoidsystem complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary function that allows the MME to directly interact with the MSC using existing MAP protocols, eliminating the need for a dedicated SGs interface. The MME acts as an intermediary that can perform VLR functions, directly querying the HLR and interacting with the MSC through standard interfaces, thus reducing system complexity while maintaining voice call support.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent makes the MME multi-functional by enabling it to perform both EPC attachment management and CS domain registration functions. The MME can handle both LTE packet-switched services and circuit-switched voice calls through a single node, eliminating the need for separate SGs interface infrastructure and reducing overall system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If SGs interface and roaming retry procedures are implemented for CSFB, then call completion is achieved, but call setup delay increases

Engineering Contradiction:

Improvecall completionVSAvoidcall setup delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent performs preliminary registration and location update actions during the initial EPC attachment process. The MME proactively registers the UE with the MSC and establishes the CS domain connection before the actual voice call is initiated, eliminating the need for delayed roaming retry procedures and reducing call setup time.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent extracts the roaming retry procedure from the call setup process by establishing the CS domain connection in advance. The complex retry logic and iterative location updates are removed from the critical call path, allowing calls to be set up directly without time-consuming retry sequences.

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If MSC is modified to support SGs interface and CSFB state machine, then CSFB functionality is achieved, but ease of manufacture and deployment deteriorates

Engineering Contradiction:

ImproveCSFB functionalityVSAvoiddeployment ease

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

Instead of modifying the MSC to support SGs interface and CSFB state machine, the patent inverts the approach by enabling the MME to directly interact with the MSC using existing MAP protocols. This eliminates the need for MSC modifications and associated state machine changes, significantly simplifying deployment while achieving the same CSFB functionality.

Inventive Principle:

Principle #13The other way round (Inversion)

4Reliability

If complex roaming retry procedures are implemented, then call completion in roaming scenarios is achieved, but device complexity and operational complexity increase

Engineering Contradiction:

Improveroaming call completionVSAvoidoperational complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent performs preliminary location registration and HLR querying during the initial EPC attachment, establishing the UE's location in the CS domain before roaming calls are attempted. This preliminary action eliminates the need for complex roaming retry procedures, as the network already has current location information ready for immediate call routing.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS8682322B2Internetworking for circuit switched fallback

Publication Date: 2014.03.25 MAVENIR SYST INC

AI summary

In some implementations, a method includes presenting a network node as a Visited Location Resource (VLR) for User Equipment (UE) to Mobile Management Entity (MME) in a Long Term Evolution (LTE) system. The network node includes an SGs interface to the MME in the LTE system and a MAP interface to a Mobile Switching Center (MSC) in a Cellular System (CS). A notification of the UE registering the LTE system is received from the MME. A network node registers, through the MAP interface, with a Home Location Resource (HLR) in the CS as the VLR for the UE.