UE Context Handling After 5G to LTE Inter-System Handover

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Solution Overview

Problem

During inter-system handover from 5G to LTE networks, there is a loss of knowledge about the original handover, leading to difficulties in maintaining improved end-user experience, especially for IMS voice calls, due to the lack of context information about active IMS voice calls and radio access bearers.

Innovation Solution

The introduction of a method where network nodes exchange context information, including indications of active IMS voice calls and radio access bearers, through messages like RETRIEVE UE CONTEXT REQUEST and RETRIEVE UE CONTEXT RESPONSE, to facilitate consistent handling and potential re-handover of UEs between 5G and LTE networks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If inter-system handover from 5G to LTE is performed, then network mobility is improved, but context information about active IMS voice calls and radio access bearers is lost

Engineering Contradiction:

Improvenetwork mobilityVSAvoidcontext information

Core Design Contradiction:

Adaptability or versatilityVSLoss of information

Solution Approach 1:

The source 5G network node performs preliminary actions by storing context information about the UE including indication of active IMS voice calls and radio access bearers before handover, and makes this information available to the target LTE network node through the handover message, ensuring the information is preserved rather than lost during the transition

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The handover message acts as an intermediary carrier that transfers context information from the source 5G network node to the target LTE network node. This intermediary mechanism ensures that critical information about active IMS voice calls and radio access bearers is communicated across the system boundary during handover

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If context information is exchanged between network nodes during handover, then UE handling consistency is improved, but signaling overhead increases

Engineering Contradiction:

ImproveUE handling consistencyVSAvoidsignaling overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts only the essential context information needed for consistent UE handling - specifically indication of active IMS voice calls and radio access bearers - from the complete UE context. This selective extraction approach maintains reliability while minimizing the amount of signaling data that needs to be exchanged between network nodes

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentEP4335167B1Handling of user equipment (UE) context information after inter-system handover

Publication Date: 2024.10.23 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

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AI summary

Embodiments include methods for a first network node (e.g., eNB) of a wireless network (e.g., EPS). Such methods include sending (610), to a second network node of the wireless network, a request to retrieve context information associated with a user equipment (UE) that has been or is being handed over from the second network node to the first network node. Such methods include receiving (620) the context information associated with the UE from the second network node. Specifically, the context information includes an indication of whether the UE has an active IP Multimedia System (IMS) voice call that was subject to a first inter-system handover from a 5G System (5GS) to the wireless network. Other embodiments include complementary methods for the second network node, as well as network nodes configured to perform such methods.