LTE Connection Retention During CSFB

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Solution Overview

Problem

During Circuit Switch Fall Back (CSFB) in LTE networks, the release of packet switched connections leads to session teardown, resulting in data loss and excessive delay, which negatively impacts applications like FTP and gaming, and can cause users to prematurely abandon call attempts due to prolonged setup times.

Innovation Solution

A mechanism to temporarily retain packet switched sessions on the LTE core network for a pre-defined period during CSFB, using a timed buffer to manage the release of context information, allowing quick re-establishment of the LTE session if the CSFB is short or fails.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the LTE packet switched connection is released during CSFB, then the circuit switched call can be established, but the data session is torn down causing data loss and requiring session re-establishment

Engineering Contradiction:

Improvevoice call establishmentVSAvoiddata loss

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The network performs preliminary actions by retaining the packet switched session context information in the core network before the CSFB occurs. This allows the data session to be quickly re-established after the voice call without requiring full re-negotiation, thereby preventing data loss while enabling reliable voice call establishment

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the LTE connection is released during CSFB, then the circuit switched network can be accessed, but excessive delay occurs in session re-establishment

Engineering Contradiction:

Improvevoice call setupVSAvoidsession re-establishment delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The core network performs preliminary action by pre-retaining the packet switched session context information before CSFB. This eliminates the need for time-consuming session re-negotiation after voice call completion, reducing re-establishment delay while ensuring reliable voice call setup

Inventive Principle:

Principle #10Preliminary action

3Productivity

If the LTE connection is retained during CSFB, then data sessions continue uninterrupted, but network resources are wasted and call setup time increases

Engineering Contradiction:

Improvedata session continuityVSAvoidcall setup time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The network applies preliminary action by retaining only the essential session context information in the core network rather than maintaining the full active connection. This allows fast re-establishment (improving productivity) while still preserving enough information to avoid complete session teardown (reducing call setup time)

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention extracts and retains only the critical session context information in the core network while releasing the full packet switched connection. This selective retention enables fast re-establishment without wasting network resources on maintaining inactive connections, balancing productivity with call setup efficiency

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentEP2753140B1A scheme of retaining LTE connection during circuit switch fall back

Publication Date: 2020.04.22 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

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AI summary

The present solution enables a packet switched connection to be temporarily released at the wireless terminal for supporting voice calls over a Circuit-Switched (CS) Fallback. The packet switched connection of the LTE core network retained for a pre-defined period of time during the CSFB session allowing the user to quickly switch back to the packet switched connection when the CSFB session is shorter than the predefined period or when the voice call CSFB attempt fails. This is accomplished by the introduction of a timed buffer to control the length of time the LTE core network connection and wireless context information will be retained.