EPS Fallback Call Processing for Tracking Area Update Failures
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Solution Overview
Problem
The success rate of establishing voice calls after a mobile device is redirected from a 5G network to a 4G network during emergency procedures fallback (EPS FB) is low due to failed tracking area updates and abnormal signaling flows, leading to calls being dropped or unable to connect.
Innovation Solution
A call processing method that includes identifying abnormal signaling flows, adding tracking area codes to a forbidden list, triggering reregistration on the 5G network, recording preferred cells for subsequent selection, and avoiding blacklisted cells to improve the likelihood of successful call establishment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mobile device follows the standard EPS FB procedure by camping on a cell within the original tracking area, then the tracking area update procedure is initiated, but the call establishment fails due to abnormal signaling flow and repeated retransmissions
Solution Approach 1:
The patent applies preliminary action by proactively selecting a cell from a pre-configured list of cells belonging to different tracking areas before attempting call establishment. When tracking area update fails, the device immediately camps on a cell from the alternative list rather than retrying the failed procedure, thereby preventing the abnormal signaling flow from occurring in the first place
Solution Approach 2:
The patent changes the parameter of cell selection by transitioning from selecting cells within the original tracking area to selecting cells from a pre-configured list of cells in different tracking areas. This parameter change bypasses the abnormal signaling conditions associated with the original tracking area and enables successful call establishment
2Productivity
If the device repeatedly retries the tracking area update procedure in the same cell, then the signaling flow is retransmitted multiple times, but the call establishment continues to fail
Solution Approach 1:
The patent applies skipping by directly transitioning to camping on a cell from the alternative list when tracking area update fails, rather than repeatedly retrying the failed procedure. This skips the time-consuming cycle of repeated failures and immediately attempts call establishment in a different tracking area, significantly improving call setup efficiency while reducing time loss
3Reliability
If the device camps on a cell in a different tracking area, then the tracking area update can succeed, but the device must maintain a pre-configured list of alternative cells
Solution Approach 1:
The patent applies preliminary action by pre-configuring a list of cells belonging to different tracking areas before the device needs to establish a call. This preparation is done in advance so that when call establishment is needed, the device can immediately select from the pre-configured list without complex real-time decision-making, thereby maintaining reliability while minimizing operational complexity
Data Source
Figure 1a~1b
Figure 2A
Figure 2B
AI summary
This application provides a call processing method and an apparatus, which are used in an electronic device. The electronic device that is called or initiates a call camps on a first cell of an LTE network after being redirected form a 5G network to the LTE network. The first cell belongs to a tracking area. The method includes: after tracking area update fails, searching, in response to identifying an abnormal signaling flow, for an available cell that does not belong to a tracking area, and initiating the tracking area update in the available cell to attempt to establish a call. The identification of the abnormal signaling flow indicates that the tracking area update may fail because signaling is not sent. Therefore, it is attempted to establish a call in the available cell that does not belong to the tracking area, which can improve a possibility of successfully establishing a call after the redirection from the 5G network to the LTE network.