SIP Timer Offset for IMS Call Fallback Reliability
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Solution Overview
Problem
Existing cellular telephony standards face challenges in efficiently managing SIP timers during fallback processes, such as EPSFB, which can lead to premature termination of calls due to timer expiries before alternative RAT connections can be established.
Innovation Solution
Implementing a selective SIP timer restart process in user equipment (UE) that adds offsets to restarted SIP timers based on specific conditions, such as receipt of an RRC Release with Redirect message or Quality of Service (QOS) timer expiry, to provide additional time for fallback processes to complete.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard SIP timer durations are used during fallback processes, then call setup efficiency is maintained, but calls may be prematurely terminated before alternative RAT connections can be established
Solution Approach 1:
The patent applies dynamics by making SIP timer durations adjustable rather than fixed. The system dynamically extends SIP timer durations when fallback conditions are detected (such as receiving a Release with Redirect message or experiencing QOS timer expiry), allowing timers to adapt their length based on the current network state and fallback requirements. This resolves the contradiction by enabling longer timer durations during fallback to prevent premature termination, while maintaining standard durations during normal operation to preserve efficiency.
Solution Approach 2:
The patent implements parameter changes by modifying SIP timer duration parameters based on specific fallback conditions. When conditions such as Release with Redirect message receipt or QOS timer expiry occur, the system changes the timer duration parameter from its standard value to an extended value. This parameter modification allows the fallback process sufficient time to complete without premature termination, directly addressing the reliability-time contradiction.
2Reliability
If SIP timers are extended to accommodate fallback processes, then fallback completion is enabled, but call setup efficiency for normal calls is reduced
Solution Approach 1:
The system uses dynamics to differentiate timer behavior between fallback and normal call scenarios. By detecting fallback conditions (Release with Redirect, QOS timer expiry) and only extending timers in those specific contexts, the system maintains efficient call setup for normal operations while providing extended timing for reliable fallback completion. This conditional dynamic adjustment resolves the contradiction between reliability and productivity.
Solution Approach 2:
The patent applies local quality by applying extended timer durations only to specific local conditions (fallback scenarios) rather than universally to all calls. The timer extension is localized to situations where fallback is detected, leaving normal call flow unaffected. This targeted approach ensures fallback reliability without compromising overall call setup efficiency.
3Reliability
If selective SIP timer restart with offsets is implemented, then fallback process completion is ensured, but device complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-defining the timer extension logic and offset values before fallback scenarios occur. The system prepares the necessary timer management mechanisms in advance, including the logic to detect fallback conditions and apply appropriate offset values. This pre-prepared approach ensures reliable fallback completion while minimizing runtime complexity, as the timer management follows predetermined rules rather than requiring complex real-time decision-making.
Data Source
AI summary
A user equipment (UE) is configured to initiate a packet-switched call via a first radio access technology (RAT) and start a plurality of session initiation protocol (SIP) timers responsive to initiating the call. Responsive to at least one condition being present with initiation of a fallback process for the call, the UE is configured to restart a set of the plurality of SIP timers for the fallback process, wherein the set can include some or all of the plurality of SIP timers started with initiation of the call. Each SIP timer has a corresponding default timer duration, and in some instances restarting a SIP timer of the set includes restarting the SIP timer with a starting duration equal to a sum of the default timer duration and an offset so that the restarted SIP timer provides for a greater duration than when originally started to better accommodate the fallback process.