Dual-Timer Call Setup Logic for Emergency Session Reliability
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Solution Overview
Problem
Existing emergency call setup timers in telecom networks can cause network traffic spikes at public safety answering points (PSAPs), leading to dropped calls and compromised emergency response services due to poorly designed timer configurations.
Innovation Solution
Implementing a dual-timer system, where a first timer expires upon receiving a 100 Trying SIP response and a second 'catch-all' timer expires after a longer period, allowing for retries on different proxy call session control function (P-CSCF) nodes using anonymous SIP requests, ensuring emergency calls are not abandoned prematurely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing emergency call setup timers are used, then call setup timeout protection is provided, but network traffic spikes occur at PSAPs causing dropped calls
Solution Approach 1:
The patent divides the single call setup timer into multiple separate timers (first timer for initial setup, second timer for retry operations). This segmentation allows different timeout behaviors for different call setup phases, preventing the network traffic spikes caused by simultaneous retry attempts from multiple UEs while maintaining reliable call establishment.
2Loss of time
If call setup timeout is reduced, then user frustration is minimized, but call establishment may fail during network issues
Solution Approach 1:
The patent implements dynamic timer values that adapt based on network conditions and call setup stage. The first timer uses a shorter timeout for initial setup to reduce user waiting time, while the second timer uses a longer timeout for retry operations to ensure call establishment succeeds during network issues. This dynamic adjustment resolves the contradiction between speed and reliability.
3Device complexity
If single timer configuration is used, then system complexity is low, but emergency call setup fails under high stress conditions
Solution Approach 1:
The patent changes the timer parameter configuration from a single fixed value to multiple adaptive values. The system monitors network conditions and adjusts the timeout parameters of different timers accordingly. This allows the system to maintain low complexity during normal operations while achieving high reliability under stress conditions through parameter adaptation.
Data Source
AI summary
Multiple timers used by a device during setup of a communication session may include a first timer and a second timer, each configured to expire after different periods of time, and each configured to start in response to the device sending a Session Initiation Protocol (SIP) request using a SIP INVITE method. The first timer is stopped on receipt of the first SIP response, which may include a 100. Trying SIP response, while the second timer is stopped on receipt of a non-100 Trying SIP response. If the first timer expires, the device may send an additional SIP request using the SIP INVITE method as a retry mechanism while the second timer continues to run. If the second timer expires, the device may halt the session setup and reattempt using a different type of access network.