DTMF Signal Evaluation for Unauthorized 3-Way Call Detection
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Solution Overview
Problem
Current methods for detecting unauthorized 3-way calls in inmate calling services are inadequate, leading to false positives, unnecessary call interruptions, and revenue loss due to the inability to reliably distinguish between valid DTMF signals and degraded or concurrent voice signals in telecommunications systems.
Innovation Solution
The system compares signal characteristics of initial DTMF signals from an authorized called party with subsequent signals received in response to prompts, analyzing power, phase, and other characteristics to verify the presence of unauthorized parties by ensuring similarity between the first and second signals, while disconnecting the talking path from the inmate to prevent interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current DTMF signal detection methods are used to identify unauthorized 3-way calls, then call security is maintained, but false positives increase and revenue is lost due to unnecessary call terminations
Solution Approach 1:
The system performs preliminary actions by disconnecting the talking path from the inmate before evaluating subsequent DTMF signals. This prevents the inmate from generating interfering signals during the evaluation phase, thereby improving the reliability of detection without causing false positives that would lead to revenue loss.
Solution Approach 2:
The system uses feedback by comparing subsequent DTMF signals with expected signal characteristics. This comparison mechanism provides feedback to determine whether an unauthorized party has been introduced, improving detection accuracy while avoiding unnecessary call terminations and maintaining revenue.
2Measurement precision
If DTMF signal evaluation is performed during ongoing calls, then unauthorized parties can be detected, but signal degradation and voice interference reduce detection accuracy
Solution Approach 1:
The system disconnects the talking path from the inmate as a preliminary action before evaluating subsequent DTMF signals. This eliminates voice signal interference and other harmful factors that would degrade DTMF signal quality, thereby improving measurement precision without compromising the ability to detect unauthorized parties.
Solution Approach 2:
The system extracts the talking path connection from the inmate during the signal evaluation phase. By removing this potential source of interference, the system improves DTMF signal detection accuracy while maintaining the ability to detect unauthorized parties through subsequent signal comparison.
3Duration of action of moving object
If the talking path remains connected during signal evaluation, then continuous communication is maintained, but false detection of unauthorized parties increases
Solution Approach 1:
The system employs periodic action by temporarily disconnecting and reconnecting the talking path at specific intervals. The path is disconnected during subsequent DTMF signal evaluation to ensure accurate detection, then reconnected to maintain call continuity. This periodic disconnection/connection cycle improves detection reliability while minimizing impact on overall call duration.
Solution Approach 2:
The system performs preliminary disconnection of the talking path before signal evaluation begins. This preliminary action ensures that no interference occurs during the critical evaluation phase, improving detection accuracy while allowing the call to resume normal operation afterward, thus maintaining overall call continuity.
Data Source
AI summary
The likelihood that a called party to a telephone call has forwarded the call to another party, or has conferenced the call to include another party is estimated by requiring that the called party supply a first signal, illustratively a first DTMF signal, later requiring that the called party provide a second signal, illustratively the same DTMF signal provided by the first signal, and comparing characteristics of said first and second signals as received at a telephone network node.