VoIP Modem Tone Synchronization via Feedback Clock Adjustment
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Solution Overview
Problem
IP-based telephone networks face issues with data transmission quality due to asynchronous clock synchronization between terminals, leading to disturbances in voice signals and errors in data transmission, particularly in VoIP networks where clock differences cause bit errors and packet loss, limiting the transmission of data such as faxes to only a few pages without error correction.
Innovation Solution
The method involves synchronizing the clocks of analog-to-digital and digital-to-analog converters at both terminals by using the timing from received VoIP packets, ensuring that the clocks are synchronized to maintain accurate digitization and conversion of modem tones, thereby reducing errors and improving data transmission quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If asynchronous clock operation is used at terminals in IP-based telephone networks, then device complexity is reduced and ease of operation is improved, but data transmission quality deteriorates due to clock differences causing bit errors and packet loss
Solution Approach 1:
The receiving terminal measures the arrival times of samples from transmitted VoIP packets and uses this feedback information to calculate and adjust the clock frequency of its D/A converter, thereby synchronizing with the transmitting terminal's clock and eliminating transmission errors
Solution Approach 2:
The patent replaces the traditional hardware-based clock synchronization mechanism with a software-based calculation approach, where the receiving terminal computes the required clock frequency based on measured sample arrival times, eliminating the need for complex hardware synchronization mechanisms
2Reliability
If clock synchronization is implemented between terminals, then data transmission quality is improved, but device complexity increases due to additional synchronization mechanisms
Solution Approach 1:
The receiving terminal autonomously performs clock synchronization by measuring sample arrival times, calculating the required clock frequency, and adjusting its D/A converter clock accordingly, without requiring external synchronization signals or complex coordination with the transmitting terminal
Solution Approach 2:
The patent changes the clock frequency parameter of the D/A converter at the receiving terminal based on measured sample arrival times, dynamically adjusting this parameter to achieve synchronization and eliminate transmission errors
3Adaptability or versatility
If packet switching is used in IP networks, then network flexibility and adaptability are improved, but transmission quality deteriorates due to longer transmission times and packet loss
Solution Approach 1:
The receiving terminal uses feedback from measured sample arrival times to calculate and adjust the D/A converter clock frequency, compensating for variations in packet transmission times and ensuring accurate reconstruction of the analog signal despite packet switching delays
Data Source
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AI summary
The present invention relates to a method for transmitting data with modem tones in a voice signal in an IP-based telephone network with a plurality of network elements, via a connection between at least one first endpoint and at least one second endpoint, wherein the data is converted into modem tones, these modem tones are sampled at a step rate via digitization of the voice signal in analog-to-digital converters arranged at the respective endpoints, the resulting sample values are transmitted in VoIP packets via the connection between the at least one first endpoint and the at least one second endpoint and are converted back into modem tones by digital-to-analog converters arranged at the respective endpoints, wherein the analog-to-digital converters and digital-to-analog converters arranged at the respective endpoints synchronize to the step rate.