Analog trunk is always in busy status even when there is no call. ( You can’t hangup the call)
It results from the incorrect configuration of “Busy Detection”. Please log in the Web Configuration Panel and check if the value of “Busy Detection” is “yes” in the Analog Trunk editing page (the default value is “yes”).
1) If the value is “No”, please change it to “yes” and test if it’s OK then.
2) If the value is “Yes”, in the case that you can get the parameters from your service provider, please configure them directly. Or you can try other busy detection setting by following the solution in the following.
Please follow the steps in the following:
Step 1. Login SSH.
For S-Series: How to Log in SSH of Yeastar S-Series VoIP PBX
For U-Series & Gateway: How to Login the SSH of Yeastar MyPBX
Step 2. Capture the FXO port signal.
Followed by this guide: How to Get the FXO/FXS/GSM Port Signal Capture
Step 3. Download the rx.raw file and analyze it.
Step 4. Use Cool Edit (a kind of software) to analyze the busy tone detail
Open the rx.raw file as
Sample Rate 8000
Formatted the rx.raw file as 16-bit Intel PCM (LSB, MSB)
Figure Sample Format As
Figure Raw data
Example busy tone signal waveform
Usually, the length of the sound (on time) and the silence (off time) of busy tone are the same. In the example below, one cycle of the busy tone is 250 ms on, 250 ms off.
Figure Busy Tone type 1
In the example below, one cycle busy tone is 210 ms on, 210 ms off, 210 ms on, 210 ms off, 210 ms on, 210 ms off 630 ms on, 210 off.
Figure busy tone type 2
Figure Busy tone type 3
Figure Polarity Reversal signal
Step4. Set up correct settings on PSTN trunk page
Figure Busy detection settings for busy tone type 1
Figure Busy Detection settings for busy tone type 2
Figure Busy Detection settings for busy tone type 3
Figure Busy Detection settings for Polarity Reversal
Yes, you can use Audicity instead of CoolEdit. Thanks for sharing us with alternative tool to analyse the analog signal waveform.