Capture the Signal of Analog/GSM/Digital Ports


This article applies for U-Series, and Gateway products.

This is a supplementary for this guide: How to Get the FXO/FXS/GSM Port Signal Capture especially for the digital ports.


Capture Procedure

Try to follow the steps to record the signal, which will help to analyze the details of some problems, like caller ID, busy tone, DTMF, voice quality.

Step 1 Login SSH. (enable ssh on web first, the username: root; password: ys123456)

Step 2 Execute command  vi /etc/dahdi/ysport.conf to check the physical port number and its respective channel number on Yeastar.

For example here is port information for U200, it follows the format: {port number} = {port type}, {channel number}

  • Port 1 means BRI trunk, the channel number is 1-2 which means it has 2 channels.
  • Port 6 means FXO trunk, the channel number is 10 which has only 1 channel.

For TE100, you can see it has 1 e1 port, and the channel numbers are 1-15 & 17-31.


For TB400, it has 4 bri ports. The channel numbers are behind the comma.


Step 3 Go to directory /persistent/ (cd /persistent).
Please DO NOT skip this step, you need to record the files in persistent folder.

Step 4 Execute command dahdi_monitor n –r rx.raw –t tx.raw, n is channel number.
for example, if you want to capture signal of channel 1, command is dahdi_monitor 1 –r rx.raw –t tx.raw.

Step 5 During the call, the channel can be random for the digital ports. So it's hard to know which channel should be captured.

You could open the other SSH session to check which channel is using.

Make the call.

Then enter the CLI and execute the command: dahdi show channels

Find the number you have dialed in the extension column. Then the channel number could be checked.

In the following, the user just dialed number 230000000, its corresponding channel number is 1


Step 6 Stop capture according to the problem type. 
Caller ID problem: Call in to the PSTN line, wait for 5 seconds, hang up the call, call in to the same PSTN line again, wait for 5 seconds, then type Ctrl + C to stop the command.

Busy tone problem: Call in to the PSTN line and pick up the call, speak for some seconds then hang up the call. It’s better to repeat the above operation, then type Ctrl + C to stop the command.

Other problems: Just hangup the call when you have replicated the problem.

Step 6 Login via FTP and get the file /persistent/rx.raw, tx.raw How to Access FTP Folder


Signal Check Basics

You could try to use Cool Edit Pro/ Adobe Audition to check the caller ID signal waveform.

Open the rx.raw file as

  • Sample Rate 8000
  • Channels Mono
  • Resolution 16-bit

Formatted the rx.raw file as 16-bit Intel PCM (LSB, MSB) 


For checking the Caller ID, Examples of Caller ID signal waveform:

Figure - FSK after first ring (Caller id signaling: US Bell FSK Caller ID start: Ring )

Figure - DTMF before Ring (Caller ID signaling: DTMF, Caller ID start: Before RING)

Open the Frequency Analysis window to check the DTMF. 

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