Why There is No Caller ID

The caller id issues often happen on PSTN trunks. The first thing we need to do is to make sure that the PSTN line’s caller ID service has been enabled. Users can connect the PSTN line directly to a normal desktop analog phone to check if the caller id works. If the caller id works on the phone, please try change the ‘caller id signaling’ and ‘Caller ID start’ on the analog trunk page. If you still fail to get the caller id works, please login MyPBX via SSH for further debug. Please follow below steps to get the detail caller id signaling.

Step 1. Log in MyPBX via SSH.
Download putty.exe from the internet. And login MyPBX via SSH. Before you login, please make sure the SSH has been enabled on LAN settings page.
1. Login MyPBX Web User Interface and go to System→Network Preferences→ LAN Settings, enable SSH and enable FTP.

2. Login MyPBX via SSH, the default username is root, password is ys123456.

Step 2. Check the channel number of the FXO port.
Execute the command to check the channel number: vi /etc/dahdi/ysport.conf

Step 3. Troubleshoot and Monitor the FXO port.

1. Go to directory /persistent by the command: cd /persistent

2.  Execute command dahdi_monitor n –r rx.raw (n is channel number).
For example, if you want to monitor channel 1’s caller id signaling, command is dahdi_monitor 1 –r rx.raw;

3. 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 press Ctrl + C to stop monitoring the FXO port.

Step 4. Download the rx.raw file and analyze it.

1.  Login MyPBX via ftp: ftp://MyPBX's IP. For example, MyPBX's IP address is You should enter in your address bar. Login username is root, default password is ys123456.

2. Download the rx.raw file in the folder /persistent. 

3. Use Cool Edit Pro 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)


Step 5. Analyze the Caller ID.

Examples of caller id signal waveform. 

Figure 3 FSK after first ring

(Caller id signaling: US Bell FSK Caller ID start: Ring)

Figure 4 DTMF before Polarity
(Caller ID signaling: DTMF, Caller ID start: Polarity)

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