One way audio on some incoming calls


I have an intermittent issue on a site where incoming audio from a SIP trunk call cannot be heard on the answering extension

Just done some testing calling site

4 calls with 2 failure

Call 1 answered – I could not be heard
Call 2 answered – No issue
Call 3 answered – No issue
Call 4 answered – caller could not be heard

Reports this morning some calls answered OK, some no caller audio

Whilst doing calls above I had a packet trace running on the PBX and can hear the audio from both parties

For some reason audio is not being passed (on incoming calls) from the PBX to the handset

Issue has been reported on multiple handsets (SNOM360, SNOM300 and SNOM725) all running latest firmware.

There never seems to be a problem with internal calls or calls made to external numbers

If someone is able to decipher the packet captures and Asterisk logs I am happy to share them

Setup is

  • FreePBX Version:

  • FreePBX Distro:12.7.8-2306-1.sng7

  • Asterisk Version:18.20.2

  • Gamma SIP Trunks

  • B4RN internet (1Gbps)

  • LAN is all layer 2 (single subnet (for admin)) all 1Gbps links

Anyone any ideas would be greatly apricated


Chris Gibson
West Lancs Scouts - IT Volunteer