How do I debug "phone doesn't answer" issue?

I’ve got a Grandstream DP750 base with a DP720 handset, and it works perfectly as a PJSIP extension, EXCEPT that it won’t answer calls. While the green button and the left-hand softkey work for making calls, neither of them work for answering incoming calls.

I can very occasionally answer a call by rapidly pressing on either Green or the “Answer” softkey, but then I’m just as likely to put the call on hold and start another one, and even that’s not reliable enough to be useful.

Is there any kind of debugging or logging that I can do to help track down if the problem is on the Grandstream side or the FreePBX Distro side?

I’ve logged a bug with Grandstream, but they are just as likely to blame it on FreePBX…

Distro Version:
Asterisk Version: 13.11.2

All modules are up to date.

A Grandstream DP715 base with two handsets works fine.


Your answer is likely to be in /var/log/asterisk/full.

Look for a call where the phone should pick up and see why it’s failing. I’m going to guess that there’s a registration problem. but there are other problems that could easily be making your phone not work.

Without log files, though, we’d be shooting blind. A little bit of information from you could go a long way to solving this for you.

Am I reading the correctly, the phone rings on an inbound call and the answer button on the phone does not answer the call? If so, don’t waste any time looking at logs on the server, this is a failure of the phone hardware, either buggy firmware or hardware misconfiguration.

re: Igaetz: That’s the one, and why I wrote up a Grandstream bug report, as this is the likeliest problem. Just wasn’t sure if there was any way to prove it from the PBX side…


Take a pcap and look at the SIP traffic to the endpoint. The invite goes out from the PBX, and you will not see a corresponding OK back from the endpoint. No OK, no answer.