HT503 Direct IP Call - Analogue extension to VoIP device



I have a VoIP Public Announcement device that I would like to call via an analogue extension from the PABX.

Can I configure the HT503 to receive an analogue extension call and direct IP call the VoIP device on the other side, without SIP registration?

It seems simple but I might be misunderstanding something.

I can direct IP call the VoIP PA device from another VoIP phone and the sounds goes out on the amplifier, but I cannot get the HT503 to make a direct IP call to the VoIP PA device

NEC SL1000 analogue ext —> Grandstream HT503 —> Snom PA1 —> PA Amplifier

The HT503 receives the call, the Line light activates, I can hear its dial tone, but I cannot get it to direct IP call the VoIP device when it receives a call.

I was told this should work, but after fiddling half the day I am not so sure anymore.


I do not know the equipment you list, often keep that sometimes instead of registering with credentials some equipment want to register in peer, check if it’s your case.


Wrong configuration Snom PA1 do not support IP calling (i do not see any option to turn off register - manual have like 1/10 options from gateway).


Thank you @damiano70. we will recheck our peer config. I am sure its how we have configured it but I might have missed something, I am not really proficient in telephony configuration.

@Marcin, I am afraid you are mistaken.

The Snom PA1 does indeed support direct IP calling, it is how I tested if the device actually works. I can even make a video of me doing it and upload it if you think I am lying.

I reset a normal VoIP handset to factory defaults, plugged it into the network, it received an IP address via DHCP with no SIP server or registration on the network. I dialed the Snom PA1 IP address from the VoIP phone for e.g. 192 * 168 * 2 * 100 and the Snom PA1 answered immediately and played the audio out its Line Out port as required.

I am sure the HT503 can do Direct IP calling and without SIP registration as the configuration options are in its config menu, I am just not sure how it must be done.

I have removed the Snom PA1 and just tried getting the HT503 to call a normal VoIP phone instead, but I get the same results. The HT503 answers and gives dial tone for a few seconds but nothing gets transferred to IP.


Sorry there is missing word:
"Wrong configuration OR Snom PA1 "

For 503 refer to this manual:


more manuals :’( /cry

Thank you @Marcin. We did follow this yesterday, but I will reset everything and try it again, maybe I missed something.

So does this mean the HT503 should in theory support what I am attempting to do? I just don’t want to be wasting my time because I am misunderstanding something about the devices capabilities.


Yes i configured it with GS phones, some random gateways etc.
For more perspective i suggest running syslog with SIP (from HT) to your PC as server.
You can install Visual syslog server on PC to catch them. You will see packets at least.


I reset the HT503 to factory defaults…

It answers a call on the FXO port and it gives me a dial tone, I can press *** then 47 and it prompts to enter the IP

As soon as I configure the device it no longer answers calls, even changing one thing. Changing it back does not fix the problem, only another factory reset.

After a few resets, I could eventually configure the device, but as soon as I enter and save the User ID under Basic Settings it does not answer a call anymore. If I reset the device it answers calls again.

Sometimes all the fields did not reset after a factory reset, the only thing I can think of doing different was the length of time I held the reset button.

Firmware upgrades to .13 also did not stick, it stays at .12

Is this device broken?