HT503 FXO PORT - PSTN Disconnect Tone



I’m using HT503 to connect a little voip network to PSTN line.
In the case of incoming call, if the phone belonging to voip network hangs up the connection is still alive for about 60 seconds before ending.
I’ve updated firmware with latest version (, but the behaviour doesn’t change.
I’m in Italy and I’ve set the PSTN Disconnect Tone equal to f1=425@-17,f2=425@-17,c=200/200-200/200.

How could I proceed to have immediate disconnection when ip phone hangs up?

Thank you very much.


Do not believe country settings. We also have different tones in my country but most often America work :confused:

Btw did you turn on tone detection and turn off impedance ?


after different mounths we have discovered that the problem doesn’t concern Grandstream HT503 but it seems to be caused by a strange behaviour of PSTN line.
HT503 is working properly.

Thank you very much.


i have same problem.
How did you solve it?
Thank you.