Premature ringing at phone


This is not so much a question about Asterisk, more about the way devices interpret its signalling. I hope it’s okay to post here.

I am experiencing a ringtone generated by a phone between 183 Session Progress and RTP Early Media. This is confusing as it means the user always hears a bit of a ringtone before the true indication.

I would expect the device only to insert it’s own ringing if it received 180 Ringing with no early media. So what it’s doing seems wrong.

The phone is a Digium D40.

The phone is connected to Asterisk 13.7 with PJSIP 2.4.5.

The problem cannot be replicated on phones from other manufacturers.

Many thanks.