SNOM phones and presence monitoring

If you have issues with your SNOM phones and presence monitoring (the little LEDs that display when another extension is ringing or busy), then maybe this will help.

We had this problem at work. When we checked the SIP traces, we could see our server was sending SIP NOTIFY packets to tell the phone “hey your collegue phone is ringing!”, but the phone:
– (very old firmware) either answered with a 200 OK but did not blink the LED;
– (latest firmware) or it answered a 481 Call/Transaction Does Not Exist and still did not blink the LED.

The issue was that the SIP NOTIFY packets were malformed by our system and the phone simply declared our server as broken, and discarded those NOTIFY packets.
We did not realize earlier the packets were malformed because it worked with other brands of phones (Aastra for example), so we thought we were OK. Sadly, we were not :-(

The fix is to set an option called “Support broken registrar” to ON and another option called “user=phone” to OFF. Both changes are needed to make the LED blink.
While this fix is described on www.voip-info.org/wiki/view/Asterisk+phone+snom and very easy to find when you look for SNOM and Asterisk, we do not use Asterisk at work and so, didn’t look for it …

I hope this post will help other people find this info.

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