[SR-Users] Lost 180 Ringing Response

[John Billings]

Hi Everyone,

We are using Kamailio 4.2.0 with TLS. It’s setup so multiple phones can register to the same account and they all ring together.

It always works great unless one of the phones is on a slower Internet connection. Occasionally that phone will start ringing after another phone has already picked up the call. The problem is that the INVITE to the slow phone is not followed by a CANCEL. So the phone keeps on ringing for a long time.

When there is no problem, the logs on the phone show:
Receive: INVITE
Send: 180 Ringing
Received: CANCEL
Send: 200 Ok

When the phone keeps ringing:
Delay: up to several seconds
Receive: INVITE
Send: 180 Ringing

The problem never seems to happen if I wait until all of the phones have received the INVITE. So is the late 180 response not getting handled by the right session?

Any ideas on how to track this down?