OK. Thanks. I'm glad to hear that it is fixed now. I was searching for it in other chapters and couldn't imagine that it is under 4.15 System Configurator 
The OPTIONS Ping function in SIP trunks could be used for monitoring the state of a trunk but it did not response to options sent by the other end. Now the support for incoming OPTIONS is added as well.
This also sounds very promising and is exactly what I need!
Thanks for confirmation!
Alex