Some situation after Dial and before begin ringback takes a long time.
How set timeout waiting of ringback (not timeout waiting of answer) ?
I’m not sure why you would want to. How would you cope with systems that provided ringback in band?
Note that SIP systems require a fairly rapid responses to INVITE, and will repeat the INVITE if they don’t get it. If the remote system is not able to give Ringing or other call progress, they require a prompt 100 Trying.