I am attempting to setup FS as an B2BUA SBC between a telco platform and a telco SIP trunk. Everything is fine except for one call-flow scenario:  

 

We need to sometimes “reject” calls by sending reason code 17, which is quite easy by sending a SIP 486. The issue is that the far-end first receives early media and then the reason code 17, and the far-end switch is bonding the B-leg media for 55 seconds instead of moving on in the dial-plan. When comparing this to our PRI build-out, the difference is that in the PRI-buildout, no early-media is sent. In the SIP world, we are sending a 183 with SDP to setup the early media…

 

If I don’t send early media, the telco will inject their own early media path… so I need a work-around.

 

The telco is asking that we send specifically a 183 WITHOUT SDP, which I am having trouble figuring out how to do. I know how to send the 180 WITHOUT SDP, a 183 WITH SDP, but I cannot find the solution to sending 183 WITHOUT SDP…

 

I know it is unusual to send 183 without SDP, but it is still RFC compliant…