Need to block early-media which was not described by SDP (restricted-latching).

Hello everyone!

 

I need to make my Acme 4250 SD (oldschool C5.1.1 firmware)  block early rtp-flow which was not described by SDP. This SBC sits in between two softswitches (A and B for simplicity and the corresponding users will also be A and . When there is a call from user A to user B user B's side responds with 180 Ringing on incoming invite. Initial invite contain's SDP, 180 does not. Softswitch A starts sending ringback tone to user A localy at this point. But despite the absence of SDP in 180 user B also starts sending early media to A. SBC then sends this rtp flow to user A and these two different media-flows make user's A equipment go mad until recieving 200 OK.