Is it possible to have an empty RTP packet sent from the port signaled in the SDP so that a far end SBC will latch onto it? I have a situation where my customer’s PBX is behind a NAT and is trying to do a call-forward. Both call legs are bridged via the PBX but the SBC is waiting on the initial RTP packet so it can latch and begin sending return packets. This causes no-audio to be sent because nothing is being sent from the far end SBC on the 2nd leg which would bridge back to the first leg. Any since the first leg has nothing to return from the second, the far end SBC has nothing to latch onto there either. It’s a game of chicken…
I tried to use the ignore early media and always play ringing but for some reason that requires transcoding.
Avaya IP office has a neat feature where it will send an empty initial RTP packet for this purpose.