One-way audio from the SBC after early media without SDP, latching issue?

Hi,

 

we are experiencing _random_ calls with one-way audio stream from the SBC. The scenario is this:

 

A network capture is made on the network (core) side of the SBC as well as on the customer (access)

side of the SBC. In the captured call the following scenario can be seen on the PBX (access) side:

 

  

-> incoming INVITE towards to PBX

 

<- 100 Trying from PBX

 

<- 180 Ringing from PBX

 

    <--- early media from the announcement server (NOTE: no SDP info at this point)

 

 

The RTP flow (early media) is sent to the original caller on the network side, even though the call is on "180 Ringing" state.