Normally when we connect FS to SM we use default UDP 5060.  

It seems that although the initial sip invite from FS to SM is done on the configured port of 5060, as the call is established for longer periods, FS would eventually start it’s RTP traffic on a different port range. Once FS started to use these ports to initiate SIP messages, SM would then reply back to FS on the port that FS started to use to communicate on. Since the firewall only really cares about the destination port and not the originating port, these messages were making it to SM without issue. But since SM started to communicate back to FS on the new RTP port, the firewall rule would no longer allow this traffic. So all SIP messages would make it to SM but no messages would make it back from SM to FS.

 Normally there aren’t firewalls in the same DC between FS and SM. But if you do run into this, here are the steps you will need to take. In order to fix it.

1.  Go into the autoload_configs.xml file in FS in the below location and edit the file using vi or some other tool
2. Find the RTP port range section of the file and uncomment the fields. I went ahead and used a port range that I saw the FS server using 10000 thru 16000. See two screen shots below
   
3. Next you can restart the FS server and then provid the UDP port range to the Firewall folks. 
   

Before:

After:

First screen shot below shows how FS (.127) is initiating traffic to SM (.41) on 12865. Second screen shot shows how SM comes back to FS on that same port.