I am having issues with my outside SIP provider (ONSIP) and my internal phones running thru a watchguard xtm505 firewall with ver 11.11 firmware.
It has to do with NAT traversal as the outside provider shows packets are being dropped.
Calls coming in will breakup where outside caller cannot hear us at times, but they sound crystal clear to us. Calls going out drop about 30 seconds in.
I have tried disabling SIP/ALG and even recreated a sip/alg proxy to no avail.
I also want to setup rules so that only the outside SIP provider can direct calls going in and out of our firewall.