We have some Cisco SPA525-G2 phones deployed with a client who is using a cloud based SIP PBX. The phones register fine, and outbound calls work fine. Inbound calls work fine for about 2-3 minutes, but after that interval time period passes, the phones become unreachable and we get a message from the PBX stating that the extension is currently unavailable.
I poked around at the NAT settings on the phone, and don't see anything too useful there. The NAT keepalive interval for the phones is set to 15 seconds. I believe the client has a Cisco or Sonicwall firewall out in front of the phones.
Any tips or pointers are much appreciated!
Cory