Calls can be dropped about 30s or 15m into a call across our Juniper firewall. This is due to the ALG (application layer gateway) service for SIP not handling packets properly. When we send a SIP re-invite, the remote VoIP gateway responds with the proper 200/OK; however, the Juniper firewall drops the 200 response and our switch hangs up the call from lack of response.

Disable ALG for SIP and also follow up with Juniper Support for the latest firmware/patches for your firewall.