Dropped calls when using a Sonicwall 2040
If you are experiencing dropped calls, this is probably the result of SIP ALG (application layer gateway) functionality being active. Basically the firewall is mangling SIP packets, of which our switch rejects. Often by canceling the phone call.
To fix this, disable the "Enable SIP Transformations" option in the VOIP tab in your Sonicwall's admin panel.