Note: Make sure you have the latest firmware for your router.
SIP ALG allows devices and applications using VoIP (Voice over IP) to communicate across NAT. Some VoIP applications and devices have the ability to discover NAT devices and work around them. This ALG may interfere with the operation of such devices. If you are having trouble making VoIP calls, try turning this ALG off.
Step 1: Open a web browser and enter http://dlinkrouter.local. or http://192.168.0.1 into the address bar. Enter your password and click Log In.
Step 2: Go to Features and then click Firewall. Click Advanced Settings and then click SIP to disable it.
Step 3: Click Save.