Use the instructions for your router’s exact model and firmware. Record the existing configuration before changing SIP ALG and choose a time when a network restart will not interrupt active calls.
DIR-625 menu
- Sign in with the router’s current administrator credentials.
- Open Advanced → Firewall Settings. Find Application Level Gateway (ALG).
- Clear SIP and save the setting. Leave unrelated firewall controls unchanged.
- Restart only when the router requests it, then reconnect the phone or PBX.
Other D-Link models
Some models place the SIP setting under Features → Firewall → Advanced Settings. Use the D-Link SIP ALG guide and your model’s manual. The DIR-625 revision C manual describes its Firewall/ALG controls.
Verify
Test registration, inbound/outbound calling, keypad tones and two-way audio. Repeat an inbound call after the phone has been idle. If the change makes no improvement, restore the earlier value and inspect the actual signaling and media path.