Log into the router, and perform the following changes...
1. Go to Advanced Settings > WAN > NAT Passthrough. Enable the SIP Passthrough feature. Apply, then immediately test, as this may cause problems on some networks.
2. Go to Advanced Settings > LAN > DHCP Server. Add an Manually Assigned IP (reservation) for your voip device, phone, or phone system. Take note of the reserved IP, and MAC, as you will need them in steps 3 and 4. Save ro Apply.
3. Go to Advanced Settings > WAN > Virtual Server / Port Forwarding. Add 2 Port Forwarding Services as follows...
Name: SIP
Source: [blank]
Range: 5004 to 5099
Local IP: [enter the IP Address of your voip device, phone, or phone system]
Local Port: [blank]
Protocol: UDP Only
Once entered, click the + sign to Add the rule.
Name: RTP
Source: [blank]
Range: 10000 to 65000
Local IP: [enter the IP Address of your voip device, phone, or phone system]
Local Port: [blank]
Protocol: UDP Only
Once entered, click the + sign to Add the rule.
Click the Apply button to save the changes.
4. Go to General > Adaptive QoS > QoS. Check the box for "Enable QoS". There are numerous ways to approach QoS with Asus routers. The following is just one easy option.
QoS Type: Adaptive
Bandwidth Setting: Automatic
Click the "Customize" button, then drag "VoIP and Instant Messaging" to the highest slot. Save the page. Apply all changes.
Other methods can be more affective, and may be required, if you have a busy network with lots of users, apps and devices to manage.
Summary: Be sure to apply changes as you go. Then go back and confirm that the settings are saved properly.
That should help your router so that it properly routes your voip call signals, and gives bandwidth priority to your phone.
Let us know if you have additional questions.
