In order to setup port forwarding, each device will need to be given a static IP address. The best way to do this is via the Bind IP to MAC option.
Please see the link below for intructions on how to log in to the device...
From the menu on the left hand side go to LAN > Bind IP to MAC
Enable: Make sure you enable the Bind IP to MAC settings
ARP (Adress Registration Protocol) Table: This shows a list of all devices in the ARP table. You can select a device here and click the add button to move the device to the IP Bind List on the right. Click OK at the bottom to save.
Add or update: If the device you are trying to add does not appear in the ARP table you can manually add the device if you know the MAC address/IP address.
Once this part is completed go to NAT > Port Redirection on the left.
This will give you a list of all of the existing port forwarding rules. To add or edit a rule, click on one of the numbers in the Index column.
The image below shows and example of how to port forward a single SIP/VoIP phone.
Mode: This allows you to add a single port and/or IP address or even a range of ports or IP addresses to port forward.
Service name: Give your port forwarding rule a name to help you identify the rule.
Protocol: You can select either TCP or UDP. If you need to add a rule that covers both UDP and TCP you will need to create 2 separate rules. VoIP uses the UDP protocol.
WAN Interface: This allows you to select which WAN interface this rule should apply to. You should select ALL. There are more advanced reasons that you may want to select other options here but these will not be covered in this guide.
Public Port: Enter the public port you wish to forward.
Private IP: Enter the IP address of the device.
Private Port: Enter the private port you wish to forward.