ADSL/VDSL router in bridge mode in conjunction with wireless router/Deco avoiding Double NAT
In the following diagram is the typical network topology:
Before you start, I would suggest to backup the TD-W9960 and C80 configuration just in case something goes wrong.
You will need these credentials for configuring PPPoE session in C80 later:
Delete the old Internet connection in TD-W9960 (PPPoE):
Add new Internet connection of type Bridge (click Save at the end):
Settings in C80:
If you ISP uses a particular VLAN for the Internet, IPTV or VOIP you can set these here (captured from TD-W9960 in the first step):
Configuring PPPoE session in C80 (captured from TD-W9960 in the first step):
After configuring the PPPoE in C80 click CONNECT (if available) and you should be able to establish the PPPoE session from C80.
You'll have an internet connection with a Single NAT in C80.
Similarly you can use other TP-Link ADSL/VDSL modem instead TD-W9960.
Also you can use Deco system (in router mode) or any other wireless router instead C80 depending on what hardware you use.