These are the most often used methods for using PTCL's modem router and another wireless router:
1) ptcl's modem in (pure) bridge mode with the wireless router controlling the pppoe connection ... useful when the wireless router is more 'advanced'
2) ptcl's router with wireless router in WAP mode ... useful when you want the ptcl router to retain all control
Option 2 might also be used to extend wireless coverage via LAN/Ethernet cable as both routers can have wifi enabled!
If however, you want to extend wireless coverage using wifi, you need either:
- WDS support in both routers ... though compatibility across different brands varies or
- Wireless Repeater Mode support in one of the routers or
- 3rd party/custom firmware support (like dd-wrt, openwrt, ...) in one of the routers that might enable extra functionality like repeater mode
You may ask here for further explanation(s) once you make a choice!