Do you require GB-port to connect at high speed to your provider?
Or do you require GB-port to connect two clients in your LAN with GB-speed?
If the later is the case use following setup.
Modem -> actual router -> DAP-1522 -> client1
-> client2
both clients can exchange data with GB speed, provided both have GB port. Speed with your provider is limit by
a) the connect speed of the modem
b) the link speed between your 'actual router' and the DAP-1522, as the DAP-1522 has GB ports the speed is limit by the port on your router since I assume this to be lower.
whichever is lower.