If you are connecting to the nbn™ network, or moving into a house that had nbn technology installed by a previous occupier, you should have an nbn connection device (NCD) that looks like the picture below. You will need this in addition to your modem to connect your FTTC broadband service.
Your NCD will only work at the premises it was originally sent to. If you move house, it’s important that you leave it where it is. Don’t take it with you. It won’t work anywhere else. Think of it as a part of the property!