An Optical Network Terminal (ONT) is used in fiber-optic installations to directly interface with the ISP's fiber-optic network. It translates the fiber-optic light signals into electrical Ethernet signals for use within the customer's network. A cable modem would be used in a coaxial cable installation, not fiber-optic. A DSL modem is for telephone line connections and a network interface card (NIC) is used as an interface in computers and does not directly connect to ISPs.