Final answer:
For an ETTS installation, the Cat5e cable should be connected to the WAN port on the gateway, as it is the correct port for establishing a connection to the internet through an ISP.
Step-by-step explanation:
During an ETTS (Ethernet to the Subscriber) installation, you should connect the Cat5e cable to the WAN (Wide Area Network) port on the gateway. The WAN port is specifically designed to connect the gateway to the internet, which is provided by an external source such as an ISP (Internet Service Provider). Connecting to the LAN (Local Area Network) port would link the cable to a local network of devices within the home or office, which is not the purpose during initial setup of an ETTS, as you are aiming to establish a connection to the wider internet. The USB and HDMI ports serve different functions: USB ports may be used for connecting peripheral devices (like storage or printers), and HDMI is used for audio/video output, neither of which are used for internet connectivity in this context.