Passive Multiplexer in European Apartment

Inside the "telecommunications cabinet" of our new Spanish apartment at Mar de Pulpi, we found a wifi router that is also a ONT for fiber-optic internet service, and this "Multiplexador pasivo" 1 in 8 out RJ45 UTP Cat 6 thing with 8 ethernet cables connected to its outputs and nothing connected to its input.

Optical Fiber ONT and WiFi Router in European Apartment

All rooms in the apartment have at least one RJ45 wall socket (the place for the TV has two). We had our own gaming wifi router that we wanted to daisy-chain to the main router. So we connected one of the RJ45 outputs of the ONT/Wifi router (Uplink GP542Z GPON / EPON ONT terminal 4x GE 1x USB SC/APC WiFi AC1200) to the input of the "passive multiplexer" and the gaming router to a wall RJ45 plug. As expected, it did not work. We were wondering how in the world would a "passive multiplexer" route data packets.

It turns out this "passive multiplexer" is a telephone device and is used for connecting landline telephones all over the apartment, using RJ45 to RJ11 cables. Indeed there was a RJ45-RJ11 cable lying around inside the telecommunications cabinet as well.

However, the ethernet cables that run from the passive multiplexer to all over the apartment are indeed CAT6 network cables. Therefore, all it takes to distribute the computer network to the RJ45 wall sockets is a network switch. We unplugged the network cables from the passive multiplexer and plugged them into a 8-port network switch along with a network cable connected from one of the ports on the switch to the existing ONT/WiFi router. We were then able to daisy-chain a second WiFi router from another RJ45 wall socket as well as have copper ethernet connections to laptops and other devices from other RJ45 wall sockets.

We found the relevant manuals online for the Passive Multiplexer and ONT/Wifi Router.

Who uses landline telephones in multiple rooms in 2024?