With this UTP cable splitter / network cable splitter you can extend 2 cables over 1 cable.
You need 2 cable splitters, 1 of which on the router side where 2 cables of the router / switch have to be plugged into the splitter, the internet cable splitter then makes of 2 cables 1 cable with 2 internet signals, the other splitter you put into the end of the cable and so you have 2 connections again. Therefore you can extend 2 internet signals over 1 cable. Port doubler / network splitter / ethernet cable splitter
1 RJ45 plug> 2 x RJ45 jack
For 10 / 100Mbit networks
Length 15 cm

NOTE : There are 2 cable splitters needed for a proper function!