On mine, I used standard Ethernet network cables and just cut the connectors off one end. I then just wired them into my controller. I believe cncdrive used to sell interfaces to allow everything to use RJ45 connectors and there's a guy in the US trying to do the same. Seemed rather pointless and expensive to me - and hardly industrial practice.

Using the s/w to see the encoder should tell you if it's connecting and if it's sending sensible info.