robots are designed to do one thing - move. pretty much everything else is an option. to communicate over ethernet (and you don't specify what kind) you need an option package for that specific use like:
OPC - common way to connect to various systems using standardized protocol
Ethernet KRL - allows robot to do acyclic exchange of messages using raw TCP
RSI - high speed (deterministic), allows "modulating" of robot motions by external signals for example
FastSendDriver (ultra fast send only, no receive - only trigger)
EthernetIP - type of industrial Ethernet (AB)
ProfiNet - another type of industrial Ethernet (Siemens)
EtherCat - another type of industrial Ethernet (Beckhoff)
MQTT - an IoT type of interface
all of those are commercial options with manuals on KUKA portal called Xpert (see READ FIRST)
there are some noncommercial or even open source options created by people that put effort to reverse engineer things.
I have created a GLOBAL variable INT. I want to read and write to that variable remotely via an ethernet connection.
"Ethernet" is a cable type. There are literally hundreds of protocols that can run over that cable. Which one do you want to use, and which ones does your robot support? As Panic says, each protocol will probably require a specific option package on the KRC4.
