"main theme of telephone exchange in any steel plant" is communication.

"what will be the working process?" Speech.

Your question fits perfectly with the theme of the evening! "Full Moon".

The telephone exchange is there to enable management to contact the morons working in the plant informing them of what to do and when to do it without having to leave the game on the PC.

Watch the instrument carefully and if it starts making a noise pick up the hand piece and say "hello".