Players on different levels

i want to know if i have like Levels(castle 1F, Castle 2F Castle 3F), how can i make networking possible if a player changes to 2F cab i continue to receive certain data. Is game like Phantasy Star Online, where one player can be on Forest 1 and other on Forest 2, and they can still chat, and get info like when a monster is killed etc…

I’m sorry for my bad English is not my first language.