Graph Coloring · Medium problem

A hub satellite $0$ relays directly to $4$ ground stations $1,2,3,4$, which also form a ring among themselves ($1\text{-}2,2\text{-}3,3\text{-}4,4\text{-}1$), giving $8$ links in all. Links meeting at the same station need different frequencies. What is the fewest frequencies needed?