Hi, How does the sockets among M publishers and N subscribers on the same topic connected? Is it a mesh MxN network?

How is the order of messages controlled in this condition. Say I have publishers P1, P2 and subscribers S1 and S2.

At time t0 P1 publishes M1 and at time t1 P2 publishes M2. Do S1 and S2 both see the messages in order of M1 and M2?

Thanks for any help.