Because the host can send, receive, and process in any order. Regardless of where they come from and where they are going. which makes it possible to several hosts to communicate simultaneously in a network.
Several hosts can communicate simultaneously because a host doesn't have any order in processing the packets, regardless of where it is going or where it is coming from. The data or the packet is handed off to the OS by a host and the OS manages the process of data transmission that enables the simultaneous communication between several hosts in a network.
