Is it possible to send messages between phones within the network (wi-fi), provided that only ip is known??

Question

Telephony

Good day. Asked a question. Is it possible to send a message from the phone to another phone within the network (wi-fi). While only the ip-address of the other contact is known. For a deeper understanding, I will describe it in another way. Let's say I connected to wi-fi in the park with the help of some program I found out the ip-addresses of all connected (mac is also known). But how to send a message to any device in this network from a phone (you can also use it from a PC)?? Provided that they do not have any third-party programs.
Is it real at all?? If realistic please explain the whole algorithm and implementation. Thanks in advance.

Answer 1

without software on the client side is not possible