Java Network Programming. Logic over the protocol or your own protocol?

Question

Java

I am developing network applications (almost always client-server architecture).
I am self-taught, so I know what I'm doing, but the theory is not enough.
Essence of the question: I moved from C # to Java and again wondered: Is it worth it (and how) to develop your own protocol (even modifying TCP \ IP) to achieve the goals, or is it better to build additional. logic over the protocol?
For example, in C#, I have a client-server core with logic on top of the protocol that ensures the safety of the connection itself (detection of a connection, disconnect, reconnect, guarantee of delivery of the entire message (taking into account packet defragmentation)), but all this could be inserted by modifying TCP \IP.