Conversation so far:
what is the function of transport layer in tcp ip
The function of transport layer in TCP IP is to facilitate the communicating hosts, provide an interface for the users to the underlying network, and provide reliable connection
what is the transport layer called in the osi model
In the OSI model the transport layer is often referred to as Layer 4, or L4
what protocol is used for simpler messaging transmissions
The connectionless User Datagram Protocol is used for simpler messaging transmissions.

Question: why is the protocol more complex
Self-contained rewrite: why is tcp more complex compared to udp