First of all, the fourth layer of OSI is the transport layer, two important protocols TCP UDP. I believe that you should be quite clear that the function of the fourth layer is to apply the four main functions of process addressing, flow control, congestion control and error control! First of all, I need your classmates to know how to realize the application of urban addressing. I believe you should know that this function is realized through the port mechanism! So your idea is completely correct! You can tell your classmate directly that what he said is wrong! I wish you progress in your study!

Please accept it, thank you!