Tcp and udp provide port numbers to identify specific application entities. ] The transmission users corresponding to the transport layer are application processes and application entities. The transport layer will correspond to multiple application processes, that is, in a multi-task or multi-user multi-task system, there are multiple processes running in parallel on a host. TCP and UDP provide "port numbers" to distinguish these processes. Both TCP and UDP retain important port numbers, such as HTTP in TCP is 80 and FTP is 2 1.