单选题 A transport layer protocol usually has several responsibilties. One is to create a process-to-process communication UDP uses ______ numbers to accomplish this. Another responsibility is to provide control mechanisms at the transport level UDP does this task at a very minimal level. There is no flow control mechanism and there is no ______ for received packet. UDP, however, does provide error control to some extent. If UDP detects an error in the received packet, it will silently drop it.
The transport layer also provides a connection mechanism for the processes. The ______ must be able to send streams of data to the transport layer. It is the responsibility of the transport layer at ______ station to make the connection with the receiver chop the stream into transportable units, number them, and send them one by one. it is the responsibility of the transport layer at the receiving end to wait until all the different units belonging to the same process have arrived, check and pass those that are ______ free, and deliver them to the receiving process as a stream.