●  A transport layer protocol has several responsibilities. One is to create aprocess-to-process (program-to-program) communication; TCP uses port  （71） to accomplishthis. Another responsibility of a transport layer protocol is to create a （72）  and error-controlmechanism at the transport level. TCP uses a sliding （73）  protocol to achieve flow control. It uses the acknowledgment packet, time-out, and retransmission to achieve （74） control. The transport layer is also responsible for providing a connection mechanism for the applicationprogram. The application program sends （75） of data to the transport layer. It is theresponsibility of the transport layer at the sending station to make a connection with the receiver.