[单项选择]

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

A. numbers
B. connections
C. diagrams
D. resources

[单项选择]
A. procedure
B. function
C. route
D. flow

[单项选择]

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

TCP uses port （） to accomplish this.
A. numbers
B. connections
C. diagrams
D. resources

[单项选择]A transport layer protocol usually has several responsibilities．One is to create a process-to-process communication；UDP uses (71) numbers to accomplish this．Another responsibility is to providecontrol mechanisms at the transport level．UDP does this task at a very minimal level．There is no flowcontrol mechanism and there is no (72) for received packet．UDP, however,does provide errorcontrol 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 (73) must be able to send streams of data to the transport layer．It is the responsibility of the transport layer at (74) station to make the connection with the receiver,chop the stream into transportable units，numberthem，and send them one by one．It is the responsibility of the transport layer at the receiving end to waituntil all the different units belonging to the same process have arrived，check
A. hop
B. port
C. route
D. packet