(完整版)川大软院计网选择题答案Chapter3(含答案).pdf

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1、CHAPTER 3:TRANSPORT LAYER 1.A transport-layer protocol provides for logical communication between _C_.A.Routers B.Hosts C.Application processes D.End systems 2.Transport-layer protocols run in _D_.A.Servers B.Clients C.Routers D.End systems 3.In transport layer,the send side breaks application messa

2、ges into _B_,passes to network layer.A.Frames B.Segments C.Data-grams D.bit streams 4.The receive side of transport layer reassembles segments into messages,passes to _A_layer.A.Application B.Networking C.Physical D.MAC 5.Services provided by transport layer include _C_.A.HTTP and FTP B.TCP and IP C

3、.TCP and UDP D.SMTP 6.Which of the following services is not provided by TCP?D A.In-order data transfers B.Reliable data transfers and flow controls C.Congestion controls D.Delay guarantees and bandwidth guarantees 7.These two minimal transport-layer services-_A_ and _-are the only two services that

4、 UDP provides A.process-to-process data delivery,error checking B.congestion control,reliable data transfer C.flow control,congestion control D.In-order data transfer,error checking 8.UDP offers which of the following benefits relative to TCP?C A.UDP guarantees that Individual packets of a transmiss

5、ion will arrive“in order”B.UDP supports a self-regulating“throttle”feature that prevents network saturation C.UDP consumes fewer computer resources by not maintaining connection state D.None of the above 9.Which of the following applications normally uses UDP services?B A.SMTP B.Streaming multimedia

6、 C.FTP D.HTTP 10.The job of gathering data chunks,encapsulating each data chunk with header information to create segments and passing the segments to the network is called _A_.A.multiplexing B.de-multiplexing C.forwarding D.routing 11.This job of delivering the data in a transport-layer segment to

7、the correct socket is called _B_.A.multiplexing B.de-multiplexing C.forwarding D.routing 12.Port numbers scope is _B_ to _.A.0,1023 B.0,65535 C.0,127 D.0,255 13.The port numbers ranging from _C_to _ are called well-known port number and are restricted.A.0,127 B.0,65535 C.0,1023 D.0,255 14.The UDP he

8、ader has only four fields,they are_A_.A.Source port number,destination port number,length and checksum B.Source port number,destination port number,source IP and destination IP C.source IP,destination IP,source MAC address and destination MAC address D.source IP,destination IP,sequence number and AC

9、K sequence number 15.The field of Length in UDP segment specifies the length of _B_.A.the UDP segment,not including the header B.the UDP segment,including the header C.the UDP segments header D.the Length field 16.Which of the following about TCP connection is not correct?A A.It is a broadcast conne

10、ction B.It is a point-to-point connection C.It is a pipelined connection D.It is a full duplex connection 17.In the following four descriptions about MSS and MTU,which one is not correct?C A.The MSS is typically set by MTU B.The MSS is the maximum size of the TCP segment including headers C.The MSS

11、is the maximum amount of application-layer data in the segment D.The MTU means the largest link-layer frame 18._A_ is the byte stream number of first byte in the segment.A.Sequence number B.ACK number C.Checksum D.port number 19._B_ is the byte sequence numbers of next byte expected from other side.

12、A.Sequence number B.ACK number C.Checksum D.port number 20.In the following four options,which one is correct?D A.Suppose that the last SampleRTT in a TCP connection is equal to 1 sec.Then the current value of TimeoutInterval will necessarily be1 sec B.The timeout should be less than the connections

13、 RTT C.Suppose that the last SampleRTT in a TCP connection is equal to 1 sec.Then the current value of TimeoutInterval will necessarily be1 sec D.The variations in the SampleRTT are smoothed out in the computation of the EstimatedRTT 21.There are two 16-bit integers:1110 0110 0110 0110,1101 0101 010

14、1 0101.Their checksum is_A_.A.0100010001000011 B.1011101110111100 C.1111111111111111 D.1000000000000000 22.Suppose host A sends host B one TCP segment with sequence number 418,acknowledgement number 571,and 4 bytes of data.Then the sequence number in the acknowledgement to this segment is _C_ A.422

15、B.418 C.571 D.575 23.Because TCP only acknowledges bytes up to the first missing byte in the stream,TCP is said to provide_D_.A.positive ACKs B.Selective acknowledgements C.3 duplicate ACKs D.Cumulative acknowledgements 24.If we define N to be the window size,base to be the sequence number of the ol

16、dest unacknowledged packet,and next-seq-num to be the smallest unused sequence number,then the interval nextseqnum,base+N-1 corresponds to packet that _A_.A.can be sent immediately B.have already been transmitted and acknowledged C.cannot be used D.have been sent but not yet acknowledged 25.Which of

17、 the following is not a pipelining protocol.A A.Rdt1.0 B.Go-Back-N C.Selective repeat D.TCP 26.What is the main difference between stop-and-wait and pipelined reliable data transfer protocol?B A.The pipelined protocol uses the NAK packets,whereas in the stop-and-wait protocol senders always wait for

18、 ACK packets.B.With the pipelined protocol,the sender can send several packets in row,whereas in the stop-and-wait protocol the sender cannot send the packets in row.C.With the pipelined protocol,the receiver must send one ACK for several packets(cumulative ACK),whereas in the stop-and-wait protocol

19、 the receiver can not send the cumulative ACK.D.The pipelined protocol uses timeouts,whereas the stop-and-wait protocol does not use the timeout.27.Fast retransmit means in the case that _D_ duplicate ACK-s are received,the TCP sender resend segment before timer expires.A.6 B.5 C.4 D.3 28._B_ is a s

20、peeding-matching service-matching the rate which the sender is sending against the rate at which the receiving application is reading.A.congestion control B.flow control C.sliding-window control D.variable control 29.TCP provides flow control by having the sender maintain a variable called the _D_.A

21、.buffer B.Congestion window C.Sliding window D.Receive window 30.Provided RcvBuffer=20,LastByteRcvd=20,LastByteRead=15,then RcvWindow=_B_.A.14 B.15 C.16 D.10 31.In the following four descriptions about TCP connection management,which one is not correct?D A.Either of the two processes participating i

22、n a TCP connection can end the connection B.If the FIN bit is set to 1,it means that it wants to close the connection C.In the first two step of the three-way handshake,the client and server randomly choose an initial sequence number D.In the three segments of the three-way handshake,the SYN bit mus

23、t be set to 1 32.How does TCP sender perceive congestion?D A.Through a timeout event B.Through a receiving duplicate ACK-s event C.Both A and B D.Either A or B 33.There are two states in TCP congestion control,which are _C_.A.safe start and congestion abandon B.safe start and congestion avoidance C.

24、slow start and congestion avoidance D.slow start and congestion abandon 34.In TCP,the timeout interval is a function of:A A.estimated RTT at the sender B.MSS and the overhead of a segment B.the size of buffer at the receiver D.the size of sending window 35.In a TCP connection,there is timeout event when the value of threshold is 32 and the size of congestion window is 16.According to the TCP congestion control policy,the new value of threshold and the new size of congestion window should be _C_,respectively.A.16,8 B.24,8 C.8,1 D.16,1