川大软院计网选择题答案Chapter3(含答案).doc

CHAPTER 3: TRANSPORT LAYER1.A transport-layer protocol provides for logical communication between _C_.A.RoutersB.HostsC.Application processesD.End systems2.Transport-layer protocols run in _D_.A.ServersB.ClientsC.RoutersD.End systems3.In transport layer, the send side breaks application messages into _B_, passes to network layer.A.FramesB.SegmentsC.Data-gramsD.bit streams4.The receive side of transport layer reassembles segments into messages, passes to _A_layer.A.ApplicationB.NetworkingC.PhysicalD.MAC5.Services provided by transport layer include _C_.A.HTTP and FTPB.TCP and IPC.TCP and UDPD.SMTP6.Which of the following services is not provided by TCP?DA.In-order data transfersB.Reliable data transfers and flow controlsC.Congestion controlsD.Delay guarantees and bandwidth guarantees7.These two minimal transport-layer services-_A_ and _-are the only two services that UDP providesA.process-to-process data delivery, error checkingB.congestion control, reliable data transferC.flow control, congestion controlD.In-order data transfer, error checking8.UDP offers which of the following benefits relative to TCP?CA.UDP guarantees that Individual packets of a transmission will arrive “in order”B.UDP supports a self-regulating “throttle” feature that prevents network saturationC.UDP consumes fewer computer resources by not maintaining connection stateD.None of the above9.Which of the following applications normally uses UDP services?BA.SMTPB.Streaming multimediaC.FTPD.HTTP10.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.multiplexingB.de-multiplexingC.forwardingD.routing11.This job of delivering the data in a transport-layer segment to the correct socket is called _B_.A.multiplexingB.de-multiplexingC.forwardingD.routing12.Port numbers scope is _B_ to _.A.0, 1023B.0, 65535C.0, 127D.0,25513.The port numbers ranging from _C_to _ are called well-known port number and are restricted.A.0, 127B.0, 65535C.0, 1023D.0,25514.The UDP header has only four fields, they are_A_.A.Source port number, destination port number, length and checksumB.Source port number, destination port number, source IP and destination IPC.source IP, destination IP, source MAC address and destination MAC addressD.source IP, destination IP, sequence number and ACK sequence number15.The field of Length in UDP segment specifies the length of _B_.A.the UDP segment, not including the headerB.the UDP segment, including the headerC.the UDP segments headerD.the Length field16.Which of the following about TCP connection is not correct?AA.It is a broadcast connectionB.It is a point-to-point connectionC.It is a pipelined connectionD.It is a full duplex connection17.In the following four descriptions about MSS and MTU, which one is not correct?CA.The MSS is typically set by MTUB.The MSS is the maximum size of the TCP segment including headersC.The MSS is the maximum amount of application-layer data in the segmentD.The MTU means the largest link-layer frame18._A_ is the byte stream number of first byte in the segment.A.Sequence numberB.ACK numberC.ChecksumD.port number19._B_ is the byte sequence numbers of next byte expected from other side.A.Sequence numberB.ACK numberC.ChecksumD.port number20.In the following four options, which one is correct?DA.Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then the current value of TimeoutInterval will necessarily be1 secB.The timeout should be less than the connections RTTC.Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then the current value of TimeoutInterval will necessarily be1 secD.The variations in the SampleRTT are smoothed out in the computation of the EstimatedRTT21.There are two 16-bit integers: 1110 0110 0110 0110, 1101 0101 0101 0101. Their checksum is_A_.A.0100010001000011B.1011101110111100C.1111111111111111D.100000000000000022.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.422B. 418C. 571D. 57523.Because TCP only acknowledges bytes up to the first missing byte in the stream, TCP is said to provide_D_.A.positive ACKsB.Selective acknowledgementsC.3 duplicate ACKsD.Cumulative acknowledgements24.If we define N to be the window size, base to be the sequence number of the oldest 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 immediatelyB.have already been transmitted and acknowledgedC.cannot be usedD.have been sent but not yet acknowledged25.Which of the following is not a pipelining protocol.AA.Rdt1.0B.Go-Back-NC.Selective repeatD.TCP26.What is the main difference between stop-and-wait and pipelined reliable data transfer protocol?BA.The pipelined protocol uses the NAK packets, whereas in the stop-and-wait protocol senders always wait for 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 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.6B.5C.4D.328._B_ is a speeding-matching service-matching the rate which the sender is sending against the rate at which the receiving application is reading.A.congestion controlB.flow controlC.sliding-window controlD.variable control29.TCP provides flow control by having the sender maintain a variable called the _D_.A.bufferB.Congestion windowC.Sliding windowD.Receive window30.Provided RcvBuffer = 20, LastByteRcvd = 20, LastByteRead = 15, then RcvWindow=_B_.A.14B.15C.16D.1031.In the following four descriptions about TCP connection management, which one is not correct?DA.Either of the two processes participating in a TCP connection can end the connectionB.If the FIN bit is set to 1, it means that it wants to close the connectionC.In the first two step of the three-way handshake, the client and server randomly choose an initial sequence numberD.In the three segments of the three-way handshake, the SYN bit must be set to 132.How does TCP sender perceive congestion?DA.Through a timeout eventB.Through a re