计算机网络试卷及答案-英文版
HUST Examination Answer SheetCourse: Computer Networks (closed-book exam) Jan.2014 Department of Electronics and Information EngineeringSolution[Question 1] Network architecture(1) Draw the architecture diagrams of ISO/OSI reference model and TCP/IP network. (2) State the differences between the two architectures.(3) Mark the names of data unit and network equipment in the bottom 4 layers of ISO/OSI diagram.Solution:（1）ISO/OSI reference model TCP/IP modelDifferences:a) TCP/IP model is the actual architecture in the Internet, while OSI model is a theoreticalarchitecture.b) TCP/IP model does not imply strict layering, while OSI model implies strict layering. c) In TCP/IP model, IP serves as the focal point for the architecture.d) TCP/IP model allows for arbitrarily many different network technologies , ranging fromEthernet to wireless to single point-to-point links.e) TCP/IP model emphasize implementations of proposed protocols. (2)Physical : bit, repeater or hubData link : frame, Ethernet switch or bridge Internet : packet, routerTransport : message, gateway[Question 2] Principles of network designSelect ONE of the following principles, tell its main ideas and provide an example. (1) Keep it simple and stupid(2) Complex edge and simple core (3) Smart sender and dumb receiverSolution:(1) KISS: Keep It Simple and StupidIt means that you should make things simple in the designing. One example following it : Ethernet(2) Complex edge and simple coreIt means that the hosts are very complex and have many functions while the nodes are very simple and have few functions.One example following it : The design of router, or the functions of TCP and IP(3) Smart sender and dumb receiverIt means that the function of sender is more complex than that of the receiver, which is help to improve the robustness and performance of communication protocol. One example following it: The flow control of TCP protocol[Question 3] Error detection(1) Tell the main idea of error detection and error correction in communication.(2) Given the CRC polynomial x 4 + x 3 + 1, if the original message is 10110011010, what is the CRC message to send?(3) Suppose the first bit of the message in (2) is inverted due to the noise in transmission. How can the receiver detect it via CRC verification?Solution:(1)1087431()M x x x x x x x =+++++, 43()1C x x x =++. So k=4.a) Multiply M(x) by 2kto get 141211875()T x x x x x x x =+++++,b) Then divide T(x) by C(x) to get the remainder 0000.c) The message that should be transmitted is 101100110100000.(2)The message received is 001100110100000.Divide it by C(x), then the remainder is 1100.So it is not divisible by C(x).So the receiver knows that an error has occurred.(1) What are the essential components to realize reliable transmission?(2) Suppose two computers are communicated via Stop-and-wait protocol. The link bandwidth is 5kbps, and the one-way propagation delay is 20ms. To reach 80% or higher link utilization, what is the minimal frame size for this communication?(3) If it is upgraded to Sliding-Window protocol. To reach the same goal with (2), what is the minimal window size, how many bits are required to describe the frame sequence in window? (Suppose the frame size is 1 or 100Byte)Solution:(1)ACK, and timerActual_throughput = Data / Total_DelayTotal_Delay = RTT + Data / BWLink_Utilization = 100 * Actual_throughput / BWSo: Data/throughput = RTT + Data/BW(BW/throughput - 1) Data = BW*RTTData = BW*RTT/(1/Utilization -1)For the stop-and-wait protocol, for each RTT only one frame is sent,Thus Frame_size = Data = BW*RTT/(1/Utilization - 1) = 5kbps * 40ms / (1/0.8 - 1)= 200 bit / 0.25 = 800 bit = 100 ByteIf the students ignore the data transmission delay, their answer isframe_size = BW*RTT*Utilization = 5000 bit/sec * 40 / 1000 sec * 0.8 = 160 bit = 20 ByteIn this case, at least -2 score.(3)For the sliding-window protocol, in each RTT the data window can be transmitted at most.Thus Window_size = Data = BW*RTT/(1/Utilization - 1) = 5kbps * 40ms / (1/0.8 - 1)= 200 bit / 0.25 = 800 bit = 100 ByteIf the frame size is 100Byte, 1 frames are allowed.To indicate the frames in both sides of sender and receiver, the sequence number should describe 2 frames, thus the [log2(2) ]=1 bitIf the students ignore the data transmission delay, their answer iswindow_size = BW*RTT*Utilization = 5000 bit/sec * 40 / 1000 sec * 0.8 = 160 bit = 20 ByteIf the frame size is 100Byte, 1 frames are allowed.To indicate the frames in both sides of sender and receiver, the sequence number should describe 2 frames, thus the [log2(2) ]=1 bitIn this case, at least -2 score.(1) What is the main idea of CSMA/CD (Carrier Sense Multiple Access/Collision Detection) in traditional Ethernet? Can it be deployed for wireless local network, why?(2) Suppose one traditional Ethernet has 1km cable, the signal propagation speed is 2*105km/s, and the transmission rate is designed to be 100Mbps. What is the minimal frame size to support carrier sensing?Solution:(1) the main idea of CSMA/CD include two parts. One is carrier sensing, which means the node should detect the channel before sending any data. If the node finds the channel is idle, it begins to transmit. Otherwise, the node stop for next round. The second issues is collision detection, which means the node should detect the channel in the duration of its data transmission. If the node finds the channel become busy, or in other word, there is a collision, it should stop transmitting immediately.CSMA/CD cannot be deployed in wireless LAN, because the wireless radio transmitter and receiver can not work in dual mode. The wireless node cannot detect collision when it is transmitting data.(2)the minimal frame should be transmitted throughout the whole traditional Ethernet.Thus t = frame_size / transmit_rate = 2 * cable_length / prop_speed.Frame_size = 100 * 106 bits/sec * 2 * 103 m / (2 * 108)m/sec = 1000 bits = 125 Byte[Question 6] Switched network(1) What are the differences between circuit switching and packet switching?(2) For the following linear topology network, each link has 2ms propagation delay and 4 Mbps bandwidth.A B C DIf we use circuit switching, circuit setup requires a 1KB message to make one round-trip on the path, which incurs a 1ms delay at each switch after the message has been completely received. Then we can send the file as one contiguous bit stream. What is the delay for circuit switching to transmit n-byte from A to D?(3) If we use packet switching in the network of (2), we can break the file into 1KB packets, which has 24byte header and 1000byte payload. The switch takes 1ms process delay after receiving the packet, and then sent it continuously. What is the condition for packet switching to have less delay performance than circuit switching?Solution:(1)(2)T pkt = Packet_Size / Bandwidth = 1 KB / 4Mbps = 1024 *8 / (4 * 106) = 2.048 ms T p = 2 ms, T s = 1 ms,T t = n B / 4MbpsIn circuit switching, Total time duration:D = Singling_Delay + Transmission_Delay = 2 * Packet_Duration + Transmission_Delay = 2 * (T pkt * 2 + T p * 3 + T s * 2 + T pkt ) + (T p * 3 + T t ) = T pkt * 6 + T p * 9 + T s * 4 + T tThus, D = 2.048 * 6 + 2 * 9 + 1 * 4 + n * 8 bits / 4Mbps = 34.288 (ms) + 2n (us)(3)Main ideaThe reliability provided by endhost The reliability provided by thenetwork Information in packet Every packet has its dest-addrin header Every packet has its temp VCIlocally Forwarding action inswitch Every packet was treatedindependentlyThe packets are processed inthe manner of VCPackets received indestinationNot in sequenceIn sequenceT pkt = Packet_Size / Bandwidth = 1 KB / 4Mbps = 1024 *8 / (4 * 106) = 2.048 msT p = 2 ms,T s = 1 ms,T t = 1.024 * n B / 4MbpsIn packet switching, Total time duration:D = Delay_at_Switch * Switch_Num + Delay_at_last_hop= (T p + T pkt +T s)*2 + (T p + T t )= T pkt * 2 + T p * 3 + T s * 2 + T tThus, D = 2.048 * 2 + 2 * 3 + 1 * 2 + 1.024 * n B / 4Mbps= 12.096 (ms) + 2.048 n (us)In order to make34.288 (ms) + 2n (us) > 12.096 (ms) + 2.048 n (us)Thus 22.192(ms) > 0.048 n(us)n < 22.192 * 1000 / 0.048 = 462333 Byte = 451.5 KB[Question 7] Ethernet Switch(1) What are the differences between hub and switch in Ethernet?(2) Suppose one server and nine clients are connected via hub in 10Mbps Ethernet, what is the maximal bandwidth for the client-server connection?(3) If the hub is upgraded to switch, can the client-server connection obtain more bandwidth? if can, how much is it?Solution:(1)hub works in Layer2, it works as the shared media and relays the frames to all the nodes connecting to hub. Switch works in Layer2, it forwards the frames to the specific node according to the destination address embedded in the frame header.(2)the max bandwidth in client-server connection is 10Mbps/(1+9)= 1Mbps(3)the max bandwidth in client-server connection is 10Mbps/9 = 1.1111MbpsAdditional 0.1111 Mbps is obtained for each connection.[Question 8] Router(1) Somebody says that, ``the only difference between switch and router is that they do switch function based on the address in different layers.’’ Is it correct? Why?(2) If we obtain the following information from one router. What kind of routing protocol does itSolution:(1)it is not fully correct. The part talking about the forwarding function is correct, while it is not the only difference. Another but not the last difference is that, router has more functions on control plane, which do routing and find the paths for packets.(2)The routing protocol is RIP.The routing table is:Destination Next hop Interface192.168.1.0/24 * Fa 0/4192.168.2.0/24 * Fa 0/6192.168.10.0/24 192.168.1.1 Fa 0/4192.168.30.0/24 192.168.2.2 Fa 0/6[Question 9] Routing algorithm(1) State the main differences between distance vector routing and link state routing.(2) For the network given in the following figure, provide the steps of forward search in Dijkstra algorithm for node A finding the shortest path to node ESolution:(1) The idea of distance vector routing is to tell the neighbors about the learned topology to all the nodes in the network. The idea of link state routing is to tell all the nodes in network about the neighborhood topology.Step 1 2 3 4 5 6 7 8 9Confirmed (A,0,-) (A,0,-) (A,0,-)(D,2,D)(A,0,-)(D,2,D)(A,0,-)(D,2,D)(B,4,D)(A,0,-)(D,2,D)(B,4,D)(A,0,-)(D,2,D)(B,4,D)(E,6,D)(A,0,-)(D,2,D)(B,4,D)(E,6,D)(A,0,-)(D,2,D)(B,4,D)(E,6,D)(C,7,D)Tentative (B,5,B)(D,2,D)(B,5,B) (B,4,D)(E,7,D)(E,7,D)(E,6,D)(C,8,D)(C,8,D) (C,7,D)A→E A→D→EA→D→B→EA→D→B→E[Question 10] IP address allocationA company has one C class IP address of 200.1.1.*. It has four departments.(1) If each department has less than 25 computers. Provide a kind of IP address allocation. Give the network address, subnet mask, and the available IP address range for each department. (2) If the four departments have 72, 35, 34, 20 computers respectively. Provide the IP address allocation scheme again.Solution:(1)Since each department has less than 25 computers, even considering the additional two more IP address for gateway and broadcast, the 64-computer subnet is enough for them.One IP address allocation scheme is to even divide the 256 IP addresses into 4 subnets, each subnet allows 64 hosts.Another IP address allocation scheme is to even divide the 256 IP addresses into 4 subnets, each subnet allows 32 hosts.(2) Since one of the department has more requirements than 64, then the even distribution scheme[Question 11] TCP protocol(1) Somebody says that, ``because of the reliable transmission service in layer 2, there is no need to provide such service again within TCP protocol in layer 4’’. Is it correct? Why?(2) State the main rules of TCP connection setup according to the following figure. Explain every word and number in the figure.Solution:(1) It is wrong. TCP is based on the un-reliable IP layer, which only provides best effort service. If TCP wants to provide reliable transmission service, it has to realize this by itself.(2)TCP use three hand-shakes to setup the connection.According to the figure, there are two nodes. The sender is with IP address of 192.168.1.163 and the receiver 192.168.1.165 respectively.●At first, the sender send a request ``SYN’’to the receiver to setup the connection. Thismessage is with the sequence number of 424CF1DC;●Secondly, the receiver reply an acknowledgment message ``SYN/ACK’’ to the sender. Thismessage has two sequence numbers. The seq in the ACK is 424CF1DD, which is to confirm the last ``SYN’’ from sender. The seq in the SYN is 30318555, which is a new message from the receiver.●Thirdly, the sender reply an acknowledgment message ``ACK’’ to the receiver. The seq in theACK is 30318556, which is to confirm the last ``SYN’’ from receiver.In the end, both the sender and receiver knows that the other side is ready for this TCP connection.[Question 12] TCP congestion control(1) Both flow control and congestion control in TCP are realized by window based packet control. How can TCP get the window sizes in these two mechanisms?(2) Assume that TCP implements an extension that allows window sizes much larger than 64 KB. Suppose that you are using this extended TCP over a 1Gbps link with a latency of 150ms. TCP packet size is 1KB, and the max receive window is 1 MB. Suppose there is no real congestion and packet loss in transmission. How many RTTs does it take until slow start opens the send window to 1 MB? How long does it take to send the complete file? ( Suppose file size is 10MB )Solution:(1) In flow control, TCP sender knows the window size by the field of advertise-window replied from the receiver. In congestion control, TCP sender learns the window size adaptively by AIMD( Additive Increase and Multiplicative Decrease) mechanism responding to the packet lossevent.(2)When TCP realizes congestion control mechanism, its effective send window size will be min (CongestionWindow, AdvertizedWindow). In original design of TCP header, the field of AdvertizedWindow is 16 bit, which is 216=26*210=64 KB. So the maximum effective window of original TCP sender is 64KB. The assumption of the first sentence in this question relaxes such constraint for TCP.In slow start, the send window starts from w0=1 packet, which is 1 KB. For each RTT after a successful transmission, the window size will be doubled. After i RTT, it will be 2i * w0. Let 2i * 1KB = 1MB, soi = log2(1MB/1KB) = log2(210) = 10.It will take 10 RTTs to reach 1MB send window.Case 1: if the receiver window remains as 1MBIn the first 10 RTTs, total (1 + 2 + 4 + … + 210) * 1KB has been transmitted.Which is (211 - 1) * 1KB = 2 MB - 1 KB, the rest file is 10MB - (2MB - 1KB) = 8MB + 1KBIn the reset transmission, each RTT can only support 1MB transmission.Thus, additional 9 RTTs are required. Total 19 RTT = 19 * 150ms = 2.85 sCase 2: if the receiver window can be changed.Since there is no congestion and loss, the maximum send window will be the bandwidth * delay for this TCP connection.w max= 1G bps * 150ms = 109 * 150 * 10-3= 150 *106 bit = 18.75 * 106 byte = 17.88 MB.So, this 10 MB file can be transferred before reaching w max. In another word, it can be sent in its slow start phase. Assume x RTT is required to send this file, then:(1 + 2 + 4 + … + 2x) * 1KB ≥ 10 MB2 * 2x–1 ≥ 10 * 1024x ≥ log2(10241) – 1 = 12.3Thus x = 13, it will take 13 RTTs to transfer this file. 13RTT = = sTotal delay = 13RTT + Filesize/BW = 13 * 150ms+ 10MB / 1Gbps =1.95 + 0.08 * 1.024^2=2.03 s11。
计算机网络英文版习题答案
P63 #5 Consider sending a packet of F bits over a path of Q links. Each link transmits at R bps. The network is lightly loaded so that there are no queuing delays. Propagation delay is negligible.a.Suppose the network is a packet-switched virtual-circuit network. Denote the VC setup time by t s seconds. Suppose the sending layers add a total of h bits of header to the packet. How long does it take to send the file from source to destination?t s+[(F+h)/R]Qb.Suppose the network is a packet-switched datagram network and a connectionless service is used. Now suppose each packet has 2h bits of header. How long does it take to send the packet?[(F+2h)/R]Qc.Finally, suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is R bps. Assuming ts setup time and h bits of header appended to the packet, how long does it take to send the packet?t s+(F+h)/RP64 #6 This elementary problem begins to explore propagation delay and transmission delay, two central concepts in data networking. Consider two hosts, A and B, connected by a single link of rate R bps. Suppose that the two hosts are separated by m meters and suppose that the propagation speed along the link is s meters/sec. Host A sends a packet of size L bits to host B.[a] Express the propagation delay, d prop, in terms of m and s.[b] Determine the transmission time of the packet, d trans, in terms of L and R.[c] Ignoring processing and queueing delays, obtain an expression for the end-to-end delay.[d] Suppose Host A begins to transmit the packets at time t=0. At time t=d trans, where is the last bit of the packet?[e] Suppose d prop is greater than d trans. At time t=d trans, where is the first bit of the packet?[f] Suppose d prop is less than d trans. At time t=d trans, where is the first bit of the packet?[g] Suppose s=2.5 x 108, L=100 bits and R=28kbps. Find the distance m so that d prop = d trans.[a] d prop = m/s[b] d trans = L/R[c] end-to-end delay = d prop + d trans=m/s+L/R[d] The beginning position of the link.[e] On the channel between A and B.[f] On the host B.[g] m/s = L/R = > m = sL/R = > m = 892.86 kmP65 #10 Consider the queueing delay in a router buffer. Suppose that all packets are L bits, the transmission rate is R bps, and that N packets simultaneously arrive at the buffer every LN/R seconds. Find the average queueing delay of a packet (in terms of L, R and N). (Hint: The queueing delay for the first packet is zero; for the second packet L/R; for the third packet 2L/R. The Nth packet has already been transmitted when the second batch of packets arrives.)As the Nth packet has already been transmitted when the next batch of packets arrive, we only need to consider the delay for a single batch of packets.Average delay = Total delay / Number of packetsDelay for 1st packet = 0Delay for 2nd packet = L/RDelay for 3rd packet = 2L/R......Delay for Nth packet = (N-1)L/RTotal delay for N packets = (0 + 1 + 2 ... +(N-1) ) * (L/R)Using the formulas for sum of integer series, this can be written as: Total delay for N packets = (N-1) * (N/2) * (L/R)Therefore, average delay for N packets = ((N-1) * L) / 2RP170 #12 What is the difference between persistent HTTP with pipelining and persistent HTTP without pipelinning? Which of the two is used by HTTP/1.1?For the persistent connection without pipelining, the client issues a new request only when the previous has been received. In this case, the client experiences one RTT in order to request and receive each of the referenced objects.For the persistent connection with pipelining, the client issues a request as soon as it encounters a reference. It is possible for only RTT to be expended for all the referenced objects.P170 #14 Telnet into a Web server and send a multiline request message. Include in the request message theIf-modified-since: header line to force a response message with the 304 Not Modified status code.GET/somedir/exp.html HTTP/1.1Host: Connection: closeUser-agent: Mozilla/4.0If-Modified-Since: Thu, 30 May 2007 12:00:00 GMTAccept-language: frP172 #6 Suppose within your web browser you click on a link to obtain a web page. The IP address for the associated URL is not cached in your local host, so a DNS look-up is necessary to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur an RTT (Round Trip Time) of RTT1, ... RTTn. Further suppose that the web page associated with the link contains exactly one object, consisting of a small amount of HTTP text. Let RTT0 denote the RTT between the local host and the remote server containing the object. Assuming zero transmission time of the object, how much time elapses from when the client clicks on the link until the client receives the object? (Hint: read pages 90 .. 93)Time to visit DNS servers and get IP address = RTT1 + RTT2 + ... + RTTnTime to establish TCP connection (SYN and SYNACK) = RTT0Time to send HTTP request and receive reply = RTT0Total time = 2 * RTT0 + (RTT1 + RTT2 + ... + RTTn)P171 #16 Suppose Alice with a Web-based e-mail account (such as Yahoo! Mail or Hotmail) sends a message to Bob, who accesses his mail from his mail server using POP3. Discuss how the message gets from Alice’s host to Bob’s host. Be sure to list the series of application-layer protocols that are used to move the message between the two hosts.The series of application-layer protocols: HTTP、SMTP、POP3Suppose that you send an e-mail message whose only data is a Microsoft Excel attachment. What might the header lines (including MIME lines) look like?From:***********To:***********Subject: helloMIME-Version: 1.0Content-Transfer-Encoding: base64Content-Type: Application/MS-ExcelP286 #5 Suppose host A sends two TCP segments back to back to host B over a TCP connection. The first segment has sequence number 90: the second has sequence number 110.a.How much data is in the first segment?a.20 bytesb.Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgement that host B sends to host A, what will be the acknowledgement number?b.ACK90P291 #27 Consider the following plot of TCP window size as a function of time. (reproduced below for you) Assuming TCP Reno is the protocol experiencing the behavior shown above, answer the following questions. In all cases, you should provide a short discussion justifying your answer.a. Identify the intervals of time when TCP slow start is operating.b. Identify the intervals of time when TCP congestion avoidance is operating.c. After the 16th transmission round, is segment loss detected by a tripleduplicate ACK or by a timeout?d. After the 22nd transmission round, is segment loss detected by a triple duplicate ACK or by a timeout?e. What is the initial value of Threshold at the first transmission round?f. What is the value of Threshold at the 18th transmission round?g. What is the value of Threshold at the 24th transmission round?h. During what transmission round is the 70th segment sent?i. Assuming a packet loss is detected after the 26th round by the receipt of a triple duplicate ACK, what will be the values of the congestion-window size and of Threshold?Solution:a.1-6, 23-26b.6-16, 17-22c.a triple duplicate ACKd.timeoute.32f.21g.13h.7i.4, 4P293 #34 Consider sending an object of size O = 100 Kbytes from server to client. Let S = 536 bytes and RTT = 100 msec. suppose the transport protocol uses static windows with window size W. (See Section 3.7.2)a.For a transmission rate of 28 kbps, determine the minimum possible latency. Determine the minimum window size that achieves this latency.b.Repeat (a) for 100 kbps.tency=28.8s W=2tency=8.2s W=4P405 #8 Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix matching and has t he following forwarding table:-----------------------------------------------------Prefix Match Interface-----------------------------------------------------00 001 110 211 3-----------------------------------------------------For each of the four interfaces, give the associated range of destination host addresses and the number of addresses in the range.6P407 #15 Consider sending a 3000-byte datagram into a link that has a MTU of 500 bytes. Suppose the original datagram is stamped with the identification number 422. How many fragments are generated? What are their characteristics?there are「2980/480」=7 fragments be generatedP408 #22 Consider the network shown in Problem 21 (reproduced below). Using Dijkstra’s algorithm, and showing your work using a table similar to Table 4.3, do the following:a. Compute the shortest path from s to all network nodesSteps D(t),P(t) D(u),P(u)D(v),P(v)D(w),P(w)D(x),P(x)D(y),P(y)D(z),P(z)0 1,s 4,s ∞∞∞∞∞1 3.t 10,t ∞∞5,t 3,t2 4,u 6,u ∞5,t 3,t3 4,u 6,u ∞5,t4 5,v 7,v 5,v5 6,w 5,v6 6,wPlease fill in the following tables using DV algorithm:For the node Z in the graph shown in the 22nd topic (P408), please fill in the following routing table in the router z about the initial distance-vector Destination node Next hop Current shortest distancevalue-DzS —∞T T 2U —∞V —∞W —∞X —∞Y Y 14Z Z 0following rout-ing table in the node z to update this routing tableDestination node Currentdistance-DyDestination node Current distance-DtS 5 S 1 T 4 T 0 U 2 U 2P493 #7 How big is the MAC address space？The IPv4 address space？The IPv6 address space?MAC address: 6 bytes, MAC address space 2^48IPV4 address: 4 bytes, IPV4 address space 2^32IPV6 address: 16 bytes, IPV6 address space 2^128P494 #4 Consider the 4-bit generator, G, shown in Figure 5.8, and suppose the D has the value 10101010. What is the value of R?G=1001, D=10101010, R=101。
计算机网络英文题库(附答案)chapter3解析
Chapter 3 Transport Layer1. A transport-layer protocol provides for logical munication between ____.A Application processesB HostsC RoutersD End systems2. Transport-layer protocols run in ____.A ServersBClientsCRoutersDEnd systems3. In transport layer, the send side breaks application messages into ____, passes to network layer.A FramesB SegmentsC Data-gramsD bit streams4. Services provided by transport layer include ____.A HTTP and FTPB TCP and IPC TCP and UDPD SMTP5. Which of the following services is not provided by TCP"A Delay guarantees and bandwidth guaranteesB Reliable data transfers and flow controlsC Congestion controlsD In-order data transfers6. These two minimal transport-layer services----____ and ____----are the only two services that UDP provides!A process-to-process data delivery, error checkingB congestion control, reliable data transferC flow control, congestion controlD In-order data transfer, error checking7. Port number’s scope is ____ to ____.A 0, 1023B 0, 65535C 0, 127D 0,2558. The port numbers ranging from ____to ____ are called well-known port number and are restricted.A 0, 1023B 0, 65535C 0, 127D 0,2559. UDP socket identified by two ponents, they are____.A source IP addresses and source port numbersB source IP addresses and destination IP addressesC destination IP address and destination port numbersD destination port numbers and source port numbers10. TCP socket identified by a (an) ____.A 1-tupleB 2-tupleC 3-tupleD 4-tuple11. Which of the following applications normally uses UDP services"A SMTPB Streaming multimediaC FTPD HTTP12.Reliable data transfer protocol over a perfectly reliable channel is____.A rdt1.0B rdt2.0C rdt3.0D rdt2.113.Reliable data transfer protocol over a channel with bit errors and packet losses is_ ___.A rdt1.0B rdt2.0C rdt3.0D rdt2.114.Which of the following about reliable data transfer over a channel with bit errors is not correct"A RDT2.0:assuming ACK and NAK will not be corruptedB RDT2.1:assuming ACK and NAK can be corruptedC RDT2.2:only use ACK-sD RDT2.2:use both ACK-s and NAK-s15.Which of the following protocols is not pipelining protocols"A TCPB rdt3.0C GO-BACK-ND selective repeat16.Which of the following is not correct about GBN protocol"A Only using ACK-sB Using cumulative ACK-sC Receiver discards all out-of-order packetsD It is not pipelined protocol17.Which of the following is not correct about SR protocol"A receiver individually acknowledges all correctly received packetsB sender only resends packets for which ACK not receivedC It limits sequence number of sent but un-ACK-ed packetsD It is not a pipelined protocol18. Which of the following about TCP connection is not correct"A It is a broadcast connectionB It is a point-to-point connectionC It is a pipelined connectionD It is a full duplex connection19. The SYN segment is used for____.A TCP connection setupB TCP flow controlC TCP congestion controlD Closing a TCP connection20. The FIN segment is used for____.A TCP connection setupB TCP flow controlC TCP congestion controlD Closing a TCP connection21.How does TCP sender perceive congestion"A Through a timeout eventB Through a receiving duplicate ACK-s eventC Both A and BD Either A or B22. Extending host-to-host delivery to process-to-process delivery is called transport-layer____ and .A multiplexing and de-multiplexingB storing and forwardingC forwarding and filteringD switching and routing23. UDP is a ____ service while TCP is a connection-oriented service.A ConnectionlessB ReliableC Connection-orientedD In-order24. The UDP header has only four fields, they are____.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 number25. There are two 16-bit integers: 1110 0110 0110 0110, 1101 0101 0101 0101. Their checksum is____.A 00011B 11100C 11111D 0000026.The maximum amount of data that can be grabbed and placed in a segment is limited by the____.A Maximum segment size (MSS)B MTUC ChecksumD Sequence number27.The MSS is typically set by first determining the length of the largest link-layerframe that can be sent by the local sending host----the so-called____.A Maximum transmission unit (MTU)B MSSC ChecksumD Sequence number28. A File size of 500,000bytes, MSS equals 1000bytes. When we want to transmit this file with TCP, the sequence number of the first segment is 0, and the sequence number of the second segment is ____.A 1000B 999C 1001D 50000029.Because TCP only acknowledges bytes up to the first missing byte in the stream, TCP is said to provide____.A Cumulative acknowledgementsB Selective acknowledgementsC 3 duplicate ACKsD positive ACKs30. Provided α=0.125, current value of Estimated-RTT is 0.4s, Sample-RTT is 0.8s, then the new value of Estimated-RTT is ____s.A 0.45B 0.6C 0.7D 0.831.Provided RcvBuffer=20,LastByteRcvd=20,LastByteRead=15, thenRcvWindow=____.A 14B 15C 16D 1032. TCP service does not provide____.A Reliable data transferB Flow controlC Delay guaranteeD Congestion control33. There are two states in TCP congestion control, which are ____.A slow start and congestion avoidanceB safe start and congestion avoidanceC slow start and congestion abandonD safe start and congestion abandon34. The transport-layer protocol provides logical munication between ____, and the network-layer protocol provides logical munication ____.A hosts, processesB processes, hostsC threads, processesD processes, threads35.To implement the multicast services the Internet employs the____protocol.A FTPB TCPC IGMPD UDP36. If an application developer chooses ____ protocol, then the application process is almost directly talking with IP.A HTTPB RIPC CSMA/CDD UDP37. ____ maintains connection-state in the end systems. This connection state includes receive and send buffers, congestion-control parameters, and sequence and acknowledgment number parameters.A UDPB TCPC DNSD HTTP38. The host that initiates the session in the Internet is labeled as ____.A serverB user agentC clientD router39. With TCP there is no _____ between sending and receiving transport-layer entities.A flow controlB handshakingC.congestion control D VC setup40. The Internet’s ____ service helps prevent the Internet from entering a state of gridlock.A datagramB congestion controlC sliding windowD timeout event41. Connection setup at the transport layer involves ____.A serverB only the two end systemsC clientD router42. A ____layer protocol provides for logical munication between applications.A transportB applicationC networkingD MAC43. In static congestion window, if it satisfies W*S/R > RTT + S/R, the Latency is ____.A W*S/R – ( RTT+ S/R)B 2RTT + O/RC 2RTT + O/R + (k-1)[W* S/R- (RTT + S/R)]D 2RTT + S/R44. The receive side of transport layer reassembles segments into messages, passes to ____layer.A ApplicationB NetworkingC PhysicalD MAC45. In the following four options, which one is correct"A The variations in the SampleRTT are smoothed out in the putation of the EstimatedRTTB The timeout should be less than the connection’s RTTC Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then the current value of TimeoutInterval will necessarily be≥1 secD Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then the current value of TimeoutInterval will necessarily be≤1 sec46. The port number used by HTTP is ____.A 80B 25C 110D 5347. The port number used by SMTP is ____.A 80B 25C 110D 5348. The port number used by pop3 is ____.A 80B 25C 110D 5349. The port number used by DNS is ____.A 80B 25C 110D 5350. The port number used by FTP is ____.A 20 and 21B 20C 21D 5351. A UDP socket identified by a ____ tuple(s).A 2B 4C 1D 352. A TCP socket identified by a ____ tuple(s).A 2B 4C 1D 353. A TCP socket does not include____.A Source MAC addressB Source port numberC Destination IP addressD Destination port number54. Which of following about UDP is not correct.A It is a reliable data transfer protocolB It is connectionlessC no handshaking between UDP sender, receiverD it is a best effort service protocol55. DNS uses ____ service.A TCPB UDPC Both TCP and UDPD None of above56. Which of following about UDP is correct"A Finer application-level control over what data is sent, and whenB No connection establishment (which can add delay), so no delay for establish a connectionC No connection state (so, UDP can typically support many active clients)D Large packet header overhead (16-B)57. Streaming media uses a ____ service normally.A TCPB UDPC Both TCP and UDPD None of above58. The UDP header has only ____ fields.A 2B 4C 1D 359. Which of the following does not included in UDP header.A Source port numberB Destination port numberC ChecksumD Sequence number60. Which of the following is not a pipelining protocol.A Rdt1.0B Go-Back-NC Selective repeatD TCP61. In the following four descriptions about MSS and MTU, which one is not correct"A The MSS is the maximum amount of application-layer data in the segmentB The MSS is the maximum size of the TCP segment including headersC The MSS is typically set by MTUD The MTU means the largest link-layer frame62. 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 multiplexingB de-multiplexingC forwardingD routing63. In the following four descriptions about the relationship between the transport layer and the network layer, which one is not correct"A The transport-layer protocol provides logical munication between hostsB The transport-layer protocol provides logical munication between processesC The services that a transport-layer protocol can provide are often constrained by the service model of the network-layer protocolD A puter network may make available multiple transport protocols64. Suppose the following three 8-bit bytes: 01010101, 01110000, 01001100. What’s the 1s plement of the sum of these 8-bit bytes"A 00010001B 11101101C 00010010D 1000100065. The following four descriptions about multiplexing and de-multiplexing, which one is correct"A A UDP socket is identified by a two-tuples consisting of a source port number and a destination port number.B If two UDP segment have different source port number, they may be directed to thesame destination process.C If two TCP segments with different source port number, they may be directed to the same destination process.D If two TCP segments with same destination IP address and destination port number, they must be the same TCP connection.66. UDP and TCP both have the fields except ____.A source port numberB destination port numberC checksumD receive window67. 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 can be sent immediatelyB have already been transmitted and acknowledgedC cannot be usedD have been sent but not yet acknowledged68. Which of the following about TCP is not correct"A It is a connectionless protocolB Point-to-point protocolC Reliable, in-order byte steam protocolD Pipelined protocol69. Which of the following about TCP is not correct"A It is a connectionless protocolB full duplex data transfer protocolC connection-oriented protocolD flow controlled protocol70. The maximum amount of data that can be grabbed and placed in a segment is limited by the ____.A Maximum segment size (MSS)B MTUC Sequence numberD Check sum71. The MSS is typically set by first determining the length of the largest link-layer frame that can be sent by the local sending host (the so-called____), and then will fit into a single link-layer frame.A Maximum segment size (MSS)B MTUC Sequence numberD Check sum72. The MSS is the maximum amount of ____layer data in the segment, not the maximum size of the TCP segment including headers.A ApplicationB TransportD Link73. Which of the following field is not used for connection setup and teardown"A Sequence numberB TSTC SYND FIN74. ____ is the byte stream number of first byte in the segment.A Sequence numberB ACK numberC ChecksumD port number75. ____ is the byte sequence numbers of next byte expected from other side.A Sequence numberB ACK numberC ChecksumD port number76. Because TCP only acknowledges bytes up to the first missing byte in the stream, TCP is said to provide ____ acknowledgements.A CumulativeB SelectiveC Single77. Fast retransmit means in the case that ____ duplicate ACK-s are received, the TCP sender resend segment before timer expires.A 3B 4C 5D 678. TCP____ means sender won’t overflow receiver’s buffer by transmitting too much, too fast.A Flow controlB Congestion controlC Reliable data transferD Connection-oriented service79. TCP provides flow control by having the sender maintain a variable called the ____.A Receive windowB Congestion windowC Sliding windowD buffer80. How does TCP sender perceive congestion"A TimeoutB 3 duplicate ACK-sC Both A and BD None of above81. Transport protocols run in ____.A ServersB ClientsC RoutersD End systems82. Which of the following services is not provided by TCP"A Delay guarantees and bandwidth guaranteesB Reliable data transfers and flow controlsC Congestion controlsD In-order data transfers83. Which service does UDP not provide"A multiplexingB de-multiplexingC error-detectionDerror-correction84. There are three major events related to data transmission and retransmission in the TCP sender, which one is not in it"A data received from application aboveB de-multiplexing segmentC timer timeoutD ACK receipt85. Which of the following applications normally uses UDP services"A SMTPB Streaming multimediaC FTPD HTTP86. Which of the following about TCP connection is not correct"A It is a broadcast connectionB It is a point-to-point connectionC It is a pipelined connectionD It is a full duplex connection87. The SYN segment is used for____.A TCP connection setupB TCP flow controlC TCP congestion controlD Closing a TCP connection88. Which service helps prevent the internet from entering a state of gridlock"A reliable data transferB flow controlC congestion controlD handshaking procedure89. The Internet’s _____is responsible for moving packets from one host to another.A application layerB transport layerC network layerD link layer90.In the following applications, which one is a bandwidth-sensitive application"AB web applicationC real-time audioD file transfer91. In the following applications, which one uses UDP"AB web applicationC file transferD DNS92. In the following four descriptions, which one is correct"A If one host’s transport layer uses TCP, then its network layer must use virtual-circuit network.B Datagram network provides connection serviceC The transport-layer connection service is implemented in the routerD The network-layer connection service is implemented in the router as well as in the end system.93.____ 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 control94. In the following four descriptions about Rcv-Window, which one is correct"A The size of the TCP RcvWindow never changes throughout the duration of the connectionB The size of the TCP RcvWindow will change with the size of the TCP RcvBufferC The size of the TCP RcvWindow must be less than or equal to the size of the TCP RcvBufferD Suppose host A sends a file to host B over a TCP connection, the number of unacknowledged bytes that A sends cannot exceed the size of the size of the RcvWindow.95. There are 6 flag fields. Which one is to indicate that the receiver should pass the data to the upper layer immediately"A PSHB URGC ACKD RST96. Suppose the TCP receiver receives the segment that partially or pletely fills in gap in received data, it will ____.A immediately send ACKB immediately send duplicate ACKC wait some time for arrival of another in-order segmentD send single cumulative97. _____ imposes constrain on the rate at which a TCP sender can send traffic into the network.A sliding windowB congestion windowC receive windowD variable window98. Flow control and congestion control are same at that they all limit the rate of the sender, but differ in that ____.A flow control limits its rate by the size of RcvWindow, but congestion control by the traffic on the linkB congestion control limits its rate by the size of RcvWindow, but flow control by the traffic on the linkC flow control mainly is acplished by the sender, but congestion control by the receiver.D flow control mainly is acplished by the receiver, but congestion control by the link.99. This job of delivering the data in a transport-layer segment to the correct socket is called ____.A multiplexingB de-multiplexingC forwardingD routing100. 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 [base, nextseqnum-1] corresponds to packet that ____.A can be sent immediatelyB have already been transmitted and acknowledgedC cannot be usedD have been sent but not yet acknowledged101. ____ are the two types of transport services that the Internet provides to the applications.A TCP and UDPB connection-oriented and connectionless serviceC TCP and IPD reliable data transfer and flow control102. In the following descriptions about persistent connection, which one is not correct"A The server leaves the TCP connection open after sending a responseB Each TCP connection is closed after the server sending one objectC There are two versions of persistent connection: without pipelining and with pipeliningD The default mode of HTTP uses persistent connection with pipelining103. The field of Length in UDP segment specifies the length of ____.A the UDP segment, not including the headerB the UDP segment, including the headerC the UDP segment’s headerD the Length field104. In TCP segment header, which field can implement the reliable data transfer"A source port number and destination port numberB sequence number and ACK numberC urgent data pointerD Receive window105. In the following four descriptions about TCP connection management, which one is not correct"A 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 1 106. Suppose host A sends two TCP segments back to back to host B over a TCP connection. The first segment has sequence number 42, and the second has sequence number 110. If the 1st is lost and 2nd arrives at host B. What will be the acknowledgment number"A 43B ACK42C 109D ACK1101.Consider sending an object of size O=500,000bytes from server to client. Let S=500bytes and RTT=0.2s. Suppose the transport protocol uses static windows with window size 5. For a transmission rate of 100Kbps, determine the latency for sending the whole object. Recall the number of windows K=O/ WS), and there is K-1 stalled state (that is idle time gaps).2.Consider the following plot of TCP congestion window size as a function of time.Fill in the blanks as follow:a) The initial value of Threshold at the first transmission round is ____. b) The value of Threshold at the 11st transmission round is ____. c) The value of Threshold at the 21st transmission round is ____. d) After the 9th transmission round, segment loss detected by ____.(A) Timeout (B) Triple duplicate ACKe) After the 19th transmission round, segment loss detected by ____.(A) Timeout (B) Triple duplicate ACKf) During ____ transmission round, the 18th segment is sent.0 00 Congestion window size Transmission round3.Consider the TCP reliable data transfer in the given graph. If in Segment 1’s Sequence number =10,data=“AC〞, please fill in the following blanks.a)In Segment 2, ACK number=____;b)In Segment 3, Sequence number =____; data=“0123456789”c)If there are some bits corrupted in segment 3 when it arrives Host B, then the ACKnumber in Segment 5 is ____; and the ACK number in Segment 6 is ____.12345674. The client A wants to request a Web page from Server B. Suppose the URL of the page is 172.16.0.200/experiment, and also it wants to receive French version of object.The time-sequence diagram is shown below, please fill in the blanks.12345Packet① to Packet③ are TCP connection’s segment, then:Packet ①: SYN flag bit= aACK flag bit= bSequence number= 92Packet ②: SYN flag bit=1ACK flag bit= cSequence number=100Packet ③: SYN flag bit= dACK flag bit=1Sequence number= e5. Consider sending an object of size O=100 Kbytes from server to client. Let S=536 bytes and RTT=100msec. Suppose the transport protocol uses static windows withwindow size W.(1) For a transmission rate of 25 kbps, determine the minimum possible latency. Determine the minimum window size that achieves this latency. (2) Repeat (1) for 100 kbps.6. Consider the following plot of TCP congestion window size as a function of time. Please fill in the blanks as below.a) The initial value of Threshold at the first transmission round is____.b) The value of Threshold at the 11th transmission round is_____.c) The value of Threshold at the 21st transmission round is_____.d) After the 9th transmission round, _____ occurs. 14 18 26 30 0 2 6 4 8 10 12 16 20 22 24 28 32 Congestion window size Transmission round 4 8 12 16e) After the 19th transmission round, ____ are detected.。
计算机网络双语试题及答案
计算机网络双语试题及答案一、选择题（共20题，每题2分，共40分）1. 当使用HTTP协议进行通信时，下列哪个是无连接的协议？A. TCPB. IPC. UDPD. FTP2. 在计算机网络中，IP地址的作用是什么？A. 标识主机在网络中的唯一地址B. 实现数据的可靠传输C. 进行主机之间的通信D. 提供远程访问服务3. 下列哪个不属于网络拓扑结构的类型？A. 总线型拓扑B. 环形拓扑C. 星型拓扑D. 布线型拓扑4. 在TCP/IP协议中，下列哪个协议用于将IP地址转换为物理地址？B. DHCPC. FTPD. ICMP5. 在计算机网络中，HTTP和HTTPS协议之间的区别是？A. HTTP使用明文传输，HTTPS使用加密传输B. HTTP使用UDP传输，HTTPS使用TCP传输C. HTTP使用IP地址，HTTPS使用域名D. HTTP使用GET请求，HTTPS使用POST请求6. 某计算机的IP地址是192.168.0.1，子网掩码是255.255.255.0，那么该计算机所在的网络号是？A. 192.168.0B. 192.168.0.1C. 192.168.0.255D. 192.168.0.07. 在计算机网络中，下列哪个协议用于将域名解析为IP地址？A. DNSB. FTPC. DHCP8. 在TCP/IP协议中，下列哪个协议用于控制数据传输的可靠性？A. ICMPB. UDPC. FTPD. TCP9. 在计算机网络中，什么是反向代理服务器（Reverse Proxy Server）？A. 将外部网络请求转发给内部服务器的服务器B. 将内部网络请求转发给外部服务器的服务器C. 将HTTP请求转发给HTTPS服务器的服务器D. 将HTTPS请求转发给HTTP服务器的服务器10. 在计算机网络中，下列哪个协议用于电子邮件的发送和接收？A. SMTPB. POP3C. HTTPD. FTP11. 在计算机网络中，下列哪个协议用于文件传输？B. SMTPC. UDPD. TCP12. 以下哪个不是IPv6地址的特点？A. 128位长度B. 冒号分隔的十六进制C. 有固定的网络号和主机号D. 全球唯一的地址13. 在计算机网络中，下列哪个技术不属于无线局域网技术？A. Wi-FiB. BluetoothC. NFCD. 4G14. 在网络中，下列哪个设备用于将不同网段的数据转发到目的主机？A. 集线器B. 路由器D. 网关15. 下列哪个网络拓扑结构具有较高的可容错性和可拓展性？A. 星型拓扑B. 总线型拓扑C. 环形拓扑D. 树型拓扑16. 在计算机网络中，下列哪个协议用于互联网上的主机进行网络配置？A. DHCPB. DNSC. HTTPD. FTP17. 在TCP/IP协议中，下列哪个协议用于检测并纠正数据传输中的错误？A. TCPB. ARPC. ICMPD. UDP18. 下列哪个是网络安全的常见攻击方式之一？A. DDoS攻击B. 数据库攻击C. 剪贴板攻击D. 社会工程学攻击19. 下列哪个不是局域网（LAN）的特点？A. 覆盖范围较小B. 速度较快C. 价格较高D. 结构较简单20. 在计算机网络中，下列哪个协议用于向局域网中的所有主机广播消息？A. UDPB. TCPC. DHCPD. ICMP二、问答题（共5题，每题10分，共50分）1. 请简要介绍HTTP协议的工作原理。
计算机网络英文题库附答案chater
Chapter 1 Computer Networks and the Internet1．The ( ) is a worldwide computernetwork, that is, a network that interconnectsmillionsofcomputing devices throughout theworld. ppt3 A public InternetB IntranetC switch netD television net2．Which kind of media is not a guidedmedia ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following optionbelongs to the circuit-switchednetworks ( )A FDMB TDMC VCnetworksD both A and B 6．( )makes sure that neither sideof a connection overwhelms theother side by sending too manypackets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch mustreceive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagramnetworksandvirtual-circuit networks differ in that ( ).A datagram networks are circuit-switched networks, and virtual-circuit networks are packet-switched networks.B datagram networks are packet-switched networks, and virtual-circuit networks are circuit-switched networks.C datagram networks use destination addresses and virtual-circuit networks use VC. numbers to forward packets toward their destination.D datagram networks use VC. numbers and virtual-circuit networks use destination addresses to forward packetstoward their destination.9．In the following options, which one is not a guided media ( )A twisted-pairwireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet ’s headerB wait to transmit the packet onto the linkC determine where to direct thepacketD check bit-error in the packet 11．In the following four descriptions, which one is correct ( )A The traffic intensity must begreater than 1.B The fraction of lost packetsincreases as the trafficintensity decreases.C If the traffic intensity isclose to zero, the averagequeuing delay will be close tozero.D If the traffic intensity isclose to one, the averagequeuing delay will be close toone.12．The Internet’s network layer is responsible for movingnetwork-layer packets known as( ) from one host to another.A frameB datagramC segmentD message13．The protocols of various layersare called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes ofpacket-switched networks: ( )networks and virtual-circuitnetworks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be looselyclassified into threecategories: residential access,company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue,R is the transmission rate, and all packets consist of L bits, then thetraffic intensity is ( 16 ), and it should no greater than ( 17 ).16． A LR ／aB La ／RC Ra ／LD LR ／a 17．A 2B 1C 0D -118．In the Internet, the equivalentconcept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics 20．End systems access to the Internet through its ( ). A modemsB protocolsC ISPD sockets21．End systems, packet switches,and other pieces of the Internet, run ( ) that control thesending and receiving ofinformation within theInternet.A programsB processesC applicationsD protocols22．There are many private networks,such as many corporate andgovernment networks, whosehosts cannot exchange messages with hosts outside of the private network. These private networks are often referred to as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) runningon its end systems to exchangedata with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionlessunreliable service and ()service.A flowcontrolB connection-oriented reliableC congestion controlD TCP25．It defines the format and theorder of messages exchangedbetween two or morecommunicating entities, as wellas the actions taken on thetransmission and/or receipt ofa message or other event. Thesentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol ( )A the format of messagesexchanged between two or morecommunicating entitiesB the order of messagesexchanged between two or morecommunicating entitiesC the actions taken on thetransmission of a message orother eventD the transmission signals aredigital signals or analogsignals27．In the following options, which is defined in protocol ( )A the actions taken on thetransmission and/or receiptof a message or other event B the objects exchanged between communicating entities C the content in the exchangedmessagesD the location of the hosts28．In the following options, whichdoes not belong to the network edge( )A end systemsB routersC clientsD servers29．In the following options, whichbelongs to the network core ( )A end systemsB routersC clientsD servers30．In the following options, whichis not the bundled with theInternet’sconnection-oriented service( )A reliable data transferB guarantee of thetransmission timeC flow controlD congestion-control31．An application can rely on theconnection to deliver all of itsdata without error and in theproper order. The sentencedescribes ( ). A flow controlB congestion-controlC reliable datatransferD connection-oriented service 32．It makes sure that neither sideof a connection overwhelms theother side by sending too manypackets too fast. The sentence describes ( ). A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internetfrom entering a state of gridlock. When a packet switchbecomes congested, its bufferscan overflow and packet loss canoccur. The sentence describes( ).A flowcontrolB congestion-controlC connection-oriented serviceD reliable data transfer 34．TheInternet ’sconnection-oriented service has aname, it is ( ).A TCPB UDPC TCP/IPD IP35．In the following options, which service does not be provided to an application by TCP( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet ’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP( )A SMTPB internet telephoneC FTPD HTTP38．In the following options, which does not use UDP( )A InternetphoneB video conferencingC streamingmultimediaD telnet39．There are two fundamentalapproaches to building a network core, ( ) and packet switching.A electrical current switchingB circuit switchingC data switchingD message switching40．In ( ) networks, the resourcesneeded along a path to provide for communication between the end system are reserved for theduration of the communicationsession.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’smessages use the resources ondemand, and as a consequence,may have to wait for access tocommunication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, foreach link used by the end-to-endconnection, the connection gets( ) of the link’s bandwidthfor the duration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rateof a circuit is equal to theframe rate multiplied by thenumber of bits in a slot.A CDMAB packet-switched networkC TDMD FDM44．( ) means that the switch mustreceive the entire packetbefore it can begin to transmitthe first bit of the packet ontothe outbound link.A Queuing delayB Store-and-forwardtransmissionC Packet lossD Propagation45．The network that forwardspackets according to host destination addresses is called( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwardspackets according tovirtual-circuit numbers iscalled ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, whichis not a kind of access network( )A residentialaccessB company accessC wirelessaccessD local access48．Suppose there is exactly onepacket switch between a sendinghost and a receiving host. The transmission rates between thesending host and the switch and between the switch and the receiving host are R 1 and R 2,respectively. Assuming that theswitch uses store-and-forwardpacket switching, what is thetotal end-to-end delay to senda packet of length L (Ignorequeuing delay, propagationdelay, and processing delay.) ( ) A L /R 1＋L /R 2B L /R 1C L /R 2D none of the above49．The time required to examine thepacket ’s header and determinewhere to direct the packet ispart of the ( ). A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagatefrom the beginning of the linkto the next router is ( ). A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of3000bits over a path of 5 links. Eachlink transmits at 1000bps. Queuingdelays, propagation delay and processing delay are negligible. (6 points)(1).Suppose the network is apacket-switched virtual circuitnetwork. VC setup time is seconds.Suppose the sending layers add atotal of 500 bits of header to eachpacket. How long does it take to sendthe file from source to destination(2).Suppose the network is a packet-switched datagram networkand a connectionless service is used.Now suppose each packet has 200 bitsof header. How long does it take tosend the file(3).Suppose that the network is acircuit-switched network. Furthersuppose that the transmission rate of the circuit between source anddestination is 200bps. Assumingsetup time and 200 bits of header appended to the packet, how longdoes it take to send the packetS olution:(1).t=5*(3000+500)/1000+=( 2).t=5*(3000+200)/1000=16s( 3).t=(3000+200)/200+=。
最新计算机网络英文题库(附答案)chapter1word版本
Chapter 1 Computer Networks and the Internet1．The ( ) is a worldwide computer network, that is, a network that interconnects millions of computing devices throughout the world.ppt3A public InternetB IntranetC switch netD television net2．Which kind of media is not a guided media? ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media? ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following option belongs to the circuit-switched networks? ( )A FDMB TDMC VC networksD both A and B6．( )makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagram networks and virtual-circuit networks differ in that ( ).A datagram networks are circuit-switched networks, andvirtual-circuit networks are packet-switched networks.B datagram networks are packet-switched networks, andvirtual-circuit networks are circuit-switched networks.C datagram networks use destination addresses and virtual-circuitnetworks use VC. numbers to forward packets toward theirdestination.D datagram networks use VC. numbers and virtual-circuit networksuse destination addresses to forward packets toward their destination. 9．In the following options, which one is not a guided media? ( )A twisted-pair wireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet’s headerB wait to transmit the packet onto the linkC determine where to direct the packetD check bit-error in the packet11．In the following four descriptions, which one is correct? ( )A The traffic intensity must be greater than 1.B The fraction of lost packets increases as the traffic intensitydecreases.C If the traffic intensity is close to zero, the average queuing delaywill be close to zero.D If the traffic intensity is close to one, the average queuing delaywill be close to one.12．The Internet’s network layer is responsible for moving network-layer packets known as ( ) from one host to another.A frameB datagramC segmentD message13．The protocols of various layers are called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes of packet-switched networks: ( ) networks and virtual-circuit networks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be loosely classified into three categories: residential access, company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue, R is the transmission rate, and all packets consist of L bits, then the traffic intensity is ( 16 ), and it should no greater than ( 17 ).16． A LR／aB La／RC Ra／LD LR／a17．A 2B 1C 0D -118．In the Internet, the equivalent concept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics20．End systems access to the Internet through its ( ).A modemsB protocolsC ISPD sockets21．End systems, packet switches, and other pieces of the Internet, run ( ) that control the sending and receiving of information within theInternet.A programsB processesC applicationsD protocols22．There are many private networks, such as many corporate and government networks, whose hosts cannot exchange messages withhosts outside of the private network. These private networks are often referred to as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) running on its end systems to exchange data with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionless unreliable service and () service.A flow controlB connection-oriented reliableC congestion controlD TCP25．It defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on thetransmission and/or receipt of a message or other event. The sentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol? ( )A the format of messages exchanged between two or morecommunicating entitiesB the order of messages exchanged between two or morecommunicating entitiesC the actions taken on the transmission of a message or other eventD the transmission signals are digital signals or analog signals 27．In the following options, which is defined in protocol? ( )A the actions taken on the transmission and/or receipt of a message orother eventB the objects exchanged between communicating entitiesC the content in the exchanged messagesD the location of the hosts28．In the following options, which does not belong to the network edge? ( )A end systemsB routersC clientsD servers29．In the following options, which belongs to the network core? ( )A end systemsB routersC clientsD servers30．In the following options, which is not the bundled with the Internet’s connection-oriented service? ( )A reliable data transferB guarantee of the transmission timeC flow controlD congestion-control31．An application can rely on the connection to deliver all of its data without error and in the proper order. The sentence describes ( ).A flow controlB congestion-controlC reliable data transferD connection-oriented service32．It makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast. The sentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internet from entering a state of gridlock. When a packet switch becomes congested, its buffers can overflow and packet loss can occur. The sentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer34．The Internet’s connection-oriented service has a name, it is ( ).A TCPB UDPC TCP/IPD IP35．In the following options, which service does not be provided to an application by TCP?( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP?( )A SMTPB internet telephoneC FTPD HTTP 38．In the following options, which does not use UDP?( )A Internet phoneB video conferencingC streaming multimediaD telnet39．There are two fundamental approaches to building a network core, ( ) and packet switching.A electrical current switchingB circuit switchingC data switchingD message switching40．In ( ) networks, the resources needed along a path to provide for communication between the end system are reserved for the duration of the communication session.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’s messages use the resources on demand, and as a consequence, may have to wait for access to communication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, for each link used by the end-to-end connection, the connection gets ( ) of thelink’s bandwidth for the duration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rate of a circuit is equal to the frame rate multiplied by the number of bits in a slot.A CDMAB packet-switched networkC TDMD FDM44．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Queuing delayB Store-and-forward transmissionC Packet lossD Propagation45．The network that forwards packets according to host destination addresses is called ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwards packets according to virtual-circuit numbers is called ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, which is not a kind of access network?( )A residential accessB company accessC wireless accessD local access48．Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R1 and R2,respectively. Assuming that the switch uses store-and-forward packetswitching, what is the total end-to-end delay to send a packet of length L? (Ignore queuing delay, propagation delay, and processing delay.)( )A L/R1＋L/R2B L/R1C L/R2D none of the above49．The time required to examine the packet’s header and determine where to direct the packet is part of the ( ).A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagate from the beginning of the link to the next router is ( ).A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of 3000bits over a path of 5 links. Each link transmits at 1000bps. Queuing delays, propagation delay and processing delay are negligible. (6 points)(1).Suppose the network is a packet-switched virtual circuit network. VC setup time is 0.1 seconds. Suppose the sending layers add a total of 500 bits of header to each packet. How long does it take to send the file from source to destination?(2).Suppose the network is a packet-switched datagram network and a connectionless service is used. Now suppose each packet has 200 bits of header. How long does it take to send the file?(3).Suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is 200bps. Assuming 0.02s setup time and 200 bits of header appended to the packet, how long does it take to send the packet?Solution: (1). t=5*(3000+500)/1 000+0.1=17.6s(2). t=5*(3000+200)/1 000=16s(3). t=(3000+200)/200+0.02=16.02s 相对压力一般指表压，是测量系统相对于大气压的压力值。
计算机网络英文题库(附答案)chapter1(推荐文档)
Chapter 1 Computer Networks and the Internet1．The ( ) is a worldwide computer network, that is, a network that interconnects millions of computing devices throughout the world.ppt3A public InternetB IntranetC switch netD television net2．Which kind of media is not a guided media? ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media? ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following option belongs to the circuit-switched networks? ( )A FDMB TDMC VC networksD both A and B6．( )makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagram networks and virtual-circuit networks differ in that ( ).A datagram networks are circuit-switched networks, andvirtual-circuit networks are packet-switched networks.B datagram networks are packet-switched networks, andvirtual-circuit networks are circuit-switched networks.C datagram networks use destination addresses and virtual-circuitnetworks use VC. numbers to forward packets toward theirdestination.D datagram networks use VC. numbers and virtual-circuit networksuse destination addresses to forward packets toward their destination. 9．In the following options, which one is not a guided media? ( )A twisted-pair wireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet’s headerB wait to transmit the packet onto the linkC determine where to direct the packetD check bit-error in the packet11．In the following four descriptions, which one is correct? ( )A The traffic intensity must be greater than 1.B The fraction of lost packets increases as the traffic intensitydecreases.C If the traffic intensity is close to zero, the average queuing delaywill be close to zero.D If the traffic intensity is close to one, the average queuing delaywill be close to one.12．The Internet’s network layer is responsible for moving network-layer packets known as ( ) from one host to another.A frameB datagramC segmentD message13．The protocols of various layers are called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes of packet-switched networks: ( ) networks and virtual-circuit networks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be loosely classified into three categories: residential access, company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue, R is the transmission rate, and all packets consist of L bits, then the traffic intensity is ( 16 ), and it should no greater than ( 17 ).16． A LR／aB La／RC Ra／LD LR／a17．A 2B 1C 0D -118．In the Internet, the equivalent concept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics20．End systems access to the Internet through its ( ).A modemsB protocolsC ISPD sockets21．End systems, packet switches, and other pieces of the Internet, run ( ) that control the sending and receiving of information within theInternet.A programsB processesC applicationsD protocols22．There are many private networks, such as many corporate and government networks, whose hosts cannot exchange messages withhosts outside of the private network. These private networks are often referred to as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) running on its end systems to exchange data with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionless unreliable service and () service.A flow controlB connection-oriented reliableC congestion controlD TCP25．It defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on thetransmission and/or receipt of a message or other event. The sentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol? ( )A the format of messages exchanged between two or morecommunicating entitiesB the order of messages exchanged between two or morecommunicating entitiesC the actions taken on the transmission of a message or other eventD the transmission signals are digital signals or analog signals 27．In the following options, which is defined in protocol? ( )A the actions taken on the transmission and/or receipt of a message orother eventB the objects exchanged between communicating entitiesC the content in the exchanged messagesD the location of the hosts28．In the following options, which does not belong to the network edge? ( )A end systemsB routersC clientsD servers29．In the following options, which belongs to the network core? ( )A end systemsB routersC clientsD servers30．In the following options, which is not the bundled with the Internet’s connection-oriented service? ( )A reliable data transferB guarantee of the transmission timeC flow controlD congestion-control31．An application can rely on the connection to deliver all of its data without error and in the proper order. The sentence describes ( ).A flow controlB congestion-controlC reliable data transferD connection-oriented service32．It makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast. The sentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internet from entering a state of gridlock. When a packet switch becomes congested, its buffers can overflow and packet loss can occur. The sentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer34．The Internet’s connection-oriented service has a name, it is ( ).A TCPB UDPC TCP/IPD IP35．In the following options, which service does not be provided to an application by TCP?( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP?( )A SMTPB internet telephoneC FTPD HTTP38．In the following options, which does not use UDP?( )A Internet phoneB video conferencingC streaming multimediaD telnet39．There are two fundamental approaches to building a network core, ( ) and packet switching.A electrical current switchingB circuit switchingC data switchingD message switching 40．In ( ) networks, the resources needed along a path to provide for communication between the end system are reserved for the duration of the communication session.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’s messages use the resources on demand, and as a consequence, may have to wait for access to communication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, for each link used by the end-to-end connection, the connection gets ( ) of thelink’s bandwidth for the duration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rate of a circuit is equal to the frame rate multiplied by the number of bits in a slot.A CDMAB packet-switched networkC TDMD FDM44．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Queuing delayB Store-and-forward transmissionC Packet lossD Propagation45．The network that forwards packets according to host destination addresses is called ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwards packets according to virtual-circuit numbers is called ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, which is not a kind of access network?( )A residential accessB company accessC wireless accessD local access48．Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R1 and R2,respectively. Assuming that the switch uses store-and-forward packetswitching, what is the total end-to-end delay to send a packet of length L? (Ignore queuing delay, propagation delay, and processing delay.)( )A L/R1＋L/R2B L/R1C L/R2D none of the above49．The time required to examine the packet’s header and determine where to direct the packet is part of the ( ).A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagate from the beginning of the link to the next router is ( ).A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of 3000bits over a path of 5 links. Each link transmits at 1000bps. Queuing delays, propagation delay and processing delay are negligible. (6 points)(1).Suppose the network is a packet-switched virtual circuit network. VC setup time is 0.1 seconds. Suppose the sending layers add a total of 500 bits of header to each packet. How long does it take to send the file from source to destination?(2).Suppose the network is a packet-switched datagram network and a connectionless service is used. Now suppose each packet has 200 bits of header. How long does it take to send the file?(3).Suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is 200bps. Assuming 0.02s setup time and 200 bits of header appended to the packet, how long does it take to send the packet?Solution: (1). t=5*(3000+500)/1 000+0.1=17.6s(2). t=5*(3000+200)/1 000=16s(3). t=(3000+200)/20 0+0.02=16.02s。
计算机网络英文题库附答案chapter定稿版
计算机网络英文题库附答案c h a p t e r精编W O R D版IBM system office room 【A0816H-A0912AAAHH-GX8Q8-GNTHHJ8】Chapter 1 Computer Networks and the Internet 1．The ( ) is a worldwide computer network, that is, a network that interconnects millions of computing devices throughout the world.ppt3A public InternetB IntranetC switch netD television net2．Which kind of media is not a guided media ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following option belongs to the circuit-switched networks ( )A FDMB TDMC VC networksD both A and B6．( )makes sure that neither side of aconnection overwhelms the other side bysending too many packets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagram networks and virtual-circuit networks differ in that ( ).A datagram networks are circuit-switchednetworks, and virtual-circuit networks arepacket-switched networks.B datagram networks are packet-switchednetworks, and virtual-circuit networks arecircuit-switched networks.C datagram networks use destinationaddresses and virtual-circuit networks useVC. numbers to forward packets towardtheir destination.D datagram networks use VC. numbersand virtual-circuit networks use destinationaddresses to forward packets toward theirdestination.9．In the following options, which one is not a guided media ( )A twisted-pair wireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet’s headerB wait to transmit the packet onto the linkC determine where to direct the packetD check bit-error in the packet11．In the following four descriptions, which one is correct ( )A The traffic intensity must be greaterthan 1.B The fraction of lost packets increases asthe traffic intensity decreases.C If the traffic intensity is close to zero,the average queuing delay will be close tozero.D If the traffic intensity is close to one, theaverage queuing delay will be close to one.12．The Internet’s network layer isresponsible for moving network-layerpackets known as ( ) from one host toanother.A frameB datagramC segmentD message13．The protocols of various layers are called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes of packet-switched networks: ( ) networks and virtual-circuitnetworks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be loosely classified into three categories: residential access,company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue, R is the transmission rate, and all packets consist of L bits, then the traffic intensity is ( 16 ), and it should no greater than ( 17 ).16．A LR／aB La／RC Ra／LD LR／a 17．A 2B 1C 0D -118．In the Internet, the equivalent concept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics20．End systems access to the Internet through its ( ).A modemsB protocolsC ISPD sockets21．End systems, packet switches, and other pieces of the Internet, run ( ) that controlthe sending and receiving of informationwithin the Internet.A programsB processesC applicationsD protocols22．There are many private networks, such as many corporate and government networks,whose hosts cannot exchange messageswith hosts outside of the private network.These private networks are often referredto as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) running on its end systems to exchange data with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionlessunreliable service and () service.A flow controlB connection-oriented reliableC congestion controlD TCP25．It defines the format and the order of messages exchanged between two or morecommunicating entities, as well as theactions taken on the transmission and/orreceipt of a message or other event. Thesentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol ( )A the format of messages exchangedbetween two or more communicatingentitiesB the order of messages exchangedbetween two or more communicatingentitiesC the actions taken on the transmission ofa message or other eventD the transmission signals are digitalsignals or analog signals27．In the following options, which is defined in protocol ( )A the actions taken on the transmissionand/or receipt of a message or othereventB the objects exchanged between communicating entitiesC the content in the exchanged messagesD the location of the hosts28．In the following options, which does not belong to the network edge ( )A end systemsB routersC clientsD servers29．In the following options, which belongs to the network core ( )A end systemsB routersC clientsD servers30．In the following options, which is not the bundled with the Internet’s connection-oriented service( )A reliable data transferB guarantee of the transmission timeC flow controlD congestion-control31．An application can rely on the connection to deliver all of its data without error andin the proper order. The sentencedescribes ( ).A flow controlB congestion-controlC reliable data transferD connection-oriented service32．It makes sure that neither side of aconnection overwhelms the other side bysending too many packets too fast. Thesentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internet from enteringa state of gridlock. When a packet switchbecomes congested, its buffers canoverflow and packet loss can occur. Thesentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer34．The Internet’s connection-oriented service has a name, it is ( ).A TCPB UDPC TCP/IPD IP 35．In the following options, which service does not be provided to an application by TCP( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP()A SMTPB internet telephoneC FTPD HTTP38．In the following options, which does not use UDP( )A Internet phoneB video conferencingC streaming multimediaD telnet39．There are two fundamental approaches to building a network core, ( ) and packetswitching.A electrical current switchingB circuit switchingC data switchingD message switching40．In ( ) networks, the resources needed along a path to provide forcommunication between the end systemare reserved for the duration of thecommunication session.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’s messages use theresources on demand, and as aconsequence, may have to wait for accessto communication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, for each link used by theend-to-end connection, the connectiongets ( ) of the link’s bandwidth for theduration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rate of a circuit is equal to the frame rate multiplied by thenumber of bits in a slot.A CDMAB packet-switched networkC TDMD FDM 44．( ) means that the switch must receive the entire packet before it can begin totransmit the first bit of the packet onto theoutbound link.A Queuing delayB Store-and-forward transmissionC Packet lossD Propagation45．The network that forwards packetsaccording to host destination addresses iscalled ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwards packetsaccording to virtual-circuit numbers iscalled ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, which is not a kind of access network()A residential accessB company accessC wireless accessD local access48．Suppose there is exactly one packet switch between a sending host and a receivinghost. The transmission rates between thesending host and the switch and betweenthe switch and the receiving host are R1and R2, respectively. Assuming that theswitch uses store-and-forward packetswitching, what is the total end-to-enddelay to send a packet of length L (Ignorequeuing delay, propagation delay, andprocessing delay.) ( )A L/R1＋L/R2B L/R1C L/R2D none of the above49．The time required to examine thepacket’s header and determine where todirect the packet is part of the ( ).A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagate from the beginning of the link to the next router is( ).A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of 3000bits over a path of 5 links. Each link transmits at 1000bps. Queuing delays, propagation delay and processing delay are negligible. (6 points) (1).Suppose the network is a packet-switched virtual circuit network. VC setup time is 0.1 seconds. Suppose the sending layers add a total of 500 bits of header to each packet. How long does it take to send the file from source to destination?(2).Suppose the network is a packet-switched datagram network and a connectionless serviceis used. Now suppose each packet has 200 bitsof header. How long does it take to send the file?(3).Suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between sourceand destination is 200bps. Assuming 0.02s setuptime and 200 bits of header appended to the packet, how long does it take to send the packet?So lution:(1).t=5*(3000+500)/1000+0.1=17.6s( 2).t=5*(3000+200)/1000=16s( 3).t=(3000+200)/200+0.02=16.02s。
计算机网络测试英语版
Network core does not include (D).A、routersB、packet switchesC、linksD、smart phonesEnd system does not include (A).© A、routerO B、smart phoneO C、PCsO D、Web serversThe original reason for the Internet to use packet switching is (A ).® A、Statistical multiplexing enables efficient sharing of expensive long-haul links. O B、Packet switching enables data to be routed faster than circuit switching.O C、It is less work for a router to process a packet than to process the data in a circuit.O D、Packet switching requires simpler hardware on the routers than circuit switching.Which of the following is not a performance in computer networks.(C)O A、delayO B、packet loss© C、packet sizeO D、end-to-end throughputBy which of the following access technology, bandwidth is not shared among the users?(D)O A、WFIFO B、HFC© C、ADSLO D、None of the aboveThe full text in English of FTTH is Fiber To The Home.The full text in English of ISP is ().The full text in English of TDM is ().答案：Internet Service Provider、Time-Division MultiplexingThere are two fundamental approaches to move data through a network of links and switches: circuit switching and (). And in a circuit-switched network, a circuit in a link is implemented with either () or TDM.答案：packet switching、frequency-division multiplexingDescribe the layers in the Internet protocol stack from top to down: application layer, () layer, () layer, () layer and physical layer.答案：transport、network、link应用层application、传输层transport、网络层network、链路层link.物理层physical OS I reference model have () layers.答案：7Packet switching allows more users to use network than circuit switching.（A）® A、trueO B、falseA host doesn't process network-layer in the Internet protocol stack.(B)O A、True© B、FalseThe full text in English of RFC is request for comments.(A)® A、TrueO B、FalseAll communication activity in Internet governed by protocols.(A)® A、TrueO B、FalsePacket switching is commonly used in traditional telephone networks(B)O A、True© B、FalseWhich of the following is not Internet application layer Protocol?(B)A、SMTPB、TCPC、FTPD、HTTPDNS runs on top of ( ) and uses the port number S5(A)A、UDPB、HTTPC、TCPD、none of the aboveFTP runs over (B).O A、UDP© B、TCPO c、HTTPO D、none of the abovewhich service of the following can be provided by TCP?(A)A、Reliable data transferB、ThroughputC、TimingD、SecurityWhich of the following is the default port number of TCP control connection in FTP?(B)O A、20© B、21Oc、25O D、80Which tool can capture network packets and display that packet data?(B)O A、Internet Explorer© B、WiresharkO c、AleZillaO D、FirefoxWhich of the following port number is the default port number of HTTP1(D)O A、23O B、21O C、20® D. 80The application of ( ) is loss-tolerant.(A)stored audio/videofile transferWeb documentstext messagingThe service of TCP is unreliable data transmission.(B)O A、True© B、FALSEStatus code 404 denotes that requested document does not exist on the server according the HTTP protocol.(A)© A、TrueO B、FALSELocal DNS name servers cache resource records, but discard them after a period of time.(A)© A、TrueO B、FALSEFor the Web application, the user agent is the user* s keyboard.(B)O A、True© B、FALSEThe Date: header in the HTTP response message indicates when the object in the response was last modified.(B)O A、True© B、FALSESuppose that host A wants to send data over TCP to host B, and host B wants to send data to host A over TCP. Two separate TCP connections -one for each direction - are needed.(B)O A、True© B、FALSEFor a P2P file-sharing application, There is no notion of client and server sides of a communication session.(B)O A、True© B、FALSEA user requests a Web page that consists of some text and three images. For this page, the client will send one request message and receive four response messages.(B)O A、True© B、FALSESocket programming with UDP, the server process must run before the client process.（B）O A、True© B、FALSEThe full text in English of HTTP is Hypertext Transfer Protocol.The full text in English of FTP is ().The full text in English of SMTP is ().The full text in English of IMAP is ().The full text in English of POP3 is ().The full text in English of DNS is ().答案：file transfer protocol、simple mail transfer protocol、Internet mail access protocol、post office protocol version 3 domain name systemThe UDP segment includes(A)checksumreceive windowsequence numberacknowledgement numberHow does an operating system identify the application to which data coming in from the network should be delivered?（B）A、By the protocol with which the data was sentB、By the port number carried by the transport protocolC、By IP address of the dataD、By the file extension of the dataThe service of TCP is ( D).A、connectionless transmissionB、unreliable data transmissionC、datagramD、reliable data transmissionConsider a TCP connection between Host A and Host B. Suppose that the TCP segments traveling from Host A to Host B have source portnumber xand destination port number y. So the source port numer is () and destination port number is ()for the segments traveling from Host B to Host A.答案：Y xIn TCP, the acknowledgement number that a host puts in a segment is the sequence number of the next byte the host is expecting from the sender.（A）® A、TrueO B、FalseSuppose that host A wants to send data over TCP to host B, and host B wants to send data to host A over TCP. Two separate TCP connections -one for each direction - are needed.(B)O A、True© B、FalseThe TCP segment has a field in its header for rwnd.(A)® A、TrueO B、FalseSuppose Host A is sending Host B a large file over a TCP connection. The number of unacknowledged bytes that A sends cannot exceed the size of the receive buffer.(A) ® A、TrueO B、FalseSuppose Host A is sending a large file to Host B over a TCP connection. If the sequence number for a segment of this connection is m, then the sequence number for the subsequent segment will necessarily be m + 1(B)O A、True© B、FalseSuppose Host A sends one segment with sequence number 38 and 4 bytes of data over a TCP connection to Host B. In this same segment the acknowledgment number is necessarily 42(B)O A、True© B、FalseThe size of the TCP rwnd never changes throughout the duration of the connection.(B)O A、True© B、FalseConsider congestion control in TCP. When the timer expires at the sender, the value of ssthresh is set to one half of its previous value.(B)O A、true© B、falseIn Internet, the two key network-layer functions are(A)A、Routing and forwardingB、Packet switching and circuit switchingC、Storing and forwardingD、Routing and packingTwo packets A and B are sent in the order A-B and will traverse a connectionless communication network. They will amve at the destination（C）in any order, after having traversed the same routein the order A-B, after possibly having traversed different routesin any order, after possibly having traversed different routesin the order A-B, after having traversed the same routeWhich layer in the Internet protocol stack doesn t a router process?(A)the transport layerthe network layerthe link layerthe physical layerHow many IP addresses does a router have?D12D、one address for each interfaceWhat is the 32-bit binary equivalent of the IP address 223.1.3.27?(D)A、11101111.00000001.00000011.00011011B、11101111.00000001.00000011.00011010C、11011111.00000001.00000011.00011010D、11011111.00000001.00000011.00011011In CIDR notation, which of the following IP and host 192.168.14.2 belong to the same subnet?(A)A、192.168.11.0/21B、192.168.10.0/22C、192.168.12.0/23D、192.168.13.0/24Consider sending a 999 byte datagram into a link that has an MTU of 500 bytes,(C)O A、2 fragments are created with offset field value 0, 500, respectivelyOB、3 fragments are created with offset field value 0,430,960, respectively© Cx 3 fragments are created with offset field value 0, 60,120, respectivelyO D、None of the aboveWhat is the name ofa network-layer packet?(C)A、messageB、segmentC、datagramD、frameIn CIDR notation, the host 192.168.11.0/21 and the host 192.168.14.2/21 belong to the same subnet（A）® A、TrueO B、FalseIP (Internet Protocol) can guaranteed delivery.（B）O A、True© B、FalseThe routers in both datagram networks and virtual-circuit networks use forwarding tables.（A）® A、trueO B、falseNetwork core does not include (D).O A、routersO B、packet switchesO C、links® D、smart phonesWhich tool can capture network packets and display that packet data?(B)A、Internet ExplorerB、WiresharkC、AleZillaD、FirefoxWhich of the following is Internet link-layer protocol?(B)A、RIPB、PPPC、OSPFD、BGPwhich of the following is not a class of multiple access protocol?(D)A、channel partitioningB、random accessC、taking turnsD、flow controlThe function of CRC is (B).A、framingB、error detectionC、reliable delivery between adjacent nodesD、flow controlWhat is the name of a hnk-layer packet?(D)A、messageB、segmentC、datagramD、frameThe mask of a subnet is 255.255.255.248. So the subnet at most can connect ( ) hosts.A、8B、6C、248D、246which of the followingis not a multiple access protocol?(D)A、TDMAB、ALOHAC、CSMAD、NATWhich of the following is a correct subnet mask?(A)© A、255.255.224.0O B、254.255.224.0O C、255.255.226.0O D、255.255.256.0Which of the following is used by the switch to forward frames?(B)A、IP addressB、MAC addressc、portD、socketWhich of the following is the protocol which is the most widely used for wired LAN at present?(A)A、802.3B、802.4c、802.5D、802.11Which of the following MAC addresses is correct?(D)A、00-45-6B-3A-34-2HB、192.168.1.55C、65-10-96-58-16DD、00-06-5B-4F-45-BAWhich size of frames are treated as invalid frames?(A)© A、frames smaller than 64O B、frames smaller than 128O C、frames smaller than 100O D、frames smaller than 512Which of the following is the decimal for the IP address 11000000 00110100 00000000 00001111?(D)O A、192.52.0.16O B、192.51.0.15O C、128.52.0.15© D、192.52.0.15MAC broadcast address is (C).0 A、FF-FF-FF-FF-FF-000 B、255.255.255.255® C、FF-FF-FF-FF-FF-FFO D、255.255.255.0What is stored in the ARP table of the Internet host?(D)A、IP addressesB、MAC addresssesC、the mapping of domain names to IP addresssesD、the mapping of IP addresses to MAC addresssesSuppose the information content of a packet is the bit pattern 0111000110101011 and an even parity scheme is being used. What would thevalue of the parity bit?()答案：1The two most important network-layer functions in a datagram networkis_________________and _______________参考答案：forwarding、routingThe full text in English of FTTH is Fiber To The Home.The full text in English of CDMA is ( ).考生答案：code division multiple accessThe full text in English of FTTH is Fiber To The Home.The full text in English of TDMA is ( ).考生答案：time division multiple accessThe full text in English of FTTH is Fiber To The Home.The full text in English of CSMA is ( ).考生答案：Carrier Sense Multiple AccessThe full text in English of FTTH is Fiber To The Home.The full text in English of ARP is ( ).考生答案：Address Resolution ProtocolThe full text in English of FTTH is Fiber To The Home.The full text in English of VLAN is ( ).考生答案：Virtual Local Area NetworksTwo kinds of communication devices commonly used in computer networksare_______________and_______考生答案：switch、routerIf all the links in the Internet were to provide reliable delivery service, the TCP reliable delivery service would be redundant.(B)A、TrueB、B、FalseThe frame structures for 10BASE-T, 100BASE-T, and Gigabit Ethernet are all same.(A)A、TrueB、FalseWhen a conflict occurs in the LAN, the hosts that encounter the collision wait for the same time to resend.(B)A、TrueB、FalseThe MAC(Media Access Control) address is the hardware address, expressed as a48-bit binary number.(A)A、TrueB、FalseA router is an interconnection device that belongs to the data link layer.(B)A、TrueB、False。
计算机网络英文题库附答案chapter3解析
计算机网络英文题库（附答案）chapter3解析-CAL-FENGHAI.-(YICAI)-Company One 1Chapter 3 Transport Layer1.A transport-layer protocol provides for logical communication between ____________・A Application processesB HostsC RoutersD End systems2.Tran sport-layer protocols run in _______ ・A ServersB ClientsC RoutersD End systems3.In transport layer, the send side breaks application messages into ___________ , passes to network layer.A FramesB SegmentsC Data-gramsD bit streams4.Services provided by transport layer inelude _________ ・A HTTP and FTPB TCP and IPC TCP and UDPD SMTP5.Which of the following services is not provided by TCPA Delay guarantees and bandwidth guaranteesB Reliable data transfers and flow controlsC Congestion controlsD In-order data transfers6.These two minimal transport-layer services——_______ and ______ ——are the only two services that UDP provides!A process-to-process data delivery, error checkingB congestion control, reliable data transferC flow control, congestion controlD In-order data transfer, error checking7.Port number's scope is _______ t o _______ ・A 0, 1023B 0. 65535C 0, 127D 0,2558.The port numbers ranging from _______ t o _____ are called well-known port numberand are restricted・A 0,1023B 0, 65535C 0, 127D 0,2559.UDP socket identified by two components, they are _________ ・A source IP addresses and source port numbersB source IP addresses and destination IP addressesC destination IP address and destination port numbersD destination port numbers and source port numbers10.TCP socket identified by a (an) _________ ・A 1-tupleB 2-tupleC 3-tupleD 4-tuple11.Which of the following applications normally uses UDP servicesA SMTPB Streaming multimediaC FTPD HTTP12.Reliable data transfer protocol over a perfectly reliable channel is __________ ・A rdt 1.0B rdt2.0C rdt3.0D rdt2.113.Reliable data transfer protocol over a channel with bit errors and packet losses isA rdt 1.0B rdt2.0C rdt3.0D rdt2.114.Which of Hie following about reliable data transfer over a channel with bit errors i s not correct?A RDT2.0: assuming ACK and NAK will not be corniptedB RDT2.1: assuming ACK and NAK can be corruptedC RDT2.2: only use ACK-sD RDT2.2: use both ACK-s and NAK-s15.Which of the following protocols is not pipelining protocols?A TCPB rdt3.0C GO-BACK-ND selective repeat16.Which of the following is not correct about GBN protocol?A Only using ACK-sB Using cumulative ACK-sC Receiver discards all out-of-order packetsD It is not pipelined protocol17.Which of the following is not correct about SR protocol?A receiver individually acknowledges all correctly received packetsB sender only resends packets for which ACK not receivedC It limits sequence number of sent but un-ACK-ed packetsD It is not a pipelined protocol18.Which of the following about TCP connection is not correctA It is a broadcast connectionB It is a point-to-point connectionC It is a pipelined connectionD It is a full duplex connection19.The SYN segment is used for ______ ・A TCP connection setupB TCP flow controlC TCP congestion controlD Closing a TCP connection20.The FIN segment is used for _______ ・A TCP connection setupB TCP flow controlC TCP congestion controlD Closing a TCP conn ection21 ・ How does TCP sender perceive congestionA Through a timeout eventB Through a receiving duplicate ACK-s eventC Both A and BD Either A or B22.Extending host-to-host delivery to process-to-process delivery is called transportlayerand _.A multiplexing and de-multiplexingB storing and forwardingC forwarding and filteringD switching and routing23.UDP is a ______ sendee while TCP is a connection-oriented service・A ConnectionlessB ReliableC Connection-orientedD In-order24.The UDP header has only four fields, they are _________ ・A Source port numbei; 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 number25.There are two 16七it integers: 1110 0110 0110 0110, 1101 0101 0101 0101. Their checksum is _______ ・A 0100010001000011B 1011101110111100C 1111111111111111D 100000000000000026.The maximum amount of data that can be grabbed and placed in a segment is limited by the _____ ・A Maximum segment size (MSS)B MTUC ChecksumD Sequence number27.The MSS is typically set by first determining the length of the largest linklayer frame that can be sent by the local sending host——the so-called ____________________ ・A Maximum transmission unit (MTU)B MSSC ChecksumD Sequence number2& A File size of 500,000bytes5 MSS equals lOOObytes. When we want to transmit this file with TCP, the sequence number of the first segment is 0, and the sequence number of the second segment is _______________________ ・A 1000B 999C 1001D 50000029.Because TCP only acknowledges bytes up to the first missing byte in thestream, TCP is said to provide _______ ・A Cumulative acknowledgementsB Selective acknowledgementsC 3 duplicate ACKsD positive ACKs30.Provided a=0・125, current value of Estimated-RTT is 0.4s, Saniple-RTT is 0.8s,then the new value of Estimated-RTT is __________ s.A 0.45B 0.6C 0.7D 0.831.Provided RcvBuffer=20,LastByteRcvd=20,LastByteRead= 15, thenRev Window 二・A 14B 15C 16D 1032.TCP service does not provide _______ ・A Reliable data transferB Flow controlC Delay guaranteeD Congestion control33.There are two states in TCP congestion control, which are __________ ・A slow start and congestion avoidanceB safe start and congestion avoidanceC slow start and congestion abandonD safe start and congestion abandon34.The transport-layer protocol provides logical communication between __________ , and the network-layer protocol provides logical communication __________ ・A hosts, processesB processes, hostsC threads, processesD processes, threads35.To implement the multicast services the Internet employs the _________ protocol.A FTPB TCPC IGMPD UDP36.If an application developer chooses ________ protocol, then the application process is almost directly talking with IP.A HTTPB RIPC CSMA/CDD UDP37. ____ maintains connection-state in the end systems. This connection stateincludes receive and send buffers, congestion-control parameters, and sequence and acknowledgment number parameters・A UDPB TCPC DNSD HTTP38.The host that initiates the session in the Internet is labeled as__________ .A serverB user agentC clientD router39.With TCP there is no _________ b etween sending and receiving transport-layer entities ・A flow controlB handshakingC・ congestion control D VC setup40.Tlie Internet's ______ s ervice helps prevent the Inteniet fi*om entering a state of gridlock ・A datagramB congestion controlC sliding windowD timeout event41 ・ Connection setup at the transport layer involves _______ ・A serverB only the two end systemsC clientD router42. A _____ layer protocol provides for logical communication between applications.A transportB applicationC networkingD MAC43.In static congestion window, if it satisfies W*S/R > RTT + S/R, the Latency isA W*S/R-( RTT+ S/R)B 2RTT + O/RC 2RTT + O/R + (k-1 )[W* S/R- (RTT + S/R)]D 2RTT + S/R44.The receive side of transport layer reassembles segments into messages, passes to l ayer.A ApplicationB NetworkingC PhysicalD MAC45.In the following four options, which one is correct?A The variations in the SampIeRTT are smoothed out in the computation of the Esti mated RTTB The timeout should be less than the connection's RTTC Suppose that the last SampIeRTT in a TCP connection is equal to 1 sec. Then the current value of Timeoutinterval will necessarily be>l secD Suppose that the last SampIeRTT in a TCP connection is equal to 1 sec. Then the current value of Timeoutinterval will necessarily be<l sec46.The port number used by HTTP is ________ .A 80B 25C 110D 5347.The port number used by SMTP is ________ .A 80B 25C 110D 534& The port number used by pop3 is _________A 80B 25C 110D 5349.The port number used by DNS is _________A 80B 25C 110D 5350.The port number used by FTP is ________ .A 20 and 21B 20C 21D 5351. A UDP socket identified by a ________ tuple(s).A 2B 4C 1D 352. A TCP socket identified by a _________ tuple(s).A 2B 4C 1D 353. A TCP socket does not include ______ .A Source MAC addressB Source port numberC Destination IP addressD Destination port number54.Which of following about UDP is not correct.A It is a reliable data transfer protocolB It is connectionlessC no handshaking between UDP sender, receiverD it is a best effort service protocol55.DNS uses ______ service・A TCPB UDPC Both TCP and UDPD None of above56.Which of following about UDP is correctA Finer application-level control over what data is sent, and whenB No connection establishment (which can add delay), so no delay for establish a connectionC No connection state (so, UDP can typically support many active clients)D Large packet header overhead (16・B)57.Streaming media uses a ______ service normally・A TCPB UDPC Both TCP and UDPD None of above58.The UDP header has only ________fields.A 2B 4C 1D 359.Which of the following does not included in UDP header.A Source port numberB Destination port numberC ChecksumD Sequence number60.Which of Hie following is not a pipelining protocol.A Rdtl.OB Go-Back-NC Selective repeatD TCP61.In the following four descriptions about MSS and MTU, which one is not correctA The MSS is the maximum amount of application-layer data in the segmentB The MSS is the maximum size of the TCP segment including headersC The MSS is typically set by MTUD The MTU means the largest link-layer frame62.The job of gathering data chunks, encapsulating each data chunk with header information to create segments and passing Hie segments to the network is called___________A multiplexingB de-multiplexingC forwardingD routing63.In the following four descriptions about the relationship between the transport layer and the network layer, which one is not correctA The transport-layer protocol provides logical communication between hostsB The transport-layer protocol provides logical communication between processesC The services that a transport-layer protocol can provide are often constrained by the service model of the network-layer protocolD A computer network may make available multiple transport protocols64.Suppose the following three 8-bit bytes: 01010101, 01110000, 01001100. Whaf s the Is complement of the sum of these 8-bit bytesA 00010001B 11101101C 00010010D 1000100065.The following four descriptions about multiplexing and de-multiplexing, which one is correctA A UDP socket is identified by a two-tuples consisting of a source port number and a destination port number・B If two UDP segment have different source port number, they may be directed to the same destination process・C If two TCP segments with different source port number, they may be directed to the same destination process・D If two TCP segments with same destination IP address and destination port number, they must be the same TCP connection・66.UDP and TCP both have the fields except _________ ・A source port numberB destination port numberC checksumD receive window67.If we define N to be the window size, base to be the sequence number of theoldest 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 can be sent immediatelyB have already been transmitted and acknowledgedC cannot be usedD have been sent but not yet acknowledged68.Which of the following about TCP is not correctA It is a connectionless protocolB Point-to-point protocolC Reliable, in-order byte steam protocolD Pipelined protocol69.Which of the following about TCP is not correctA It is a connectionless protocolB full duplex data transfer protocolC connection-oriented protocolD flow controlled protocol70.The maximum amount of data that can be grabbed and placed in a segment is limited by the ______ ・A Maximum segment size (MSS)B MTUC Sequence numberD Check sum71.The MSS is typically set by first determining the length of the largest link-layer frame that can be sent by the local sending host (the so-called _________ ), and then will fit into a single link-layer frame・A Maximum segment size (MSS)B MTUC Sequence numberD Check sum72.The MSS is the maximum amount of _________ l ayer data in the segment, not the maximum size of the TCP segment including headers・A ApplicationB TransportC NetworkingD Link73.Which of the following field is not used for connection setup and teardownA Sequence numberB TSTC SYND FIN74. ____ is the byte stream number of first byte in the segment・A Sequence numberB ACK numberC ChecksumD port number75. ____ is the byte sequence numbers of next byte expected from odier side・A Sequence numberB ACK numberC ChecksumD port number76.Because TCP only acknowledges bytes up to the first missing byte in the stream, TCP is said to provide ________ acknowledgements・A CumulativeB SelectiveC SingleD Negative77.Fast retransmit means in the case that _______ duplicate ACK-s are received, the TCP sender resend segment before timer expires・A 3B 4C 5D 67& TCP ______ means sender won't ov©rflow receivei^s buffer by transmitting too much, too fast.A Flow controlB Congestion controlC Reliable data transferD Connection-oriented service79.TCP provides flow control by having the sender maintain a variable called theA Receive windowB Congestion windowC Sliding windowD buffer80.How does TCP sender perceive congestionA TimeoutB 3 duplicate ACK-sC Both A and BD None of above81 ・ Transport protocols run in ______・A ServersB ClientsC RoutersD End systems82.Which of the following services is not provided by TCPA Delay guarantees and bandwidth guaranteesB Reliable data transfers and flow controlsC Congestion controlsD In-order data transfers83.Which service does UDP not provideA multiplexingB de-multiplexingC error-detectionD error-correction84.There are three major events related to data transmission and retransmission in the TCP sender, which one is not in it?A data received from application aboveB de-nmltiplexing segmentC timer timeoutD ACK receipt85.Which of the following applications normally uses UDP services?A SMTPB Streaming multimediaC FTPD HTTP86.Which of the following about TCP connection is not correct?A It is a broadcast connectionB It is a point-to-point connectionC It is a pipelined connectionD It is a full duplex connection87.The SYN segment is used for _______ ・A TCP connection setupB TCP flow controlC TCP congestion controlD Closing a TCP connection8& Which service helps prevent the internet from entering a state of gridlockA reliable data transferB flow controlC congestion controlD handshaking procedure89.Tlie Internet's ________ is responsible fbr moving packets from one host to another.A application layerB transport layerC network layerD link layer90.In the following applications, which one is a bandwidth-sensitive application?A E-mailB web applicationC real-time audioD file transfer91.In the following applications, which one uses UDP?A E-mailB web applicationC file transferD DNS92.In the following four descriptions, which one is correct?A If one host's transport layer uses TCP, then its network layer must use \-iitiial- circuit network・B Datagram network provides connection serviceC The transport-layer connection service is implemented in the routerD The network-layer connection service is implemented in the router as well as in the end system.93.____ is a speeding-matching service一-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 control94.In the following four descriptions about Rev-Window, which one is correct?A The size of the TCP RcvWindow never changes throughout the duration of the connectionB The size of the TCP RcvWindow will change with the size of the TCP RcvBufferC The size of the TCP RcvWindow must be less than or equal to the size of the TCP RcvBufferD Suppose host A sends a file to host B over a TCP connection, the number of unacknowledged bytes that A sends cannot exceed the size of the size of the RcvWindow. 95.There are 6 flag fields. Which one is to indicate that the receiver should pass the data to the upper layer immediately?A PSHB URGC ACKD RST96.Suppose the TCP receiver receives the segment that partially or completely fills ingap in received data, it will ________ .A immediately send ACKB immediately send duplicate ACKC wait some time for arrival of another in-order segmentD send single cumulative97. _____ imposes constrain on the rate at which a TCP sender can send traffic intothe network・A sliding windowB congestion windowC receive windowD variable window98.Flow control and congestion control are same at that they all limit the rate of the sender, but differ in that _______ ・A flow control limits its rate by the size of RcvWindow, but congestion control by the traffic on the linkB congestion control limits its rate by the size of RcvWindow, but flow control by the traffic on the linkC flow control mainly is accomplished by the sender, but congestion control by the receiver.D flow control mainly is accomplished by the receiver, but congestion control by the link.99.This job of delivering the data in a transport-layer segment to the correct socket is called ______ ・A multiplexingB de-muitiplexingC forwardingD routing100.If we define N to be the window size, base to be the sequence number of theoldest unacknowledged packet, and next-seq-num to be the smallest unused sequence number, then the interval [base, nextseqnunvl] corresponds to packet 什lat ____________ ・A can be sent immediatelyB have already been transmitted and acknowledgedC cannot be usedD have been sent but not yet acknowledged101.____ are the two types of transport services that the Internet provides to the applications.A TCP and UDPB connection-oriented and connectionless serviceC TCP and IPD reliable data transfer and flow control102.In the following descriptions about persistent connection, which one is not correct?A The server leaves the TCP connection open after sending a responseB Each TCP connection is closed after the server sending one objectC There are two versions of persistent connection: without pipelining and with pipeliningD The default mode of HTTP uses persistent connection with pipelining103.The field of Length in UDP segment specifies the length of __________ ・A the UDP segment, not including the headerB the UDP segment, including the headerC the UDP seginenf s headerD the Length field104.In TCP segment header, which field can implement the reliable data transfer?A source port number and destination port numberB sequence nuniber and ACK numberC urgent data pointerD Receive window105.In the following four descriptions about TCP connection management, which one is not correct?A 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 1106.Suppose host A sends two TCP segments back to back to host B over a TCP connection. The first segment has sequence number 42, and the second has sequence number 110. If the l sl is lost and 2nd arrives at host B. What will be the acknowledgment number?A 43 C 109B ACK42 D ACK110Choices:1 〜5 ADBCA 6-10 ABACD11〜15 BACDB16〜20 DDAAD 21~25DAAAA 26 〜30 AAAAA31 〜35 BCABC 36-40DBCDB 41V5 BACAA46 〜50 AB CD A 51 〜55ABAAB 5640 DBBDA6145 BAABB 66 〜DAAAA 71-75 BAAAB76-80 AAAAC 81 〜85DADBB 86®AACCC91 〜95 DDBCB 95 〜CBABD 101-106 ABABDB1.Consider sending an object of size 0=500,OOObytes from server to client. Let S=500bytes and RTT=0.2s. Suppose the transport protocol uses static windows with window size 5. For a transmission rate of 100Kbps, determine the latency for sending the whole object. Recall the number of windows K=O/ WS), and there is K-l stalled state (that is idle time gaps).1- SolutionK=0/'(\VS)=500*8* 1000/(5 * 5 000*8)=200Latency=2RTT+ORKK-l )(S,R+RTT-WS‘R)=0.4+500*1000*8'100000+(200-1>(5 00*8/100000+02-5*500*8/1000QQ)=48.36s2.Consider the following plot of TCP congestion window size as a function of time.Fill in the blanks as follow:a) The initial value of Threshold at the first transmission round is ____________ b) The value of Threshold at the 11st transmission round is __________ ・ c) The value of Threshold at the 21st transmission round is __________ ・ d) After the 9th transmission round, segment loss detected by __________ ・(A) Timeout(B) Triple duplicate ACKe) After the 19lh transmission round, segment loss detected by _________ ・(A) Timeout(B) Triple duplicate ACKf) During_______ t ransmission round, the 18lh segment is sent ・2. Solutiona) 12 b) Sc) 7d)Ae)Bf)53. Consider the TCP reliable data transfer in the given graph ・ If in Segment l ，s Sequence number =10,data=u AC'\ please fill in the following blanks ・ a) In Segment 2, ACK number 二 ：b) In Segment 3, Sequence number =_______ ; data=u 0123456789^c) If there are some bits corrupted in segment 3 when it arrives Host B, then the ACKnumber in Segment 5 is : and the ACK number in Segment 6 is ,Transmission roundb n 8congestion、f4. The client A wants to request a Web page from Server B ・ Suppose the URL of the page is 172.16.0.200/experiment, and also it wants to receive French version of object. The time-sequence diagram is shown below, please fill in the blanks ・Packet® to Packet③ are TCP connection's segment, then: Packet ①：SYN flag bit 二 aACK flag bit=_b Sequence number= 92 Packet ®: SYN flag bit=l3. Solution:a) 12b)12 c) 12; 22ACK flag bit=_cSequence number= 100 Packet ®: SYN flag bit=_dACK flag bit=l Sequence number= e 4. Solution:a)l b)0 c)l d)0 e)935・ Consider sending an object of size 0=100 Kbytes from server to client. Let S=536 bytes and RTT= 100msec ・ Suppose the transport protocol uses static windows with window size W ・(1) For a transmission rate of 25 kbps, determine the minimum possible latency. Determine the minimum window size that achieves this latency. (2) Repeat (1) for 100 kbps. 5. Solution:(1) Latency=2RTT + OR =2*0.1+100*8/25= 0.2+32=32.2 (s)W* S R > S.R+RTT —- W>L6= so W=2 (2)Latency =2RTT+ O,R=2«0.1+100*8/'100=0.2+8=82 (s) W* S,R> SR+RTT —-W3.3, so W=46. Consider the following plot of TCP congestion window size as a function of time. Please fill in the blanks as below.Aa) The initial value of Threshold at the first transmission round is b) The value of Threshold at die 11th transmission round is ___________ ・ c) The value of Threshold at the 21st transmission round is・congestion window﹃4︱TITIT丄|︱rlrL ︱lrlrL ︱︱LILILIklklrlrlrL ︱IL ︱﹂︱﹂︱ J.IJ.1/Transmission roundd)After the 9th transmission round, _________e)After the 19th transmission round, ________6. Solution:a) 12 b) 8 c) 7 d) timeouttriple ACK occurs・ are detected.e) 321。
计算机网络英文题库(附答案)chapte4
计算机网络英文题库(附答案) chapter 41. What is the purpose of the Network Layer in the OSI Model?The Network Layer, also known as the fourth layer in the OSI Model, is responsible for the logical addressing and routing of data packets between different networks. Its purpose is to enable the transfer of data between devices that may be located on different networks.2. What are the main functions of the Network Layer?The Network Layer performs the following main functions:•Logical Addressing: The Network Layer assigns logical addresses to devices, allowing them to be uniquelyidentified on a network. This is done using protocols suchas IP (Internet Protocol).•Routing: The Network Layer determines the optimal path for data packets to be transmitted from thesource to the destination. It uses routing algorithms andprotocols to make routing decisions and manage networktraffic.•Packet Switching: The Network Layer breaks data into smaller packets and adds control information to eachpacket. These packets are then transmitted independently over the network and reassembled at the destination.•Congestion Control: The Network Layer is responsible for managing network congestion andpreventing network resources from becomingoverwhelmed. It uses techniques such as traffic shapingand packet prioritization to ensure efficient and reliabledata transmission.•Network Interoperability: The Network Layer enables different types of networks to interconnect andcommunicate with each other. It provides mechanisms to facilitate the exchange of data between networks withdifferent protocols and technologies.3. What is IP addressing?IP addressing refers to the assignment and use of unique logical addresses, called IP addresses, to devices connected to an IP network. IP addresses are used by the Network Layer to identify and locate devices on a network.An IP address is a 32-bit binary number, typically represented in a dotted decimal notation (e.g., 192.168.0.1). It consists of two parts: the network part and the host part. The network part identifies the specific network to which the device is connected, while the host part identifies the individual device on that network.There are two types of IP addresses: IPv4 (32-bit) and IPv6 (128-bit). IPv4 is the most widely used addressing scheme and provides approximately 4.3 billion unique addresses. IPv6 is the next generation IP addressing scheme, designed to address the limitations of IPv4 and provide a significantly larger address space.4. What is routing? How does it work?Routing is the process of determining the optimal path for data packets to be transmitted from the source to the destination across a network. It is a key function of the Network Layer.When a device wants to send data to a destination device, it determines the destina tion’s IP address. It then consults its routing table, which contains information about the network topology and available paths. The routing table helps the device identify the next hop, which is the next device that will receive the data packet and forward it towards the destination.The routing table is populated through various methods, such as static routing (manually configured routes) and dynamic routing (automatically updated routes based on routing protocols). Routing protocols, such as RIP (Routing Information Protocol) and OSPF (Open Shortest Path First), are used to exchange information between routers and ensure accurate routing decisions.Routers use routing algorithms and metrics to calculate the best path for data packets. These algorithms consider factors such as the number of hops, link speeds, and network congestion to determine the most efficient route. Once the next hop is determined, the data packet is forwarded to that device, and the process is repeated until the packet reaches its destination.5. What is packet switching? How does it differ from circuit switching?Packet switching is a method of data transmission in which data is divided into smaller packets and transmitted independently over a network. It is the primary mode of transmission used in modern computer networks, including the Internet.In packet switching, data is broken into packets, each containing a portion of the original data and control information. Each packet is then labeled with the source and destination IP addresses. These packets are transmitted individually over the network and can take different paths to reach the destination. At the destination, the packets are reassembled to reconstruct the original data.Packet switching differs from circuit switching, which was commonly used in traditional telephone networks. In circuit switching, a dedicated communication path, known as a circuit, is established between the source and destination for the duration of the communication session. The entire message is transmitted along this dedicated circuit, without being divided into smaller units. This approach requires the reservation of network resources for the entire duration of the communication, even if no data is being transmitted.Packet switching offers several advantages over circuit switching, including better resource utilization, improved network efficiency, and the ability to handle variable network conditions. It allows multiple devices to share the same network resources and adapt to changing traffic patterns. Additionally, packet switching enables the transmission ofdiverse data types, such as voice, video, and text, over the same network.ConclusionThe Network Layer plays a crucial role in computer networks by facilitating the logical addressing, routing, and interconnectivity of devices across networks. It provides essential functions such as IP addressing, routing, packet switching, congestion control, and network interoperability. Understanding the concepts and principles of the Network Layer is vital for effective network design, management, and troubleshooting.This chapter has covered the purpose of the Network Layer, its main functions, IP addressing, routing, and packet switching. By grasping these concepts, you are now well-equipped to navigate the complexities of computer networks and ensure efficient data transmission.Keep learning and exploring the fascinating world of computer networking!。