东北大学计算机网络B卷(附答案).pdf

本试卷 共 4 页第 1 页 东 北 大 学 考 试 试 卷 B卷 2009 2010学年第 一 学期 课程名称 计算机网络 Computer Networks 总分一二三四五 学院 班级 学号 姓名 密 封 线 Multiple Choice 20 points 1 point for each Directions Choose the correct answer for each question and fill it in the corresponding blank There is ONLY ONE correct answer for each question 1 There are two kinds of coaxial cables usually used One is the baseband cable and the other is the broadband cable The impedance of the broadband cable is A 50 B 70 C 75 D 90 2 According to the ISO OSI reference model the router works on A Data link layerB Network layerC Transport layerD Presentation layer 3 Which device extends the LAN on data link layer A RepeaterB HubC SwitchD Router 4 The communication which can transmit data bi directionally 双向 on the same channel at the same time is called A simplexB half duplexC full duplexD none of the above 5 10Base5 network takes A thick coaxial cable star topologyB thick coaxial cable bus topology C thin coaxial cable star topologyD thin coaxial cable bus topology 6 When two computers communicate via a LAN which of the following device is necessary A network adapter B MODEMC repeaterD coaxial cable 7 If a package is to be broadcasted to the local network then the destination IP address of the package should be A 255 255 255 255B 0 0 0 0 C the lowest address of the subnetD the highest address of the subnet 8 What many bytes are there in the payload of an ATM cell A 48B 53C 64D 36 9 The core of the Internet protocols is A IPX SPXB PPPC TCP IPD SLIP 10 With respect to protocol layer the RARP protocol in TCP IP corresponds to A physical layerB data link layerC network layerD transport layer 11 The lower layer of RIP protocol uses A UDPB TCPC ARPD IP 12 Which port on sever does the SMTP protocol use A 20B 23C 25D 110 13 What is the mask for a smallest subnet usable in practice A 255 255 255 0B 255 255 255 254C 255 255 255 252D 255 255 255 255 14 Which of the following is true of the IP address 198 0 0 10 using default mask A The netid is 198 B The hostid is 0 10 C The network address is 198 0 0 0D The hostid is 0 0 10 15 When connecting computers via twisted pairs the interface standard we take is A X 25B RJ11C RS232D RJ45 16 Which of the following is true about IP routing A The destination IP address changes at each hop B The source IP address changes at each hop C The frame does not change at each hop D The frame changes at each hop 17 Which of the following ranges is considered as well known port number A 1 1023B 1024 and aboveC 1 256D 1 65534 18 Which of the following services is used to translate a web address URL into an IP address A DNSB HTTPC DHCPD Telnet 19 The Internet can be traced back to its origin A ARPANETB ALOHAC NEFNETD Ethernet 20 Which of the following IPv6 addresses is correct A 2001 8 417AB 12 20 3 3 0 0 0 0 0 FFFF C 145 20 15 29D 145 20 15 29 本试卷 共 4 页第 2 页 学院 班级 学号 姓名 密 封 线 1 The length of an IPv4 header is 40 bytes 2 The ISO OSI protocol consists of 7 how many layers 3 ping 127 0 0 1 command will test the internal loopback of a computer fill the complete command 4 65534 how many usable subnets are created by applying the subnet mask 255 255 255 0 to a Class Anetwork 5 FF FF FF FF FF FF is a Layer 2 broadcast address 6 In Internet we use IP address and port number as the identification of a process 7 The common used guided transmission media are coaxial cable twisted pair and optical fiber Fill in the blanks 10 points 1 point for each blank Directions Fill proper contents into the blanks according to the context True or False 10 points 1 point for each Directions Answer the following using True False You do not need to explain your answers T 1 During connection establishment each party uses a random number generator to create an initial sequence number F 2 At high load efficiency of an ALOHA channel is high F 3 The hubs can interconnect a token ring network and an Ethernet F 4 8 broadcast domains are created when you segment a network with an 8 port switch T 5 Packet switching networks place a tight upper limit on block size T 6 Network Address Translation technology is a solution to expand the number of IP addresses available for public use T 7 Latency through the store and forward switch varies with frame length T 8 Encryption and decryption are functions of the presentation layer T 9 OSPF is an intra AS routing protocol while BGP is an inter AS routing protocol T 10 In Time Division Multiplexing each user can get all of the bandwidth periodically during its slot 1 Make a comparison among the three network interconnection devices hubs routers and switches Fill in Yes or NO in the blanks of the following to say whether the device can per the corresponding function 6 points HubsRoutersSwitches Traffic IsolationNoYesYes Plug PlayYesNoYes Optimal RoutingNoYesNo Cut ThroughYesNoYes 2 Consider the TCP IP protocol suite 1 Fill the names of protocol data units corresponding to each layer in the PDU colunm 4 points 2 Match the following functions to one of the five layers in the Function colunm 10 points Reliable process to process message delivery Packet switching Defines frames Provides user services such as email and file transfer Transmission of bit stream across physical medium Mechanical electronical and functional interface Reassembly of data packets Ensure reliable transmission of data Network selection Route determination LayerPDUFunctions Application LayerMessage Transport LayerSegment Network LayerPacket Data Link LayerFrame Physical LayerBits on the wire Fill in the s 20 points Directions Fill proper contents into the s 本试卷 共 4 页第 3 页 学院 班级 学号 姓名 密 封 线 1 5 points How long does it take to send a file of 640K bits from host A to host B over a circuit switched network All links are 1 536 Mbps Each link uses FDM with 24 channels 500 milliseconds to establish end to end circuit Solution Transmission Speed 1 536Mbps 24 64Kbps Transmission Time 640K 64Kbps 10s Connection Establishment Time 0 5s File sending time 10 5s 2 5 points The distance between host A and host B is L 10000Km The bandwidth of the link is R 1Mbps 220bps Suppose the propagation speed over this link is V 2 5 108m s 1 What is the propagation time Tp 2 During this time how many bits have been sent to the link by host A 3 What is the distance d between two adjacent bits Solution Tp L V 0 04s Numb Tp R 41943 d L Numb 238m Comprehensive Calculation 40 points 3 6 points Use Dijkstra Algorithm to find out the shortest paths from origin E to every other node in the following graph and calculate corresponding costs Solution E A E A cost E A 4 E B E D B cost E B 4 E C E D C cost E C 4 E D E D cost E D 2 A C B D E 4 2 1 2 2 1 2 本试卷 共 4 页第 4 页 学院 班级 学号 姓名 密 封 线 4 9 points An organization is granted an IP address 211 17 180 0 The network administrator wants to create 32 subnets 1 Find out the subnet mask 2 Find out the number of host addresses in each subnet 3 Find out the network address of the second subnet 4 Find out the first and last host addresses in the second subnet 5 Find out the subnet directed broadcast address and limited broadcast address in the second subnet Solution 1 255 255 255 252 2 2 3 217 17 180 8 4 217 17 180 9 217 17 180 10 5 211 17 180 11 255 255 255 255 5 15 points Consider a router with the following routing table DestinationAddressSubnet MaskNext Hop 61 45 78 35Interface 0 61 45 78 32255 255 255 224Interface 1 63 56 7 0255 255 255 128R2 65 45 34 0255 255 255 224R3 DefaultR4 This router can forward packets directly through Interface 0 and Interface 1 and it can also forward packets through neighboring routers R2 R3 or R4 Suppose the router received 5 packets with the following IP addresses respectively 1 63 56 7 91 2 64 45 34 44 3 61 45 78 58 4 63 56 7 191 5 61 45 78 35 Try to calculate the next hop of each packet Solution 1 The result of 63 56 7 91 AND 255 255 255 128 is 63 56 7 0 so Packet 1 is forwarded to R2 3 points 2 The result of 64 45 34 44 AND MASK cannot match any entry so Packet 2 is forwarded to R4 3 points 3 The result of 61 45 78 58 AND 255 255 255 224 is 61 45 78 32 so Packet 3 is forwarded to Interface 1 3 points 4 The result of 63 56 7 191 AND MASK cannot match any entry so Packet 4 is forwarded to R4 3 points 5 61 45 78 35 has the single IP entry so Packet 5 is forwarded to Interface 0 3 points