1、计算机网络 08 级试题NOTE: This is a CLOSED BOOK, 120-minute exam. No textbooks, notes or dictionaries are allowed. It consists of four sections with a total of 100 marks. You are encouraged to WRITE YOUR ANSWERS IN ENGLISH. If you do, you will get 1-5 marks additionally. Thank you, and Good luck!Section One
2、: Multiple Choice (10 Marks):Please choose the best answer for each of the following ten questions.C1. The sliding window protocol is used at the(A) physical layer and data link layer(B) data link layer and network layer(C) data link layer and transport layer(D) transport layer and application layer
3、D2. The Transmission Control Protocol (TCP) is(A) a connectionless network layer protocol(B) a connection-oriented network layer protocol(C) a connectionless transport layer protocol(D) a connection-oriented(面向连接的) transport layer protocolB3. Packet-switched networks move data in separate, small blo
4、cks, i.e. packets, (A) based on the destination MAC address in each frame.(B) based on the destination IP address in each packet.(C) based on the packet size.(D) along a dedicated point-to-point connections set up during the call.D4. Which one of following networking devices has two or more differen
5、t IP addresses with different net-id?(A) Repeater (B) Hub(C) Bridge (D) RouterA5.”00:e0:f9:23:a8:20” is(A) a MAC address (B) an IP address(C) a Port number (D) none of aboveD6. Which layer provides communication between two processes running on two different hosts.(A) Physical layer (B) Data link la
6、yer(C) Network layer (D) Transport layerC7. The Ethernet standard defines a minimum frames size as 64 bytes because(A) users never send small data files.(B)Ethernet can not define a small sending window.(C) the CSMA/CD is characterized by “non-deterministic when sending”.(D) none of the above.B8. On
7、 an Ethernet, a host always listens to the channel while it is transmitting data. As soon as detecting a collision, it aborts transmission, waits for a while, and then retransmit the same frame. The amount of waiting time is(A) a constant. i.e. one second.(B) determined by the binary exponential bac
8、k-off algorithm.(C) determined by the receiving host.(D) determined by the network administrator.A9. Which kind of delay in a packet-switched network depends on congestion level of router?(A) Queuing delay（排队时延） (B) Transmission delay（发送时延）(C) Propagation delay（传播时延） (D) Nodal processing delay（节点处理时
9、延）C10. According to the OSI model, the Network Layer decides (A) how to transmit bits to the channel.(B) how to transmit frames to adjacent node (neighbour), over a single link.(C) how to route packets to a host on the other side, across networks.(D) how to send data segments to a process running on
10、 another host, across networksSection Two: Blank Filing (20 Marks) Please fill blanks in the following sentences/descriptions.11. TCP provides a connection-oriented, reliable, byte stream service. The term connection-oriented means the two applications using TCP must establish _connection_ before th
11、ey can exchange data. TCP includes _flow control_mechanism for each of these byte streams that allows the receiver to limit how much data the sender.12. Using “Stop and Wait“ protocol, if the _timer_goes off before the acknowledgement comes in, the sender will retransmit the frame. However, frame re
12、transmissions may introduce duplicate frames received by receiver. One solution is to _ sequence numbers _for every frame, so that the receiver can distinguish between new frames and old copies.13. In terminology “100BaseT“, “100“ stands for_data rate_ , ”Base” stands for_baseband_ _, ”T” stands for
13、_twisted pair star network_.14. If nodes are connected using an Ethernet hub and twisted pair, the physical topology of the network is _star_, however, the logical topology is _bus line_.5. From the Internets point of view, two or more LANS, which are connected by Repeaters at the _physical_ Layer o
14、r Bridges at the _data link_ Layer, have the same net-id. i.e. It is considered as a single network.16. In the Internet, routers running at the _network_ Layer connect two or more networks, with different net-id.17. In IEEE 802.11 WLAN, a sender is allowed to “reserve“ channel rather than random acc
15、ess of data frames, in order to avoid collisions of long data frames. In this mechanism, the sender first transmits _RTS_ to receiver using _ media access protocol. The receiver, after having got it, broadcasts _CTS_ inn response to it.18. In CSMA/CD Ethernet, when a station has data to send, it fir
16、st listens to the channel. Only when it detects that _channel is idle_, it begins to transmit frame, meanwhile listens to the channel in all time. It aborts transmission as soon as it detects a collision_ rather than finish transmitting its frames.19. In an IEEE802.11 WLAN with Infrastructure mode,
17、an _ Access Point(接入点) _ provides access to wired network. Via this device, mobile stations in the WLAN can communicate with stations on wired network.20. In the Internet, _ARP_ protocol is used to map IP addresses onto MAC addresses. However, _Name Server_ is used to translate host names to IP Addr
18、esses.Section Three: Networking Terminology (40 Marks)21. Please describe “Carrier Sense Multiple Access (CSMA)” (10 Marks)22. (10 Marks) Four LANs (LAN1, LAN2, LAN3, and LAN4) are interconnected by router R13, R24 and R34.(1)Please configure default gateway for Host H11 and H22 respectively.Host De
19、fault Gateway Subnet MasksH11 222.1.1.4 255.255.255.0H22 222.1.2.5 255.255.255.0(2)Please configure the following routing tables manually for router R24 and R34 respectively.Router R24Destination Network Subnet Masks Next Hop222.1.1.0 255.255.255.0 222.1.4.2222.1.3.0 255.255.255.0 222.1.4.2Router R3
20、4Destination Network Subnet Masks Next Hop222.1.1.0 255.255.255.0 222.1.3.1222.1.2.0 255.255.255.0 222.1.4.123. (10 Marks) Please explain the TCP Transmission Policy in the following figure. (P583)24. (10 Marks) The following figure illustrates the basic operation of a TCP control mechanism which is
21、 widely used in the Internet. What is this mechanism used for? What are two phases that the mechanism includes? (Note: A detailed description is not necessary. However, you need to indicate the phases on the figure.) (P596)Section Four: Problems and Solutions (30 Marks) 25. (16 Marks) A large number
22、 of consecutive IP address are available starting at 192.168.0.0. Suppose that four organizations, A, B, C, and D, request 1000, 4000, 2000, and 8000 addresses, respectively, and in that order. For each of these, give the first IP address assigned, the last IP address assigned, and the mask in the w
23、.x.y.z/s notation (Note: all the requests are rounded up to a power of two).(课后习题 5.27)26. (14 Marks) An Ethernet consists of 5 segments connected by 4 repeaters. Each segment is 500 meter long.The signal propagation speed is 2x108 m/sec.The delay caused by each repeater is 2.5 sec.The Transmission
24、rate (bandwidth) is 10 Mbps.Now we have two hosts, say A and B, which are located at far ends of the LAN.(1) (7 Marks) Please calculate the signal propagation delay from Host A to B.(2) (7 Marks) When hosts compete the shared the channel using CSMA/CD, please calculate the minimum frame size (in bit) for any sending host to detect the collision.
