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2007-2008第一学期计算机网络试卷1A


天津理工大学考试试卷

2007

~ 2008 学年度第 1 学期 期末考试试卷

《计算机网络原理》

课程代码: 0660086 答题时限: 120

试卷编号: 分钟

1-A

命题日期:

2007 年

12

月 10 日

考试形式:闭卷笔试

得分统计表: 大题号 总分







PART Ⅰ: Choice (2 point per question – total: 30 points)
Instructions: Select one of the letters beside the choice that is the best answer for each question. 得分

Q A

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

1. Which of the following services does not the transport layer provide for theapplication layer? A. In-order delivery of data segments between processes B. Best effort delivery of data segments between communicating hosts C. Multiplexing and demultiplexing of transport layer segments D. Congestion control 2. What are the two of the most importmant protocols in the Internet? A. TCP and IP B. TCP and UDP C. TCP and SMTP D. ARP and DNS 3. The Internet provides two services to its distributed applications: a connection oriented reliable service and a ( ). A. connection oriented unreliable service B. connectionless reliable service C. connectionless unreliable service
试卷编号: 1-A 第 1 页 共 10 页

D. In order data transport service 4. Processes on two different end systems communicate with each other by exchanging ( across the computer network. A. packets B. datagram C. frames D. messages 5. The job of delivering the data in a transport-layer segment to the correct socket is called ( A. demultiplexing B. multiplexing C. TDM ).

)

D. FDM 6. Two important reasons that the Internet is organized as a hierarchy of networks for the purposes of routing are: A. Least cost and maximum free circuit availability B. Message complexity and speed of convergence C. Scale and administrative autonomy D. Link cost changes and link failure 7. Which of characters is not distance-vector algorithm’s characters?( A. iterative B. global C. asynchronous D. distributed 8. The length of IPV6 address is ( )bits. A. 32 B. 48 C. 64 D. 128 )

9. The host component of a CIDR address of the form a.b.c.d/25 can contain addresses for: A. 225 hosts (minus “special” hosts) B. 512 hosts (minus “special” hosts) C. 2(32-25) hosts (minus “special” hosts) D. 25 hosts (minus “special” hosts) 10. The primary function of the address resolution protocol (ARP) that resides in Internet hosts and routers is: A. To provide LAN router functions B. To translate between LAN addresses and physical interface addresses C. To translate IP addresses to LAN addresses D. To calculate the shortest path between two nodes on a LAN
试卷编号: 1-A 第 2 页 共 10 页

11. The POP3 protocol runs over ____ and uses port ____. A. TCP 110 B. UDP 110 C. UDP 25 D. TCP 25 12. When a destination host transport layer receives data from the network layer, it unambiguously identifies the appropriate process to pass the data to by using a triplet consisting of: A. Source port #, destination IP address, and source IP address B. Destination port #, source port #, process ID# C. Destination port #, source port #, destination IP address D. Destination port #, source port #, source IP address 13. From the list below, select the items found in the TCP segment structure that are not found in the UDP segment structure: A. Application Generated Data B. Destination Port # C. Source Port # D. Sequence # 14. The RIP routing protocol is based on an algorithm that is: A. Based on information received only from link “neighbors” B. A link state algorithm C. An OSPF algorithm D. A centralized routing algorithm 15. With an exterior routing protocol, which of the following issues generally dominates the routing decisions? A. Geographical distance between AS’s B. Policy C. Number of AS’s traversed D. Current congestion levels in the AS’s

PART Ⅱ: Briefly answer the following questions. (Total: 40 points).
得分 1.(3points) What is the difference between a host and end system? List the types of end systems. Is a Web Server an end system?

2.(3points) Please briefly describe the function of the five layers in TCP/IP architecture (NOTE: include the protocol data unit)

试卷编号:

1-A

第 3 页 共 10 页

3. (3points) Consider accessing your email with POP. Suppose you have configured your pop mail client to operate in the down-load-and-delete mode. Complete the following transaction. C: list S: 1 498 S: 2 912 S: . C: retr 1 S: blah blah … S: …………blah S: . ? ? ?

4. (3points) Where can queuing occur in a router? Briefly explain the conditions that lead to such queuing.

5. (3points) Describe why an application developer might choose to run an application over UDP rather than TCP.

试卷编号:

1-A

第 4 页 共 10 页

6. (3points)Suppose Client A initiates a Telnet session with Server S. At about the same time, Client B also initiates a Telnet session with Server S. Provide possible source and destination port number for a. The segments sent from A to S

b. The segments sent from B to S

c. The segments sent from S to A

d. The segments sent from S to B

e. If A and B are different hosts, is it possible that the source port number in the segments from A to S is the same as that from B to S?

f. How about if they are the same host?

7. (4points) Fill in the blank: 1) RIP advertisements typically announce the number of ( ) to various destinations. 2) BGP updates announce the ( ) to various destinations 3) For Selective Repeat protocol, sequence number space >=( )times window size. 4) The efficiency of Slotted ALOHA =( ) times bigger than Pure ALOHA. 8. (3points)Consider sending a packet over a path of N links. Assume that each packet has L bits. Each link transmits at R bps. The network is lightly loaded so that there are no queuing delays. Propagation delay and node processing delay are negligible. 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?

9.(3points)If all the links in the Internet were to provide the reliable delivery service, would the TCP reliable delivery service be redundant? Why or Why not?

试卷编号:

1-A

第 5 页 共 10 页

10. (Total 4 points)CDMA
Suppose that four nodes using CDMA (Code Division Multiple Access) protocol to transport their data. The chipping sequences are listed respectively as below:

A: (-1,+1,–1,+1,+1,+1,–1,-1) B: (-1, +1,–1, –1,–1,–1, +1,-1) C: (-1,–1,–1,+1,+1,–1,+1,+1) D: (-1,–1,+1,–1,+1,+1,+1,-1) (Computing process is needless) Suppose that a CDMA receiver has received an encoded data as (-1,+1,-3,+1,-1,-3,+1,+1) from an aggregate signal channel in one bit-slot time, which node/nodes has/have sent data? What’s the corresponding data bit each of them sent? (3points)

11.(2points) In the figure below, H1 remains in same IP subnet, briefly describe how the switch would know which AP is associated with H1 when H1 is moving within BSS1 and BSS2.

试卷编号:

1-A

第 6 页 共 10 页

12. (3points) This question is about the “GSM: handoff with common MSC”. According to the figure below, ordering the 8 steps.

A. Old BSS informs MSC of impending handoff, provides list of 1+ new BSSs B. Old BSS tells mobile: perform handoff to new BSS C. New BSS allocates radio channel for use by mobile D. New BSS signals MSC, old BSS: ready E. MSC-old BSS resources released F. MSC sets up path (allocates resources) to new BSS G. Mobile signals via new BSS to MSC: handoff complete. MSC reroutes call H. Mobile, new BSS signal to activate new channel 13. (3points) Why is an ARP query sent within a broadcast frame? Why is an ARP response sent within a frame with a specific destination MAC address?

试卷编号:

1-A

第 7 页 共 10 页

PART Ⅲ: Answer the following questions. (Total: 30 points).
得分 1. (total: 15 points) Consider the network shown below. Run Dijkstra’s algorithm to compute the shortest paths from A to all other nodes in the network. While selecting the next node, if several nodes have the same min cost, select the one with lowest id, (e.g., if B and D have the same min cost, then select B).
F 2 6 A 4 B 3 5 2 3 D 5 K 3 L 2 3 E 2 M 3 1 1 C 2 J 4 G 3 4 H 7 I

Determine the routing table (destination, next-node, and cost) at node A. Destination B C D E F G I J
试卷编号: 1-A 第 8 页 共 10 页

Next Node B

Cost 4

K L M

2. (10points)Consider the following plot of TCP window size as a function of time.
45 40 35 30 33 34 35 36 38 39 40 41 42

37

32

拥塞窗口长度

25 21 20 16 15 10 5 1 0 4 2 8

22

23

24

25

26

8 4 1 2

周期

Assuming TCP Reno is protocol experiencing the behavior show above, answer the following question. a. Identify the intervals of time when TCP slow start is operating. b. Identify the intervals of time when TCP congestion avoidances is operating. c. After the 16th transmission round, is segment loss detected by a triple duplicate 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 an the first transmission round? f. What is the value of Threshold an the 18th transmission round? g. What is the value of Threshold an 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?

试卷编号:

1-A

第 9 页 共 10 页

3. (5points)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 the propagation speed along the link is s meters/sec. Host A is to send a packet of size L bits to Host B a. Ignoring processing and queuing delays, obtain an expression for the end-to-end delay. b. Suppose Host A begins to transmit the packet at time t=0. At time t=dtrans, where is the last bit of the packet? c. Suppose dprop is greater than dtrans. At time t=dtrans, where is the first bit of the packet? d. Suppose s=2.5×108, L=100bits,and R=28kbps. Find the distance m so that dtrans. Equals dtrans

试卷编号:

1-A

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