08级IP网络技术基础(英)试卷A-答案

南京邮电大学 2010/2011学年第 一 学期

《 IP 网络技术基础（英） 》期末试卷（A ）

院(系) 班级 学号 姓名

一、Give the full form of the following abbreviation:(1.5×10 points) 1. ARQ: Automatic repeat request 2. SMTP: Simple Mail Transfer Protocol 3.

OSPF: Op en Systems Path First

4. FDDI: Fiber Distributed Data Interface

5. CSMA/CD : Carrier Sense Multiple Access with Collision Detect

6. FTP: File Transfer Protocol

7. IEEE: Institute of Electrical and Electronic Engineers 8. IPv4: Internet Protocol version 4 9. ICMP : Internet Control Message Protocol Transmission Control Protocol 二、Choose the correct answer among four options. (2×10 points)

1. The address 230.200.104.32 can be classified as Class ( D ). A. A B. B C. C D. D

2. If there is an empty entry for the destination of a frame, a transparent

bridge will ( C ). A. discard the packet B. create an error report

C. use the flooding algorithm.

D. forward it to a default bridge 3. The network shown in the following picture uses ( B ) topology.

A. star

B. bus

C. ring

D. fully connected 4. IEEE 802.11 uses ( D ) as its MAC protocol.

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A. IP

B. CSMA/CD

C. ARP

D. CSMA/CA

5. Cable TV uses ( C ) as its multiplexing technique.

A. WDMA

B. TDM

C. FDM

D.CDM

6. An IPv6 address has ( D ) bits.

A. 16

B. 32

C. 64

D. 128

7. The tasks of transport layer don’t include ( D ).

A. connection management

B. flow control

C. error detection

D. forwarding segments

8. Switching hubs are ( B ) equipments.

A. layer 1

B. layer 2

C. layer 3

D. layer 4

9. The Data Link layer is divided into MAC sublayer and ( C )

A. Presentation layer

B. Session layer

C. Logic Link layer

D. Transport layer

10. The advantages which IPv6 has beyond IPv4 do not include ( D ).

A. the capability of address

B. host mobility

D. feasibility

三、Are the following statements TURE or FALSE? (1×10 points)

1. In the case of message switching, routers are dedicated and may not

be reused immediately after the transmission of a message. ( ×) 2. Now LANs are often connected using coaxial cable instead of twisted wires

because of the better bit rates and resistance to external noise. ( ×)

3. 0-persistent CSMA is the same with nonpersistent CSMA. ( ×)

4. Stop-and-wait protocol must wait for a separate ACK for each frame before sending the next. ( √)

5. CSMA/CD doesn’t require explicit acknowledgement. ( √)

6. Transceiver has a hardware address. ( ×)

7. UDP offers connectionless service. ( √)

8. Error detection in transport layer is redundant. ( × )

9. Repeaters allow interconnecting different types of LANs. ( ×)

( √)

四、Answer the following questions.(16 points)

1. Determine whether or not the following IPv6 address notation are

correct: (4 points)

(a) :: 0F53:6382:AB00:67DB:BB27:7332 CORRECT

(b) ::4BA8:95CC::DB97:4EAB INCORRECT

2. Consider hosts X,Y,Z,W and learning bridges B1,B2,B3, with initially empty forwarding table, as in figure. (6 points)

(c) Finally, suppose Y now sends to X. Which bridges learn where Y is? Does Z ’s network interface see this packet?

B1,B2,B3 ; yes (b)B1,B2,B3 ; no (c)B1,B2 ; no

3. Fill the blank in the figure. (6 points)

五、Calculating Question (23 points)

1. Consider a point-to-point link 2km in length. At what bandwidth would propagation delay (at a speed of 2×108m/sec) equal transmit delay for 100-byte packets? What about 512-byte packets? (8 points)

Prop. Delay=2000m/2×108m/sec]=10μs B1=100×8/Prop.Delay=80Mbps; B2=512×8/Prop.Delay=409.6Mbps

2. Let A and B be two stations attempting to transmit on an Ethernet. Each has a steady queue of frame ready to send; A ’s frames will be numbered A 1, A 2, and so on, and B ’s similarly. Let T=51.2μs be the exponential backoff base unit. Suppose A and B simultaneously attempt to send frame 1, collide, and happen to choose backoff times of 0×T and 1×T, respectively, meaning A wins the race and transmits A 1 while B waits. At the end of this transmission, B will attempt to retransmit B 1 while A will attempt to transmit A 2. These first attempts will

(a) Suppose X sends to Z. Which bridges learn where X is? Does Y ’s network interface see this packet?

(b) Suppose Z now sends to X. Which bridges learn where Z is? Does Y ’s network interface see this packet?

collide, but now A backs off for either 0×T or 1×T, while B backs off for time equal to one of 0×T,…, 3×T. (15 points)

(a) Give the probability that A wins this second backoff race immediately after this first collision, that is, A ’s first choice of backoff time k×T is less than B ’s. (b) Suppose A wins this second backoff race. A transmits A 2, and when it is finished, A and B collide again as A tries to transmit A 3 and B tries once more to transmit B 1. Give the probability that A wins this third backoff race immediately after the first collision.

(c) Give a reasonable lower bound for the probability that A wins all the remaining backoff races.

(a) 1-P tB=0-P tB=1&tA=1=1-1/4-1/4×1/2=5/8 (b) 1- P tB=0-P tB=1&tA=1=1-1/8-1/8×1/2=13/16 (c) Probability of A winning the nth race: 1- P tB=0-P tB=1&tA=1=1-2-n -2-n ×1/2=1-3×2-n-1 > 1-2-n+1

So the lower bound for probability that A wins all the remaining backoff races:

...>1-1/8-1/16...=3/4 六、Essay Question: (16 points)

Answer the following questions about the IP network: 1、Illustrate the Internet architecture and the relation with OSI model ； 2、Give some typical protocol according to the TCP/IP layers (two

protocols for each layer).

1、

2、There would be many possibility. The following is one possible answer.

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