2004-2005春夏学期《计算机网络基础》期末试卷(2)

40. The main public-key algorithm is ____________________ which derives its strength from the fact that it is very difficult to factor large numbers. A. DES B. AES C. MD5 D. RSA

41. Various schemes have been devised for digital signatures, using both symmetric-key and ________-key algorithms.

A. public B. private C. one time D. one way

42. Often, authentication is needed but secrecy is not, based on the idea of a one-way hash function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string. This hash function, MD, often called a ________.

A. message digest B. packet-switched C. message-detect D. mini data

43. URL(Uniform Resource Locator) have three parts: the ________, the DNS name of the machine on which the page is located, and a local name uniquely indicating the specific page. A. protocol B. address C. port number D. name

44. HTTP1.1, which supports ________ connections. With them, it is possible to establish a TCP connection, send a request and get a response, and then additional requests and get additional response.

A. one time B. persistent C. stop and wait D. one-way

45. _______, when it is used, a bad frame that is received is discarded, but the good frames received after it are buffered.

A. selective repeat B. go back N C. sliding window D. stop and wait 46. How does the FDM multiplexing schemes work like?

A. each user having exclusive possession of some band

B. each user take turns, periodically getting the entire bandwidth for a litter burst of time C. each user transmit over the entire frequency spectrum all the time with different coding D. each user transmit over a shared fiber using different wavelength

47. When we use a modem, which use 16 phases signal to modulation, then how much can we get the maximum data rate in a 2400 baud channel (in noiseless channel)?

A. 400bps B. 2400bps C. 9.6kbps D. 14.4kbps

48. ______ is a small java program that has been compiled into binary instruction running in JVM,

and can be embedded into HTML pages, interpreted by JVM-capable browsers. A. JavaScript B. JavaBean C. Applet D. JSP

49. Which of the following best describes the function of the OSI reference model’s transport layer?

A. It sends data by using flow control B. It provides the best path for delivery C. It determines network addresses D. It provides error-correcting

50. What is the most efficient subnet mask to use on point-to-point WAN links? A. 255.255.255.0 B. 255.255.255.224 C. 255.255.255.252 D. 255.255.255.248

二、　Please choose true(Ｔ) or false( Ｆ) for the following questions (15 points) 1. Error-correcting and error-detecting are two types of technique in error control.

2. Link state dynamic routing algorithms operate by having each router maintain a table giving the best known distance to each destination and which line to use to get there. These tables are updated by exchanging information with the neighbors.

3. With Manchester encoding, each bit period is divided into two equal intervals. A binary 1 bit is sent by having the voltage set high during the first interval and low in the second one. A binary 0 is just the reverse: first low and then high.

4. A connection is established in TCP by means of the two-way handshake.

5. The range of frequencies transmitted without being strongly attenuated is called bandwidth. 6. Shannon’s major result is that the maximum data rate of a noisy channel whose bandwidth is H Hz, and whose signal-to-noise ratio is S/N, is given by Maximum number of baud/sec = H log2 (1+S/N)

7. Two different switching techniques are widely used nowadays: circuit switching and packet switching.

8. The protocols used to determine who goes next on a multi-access channel belong to a sub-layer of the data link layer called the LLC sublayer.

9. The basic function of RTP is to multiplex several real-time data streams onto a single stream of UDP packets.

10. The Internet solution is to realize that two potential problems exist network capacity and receiver capacity and to deal with each of them separately. To do so, each sender maintains two windows: the window the receiver has granted and a second window, the congestion window.

11. Selective repeat, is for the receiver simply to discard all subsequent frames, sending no acknowledgments for the discarded frames.

12. The IPSec is a set of open standards that provides data confidentiality, data integrity, and authentication between participating peers at the IP layer. 13. B2C, the full name is Business to Company.

14. One type of person-to-person communication often goes by the name of end-to-end communication, to distinguish it from the client-server model.

15. An issue that occurs at every level is how to keep a fast sender from swamping a slow received with data. This subject is called flow control.

三、　Please answer the following questions briefly.

1. What are the principal differences between connectionless communications and

connection-oriented communications? (5 points)

2. Data link protocols almost always put the CRC in a trailer rather than in a header. Why? (5

points)

3. Suppose that the TCP congestion window is set to 18KB and a timeout occurs. How big will

the window be if the next four transmission bursts are all successful? Assume that the maximum size of segment is 1KB. (5 points)

四、　A large number of consecutive IP address are available starting at 198.16.0.0. Suppose that four organizations, A, B, C, and D, request 4000,2000,4000, 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.x.y.z/s n …… 此处隐藏：4025字，全部文档内容请下载后查看。喜欢就下载吧 ……