2004-2005春夏学期《计算机网络基础》期末试卷(7)

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 notation. (8 points) (Notice: To start with, all the requests are rounded up to a power of two.)

五、　The following figure describes a simple authentication protocol. Assume you are Trudy, please

use reflection attack to attack Bob.

(1). Draw the attack figure and give clear the steps of the attach

(2). What are the differences between authentication and authorization? (12 points)

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