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In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.Microwave communication uses high-frequency (26) waves that travel in straightlines through the air. Because the waves cannot (27) with the curvature of the earth, they can be (28) only over short distance. Thus, microwave is a good (29) for sendingdata between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of "dishes" or (30) . These can be installed on towers, high buildings, and mountain tops. （28）是（）
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In low-speed network, it is usually adequate to wait for congestion to occur and then react to it by telling the source of packets to slow down. In high-speed networks, this approach often works poorly, because in the (61) between sending the notification and notification arriving at the source, thousands of additional (62) may arrive. In ATM network, a major tool for preventing (63) is (64) control. When a host wants a new virtual (65) , it must describe the traffic to be offered and the service expected. （63）是（）
In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.Microwave communication uses high-frequency (26) waves that travel in straightlines through the air. Because the waves cannot (27) with the curvature of the earth, they can be (28) only over short distance. Thus, microwave is a good (29) for sendingdata between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of "dishes" or (30) . These can be installed on towers, high buildings, and mountain tops. （29）是（）
For each blank, choose the best answer from the four choices and write down on the answer sheet.(11) is a protocol that a host uses to inform a router when it joins Or leaves an Internet multicast group.(12) is an error detection code that most data communication networks use.(13) is an interior gateway protocol that uses a distance vector algorithm to propagate routing information.(14) is a transfer mode in which all types of information are organized into fixed form cells on an asynchronous or non-periodic basis over a range of media.(15) is an identifier of a web page. （13）是（）
In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.Spread spectrum simply means that data is sent in small pieces over a number of the (16) frequencies available for use at any time in the specified range. Devices using (17) spread spectrum(DSSS) communicate by (18) each byte of data into several parts and sending them concurrently on different (19) . DSSS uses a lot of the available (20) , about 22 megahertz(MHz). （20）是（）
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