问题 单项选择题

与线路交换相比,分组交换最大的优点是 (1) ,最大的缺点是 (2) 。设待传送数据总长度为L位分组长度为P位,其中头部开销长度为H位,源节点到目的节点之间的链路数为h,每个键路上的延迟时间为D秒,数据传输率为B bit/s,线路交换和虚电路建立连接的时间都为Ss,在分组交换方式下每个中间节点产生d bit的延迟时间,则传送所有数据,线路交换需时间为 (3) s,虚电路分组交换所需时间为 (4) s,数据报分组交换所需时间为 (5) s。([X]表示对X向上取整)

4()

A.S+(hd/B+P/B)×|L/(P-H)|

B.S+(hD+P/B)×[L/(P-H)]

C.S+[(h,-1)D+P/B]×[L/(P-H)]

D.S+[(h-1)d/B+hD+P/B]X×{L/(P-H)}

答案

参考答案:D

阅读理解

阅读理解

     When I was a boy, my father told me that he could do anything he wanted to.Dad said that he wanted

to be the first to develop color prints in our city, and so he did.

     When I was 16, Dad looked closely at the violin I played and announced that he wanted to make

one.  He read about violin making, and then became a violinmaker at the age of 43.He bought the tools

and materials, opened a small store and set Mom up as the shopkeeper, while he worked at a local

company.He retired from the company 17 years later and continued to make violins and other instruments.

     Dad often guessed why the Stradivarius violins sound so beautiful.Some experts claimed that it was

the unique varnish that gave those instruments their beautiful sound.Dad argued that chemists could

analyze the varnish-if that were the answer.

      One of Dad's friends asked him once which kind of wood wasused to make violins.When Dad

explained that the top wasmade of spruce, his friend said that he had an old pieceof spruce Dad might be

interested in.He worked for the next 12 months making a violin from thewood that his friend had given

him.It proved to be a superior violin and it would become Dad's masterpiece.He was convinced that the

secret of the Stradivarius sound was in the wood itself.

     Later, the instrument was stolen.Dad's spirit was broken by the robbery, and he stopped making

instruments.But he kept the music shop until he was 80 years old, selling guitars and violins.

     My father has been gone for 14 years now.The violin has been missing for more than 25 years.

Somewhere a musician is playing a late20thcentury violin with an excellent tone.The owner today may

never understand why this ordinarylooking violin sounds so much like a Stradivarius.

1.The author mentions his father's developing color prints____  .

A. to show that his father's real interest was not in makingviolins

B. to prove that his father could do anything he wanted to

C. to give an example proving that his father was an inventor

D. to describe the real thing that made the author believe his father

2.What did the author's father think about Stradivarius violins?

A.The varnish was different from the others.

B.The way of making them was special.

C.The wood of the violins was special.

D.They could only be analyzed by chemists.

3.From the underlined sentence, we can learn that the author's father ____.

A. liked the violin very much

B. got crazy after this happened

C. lost interest in instruments        

D. didn't want to become famous

4.How long did the author's father live after the violin was stolen?

A. About 11 years.              

B. About 14 years.

C. About 25 years.                    

D. About 80 years.

5.We can infer from the last paragraph that the author  ____ .

A.really hates the thief

B.misses his father a lot

C.really wants to play the violin

D.wonders who's playing the violin now

判断题