问题 单项选择题

SDH网络通常采用双环结构,其工作模式一般为()。

A.一个作为主环,另一个作为备用环,正常情况下只有主环传输信息,在主环发生故障时可在50ms内切换到备用环传输信息

B.一个作为主环;另一个作为备用环。但信息在两个环上同时传输,正常情况下只接收主环上的信息,在主环发生故障时可在50ms内切换到从备用环接收信息

C.两个环同时用于通信,其中一个发生故障时,可在50ms内屏蔽故障环,全部信息都经另一个环继续传输

D.两个环同时用于通信,任何一个发生故障时,相关节点之间的通信不能进行,等待修复后可在50ms内建立通信连接继续通信

答案

参考答案:B

解析:

本题考查广域网中SDH网络的基本知识。

SDH是一种将复接、线路传输及交换功能融为一体、并由统一网管系统操作的综合信息传送网络,是美国贝尔通信技术研究所提出来的同步光网络(SynchronousOpticalNetwork,SONET)。ITU-T于1988年接受了SONET概念并重新命名为SDH,使其成为不仅适用于光纤也适用于微波和卫星传输的通用技术体制。它可实现网络有效管理、实时业务监控、动态网络维护、不同厂商设备间的互通等多项功能,能大大提高网络资源利用率、降低管理及维护费用、实现灵活可靠和高效的网络运行与维护,因此是当今世界信息领域在传输技术方面的发展和应用的热点,受到人们的广泛重视。

SDH由于其自身的特点,所以能快速发展,它的具体特点如下:

(1)SDH有统一的帧结构,数字传输标准速率和标准的光路接口,向上兼容性能好,能与现有的PDH完全兼容,并容纳各种新的业务信号,形成了全球统一的数字传输体制标准,提高了网络的可靠性。

(2)SDH的码流在帧净负荷区内排列非常有规律,而净负荷与网络是同步的,它简化了DXC,减少了背靠背的接口复用设备,改善了网络的业务传送透明性。

(3)采用较先进的分插复用器(Add-DropMultiplexer,ADM)、数字交叉连接(DigitalCrossConnect,DXC)、网络的自愈功能和重组功能非常强大。

(4)SDH有多种网络拓扑结构,运行管理和自动配置功能,优化了网络性能,同时也使网络运行灵活、安全、可靠,使网络的功能非常齐全和多样化。

(5)SDH可以在多种介质上传输。

(6)SDH是严格同步的,误码少,且便于复用和调整。

SDH网络具有链状、星状、环状、树状、网孔状等结构。

双环结构式一种常用的形式,因其具有自愈功能,能提供较高的可靠性。一个作为主环,另一个作为备用环,但信息在两个环上同时传输,正常情况下只接收主环上的信息,在主环发生故障时可在50ms内切换到从备用环接收信息。

完形填空
It was her giggling that draw my attention. Note taking really wasn’t all that funny.
Walking over to the offender, I asked for the   46 . Frozen, she refused to give it to me. I waited, all attention in the classroom on the quiet   47  between teacher and student. When she finally   48  it over she whispered, “Okay, but I didn’t draw it.”
It was a hand-drawn   49  of me, teeth blackened and the words “I’m stupid” coming out of my mouth.
I managed to fold it up calmly. My mind,  50  , was working angrily as I struggled not to   51 . I figured I knew the two most likely candidates for drawing the picture. It would do them some   52  to teach them a lesson, and maybe it was high time that I did it!
Thankfully, I was able to keep myself   53 .
When there were about six minutes remaining, I showed the class the picture. They were all silent as I told them how   54  this was for me. I told them there must be a reason behind and now was their   55   to write down anything they needed to tell me. Then I let them write silently   56  I sniffed in the back of the classroom.
As I   57  the notes later, many of them said something like, “I’ve got nothing against you.” or “I’m sorry you were hurt.” Some kids said, “We’re afraid of you.” But two notes, from the girls who I   58  were behind the picture, had a list of issues. I was too   59 , too strict …
Reading those notes, I realized that over the course of this year, instead of   60  my student, I had begun commanding them to   61 . Where I thought I was driving them to success I was   62  driving them away.
I had some apology to do. But the next day I the classroom, one boy and one girl each handed me a card. The one   63  by all the boys expressed sincere regret for the ugly joke. The one from the girls asked for   64 .
This was a lesson for both the kids and me. Forgiveness does not change the past, but it does enlarge the   65 .
小题1:
A.noteB.adviceC.reasonD.help
小题2:
A.battleB.competitionC.argumentD.conversation
小题3:
A.tookB.passedC.turnedD.handed
小题4:
A.statueB.graphC.pictureD.poster
小题5:
A.otherwiseB.howeverC.thereforeD.besides
小题6:
A.leaveB.cryC.explainD.argue
小题7:
A.goodB.harmC.favorD.punishment
小题8:
A.amusedB.controlledC.uninterestedD.relaxed
小题9:
A.meaningfulB.forgetfulC.regretfulD.hurtful
小题10:
A.turnB.chanceC.honourD.attempt
小题11:
A.whenB.beforeC.afterD.while
小题12:
A.wroteB.finishedC.readD.collected
小题13:
A.figuredB.promisedC.concludedD.confirmed
小题14:.
A.talkativeB.meanC.secureD.terrible
小题15:
A.forcingB.encouragingC.comfortingD.teaching
小题16:.
A.appreciateB.apologizeC.masterD.achieve
小题17:
A.actuallyB.normallyC.immediatelyD.generally
小题18:
A.decoratedB.offeredC.signedD.bought
小题19:
A.thankfulnessB.forgivenessC.communicationD.happiness
小题20:
A.friendshipB.educationC.knowledgeD.future
单项选择题