问题 单项选择题

以下关于IEE 802.3ae标准的描述中,错误的是______。

A.支持802.3标准中定义的最小和最大帧长
B.支持IEE802.3ad链路汇聚协议
C.使用1310nm单模光纤作为传输介质,最大段长可达10千米
D.使用850nm多模光纤作为传输介质,最大段长可达10千米

答案

参考答案:D

解析: IEEE 802.3ae万兆以太网技术标准的物理层只支持光纤作为传输介质,但提供了两种物理连接。一种是与传统以太网进行连接的、速率为10Gb/s的LAN物理层设备,即LAN PHY;另一种是与SDH/SONET进行连接的速率为9.58464Gb/s的WAN物理层设备,即WAN PHY。通过引入WAN PHY,万兆以太网的帧可以与SONETOC-192帧结构融合,从而能够通过SONET城域网提供端到端的以太网连接。
每种物理连接都可使用10GBASE-S<850nm短波)、10GBASE-L(1310nm长波)和10GBASE-E(1550nm长波)这三种规格的传输介质,最大传输距离分别为300m、10000m和40000m。
在物理拓扑上,万兆位以太网既支持星型连接(或扩展星型连接),也支持点到点连接,以及星型连接与点到点连接的组合。在万兆位以太网的MAC子层,已不再采用CSMA/CD机制,只支持全双工传输方式。另外,万兆以太网还继承了802.3以太网的帧格式和最大/最小帧长度,从而能充分兼容已有的以太网技术,进而降低了对现有以太网进行万兆位升级的成本。

阅读理解

When Mark first arrived in Thailand, he saw an old man selling something cheap in the street of Chiang Mai. The old man was one of the poor people in Chiang Mai and there was no difference from beggars (乞丐). Most of them were some lonely old people. Their life had no support.

Mark was a kind man, so he gave some changes to him without thinking. The old man told him to pick something he liked. Mark didn’t choose anything and left.

But the old man followed him closely. AT first, Mark didn’t think a lot, just supposing he wanted to go home. But when he went out very far saw the old man still following him, he was a bit tired, thinking the old man must feel he was kind and wanted to beg more money from him.

Mark turned back and told him not to follow him because he hadn’t much money. But the old man seemed not to understand what he meant, still following him. The bag on his back made him sweat (流汗) all over.

Mark happened to meet his Thai colleague (同事) in the street and his colleague heard this. The colleague turned to ask why the old man was following his friend.

The old man said out of breath, “My son, you gave me money, but didn’t want my things, so I have to give you something. I see you are a foreigner, likely not to familiar with here. I just want to follow you and show you the way. All I can do for you is this.”

Mark was shocked. He said he didn’t know why, when he felt the old man was just like his father.

小题1:What did Mark do when he first found the old man following him?

A.He didn’t think a lot and went on walking

B.He asked the old man why he was following him

C.He was shocked and asked his colleague to come.

D.He gave him more money without thinking.小题2:The old man followed Mark closely         .

A.because he wanted to go back home

B.because he wanted to sell more things to Mark

C.because he wanted to beg more money

D.because he wanted to show Mark the way小题3:Which of the following is true according to the passage?

A.Mark didn’t like this old man at all.

B.The old man was Mark’s father.

C.The old man sold something cheap to make a living.

D.Mark didn’t give the old man anything at the beginning.小题4:How did Mark feel about the old man at last?

A.He felt the old man was kind and warm.

B.He felt pity for the old man.

C.He felt angry with the old man

D.He felt doubt if the old man was a thief.

单项选择题