第一章 计算机网络概述

Identify the five components of a data communications system.

(数据通信系统5个组成部分：报文 发送方 接受方 传输介质 协议)

message,sender,receiver,transmission medium and protocol.

What are the three criteria necessary for an effective and efficient network?

performance, reliability,and security.

What is an internet(互联网)? What is the Internet(因特网)?

★ An internet is an interconnection of networks which is a collection of networks connected by internetworking devices such as routers. ★ The Internet is the name of a specific worldwide network that uses the TCP/IP protocol suite and is the largest internet in the world.

第二章 数据和信号

Which practical methods are used for analysis of a signal? And which is suitable for network techniques? 研究电磁信号的方法是哪两种？适用于网络技术的？

①Time domain and frequency domain ②frequency domain

Why can't any digital signal be transferred with no distortion in communication transmission?(数字信号为什么不能无失真传输？)

1.Because to receive an exact replica of the digital signal, all of the frequency components must be faithfully through the transmission medium, if certain harmonic cannot transfer successful, the signal we receive will be distorted. However, any medium transfers signals only within certain frequency ranges, that is, has a limited bandwidth.

2.Transmission impairments of signals (attenuation, distortion and noise) always exist, so signal errors unavoidable.

What's the bandwidth(带宽)? Explain briefly what correlation do bandwidth, data rate and cost have in communication process?带宽、数据率、成本之间的关系？

The range of frequencies contained in a composite signal is its bandwidth.

In networking, we use the term bandwidth in two contexts with two different measuring values: Bandwidth in Hertz is the range of frequencies in a composite signal or the range of frequencies that a channel can pass, usually used to present the performance of analog channels and transmission media. (Another is) Bandwidth in bits per second is the speed of bit transmission in a channel,a link