Unit１【中译英】(1)信号:signal (2)波特率:the baud rate (3)单工:simplex (4)同步:synchronous (5) 信道:communications channel (6) 模拟:analog (7) 数字:digital (8) 电磁的:electromagnetic (9) 串行口:serial port (10) 带宽:bandwidth【英译中】(1)baud:波特(2) asynchronous:异步的(3) full duplex:全双工(4) parallel:并行(5) electromagnetic:电磁的(6) discrete:离散的(7) simultaneously:同时发生地(8) parity:奇偶校验【句子翻译（英译中）】1. Since transmitted data can be assigned to different frequencies,the wider the bandwidth,the more the frequencies,and the more data can be transmitted at the same time.因为传输的数据能被分配到不同频率，所以带宽越宽频率越多，同一时间能被传输的数据就越多。
2. To distinguish where one character stops and another starts,the asynchronous communication mode uses a start and a stop bit.为了辨别一个字符在什么地方结束而另一个字符在什么地方开始，异步通信模式使用一个起始位和一个结束位。
3. More technical manes for the serial port are RS-232C connector and asynchronous communication port.串行端口技术上又叫做RS-232C连接器和异步通信接口。
【段落翻译（英译中）】The third is the transmission mode. Transmission modes include the asynchronous mode and the synchronous mode. In the asynchronous transmission mode, individual characters (made up of bits) are transmitted at irregular intervals, for example. When a user enters data. To distinguish where one character stops and another starts, the asynchronous communication mode uses a start and a stop bit. An additional bit called a parity bit is sometimes included at the end of each character. Parity bits are used for error checking. The asynchronous transmission mode is used for lower speed data transmission and is used with most communication equipment designed for personal computers.第三是传输模式。
传输模式包括异步和同步。
在异步传输模式中，单独的字符(由比特组成)以不规则的时间间隔传输，例如当用户输入数据时。
为了辨别一个字符在什么地方停止而另一个字符在什么地方开始，异步通信模式使用一个起始位和一个停止位。
一个称为奇偶位的附加位有时包含在每个字符的末端。
奇偶位用于错误校验。
异步传输模式用于低速数据传输以及用在设计适合个人计算机的大多数的通信设备中。
[第一段翻译]The need to communicate is part of man’s nature. Since the beginning of time man has used different techniques and methods to communicate. Circumstances and available technology have dictated the method and means of communications. Date communication concerns itself with the transmission (sending and receiving) of information between two parties. Now let’s learn the foundation knowledge of data communication.通信是人类固有需求的一部分，人类一开始就使用不同的技术和方式进行交流，而环境和可利用的技术也限定了人类通信的方法和方式。
数据通信涉及在通信双方间传递信息。
现在我们共同来学习关于数据通信的基本知识。
Unit 3【中译英】（1）载波：Carrier Frequencies （2）多路复用：Multiplexing（3）载波振荡频率：the frequency at which the station’s carrier oscillates （4）频分复用：Frequency Division Multiplexing （5）旋转开关：round-robin scheme （6）时分复用：Time Division Multiplexing【缩写翻译】FDM：Frequency Division Multiplexing 频分复用TDM：Time Division Multiplexing 时分复用【句子翻译（英译中）】（1）In fact，a channel number is merely shorthand for the frequency at which the station’s carrier oscillates.实际上，频道号码就是电视台载波用的振荡频率的速记。
（2）A receiver configured to accept a carrier at a given frequency will not be affected by signal sent at other frequencies.一个接收器被设置成接收给定频率的载波，它将不会受其他频率信号的影响（或干扰）。
（3）Frequency Division Multiplexing(FDM) is the technical term applied to a network system that uses multiple carrier frequencies to allow independent signals to travel through a medium.频分复用（FDM）是使用多个载波频率在一个介质中同时传输多个独立信号的计算机网络系统术语。
（4）In practice, however, two carriers operating at almost the same frequency or at exact multiples of a frequency can interfere with one another.实际上，两个频率相近或频率成整数倍的载波会彼此干扰。
（5）The mandate for large gape between the frequencies assigned to carriers means that underlying hardware used with FDM can tolerate a wide range of frequencies.在各载波的频率之间的大间隔意味着FDM所用的硬件能容纳很宽的频率范围。
（6）The general alternative to FDM is time division multiplexing(TDM), in which sources sharing a medium take turns.与FDM不同的另一种复用形式是时分多路复用（TDM），按这种方式各发送源轮流使用共享的通信介质。
【段落翻译（英译中）】Dividing data into small packets ensures that all sources receive prompt service because it prohibits one source from gaining exclusive access for an arbitrarily long time. In particular, if one source has a few packets to send and the other has many, allowing both sources to take turns sending packets which guarantees that the source with a small amount of data will finish promptly.将数据分成小包以确保所有的信源都能得到及时服务，因为这时是禁止一个信源获取一个独占的长时服务。
尤其是，如果一个信源需要发送的数据包数量较少，而另一个信源需要发送的数据包较多时，采用时间片轮转方式使两个信源轮流发送数据包以确保数据包较少的信源的数据发送能及时完成。
[第一段翻译]Computer networks that use a modulated carrier wave to transmit data are similar to television stations that used a modulated carrier wave to broadcast video. The similarities provide the intuition needed to understand a fundamental principle: Two or more signals that use different carrier frequencies can be transmitted over a single medium simultaneously without interference.计算机网络使用调制载波传输数据与电视台使用载波广播视频的方式很类似。