mooc数字通信原理期末答案(慕课2023课后作业答案)

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第一章 数据通信、数字数据网络和因特网

第4周测试

1、通信Data transferred in the Data Link Layer is 原理in the form
A、Physical
B、期末Transport
C、答案答案Network Network layer
D、慕课MAC sublayer of the data link layer

2、课后Which one of the following networking terms is 作业not associated with the same OSI layer as the others?
A、Router
B、数字Packets
C、通信Tcp
D、原理IP

3、期末Which of the following functions is 答案答案not performed by TCP?
A、Flow control
B、慕课Sequencing
C、课后Error checking
D、Subnetting

4、Bit synchronization is handled at which layer?
A、Data link
B、Transport
C、Session
D、Physical

5、Identify the order of the 5 step encapsulation? 1. Create the segment 2. Convert the Frame to bits 3. Create the packet 4. Create the frame 5. user creates the data
A、1,2,4,2,5
B、2,1,3,4,5,
C、5,1,3,4,2,
D、5,3,4,1,2,

6、Which layers of the OSI model are included in the lower layers？
A、Application, Session, Presentation
B、Physical, Transport, Data link, network
C、Data link, physical, Network
D、Session, Data link, Physical

7、IP is implemented at which OSI model layer?
A、Transport
B、Session
C、Data link
D、Network

8、Where is encapsulation used in the osi model?
A、All seven layers of the receiving station
B、At peer layers of the sending station and receiving station
C、Only at the Network layer
D、At the sending Station

9、What is the Protocol Data Unit (PDU) employed at the Data Link Layer?
A、Bits
B、Frames
C、Packets
D、Segments

10、Which of the following protocols are examples of TCP/IP network access layer protocols?
A、Ethernet
B、HTTP
C、UDP
D、TCP

11、Transport layer protocols that establish a connection with another node before they begin transmitting data are known as :
A、Connectionless protocols
B、Syn-oriented protocols
C、Connection-oriented protocols
D、Ask.oriented protocols

12、A network layer protocols that reports on the success or failure of data delivery is :
A、IP
B、TCP
C、ARP
D、ICMP

13、Encryption takes place at which layer?
A、Application
B、Presentation
C、Session
D、Transport

14、Which layer establishes, maintains, and terminates communications between applications located on different devices?
A、Application
B、Presentation
C、Session
D、Network

15、Which layer uses the Segments as a Protocol Data Unit (PDU)?
A、Network
B、Physical
C、Data link
D、Transport

16、Which OSI layer defines the standards for cabling and connection ?
A、Layer 1
B、Layer 2
C、Layer 3
D、Layer 4

17、Packets are found at which layer?
A、Data link
B、Transport
C、Network
D、Session

18、What are the OSI layers above and below the Session layer？
A、Application, presentation, session, transport, network, data link, physical
B、Session, presentation, data transport, MAC, network, physical
C、Physical, data link, network, transport, session, presentation, application
D、Presentation, application, session, network, transport, data link, physical

19、What are the OSI layer above and below the Session layer.
A、Application and Physical layer
B、Application and Session layer
C、Presentation and Transport layer
D、Transport and Physical layer

20、. In the Data link layer for the OSI model, error checking is accomplished by a:
A、Transport
B、Network
C、Session
D、Data link

21、Error detection and recovery takes place at which layer?
A、Transport
B、Presentation
C、Data link
D、Network

22、Which layer handles the formatting of application data so that it will be readable by the destination system?
A、Application
B、Presentation
C、Transport
D、network E. Data link

23、The network layer uses physical addresses to route data to destination hosts.
A、True
B、False
C、字数补丁
D、字数补丁

24、Which layer falls between the Presentation layer and the Transport Layer?
A、Application
B、Session
C、Physical
D、Network

Week 10

Exam

1、The _______ layer is responsible for delivering data units from one station to the next without errors.
A、physical
B、data link
C、trnsport
D、network

2、The _______ model shows how the network functions of a computer ought to be organized.
A、CCITT
B、ANSI
C、OSI
D、ISO

3、TCP/IP is a ______ hierarchical protocol suite developed _____ the OSI model.
A、five-layer; before
B、five-layer; after
C、six-layer; before
D、seven-layer; before

4、Which of the following is an application layer service?
A、All of these
B、File transfer and access
C、Mail service
D、Remote log-in

5、The_________ layer is responsible for the delivery of a message from one process to another.
A、physical
B、transport
C、network
D、none of these

6、Communication between a computer and a keyboard involves ______________ transmission.
A、simplex
B、half-duplex
C、full-duplex
D、automatic

7、_______ refers to the structure or format of the data, meaning the order in which they are presented.
A、All of these
B、Syntax
C、Semantics
D、Timing

8、The information to be communicated in a data communications system is the _______.
A、Medium
B、Protocol
C、Message
D、Transmission

9、________ is a collection of many separate networks.
A、A WAN
B、An internet
C、A LAN
D、None of these

10、In _______ transmission, the channel capacity is shared by both communicating devices at all times.
A、simplex
B、half-duplex
C、half-simplex
D、full-duplex

11、This was the first network.
A、CSNET
B、NSFNET
C、ARPANET
D、ANSNET

12、_______ describes the position of the waveform relative to time 0.
A、Amplitude
B、Frequency
C、Voltage
D、Phase

13、A(n)_________ signal is a composite analog signal with an infinite bandwidth.
A、either digital or analog
B、analog
C、neither digital nor analog
D、digital

14、A sine wave in the ______ domain can be represented by one single spike in the _____ domain.
A、phase; time
B、time; frequency
C、frequency; time
D、time; phase

15、As frequency increases, the period ________.
A、doubles
B、remains the same
C、increases
D、decreases

16、________ is a type of transmission impairment in which the signal loses strength due to the resistance of the transmission medium.
A、Distortion
B、Noise
C、Decibel
D、Attenuation

17、The _________ product defines the number of bits that can fill the link.
A、bandwidth-delay
B、bandwidth-period
C、frequency-amplitude
D、delay-amplitude

18、________ is a type of transmission impairment in which an outside source such as crosstalk corrupts a signal.
A、Distortion
B、Noise
C、Attenuation
D、Decibel

19、If the bandwidth of a signal is 5 KHz and the lowest frequency is 52 KHz, what is the highest frequency?
A、57 KHz
B、47 KHz
C、10 KHz
D、5 KHz

20、AM and FM are examples of ________ conversion.
A、analog-to-analog
B、digital-to-digital
C、analog-to-digital
D、digital-to-analog

21、_________ utilization is the use of available bandwidth to achieve specific goals.
A、Amplitude
B、Frequency
C、Bandwidth
D、None of these

22、The sharing of a medium and its link by two or more devices is called _______.
A、line discipline
B、encoding
C、multiplexing
D、modulation

23、_________ cable consists of an inner copper core and a second conducting outer sheath.
A、Fiber-optic
B、Coaxial
C、Shielded twisted-pair
D、Twisted-pair

24、he inner core of an optical fiber is _________ in composition.
A、bimetallic
B、glass or plastic
C、copper
D、liquid

25、Signals with a frequency above 30 MHz use _______propagation.
A、none of these
B、ground
C、sky
D、line-of-sight

26、A(n) _________ medium provides a physical conduit from one device to another.
A、None of these
B、unguided
C、guided
D、either unguided or guided

27、In fiber optics, the signal is _______ waves.
A、radio
B、light
C、infrared
D、very low-frequency

28、_________ media transport electromagnetic waves without the use of a physical conductor.
A、Unguided
B、Guided
C、Either Guided or Unguided
D、None of these

29、________ cable is used for voice and data communications.
A、Fiber-optic
B、Twisted-pair
C、Coaxial
D、None of these

30、__________ consists of a central conductor and a shield.
A、Twisted-pair
B、Coaxial
C、Fiber-optic
D、None of these

31、In _______ transmission, bits are transmitted over a single wire, one at a time.
A、synchronous serial
B、asynchronous serial
C、parallel
D、asynchronous serial and synchronous serial

32、What is the major factor that makes coaxial cable less susceptible to noise than twisted-pair cable?
A、insulating material
B、inner conductor
C、diameter of cable
D、outer conductor

33、________ are used for short-range communications such as those between a PC and a peripheral device.
A、Radio waves
B、Infrared waves
C、Microwaves
D、None of these

34、Radio waves are _________.
A、None of these
B、unidirectional
C、omnidirectional
D、bidirectional

35、Transmission media are usually categorized as _______.
A、determinate or indeterminate
B、metallic or nonmetallic
C、fixed or unfixed
D、guided or unguided

36、When a beam of light travels through media of two different densities, if the angle of incidence is greater than the critical angle, _______ occurs.
A、refraction
B、criticism
C、reflection
D、incidence

37、A parabolic dish antenna is a(n) _________ antenna.
A、unidirectional
B、horn
C、omnidirectional
D、bidirectional

38、Which of the following is not a guided medium?
A、atmosphere
B、fiber-optic cable
C、coaxial cable
D、twisted-pair cable

39、_______ signals can have only a limited number of values.
A、either digital or analog
B、digital
C、analog
D、neither digital nor analog

40、For a ______ channel, the Nyquist bit rate formula defines the theoretical maximum bit rate.
A、noisy
B、bandpass
C、noiseless
D、low-pass

41、_________ can impair a signal.
A、Noise
B、Attenuation
C、Distortion
D、All of these

42、What is the bandwidth of a signal that ranges from 1 MHz to 4 MHz?
A、3 MHz
B、none of these
C、1 KHz
D、4 MHz

43、Given two sine waves A and B, if the frequency of A is twice that of B, then the period of B is ________ that of A.
A、twice
B、the same as
C、one-half
D、indeterminate from

44、________ is a type of transmission impairment in which the signal loses strength due to the different propagation speeds of each frequency that makes up the signal.
A、Attenuation
B、Distortion
C、Decibel
D、Noise

45、A periodic signal completes one cycle in 0.001 s. What is the frequency?
A、100 Hz
B、1 MHz
C、1 Hz
D、1 KHz

46、The ____ address uniquely defines a host on the Internet.
A、physical
B、IP
C、port
D、specific

47、The _______ is the physical path over which a message travels.
A、Protocol
B、Signal
C、Medium
D、All of these

48、A ________ is a set of rules that governs data communication.
A、None of these
B、protocol
C、standard
D、forum

49、In a ______ connection, two and only two devices are connected by a dedicated link.
A、multipoint and point-to-point
B、point-to-point
C、None of these
D、multipoint

50、In a ________ connection, three or more devices share a link.
A、None of these
B、point-to-point
C、point-to-point and multipoint
D、multipoint

51、Signals with a frequency between 2 MHz and 30 MHz use _______ propagation.
A、none of these
B、sky
C、line-of-sight
D、ground

52、In a fiber-optic cable, the signal is propagated along the inner core by _______.
A、refraction
B、reflection
C、modulation
D、None of these

53、________ cable can carry signals of higher frequency ranges than _______ cable.
A、Coaxial; fiber-optic
B、Twisted-pair; fiber-optic
C、Coaxial; twisted-pair
D、None of these

54、________ cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket.
A、Twisted-pair
B、Coaxial
C、None of these
D、Fiber-optic

55、_________ are used for cellular phone, satellite, and wireless LAN communications.
A、Infrared waves
B、Radio waves
C、None of these
D、Microwaves

56、Which of the following primarily uses guided media?
A、radio broadcasting
B、cellular telephone system
C、satellite communications
D、local telephone system

57、A signal is measured at two different points. The power is P1 at the first point and P2 at the second point. The dB is 0. This means ________.
A、P2 equals P1
B、P2 is zero
C、P2 is much larger than P1
D、P2 is much smaller than P1

58、Signals can be ________.
A、digital
B、analog
C、either digital or analog
D、neither digital nor analog

59、A sine wave is ________.
A、periodic and continuous
B、aperiodic and discrete
C、aperiodic and continuous
D、periodic and discrete

60、________is the rate of change with respect to time.
A、Time
B、Frequency
C、Voltage
D、Amplitude

学习通数字通信原理

数字通信是一种信息传输方式，它使用数字信号来传输和处理信息。数字通信原理包括信号的调制、传输、解调和处理，其中最重要的部分是数字信号的调制和解调。

数字信号的调制是将原始信息转换为数字信号的过程。根据信号的频率特性和调制方式，数字信号的调制可以分为幅度调制（AM）、频率调制（FM）、相位调制（PM）和脉冲调制（PCM）等几种类型。

在数字通信中，调制的基本目的是将原始信号转换为一种能够在信道中传输的信号。数字信号可以通过数字方式传输或者通过模拟方式传输。

数字信号的解调是将数字信号转换为原始信息的过程。解调的方法通常与调制的方式相对应，例如，如果原始信号是用频率调制方式调制的，则数字信号也应该用频率解调的方法来解调。

在数字通信中，信道是指信号传输的媒介或介质。数字信号在传输过程中常常受到很多噪声和干扰的影响，这些影响会导致数字信号的错误。因此，数字通信系统通常需要采用一些纠错码或冗余编码技术来保证数据的正确性。

数字通信的应用十分广泛，例如在电话网络、电视广播、互联网和移动通信等领域都有广泛应用。数字通信的快速发展促进了现代通信技术的发展，使我们的生活和工作变得更加便捷和高效。

数字信号的调制

数字信号的调制是将原始信息转换为数字信号的过程。在数字通信中，最常用的调制方式是正交振幅调制（QAM）和相位移键（PSK）调制。

正交振幅调制（QAM）

正交振幅调制是利用两路正交的基带信号进行调制的一种调制方式。QAM调制的基本思想是将数字信号分成两路信号进行调制，然后通过合并两路信号来得到一个更高速率的数字信号。

在QAM调制中，需要将数字信号转换为两路基带信号，分别为I路和Q路信号。I路信号通常用于调制正弦波，Q路信号用于调制余弦波。通过改变I路和Q路信号的幅度和相位，可以得到不同的数字信号。

QAM调制的优点是可以在较小的带宽内传输更多的信息，因此在数字通信中得到广泛应用。

相位移键（PSK）调制

相位移键调制是利用数字信号的相位差异进行调制的一种调制方式。在PSK调制中，数字信号所对应的二进制码被转换为不同的相位角，然后用一定的载波进行调制。

PSK调制的优点是比较简单，易于实现，同时在数字通信中也得到了广泛的应用。

数字信号的解调

数字信号的解调是将数字信号转换为原始信息的过程。在数字通信中，数字信号的解调通常与调制的方式相对应。

正交振幅调制（QAM）解调

在QAM调制中，需要将接收到的数字信号分为I路和Q路信号，然后分别进行解调。解调的过程是将接收到的信号与正弦波和余弦波相乘，然后进行滤波，最终得到原始信息。

QAM解调的过程比较复杂，需要进行多次运算和滤波。但是由于QAM调制具有较好的性能，因此在数字通信中得到了广泛的应用。

相位移键（PSK）解调

在PSK调制中，接收到的数字信号与相应的载波进行乘法运算，然后进行滤波，最终得到原始信息。

PSK解调的过程比较简单，只需要进行一次运算和滤波即可。因此在数字通信中得到了广泛的应用。

数字通信的信道编码

数字通信中，信道编码是用于纠正信道中错误的一种技术。通常的信道编码技术包括前向纠错码（FEC）和自适应纠错码（ARQ）。

前向纠错码（FEC）

前向纠错码是一种错误检测和纠正技术。在数字通信中，FEC通常使用哈密尔顿码、CRC校验和卷积码等编码方式。当接收到的码字发生错误时，FEC会根据码字的编码方式自动进行错误检测和纠正。

自适应纠错码（ARQ）

自适应纠错码是一种动态调整错误检测和纠正方法的技术。当接收到的码字发生错误时，ARQ会向发送方发送一个重传请求，要求重新发送数据。ARQ技术可以通过调整重传次数和重传的码字数量来适应不同的信道条件。

总结

数字通信是一种使用数字信号进行信息传输的技术。数字通信的基本原理包括数字信号的调制、传输、解调和处理。在数字通信中，最常用的调制方式是正交振幅调制和相位移键调制。数字信号的解调通常与调制的方式相对应。数字通信中还使用了一些纠错码和冗余编码技术来保证数据的正确性。数字通信的应用十分广泛，可以在电话网络、电视广播、互联网和移动通信等领域得到广泛应用。

爱因斯坦曾说“如果蜜蜂从地球上消失，人类将只能再存活（ ）。”

A.赛车鞋（皮革制鞋面、塑料制鞋底）
B.两个串联互感线圈的感应电压极性，取决于电流流向，与同名端无关。
C.32.文件系统中分配存储空间的基本单位不是记录。
D.设计代码前首先要进行（ ）

酸辣禾花鱼适合在芒种食用

A.以下哪一项不属于二手车交易过程中发生的费用（ ）。
B.鋬耳金杯是蒙古族人民普遍使用的一种日常饮酒器具。
C.碳酸盐岩地层中构造裂缝的发育程度和分布规律主要受 控制。
D.出国后要养成随身带零钱的习惯。

下列SPSS软件“分析”—“描述统计”中没有描述性统计指标计算的模块是（ ）。

A.对新药临床Ⅱ期试验的描述，正确项是（ ）
B.一般来说，材料的孔隙率与下列性能没有关系的是（）。
C.C语言的 % 运算符按运算对象的个数属（ ）。
D.智慧职教: 系统只允许以系统管理员的身份注册进入系统管理。( )

完成本单元项目实践，并自选主题完成一副或一组计算机图像动画设计

A.儿童与成人的注意一样，都是以有意注意为主。（ ）
B.拜堂是古代婚俗“六礼”之中的一个礼仪。
C.结构功能主义理论认为：对个体而言，仪式具有（ ）的功能。
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保守力做正功时，系统内相应的机械能增加。

A.以下选项中不是换气方法的是（）
B.下列有关组织沟通的陈述中，错误的陈述是
C.外部招聘是改变人员组织结构的根本出路。
D.冲火的蔓延速度（ ）坐火的蔓延速度。

波长为500nm的绿色光其能量（ ）。

A.在短期内，厂商的成本可以分为 成本部分和 成本部分。
B.定位基主要影响了苯环邻对位电子云密度。
C.影响结合橡胶生成量的因素有哪些
D.使用FileInfo类的Copy()方法可以复制文件。（ ）

清朝皇帝的帽子有严格的规定，并且和（）是分不开的

A.王维不善于赋予静态的画面
B.按鸡尾酒的容量分类，鸡尾酒可分为高酒度鸡尾酒和低酒度鸡尾酒。（）
C.中药炮制起源于（ ）时期。
D.《白秋练》是出自作者亲身感受而发的。

为了更容易的设计衬线大写字母，可以按照形状相似性将字母分成（）几类

A.干细胞的自我更新能力是通过对称分裂和不对称分裂两种形式进行，但主要是对称分裂。
B.移动运营商、银行、卡组织（或第三方机构）是移动支付供给方的核心参与者
C.已知圆柱被截切后的主视图和左视图，正确的俯视图是（ ） A B C
D.德尔斐城邦的保护神是酒神狄奥尼索斯。

反映了一定社会阶级（阶层）的价值追求，同时也对德育活动的结果作了某种限定。

A.有关氧自由基的正确说法有
B.已知是齐次线性方程组的基础解系，那么基础解系也可以是（ ）.
C.王齐老师制作的“随意春芳歇”是比赛制作的插花吗
D.笔记本电脑系统中，主板上的I/O芯片主要控制（ ）

组成核酸的元素主要有C、H、O、N、P、S

A.植物细胞内ATP酶活性与吸收无机离子呈负相关。
B.N个顶点的连通图的生成树含有( )条边
C.已知半径为R的圆弧与某一直线相切，其圆心的位置
D.回流比的（ ）值为全回流。

萃取精馏溶剂选择的方法主要包括

A.抽筋在医学上的专业术语叫（ ）。
B.存货策略的常用概念包括（）。
C.蒙特哥菲儿兄弟用一下那些物质制作出了热气球：
D.《菩萨蛮》和《菩萨蛮慢》所配的音乐是相同的。

液压油液的粘度值随着温度的升高而减小。

A.关于幼儿故事，下面说法错误的是
B.成人结核菌素阳性可能表示（ ）。
C.哈佛大学教授梅尔比亚研究发现，人与人之间的沟通效果，肢体语言占比为（ ）
D.With his wife.

在“图片工具”下的（）组中可以对图片进行添加边框的操作。

A.马东认为，好的文化产品应该是：
B.呼び掛けられたら「あぁ」と返事する。
C.民族关系是以民族因素为内涵的特殊的社会关系
D.盐渍土在浸水后强度明显( )

恒星的体积越大，其表面温度一定越高

A.练习方式、练习条件或环境的变换上。
B.工程量是计算和统计通信工程建设过程中
C.若项目的（ ）大于或等于零，从经济效益看该项目可以被接受。
D.交感神经节前纤维释放的神经递质为Ach。