## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|CS155

statistics-lab™ 为您的留学生涯保驾护航 在代写计算机及网络安全Computer and Network Security方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写计算机及网络安全Computer and Network Security方面经验极为丰富，各种代写计算机及网络安全Computer and Network Security相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Multiplexing of Transmission Signals

Quite often during the transmission of data over a network medium, the volume of transmitted data may far exceed the capacity of the medium. Whenever this happens, it may be possible to make multiple signal carriers share a transmission medium. This is referred to as multiplexing. There are two ways in which multiplexing can be achieved: time-division multiplexing (TMD) and frequency- division multiplexing (FDM).

In FDM, all data channels are first converted to analog form. Since a number of signals can be carried on a carrier, each analog signal is then modulated by a separate and different carrier frequency, and this makes their recovery possible during the demultiplexing process. The frequencies are then bundled on the carrier. At the receiving end, the demultiplexer can select the desired carrier signal and use it to extract the data signal for that channel in such a way that the bandwidths do not overlap. FDM has the advantage of supporting full-duplex communication.

TDM, on the other hand, works by dividing the channel into time slots that are allocated to the data streams before they are transmitted. At both ends of the transmission, if the sender and receiver agree on the time-slot assignments, then the receiver can easily recover and reconstruct the original data streams. Thus, multiple digital signals can be carried on one carrier by interleaving portions of each signal in time.

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Wired Transmission Media

Wired transmission media are used in fixed networks physically connecting every network element. There are different types of physical media, the most common of which are copper wires, twisted pairs, coaxial cables, and optical fibers.

Copper Wires have been traditionally used in communication because of their low resistance to electrical currents that allows signals to travel even further. However, copper wires suffer interference from electromagnetic energy in the environment, and thus they must always be insulated.

Twisted Pair is a pair of wires consisting of one insulated copper wire wrapped around the other, forming frequent and numerous twists. Together, the twisted, insulated copper wires act as a full-duplex communication link. The twisting of the wires reduces the sensitivity of the cable to electromagnetic interference and also reduces the radiation of radio frequency noises that may interfere with nearby cables and electronic components. The capacity of the transmitting medium can be increased by bundling more than one pair of the twisted wires together in a protective coating. Because twisted pairs were far less expensive, easy to install, and had a high quality of voice data, they were widely used in telephone networks. However, because they are poor in upward scalability in transmission rate, distance, and bandwidth in LANs, twisted pair technology has been abandoned in favor of other technologies. Figure $1.8$ shows a twisted pair.

Coaxial Cables are dual-conductor cables with a shared inner conductor in the core of the cable protected by an insulation layer and the outer conductor surrounding the insulation. These cables are called coaxial because they share the inner conductor. The inner core conductor is usually made of solid copper wire but, at times, can also be made up of stranded wire. The outer conductor, which is made of braided wires, but sometimes made of metallic foil or both, commonly forms a protective tube around the inner conductor. This outer conductor is also further protected by annther outer enating called the sheath. Figure $1.9$ shows a enaxial eable. Coaxial cables are commonly used in television transmissions. Unlike twisted pairs, coaxial cables can be used over long distances. There are two types of coaxial cables: thinnet, a light and flexible cabling medium that is inexpensive and easy to install, and the thicknet, which is thicker and harder to break and can carry more signals for a longer distance than thinnet.

## 广义线性模型代考

statistics-lab作为专业的留学生服务机构，多年来已为美国、英国、加拿大、澳洲等留学热门地的学生提供专业的学术服务，包括但不限于Essay代写，Assignment代写，Dissertation代写，Report代写，小组作业代写，Proposal代写，Paper代写，Presentation代写，计算机作业代写，论文修改和润色，网课代做，exam代考等等。写作范围涵盖高中，本科，研究生等海外留学全阶段，辐射金融，经济学，会计学，审计学，管理学等全球99%专业科目。写作团队既有专业英语母语作者，也有海外名校硕博留学生，每位写作老师都拥有过硬的语言能力，专业的学科背景和学术写作经验。我们承诺100%原创，100%专业，100%准时，100%满意。

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|ICCWS2022

statistics-lab™ 为您的留学生涯保驾护航 在代写计算机及网络安全Computer and Network Security方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写计算机及网络安全Computer and Network Security方面经验极为丰富，各种代写计算机及网络安全Computer and Network Security相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Analog Encoding of Digital Data

Recall that digital information is in the form of $1 \mathrm{~s}$ and $0 \mathrm{~s}$. To send this information over some analog medium such as the telephone line, for example, which has limited bandwidth, digital data needs to be encoded using modulation and demodulation to produce analog signals. The encoding uses a continuous oscillating wave, usually a sine wave, with a constant frequency signal called a carrier signal.

The carrier has three modulation characteristics: amplitude, frequency, and phase shift. The scheme then uses a modem, a modulation-demodulation pair, to modulate and demodulate the data signal based on any one of the three carrier characteristics or a combination. The resulting wave is between a range of frequencies on both sides of the carrier, as shown below [1]:

• Amplitude modulation represents each binary value by a different amplitude of the carrier frequency. The absence of or low carrier frequency may represent a 0 , and any other frequency then represents a 1 . However, this is a rather inefficient modulation technique and is therefore used only at low frequencies up to 1200 bps in voice grade lines.
• Frequency modulation also represents the two binary values by two different frequencies close to the frequency of the underlying carrier. Higher frequencies represent a 1 , and low frequencies represent a 0 . The scheme is less susceptible to errors.
• Phase shift modulation changes the timing of the carrier wave, shifting the carrier phase to encode the data. A 1 is encoded as a change in phase by $180^{\circ}$, and a 0 may be encoded as a 0 change in phase of a carrier signal. This is the most efficient scheme of the three, and it can reach a transmission rate of up to 9600 bps.

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Digital Encoding of Digital Data

In this encoding scheme, which offers the most common and easiest way to transmit digital signals, two binary digits are used to represent two different voltages. Within a computer, these voltages are commonly 0 and 5 volts. Another procedure uses two representation codes: nonreturn to zero level $(N R Z-L)$, in which negative voltage represents binary one and positive voltage represents binary zero, and nonreturn to zero, invert on ones (NRZ-I). See Figs. $1.6$ and $1.7$ for an example of these two codes. In NRZ-L, whenever a 1 occurs, a transition from one voltage level to another is used to signal the information. One problem with NRZ signaling techniques is the requirement of a perfect synchronization between the receiver and transmitter clocks. This is, however, reduced by sending a separate clock signal. There are yet other representations such as the Manchester and differential Manchester, which encode clock information along with the data.

One may wonder, why go through the hassle of digital encoding and transmission? There are several advantages over its cousin, analog encoding. These include the following:

• Plummeting costs of digital circuitry
• More efficient integration of voice, video, text, and images
• Reduction of noise and other signal impairment because of the use of repeaters
• The capacity of channels is utilized best with digital techniques
• Better encryption and hence better security than in analog transmission

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Analog Encoding of Digital Data

• 幅度调制通过载波频率的不同幅度来表示每个二进制值。载波频率的缺失或低可以表示 0 ，而任何其他频率则表示 1 。然而，这是一种相当低效的调制技术，因此仅用于语音等级线路中高达 1200 bps 的低频。
• 频率调制还通过接近底层载波频率的两个不同频率来表示两个二进制值。高频代表 1 ，低频代表 0 。该方案不易出错。
• 相移调制改变载波的时序，移动载波相位以对数据进行编码。A 1 被编码为相位变化180∘，并且0可以被编码为载波信号的相位变化0。这是三者中效率最高的方案，它可以达到高达 9600 bps 的传输速率。

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Digital Encoding of Digital Data

• 数字电路成本直线下降
• 更高效的语音、视频、文本和图像的集成
• 由于使用中继器，减少了噪音和其他信号损伤
• 数字技术最好地利用信道容量
• 比模拟传输更好的加密，因此更好的安全性

## 广义线性模型代考

statistics-lab作为专业的留学生服务机构，多年来已为美国、英国、加拿大、澳洲等留学热门地的学生提供专业的学术服务，包括但不限于Essay代写，Assignment代写，Dissertation代写，Report代写，小组作业代写，Proposal代写，Paper代写，Presentation代写，计算机作业代写，论文修改和润色，网课代做，exam代考等等。写作范围涵盖高中，本科，研究生等海外留学全阶段，辐射金融，经济学，会计学，审计学，管理学等全球99%专业科目。写作团队既有专业英语母语作者，也有海外名校硕博留学生，每位写作老师都拥有过硬的语言能力，专业的学科背景和学术写作经验。我们承诺100%原创，100%专业，100%准时，100%满意。

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|ClS654

statistics-lab™ 为您的留学生涯保驾护航 在代写计算机及网络安全Computer and Network Security方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写计算机及网络安全Computer and Network Security方面经验极为丰富，各种代写计算机及网络安全Computer and Network Security相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Computer Network Models

There are several configuration models that form a computer network. The most common of these are the centralized and distributed models. In a centralized model, several computers and devices are interconnected and can talk to each other. However, there is only one central computer, called the master, through which all correspondence must take place. Dependent computers, called surrogates, may have reduced local resources, such as memory, and sharable global resources are controlled by the master at the center. Unlike the centralized model, however, the distributed network consists of loosely coupled computers interconnected by a communication network consisting of connecting elements and communication channels. The computers themselves may own their resources locally or may request resources from a remote computer. These computers are known by a string of names, including host, client, or node. If a host has resources that other hosts need, then that host is known as a server. Communication and sharing of resources are not controlled by the central computer but are arranged between any two communicating elements in the network. Figures $1.2$ and $1.3$ show a centralized network model and a distributed network model, respectively.

A computer network with two or more computers or clusters of network and their resources connected by a communication medium sharing communication protocols and confined in a small geographic area, such as a building floor, a building, or a few adjacent buildings, is called a local area network (LAN). The advantage of a LAN is that all network elements are close together, and thus the communication links maintain a higher speed of data movement. Also, because of the proximity of the communicating elements, high-cost and high-quality communicating elements can be used to deliver better service and high reliability. Figure $1.4$ shows a LAN.

## 电子工程代写|计算机及网络安全代写Computer and Network Security代考|Transmission Technology

The media through which information has to be transmitted determine the signal to be used. Some media permit only analog signals. Some allow both analog and digital. Therefore, depending on the media type involved and other considerations, the input data can be repreesenteed as either a digital or an analog signal. In an analog format, data is sent as continuous electromagnetic waves on an interval representing things such as voice and video and propagated over a variety of media that may include copper wires, a twisted coaxial pair or cable, fiber optics, or wireless. We will discuss these media later in the chapter. In a digital format, on the other hand, data is sent as a digital signal, a sequencé of voltage pulses that can be reepreesenteed as a stream of binary bits. Both analog and digital data can be propagated and oftentimes represented as either analog or digital.

Transmission itself is the propagation and processing of data signals between network elements. The concept of representation of data for transmission, either as an analog or a digital signal, is called an encoding scheme. Encoded data is then transmitted over a suitable transmission medium that connects all network elements. There are two encoding schemes, analog and digital. Analog encoding propagates analog signals representing analog data such as sound waves and voice data. Digital encoding, on the other hand, propagates digital signals representing either an analog or a digital signal representing digital data of binary streams by two voltage levels. Since our interest in this book is in digital networks, we will focus on the encoding of digital data.

## 广义线性模型代考

statistics-lab作为专业的留学生服务机构，多年来已为美国、英国、加拿大、澳洲等留学热门地的学生提供专业的学术服务，包括但不限于Essay代写，Assignment代写，Dissertation代写，Report代写，小组作业代写，Proposal代写，Paper代写，Presentation代写，计算机作业代写，论文修改和润色，网课代做，exam代考等等。写作范围涵盖高中，本科，研究生等海外留学全阶段，辐射金融，经济学，会计学，审计学，管理学等全球99%专业科目。写作团队既有专业英语母语作者，也有海外名校硕博留学生，每位写作老师都拥有过硬的语言能力，专业的学科背景和学术写作经验。我们承诺100%原创，100%专业，100%准时，100%满意。

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。