assignmentutor-lab™ 为您的留学生涯保驾护航 在代写计算机网络概论Introduction to Computer Networking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网络概论Introduction to Computer Networking方面经验极为丰富，各种代写计算机网络概论Introduction to Computer Networking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|计算机网络概论代写Introduction to Computer Networking代考|Error Control Methods

Signal impairment can lead to errors in bit transmission. Data error rates are usually defined in terms of a ratio. For example, 1/1000 means that for every 1000 bits, one bit will be transmitted in error. This can also be represented as an error rate of $10^{-3}$.

Finding out whether errors have occurred (error detection) and correcting these errors (error correction) can be important because of the potential cost of data error. As a simple example of this, consider the following: A figure representing a bank balance is sent over a network. An error occurs in only one digit of this balance, but that is enough to make the received figure differ by thousands of euros from what it should be.

All error control methods involve adding extra, redundant bits to the message that is to be transmitted. We can classify these methods into automatic repeat request (ARQ) and forward error correction (FEC).

电子工程代写|计算机网络概论代写Introduction to Computer Networking代考|Automatic Repeat Request

The idea behind $\mathrm{ARQ}$ is for the transmitter to add enough redundant bits to the block of data that it is sending out to make it possible for the receiver to tell if there and so it asks for a retransmission of the data block that contains the error.

Parity (see Section 2.2.1) could provide a simple form of ARQ. A parity failure would provoke the receiver into asking the sender to resend the data block in question. However, if there were more than one error, such a simple system might fail to detect any error. For example, let us imagine that even parity is in use. The data that the sending computer transmits is 1010111 . To give even parity it adds a 1 bit, making the message 10101111. During transmission, two bit errors occur and the bits get changed to 00100111. But when the receiver checks for parity, it finds an even number of 1 bits and is satisfied that there have been no errors. For this reason, simple parity is not used for ARQ in practice.

A more satisfactory alternative to simple parity is the checksum method. Here, the sending computer adds up all the data bytes of the message to be transmitted. The resulting figure, the checksum, is transmitted along with the data. At the other end, the receiver performs the same operation on the data and compares the checksum it has calculated with the one that the sending computer included in the message. If these two checksums are not the same, the receiving computer concludes that there has been an error during transmission and asks for a retransmission. The size of checksums is kept within reasonable bounds by, for example, the sending device throwing away any carries beyond 8 bits. One protocol that uses checksums is TCP (although the calculation involved is slightly more sophisticated than that described here). The TCP protocol is explained in Chapter 6 .

计算机网络概论代考

电子工程代写|计算机网络概论代写Introduction to Computer Networking代考|Automatic Repeat Request

Parity（参见第 2.2.1 节）可以提供一种简单的 ARQ 形式。奇偶校验失败会促使接收方要求发送方重新发送有问题的数据块。但是，如果有多个错误，那么这样一个简单的系统可能无法检测到任何错误。例如，让我们假设正在使用偶校验。发送计算机传输的数据是 1010111 。为了给偶校验，它添加了一个 1 位，使消息为 10101111。在传输过程中，发生了两个位错误，位变为 00100111。但是当接收器检查奇偶性时，它发现偶数个 1 位并满足没有错误。由于这个原因，ARQ 在实践中不使用简单奇偶校验。

有限元方法代写

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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。

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