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- Data Communications and Networking - 5th Edition
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- Data Communications and Networking - 5th Edition

Title: Data Communications and Networking, 5th Edition Author: Behrouz A. Forouzan Length: pages. Edition: 5. Language: English. Notes. This book is designed to help students understand the basics of data communications and networking in general and the protocols used. AND. NETWORKING. Fourth Edition. Behrouz A. Forouzan. DeAnza College with . Sophia Chung Fegan. #. Higher Education. Boston Burr Ridge, IL Dubuque.

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Don't forget to check out the Online Learning Center, freezovralomi.cf for additional resources! Instructors and students using Data Communications. McGraw-Hill Forouzan Networking Series. Titles by Behrouz A. Forouzan: Data Communications and Networking. TCPflP Protocol Suite. Local Area Networks. data communication and networking by behrouz a. forouzan 4th freezovralomi.cf - Ebook download as PDF File .pdf) or read book online. data communication.

This preview shows page 1 - 11 out of 11 pages. Subscribe to view the full document. For most applications, a system must guarantee that the data received are identical to the data transmitted. Any time data are transmitted from one node to the next, they can become corrupted in passage. Many factors can alter one or more bits of a message. Some applications require a mechanism for detecting and correcting errors. Data can be corrupted during transmission. Some applications require that errors be detected and corrected. Some applications can tolerate a small level of error. For example, random errors in audio or video transmissions may be tolerable, but when we transfer text, we expect a very high level of accuracy. This interference can change the shape of the signal. In a single—bit error, a 0 is changed to a l or a 1 to a 0. In a burst error, multiple bits are changed. Single-Bit Error The term single-bit error means that only 1 bit of a given data unit such as a byte, character, or packet is changed from 1 to 0 or from O to l.

Correction by retransmission is a technique in which the receiver detects the occurrence of an error and asks the sender to resend the message. Resending is repeated until a message arrives that the receiver believes is error-free usually, not all errors can be detected. Coding Redundancy is achieved through various coding schemes.

The sender adds redundant bits through a process that creates a relationship between the redundant bits and the actual data bits. The receiver checks the relationships between the two sets of bits to detect or correct the errors. The ratio of redundant bits to the data bits and the robust- ness of the process are important factors in any coding scheme.

Figure shows the general idea of coding. We can divide coding schemes into two broad categories: block coding and convo- lution coding. In this book, we concentrate on block coding; convolution coding is more complex and beyond the scope of this book. Our intent here is not to delve deeply into the mathematics of this topic; we present just enough information to provide a background to materials discussed in this chapter.

In modular arithmetic, we use only a limited range of integers. We then use only the integers 0 to N — l, inclusive. This is modulo—N arithmetic. For example, if the modulus is 12, we use only the integers 0 to 11, inclusive. An example of modulo arithmetic is our clock system. It is based on modulo arithmetic, substituting the number 12 for 0. In a modulo—N system, if a number is greater than N, it is divided by N and the remainder is the result. If it is neg- ative, as many Ns as needed are added to make it positive.

Consider our clock system again. If we start a job at 11 AM.

In modulo-N arithmetic, we use only the integers in the range 0 to N —— 1, inclusive. Addition and subtraction in modulo arithmetic are simple. There is no carry when you add two digits in a column. There is no carry when you subtract one digit from another in a column.

Module-2 Arithmetic Of particular interest is modulo-2 arithmetic. In this arithmetic, the modulus N is 2. We can use only 0 and 1. Operations in this arithmetic are very simple. The following shows how we can add or subtract 2 bits. The result of an XOR operation is 0 if two bits are the same; the result is 1 if two bits are different. Two bits are the same, the result is 0. Two bits are different, the result is 1. The principle is the same; we use numbers between 0 and N — 1. If the modulus is not 2, addition and subtraction are distinct.

If we get a negative result, we add enough multiples of N to make it positive. The resulting n—bit blocks are called codewords. How the extra r bits is chosen or calculated is something we will discuss later.

For the moment, it is important to know that we have a set of datawords, each of size It, and a set of codewords, each of size of n. With k bits, we can create a com- bination of 2" datawords; with 11 bits, we can create a combination of 2" codewords. The block coding process is one-to-one; the same dataword is always encoded as the same codeword.

We call these codewords invalid or illegal. We saw that 16 out of 32 codewords are used [or message transfer and the rest are either used for other purposes or unused. Error Detection How can errors be detected by using block coding? If the following two conditions are met, the receiver can detect a change in the original codeword.

The original codeword has changed to an invalid one. Each codeword sent to the receiver may change during transmission. If the received codeword is the same as one of the valid code— words, the word is accepted; the corresponding dataword is extracted for use. If the received codeword is not valid, it is discarded.

Coding Redundancy is achieved through various coding schemes. The sender adds redundant bits through a process that creates a relationship between the redundant bits and the actual data bits. The receiver checks the relationships between the two sets of bits to detect or correct the errors.

The ratio of redundant bits to the data bits and the robust- ness of the process are important factors in any coding scheme. Figure shows the general idea of coding.

We can divide coding schemes into two broad categories: block coding and convo- lution coding. In this book, we concentrate on block coding; convolution coding is more complex and beyond the scope of this book. Our intent here is not to delve deeply into the mathematics of this topic; we present just enough information to provide a background to materials discussed in this chapter.

In modular arithmetic, we use only a limited range of integers. We then use only the integers 0 to N — l, inclusive.

This is modulo—N arithmetic. For example, if the modulus is 12, we use only the integers 0 to 11, inclusive. An example of modulo arithmetic is our clock system. It is based on modulo arithmetic, substituting the number 12 for 0.

In a modulo—N system, if a number is greater than N, it is divided by N and the remainder is the result. If it is neg- ative, as many Ns as needed are added to make it positive. Consider our clock system again. If we start a job at 11 AM. In modulo-N arithmetic, we use only the integers in the range 0 to N —— 1, inclusive. Addition and subtraction in modulo arithmetic are simple.

There is no carry when you add two digits in a column. There is no carry when you subtract one digit from another in a column.

Module-2 Arithmetic Of particular interest is modulo-2 arithmetic. In this arithmetic, the modulus N is 2. We can use only 0 and 1. Operations in this arithmetic are very simple. The following shows how we can add or subtract 2 bits. The result of an XOR operation is 0 if two bits are the same; the result is 1 if two bits are different. Two bits are the same, the result is 0.

Two bits are different, the result is 1. The principle is the same; we use numbers between 0 and N — 1. If the modulus is not 2, addition and subtraction are distinct.

If we get a negative result, we add enough multiples of N to make it positive. The resulting n—bit blocks are called codewords. How the extra r bits is chosen or calculated is something we will discuss later. For the moment, it is important to know that we have a set of datawords, each of size It, and a set of codewords, each of size of n. With k bits, we can create a com- bination of 2" datawords; with 11 bits, we can create a combination of 2" codewords.

The block coding process is one-to-one; the same dataword is always encoded as the same codeword.

We call these codewords invalid or illegal. We saw that 16 out of 32 codewords are used [or message transfer and the rest are either used for other purposes or unused. Error Detection How can errors be detected by using block coding? If the following two conditions are met, the receiver can detect a change in the original codeword. The original codeword has changed to an invalid one. Each codeword sent to the receiver may change during transmission. If the received codeword is the same as one of the valid code— words, the word is accepted; the corresponding dataword is extracted for use.

If the received codeword is not valid, it is discarded. However, if the codeword is corrupted during trans— mission but the received word still matches a valid codeword, the error remains undetected.

This type of coding can detect only single errors. Transport layer is covered in chapter 23 and It starts with describing the meaning of node-to-node, host-to-host and process-to-process communication. Flow and congestion control have been revisited with updates when compared with the flow control mechanism of DLL. They also have been covered in a logical manner.

I enjoyed reading most of the topics covered in the book Dr. Ravinder Nath Rajotiya.