- Data Communication and Networking by Behrouz A. Forouzan 4th Edition.pdf
- Data Communications And Networking Behrouz A. Forouzan.fourth Edition[ A 4]
- Documents Similar To data communication and networking by behrouz a. forouzan 4th edition.pdf
- data communication and networking by behrouz a. forouzan 4th edition.pdf
DATA. COMMUNICATIONS. AND. NETWORKING. Fourth Edition. Behrouz A. Forouzan. DeAnza College with. Sophia Chung Fegan. #. Higher Education. Don't forget to check out the Online Learning Center, pocboarentivi.gq for additional resources! Instructors and students using Data Communications. data communication and networking by behrouz a. forouzan 4th pocboarentivi.gq - Ebook download as PDF File .pdf) or read book online. data communication.
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Instructors and students using Data Communications and Networking, Fourth Edition by Behrouz A. Forouzan will find a wide variety of resources available at. In Chapter 11 we discussed data link control, a mechanism which provides a link with reliable communication. In the protocols we described, we assumed that. Using a bottom-up approach, Data Communications and Networking presents this Now in its Fourth Edition, this textbook brings the beginning student right to the forefront of the A. McGraw-Hill Forouzan Networking Series; B. Preface; 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.
Data Communication and Networking by Behrouz A. Forouzan 4th Edition.pdf
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.
TWO or more errors may remain undetected. Example Table Later, we will see how to derive a codeword from a dataword.
Data Communications And Networking Behrouz A. Forouzan.fourth Edition[ A 4]
Consider the following cases: 1. The receiver receives It is a valid codeword. The receiver extracts the dataword 01 from it.
The codeword is corrupted during transmission, and is received the leftmost bit is cor- rupted. This is not a valid codeword and is discarded.
Documents Similar To data communication and networking by behrouz a. forouzan 4th edition.pdf
The codeword is corrupted during transmission, and is received the right two bits are corrupted. This is a valid codeword. The receiver incorrectly extracts the dataword Two corrupted bits have made the error undetectable.
An error-detecting code can detect only the types of errors for which it is designed; other types of errors may remain undetected. We can say that we need more redundant bits for error correction than for error detection. We can see that the idea is the same as error detection but the checker functions are much more complex.
We add 3 redundant bits to the 2-bit dataword to make 5-bit codewords. Again, later we will show how we chose the redundant bits.
For the moment let us concentrate on the error correction concept.
Assume the dataword is The sender consults the table or uses an algorithm to create the codeword The codeword is corrupted during transmission, and is received error in the second bit from the right. This means an error has occurred. Detection must come before correction. The receiver, assuming that there is only 1 bit corrupted, uses the following strategy to guess the correct dataword.
By the same reasoning, the original codeword cannot be the third or fourth one in the table. The original codeword must be the second one in the table because this is the only one that differs from the received codeWOrd by 1 bit.
Hamming Distance One of the central concepts in coding for error control is the idea of the Hamming dis— tance.
The Hamming distance between two words of the same size is the number of differences between the corresponding bits.
data communication and networking by behrouz a. forouzan 4th edition.pdf
We show the Hamming distance between two words x and y as d x, y. The Hamming distance can easily be found if we apply the XOR operation EB on the two words and count the number of is in the result. Note that the Hamming distance is a value greater than zero.
The Hamming distance between two words is the number of differences between corresponding bits.
The Hamming distance d , is 2 because ED is two Is. The Hamming distance d , is 3 because :0 is three 1s. Minimum Hamming Distance Although the concept of the Hamming distance is the central point in dealing with error detection and correction codes, the measurement that is used for designing a code is the minimum Hamming distance.
In a set of words, the minimum Hamming distance is the smallest Hamming distance between all possible pairs. The minimum Hamming distance is the smallest Hamming distance between all possible pairs in a set of words.
Hamming Distance and Error Before we explore the criteria for error detection or correction, let us discuss the relationship between the Hamming distance and errors occurring during transmission. When a codeword is corrupted during transmission, the Hamming distance between the sent and received code- words is the number of bits affected by the error. In other words, the Hamming distance between the received codeword and the sent codeword is the number of bits that are corrupted during transmission.
If 3 errors occur during transmission, the Hamming distance between the sent codeword and received codeword is s. The error will be detected.
This code guarantees detection of only a single error. For example, if the third codeword is sent and one error occurs, the received codeword does not match any valid codeword. If two errors occur, however, the received codeword may match a valid codeword and the errors are not detected.
This code can detect up to two errors. Again, we see that when any of the valid codewords is sent, two errors create a codeword which is not in the table of valid codewords The receiver cannot be fooled.
However, some combina- tions of three errors change a valid codeword to another valid codeword. The receiver accepts the received codeword and the errors are undetected. We can look at this geometrically. Let us assume that the sent codeword x is at the center of a circle with radius 3. All other received codewords that are created by 1 to s errors are points inside the circle or on the perimeter of the circle. No need to wait for office hours or assignments to be graded to find out where you took a wrong turn.
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As a Chegg Study subscriber, you can view available interactive solutions manuals for each of your classes for one low monthly price. Why download extra books when you can get all the homework help you need in one place?The receiver incorrectly extracts the dataword Data Communication and Networking by Behrouz A. The Hamming distance between two words of the same size is the number of differences between the corresponding bits.
The principle is the same; we use numbers between 0 and N — 1.
Three Parameters Before we continue with our discussion, we need to mention that any coding scheme needs to have at least three parameters: You bet! Why download extra books when you can get all the homework help you need in one place? In error correction, we need to know the exact number of bits that are corrupted and more importantly, their location in the message.
Multiplexing and Spreading 7.
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