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Computer Network

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- 1. Error Detection and Correction
- 2. Coding: Redundancy is achieved through various coding Scheme. The sender adds the redundancy bit to the original message and create relationship. The receiver checks the relationship b/w two sets of bits to detect (or) correct the errors. Robustness of the process are important factors in any coding scheme.
- 3. The Structure of encoder and decoder
- 4. 2 categories Block coding 2. Convolution coding-more complex(less use) 1.
- 5. Modular Arithmetic Use only limited range of integers. We, define upper limit, called a ,modulus N. Then use only the integers 0 to N-1. This is modulo-N arithmetic.
- 6. Modulo-2 Arithmetic Here modulus N is 2. we can use only 0 and 1. operation in this arithmetic are very simple. The addition and subtraction give the same results. Here, we use XOR operation for both the add and sub. The result of an XOR operation is 0(if both the bits are same. The result is 1 if the any of the two bit is different.)
- 7. Block coding Divide the message into blocks, each of k bits, called datawords. Then add r redundant bit to make length n=k+r The resulting n-bit blocks are called codewords.
- 8. Error Detection The receiver can detect a change in the original codeword. by 1. The receiver has a list of valid codewords. 2. The original codeword has changed to an invalid one.
- 9. Error Detection
- 10. Example code word
- 11. Error Correction

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