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Cnlab 1

The document outlines various error detection and correction techniques in computer networks, including Hamming Code, Cyclic Redundancy Check (CRC), 2-D Parity Check, and Checksum. Each section includes an aim, algorithm, and a corresponding C++ program that demonstrates the implementation of the technique. The programs cover data input, error introduction, and verification of the data integrity.

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2 views29 pages

Cnlab 1

The document outlines various error detection and correction techniques in computer networks, including Hamming Code, Cyclic Redundancy Check (CRC), 2-D Parity Check, and Checksum. Each section includes an aim, algorithm, and a corresponding C++ program that demonstrates the implementation of the technique. The programs cover data input, error introduction, and verification of the data integrity.

Uploaded by

ekanshk7
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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COMPUTER NETWORKS LAB DA-1

23BCE0414
EKANSH KUMAR
1.HAMMING CODE:
AIM AND ALGORITHM:
PROGRAM:

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <random>

using namespace std;

random_device rd;
mt19937 gen(rd());

void printWord(const vector<int>& word) {


for (int bit : word) cout << bit;
cout << endl;
}

void printRevWord(const vector<int>& word) {


for (int i = word.size() - 1; i >= 0; --i) cout << word[i];
cout << endl;
}

int getCodewordLength(int n) {
int r = 0;
while ((1 << r) < (n + r + 1)) r++;
return n + r;
}

bool isPowerOfTwo(int n) {
return n > 0 && (n & (n - 1)) == 0;
}

int findParity(const vector<int>& codeWord, int pos, int parityType) {


int parity = (parityType == 1) ? 1 : 0;
for (int i = 1; i <= codeWord.size(); ++i) {
if (i & pos) {
parity ^= codeWord[i - 1];
}
}
return parity;
}

void generateHammingCode(vector<int>& dataWord, vector<int>&


codeWord, int parityType) {
int n = dataWord.size();
int k = codeWord.size();
int j = n - 1;

for (int i = 1; i <= k; ++i) {


if (isPowerOfTwo(i))
codeWord[i - 1] = 0;
else
codeWord[i - 1] = dataWord[j--];
}

cout << "Parity Bits:\n";


for (int i = 0; i < k - n; ++i) {
int pow = 1 << i;
int parity = findParity(codeWord, pow, parityType);
codeWord[pow - 1] = parity;
cout << "R" << pow << ": " << parity << endl;
}

cout << "Codeword: ";


printRevWord(codeWord);
cout << endl;
}

int convertToDecimal(const vector<int>& word) {


int dec = 0;
for (int i = 0; i < word.size(); ++i)
dec += word[i] * (1 << i);
return dec;
}

void verifyCodeword(vector<int>& codeWord, int r, int parityType) {


vector<int> parityWord;
cout << "Parity Bits:\n";
for (int i = 0; i < r; ++i) {
int pow = 1 << i;
int parity = findParity(codeWord, pow, parityType);
parityWord.push_back(parity);
cout << "C" << pow << ": " << parity << endl;
}

int errorPosition = convertToDecimal(parityWord);


cout << "Result of verification logic: ";

if (errorPosition == 0) {
cout << "No error detected.\n";
} else {
cout << "Error in bit position " << errorPosition << endl;
codeWord[errorPosition - 1] ^= 1;
cout << "Codeword after correction: ";
printRevWord(codeWord);
}

vector<int> data;
for (int i = 1; i <= codeWord.size(); ++i) {
if (!isPowerOfTwo(i))
data.push_back(codeWord[i - 1]);
}

cout << "Dataword: ";


printRevWord(data);
}

int main() {
int n, parityType, hasError, manual, errorBit;

cout << "\nEnter Length of Data Word: ";


cin >> n;

cout << "Input the Data Word: ";


vector<int> dataWord(n);
for (int& bit : dataWord) cin >> bit;

int codewordLength = getCodewordLength(n);


vector<int> codeWord(codewordLength, 0);

cout << "Input Parity (Odd-1 / Even-0): ";


cin >> parityType;

cout << "Enter choice (Error-1 / Errorless Transmission-0): ";


cin >> hasError;

if (hasError == 1) {
cout << "Introduce Error (Manual-1 / Random-0): ";
cin >> manual;
if (manual == 1) {
cout << "Enter Error Bit: ";
cin >> errorBit;
} else if (manual == 0) {
errorBit = uniform_int_distribution<int>(1, codewordLength)(gen);
} else {
cout << "Invalid choice\n";
return 0;
}
}

cout << "\nSender Side:\n";


cout << "Given Data Word: ";
printRevWord(dataWord);

generateHammingCode(dataWord, codeWord, parityType);

cout << "Receiver Side:\n";

if (hasError == 1) {
if (manual == 1)
cout << "Error introduced at Bit " << errorBit << " manually.\n";
else
cout << "Error introduced at Bit " << errorBit << " randomly.\n";

codeWord[errorBit - 1] ^= 1;
cout << "Received Codeword with Error: ";
printRevWord(codeWord);
} else {
cout << "No Error introduced.\n";
}

verifyCodeword(codeWord, codewordLength - n, parityType);

return 0;
}

EXECUTION:
2.CYCLIC REDUNDANCY CHECK-(CRC):
AIM AND ALGORITHM:
PROGRAM:

#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
using namespace std;

string xorStrings(string a, string b) {


string result = "";
for (int i = 1; i < b.length(); i++)
result += (a[i] == b[i]) ? '0' : '1';
return result;
}

string mod2div(string dividend, string divisor) {


int pick = divisor.length();
string temp = dividend.substr(0, pick);
while (pick < dividend.length()) {
if (temp[0] == '1')
temp = xorStrings(divisor, temp) + dividend[pick];
else
temp = xorStrings(string(pick, '0'), temp) + dividend[pick];
pick++;
}
if (temp[0] == '1')
temp = xorStrings(divisor, temp);
else
temp = xorStrings(string(pick, '0'), temp);
return temp;
}
string generateCodeword(string data, string key) {
string appended = data + string(key.length() - 1, '0');
string remainder = mod2div(appended, key);
return data + remainder;
}

string introduceError(string codeword, int type) {


string corrupted = codeword;
int len = corrupted.length();

if (type == 1) {
int pos = rand() % len;
corrupted[pos] = (corrupted[pos] == '0') ? '1' : '0';
cout << "Single-bit error introduced at position: " << pos << endl;
}
else if (type == 2) {
int count = 3;
cout << "Introducing " << count << " random bit flips (odd)\n";
for (int i = 0; i < count; i++) {
int pos = rand() % len;
corrupted[pos] = (corrupted[pos] == '0') ? '1' : '0';
}
}
else if (type == 3) {
int burstLen = 5;
int start = rand() % (len - burstLen);
cout << "Burst error introduced from position " << start
<< " to " << start + burstLen - 1 << endl;
for (int i = 0; i < burstLen; i++) {
corrupted[start + i] = (corrupted[start + i] == '0') ? '1' : '0';
}
}
return corrupted;
}

int main() {
srand(time(0));
string data, key;

cout << "Input 16-bit dataword: ";


cin >> data;
if (data.size() != 16) {
cout << "Invalid input. Dataword must be 16 bits.\n";
return 1;
}

cout << "Input generator polynomial (e.g., 100000111): ";


cin >> key;
if (key.size() < 3) {
cout << "Invalid polynomial. Try again.\n";
return 1;
}
string codeword = generateCodeword(data, key);
cout << "\nSender Side:\nDataword: " << data << "\nGenerator
Polynomial: " << key
<< "\nCodeword (Data + CRC bits): " << codeword << endl;

cout << "\nTransmission Mode (0: Errorless | 1: Single-bit error | 2: Odd-


bit error | 3: Burst error): ";
int choice;
cin >> choice;

string received;
if (choice == 0) {
received = codeword;
cout << "No error introduced.\n";
} else {
received = introduceError(codeword, choice);
cout << "Received Codeword: " << received << endl;
}

cout << "\nReceiver Side:\nReceived Codeword: " << received << endl;
string remainder = mod2div(received, key);

if (remainder.find('1') == string::npos)
cout << "Result of verification logic: ✅ No error detected (Remainder
= 0)\n";
else
cout << "Result of verification logic: ❌ Error detected (Remainder = "
<< remainder << ")\n";

return 0;
}

EXECUTION:

3.2-D PARITY CHECK:


AIM AND ALGORITHM:
PROGRAM:
#include <iostream>
#include <vector>
#include <ctime>
#include <cstdlib>
using namespace std;

typedef vector<vector<int> > Matrix;

Matrix getDataMatrix(string data16) {


Matrix mat(4, vector<int>(4));
for (int i = 0; i < 16; i++) {
mat[i / 4][i % 4] = data16[i] - '0';
}
return mat;
}

void addParity(Matrix& mat) {


for (int i = 0; i < 4; i++) {
int rowParity = 0;
for (int j = 0; j < 4; j++) rowParity ^= mat[i][j];
mat[i].push_back(rowParity);
}

vector<int> colParity;
for (int j = 0; j < 5; j++) {
int p = 0;
for (int i = 0; i < 4; i++) p ^= mat[i][j];
colParity.push_back(p);
}
mat.push_back(colParity);
}

void printMatrix(Matrix mat, string label) {


cout << label << endl;
for (int i = 0; i < mat.size(); i++) {
for (int j = 0; j < mat[0].size(); j++)
cout << mat[i][j] << " ";
cout << endl;
}
}

Matrix simulateError(Matrix mat, int type) {


if (type == 0) return mat;

int r1, r2, r3, c1, c2, c3;


switch (type) {
case 1: // single bit error
r1 = rand() % 4;
c1 = rand() % 4;
mat[r1][c1] ^= 1;
break;
case 2: // 2-bit error in same row
r1 = rand() % 4;
c1 = rand() % 4;
do { c2 = rand() % 4; } while (c2 == c1);
mat[r1][c1] ^= 1;
mat[r1][c2] ^= 1;
break;
case 3: // three bit errors in different rows/columns
r1 = rand() % 4; c1 = rand() % 4;
r2 = (r1 + 1) % 4; c2 = (c1 + 1) % 4;
r3 = (r2 + 1) % 4; c3 = (c2 + 1) % 4;
mat[r1][c1] ^= 1;
mat[r2][c2] ^= 1;
mat[r3][c3] ^= 1;
break;
case 4: // 4-bit rectangle error
r1 = rand() % 3;
c1 = rand() % 3;
for (int i = r1; i < r1 + 2; i++)
for (int j = c1; j < c1 + 2; j++)
mat[i][j] ^= 1;
break;
}
return mat;
}

void detectError(Matrix mat) {


int rowErr = -1, colErr = -1;
for (int i = 0; i < 4; i++) {
int parity = 0;
for (int j = 0; j < 4; j++) parity ^= mat[i][j];
if (parity != mat[i][4]) {
rowErr = i;
break;
}
}
for (int j = 0; j < 4; j++) {
int parity = 0;
for (int i = 0; i < 4; i++) parity ^= mat[i][j];
if (parity != mat[4][j]) {
colErr = j;
break;
}
}
if (rowErr != -1 && colErr != -1) {
cout << "⚠ Error detected at position: Row " << rowErr + 1 << ",
Column " << colErr + 1 << endl;
}
else if (rowErr != -1 || colErr != -1) {
cout << "⚠ Parity mismatch found, but unable to localize (Multiple
errors)\n";
}
else {
cout << "✅ No error detected. Parity checks passed.\n";
}
}

int main() {
srand(time(0));
string data;
cout << "Enter 16-bit binary dataword: ";
cin >> data;

if (data.length() != 16) {
cout << "Invalid input! Must be 16 bits.\n";
return 1;
}

Matrix senderMatrix = getDataMatrix(data);


addParity(senderMatrix);

printMatrix(senderMatrix, "\nSender Side Matrix (With Parity):");

int mode;
cout << "\nTransmission Mode:\n0. No Error\n1. Single Bit Error\n2. Two
Errors (Same Row)\n3. Three Errors (Different Rows/Columns)\n4. Four Bit
Rectangle Error\nEnter your choice: ";
cin >> mode;
Matrix receivedMatrix = simulateError(senderMatrix, mode);

printMatrix(receivedMatrix, "\nReceiver Side Matrix (Received):");

detectError(receivedMatrix);

return 0;
}

EXECUTION:

4. CHECKSUM:
AIM AND ALGORITHM:
PROGRAM:

#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
#include <ctime>
#include <sstream>
using namespace std;

unsigned short calculateChecksum(vector<unsigned short> words) {


unsigned int sum = 0;
for (auto word : words) sum += word;
while (sum >> 16) sum = (sum & 0xFFFF) + (sum >> 16);
return ~sum;
}

bool validateChecksum(vector<unsigned short> words, unsigned short


checksum) {
words.push_back(checksum);
return calculateChecksum(words) == 0xFFFF;
}

vector<unsigned short> parseBinaryString(string bin, int length) {


vector<unsigned short> words;
for (int i = 0; i < length; i += 16) {
string part = bin.substr(i, min(16, (int)bin.size() - i));
unsigned short val = 0;
for (char c : part) val = (val << 1) | (c == '1');
words.push_back(val);
}
return words;
}

vector<unsigned short> parseOctalString(string ocs, int count) {


vector<unsigned short> words;
for (int i = 0; i < ocs.length(); i += 6) {
string part = ocs.substr(i, min(6, (int)ocs.size() - i));
unsigned short val = stoi(part, nullptr, 8);
words.push_back(val);
}
return words;
}

vector<unsigned short> parseHexString(string hex, int count) {


vector<unsigned short> words;
for (int i = 0; i < hex.length(); i += 4) {
string part = hex.substr(i, min(4, (int)hex.size() - i));
unsigned short val = stoi(part, nullptr, 16);
words.push_back(val);
}
return words;
}

void flipRandomBit(vector<unsigned short>& words) {


int totalBits = words.size() * 16;
int bitPos = rand() % totalBits;
int wordIdx = bitPos / 16;
int b = 15 - (bitPos % 16);
words[wordIdx] ^= (1 << b);
}

void flipManualBit(vector<unsigned short>& words) {


int totalBits = words.size() * 16;
cout << "Enter bit position to flip (1 to " << totalBits << "): ";
int pos; cin >> pos;
pos--; // zero based
int wordIdx = pos / 16;
int b = 15 - (pos % 16);
words[wordIdx] ^= (1 << b);
}

int main() {
srand(time(0));
cout << "Choose data input:\n1. 16-bit Binary\n2. 10-Octet Octal\n3. 16-
Octet Hexadecimal\nEnter choice: ";
int choice; cin >> choice;

vector<unsigned short> words;


string inStr;
if (choice == 1) {
cout << "Enter 16-bit binary dataword: ";
cin >> inStr;
if (inStr.length() != 16) { cout << "Invalid – must be 16 bits.\n"; return 1;
}
words = parseBinaryString(inStr, inStr.length());
} else if (choice == 2) {
cout << "Enter 10-octet octal string (30 digits): ";
cin >> inStr;
if (inStr.length() != 30) { cout << "Invalid – must be 30 digits.\n"; return
1; }
words = parseOctalString(inStr, 10);
} else if (choice == 3) {
cout << "Enter 16-octet hex string (32 digits): ";
cin >> inStr;
if (inStr.length() != 32) { cout << "Invalid – must be 32 digits.\n"; return
1; }
words = parseHexString(inStr, 16);
} else {
cout << "Invalid choice!\n"; return 1;
}

unsigned short checksum = calculateChecksum(words);

cout << "\nSender Side:\n";


cout << "Words: ";
for (auto w : words) printf("%04x ", w);
cout << "\nChecksum: " << std::hex << checksum << std::dec << endl;

cout << "Transmission mode (0: Errorless, 1: Random error, 2: Manual


bit error): ";
int mode; cin >> mode;

vector<unsigned short> rxWords = words;


unsigned short rxChecksum = checksum;

if (mode == 1) {
flipRandomBit(rxWords);
cout << "Random bit flipped in the block.\n";
} else if (mode == 2) {
flipManualBit(rxWords);
cout << "Manual bit flipped in the block.\n";
} else {
cout << "No error introduced.\n";
}

cout << "\nReceiver Side:\n";


cout << "Received Words: ";
for (auto w : rxWords) printf("%04x ", w);
cout << "\nReceived Checksum: " << std::hex << rxChecksum <<
std::dec << endl;

if (validateChecksum(rxWords, rxChecksum))
cout << "Result of verification: ✅ No error detected\n";
else
cout << "Result of verification: ❌ Error detected\n";

return 0;
}

EXECUTION:

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