Error detection (parity, CRC, checksum) in Computer Networks - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the parity bit for a given byte.

Computer Networks

def calculate_parity(byte):
    count = 0
    for bit in byte:
        if bit == '1':
            count += [1]
    return '1' if count % 2 != 0 else '0'

Drag options to blanks, or click blank then click option'

A1

B2

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of 1 to count bits.

Adding 2 or more per bit instead of 1.

The parity bit counts the number of '1's. Each '1' adds 1 to the count.

2fill in blank

medium

Complete the code to compute the checksum by summing all bytes and taking modulo 256.

Computer Networks

def checksum(data):
    total = 0
    for byte in data:
        total += [1]
    return total % 256

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Atotal

Blen(byte)

C1

Dbyte

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the length of the byte instead of its value.

Adding a constant instead of the byte.

The checksum sums the value of each byte in the data.

3fill in blank

hard

Fix the error in the CRC calculation loop by completing the missing operation.

Computer Networks

def crc(data, poly):
    crc = 0
    for bit in data:
        crc = (crc << 1) | int(bit)
        if crc & (1 << (len(poly) - 1)):
            crc = crc ^ [1]
    return crc

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Adata

Bpoly

Cbit

Dcrc

Attempts:

3 left

💡 Hint

Common Mistakes

XORing with data or bit instead of the polynomial.

Not XORing at all.

The CRC is XORed with the polynomial when the highest bit is set.

4fill in blank

hard

Fill both blanks to complete the parity check function that returns True if parity matches.

Computer Networks

def check_parity(data, parity_bit):
    count = sum(1 for bit in data if bit == '1')
    return (count [1] 2) == [2]

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A%

B==

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' for comparison.

Using '>' instead of modulo operator.

The function checks if the count of '1's modulo 2 equals the parity bit.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each byte to its checksum if checksum is greater than zero.

Computer Networks

checksums = {{'{'}}[1]: [2] for [1], [2] in data.items() if [2] [3] 0{{'}}'}}

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Abyte

Bchecksum

C>

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'data' as a variable name inside the comprehension.

Using '<' instead of '>' in the condition.

The comprehension creates a dictionary of bytes and their checksums where the checksum is positive.