Data compression techniques in SCADA systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Lossless Compression in SCADA Data

Which of the following best describes lossless data compression in SCADA systems?

A Data is compressed by converting it into a smaller image format.

B Data is compressed by removing less important parts, losing some details permanently.

C Data is encrypted to prevent unauthorized access during compression.

D Data is compressed and can be perfectly restored to original without any loss.

💡 Hint

Think about whether the original data can be fully recovered after compression.

Lossless compression means no data is lost and the original data can be exactly restored after decompression.

💻 Command Output

intermediate

Output of gzip Compression Command

What is the output of running gzip -l compressed_data.gz on a valid gzip file?

SCADA systems

gzip -l compressed_data.gz

A Lists the original and compressed file sizes and compression ratio.

B Displays the contents of the compressed file as plain text.

C Shows an error that the file is not found.

D Deletes the compressed file after listing.

💡 Hint

Consider what the -l option does in gzip.

The -l option lists compression statistics like original size, compressed size, and ratio.

❓ Configuration

advanced

Configuring SCADA Data Compression with zlib

Which configuration snippet correctly sets zlib compression level to maximum in a SCADA data pipeline?

A compression_level = 0

B compression_level = 10

C compression_level = 9

D compression_level = -1

💡 Hint

Compression levels usually range from 0 to 9 in zlib.

In zlib, 9 is the highest compression level, 0 means no compression.

❓ Troubleshoot

advanced

Troubleshooting Corrupted Compressed Data

You receive an error when decompressing SCADA data: 'unexpected end of file'. What is the most likely cause?

A The compressed file is incomplete or corrupted.

B The decompression tool is outdated but file is fine.

C The original data was not compressed at all.

D The file permissions prevent reading the file.

💡 Hint

Think about what 'unexpected end of file' means during decompression.

This error usually means the compressed file is cut off or corrupted, missing data needed to decompress.

🔀 Workflow

expert

Optimal Workflow for SCADA Data Compression and Transmission

Which workflow sequence ensures efficient compression and secure transmission of SCADA data?

A 3,1,2,4

B 1,2,3,4

C 2,1,3,4

D 1,3,2,4

💡 Hint

Think about the order: data collection, compression, encryption, then transmission.

Data must be collected first, then compressed to reduce size, encrypted to secure, and finally transmitted.

Practice

1. What is the main purpose of data compression in SCADA systems?

easy

A. To reduce the size of data for easier storage and faster transfer

B. To increase the size of data for better security

C. To convert data into a different format for display

D. To delete unnecessary data permanently

Solution

1. Step 1: Understand data compression purpose

   Data compression reduces the size of data to save space and speed up transfer.

2. Step 2: Apply this to SCADA systems

   In SCADA, smaller data means faster communication and less storage needed.

3. Final Answer:

   To reduce the size of data for easier storage and faster transfer -> Option A

4. Quick Check:

   Compression = smaller data size [OK]

Hint: Compression makes data smaller to save space and time [OK]

Common Mistakes:

• Confusing compression with encryption
• Thinking compression deletes data
• Believing compression changes data meaning

2. Which of the following is the correct syntax to compress data using a function named compress in a SCADA script?

easy

A. compressed_data = compress(data)

B. compressed_data = compress data

C. compressed_data <- compress(data)

D. compressed_data = compress[data]

Solution

1. Step 1: Identify correct function call syntax

   Functions are called with parentheses enclosing arguments, like compress(data).

2. Step 2: Check each option

   compressed_data = compress(data) uses correct syntax with parentheses and assignment.

3. Final Answer:

   compressed_data = compress(data) -> Option A

4. Quick Check:

   Function call syntax = parentheses [OK]

Hint: Use parentheses to call functions with arguments [OK]

Common Mistakes:

• Omitting parentheses in function calls
• Using wrong assignment operators
• Using brackets instead of parentheses

3. Given the following SCADA script snippet:

data = "sensor_reading_12345"
compressed = compress(data)
decompressed = decompress(compressed)
print(decompressed)

What will be the output?

medium

A. compressed data bytes

B. Error: decompress function not found

C. sensor_reading_12345

D. sensor_reading

Solution

1. Step 1: Understand compression and decompression

   compress() shrinks data, decompress() restores it to original form.

2. Step 2: Follow the script flow

   Data is compressed then decompressed, so print shows original data.

3. Final Answer:

   sensor_reading_12345 -> Option C

4. Quick Check:

   Decompress(compress(data)) = original data [OK]

Hint: Decompress reverses compress, output original data [OK]

Common Mistakes:

• Thinking print shows compressed bytes
• Assuming decompress changes data
• Ignoring function order

4. A SCADA script uses compressed = compress(data) but later decompressed = decompress(data) is called instead of decompress(compressed). What is the likely problem?

medium

A. Data will be compressed twice

B. Compression will fail because decompress is called too early

C. No problem, decompress can use original data

D. Decompression will fail or give wrong data because wrong variable is used

Solution

1. Step 1: Identify variable usage error

   Decompress must use compressed data, not original data variable.

2. Step 2: Understand effect of wrong variable

   Using original data in decompress causes failure or incorrect output.

3. Final Answer:

   Decompression will fail or give wrong data because wrong variable is used -> Option D

4. Quick Check:

   Decompress(compressed) needed, not decompress(data) [OK]

Hint: Always decompress the compressed variable [OK]

Common Mistakes:

• Passing original data to decompress
• Assuming decompress auto-detects input
• Mixing variable names

5. You need to compress SCADA data but want to keep it quickly accessible for real-time monitoring. Which compression technique is best?

hard

A. No compression to avoid delay

B. Lossless compression for exact data recovery

C. Lossy compression to reduce size drastically

D. Encrypt data instead of compressing

Solution

1. Step 1: Understand real-time monitoring needs

   Real-time needs exact data quickly without loss.

2. Step 2: Choose compression type

   Lossless compression keeps data exact and fast to decompress.

3. Step 3: Evaluate other options

   Lossy loses data, no compression wastes space, encryption is different.

4. Final Answer:

   Lossless compression for exact data recovery -> Option B

5. Quick Check:

   Real-time + exact data = lossless compression [OK]

Hint: Use lossless compression for exact, fast data access [OK]

Common Mistakes:

• Choosing lossy compression for critical data
• Skipping compression to save time
• Confusing encryption with compression