CBOR for constrained devices in IOT Protocols - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

CBOR Encoding Output

What is the output of encoding the integer 10 using CBOR in hexadecimal format?

IOT Protocols

import cbor2
encoded = cbor2.dumps(10)
print(encoded.hex())

A a0

B 0x0a

C 0a

D 0a00

💡 Hint

CBOR encodes small positive integers in a single byte with major type 0.

CBOR encodes small positive integers (0-23) as a single byte where the first 3 bits are the major type (0 for unsigned integers) and the last 5 bits are the value. For 10, this is 0x0a.

🧠 Conceptual

intermediate

Why Use CBOR in Constrained Devices?

Which of the following is the main reason CBOR is preferred for constrained IoT devices?

A It requires no parsing on the device

B It uses human-readable JSON format for easy debugging

C It encrypts data automatically for security

D It provides compact binary encoding to save bandwidth and storage

💡 Hint

Think about saving data size and transmission efficiency.

CBOR is a compact binary format designed to minimize data size and processing overhead, which is ideal for devices with limited resources.

❓ Troubleshoot

advanced

Decoding CBOR Data Error

You receive this CBOR byte sequence: 'bf61616161626162ff'. When decoding, an error occurs. What is the cause?

A The byte sequence is incomplete; the map is not properly closed

B The data contains invalid UTF-8 strings

C The CBOR major type is not supported by the decoder

D The byte sequence uses indefinite-length array instead of map

💡 Hint

Check the CBOR map start and end markers.

The byte sequence 'bf61616161626162ff' starts an indefinite-length map ('bf'). It defines key "a" (6161) with value "b" (6162), then another key "b" (6162), but lacks a value for the second key before the break ('ff'), making the map incomplete and causing the decoding error.

🔀 Workflow

advanced

CBOR Encoding Workflow for Sensor Data

Which sequence correctly describes the workflow to encode sensor data (temperature and humidity) into CBOR for transmission?

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,2,1,4

💡 Hint

Think about the logical order from data collection to transmission.

First, collect sensor data, then organize it into a structure, encode it with CBOR, and finally transmit the encoded bytes.

✅ Best Practice

expert

Best Practice for CBOR in Constrained Devices

Which practice is best to minimize memory usage when encoding large CBOR messages on constrained devices?

A Convert CBOR to JSON before sending to reduce size

B Use streaming encoding to encode and send data in chunks

C Encode the entire message in memory before transmission

D Use indefinite-length arrays without limits to simplify encoding

💡 Hint

Consider memory limits and how to handle large data efficiently.

Streaming encoding allows encoding data piece by piece, reducing peak memory usage, which is critical for constrained devices.

Practice

1. What is the main advantage of using CBOR on constrained devices?

easy

A. It uses a compact binary format to save space and power

B. It requires a lot of memory to encode data

C. It only works with large servers

D. It converts data into plain text for readability

Solution

1. Step 1: Understand CBOR format purpose

   CBOR is designed to be a compact binary format, which means it uses less space than text formats.

2. Step 2: Relate to constrained devices needs

   Small devices have limited memory and power, so saving space and power is crucial.

3. Final Answer:

   It uses a compact binary format to save space and power -> Option A

4. Quick Check:

   Compact binary = saves space and power [OK]

Hint: CBOR is compact binary, perfect for small devices [OK]

Common Mistakes:

• Thinking CBOR uses more memory
• Assuming CBOR is text-based
• Believing CBOR only works on big servers

2. Which of the following is the correct way to represent an integer value 10 in CBOR hex notation?

easy

A. 0x0F

B. 0x1A

C. 0x18 0A

D. 0x0A

Solution

1. Step 1: Recall CBOR integer encoding

   Small integers 0-23 are encoded directly in the initial byte with major type 0.

2. Step 2: Check hex for integer 10

   Integer 10 fits in 0-23 range, so encoded as 0x0A (major type 0 + value 10).

3. Final Answer:

   0x0A -> Option D

4. Quick Check:

   Small int 10 = 0x0A [OK]

Hint: Small ints 0-23 encoded as single byte 0x00 to 0x17 [OK]

Common Mistakes:

• Using 0x1A which is for 32-bit integers
• Adding extra bytes unnecessarily
• Confusing hex values for different types

3. Given the CBOR byte sequence 0x83 0x01 0x02 0x03, what is the decoded data?

medium

A. [1, 2, 3]

B. {\"1\": 2, \"3\": 4}

C. [0x83, 0x01, 0x02, 0x03]

D. Error: invalid CBOR

Solution

1. Step 1: Interpret initial byte 0x83

   0x83 means array of length 3 (major type 4 + 3).

2. Step 2: Decode following bytes

   Next three bytes 0x01, 0x02, 0x03 are integers 1, 2, 3 respectively.

3. Final Answer:

   [1, 2, 3] -> Option A

4. Quick Check:

   0x83 = array(3), then 1,2,3 [OK]

Hint: 0x80+N means array of length N [OK]

Common Mistakes:

• Confusing array with map
• Reading bytes as hex literals
• Assuming syntax error without checking

4. You try to decode the CBOR data 0xA2 0x01 0x02 0x03 but get an error. What is the likely cause?

medium

A. 0x03 is not a valid CBOR byte

B. Integer keys must be strings in CBOR maps

C. Map length byte 0xA2 says 2 pairs but only 1 pair provided

D. CBOR does not support maps

Solution

1. Step 1: Analyze map length byte 0xA2

   0xA2 means a map with 2 key-value pairs expected.

2. Step 2: Count provided pairs

   Only bytes 0x01 and 0x02 provide one pair; 0x03 is extra byte, so incomplete data.

3. Final Answer:

   Map length byte 0xA2 says 2 pairs but only 1 pair provided -> Option C

4. Quick Check:

   Map length mismatch = error [OK]

Hint: Map length byte must match actual pairs [OK]

Common Mistakes:

• Thinking keys must be strings
• Assuming 0x03 is invalid byte
• Believing CBOR lacks map support

5. You want to encode a sensor reading with temperature 22 and humidity 55 as a CBOR map. Which byte sequence correctly encodes this data?

hard

A. 0xA2 0x01 0x16 0x02 0x37

B. 0xA2 0x6B 0x74 0x65 0x6D 0x70 0x65 0x72 0x61 0x74 0x75 0x72 0x65 0x16 0x68 0x68 0x75 0x6D 0x69 0x64 0x69 0x74 0x79 0x37

C. 0xA1 0x01 0x16 0x02 0x37

D. 0x82 0x16 0x37

Solution

1. Step 1: Understand CBOR map encoding

   0xA2 means a map with 2 key-value pairs.

2. Step 2: Check keys and values encoding

   Keys are text strings: "temperature" (length 11 = 0x6B) and "humidity" (length 8 = 0x68). Values 22 (0x16) and 55 (0x37) are small integers.

3. Step 3: Verify full byte sequence

   Sequence matches map with keys and values correctly encoded as text strings and integers.

4. Final Answer:

   0xA2 0x6B 0x74 0x65 0x6D 0x70 0x65 0x72 0x61 0x74 0x75 0x72 0x65 0x16 0x68 0x68 0x75 0x6D 0x69 0x64 0x69 0x74 0x79 0x37 -> Option B

5. Quick Check:

   Map with 2 text keys and int values = 0xA2 0x6B 0x74 0x65 0x6D 0x70 0x65 0x72 0x61 0x74 0x75 0x72 0x65 0x16 0x68 0x68 0x75 0x6D 0x69 0x64 0x69 0x74 0x79 0x37 [OK]

Hint: Map header 0xA2 + text keys + int values [OK]

Common Mistakes:

• Using array instead of map
• Encoding keys as integers
• Incorrect map length byte