Block-wise transfer for large payloads in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the block size for block-wise transfer.

IOT Protocols

block_size = [1]  # Set block size in bytes

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

A1024

B512

C2048

D256

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a block size too small or too large can cause inefficiency or errors.

The standard block size for block-wise transfer is 1024 bytes to balance efficiency and resource use.

2fill in blank

medium

Complete the code to calculate the number of blocks needed for a payload.

IOT Protocols

num_blocks = (payload_size + [1] - 1) // [1]

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

Ablock_size

Bchunk_size

Cmax_block

Dpayload_size

Attempts:

3 left

💡 Hint

Common Mistakes

Using payload_size instead of block_size causes incorrect calculation.

We use block_size to divide the payload size and calculate how many blocks are needed.

3fill in blank

hard

Fix the error in the block number calculation for the last block.

IOT Protocols

last_block_num = total_blocks [1] 1

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

A*

B+

C//

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 1 instead of subtracting causes out-of-range block number.

The last block number is total_blocks minus 1 because block numbering starts at zero.

4fill in blank

hard

Fill both blanks to correctly create a block option header with block number and size.

IOT Protocols

block_option = ([1] << 4) | [2]  # Compose block option value

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

Ablock_num

Bblock_size_code

Cpayload_len

Dblock_index

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping block number and size code causes incorrect header.

The block number is shifted left by 4 bits and combined with the block size code using bitwise OR.

5fill in blank

hard

Fill all three blanks to extract block number and size code from block option.

IOT Protocols

block_num = (block_option >> [1]) & [2]
block_size_code = block_option & [3]

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

A4

B0x0F

C0xF0

D8

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong shift or mask values leads to incorrect extraction.

Shift right by 4 bits to get block number, mask with 0x0F to get size code from lower 4 bits.

Practice

1. What is the main purpose of block-wise transfer in IoT protocols?

easy

A. To compress data to save bandwidth

B. To split large data into smaller blocks for easier transmission

C. To encrypt data before sending

D. To prioritize urgent messages over others

Solution

1. Step 1: Understand the problem of large data in IoT

   Large data can be hard to send in one go because devices have limited memory and networks can be unstable.

2. Step 2: Identify the role of block-wise transfer

   Block-wise transfer breaks big data into smaller blocks, making it easier and safer to send piece by piece.

3. Final Answer:

   To split large data into smaller blocks for easier transmission -> Option B

4. Quick Check:

   Block-wise transfer = splitting data [OK]

Hint: Block-wise means breaking big data into small pieces [OK]

Common Mistakes:

• Confusing block-wise transfer with encryption
• Thinking it compresses data
• Assuming it prioritizes messages

2. Which of the following is the correct format to indicate a block-wise transfer request with block number 3 and more blocks to come in CoAP?

easy

A. Block1: num=3; more=1; size=64

B. Block2: num=3; more=1; size=64

C. Block2: num=3; more=0; size=64

D. Block2: num=1; more=3; size=64

Solution

1. Step 1: Identify the correct block option name

   In CoAP, Block1 is used for block-wise transfer of request payloads, and Block2 for responses. Since this is a request, Block1 is correct.

2. Step 2: Check block number and more flag

   Block number is 3, 'more' flag is 1 meaning more blocks follow, and size is 64 bytes. Block1: num=3; more=1; size=64 matches all correctly.

3. Final Answer:

   Block1: num=3; more=1; size=64 -> Option A

4. Quick Check:

   Block1 with num=3 and more=1 means block 3 with more blocks [OK]

Hint: Block1 is for request blocks; 'more=1' means more blocks coming [OK]

Common Mistakes:

• Using Block2 instead of Block1 for request
• Setting 'more' flag to 0 when more blocks exist
• Mixing block number and more flag values

3. Given the following CoAP block-wise transfer sequence, what is the block number of the last block received?

Block2: num=0; more=1; size=64
Block2: num=1; more=1; size=64
Block2: num=2; more=0; size=64

medium

A. 3

B. 1

C. 0

D. 2

Solution

1. Step 1: Analyze the 'more' flag in each block

   Blocks 0 and 1 have 'more=1', meaning more blocks follow. Block 2 has 'more=0', meaning it is the last block.

2. Step 2: Identify the last block number

   Since block number 2 has 'more=0', it is the last block received.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Last block has more=0 and num=2 [OK]

Hint: 'more=0' means last block number is current num [OK]

Common Mistakes:

• Choosing block with more=1 as last block
• Confusing block numbers with sequence count
• Ignoring the 'more' flag

4. A device is sending a large payload using block-wise transfer but the receiver never acknowledges block number 2. What is the most likely cause of the problem?

medium

A. The sender did not set the 'more' flag correctly for block 2

B. The receiver has limited memory and dropped block 2

C. The sender skipped sending block 2

D. The block size is too large for the network

Solution

1. Step 1: Understand the role of acknowledgments in block-wise transfer

   Each block must be acknowledged by the receiver to confirm it was received correctly.

2. Step 2: Analyze why block 2 is not acknowledged

   If block 2 is never acknowledged, it likely means the sender never sent it, causing the receiver to wait indefinitely.

3. Final Answer:

   The sender skipped sending block 2 -> Option C

4. Quick Check:

   No ack for block means block not sent [OK]

Hint: Missing ack usually means block was never sent [OK]

Common Mistakes:

• Blaming 'more' flag for missing ack
• Assuming receiver dropped block without evidence
• Thinking block size alone causes missing ack

5. You need to send a 200-byte payload using block-wise transfer with a block size of 64 bytes. How many blocks will be sent, and what will be the 'more' flag value for the last block?

hard

A. 4 blocks; 'more' flag = 0 on last block

B. 3 blocks; 'more' flag = 1 on last block

C. 4 blocks; 'more' flag = 1 on last block

D. 3 blocks; 'more' flag = 0 on last block

Solution

1. Step 1: Calculate number of blocks needed

   Payload size is 200 bytes, block size is 64 bytes. 200 / 64 = 3.125, so 4 blocks are needed to send all data.

2. Step 2: Determine 'more' flag for last block

   For all blocks except the last, 'more' flag is 1. For the last block, it is 0 to indicate no more blocks follow.

3. Final Answer:

   4 blocks; 'more' flag = 0 on last block -> Option A

4. Quick Check:

   Payload/size = 4 blocks; last block more=0 [OK]

Hint: Divide payload by block size, last block 'more' = 0 [OK]

Common Mistakes:

• Rounding down number of blocks
• Setting 'more' flag to 1 on last block
• Ignoring partial block for last piece