Block-wise transfer for large payloads in IOT Protocols - Step-by-Step Execution

Process Flow - Block-wise transfer for large payloads

Start Transfer

↓

Split Payload into Blocks

↓

Send Block 1

↓

Wait for ACK

↓

Send Next

↓

More Blocks?

No→End Transfer

The large payload is split into smaller blocks. Each block is sent and acknowledged before sending the next. If no acknowledgment, the block is resent. This repeats until all blocks are sent.

Execution Sample

IOT Protocols

payload = 'LargeDataPayload'
block_size = 5
blocks = [payload[i:i+block_size] for i in range(0, len(payload), block_size)]
for block in blocks:
    send(block)
    wait_for_ack()

This code splits a large payload into blocks of 5 characters ('Large', 'DataP', 'ayloa', 'd') and sends each block waiting for acknowledgment before continuing.

Process Table

Step	Block Sent	ACK Received?	Action	Next Step
1	Large	Yes	Send block 1	Send block 2
2	DataP	Yes	Send block 2	Send block 3
3	ayloa	No	Resend block 3	Wait for ACK
4	ayloa	Yes	Send block 3	Send block 4
5	d	Yes	Send block 4	End transfer

💡 All blocks sent and acknowledged, transfer complete

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
blocks	[]	['Large', 'DataP', 'ayloa', 'd']	['Large', 'DataP', 'ayloa', 'd']	['Large', 'DataP', 'ayloa', 'd']	['Large', 'DataP', 'ayloa', 'd']	['Large', 'DataP', 'ayloa', 'd']
current_block	None	'Large'	'DataP'	'ayloa'	'd'	None
ack_received	False	True	True	False	True	True

Key Moments - 2 Insights

Why do we resend a block when no ACK is received?

Because the receiver did not confirm receiving the block, so to ensure data integrity, the sender resends the same block as shown in step 3 of the execution_table.

What happens after all blocks are sent and acknowledged?

The transfer ends successfully, as indicated in the exit_note and step 5 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what block is resent due to missing ACK?

A Block 'DataP'

B Block 'ayloa'

C Block 'Large'

D No block is resent

💡 Hint

Check step 3 in execution_table where ACK is 'No' and action is 'Resend block 3'

At which step does the transfer complete successfully?

A Step 2

B Step 3

C Step 5

D Step 1

💡 Hint

Look at the exit_note and the last step in execution_table

If the block size was increased to 7, how would the number of blocks change?

A Fewer blocks would be created

B More blocks would be created

C Number of blocks stays the same

D Blocks would be empty

💡 Hint

Refer to variable_tracker 'blocks' and how block_size affects splitting

Concept Snapshot

Block-wise transfer splits large data into small blocks.
Each block is sent and waits for acknowledgment (ACK).
If ACK missing, resend the block.
Repeat until all blocks are sent and confirmed.
Ensures reliable transfer of large payloads in small parts.

Full Transcript

Block-wise transfer breaks a large payload into smaller blocks to send over a network. Each block is sent one at a time, waiting for an acknowledgment from the receiver before sending the next. If the acknowledgment is not received, the sender resends the same block to ensure no data is lost. This process continues until all blocks are sent and acknowledged, completing the transfer successfully.

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