Why TCP provides reliable delivery in Computer Networks - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to explain how TCP ensures data is received correctly.

Computer Networks

TCP uses [1] to confirm that data packets have arrived safely.

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

Aacknowledgments

Bchecksums

Cbroadcasting

Dencryption

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing acknowledgments with encryption or checksums.

TCP uses acknowledgments to confirm that the receiver has successfully received data packets. This helps ensure reliable delivery.

2fill in blank

medium

Complete the sentence to describe how TCP handles lost packets.

Computer Networks

If a packet is lost, TCP will [1] the packet to ensure it reaches the destination.

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

Aignore

Bretransmit

Ccompress

Ddelay

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking TCP ignores lost packets or delays them instead.

TCP retransmits lost packets to make sure all data arrives correctly and in order.

3fill in blank

hard

Fix the error in the explanation about TCP's ordering of packets.

Computer Networks

TCP ensures data arrives in order by using [1] numbers for each packet.

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

AIP

Bport

Csequence

Dchecksum

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing sequence numbers with port numbers or IP addresses.

TCP assigns sequence numbers to packets so the receiver can reorder them correctly if they arrive out of order.

4fill in blank

hard

Fill both blanks to complete the explanation of TCP's flow control.

Computer Networks

TCP uses a [1] window to control the amount of data sent before waiting for an [2].

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

Asliding

Backnowledgment

Cfixed

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fixed' window or confusing acknowledgment with error.

The sliding window controls how much data can be sent before waiting for an acknowledgment, helping TCP manage flow control.

5fill in blank

hard

Fill all three blanks to explain how TCP detects errors and recovers.

Computer Networks

TCP uses [1] to detect errors, [2] to confirm receipt, and [3] to resend lost data.

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

Achecksums

Backnowledgments

Cretransmission

Dencryption

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing encryption with error detection or retransmission.

TCP uses checksums to detect errors, acknowledgments to confirm receipt, and retransmission to resend lost data, ensuring reliable delivery.

Practice

1. Why does TCP provide reliable delivery of data over a network?

easy

A. Because it uses acknowledgments and retransmissions to ensure data arrives correctly

B. Because it sends data without checking for errors

C. Because it uses a fixed packet size for all transmissions

D. Because it only sends data once without retries

Solution

1. Step 1: Understand TCP's error checking

   TCP uses acknowledgments to confirm receipt of data and detects lost packets.

2. Step 2: Recognize retransmission mechanism

   If a packet is lost or not acknowledged, TCP resends it to ensure delivery.

3. Final Answer:

   Because it uses acknowledgments and retransmissions to ensure data arrives correctly -> Option A

4. Quick Check:

   TCP reliability = acknowledgments + retransmissions [OK]

Hint: Remember: TCP confirms and resends lost data [OK]

Common Mistakes:

• Thinking TCP sends data only once
• Confusing TCP with UDP which is unreliable
• Believing fixed packet size ensures reliability

2. Which of the following is a correct feature of TCP that helps in reliable delivery?

easy

A. Does not use acknowledgments

B. Uses sequence numbers to order packets

C. Ignores lost packets

D. Sends packets without any control

Solution

1. Step 1: Identify TCP's packet ordering method

   TCP assigns sequence numbers to packets to keep track of their order.

2. Step 2: Confirm role of sequence numbers in reliability

   Sequence numbers help TCP detect missing or out-of-order packets for retransmission.

3. Final Answer:

   Uses sequence numbers to order packets -> Option B

4. Quick Check:

   Sequence numbers = packet order in TCP [OK]

Hint: Sequence numbers keep packets in order [OK]

Common Mistakes:

• Believing TCP ignores lost packets
• Thinking TCP does not use acknowledgments
• Assuming TCP sends packets without control

3. Consider this simplified TCP process:

Sender sends packets 1, 2, 3.
Receiver acknowledges packets 1 and 3 only.
What will TCP do next?

medium

A. Resend packet 2 because it was not acknowledged

B. Stop sending any packets

C. Resend packets 1 and 3 again

D. Ignore missing acknowledgments and continue

Solution

1. Step 1: Analyze acknowledgments received

   Packets 1 and 3 are acknowledged, but packet 2 is missing acknowledgment.

2. Step 2: Understand TCP retransmission behavior

   TCP will resend packet 2 because it assumes it was lost or not received.

3. Final Answer:

   Resend packet 2 because it was not acknowledged -> Option A

4. Quick Check:

   Missing ack triggers retransmission [OK]

Hint: Unacknowledged packets get resent by TCP [OK]

Common Mistakes:

• Assuming TCP stops sending after missing ack
• Thinking TCP resends already acknowledged packets
• Believing TCP ignores missing acknowledgments

4. A programmer wrote this about TCP:

"TCP does not resend lost packets, it just waits for the receiver to ask again."

What is wrong with this statement?

medium

A. TCP uses UDP to resend lost packets

B. TCP never resends packets

C. TCP actively resends lost packets without waiting for receiver requests

D. TCP sends packets only once and ignores losses

Solution

1. Step 1: Understand TCP retransmission mechanism

   TCP uses timers and acknowledgments to detect lost packets and resends them automatically.

2. Step 2: Identify error in the statement

   The statement wrongly says TCP waits for receiver requests, but TCP resends proactively.

3. Final Answer:

   TCP actively resends lost packets without waiting for receiver requests -> Option C

4. Quick Check:

   TCP retransmits lost packets automatically [OK]

Hint: TCP resends lost packets without waiting [OK]

Common Mistakes:

• Thinking receiver must request retransmission
• Confusing TCP with protocols that do not resend
• Believing TCP uses UDP for retransmission

5. In a network with frequent packet loss, how does TCP maintain reliable delivery while avoiding network congestion?

hard

A. By switching to UDP when packet loss is detected

B. By sending all packets repeatedly without checking acknowledgments

C. By ignoring lost packets and continuing to send new data quickly

D. By using acknowledgments, retransmissions, and adjusting sending rate with congestion control

Solution

1. Step 1: Recognize TCP's reliability features

   TCP uses acknowledgments and retransmissions to ensure all data arrives correctly.

2. Step 2: Understand TCP congestion control

   TCP adjusts its sending rate based on network feedback to avoid overwhelming the network.

3. Step 3: Combine reliability and congestion control

   These mechanisms together allow TCP to deliver data reliably even with packet loss and avoid congestion collapse.

4. Final Answer:

   By using acknowledgments, retransmissions, and adjusting sending rate with congestion control -> Option D

5. Quick Check:

   Reliability + congestion control = TCP success [OK]

Hint: TCP controls speed and resends lost data [OK]

Common Mistakes:

• Thinking TCP sends packets repeatedly without control
• Believing TCP ignores packet loss
• Assuming TCP switches to UDP automatically