Protocol Data Units at each layer in Computer Networks - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the Protocol Data Unit (PDU) at the Network layer.

Computer Networks

The PDU at the Network layer is called a [1].

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

AFrame

BPacket

CSegment

DBit

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the Network layer PDU with the Data Link layer PDU (Frame).

Thinking the Transport layer PDU (Segment) is used here.

The Network layer uses packets as its Protocol Data Unit (PDU). Packets contain the data along with network addressing information.

2fill in blank

medium

Complete the code to identify the PDU at the Transport layer.

Computer Networks

At the Transport layer, the PDU is called a [1].

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

ASegment

BPacket

CFrame

DBit

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the Transport layer PDU with the Network layer PDU (Packet).

Confusing it with the Data Link layer PDU (Frame).

The Transport layer breaks data into segments for transmission, adding port information for communication between applications.

3fill in blank

hard

Fix the error in the statement about the Data Link layer PDU.

Computer Networks

The PDU at the Data Link layer is called a [1].

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

APacket

BSegment

CFrame

DBit

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the Data Link layer PDU a packet or segment.

Confusing bits (Physical layer) with frames.

The Data Link layer uses frames as its PDU. Frames include physical addressing and error checking.

4fill in blank

hard

Fill both blanks to complete the statement about the Physical layer PDU and the Data Link layer PDU.

Computer Networks

The Physical layer transmits data as [1], while the Data Link layer organizes data into [2].

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

Abits

Bframes

Cpackets

Dsegments

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up bits and frames between the two layers.

Confusing packets or segments with Physical or Data Link layer PDUs.

The Physical layer transmits raw bits over the medium. The Data Link layer groups bits into frames for error detection and control.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that maps OSI layers to their PDUs.

Computer Networks

osi_pdus = {"Physical": [1], "Data Link": [2], "Network": [3]

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

A"bits"

B"frames"

C"packets"

D"segments"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping PDUs between layers.

Using segments or packets incorrectly for Physical or Data Link layers.

This dictionary maps OSI layers to their Protocol Data Units: Physical layer uses bits, Data Link layer uses frames, and Network layer uses packets.

Practice

1. Which Protocol Data Unit (PDU) name is used at the Network layer in the OSI model?

easy

A. Segment

B. Frame

C. Packet

D. Bit

Solution

1. Step 1: Recall OSI model layers and their PDUs

   The OSI model has seven layers. Each layer uses a specific PDU name. The Network layer is the third layer.

2. Step 2: Identify the PDU for the Network layer

   The Network layer uses the term 'Packet' for its PDU, which contains logical addressing information.

3. Final Answer:

   Packet -> Option C

4. Quick Check:

   Network layer PDU = Packet [OK]

Hint: Network layer always uses 'Packet' as its PDU name [OK]

Common Mistakes:

• Confusing Frame (Data Link layer) with Packet
• Mixing Segment (Transport layer) with Packet
• Thinking Bit is a PDU name at any layer

2. Which of the following correctly matches the PDU name with the Transport layer?

easy

A. Frame

B. Bit

C. Packet

D. Segment

Solution

1. Step 1: Identify the Transport layer in the OSI model

   The Transport layer is the fourth layer and is responsible for end-to-end communication.

2. Step 2: Recall the PDU name for the Transport layer

   The Transport layer uses 'Segment' as its PDU name, which contains data with transport headers.

3. Final Answer:

   Segment -> Option D

4. Quick Check:

   Transport layer PDU = Segment [OK]

Hint: Transport layer PDU is always called Segment [OK]

Common Mistakes:

• Choosing Frame which belongs to Data Link layer
• Selecting Packet which belongs to Network layer
• Confusing Bit with a PDU name

3. Consider this simplified data flow: Application data is passed down to the Transport layer, then to the Network layer, and finally to the Data Link layer. What is the correct sequence of PDUs at each layer?

medium

A. Packet -> Segment -> Frame

B. Segment -> Packet -> Frame

C. Frame -> Packet -> Segment

D. Bit -> Segment -> Packet

Solution

1. Step 1: Identify PDUs for each layer in order

   Transport layer uses Segment, Network layer uses Packet, Data Link layer uses Frame.

2. Step 2: Arrange PDUs in the order data passes down

   Data flows from Transport (Segment) -> Network (Packet) -> Data Link (Frame).

3. Final Answer:

   Segment -> Packet -> Frame -> Option B

4. Quick Check:

   Transport=Segment, Network=Packet, Data Link=Frame [OK]

Hint: Remember data flows: Segment, Packet, then Frame [OK]

Common Mistakes:

• Mixing order of PDUs
• Confusing Packet and Segment
• Including Bit as a PDU in this sequence

4. A student wrote this statement: "The Data Link layer PDU is called a Packet." What is wrong with this statement?

medium

A. Packet is the PDU for the Network layer, not Data Link layer.

B. Packet is the PDU for the Transport layer, not Data Link layer.

C. Packet is the PDU for the Application layer, not Data Link layer.

D. Packet is the PDU for the Physical layer, not Data Link layer.

Solution

1. Step 1: Identify the correct PDU for Data Link layer

   The Data Link layer uses 'Frame' as its PDU, not 'Packet'.

2. Step 2: Identify which layer uses 'Packet'

   The Network layer uses 'Packet' as its PDU.

3. Final Answer:

   Packet is the PDU for the Network layer, not Data Link layer. -> Option A

4. Quick Check:

   Data Link = Frame, Network = Packet [OK]

Hint: Data Link layer PDU is Frame, not Packet [OK]

Common Mistakes:

• Confusing Packet with Frame
• Mixing up Network and Data Link layers
• Assuming Packet is a general PDU name

5. In a network communication, data is encapsulated at each layer with its PDU. If a message is 1000 bytes at the Application layer, and each layer adds a header of 20 bytes (Transport), 30 bytes (Network), and 14 bytes (Data Link), what is the total size of the Frame sent over the Physical layer?

hard

A. 1064 bytes

B. 1066 bytes

C. 1064 bits

D. 1064 kilobytes

Solution

1. Step 1: Calculate total header size added by layers

   Transport header = 20 bytes, Network header = 30 bytes, Data Link header = 14 bytes. Total headers = 20 + 30 + 14 = 64 bytes.

2. Step 2: Add headers to original Application data size

   Application data = 1000 bytes. Total Frame size = 1000 + 64 = 1064 bytes.

3. Final Answer:

   1064 bytes -> Option A

4. Quick Check:

   1000 + 20 + 30 + 14 = 1064 bytes [OK]

Hint: Add all headers in bytes to original data size [OK]

Common Mistakes:

• Confusing bytes with bits
• Adding headers incorrectly
• Misreading units as kilobytes