Protocol Data Units at each layer in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Protocol Data Unit (PDU)?

A Protocol Data Unit (PDU) is a unit of data specified at a particular layer of the network model. It includes the data and the control information needed for communication at that layer.

beginner

What is the PDU called at the Application layer?

At the Application layer, the PDU is called Data. It represents the actual information sent by the user or application.

intermediate

Name the PDU at the Transport layer and its role.

The PDU at the Transport layer is called a Segment (TCP) or Datagram (UDP). It breaks data into manageable pieces and adds control information for delivery.

intermediate

What is the PDU at the Network layer and what does it do?

At the Network layer, the PDU is called a Packet. It contains the data plus source and destination addresses to route the data across networks.

intermediate

Identify the PDU at the Data Link layer and its purpose.

The PDU at the Data Link layer is called a Frame. It packages data for transmission over a physical link and includes error checking information.

What is the PDU called at the Physical layer?

A Segments

B Frames

C Packets

D Bits

At the Physical layer, data is transmitted as raw bits (0s and 1s) over the physical medium.

Which PDU contains source and destination IP addresses?

A Segment

B Packet

C Frame

D Data

Packets at the Network layer include source and destination IP addresses for routing.

Which layer's PDU is responsible for error detection on a local link?

A Application layer

B Transport layer

C Data Link layer

D Network layer

The Data Link layer's Frame includes error checking to detect transmission errors on the local link.

What is the main difference between a Segment and a Datagram?

A Segment is used in TCP, Datagram in UDP

B Segment is at Network layer, Datagram at Transport layer

C Segment contains IP addresses, Datagram does not

D Segment is raw bits, Datagram is framed data

Segments are used in TCP (connection-oriented), while Datagrams are used in UDP (connectionless) at the Transport layer.

Which PDU is directly transmitted over the physical medium?

A Bits

B Frame

C Segment

D Packet

Bits are the raw electrical or optical signals sent over the physical medium at the Physical layer.

Explain the different Protocol Data Units (PDUs) at each layer of the OSI or TCP/IP model and their roles.

Think about how data is packaged and handled as it moves down the layers.

Describe how the PDU changes as data moves from the Application layer down to the Physical layer during transmission.

Consider the encapsulation process in networking.