Understanding the OSI Model

Question 1

What does “OSI Model” stand for?

Answer 1

Open Systems Interconnection Reference Model

Question 2

Name all the layers of the OSI model.

Answer 2

Layer 1 - Physical
Layer 2 - Data Link
Layer 3 - Network
Layer 4 - Transport
Layer 5 - Session
Layer 6 - Presentation
Layer 7 - Application

(APSTNDP - All People Seem To Need Data Processing)

Question 3

What is the Physical Layer (1)?

Answer 3

The physical components of the network, such as signaling/cabling/connectors.

Question 4

What is the Data Link Layer (2)?

Answer 4

The basic network “language”; the foundation of communication at the data link layer.
The data link layer on Ethernet would be the MAC address.

Question 5

What is the Network Layer (3)?

Answer 5

The Internet Protocol layer, aka the “routing” layer.
Responsible for fragmenting data so they can traverse different networks.
I.E. IP Address, Router, Packet.

Question 6

What is IP fragmentation? What layer is responsible for this?

Answer 6

When data is too large to go to it’s destination, so it is fragmented into smaller pieces so those pieces can be sent through the network. Network Layer (3) is responsible for this.

Question 7

What is the Transport Layer (4)?

Answer 7

This is the “post office” layer. When packets of data are transported across the network, this would be the Transport Layer. Uses TCP and UDP.

Question 8

What is the Session Layer (5)?

Answer 8

This layer is responsible for communication between devices. Control protocols and tunneling protocols are found here.

Question 9

What is the Presentation Layer (6)?

Answer 9

This layer is where character encoding and data encryption occur (SSL/TLS). Often combined with the application layer.

Question 10

What is the Application Layer (7)?

Answer 10

This is the layer that we can physically see.

I.E. a browser window, a file being transferred, or downloading some mail.