Chapter 2 - The OSI Model

Question 1

What does the OSI Model stand for?

Answer 1

Open Systems Interconnection Reference Model

Question 2

What is Layer 1 in the OSI Model?

Answer 2

Layer 1 - Physical

Question 3

What is Layer 2 in the OSI Model?

Answer 3

Layer 2 - Data Link

Question 4

What is Layer 3 in the OSI Model?

Answer 4

Layer 3 - Network

Question 5

What is Layer 4 in the OSI Model?

Answer 5

Layer 4 - Transport

Question 6

What is Layer 5 in the OSI Model?

Answer 6

Layer 5 - Session

Question 7

What is Layer 6 in the OSI Model?

Answer 7

Layer 6 - Presentation

Question 8

What is Layer 7 in the OSI Model?

Answer 8

Layer 7 - Application

Question 9

What are the 7 OSI Model layers?

Answer 9

All = Application (Layer 7)
People = Presentation (Layer 6)
Seem = Session (Layer 5)
To = Transport (Layer 4)
Need = Network (Layer 3)
Data = Data Link (Layer 2)
Processing - Physical (Layer 1)
Remember the mnemonic, All People Seem To Need Data Processing
Application, Presentation, Session, Transport, Network, Data Link, and Physical layers.

Question 10

Describe what Layer 1 does.

Answer 10

The Physical layer handles the physical cables and electrical signals sent across the network.

Question 11

Describe what Layer 2 does.

Answer 11

The Data Link layer handles the ethernet frames, source and destination MAC addresses and is also used by switches.

Question 12

Describe what Layer 3 does.

Answer 12

The Network Layer handles IP encapsulation, the source and destination IP addresses, IP packets, and routing. It also fragments frames to travel across the network.

Question 13

Describe what Layer 4 does.

Answer 13

The Transport layer handles TCP/UDP encapsulation, segments, and the ports used. It also separates and reassembles frames.

Question 14

Describe what Layer 5 does.

Answer 14

The Session layer handles communication management between devices. It also does the control and tunneling protocols and links to the transportation layer.

Question 15

Describe what Layer 6 does.

Answer 15

The Presentation layer handles encryption (SSL/TLS) and character encoding (HTTPS) and works with the Application Layer.

Question 16

Describe what Layer 7 does.

Answer 16

The Application layer is what you the end-user sees when using an application or browsing the web.

Question 17

Describe how data is sent and received using the OSI Model

Answer 17

The source device starts at layer 7 with the application data and encapsulates each layer downward. Layer 4 adds the TCP/UDP header, then the IP header, and the Frame header and trailer before it’s sent across layer 1. The receiving device gets the signal at layer 1 it then decapsulates in reverse with removing the Frame header and trailer, then the IP header, and then the TCP/UDP header before moving the application data up through layers 5, 6, and finally 7.

Question 18

How does encapsulation work?

Answer 18

Encapsulation starts with the Application data at layer 7 and encapsulates each layer’s data below it. When it reaches layer 4 the TCP/UDP header is added. From there the IP header is added at layer 3 then the Frame header and trailer is added at layer 2 before going to layer 1 to be transmitted as bits to its destination.