Objective 1.1

Question 1

What is the OSI model?

Answer 1

A 7-layer conceptual framework that standardizes the functions of a network.

Question 2

What is the OSI model used for?

Answer 2

It’s used to understand and troubleshoot how data is sent and received, ensuring different vendor products can work together.

Question 3

List the 7 layers of the OSI model from Layer 7 to Layer 1.

Answer 3

• Application
• Presentation
• Session
• Transport
• Network
• Data Link
• Physical

Question 4

What is a popular mnemonic for remembering the OSI layers from 7 down to 1?

Answer 4

All People Seem To Need Data Processing.

Question 5

Function:

Layer 7

Answer 5

The Application Layer provides the interface for user applications to access network services.

It’s the layer closest to the end-user.

Example: Your web browser using HTTP.

Question 6

What is the Protocol Data Unit (PDU) for the Application, Presentation, and Session layers?

Answer 6

Data.

Question 7

Name some common protocols that operate at the Application Layer (Layer 7).

Answer 7

HTTP, HTTPS, FTP, SMTP, DNS, RDP, SNMP, Telnet.

Question 8

Layer 6: Function

Answer 8

The Presentation Layer acts as a data translator for the network. It handles character encoding, data compression, and encryption/decryption.

Question 9

What are the three primary responsibilities of the Presentation Layer (Layer 6)?

Answer 9

1. Translation (e.g., ASCII to EBCDIC)
2. Compression
3. Encryption & Decryption (e.g., formatting for SSL/TLS)

Question 10

Layer 5: Function

Answer 10

The Session Layer establishes, manages, and terminates connections (sessions) between two applications on different hosts.

Question 11

What are the primary tasks of the Session Layer (Layer 5)?

Answer 11

Establishing, maintaining, and terminating the communication session.

It also handles dialogue control (determining who can send data and when).

Question 12

Layer 4: Function

Answer 12

The Transport Layer provides host-to-host communication, handling data segmentation, reassembly, and error control.

It defines how data is sent.

Question 13

What is the Protocol Data Unit (PDU) at the Transport Layer (Layer 4)?

Answer 13

Segment.

Question 14

What are the two primary protocols at the Transport Layer (Layer 4)?

Answer 14

1. TCP (Transmission Control Protocol): Reliable, connection-oriented.
2. UDP (User Datagram Protocol): Unreliable, connectionless.

Question 15

What makes TCP a “reliable” protocol?

Answer 15

It uses a three-way handshake to establish a connection and uses sequencing and acknowledgments to ensure all data arrives in the correct order without errors.

Question 16

Why would you use UDP if it’s “unreliable”?

Answer 16

It is much faster than TCP because it does not have the overhead of acknowledgments or sequencing.

It’s ideal for time-sensitive applications like voice/video streaming or DNS lookups where speed is more important than perfect reliability.

Question 17

Layer 3: Function

Answer 17

The Network Layer is responsible for routing data between different networks.

It handles logical addressing (IP addresses).

Question 18

What is the Protocol Data Unit (PDU) at the Network Layer (Layer 3)?

Answer 18

Packet.

Question 19

What is the primary type of address used at the Network Layer (Layer 3)?

Answer 19

Logical Address, specifically the IP address (IPv4 or IPv6).

Question 20

What is the primary network device that operates at Layer 3?

Answer 20

A Router. Routers make forwarding decisions based on IP addresses to send data to other networks.

A multilayer switch also performs Layer 3 functions.

Question 21

Layer 2: Function

Answer 21

The Data Link Layer is responsible for transferring data within a local network segment.

It handles physical addressing (MAC addresses) and error detection.

Question 22

What is the Protocol Data Unit (PDU) at the Data Link Layer (Layer 2)?

Answer 22

Frame.

Question 23

What is the primary type of address used at the Data Link Layer (Layer 2)?

Answer 23

Physical Address, specifically the MAC (Media Access Control) address.

Question 24

What is the primary network device that operates at Layer 2?

Answer 24

A Switch. Switches make forwarding decisions based on MAC addresses to send data to the correct device on the local network.

Question 25

What are the two sublayers of the Data Link Layer?

Answer 25

1. **LLC (Logical Link Control):** Talks to the Network Layer above. Handles flow control. 2. **MAC (Media Access Control):** Talks to the Physical Layer below. Controls access to the media and handles physical addressing.

Question 26

Layer 1: Function

Answer 26

The **Physical Layer** is responsible for the actual transmission and reception of raw data bits over a physical medium (e.g., cables, radio waves).

Question 27

What is the Protocol Data Unit (PDU) at the Physical Layer (Layer 1)?

Answer 27

**Bits**.

Question 28

What are some examples of hardware or standards defined at the Physical Layer (Layer 1)?

Answer 28

Cables (Ethernet, fiber), connectors (RJ45), hubs, repeaters, transceivers, and signaling (voltages, light pulses, radio frequencies).

Question 29

What is **encapsulation**?

Answer 29

The process of adding a header (and sometimes a trailer) to data as it moves down the OSI stack on the sending device. ## Footnote Each layer wraps the data from the layer above it.

Question 30

Describe the data encapsulation process, including the PDU names.

Answer 30

Data from the Application layer becomes a **Segment** or **Datagram** at the Transport layer, a **Packet** at the Network layer, a **Frame** at the Data Link layer, and finally **Bits** on the Physical layer.

Question 31

What is decapsulation?

Answer 31

The process of removing headers and trailers as data moves up the OSI stack on the receiving device. ## Footnote Each layer "unwraps" the data and passes it up to the next layer.