1.1 Understanding the OSI Model

What does OSI Model stand for?

Open Systems Interconnection Reference Model.

What is the OSI Model?

Describes the process data takes as it traverses the network.

What is a mneumonic for all layers?

All People Seem To Need Data Processing.

What is Layer 1 known as?

The physical layer.

What happens in Layer 1 (physical layer)?

Physical signals are sent between cables and fibers on the network.

How do you troubleshoot Layer 1 (physical layer) issues?

Run loopback tests, test and replace cables, and swap adapted cards.

What is Layer 2 known as?

Data Link Layer.

What happens in Layer 2 (data link layer)?

Responsible for communication between two devices on the network.

What are some other common names for Layer 2?

Data Link Control (DLC) layer, Media Access Control (MAC) layer, and switching layer.

What is Layer 3 known as?

Network Layer.

What happens in Layer 3 (network layer)?

Looks at the destination IP address for the next hop, fragmenting frames to traverse different networks.

What is Layer 3 (network layer) also known as and why is it known like that?

Called the routing layer because routers are used to figure out how to forward traffic.

What is Layer 4 known as?

Transport Layer.

What happens in Layer 4 (transport layer)?

Information is transported from one device to the other.

What is Layer 4 (Transport Layer) also called?

The post office layer.

What protocols are used in Layer 4 (transport layer)?

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are used.

What is Layer 5 known as?

Session Layer.

What happens in Layer 5 (session layer)?

Provides communication management between two points.

What is Layer 6 known as?

Presentation Layer.

What happens in Layer 6 (presentation layer)?

Puts data into a format we can see, using character encoding and application encryption.

What is Layer 6 (presentation layer) often combined with?

Application layer.

What is Layer 7 known as?

Application Layer.

What happens in layer 7 (application layer)?

It’s the layer that we see and can interact with.

What ports are used in Layer 7 (application layer)?

HTTP, HTTPS, FTP, DNS, and POP3.

What are the real world uses of layer 1 (physical)?

Cables, fiber optics, and signals.

What are the real world uses of layer 2 (data link)?

Frames, MAC address, extended unique identifier (EUI-48, EUI-64), and switches.

What are the real world uses of layer 3 (network)?

IP Addresses, routers, and packets.

What are the real world uses of layer 4 (transport)?

TCP segments and UDP datagrams.

What are the real world uses of layer 5 (session)?

Control protocols and tunneling protocols.

What are the real world uses of layer 6 (presentation)?

Application encryption (SSL/TLS).

What are the real world uses of layer 7 (application)?

It’s the actual use of the application by you.