Chapter 2 - The OSI Model Flashcards
What does the OSI Model stand for?
Open Systems Interconnection Reference Model
What is Layer 1 in the OSI Model?
Layer 1 - Physical
What is Layer 2 in the OSI Model?
Layer 2 - Data Link
What is Layer 3 in the OSI Model?
Layer 3 - Network
What is Layer 4 in the OSI Model?
Layer 4 - Transport
What is Layer 5 in the OSI Model?
Layer 5 - Session
What is Layer 6 in the OSI Model?
Layer 6 - Presentation
What is Layer 7 in the OSI Model?
Layer 7 - Application
What are the 7 OSI Model layers?
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.
Describe what Layer 1 does.
The Physical layer handles the physical cables and electrical signals sent across the network.
Describe what Layer 2 does.
The Data Link layer handles the ethernet frames, source and destination MAC addresses and is also used by switches.
Describe what Layer 3 does.
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.
Describe what Layer 4 does.
The Transport layer handles TCP/UDP encapsulation, segments, and the ports used. It also separates and reassembles frames.
Describe what Layer 5 does.
The Session layer handles communication management between devices. It also does the control and tunneling protocols and links to the transportation layer.
Describe what Layer 6 does.
The Presentation layer handles encryption (SSL/TLS) and character encoding (HTTPS) and works with the Application Layer.
Describe what Layer 7 does.
The Application layer is what you the end-user sees when using an application or browsing the web.
Describe how data is sent and received using the OSI Model
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.
How does encapsulation work?
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.
