Understand the OSI Model
This skill provides an in-depth understanding of the OSI Model, a foundational concept in computer networking. It explores each of the seven layers, detailing their functions and significance in data transmission across networks. The skill contrasts the OSI Model with the TCP/IP Model, highlighting their differences and practical applications in network troubleshooting. Key concepts such as logical and physical addressing, data encapsulation, and protocols like TCP and UDP are thoroughly examined to equip learners with essential networking knowledge.
Full skill from HPE6-A86. Preview the training IT teams trust.
Updated
Skill 1 of 28 in HPE6-A86
What you'll learn
- Identify the seven layers of the OSI model in order and explain why the model helps isolate network troubleshooting
- Compare the OSI model with the TCP/IP model and explain how TCP/IP combines the application, presentation, and session layers
- Describe how the presentation layer handles encryption, compression, and data formatting and how the session layer manages connections
- Choose between TCP and UDP for an application, such as SSH on port 22 versus real-time video conferencing
- Explain how the TCP three-way handshake uses SYN, SYN-ACK, and ACK messages to establish a reliable connection
- Describe encapsulation and decapsulation from segments to packets to frames and how routers and switches use layer 3 and layer 2 addresses
Free 48-minute video lesson with a full transcript and knowledge checks. No account needed to watch.
Introduction
Let's discuss what we plan to learn in this skill!
What is the OSI Model?
The OSI model consists of 7 different layers. Whilst it does not accurately model the reality of modern networking, it is referenced extensively within the industry. In this video we discuss what the OSI model is, why it is important and contrast it against the TCP/IP model.
Knowledge Check
Which layer in the OSI model is responsible for establishing, managing, and terminating sessions between applications?
Application, Presentation and Session Layers
In this video we explore the top layers of the OSI model. Namely the Application, Presentation and Session layers. Let's dive in and find out what operations are performed within these layers!
Knowledge Check
Which layer of the OSI model is responsible for handling encryption and data formatting?
The Transport Layer
Now let's turn our attention to the fourth layer within the OSI model - the transport layer. We discuss what is controlled at the transport layer and discuss two very important protocols - TCP and UDP!
Knowledge Check
Which protocol is used for reliable data transmission at the transport layer of the OSI model?
The 3 Way Handshake
The 3 way handshake is the vital first step in establishing a TCP connection. It is used to ensure both parties are ready and able to transmit and receive data. In this video we walk through how the TCP handshake is used to create reliable connections and identify potential problems when data is lost or corrupted.
Knowledge Check
What is the correct sequence of messages in a TCP three-way handshake?
The Network Layer
The network layer is defined via the use of "packets". This is the layer used for logical addressing in the form of IP addresses. In this video we discuss the purpose of layer 3 addresses and highlight the role of routers in moving packets across different networks.
Knowledge Check
Which of the following is a primary function of the network layer in the OSI model?
The Data Link and Physical Layers
The last 2 layers in the OSI model are the data link layer and the physical layer. These layers deal with data frame and binary bits. In this video we discuss the use of MAC addresses and how data is transported across physical media!
Knowledge Check
What is the primary purpose of the Data Link Layer in the OSI model?
Validation
Let's now validate what we've learned in this skill with a series of questions:
Knowledge Check
Which layer of the OSI model deals with "segments"
Knowledge Check
Which layer of the OSI model deals with "frames"?
Knowledge Check
Which layer of the OSI model deals with "packets"?
Knowledge Check
Which layer of the OSI model deals with "bits"?
Knowledge Check
Match the layers of the OSI model to the layers within the TCP./IP model.
This interactive assessment is available in the full learning experience.
Knowledge Check
Match the OSI layers with the correct value.
This interactive assessment is available in the full learning experience.
Frequently asked questions
What does the Understand the OSI Model lesson cover?
The lesson walks through the seven OSI layers in order (application, presentation, session, transport, network, data link, and physical) and explains what each contributes to moving data between two devices. It also covers the TCP/IP model, TCP versus UDP, the TCP three-way handshake, and encapsulation and decapsulation from segments to packets to frames.
How long is the OSI model lesson and where does it fit in the HPE6-A86 course?
The lesson runs 48 minutes and is the opening skill of the HPE Aruba Networking Certified Associate (HPE6-A86) course, which maps to the HPE Network Switching Associate certification. It sets the networking foundation for later course topics such as Layer 2 switching, IPv4 and IPv6, VLANs, OSPF, and ACLs, across roughly 23.4 hours of training per learner.
Why do network teams still use the OSI model if real networks follow TCP/IP?
The lesson explains that the seven layers are not how traffic operates in reality, but they let a team isolate a problem precisely, such as separating a transport layer issue from a data link issue. Real-world behavior is more closely modeled by TCP/IP, which combines the application, presentation, and session layers into a single application layer.
When should an application use TCP instead of UDP?
The lesson contrasts SSH on port 22, which uses TCP for a reliable connection, with real-time video conferencing, which uses UDP because it is lightweight and fast. The team member learns why losing some data in a live call matters less than speed, and why TCP establishes connections with a SYN, SYN-ACK, and ACK three-way handshake.
How do routers and switches relate to OSI layers 2 and 3?
The lesson shows data being encapsulated from a layer 4 segment into a packet and then a frame before transmission as bits over physical media, then decapsulated in reverse at the destination. Routers route packets using layer 3 addresses, while switches forward frames using layer 2 addresses.
How can an IT Director or Training Manager use this lesson when onboarding junior network staff?
The course Technical Copy recommends assigning the training before newer staff get independent access to network changes, then pairing completion with internal runbooks and supervised maintenance windows. Playlists help sequence the course into onboarding paths, and Team Reporting shows per-learner progress and completion across assigned learners.
Team training path
Turn this skill into assignable team training
This free skill is a preview of the courses your team can assign, track, and report on with CBT Nuggets.
Free training library
More free lessons from CBT Nuggets
Microsoft Windows Server
Microsoft PowerShell 4 Foundations
Free lesson from PowerShell · 7h 57m
DevOps
Docker (v18.06.3)
Free lesson from Docker · 2h 6m
Networking
Border Gateway Protocol (BGP): Basic Operations
Free lesson from Border Gateway Protocol (BGP) · 60m
Networking
Define Wireless Network Architectures
Free lesson from Wireless Design Professional Training · 55m
Python
Introduction to Programming and Python
Free lesson from Certified Associate in Python Programming (PCAP) · 57m
Azure
Understand the Point of the Cloud
Free lesson from Microsoft Certified: Azure Fundamentals (AZ-900) · 1h 4m
$59
seat / mo, billed annually