what is TCP/IP and OSI? // FREE CCNA // EP 3

Summary

The episode introduces why networking models exist, explains the TCP/IP and OSI models, and uses device examples and quiz questions to show how network equipment maps to OSI layers.

Why networking models matter

Early computer networks were often built independently by different organizations and companies. Their proprietary designs used incompatible technologies, so one company’s network could not necessarily communicate with another’s.

ARPANET, created in 1969 with U.S. Department of Defense involvement, demonstrated that computers could be connected and exchange data using packet switching. However, a shared idea for networking did not by itself guarantee compatibility.

Networking models and standards provide common rules that allow devices made by different companies to communicate.

TCP/IP model

The TCP/IP model is presented as the model broadly implemented by modern computers. It organizes networking functions into layers, making the system easier to understand and build.

The episode describes a traditional four-layer version:

• Physical: The means of transmitting signals, such as cables.
• Network: IP addressing and routing packets between networks.
• Transport: TCP, UDP, and port numbers.
• Application: Protocols used by applications, such as when a web browser connects to a website.

In the course’s Cisco-oriented view, the Physical layer is split into Physical and Data Link, creating a five-layer version. The Data Link layer covers MAC addresses and communication between devices on the same network. Switches use these addresses to forward information.

OSI model and why it is still used

The OSI model has seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

Its first four layers align with the corresponding layers in the five-layer TCP/IP view. The TCP/IP model groups the OSI Session and Presentation functions into its Application layer rather than treating them as separate layers.

Although TCP/IP became the more widely adopted model, the OSI model remains common in networking terminology and troubleshooting. Network engineers often identify a problem by its OSI layer—for example, a Layer 1 physical issue or a Layer 7 application issue.

The episode advises CCNA students to learn both models, especially the seven OSI layer names and their order.

OSI layer mnemonics

• Top to bottom (Application to Physical): “All People Seem To Need Data Processing.”
• Bottom to top (Physical to Application): “Please Do Not Throw Sausage Pizza Away.”

Device examples and quiz lessons

• Switch: Primarily Layer 2, the Data Link layer; it uses MAC addresses.
• Router: Layer 3, the Network layer; it uses IP addresses to route packets.
• Hub: Primarily Layer 1, the Physical layer; it repeats electrical signals and does not interpret MAC addresses.
• Repeater: Layer 1; it repeats signals.
• Bridge: Layer 2; like a switch, it deals with Layer 2 information.
• Wireless access point: Can operate at Layers 1 and 2. In the quiz, the switch is the best answer for the device that primarily operates at Layer 2.

Speakers and sources featured

• Speaker: NetworkChuck, the video’s narrator and instructor.
• Sponsor: Boson Software, identified by the narrator as the course sponsor.
• Historical organizations and companies mentioned: The U.S. Department of Defense, ARPANET, IBM, Apple, and Microsoft.