Free CCNA | OSI Model & TCP/IP Suite | Day 3 | CCNA 200-301 Complete Course

Welcome to the CCNA Course

Introduction to the Course

• This course is a complete guide for the CCNA (Cisco Certified Network Associate) exam, offered by Jeremy’s IT Lab and is 100% free.

• Viewers are encouraged to stay until the end of the video for a quiz that will test their knowledge on the material covered.

• Anki flashcards are available for download via a link in the description, aiding in study and retention.

Understanding Networking Models

Overview of Networking Models

• The lesson focuses on two primary networking models: OSI Model and TCP/IP Suite, with TCP/IP often referred to simply as TCP/IP.

• Networking models categorize and structure networking protocols and standards, which define how network devices communicate.

Importance of Protocols

• A networking protocol consists of rules that dictate how devices and software should interact; examples include Ethernet standards discussed previously.

• Without standardized models like OSI or TCP/IP, different devices (e.g., Dell PCs vs iMacs) would be unable to communicate due to incompatible protocols.

The OSI Model Explained

Definition and Purpose

• The OSI model stands for Open Systems Interconnection model; it aims to standardize network communications across various systems.

• Developed by ISO in the late 1970s/early 1980s, it categorizes network functions into seven layers, facilitating interoperability among diverse devices.

Layers of the OSI Model

1. Layer 1 - Physical Layer: Involves standards for cables/interfaces relevant from previous discussions.

2. Layer 7 - Application Layer: Closest layer to end-users; interacts with applications like web browsers using protocols such as HTTP/HTTPS.

3. Encapsulation Process: Data sent through layers undergoes encapsulation where additional information is added at each layer before transmission over physical media; this process reverses at the receiving end (de-encapsulation).

Functions of Different Layers

Application Layer Functions

• The application layer identifies communication partners and synchronizes communication between systems during data exchange processes.

Presentation Layer Role

Understanding the OSI Model Layers

Presentation Layer Overview

• The presentation layer ensures that only the intended recipient can read the data through encryption and decryption as it is received. It translates between different application-layer formats to ensure compatibility with the receiving host.

• This layer's primary function is to translate data into an appropriate format for transmission.

Session Layer Functions

• The session layer (Layer 5) manages dialogues, or sessions, between communicating hosts. It establishes, maintains, and terminates connections between local applications (e.g., web browsers) and remote applications (e.g., YouTube).

• While understanding these layers is important, network engineers typically do not work directly with them; this responsibility falls to application developers.

Transport Layer Insights

• Data from the top three layers is sent down to the transport layer (Layer 4), which adds a header in front of the data for segmentation.

• The transport layer segments large pieces of data into smaller units for easier transmission and error management. This process minimizes issues during data transfer.

• It provides both host-to-host communication and process-to-process communications for applications.

Network Layer Responsibilities

• After segmentation, a Layer 3 header is added by the network layer, which provides connectivity across different networks using logical addressing (IP addresses).

• The network layer also selects optimal paths for data transmission among multiple possible routes. Routers operate at this layer.

Encapsulation Process Explained

• The encapsulation process involves preparing data at upper layers: adding a Layer 4 header creates a segment; then a Layer 3 header forms a packet.

• At Layer 2 (Data Link Layer), both a header and trailer are added to create a frame. This layer facilitates node-to-node connectivity and error detection/correction on physical media.

Physical Layer Characteristics

• Finally, at Layer 1 (Physical Layer), characteristics such as voltage levels and maximum transmission distances are defined. Digital bits are converted into electrical or radio signals for transmission over various mediums.

De-Encapsulation Process in Networking

Understanding De-Encapsulation

• The process of de-encapsulation occurs when data reaches a remote device, reversing encapsulation. The Data Link Layer translates raw physical data back into a complete frame.

• After removing the Layer 2 header and trailer, the remaining Layer 3 packet is left. This continues with the removal of the Layer 3 header to reveal the Layer 4 segment.

• Finally, upon removing the Layer 4 header, we retrieve the original data prepared by upper layers of the original device.

Key Terminology in OSI Model

• When an application sends data, it interacts with the Application layer. The combination of data and Layer 4 header is termed a Segment; adding a Layer 3 header creates a Packet; and adding a Layer 2 header results in a Frame.

• All these units are collectively referred to as Protocol Data Units (PDUs). For instance, at Layer 1 (Physical), PDUs are called bits.

Acronyms for OSI Model Layers

Memory Aids for OSI Layers

• To help remember OSI model layers, two acronyms are provided:

• From layer 7 to layer 1: "ALL PEOPLE SEEM TO NEED DATA PROCESSING."

• From layer 1 to layer 7: "PLEASE DO NOT TEACH STUDENTS POINTLESS ACRONYMS."

Introduction to TCP/IP Suite

Overview of TCP/IP Model

• The TCP/IP suite is another conceptual model used primarily on the Internet and other networks. It derives its name from foundational protocols TCP and IP.

• Developed by DARPA under the U.S. Department of Defense, it has fewer layers than OSI but is more relevant in modern networking practices.

Comparison Between OSI and TCP/IP Models

• The Application, Presentation, and Session layers of OSI correspond to one Application layer in TCP/IP. Network engineers often refer to these using OSI terminology despite using TCP/IP in practice.

• Both models share a Transport layer; however, their definitions differ at higher levels—OSI's Network maps to TCP/IP's Internet layer.

Data Transmission Example Using Hosts

Host Communication Process

• An example illustrates Host A sending video/audio data via Skype to Host B through two routers. Each host utilizes its respective TCP/IP stack during this communication.

Router Functionality During Transmission

• Routers operate at Layer 3 (Internet), focusing on IP addresses for forwarding packets without needing awareness of higher-layer protocols.

Final Steps in Data Reception

Understanding Same-Layer Interaction in TCP/IP

Overview of Communication Process

• The communication process between Skype on Host A and Host B exemplifies same-layer interaction, occurring multiple times during a call.

• The transport layer segment remains unchanged throughout the communication, simulating direct host-to-host interaction.

• Industry standard protocols (TCP/IP) ensure compatibility across different devices, allowing diverse systems to communicate seamlessly.

Learning Resources

• Supplementary materials will be provided for better retention of information covered in the lesson.

• An end-of-video quiz and pre-made flashcards will assist in memorization; links are available in the description.

• A Packet Tracer practice lab featuring 'simulation mode' will help analyze network traffic.

Quiz Questions and Answers

Question 1: HTTP Data Interaction

• The question asks about HTTP data from a YouTube server displayed via a web browser, with the correct answer being B, same-layer interaction.

• Adjacent-layer interaction involves different OSI layers; here both entities operate at Layer 7 (HTTP), making option A incorrect.

Question 2: PDU Naming

• The second question addresses encapsulated HTTP data with three headers and one trailer. The correct answer is C, Frame.

• Definitions clarify that packets refer to Layer 3 PDUs while segments pertain to Layer 4 PDUs; thus options A and B are incorrect.

Question 3: Relevant OSI Layers for Network Engineers

• This question identifies relevant OSI layers for network engineers. Answer A (transport, network, data link, physical) is correct as it includes all necessary layers.

Understanding TCP/IP Model Equivalents

Link Layer Equivalence

• The Link layer of the TCP/IP model corresponds to both the Data Link and Physical layers of the OSI model; hence D is correct.

Final Quiz Question: Host-to-Host Communications

• The last question focuses on which OSI layer provides host-to-host communications. Answer C (Transport layer) is confirmed as correct since it facilitates this type of communication.

Conclusion and Support Information

Video Wrap-Up

• Viewers are encouraged to support by subscribing, liking, commenting, or sharing the video with others studying for CCNA.