Recording-2025-02-21T20:40:18.488Z

OSI Model Basics

• Definition: A theoretical framework for understanding networking, dividing communication into seven abstraction layers.

Layers of the OSI Model

1. Physical Layer

• Responsible for transmitting raw bits.

2. Data Link Layer

• Organizes raw bits into frames.

• Ensures correct delivery of frames; Ethernet is key here.

3. Network Layer

• Responsible for routing data frames across networks.

• Uses IP for routing; can be understood through the envelope analogy—encapsulates data for transport.

4. Transport Layer

• Handles end-to-end communication between nodes.

• Two main protocols: TCP and UDP.

  • TCP (Transmission Control Protocol): Provides reliable communication, segments data, orders packets, and checks for errors.

  • UDP (User Datagram Protocol): Faster, simpler, with less error checking; responsibility lies with the receiving device to verify packets.

Higher Layers (Session, Presentation, Application)

• Individually, these layers are less emphasized in real-world applications, often collapsed into one for simplicity.

• Example protocols like HTTP operate at layer 7.

Data Transmission Example

• HTTP request sent to web server goes through:

  • Application Layer: Adds HTTP headers.

  • Network Layer: IP headers added (source/destination IP addresses).

  • Data Link Layer: MAC headers added (source/destination MAC addresses).

  • Physical Layer: Transmits raw bits.

• At the web server, headers are removed layer-by-layer to process the request.

Real-World Application and Load Balancing

• OSI model serves as a common language among networking professionals, despite its abstraction from reality.

• Load balancers categorized as Layer 4 (TCP level) and Layer 7 (application level, such as HTTP).

• Example of load balancing is traffic management, similar to routing cars around congestion.