gen-define-the-osi-model-and-give-one-short-worked-example-7cb0

Define the OSI model and give one short worked example.

# OSI Model Definition The **OSI (Open Systems Interconnection) Model** is a conceptual framework that standardizes network communication into **7 layers**. Each layer performs specific functions and communicates with the layers directly above and below it. ## The 7 Layers (top to bottom): 1. **Application** - User interface and network services (HTTP, FTP, DNS) 2. **Presentation** - Data formatting, encryption, compression 3. **Session** - Establishes/manages connections between applications 4. **Transport** - Reliable data transfer, segmentation (TCP, UDP) 5. **Network** - Logical addressing and routing (IP) 6. **Data Link** - Physical addressing, frame creation (MAC addresses, Ethernet) 7. **Physical** - Raw bit transmission over physical medium (cables, signals) ## Short Worked Example: Sending an Email **Sending (top-down):** - **L7-Application**: Email client uses SMTP protocol - **L6-Presentation**: Email encoded in MIME format, possibly encrypted - **L5-Session**: SMTP session established with mail server - **L4-Transport**: TCP breaks email into segments, adds port numbers - **L3-Network**: IP adds source/destination IP addresses - **L2-Data Link**: Ethernet adds MAC addresses, creates frames - **L1-Physical**: Frames converted to electrical signals on network cable **Receiving (bottom-up):** The process reverses—signals become bits, frames, packets, segments, then readable email data.