OSI (Open Systems Interconnection) Model
Memonic
1 Physical -data cables, cat6
2 Data - Switching, MAC address
3 Network - IP address, routing
4 Transport - TCP/UDP
5 Session - Session Management
6 Presentation - WMV, JPEG, MOV
7 Application - HTTP, SMTP
Upper Layers (Software-Focused)
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Layer 7: Application Layer
- Function: Directly interacts with the software application, providing network services to the user.
- Examples: HTTP, HTTPS, FTP, SMTP, DNS.
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Layer 6: Presentation Layer
- Function: Ensures data is readable by the receiving system. Handles data formatting, encryption, and compression.
- Examples: SSL/TLS, JPEG, MPEG.
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Layer 5: Session Layer
- Function: Establishes, maintains, and terminates communication sessions (dialogues) between applications.
- Examples: NetBIOS, RPC (Remote Procedure Call).
Lower Layers (Hardware & Data-Focused)
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Layer 4: Transport Layer
- Function: Ensures the reliable, sequential, and error-free delivery of data between systems. Handles data segmentation and flow control.
- Examples: TCP, UDP.
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Layer 3: Network Layer
- Function: Handles logical addressing (e.g., IP addresses) and routing, determining the best physical path for data across different networks.
- Examples: IP (IPv4/IPv6), ICMP, Routers.
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Layer 2: Data Link Layer
- Function: Facilitates node-to-node data transfer. It packages data into frames and uses physical hardware addresses (MAC addresses).
- Examples: Ethernet, Wi-Fi (802.11), Switches.
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Layer 1: Physical Layer
- Function: Manages the actual physical hardware. It translates data frames into raw electrical, optical, or radio signals to transmit bits across a medium.
- Examples: Cables (Twisted-pair, Fiber optic), Hubs, Repeaters.