OSI Reference Model (Open Systems Interconnection Model)
The OSI model is a conceptual framework developed by the International Organization for Standardization (ISO) to standardize the functions of a communication system into seven distinct layers. It helps understand how data travels from one device to another across a network by breaking down the communication process into manageable parts.
🔹 Layer 1: Physical Layer
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Manages the physical connection between devices. It deals with hardware elements like cables, switches, voltage levels, and data transmission rates.
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Think of it as the road system where data travels in the form of electrical signals or light pulses.
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Examples: Ethernet cables, fiber optics, hubs, physical ports.
🔹 Layer 2: Data Link Layer
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Ensures that data transferred between two directly connected nodes is error-free and properly framed.
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Acts as the traffic cop, organizing data into frames and managing physical addressing through MAC (Media Access Control) addresses.
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Examples: Switches, MAC addresses, Ethernet protocol.
🔹 Layer 3: Network Layer
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Handles routing—determining the best path for data to travel across interconnected networks.
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Network Layer acts like a digital map, using IP addresses to help data find the best route to its destination.
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Examples: Routers, IP, ICMP.
🔹 Layer 4: Transport Layer
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Manages end-to-end communication, ensuring data is delivered in order, without loss, duplication, or errors.
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It's the delivery service—breaking data into segments and ensuring everything arrives safely and in order.
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Examples: TCP (reliable), UDP (faster but less secure).
🔹 Layer 5: Session Layer
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Session Layer acts like a coordinator that starts, manages, and ends conversations between applications.
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Acts like a conversation manager, keeping track of who is talking to whom and ensuring the dialogue stays on track.
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Examples: Remote Procedure Calls (RPC), NetBIOS.
🔹 Layer 6: Presentation Layer
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Translates data between the application layer and the network format. It formats the data, compresses it, and keeps it secure through encryption.
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Think of it as a translator, making sure data is in a readable and usable format for both sender and receiver.
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Examples: SSL/TLS, JPEG, ASCII, MPEG.
🔹 Layer 7: Application Layer
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Provides network services directly to user applications like browsers and email clients.
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It’s the interface to the user, enabling interactions like browsing, emailing, or file transfers.
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Examples: HTTP, FTP, SMTP, DNS, Telnet.
TCP/IP Model (Transmission Control Protocol / Internet Protocol)
The TCP/IP model is a real-world, practical networking model that forms the backbone of the internet. Developed by the U.S. Department of Defense, it's more streamlined than the OSI model and focuses on how data actually moves across networks.
🔸 Layer 1: Network Interface Layer (Link Layer)
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Handles the physical transmission of data over network hardware, including framing and MAC addressing.
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Functions as the physical connection handler, communicating directly with the hardware.
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Examples: Ethernet, Wi-Fi, ARP.
🔸 Layer 2: Internet Layer
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Responsible for logical addressing, packet forwarding, and routing. It decides how packets travel from source to destination.
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Works like a post office, assigning addresses and sending data to the correct recipient.
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Examples: IP, ICMP, IGMP.
🔸 Layer 3: Transport Layer
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Ensures reliable or fast communication between systems. TCP ensures reliability; UDP offers speed.
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Similar to a logistics system, managing delivery speed, error checking, and reordering.
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Examples: TCP, UDP.
🔸 Layer 4: Application Layer
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Offers services and applications for end-users. This includes everything from web browsing to email to file transfers.
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It is the user-facing layer that powers most online activities.
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Examples: HTTP, FTP, DNS, Telnet, SMTP.