The OSI model (Open Systems Interconnection model) is a conceptual framework used to understand and design how data is transmitted over a network. It divides the networking process into seven distinct layers, each with specific roles and responsibilities. Think of it as a universal language for computer networking.
Application Layer (Layer 7)
- Purpose: Interface for end-user processes and applications.
- Examples: HTTP, FTP, SMTP, DNS
- Analogy: The app you’re using (like a web browser).
Presentation Layer (Layer 6)
- Purpose: Translates data formats, encryption/decryption, compression.
- Examples: SSL/TLS, JPEG, MPEG
- Analogy: The translator that makes sure both ends understand the data (e.g., translating from English to French).
Session Layer (Layer 5)
- Purpose: Manages connections (sessions) between applications.
- Examples: NetBIOS, RPC
- Analogy: A moderator keeping a conversation on track and orderly.
Transport Layer (Layer 4)
- Purpose: Reliable data transfer with error checking, flow control.
- Examples: TCP, UDP
- Analogy: A delivery truck ensuring your packages are sent and received in order.
Network Layer (Layer 3)
- Purpose: Routing, addressing, and delivering packets between networks.
- Examples: IP, ICMP, IPsec
- Analogy: GPS or map used by the delivery truck to find the right address.
Data Link Layer (Layer 2)
- Purpose: Provides reliable data transfer across the physical link. Handles MAC addressing.
- Examples: Ethernet, PPP, MAC addresses
- Analogy: The street address or apartment number on the envelope.
Physical Layer (Layer 1)
- Purpose: Transmits raw bits over physical medium (electrical, light, radio).
- Examples: Cables, switches, radio signals
- Analogy: The actual wires or Wi-Fi signals that carry the envelope.
Mnemonic to Remember:
“Please Do Not Throw Sausage Pizza Away”
(Physical, Data Link, Network, Transport, Session, Presentation, Application)