| Layer | Function | Protocols |
|---|---|---|
| 7. Application | User interface (HTTP, SMTP, FTP) | HTTP, FTP, SMTP, DNS, WebSocket |
| 6. Presentation | Data translation (encryption, compression) | SSL/TLS, JPEG, MPEG, ASCII |
| 5. Session | Manages connections (establish, maintain, terminate) | NetBIOS, RPC, SIP |
| 4. Transport | End-to-end communication (reliability, flow control) | TCP, UDP, SCTP |
| 3. Network | Logical addressing & routing | IP (IPv4, IPv6), ICMP, BGP, OSPF |
| 2. Data Link | Physical addressing (MAC), error detection | Ethernet, Wi-Fi (802.11), PPP |
| 1. Physical | Raw bit transmission (cables, signals) | DSL, USB, Fiber Optic, Bluetooth |
| Layer | OSI Equivalent | Protocols |
|---|---|---|
| Application | L5-L7 | HTTP, FTP, DNS, SMTP, SSH |
| Transport | L4 | TCP, UDP |
| Internet | L3 | IP, ICMP, ARP |
| Network Access | L1-L2 | Ethernet, Wi-Fi, PPP |
| Protocol | Port | Use Case | Key Features |
|---|---|---|---|
| HTTP/HTTPS | 80/443 | Web browsing | Stateless, RESTful APIs, TLS encryption |
| FTP/SFTP | 21/22 | File transfer | FTP (unencrypted), SFTP (SSH-based) |
| SMTP | 25 | Email sending | Simple Mail Transfer Protocol |
| DNS | 53 | Domain name resolution | Converts domain names to IPs |
| SSH | 22 | Secure remote access | Encrypted alternative to Telnet |
| WebSocket | 80/443 | Real-time communication | Full-duplex, persistent connection |
| Protocol | Reliability | Speed | Use Case |
|---|---|---|---|
| TCP | ✅ (Acks, retransmission) | Slower | Web, email, file transfer |
| UDP | ❌ (No guarantees) | Faster | Video streaming, gaming, VoIP |
| SCTP | ✅ (Multi-streaming) | Medium | Telecom, VoIP |
| Protocol | Purpose |
|---|---|
| IP (IPv4/IPv6) | Logical addressing & routing |
| ICMP | Error reporting (e.g., ping) |
| ARP | Maps IP to MAC address |
| BGP | Internet routing (between ISPs) |
| OSPF | Internal network routing (within AS) |