TCP/IP — The Internet Protocol Suite
Learn how TCP and IP work together to transmit data reliably across the internet.
What is TCP/IP?
TCP/IP (Transmission Control Protocol / Internet Protocol) is the fundamental suite of protocols that powers the internet. While the OSI model has 7 layers, the TCP/IP model simplifies this into 4 layers.
The TCP/IP Model Layers
- Application Layer — HTTP, FTP, DNS, SMTP. What users and apps interact with.
- Transport Layer — TCP and UDP. Handles end-to-end communication.
- Internet Layer — IP protocol. Handles addressing and routing packets.
- Network Access Layer — Ethernet, Wi-Fi. Physical transmission of data.
IP — Internet Protocol
IP is responsible for addressing and routing packets from source to destination across networks.
- IPv4 — 32-bit addresses (e.g., 192.168.0.1). About 4.3 billion addresses. Nearly exhausted.
- IPv6 — 128-bit addresses (e.g., 2001:db8::1). Virtually unlimited addresses. The future of networking.
TCP — Transmission Control Protocol
TCP provides reliable, ordered, error-checked delivery of data. Before sending data, TCP performs a 3-way handshake:
- SYN — Client says "I want to connect."
- SYN-ACK — Server replies "Acknowledged, go ahead."
- ACK — Client confirms "Connected."
Used for: web browsing (HTTP/HTTPS), email, file transfers.
UDP — User Datagram Protocol
UDP is fast but unreliable. It sends data without establishing a connection and without guaranteeing delivery or order. Used for: video streaming, online gaming, DNS lookups — where speed matters more than perfection.
Ports
Ports allow a single IP address to run multiple services simultaneously. Common port numbers:
- Port 80 — HTTP
- Port 443 — HTTPS
- Port 22 — SSH
- Port 25 — SMTP (Email)
- Port 53 — DNS
What's Next?
See TCP/IP in action with HTTP & HTTPS, or learn how domain names map to IP addresses with DNS Explained.