The Rules of the Road
Protocols are the shared languages and procedures that let billions of different devices communicate seamlessly.
Encapsulation Stepper
Your browser builds a plain request. At this point there is no addressing, no ports, no error checking — just the message itself.
| Method | GET | What the client wants to do |
| Path | /index.html | Resource being requested |
| Host | example.com | Which site on this server |
| User-Agent | Mozilla/5.0 | Client identification |
TCP Three-Way Handshake
The client opens the connection by picking a random initial sequence number and sending a segment with only the SYN flag set. No application data travels yet.
| Source Port | 51544 | Ephemeral client port |
| Dest Port | 443 | HTTPS listener |
| Seq | 1829371002 | Random client ISN |
| Ack | 0 | Nothing to acknowledge yet |
| Flags | SYN | Request to synchronize |
| Window | 64240 | Client receive buffer |
| Options | MSS=1460, SACK, WS=8 | Capabilities offered |
IP: The Addressing Layer
The Internet Protocol (IP) is responsible for addressing and routing packets. Every device connected to the internet has an IP address, and every packet header contains a source and destination IP. IP's job is to get packets as close to the destination as possible, but it doesn't guarantee delivery.
TCP: The Reliable Delivery Layer
The Transmission Control Protocol (TCP) sits on top of IP and adds reliability. It breaks data into segments, numbers them, acknowledges receipt, and retransmits anything that gets lost. It also manages flow control so a fast sender doesn't overwhelm a slow receiver.
HTTP: The Web Layer
HyperText Transfer Protocol (HTTP) is the language web browsers and servers use to request and deliver web pages, images, and APIs. When you visit a URL, your browser sends an HTTP request; the server replies with an HTTP response containing the requested resource.
Key Term
Protocol Stack
A layered architecture where each layer handles a specific job and relies on the layers below it. This modularity is why the internet can evolve one layer at a time.