Start from zero: what a computer network actually is
A network is machines exchanging packets. This lesson defines the eight terms every networking unit assumes — packet, IP address, port, protocol, client/server, router, DNS, latency/bandwidth — and traces one URL from your browser to a server.
You type https://example.com and press Enter. Half a second later, a web page appears. In that half-second your request left your laptop, crossed potentially thousands of kilometres of cable and fibre, found a specific machine out of billions connected to the internet, and came back with an answer — all without you doing a thing. That journey is not magic. It is a stack of agreements — protocols — that every device on the planet honours. This lesson names the eight ideas behind those agreements, so every unit that follows has somewhere to hang its details.
The one idea networking is built on
No two computers on earth are directly wired together. Instead, every machine talks to its nearest neighbour, which passes the message on, and so on until it arrives. The message travels as small chunks called packets, and every device along the way makes one small forwarding decision. That is the whole idea. Everything else — speed, reliability, security, naming — is a layer of agreements built on top of that single forwarding loop. The senior units in this track each zoom into one of those layers. This lesson gives you the vocabulary to read them without getting stuck on definitions.
The eight words the rest of the track assumes
These eight terms appear in every networking unit without re-introduction. If you have ever wondered why a page loads slowly on a fast connection, or why a server can handle thousands of users at once, the answer lives somewhere in this table. Spend two minutes here and the rest of the track will make sense on first read.
| Word | What it is | Why it exists |
|---|---|---|
| Packet | A small, fixed-size chunk of data with a destination address attached. | So many senders can share the same wire without waiting for each other to finish. |
| IP address | A unique number assigned to every device on a network (e.g. 93.184.216.34). | So packets know where to go — like a postal address for data. |
| Port | A number (0–65535) that identifies which program on a machine should receive a packet. | So one machine can run a web server (port 443) and a mail server (port 25) at the same time. |
| Protocol | A written agreement about the exact format and order of messages two machines exchange. | So devices built by different manufacturers can talk to each other without prior arrangement. |
| Client / server | The client asks; the server answers. Your browser is a client; example.com is a server. | So resources can live in one place and be served to many requesters on demand. |
| Router | A device that reads a packet’s destination IP and forwards it one hop closer to that destination. | So packets can cross the world through thousands of intermediate devices with no central switchboard. |
| DNS | A distributed system that translates human-readable names (example.com) into IP addresses. | So you can type a name instead of memorising a number, and the number can change without notice. |
| Latency / bandwidth | Latency is the delay before data starts arriving; bandwidth is how much can arrive per second. | So engineers can reason about why a page feels slow (high latency) versus why a download stalls (low bandwidth). |
How they fit together
Read these words in order and they tell the story of one request. You type https://example.com. Your browser asks a DNS resolver to turn that name into an IP address. Armed with an IP, it sends packets — each carrying that IP plus port 443 — across your local router, which passes them hop by hop through the internet’s backbone routers to the destination machine. That machine is a server running a web program; your laptop is the client. TCP (the protocol you will study in Unit 03) makes sure every packet arrives intact and in order. TLS (Unit 05) encrypts them so no one in between can read them. The server sends its response back the same way. Latency tells you how long the first byte took; bandwidth tells you how fast the rest poured in. That single journey — type URL, get page — is the thread every later unit pulls on.
▸Why this works
Why break data into packets at all, instead of sending one continuous stream? Because a shared cable can only carry one signal at a time. If your video call held the cable for its entire duration, nobody else on your street could load a web page. Packets let thousands of conversations interleave on the same wire, each grabbing a slot, so everyone gets a fair share. This idea — packet switching — was invented in the 1960s and is still the foundation of the internet today.
What does DNS do and why does it exist?
Order the steps a browser takes from the moment you press Enter to the page loading:
- 1 DNS resolves the domain name to an IP address
- 2 Browser sends packets to that IP address on port 443
- 3 Routers forward the packets hop by hop to the server
- 4 Server responds and the browser renders the page
- 01Why are messages broken into packets instead of sent as one continuous stream?
- 02Trace the journey from typing a URL to the page appearing, naming each concept.
A network is, at its core, machines forwarding small chunks of data — packets — toward a destination address. IP addresses identify every device; ports identify which program on that device should handle the data; protocols define the exact rules two sides follow. DNS translates the names you type into the numbers machines need. Routers make thousands of small forwarding decisions so packets can cross the globe with no central switchboard. Latency measures how long data takes to start arriving; bandwidth measures how much can flow per second. TCP and TLS — which you will study in Units 03 and 05 — add reliability and security on top of this foundation. Now when you see a page load slowly, you can ask the right question: is it high latency (the first byte took too long), low bandwidth (the data poured in too slowly), or a DNS failure (the name never resolved at all)? That question is your first step from user to engineer.
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