1The whole trip

You press Enter. Your request sets off across half the world.

Enter
waiting for shop.example
Milliseconds since you pressed Enter0 ms

Illustrative model. Distances are straight-line estimates. Time per round trip = 2 × distance × 1.5 for indirect routes ÷ 200,000 km/s, the speed of light in glass fibre.

2DNS line

Finding the address

Computers find each other by number, called an IP address. The Domain Name System (DNS) is the internet's address book. It turns a name like shop.example into a number.

  1. Your browser asks a resolver, a lookup service run by your internet provider.
  2. The resolver asks a root server, which knows who runs each ending, such as .example.
  3. The .example registry points to the server that holds the records for shop.example.
  4. That authoritative server answers with the number 203.0.113.42.

The resolver keeps an answer for its time to live (TTL), here 300 seconds. The ring runs 10 times faster than real time.

Lookup time0 ms
Round trips4
Saved by cache0 ms
13root server identities, named A to M
12independent organisations run them
1,800+copies of them around the world

Your resolver talks to the nearest copy, so the root is rarely far away. Source: root-servers.org.

3TCP, TLS and HTTP lines

Shaking hands

One way
Round trip
Round trips
First byte at

Bar: time to first byte in ms, on a fixed 0 to 1,000 ms scale. Illustrative model: light in fibre at 200,000 km/s, routes 1.5 times the straight line. Trains run 10 times slower than real time.

4CDN line

The nearby copy

A content delivery network (CDN) keeps copies of a site on edge servers in many cities. Your browser talks to the closest one instead of the origin, the site's home server.

Round trips3
Km of fibre
First byte at
Saved

5Packet lines

Packets, not files

Networks move data in small pieces called packets. A standard Ethernet packet holds up to 1,500 bytes. About 40 of those are headers: the addresses and a sequence number.

Packets needed
Sent
Lost
Resent
In order

6Rendering line

Building the page

HTML: what is on the page<nav>Shop</nav> <h1>Today's menu</h1> <img src="dish-1.jpg">
CSS: how it looksnav { background: black; } h1 { font-weight: 800; } img { border-radius: 8px; }
shop.example/menu
ShopMenu · Order · Visit
Today's menuFresh from the kitchen, served until 10 pm
Grilled tikkaPKR 1,450
Garden bowlPKR 990
Mango sundaePKR 650
Order for pickup

7All lines at once

The waterfall

Load time
Bytes sent
Requests
No data flowing

Illustrative model: one 20 Mbit/s line shared by all downloads, round trips from the scene 3 model, six connections per host unless HTTP/2 is on. Server time and TCP slow start are left out.

Under a second, a dozen stops, thousands of kilometres.

Sources: root-servers.org, Root Server System (13 identities, 12 operators, instance count). IETF RFC 8446, TLS 1.3 (one round trip handshake). IETF RFC 894 and common MTU references (1,500-byte Ethernet packets, 20-byte IPv4 and 20-byte TCP headers). Fiber Optic Association training material (light in glass at about 200,000 km/s). HTTP Archive, Web Almanac 2025, Page Weight chapter (July 2025 crawl). Distances are great-circle estimates. All timings are an illustrative model.

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