Where the Internet Came From
The Internet did not start as a commercial product. It grew out of a research project funded by the U.S. government in the 1960s through an agency called DARPA (Defense Advanced Research Projects Agency). The original goal was to build a communication network that could survive partial failures — one that would keep functioning even if parts of it were destroyed or went offline.
Over the following decades, the project expanded from a handful of research universities to a global system used by billions of people. The development passed through government hands, into academic institutions, and eventually became the largely commercial enterprise it is today. What held it together through all of that growth was a commitment to open standards — anyone could build for the Internet without paying fees or asking permission.
Today the Internet links a worldwide combination of LANs, WANs, and wireless networks involving billions of devices. Understanding how that enormous system is organized — and how any device finds any other device on it — is what this reading is about.
How the Internet Is Organized: ISPs
The Internet is not a single network owned by a single organization. It is a collection of networks, each built and maintained by different organizations — primarily companies called Internet Service Providers (ISPs). ISPs are in the business of providing Internet connectivity: to homes, schools, businesses, and to other ISPs.
ISPs are organized in a rough hierarchy based on their scale and role.
Tier-1 ISPs: The Backbone
At the top of the hierarchy are a small number of tier-1 ISPs — very large companies that operate high-speed, high-capacity networks spanning continents and crossing oceans. These networks form the backbone of the Internet: the main arteries through which enormous volumes of traffic flow between countries and regions. You may not have heard of most tier-1 ISPs by name, but every piece of data you send or receive almost certainly travels through one of their networks at some point.
Tier-1 ISPs are typically large telecommunications companies that began as telephone or cable television providers and expanded into data networking. They connect directly to each other, allowing traffic to flow seamlessly across the global Internet.
Tier-2 ISPs: Regional Networks
Below the tier-1 backbone are tier-2 ISPs, which tend to be more regional in scope. A tier-2 ISP might serve an entire country or a large region within a country. Tier-2 ISPs connect to the tier-1 backbone to reach the rest of the Internet, and they provide connectivity to smaller ISPs and large organizations in their region.
Access ISPs: The Last Connection
At the bottom of the hierarchy are access ISPs (sometimes called tier-3 ISPs) — the companies and organizations that actually connect end users to the Internet. Your home internet provider (a cable company, telephone company, or fiber provider) is an access ISP. Your school district's internet provider is an access ISP. Universities often function as their own access ISPs for students and staff.
Access ISPs connect to tier-2 ISPs (and sometimes directly to tier-1 ISPs), and they are the point at which individual devices enter the global Internet.
Why redundancy matters: The many possible pathways through the tier-1 and tier-2 networks mean that the Internet has built-in redundancy — if one router or network link fails, traffic can be rerouted through alternative paths. This is not an accident. It was a design goal from the beginning: the Internet was specifically built to keep functioning even when parts of it go down.
Intranets: Private Internets
Many organizations operate their own private internal networks that are structured like the Internet — using the same protocols, connecting multiple internal networks through routers — but that are not part of the public Internet. These are called intranets.
A school district might run an intranet connecting all its schools, with internal systems (student information databases, file servers, printers) accessible only to devices within the district network. A corporation might run an intranet connecting offices in multiple cities. The intranet uses Internet technology but keeps its resources private.
The distinction matters: the Internet is the global public network. An intranet is a private network built on the same technology, accessible only to authorized users within a particular organization.
How Devices Are Addressed: IP Addresses
For any device on the Internet to communicate with any other device, every device needs a unique address. On the Internet, these addresses are called IP addresses (IP stands for Internet Protocol, the fundamental communication standard of the Internet).
Every device connected to the Internet — your laptop, your phone, the server hosting a website, the router in your school — has an IP address. Think of it like a postal address: just as every house on a street needs a unique address so mail can be delivered to the right place, every device on the Internet needs a unique IP address so data can be delivered to the right destination.
IP addresses are managed hierarchically. Blocks of addresses are assigned to ISPs by a nonprofit organization called ICANN (Internet Corporation for Assigned Names and Numbers), which coordinates the Internet's global addressing system. ISPs then allocate individual addresses from their block to their customers — homes, schools, businesses.
What an IP address looks like: A traditional IP address is
written as four numbers separated by periods — for example,
192.168.1.1. Each number represents one byte of a 32-bit address.
You do not need to be able to convert these to binary or calculate anything from
them — what matters is understanding that every device has one, that they
are unique, and that the Internet uses them to route data to the right destination.
Human-Readable Addresses: Domain Names
IP addresses are fine for computers but not for humans. Remembering that your
favorite website lives at 142.250.80.46 is not realistic.
For this reason, the Internet has a parallel addressing system based on
human-readable names: domain names.
A domain is a named region of the Internet operated by a single authority — a university, a company, a government agency, or an individual. Each domain is registered with ICANN and assigned a unique domain name. Domain names are hierarchical, read from right to left, with the most general category on the right.
Top-Level Domains (TLDs)
The rightmost part of a domain name is called the top-level domain (TLD). Original TLDs were chosen to reflect the type of organization:
.edu— educational institutions (universities, colleges).com— commercial organizations.gov— U.S. government agencies.org— nonprofit organizations.net— originally for ISPs, now broadly used.mil— U.S. military
Country-specific TLDs were later added — .uk for the United
Kingdom, .ca for Canada, .au for Australia. In recent
years, hundreds of new TLDs have been introduced (.museum,
.app, .edu, .school and many more).
How Domain Names Are Structured
To the left of the TLD is the organization's registered name. For example,
uni.edu is the domain for the University of Northern Iowa —
uni is the organization's name, .edu is the TLD.
Organizations can extend their domain name further to the left to identify
specific machines or subdomains within their domain. For example,
cs.uni.edu might identify the Computer Science department's
servers within the UNI domain. The hierarchy reads from right (most general)
to left (most specific).
The Phone Book of the Internet: DNS
Here is the practical problem: humans use domain names like
google.com, but the Internet routes data using IP addresses.
Something needs to translate between the two. That something is the
Domain Name System (DNS).
DNS is a worldwide distributed system of servers — called name servers or DNS servers — that maintain directories mapping domain names to their corresponding IP addresses. When you type a URL into your browser, one of the first things your device does is contact a DNS server to look up the IP address for that domain name. This lookup is called a DNS lookup.
The phone book analogy: DNS works like a phone book. You know a person's name (the domain name) but you need their phone number (the IP address) to actually call them. You look up the name in the directory to get the number. DNS does this automatically, invisibly, thousands of times per day on your behalf.
DNS servers are organized hierarchically to match the structure of domain names. Your device is configured to contact a local DNS server (usually provided by your ISP or your school's network). If that server does not know the IP address for a domain, it asks a higher-level DNS server, which may ask another, working its way up the hierarchy until an authoritative answer is found. In practice, frequently visited domains are cached (stored temporarily) by DNS servers along the way, making most lookups nearly instantaneous.
DNS is why you can type wikipedia.org into a browser rather than
memorizing a numeric address. It is also why changing a website's IP address
(moving it to a new server) does not require everyone who links to it to update
their links — they update the DNS record instead, and the name continues
to work.
A classroom connection: DNS is an example of a system your students use constantly without knowing it exists. Explaining that typing a web address triggers an invisible lookup process — like a phone book consultation happening in milliseconds — is often a genuine "oh, that's what's happening" moment for students at every grade level.
What Comes Next
You now understand how the Internet is built (through a hierarchy of ISPs), how devices are uniquely identified (IP addresses), how humans refer to those devices (domain names), and how the two addressing systems are linked (DNS). Reading 2 moves from the infrastructure to what runs on top of it: the World Wide Web, the applications that use the Internet, and the servers that make it all possible.