4.2 Internet Service Providers and Network Tiers
In the previous section, we learned that IP addresses help identify devices and destinations, while routing helps determine the path that data takes across networks.
In this section, we will look at who actually provides Internet connectivity.
When you open a website, stream a video, send a message, or join a video call, your data travels across networks owned and operated by many different organizations.
The Internet is not owned by one company, one government, or one organization. Instead, it is a massive collection of interconnected networks that cooperate to move data around the world.
One of the most important parts of this system is the Internet Service Provider.
What Is an Internet Service Provider?
An Internet Service Provider, or ISP, is a company or organization that provides Internet access.
Most people interact with an ISP every day, even if they rarely think about it.
When a home connects to the Internet, it usually does so through an ISP.
Examples of Internet service providers in the United States include companies that offer fiber, cable, cellular, fixed wireless, and satellite Internet services.
An ISP provides the connection between a local network and the wider Internet.
For example, imagine a home network containing:
- A laptop
- A phone
- A tablet
- A smart television
- A gaming console
These devices may communicate with one another through a home router. However, if the user wants to visit a website or communicate with a server somewhere else in the world, the traffic must leave the local network.
The ISP provides that connection.
One simple way to think about it is this:
- Your home network is like a neighborhood street.
- Your ISP provides the roads that connect your neighborhood to the rest of the world.
Without an ISP, most homes would have no practical way to reach the global Internet.
Different Ways to Connect to an ISP
Internet access can be delivered in several different ways.
- Fiber-optic Internet uses thin strands of glass and pulses of light to transmit information. Fiber connections are often among the fastest and most reliable forms of Internet access available today.
- Cable Internet uses infrastructure that was originally developed for cable television. It remains common in many regions.
- DSL uses traditional telephone lines. Although DSL is less common than it once was, it still exists in some areas.
- Fixed wireless Internet uses radio links between towers and customer equipment. This approach is often used in rural regions where wired connections may be difficult to install.
- Satellite Internet uses satellites to provide connectivity. Modern low-Earth-orbit satellite systems have significantly improved performance compared to many older satellite services.
- Cellular providers can also act as Internet service providers. Smartphones, tablets, and mobile hotspots often connect through cellular networks using technologies such as 4G LTE and 5G.
Although these technologies differ, they all serve the same basic purpose:
They connect users to larger Internet networks.
The Internet Is a Network of Networks
It is tempting to imagine the Internet as one giant network. In reality, the Internet is made up of thousands of separate networks operated by different organizations.
Internet service providers (ISPs) operate networks.
Universities operate networks.
Governments operate networks.
Cloud providers operate networks.
Large businesses operate networks.
Content providers operate networks.
These independent networks must cooperate so that users can communicate across the world.
For example, a customer of one ISP may want to visit a website hosted on another network. The data must travel between multiple organizations before reaching its destination. This cooperation is one of the reasons the Internet is often described as a network of networks.
Autonomous Systems and ASN
Many large networks on the Internet are known as Autonomous Systems.
An Autonomous System, often abbreviated AS, is a network or group of networks that is managed by a single organization and follows a common routing policy.
Internet service providers often operate Autonomous Systems.
Large cloud providers operate Autonomous Systems. Universities, governments, and major companies may also operate Autonomous Systems.
Each Autonomous System is assigned a unique Autonomous System Number, or ASN. For example:
- Google: AS15169
- Amazon (AWS): AS16509
These numbers help identify networks as they exchange routing information with one another.
Most Internet users never see ASNs directly, but Autonomous Systems play a major role in how Internet traffic moves around the world.
How Networks Learn About Other Networks
Earlier, we learned that routers use routing tables to help determine where traffic should go.
On a small network, an administrator may manually configure routes. However, the global Internet is far too large for that approach. Instead, large networks exchange routing information.
One of the most important technologies involved is Border Gateway Protocol, commonly called BGP.
BGP allows routers on different networks to talk to each other and share information about which IP address ranges they can reach. By sharing routing tables and reachability information, BGP routers can figure out the best path for data to travel across the world, ensuring that traffic takes the most efficient route possible.
One way to think about it is that BGP allows large networks to tell one another:
“If you need to reach these destinations, send the traffic through us.”
This information helps networks build routing tables and make forwarding decisions. Although the details can become very technical, the important idea is that the Internet relies on cooperation between thousands of independent networks.
Internet Exchanges (IXP)
In many cases, networks connect through facilities called Internet Exchange Points, often shortened to IXPs.
An Internet Exchange Point is a physical location where different networks—like Internet Service Providers (ISPs), content delivery networks (CDNs), and cloud providers—interconnect their infrastructure directly. It can be thought of as a massive, super-secure digital roundabout located inside a neutral data center. By plugging into a central high-speed switch, these networks bypass third-party transit routes, significantly reducing latency and lowering data delivery costs.
Instead of sending all traffic through a third-party provider, networks at an exchange can often communicate more efficiently.
Many major cities around the world contain large Internet exchange facilities. Although most users never see them, they are important pieces of Internet infrastructure.
Peering and Transit
When networks connect to one another, they generally do so through arrangements known as peering or transit.
Peering occurs when two networks agree to exchange traffic directly. For example, two large networks may determine that it is beneficial to connect to each other and exchange traffic without involving another provider.
In a transit relationship, one network pays another network to carry traffic to destinations beyond its own network.
A useful analogy is transportation.
- Peering is somewhat like two neighboring cities building a direct road between themselves.
- Transit is more like paying a larger highway system to carry traffic across many destinations.
Both peering and transit are important parts of how the Internet functions.
Network Tiers
The idea of network tiers is a simplified way of describing the relationships between different Internet providers. The internet is a global web of networks divided into three distinct levels: Tier 1, Tier 2, and Tier 3.
Tier 1
Tier 1 networks sit near the top of the global Internet hierarchy.
A Tier 1 network can generally reach every other network on the Internet without purchasing transit from another network.
Instead, Tier 1 networks primarily exchange traffic with one another through peering relationships.
Examples of Tier 1 networks include: Lumen Technologies (formerly CenturyLink/Level 3), Verizon, and AT&T.
Tier 2
Tier 2 networks are large networks that typically use a combination of peering and purchased transit.
They may exchange traffic directly with some networks while paying other networks for broader connectivity.
Many regional and national providers fall into this category.
Examples of Tier 2 networks include: Comcast, Charter Communications (Spectrum), British Telecom (BT), and China Telecom.
Tier 3
Tier 3 networks are generally closer to end users.
They often purchase connectivity from larger providers and then deliver Internet access to homes, businesses, schools, and other customers.
The boundaries between these categories are not always perfectly defined, and the Internet continues to evolve.
However, the tier model provides a useful way to understand how connectivity is organized.
Why This Matters
Most people think of the Internet as a single system.
In reality, it is a cooperative system built from thousands of independent networks.
Internet service providers connect users to the Internet.
Autonomous Systems operate large networks.
BGP helps networks exchange routing information.
Internet exchanges provide places for networks to connect.
Peering and transit allow traffic to move between organizations.
Together, these systems make global communication possible.
Every time you visit a website, stream a video, send an email, or join a video call, your data may pass through multiple networks owned by multiple organizations before reaching its destination. The Internet works because those networks cooperate.
Looking Ahead
So far, we have examined how data is addressed, routed, and carried across networks.
The next questions will look at are:
- What physical infrastructure actually connects continents together?
- How does information travel across oceans?
- How do remote regions connect to the global Internet?
In the next section, we will explore undersea cables, satellites, fiber-optic networks, and the physical infrastructure that makes worldwide Internet communication possible.