Understanding the Structure of the Internet: Routers, ISP Tiers, and Peering

As I continue learning about Information Technology, I've been exploring how the Internet works behind the scenes.

We use the Internet every day to browse websites, send messages, stream videos, and access online services. However, have you ever wondered how information travels from one computer to another, sometimes across different continents, within seconds?

In this article, I'm sharing my understanding of some fundamental concepts that make global Internet communication possible.

1. Understanding Routers

A router is a specialised networking device that connects different networks and directs data packets towards their intended destinations.

Think of a router as a traffic controller. Just as traffic officers help vehicles follow the correct routes, routers help data travel through the appropriate network pathways.

Routers perform two important functions:

• Prevent unnecessary traffic: They ensure information is not sent to networks where it is not needed.
• Forward data: They determine where information should go so that it reaches its intended destination.

For example, when you send a WhatsApp message to someone in another country, your data may pass through several routers and networks before reaching its destination.

Without routers, communication between different networks would be difficult.

2. Understanding the Internet Network Hierarchy

One interesting thing I've learned is that the Internet is not owned or operated by one organisation.

Instead, it is a global collection of independent networks operated by different Internet Service Providers (ISPs), businesses, and organisations.

These networks communicate using common technologies, including:

• IP (Internet Protocol): Provides addressing that allows devices and networks to be identified.
• BGP (Border Gateway Protocol): Allows networks to exchange routing information and determine how traffic can reach other networks.

To understand how these networks connect, it helps to look at the three main ISP tiers.

3. The Three ISP Tiers

Internet Service Providers are commonly classified into three tiers based on their network size, coverage, and relationships with other networks.

Tier 1 ISPs

Tier 1 providers operate large Internet backbone networks with international coverage.

They have extensive infrastructure, including routers, switches, and high-capacity connections.

Some of their characteristics include:

• Global network coverage.
• Direct connections with other Tier 1 providers.
• Settlement-free peering arrangements with qualifying networks.
• Ability to reach the entire Internet through their peering relationships.

In simple terms, Tier 1 ISPs form a major part of the global Internet backbone.

Tier 2 ISPs

Tier 2 providers are generally smaller than Tier 1 providers and commonly operate at regional or national levels.

They may connect directly with other Tier 2 providers through peering agreements. However, they also purchase transit services from Tier 1 providers to access networks beyond their direct connections.

Their main characteristics include:

• Regional or national coverage.
• Connections with other Tier 2 networks.
• Dependence on higher-tier providers for some Internet routes.
• Services for businesses and other organisations.

Tier 3 ISPs

Tier 3 providers mainly serve local customers, including households, individuals, and small businesses.

They provide the local connection that allows ordinary users to access the wider Internet.

Their characteristics include:

• Limited geographical coverage.
• Focus on local consumers and businesses.
• Dependence on higher-tier providers for wider Internet connectivity.
• Often purchase Internet transit services from Tier 1 or Tier 2 providers.

For example, a local Internet provider offering home fibre or wireless Internet services may operate at Tier 3.

Comparing the Three Tiers

4. Points of Presence (PoPs) and Network Access Points (NAPs)

Another important concept is understanding where different networks connect.

Points of Presence (PoPs)

A Point of Presence is a physical location where an ISP connects its network to customers or other networks.

PoPs help ISPs extend their services and establish connections with other networks.

Network Access Points (NAPs)

A Network Access Point is a facility where different networks connect and exchange Internet traffic.

These facilities help independent networks communicate with one another.

A simple way to distinguish them:

• PoP: A connection point within an ISP's network.
• NAP: A location where different networks exchange traffic.

5. Understanding Public and Private Peering

Peering is an arrangement where two or more networks connect to exchange Internet traffic.

The main purpose is to improve connectivity, reduce dependence on third-party transit providers, and manage network traffic efficiently.

There are two common forms of peering.

Private Peering

Private peering involves a direct connection between two networks.

It is commonly used by providers with significant traffic volumes and network capacity.

Benefits include:

• Direct traffic exchange.
• Greater control over network performance.
• Reduced dependence on transit providers.
• Potential improvements in latency and packet delivery.

Public Peering

Public peering allows multiple networks to exchange traffic through a shared facility, commonly an Internet Exchange Point (IXP).

Instead of establishing separate direct connections with every network, providers can connect through the shared exchange infrastructure.

Benefits include:

• Easier interconnection between multiple networks.
• Reduced connectivity costs.
• Improved opportunities for local traffic exchange.
• Less dependence on distant networks for traffic that can be exchanged locally.

Private vs Public Peering

6. Putting Everything Together

Let's use a simple example.

Imagine you are in Nairobi and want to access a website hosted on a server in another country.

Here is a simplified explanation of what happens:

1. Your device sends a request through your local Internet connection.
2. Your ISP receives the request and uses routers to forward the data.
3. The traffic may pass through higher-tier networks.
4. Different networks exchange traffic through peering or transit arrangements.
5. Routers continue forwarding the data towards the destination server.
6. The server responds, and the information travels back to your device.

This process happens extremely quickly, even though the information may cross several networks and geographical locations.

7. Key Takeaways

Here are the main concepts I'm taking away from this topic:

• Routers connect networks and direct data packets towards their destinations.
• The Internet is a global collection of interconnected independent networks.
• IP addressing and BGP help make communication between networks possible.
• Tier 1 ISPs provide global backbone connectivity.
• Tier 2 ISPs provide regional or national connectivity.
• Tier 3 ISPs provide local Internet access to end users.
• PoPs are network connection locations, while NAPs facilitate traffic exchange between networks.
• Peering allows networks to exchange traffic directly or through shared exchange facilities.

Final Thoughts

One thing I appreciate about learning Information Technology is discovering how the systems we use every day work behind the scenes.

Before studying this topic, I mainly thought about the Internet from the user's perspective: connecting to Wi-Fi, browsing websites, and accessing online services.

Understanding routers, ISP tiers, and peering has helped me appreciate the infrastructure and cooperation required to keep the Internet connected globally.

I'm sharing these notes as part of my learning journey. If you notice anything that needs clarification or improvement, feel free to share your thoughts. I'm always open to learning.