Internet Ecosystem Hierarchy

💡 The Core Idea

The Internet is not a single network but a Network of Networks organized into a loose hierarchy based on size and reach.

🧠 Structure

• Tier-1 ISPs: The “Backbone” (e.g., AT&T, Level-3). They operate globally and peer with every other Tier-1 ISP to reach the entire internet without paying settlement fees.
• Tier-2 (Regional) ISPs: Connect to Tier-1 networks and provide connectivity to smaller local ISPs.
• Tier-3 (Access) ISPs: Provide the “last mile” connection to homes and businesses.
• CDNs: Content Delivery Networks (Google, Netflix) flatten this hierarchy by connecting directly to Access ISPs or IXPs to bypass the backbone.

🔗 Connections

• Source: Source - Autonomous Systems and Internet Interconnection