Tier 1 Networks and Internet Transit

The internet is not a single network — it is a collection of tens of thousands of independently operated networks (Autonomous Systems) that agree to exchange traffic. Understanding how these networks relate to each other, who pays whom, and which networks sit at the top of the hierarchy explains a great deal about the economics and politics of the internet.

The Three-Tier Model

Networks are informally categorized into three tiers based on their connectivity and business relationships:

Tier 1: The Backbone

A Tier 1 network can reach every other network on the internet entirely through settlement-free peering — that is, without paying anyone for transit. Tier 1 networks are directly connected to every other Tier 1 network via peering agreements, forming a fully meshed backbone.

To qualify as Tier 1, a network must have peering agreements with all other Tier 1 networks. If a network must pay any other network for transit to reach some portion of the internet, it is not Tier 1.

Tier 2: Regional and National ISPs

Tier 2 networks peer freely with some networks but must purchase transit from one or more Tier 1 networks to achieve full global connectivity. Most national and large regional ISPs fall into this category. They may have rich peering at IXPs and private peering with content providers, but they still depend on Tier 1 transit for routes they cannot reach otherwise.

Tier 3: Access Networks / Last-Mile ISPs

Tier 3 networks are typically local or regional ISPs, cable companies, and mobile operators that primarily connect end users. They purchase transit from Tier 1 or Tier 2 providers for essentially all their upstream connectivity. They may peer at local IXPs to reduce costs for regional traffic, but they do not have the geographic scope for extensive peering.

Settlement-Free Peering: The Tier 1 Club

The defining characteristic of Tier 1 networks is that they reach full internet connectivity through settlement-free peering (SFP) — mutual agreements where neither party pays the other for traffic exchange.

SFP makes economic sense when the traffic between two networks is roughly balanced and when both networks benefit equally from the interconnection. Two large backbone providers carry each other's traffic, with the assumption that the arrangement is roughly symmetric.

The "Tier 1 club" is small and exclusive. Admission requires reaching peering agreements with every existing Tier 1, which existing members may resist to protect the competitive advantage of their settlement-free status. When a Tier 2 network grows large enough to threaten the peering balance, it can attempt to negotiate SFP with Tier 1 networks — a process that can take years and sometimes involves public disputes called de-peering events.

Major Tier 1 Networks

The globally recognized Tier 1 networks (as of 2025) include:

The exact list is debated — the boundaries shift as networks grow, merge, or change their peering strategies. Some analysts include fewer networks; some include more.

Internet Transit: How It Works

When a network (say, a small regional ISP) purchases transit from a Tier 1 provider, it is buying the ability to send and receive traffic to and from any IP address on the internet via the Tier 1's backbone.

What You Buy with Transit

• Full routing table — The transit provider sends BGP routes for all IP prefixes it can reach (approximately 900,000+ IPv4 prefixes as of 2025).
• Bandwidth capacity — You purchase a port of a given speed (1 GbE, 10 GbE, 100 GbE) and may have committed or burstable rates.
• Geographic reach — Your traffic can reach any destination via the provider's backbone.

Transit Pricing

Transit is typically priced in one of two models:

• Per-Mbps (95th percentile) — You pay per megabit based on your 95th percentile usage over the billing period. The 95th percentile billing means the highest 5% of 5-minute average samples are discarded, giving some tolerance for traffic spikes. Rates have fallen dramatically — from $200+/Mbps in 2000 to $0.50–$2/Mbps in major cities today.

• Flat rate / blended — Fixed monthly fee for a committed bandwidth level, often with an allowance for burst. Common for smaller customers.

Transit prices vary significantly by geography: they are cheapest in North America and Western Europe (where competition among Tier 1 and Tier 2 providers is intense) and most expensive in Africa, the Pacific Islands, and parts of Latin America (where submarine cable capacity is limited).

Peering vs. Transit: The Economic Choice

Networks constantly evaluate whether to peer with a given counterpart or pay for transit:

A large content provider like Netflix invests heavily in peering because it sends enormous volumes of video traffic to ISPs. By building direct connections (private peering or IXP peering) with ISPs, Netflix avoids paying transit fees on those gigabytes and improves streaming quality for its users. Netflix's Open Connect program — where Netflix deploys its own servers directly inside ISP networks — takes this to an extreme.

De-Peering: When It Goes Wrong

When two large networks disagree over the terms of their interconnection, either party can terminate the peering agreement — a process called de-peering. The results can be dramatic: traffic that previously took a direct path now traverses expensive third-party transit, quality degrades, and both parties' customers suffer.

High-profile de-peering disputes:

• Level 3 vs. Cogent (2005) — The two Tier 1 networks de-peered, causing portions of the internet to become unreachable from each side without going through a third provider.
• Cogent vs. France Telecom / Orange (2013) — A dispute over traffic ratios led to a peering termination that degraded transatlantic performance.
• Netflix vs. Comcast (2014) — Not a de-peering exactly, but Comcast's congestion of interconnect links to Netflix's transit providers led to a highly publicized dispute about interconnection economics and net neutrality.

The Backbone's Physical Infrastructure

Tier 1 networks own or lease vast physical infrastructure:

• Long-haul fiber — Thousands of kilometers of terrestrial fiber spanning continents.
• Submarine cable capacity — Tier 1s have capacity on most major submarine cable systems.
• Data center presence — Tier 1 routers are collocated in major carrier hotels (e.g., 111 8th Avenue in New York, Telx in Atlanta, Interxion in Amsterdam) to facilitate peering.
• Backbone routers — High-end chassis routers (Cisco CRS, Juniper PTX, Nokia SR) with 100s of Tbps of aggregate capacity.

The Changing Landscape

The traditional Tier 1 model is evolving:

• Hyperscaler networks — Google, Microsoft, Meta, and Amazon now operate massive private backbone networks that span the globe. They are not traditional Tier 1 networks (they don't sell transit) but they have reduced their dependence on the Tier 1 club significantly. Google's backbone, for example, carries a large fraction of its YouTube and Search traffic on privately owned fiber.

• Content-centric internet — As more traffic originates from a small number of content providers (Netflix, YouTube, Meta, TikTok), the symmetric traffic assumptions underlying SFP no longer hold. ISPs that carry far more inbound than outbound traffic argue they are subsidizing content providers; content providers argue ISPs' customers are the ones demanding the content.

• Regional consolidation — Several acquisitions (Level 3 by CenturyLink, which became Lumen; XO Communications by Verizon) have reduced the number of major US backbone providers.

The Tier 1 hierarchy remains the fundamental organizing principle of global internet routing — but the economics are shifting as content giants build their own infrastructure and peering relationships become increasingly asymmetric.