What is a Tier 1 network?

What is a Tier 1 network?

A Tier 1 network is “an IP (Internet Protocol) network that can reach every other network on the Internet solely via settlement-free interconnection”[2] (that is, they can reach the entire internet via settlement-free peering).

You can think of Tier 1 networks as having a kind of “golden VIP pass” with each other, and each Tier 1 network can exchange traffic with other Tier 1 networks without paying any fees for the exchange of traffic in either direction. (This contrasts with some Tier 2 networks and all Tier 3 networks which must pay to transmit traffic on other networks.)

Universally recognized Tier 1 networks include AT&T, Verizon, T-Mobile US (formerly Sprint), Deutsche Telekom, and Orange.

NOTE that there is no authority that defines tiers of networks participating in the Internet:

It can be difficult to determine whether a network is paying for peering or transit, as these business agreements are rarely public information, or are covered under a non-disclosure agreement. The Internet peering community is roughly the set of peering coordinators present at the Internet exchange points on more than one continent. The subset representing Tier 1 networks is collectively understood in a loose sense, but not published as such.

Common definitions of Tier 2 and Tier 3 networks:

Tier 2 network: A network that peers for free with some networks, but still purchases IP transit or pays for peering to reach at least some portion of the Internet.

Tier 3 network: A network that solely purchases transit/peering from other networks to participate in the Internet.

via Wikipedia