Internet Backbone Tiers (Tier 1, 2 and 3 Networks)
Internet networks are loosely ranked in tiers: Tier 1 networks reach the whole internet through peering alone, Tier 2 networks peer but also buy transit, and Tier 3 networks buy all their upstream connectivity.
What is Internet Backbone Tiers (Tier 1, 2 and 3 Networks)?
Tier 1 carriers, such as Lumen, NTT and Arelion, exchange traffic with each other without payment (settlement-free peering). Tier 2 networks, such as many national ISPs, peer at exchanges and pay for transit to reach the rest. Tier 3 networks are usually small access providers. The tiers are informal, not a formal classification.