Tier 1 network
An operator that can reach the entire internet solely through settlement-free peering — without ever paying anyone for transit. They form the internet's global backbone; everyone else ultimately reaches the internet via them, directly or indirectly.
Definition: a Tier 1 network never buys transit (never pays to reach any part of the internet) but reaches everything via mutual, free peering with the other Tier 1 operators. For this to add up, together they must peer so the whole "default-free zone" is covered. Examples: AT&T, Lumen (CenturyLink), Telia Carrier/Arelion, Tata, GTT, NTT, Deutsche Telekom. Tier 2 operators peer some but also buy transit; Tier 3 only buy transit. Note that "Tier" isn't about size or quality but about business relationships (whether you buy transit or not). Tier 1 status is partly political — it rests on the other Tier 1s agreeing to peer. The internet's top layer. Related to transit vs peering and autonomous system number.