Classification indicating the size of a service provider. Tier 1 providers are the largest, such as AT&T, CenturyLink, Zayo, and Verizon, with network systems that span the globe. They can generally send data anywhere without having to pay transit fees, either because they own the network or they have peering agreements with other networks. A Tier 2 network “peers” with many networks, but also has to pay some transit fees. A Tier 3 service provider must pay transit fees to access the Internet.