A Tier 1 network is an Internet Protocol (IP) network that can reach every other network on the Internet solely via settlement-free interconnection (also known as settlement-free peering). Tier 1 networks can exchange traffic with other Tier 1 networks without paying any fees for the exchange of traffic in either direction. In contrast, some Tier 2 networks and all Tier 3 networks must pay to transmit traffic on other networks. Common definitions of Tier 2 and Tier 3 networks: