What is an ISP? — Internet Service Provider
An Internet Service Provider (ISP) is a company that provides transport of Internet traffic on behalf of other ISPs, businesses or other non-ISP organizations, and individuals. ISPs are classified into a 3-tier model that categorizes them depending on the type of Internet services they provide.
A Tier 1 ISP is an Internet provider that only exchanges Internet traffic with other Tier 1 providers on a non-commercial basis. These Tier 1 ISP exchanges of traffic are known as settlement-free peerings.
Tier 1 Internet service providers are the networks that provide the backbone of the Internet. They are referred to as backbone Internet providers. These providers build infrastructure such as the Atlantic Internet sea cables. They provide traffic to all other Internet providers, not end users.
A Tier 2 ISP is a service provider that utilizes a combination of paid transit and peering to deliver traffic to the Internet. Tier 2 ISPs are typically regional or national providers.
A Tier 3 ISP is a provider that strictly purchases Internet transit. A Tier 3 provider is by definition primarily engaged in delivering Internet connections to end customers.