Tier 1:
That can reach every other network on the Internet without purchasing IP transit or paying settlements. (considered part of the backbone itself)(only one company is involved) [only settlement free peers]

‧ AT&T Services, Inc.
‧ Global Crossing, Ltd.
‧ NTT Communications Corp.
‧ Qwest Communications International, Inc.
‧ Savvis, Inc.
‧ Sprint Nextel Corp.
‧ Tata Communications, Ltd.
‧ TeliaSonera International Carrier.
‧ Tinet.
‧ Verizon Business (UUNet).

Tier 2:
A network that peers with some networks, but still purchases IP transit or pays settlements to reach at least some portion of the Internet.

Tier 3:
A network that solely purchases transit from other networks to reach the Internet.