Data centers can be classified by Tiers, with Tier 1 being the most basic and inexpensive, and Tier 4 being the most robust and costly. According to definitions from the Uptime Institute and the latest draft of TIA/EIA-942 (Telecommunications Infrastructure Standard for Data Centers), a Tier 1 data center is not required to have redundant power and cooling infrastructures. It needs only a lock for security and can tolerate up to 28.8 hours of downtime per year. In contrast, a Tier 4 data center must have redundant systems for power and cooling, with multiple distribution paths that are active and fault tolerant. Furthermore, access should be controlled with biometric readers and single-person entryways, gaseous fire suppression is required, the cabling infrastructure should have a redundant backbone, and the facility can permit no more than 0.4 hours of downtime per year.

Tier 1 or 2 is usually sufficient for enterprise data centers that primarily serve users within a corporation. Financial data centers are typically Tier 3 or 4 because they are critical to our economic stability and, therefore, must meet higher standards set by our government. Public data centers that provide disaster recovery / backup services are also built to higher standards.

A Tier 1 Network is an IP network (typically but not necessarily an Internet Service Provider ) which connects to the entire Internet solely via Settlement Free Interconnection, commonly known as peering . Another name for a Tier 1 network is "transit-free", because it does not receive a full transit table from any other network.

Although there is no formal definition of the "Internet Tier hierarchy", the generally accepted definition among networking professionals is:

• Tier 1 - A network that peers with every other network to reach the Internet.
• Tier 2 - A network that peers with some networks, but still purchases IP transit to reach at least some portion of the Internet.
• Tier 3 - A network that solely purchases transit from other networks to reach the Internet.