Within a data center, if you have dual path connectivity between the primary entrance room and secondary entrance room, in addition to dual connectivity between these two rooms and the main…

Tier I is basic site infrastructure with a single, non-redundant distribution path and no redundant capacity components.

Tier II adds redundant capacity components in an N+1 configuration but still relies on a single, non-redundant distribution path.

Tier III supports concurrent maintainability with multiple paths but only one active at a time, which does not match the dual active path design described.

Tier IV requires fully redundant, simultaneously active paths between every segment of the data center infrastructure, meaning dual connectivity between both entrance rooms and between those rooms and all distribution areas satisfies the fault-tolerant design requirement. This configuration ensures that no single failure of any path, component, or segment interrupts operations. The Uptime Institute defines Tier IV as having 2N redundancy with no single points of failure across the entire facility.

Tier V does not exist in the Uptime Institute tier classification system, which defines only Tiers I through IV.