Of major importance for equipment installed in a central office is uptime, network integrity, equipment compatibility and natural disaster survivability. Strict environmental and physical packaging requirements are defined by telephone service providers for telecom equipment manufacturers to ensure that switches and other central office equipment always continue to function.

The central office packaging testing requirements are defined by the Bellcore Network Equipment Building System in North America and the European Telecommunication Standard Institute in Europe. These are known as capability sets.

The central office code refers to the first three digits of local phone numbers.