Before revision: when, and only when, adding to an existing installation that uses the T568B wiring pattern , being those that pre-dated ANSI/TIA-568 and used the previous AT&T 258A (Systimax) standard.
After revision: when, and only when, adding to an existing installation that usedbefore it was defined the T568B wiring pattern , being those that pre-dated ANSI/TIA-568 and used the previous AT&T 258A (Systimax) standard.