3M APICS 1121 OFFICE UNIT &1122 FIELD UNIT SET REPAIRED The Dynatel APICS 1121/1122 System consists of a Central Office unit and a field unit. The CO unit is attached to 100 pairs at a time on the main distribution frame (MDF) in the central office. Together, the Central Office unit and the field unit perform the following functions depending on the field unit used: Identification of cable pairs; assessment of the condition of the cable pairs; cable fault diagnostics; cable acceptance testing; circuit transfers from one cable pair to another without interruption of service