KNX System Components KNX Line Coupler Basic functionality of the TP line coupler ITR901-002 is coupling two KNX TP lines (main line and subline) providing galvanic isolation in between. Due to its flexibility ITR901-002 coupler unit can be used as KNX line coupler or KNX area coupler (to connect a TP line to a TP area or backbone) or KNX repeater (without filtering). Operational and filtering states, malfunction and faulty communication are indicated by LEDs. ITR901-002 is able to filter the traffic according to the installation place in the bus system hierarchy and according to the built-in filter tables for group oriented communication.