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      TP/TP Couplers in Repeater Mode

      Michael Critchfield
      • Updated

      KNX Repeater:

      A KNX Repeater is a standardized device profile used in KNX installations. Its function is often integrated into KNX TP/TP Line Couplers rather than as a standalone device.

      KNX Repeater does

      A Repeater repeats telegrams between two parts of the same TP line: 

      • Forwards all telegrams between line segments without filtering.
      KNX Repeater does not do

      Unlike other couplers, a Repeater does not use Filter Tables, meaning:

      • All telegrams and addresses are forwarded, increasing bus load.
      • Messages may reach unintended areas, affecting security and third-party integration.
      How to Detect in ETS
      • In ETS, a line coupler supporting the Repeater profile can be placed anywhere on a TP line.
      • From ETS 6.4, it explicitly shows when a Line Coupler is in Repeater Mode.
      Risks & Recommendations:

      Since Repeaters forward everything, secure your installation by:

      • Using KNX Secure when possible.
      • Setting a BCU Key for classic devices (keep the key safe; losing it prevents reset or re-download).
      • Consider replacing Repeaters with the modern Segment Coupler.

      KNX Segment Coupler:

      A Segment Coupler is a newer KNX device profile, often integrated into TP-TP Line Couplers, offering key improvements over Repeaters.

      Segment Coupler does
      • Connects KNX TP lines (e.g., Line to Segment).
      • Supports Filter Tables to forward only relevant telegrams.
      • ETS programs filters automatically.
      Why use a Segment Coupler instead of a Repeater?
      • Reduced Bus Load: Only necessary telegrams pass through.
      • Cleaner Topology: Telegrams stay within intended segments.
      • Better Security & Control: Filtering limits unwanted traffic.

      ✅ Recommendation: Use a Segment Coupler whenever possible and secure your installation with KNX Secure or a carefully managed BCU Key for legacy devices.

      FeatureKNX RepeaterKNX Segment Coupler
      Device ProfileOlder profile, rarely standalone todayNewer profile with advanced functions
      IntegrationOften in older TP-TP Line CouplersPart of newer TP-TP Line Couplers
      FunctionRepeats all telegrams between line segmentsCouples TP lines/segments with control
      Filtering❌ No filtering; all forwarded✅ Supports filtering; only relevant telegrams forwarded
      Bus LoadHigher due to all trafficLower by filtering unnecessary traffic
      Security ImpactTelegrams may reach unintended areasControlled communication improves security
      ETS IndicationETS 6.4 shows Repeater modeETS auto-configures filter tables
      Recommended UseOnly for special or legacy casesPreferred for modern KNX installations

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