Protocols & Profiles

Connection Subrating

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BLE 5.3 feature allowing dynamic adjustment of connection parameters to switch between low-latency and power-saving modes.

    


    
    
  


  




  
  

    
Connection Subrating


Connection Subrating is a Bluetooth 5.3 feature that allows a BLE connection to dynamically switch between different effective Connection Intervals without a full parameter update procedure. This enables devices to rapidly toggle between low-latency active mode and power-saving idle mode.


The Problem It Solves


Before Connection Subrating, changing the connection interval required an L2CAP Connection Parameter Update Request, which takes several connection events to negotiate and apply. For a wearable that needs to respond instantly to user interaction but conserve power during idle periods, this negotiation latency (often 100-500 ms) made rapid switching impractical.


How It Works


Connection Subrating introduces a subrate factor that effectively multiplies the base Connection Interval. The devices agree on a base interval (e.g., 7.5 ms) and a subrate factor (e.g., 40). During idle periods, the effective interval becomes 7.5 ms x 40 = 300 ms. When the device needs to transmit data, it transitions to the base interval (7.5 ms) within a single connection event -- no negotiation delay.


The key parameters are:
- Subrate Factor: Multiplier applied to the base interval (1 = no subrating)
- Continuation Number: How many base intervals to use at full rate before reverting
- Supervision Timeout: Adjusted to accommodate the longer effective interval


Use Cases


Connection Subrating is particularly valuable for:


    

  • Wearables: Sleep tracking at low duty cycle, instant responsiveness for Notifications or touch interaction
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  • Keyboards and mice: Ultra-low power in idle, instant low-latency response on keypress
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  • Sensors: Long idle periods with burst transmissions when threshold events occur
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  • LE Audio: Background maintenance at low rate, rapid audio setup when a call arrives
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Hardware Support


Connection Subrating requires Bluetooth 5.3 support in both the Central and Peripheral. Chips supporting this feature include the nRF54L15 and nRF54H20. The feature is configured through HCI commands and is typically exposed through the SDK's connection management API.

  

  

  
  
  




  
  
Related Terms

  

  

    
    Connection Interval
    
  





  

  
  

  
  

  
  
  

    
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Frequently Asked Questions


  

    
    

      
      

        
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