Fundamentals

Connection Event

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A scheduled exchange of data packets between a central and peripheral device during an active BLE connection.

    


    
    
  


  




  
  

    
Connection Event


A connection event is a scheduled exchange of data packets between a central and peripheral device during an active BLE link. Connection events occur at regular intervals defined by the connection interval and form the fundamental mechanism through which BLE devices communicate after establishing a connection.


Anatomy of a Connection Event


Each connection event begins when both devices wake their radios at the agreed-upon time. The central transmits first, sending one or more data PDUs (Protocol Data Units). The peripheral responds with its own PDUs. This ping-pong exchange continues until either side has no more data to send or the next connection event is approaching.


The minimum connection event consists of a single packet from the central and a single response from the peripheral, even if both packets carry empty payloads. This keep-alive exchange maintains the connection and allows the link layer to update parameters or exchange control messages. The inter-frame spacing (T_IFS) between central and peripheral packets is fixed at 150 microseconds.


Timing and Synchronization


Both devices maintain a shared anchor point -- the precise timestamp of the first packet in each connection event. The peripheral uses this anchor point plus a configurable window widening factor to determine when to activate its receiver. Clock drift between the two devices causes the window to widen over time; more frequent connection events keep the window narrow and reduce radio-on time.


If a connection event is missed (the peripheral does not hear the central's packet within the receive window), the peripheral will listen again at the next scheduled event. After a configurable supervision timeout (typically 2--6 seconds), the connection is considered lost and both devices return to advertising/scanning states.


Throughput Implications


Multiple packets can be exchanged within a single connection event, a capability that becomes especially important when combined with DLE (Data Length Extension) and LE 2M PHY. With DLE enabling 251-byte payloads and 2M PHY doubling the air data rate, a single connection event at 7.5 ms CI can transfer several kilobytes of data. This burst-then-sleep pattern is central to BLE's power efficiency model and distinguishes it from always-on protocols like Wi-Fi.

  

  

  
  
  




  
  
Related Terms

  

  

    
    Connection Interval
    
    Central
    
    Slave Latency
    
  





  

  
  

  
  

  
  
  

    
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Frequently Asked Questions


  

    
    

      
      

        
Our glossary covers 90+ BLE technical terms organized by category. Each term includes a definition, related terms, and links to relevant chips and guides.