Mesh

Directed Forwarding

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Mesh 1.1 feature that uses discovered paths to forward messages directly instead of flooding, reducing network traffic.

    


    
    
  


  




  
  

    
What Is Directed Forwarding?


Directed Forwarding is a routing optimization introduced in the Bluetooth Mesh Protocol 1.1 specification that allows mesh messages to follow discovered paths instead of being flooded through every relay node in the network. By maintaining per-destination forwarding tables, directed forwarding dramatically reduces the number of unnecessary rebroadcasts, lowering airtime consumption, latency, and power usage compared to pure managed flooding.


How It Works


Directed forwarding operates in two phases:


Path Discovery. When a node needs a directed path to a destination that is not yet in its forwarding table, it initiates a path discovery procedure. A Path Request message is flooded through the network (ironically, using the same flooding mechanism it aims to replace). Each node that forwards the request records the previous hop. When the request reaches the destination, a Path Reply is sent back along the reverse path. Each node along the reply path creates a forwarding table entry mapping the destination to the next hop.


Message Forwarding. Once a path exists, directed messages are tagged with a special network header flag. Relay nodes that support directed forwarding check their forwarding table: if an entry exists for the destination, the message is forwarded only to the next hop on the path. Nodes without a matching entry do not rebroadcast, eliminating the flood.


Path Lifetime and Maintenance


Forwarding table entries have a configurable lifetime (Path Lifetime, typically 2 -- 24 hours). When an entry expires, the next message to that destination triggers a new path discovery. If the network topology changes (a relay node goes offline), the forwarding will fail, and the sender falls back to flooding until a new path is discovered.


Coexistence with Managed Flooding


Directed forwarding does not replace managed flooding entirely. The two mechanisms coexist:






Message Type
Delivery Method






Unicast (path exists)
Directed forwarding




Unicast (no path)
Flooding + concurrent path discovery




Group / Multicast
Managed flooding




All-nodes broadcast
Managed flooding






This hybrid approach leverages directed forwarding's efficiency for point-to-point communication while retaining flooding's reliability for multicast scenarios.


Performance Benefits


In a network of 200 nodes arranged in a grid, a unicast message via managed flooding generates approximately 200 rebroadcasts. The same message via directed forwarding generates rebroadcasts only along the discovered path -- typically 5 -- 15 hops. This represents a 10 -- 40x reduction in airtime, which directly translates to:


    

  • Lower collision probability on the advertising channels.
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  • Reduced latency (fewer competing transmissions).
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  • Lower power consumption for mains-powered relay nodes.
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  • Better scalability beyond 100 nodes.
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Requirements


Directed forwarding requires all nodes along the path to support the Directed Forwarding feature (Mesh 1.1). Mixed networks with legacy (1.0) and updated (1.1) nodes can still operate, but directed paths will route around non-supporting nodes, potentially finding suboptimal paths. The provisioner should upgrade all relay nodes to Mesh 1.1 firmware before enabling directed forwarding network-wide.

  

  

  
  
  




  
  
Related Terms

  

  

    
    Bluetooth Mesh
    
    Managed Flooding
    
  





  

  
  

  
  

  
  

  
  




  
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.