Development

BLE GATT Server Implementation Guide

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Building custom services and characteristics

  
  

    
    
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    2 min read
    
  


  
  







  
  

    
    
      
      
  1. 
        GATT Server Implementation
      
    2. 
      
      
  2. 
        Service Design
      
    3. 
      
      
  3. 
        Characteristic Properties
      
    4. 
      
      
  4. 
        Notifications and Indications
      
    5. 
      
      
  5. 
        MTU and Throughput
      
    6. 
      
      
  6. 
        Security
      
    7. 
      
    

  









  
  

  
  

    
    

      
GATT Server Implementation


A GATT server hosts BLE data — it exposes services, characteristics, and descriptors that clients can read, write, and subscribe to. Implementing a well-structured ATT">GATT server is the core of most BLE peripheral development.


Service Design


Services group related characteristics. Each is identified by a UUID — either a 16-bit Bluetooth SIG-assigned UUID or a 128-bit vendor-specific UUID.






UUID Type
Size
Example
Source






16-bit
2 bytes
0x180F (Battery)
Bluetooth SIG




128-bit
16 bytes
6e400001-b5a3-...
Vendor/developer






Use the BLE UUID Generator to generate vendor-specific UUIDs. Use the GATT Profile Browser to find existing standard definitions before creating custom ones.


Characteristic Properties






Property
Bit
Meaning






Read
0x02
Client can read the value




Write without response
0x04
Client writes, no ACK




Write
0x08
Client writes with ACK




Notify
0x10
Server pushes updates, no ACK




Indicate
0x20
Server pushes updates with ACK






Notifications and Indications


Notifications and indications are the primary mechanism for server-initiated data push. The client must write to the CCCD (UUID 0x2902) to enable them.


Indication requires client acknowledgment and retransmits on failure — suitable for critical data. Notification is fire-and-forget with lower overhead.


/* Zephyr: send notification */
bt_gatt_notify(conn, attr, data, len);



MTU and Throughput


The default ATT MTU is 23 bytes, yielding 20 bytes of characteristic data per packet. Negotiating a larger MTU with DLE dramatically increases throughput.






MTU
Payload per packet
Notes






23 (default)
20 bytes
No negotiation needed




247
244 bytes
Requires DLE on the link




517
514 bytes
Maximum per spec






Security






Security Level
Requirement
Use Case






No security
Open
Non-sensitive data




Unauthenticated encryption
Just Works pairing
Eavesdropping protection




Authenticated encryption
MITM-protected pairing
Sensitive commands






For the full pairing and bonding flow, see BLE Protocol Stack Architecture.

    

    

    
    

    
    
    
    

    
    

      




  
Frequently Asked Questions


  

    
    

      
      

        
Yes, our guides range from beginner introductions to advanced topics. Each guide indicates its difficulty level and prerequisites so you can find the right starting point.