Maximum packet length for Bluetooth LE?

Question

I was wondering what is the maximum packet length in Bluetooth Low Energy. A limit of 20 bytes, if often said, for here here

"BLE allows you to transmit a maximum of 20 bytes."

"You are correct that the BLE specification does not allow write operations greater than 20 bytes."

However, reading the Bluetooth core specification, we see that the ATT_MTU value is written with 2 bytes, which means that it can reach 65,535 bytes.

What is the truth behind all this?

Answer 1

The specification is always correct!

Bluetooth 4.0 BLE ​​33 ( Access Address CRC). :

• 2 ( ),
• 4 MIC ( ),
• 4 L2CAP ( ),
• ATT 23 , MTU ATT.

ATT ( ) 3 , 20 .

ATT :

• L2CAP:

  L2CAP ATT PDU 27 (23 ).

  :

  • ,
  • , ( L2CAP, )

• , Bluetooth 4.2:

  251 , 238 .

  :

  • , , ( ​​ BLE 4.2),

  • , .

, L2CAP .