title: BLE: Lower MTU value size(big difference) after MTU exchange
body: <p>I am new to the BLE development. I want to send some large amount of data over a BLE connection with maximum throughput.</p>
  
  <p>I have a GATT server, which is running on Linux, and a client which is running as an app on Android. I have created a custom characteristic with the maximum allowed size(512 bytes). I am requesting it from the app with a read operation. Every time I receive a call for reading on the server side I change it's value until I am finished with all the data(I know this isn't the best way but that's not the problem for now).</p>
  
  <p>As for the connection parameters using android's requestConnectionPriority(CONNECTION_PRIORITY_HIGH) i can see that they are trying to negotiate a connection interval of 7.5ms but for some reason, it changes to 15ms and it remains there. Maybe my phone doesn't support it but I don't think so.</p>
  
  <p>The next thing and the main problem is the MTU. Using hcidump, I can see that they are starting to negotiate the MTU as I can see an MTU Request from the client with a value of 517(by default) and a server Response with the same value. But when I trigger the data exchange I can see(using Wireshark) that the packets are containing only 32 bytes of payload. I don't know if it's a restriction with my Bluetooth adapter.</p>