Setting MTU size through nRF connect mobile app not working properly with Samsung mobile

[dpknyk]

Hi,

 I am working on a project with nRF52832 chipset(custom board).

When I am trying to set MTU size to 247 bytes with nRF connect mobile app, I am getting max_rx_octets & max_rx_octets size as 251 bytes in BLE_GAP_EVT_DATA_LENGTH_UPDATE event.

This is working fine with all phones except Samsung Phones with Android Version 12, with this phone when I set MTU size as 247, I am getting max_rx_octets & max_rx_octets size as 247 bytes in BLE_GAP_EVT_DATA_LENGTH_UPDATE event.

I have tested this with other phones having android version 12 but didn't see this problem.

Anyone knows why this behavior with Samsung phones with android version 12?

Thank you in advance for any help.

[Torsten Robitzki]

The Bluetooth standard allows to have MTU sizes as low as 23, so 247 is already quite high. You can simply not rely on benign able to set the MTU size to higher values as 23. In practice, most phones implement GATT MTUs much higher than that, but you can not really rely on it.