Is MTU of all BLE devices limitted to 23 bytes when using ATT protocol?

[JoonDong]

Is MTU of all BLE devices limitted to 23 bytes when using ATT protocol?

I don't know explicitly.

Some say it is possible to use MTU longer than 23 bytes.

Others say it is possible to use MTU longer than 23 bytes in softdevice(except to s132)

Is it impossible to use MTU longer than 23 bytes at Only softdevice?

does other vender implement MTU longer than 23 bytes for ATT protocol?

[endnode]

Hi JoonDong,

Trying to answer the questions one by one:

• "Is MTU of all BLE devices limited to 23 bytes when using ATT protocol?" - NO, 23 bytes is just default ATT_MTU size, can be negotiated higher.
• "Is it impossible to use MTU longer than 23 bytes at Only softdevice?" - Soft Device S130 (for nRF51) and S132 (for nRF52832) support extended ATT_MTU since v2.x, S140 and others as well.
• "does other vender implement MTU longer than 23 bytes for ATT protocol?" - Yes. Also note that you don't need to use Nordic BLE stack (Soft Device) on nRF5x, there are alternatives in open source projects such as Zephyr or Mynewt.

Cheers Jan

[JoonDong]

Isn't it meaningful to set to MTU longer than 23 byte if peer support just 23 bytes?