ATT MTU Size

Mihir Tailor

Prodigy 100 points

Hello.

Can anyone explain why ATT MTU Size is 23 Bytes by default?

Kindly explain in the way of size of packets required at each layer of ble stack.

Thanks

over 7 years ago

0 Jessica H. over 7 years ago

TI__Genius 11535 points

Hi Mihir,

Which BLE version and device are you using?

If you look at ble_user_config.h in one of the BLE examples, it states:
// Maximum size in bytes of the BLE HCI PDU. Valid range: 27 to 255
// The maximum ATT_MTU is MAX_PDU_SIZE - 4.

So PDU_SIZE - 4 = 27 - 4 = 23 bytes.

This post on Stack Overflow has a good explanation: stackoverflow.com/.../maximum-packet-length-for-bluetooth-le

Also this is an interesting post on ATT MTU: e2e.ti.com/.../650671

0 Mihir Tailor over 7 years ago in reply to Jessica H.

Prodigy 100 points

I am using BLE 5.0 based Nordic development board....

0 Erling over 7 years ago in reply to Mihir Tailor

TI__Intellectual 1708 points

Mihir,

I suggest you get a TI development board then. Here is a good choice: http://www.ti.com/tool/launchxl-cc26x2r1

This board enables full BLE5 development incl all optional features of the BLE5 standard (high data rate, advertisement extensions, long range modes). It also enables full evaluaiton of Zigbee and Thread stacks. Did you know that TI also does concurrent multi protocol with BLE5? If you want to combine BLE5 with sub1-GHz RF you can also look at this board: http://www.ti.com/tool/launchxl-cc1352r1

Erling

Bluetooth®︎

Bluetooth forum

ATT MTU Size