Maximum GATT MTU SIZE possible in nRF52832

[amey3]

Hello,

We are using nrf52832 soc for our product development and using that we are trying to increase the throughput of our device using the information from the following forum:

Novel Bits throughput guide 

In this forum it states that the Maximum GATT MTU SIZE possible is 247 bytes in which 244 bytes of data is the actual payload size and if the data is greater than the limit, then it will split into multiple packets. So we tried to send more that 247 bytes of data just to check how the data split in multiple packet is working. We tried to sent 256 bytes of data and we were able to get 255 bytes of data without any splitting, which is more than 247 bytes. So we are wondering what is the Maximum GATT MTU SIZE possible in nrf52832 soc. 

We also looked into the throughput example provided by the nordic (ble_app_att_mtu) and in that MTU size is set to 247 and data length is set to 251 which is less that what we are able to send from nrf52832 to phone, is there any possible explanation for this?

[Edvin]

Hello,

we were able to get 255 bytes of data without any splitting

How do you determine whether the packet is split or not? Do you look at the packets on the phone app, or did you actually try to capture a sniffer trace of the connection?

I suspect that you are determining this based on how many events you receive on the phone, while the packets are actually split up on the air. Try to capture a sniffer trace using the nRF Sniffer for Bluetooth and see if you can see when the packets are split and when they aren't.

Best regards,

Edvin

[amey3]

We used the nrf Sniffer and we saw only single packet with 255 bytes of data and it was without including header data?

[Edvin]

Can you please share the sniffer trace that you captured (save it as my_trace.pcapng and upload it here), and the project that you used for testing?

Best regards,

Edvin

[amey3]

Hello Edvin,

PFA images of sniffer traces.

[Edvin]

Can you please send me the application that you used to test this?

Best regards,

Edvin

[amey3]

we captured the sniffer traces using wireshark

[Edvin]

I was thinking of the application that was running on the nRFs that you are sniffing. And feel free to send the sniffer trace as a .pcapng file as well, and not only the screenshot.

BR,

Edvin