Throughput ATT_MTU

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?

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  • Hi

    Sorry about the misunderstanding. Are all 255 bytes part of the payload/ATT data? As you can see from this picture, a packet consists of up to 266 bytes (2M PHY) or 265 bytes (1M PHY). Then the PDU can be up to 257 bytes, the payload up to 251 bytes, and the ATT payload (which is the data fully configurable that you'll see on the receiving end) up to 244 bytes. It's not possible to receive 255 bytes of ATT payload in one Uncoded LE data packet.

    Best regards,

    Simon

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  • Hi

    Sorry about the misunderstanding. Are all 255 bytes part of the payload/ATT data? As you can see from this picture, a packet consists of up to 266 bytes (2M PHY) or 265 bytes (1M PHY). Then the PDU can be up to 257 bytes, the payload up to 251 bytes, and the ATT payload (which is the data fully configurable that you'll see on the receiving end) up to 244 bytes. It's not possible to receive 255 bytes of ATT payload in one Uncoded LE data packet.

    Best regards,

    Simon

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