nRF52 throughput test

[Mehdi]

Hello,

I'm testing the ble_app_att_mtu_throuput example on SDK15.2, I found that the throughput becomes very fast by just changing the 'data_length' from 27 to 251 compared with the default configuration. 

Default configuration : 

ATT MTU = 247

PHY         = 2Mbit/s

So I want to know why just changing 'data_length' led to express the data exchange knowing that the ATT MTU is always 247.

Best Regards,

Mehdi.

[Bjørn Kvaale]

Hi Mehdi,

By increasing the data length (data length extension, DLE), you are increasing the number of bytes that can sent in each on-air packet. If you do not have a lot of wireless interference, it can be very quick to set the DLE to 251. If you have a lot of wireless interference, it can be better to use a smaller value because if a packet does not arrive, the contents of that packet need to be retransmitted.

The reason that ATT MTU is less than the DL is because there are 4 header packets that cannot be used to send data on (link layer header I believe). 

The best idea is to read this blog post carefully. Everything is explained very well there.

Kind Regards,

Bjørn