Nrf connect 2.3.0 dfu a lot slower than nrf connect 2.2.1

[bds]

Nrf connect 2.3.0 is at least 4 times slower than nrf connect 2.2.1 when updating a device ota.

Is this expected?

Anyone with the same results?

[bjorn-spockeli]

bds: I've done the sniffer traces now and it seems that in our eagerness to maximize DFU throughput in SDK v15 we've actually lowered the througput for older bootloaders. 

nRF Connect v2.3.0 has been optimized to be as fast as possible with the latest bootloader in SDK v15.0.0 and is using a ATT MTU size of 247 bytes and sending one packet per connection interval. 

The older bootloader from SDK v12.1.0 will not repond to the request for a larger MTU size, i.e. it stays at its default value of 27, but nRF Connect v2.3 will still only send one packet per connection interval, significantly reducing the throughput compared to nRF Connect v2.2.1 that sent up-to 8 packets per connection interval with the ATT MTU size set to 27. 

I have reported this internally. 

Best regards
Bjørn