DLE enabled with secure BLE connection causes immediate disconnect when writing more than 20 bytes of data

[gn98122]

I am experiencing an immediate BLE disconnect when trying to use DLE. I can write up to 20 bytes of data, but if I try to write more 21 bytes or more I get an immediate BLE disconnect. There are no other BLE events (no write request or indication of error).

I am using the Nordic nRF52840, SDK v15.3.0, SoftStack S140 V6.1.1. The BLE connection uses MITM protection.

I am able to successfully connect using a secure BLE connection with MITM protection, update the data length to 174 bytes and the MTU to 247 bytes. Writing up to 20 bytes is fine, but writing 21 bytes or more causes an immediate BLE disconnect. 

With a normal BLE connection (no encryption) I can successfully write up to 244 bytes. 

Is there a restriction on the using DLE with a secure BLE connection?

[Marjeris Romero]

Hi George,

There's is no DLE restriction when using LESC. After the link is encrypted it should behave the same as in legacy pairing. Can you provide us with a sniffer trace? It would be of great help to understand what is going on. 

Best regards,

Marjeris