Bluetooth mesh concepts — nRF Connect SDK 1.5.1 documentation
Generic Access Profile (GAP) — BLE-Stack User's Guide for Bluetooth 4.2 3.01.01.00 documentation
Bluetooth GATT: How to Design Custom Services & Characteristics
In nRF52832, GATT, unknown service is not executed except GAP in basic service program (GAP, GATT, unKnown service - uart) - Nordic Q&A - Nordic DevZone - Nordic DevZone
Building a Bluetooth application on nRF Connect SDK - Comparing and contrasting to SoftDevice Part 1 - Software - nRF Connect SDK guides - Nordic DevZone