I'm a newby. I'm troubles understanding what NUS is . How it is related with BLE Services , Characteristics and so on ?
The Nordic UART Service is a proprietary bluetooth service. This essentially means that it has a 128 bit UUID base, which is random generated (according to UUID generation spec), as compared to adopted profiles and services from Bluetooth SIG which are addressed using a 16 bit UUID.
We have some tutorials for people that are new to bluetooth low energy here:
This one should cover your questions on BLE services:
Thank you for material. But i didn't find an answer. What is supposed NUS service to do. Is it a default service on Nordic nrf51822 ? For what purpose has been created ?
You should look into proprietary services more in detail, because that's what NUS is.
BLE NUS is a proprietary BLE service, which has a service named "UART service" to mimic the older Bluetooth classic RFCOMM profile (UART over BT). This is one of the proprietary profiles that we have included in our nRF5x SDK, and it is provided with support both on the nRF side, as well as the central side (Android/PC/iOS).
NUS sets up one "RX" (characteristic with "write" properties) and one "TX" (characteristic with "notify" properties) datachannel, to fit basic UART communication needs. It can very well be 4 write characteristics, and 2 notify characteristics, but that will be overkill for UART communication, but you are still free to do this as a developer. This is the beauty of proprietary services, such as NUS, that you can set them up to specifically fit your application needs (if none of the approved BLE services fits your needs of course).