Event received by BLE peripheral device when server requests to read from characteristic

Hello All,

I am developing an application using Nordic nRF_SDK_15.0.0, in which I need to make my BLE peripheral device as a peer device which will get/set data from/to the other micro-controller (Host device) through UART communication through set of command and response frames. I will be developing a set of custom characteristics with read / write / notify permissions. 

For reference, I am using 'ble_app_uart' example and performing modifications in same to obtain my application. Through this example I am clear about how to write data into characteristic (through BLE_GATTS_EVT_WRITE event) and how to generate data for notifications, at peripheral side. But I am not able to get that how to read from characteristic? In other words, what event will be generated at peripheral side so that my peripheral device will come to know that central device need to read from characteristic? This event will make my BLE peripheral device to  send corresponding command on UART to my Host device to get the required parameter value in response frame and display that value through characteristic.

Thanks in advance for your help.