How to Detect disconnected device from the WIFI network

Hi All,

I am creating the offline data transfer application.Now i need to detect the disconnected device.

For example device A,B,C were connected in the WIFI(no internet).We are transfering the data to A and B and C. A and B received successfully,C device did not received because C is disconnected from the WIFI network(due to distance between device and WIFI exceeds).

Please suggest me if anybody have an idea to overcome this issue.

Thanks in advance