As a user, we use internet. But sometimes we don't realize at what speed the data consumes. There are third party apps, which shows the speed in notification panel. We can even use them, but it is extra memory consumption and using third party app.
If we have it as a system app, which give system tray icon in notification panel which displays current up and downlink speed of the device.
Firstly I want to say that you can't have system app untill it is provided by manufacturer and samsung doesn't provide this feature. hence if you want third party app then try app named 'Network speed' it is quite good and provide you exact consumed data and various functions.I am using it and I am beta tester also.