How to keep track of the network traffic on 3G/wifi on an iOS device? [duplicate]

Question

I am trying to understand how does an app like DataMan work. Even if it runs on the background, how can it measure the bandwidth allocation of the other apps?

Answer 1

Most apps like that inject a proxy to all your data calls. Through that they measure the amount of bandwidth you are consuming.

There is no way to measure data you are using outside of your app. You can track it for your own network call within your app though.