How to monitor the network usage of specific apps on iOS? I am currently helping someone who has experienced large amounts of data being transferred over her DSL connection. After long research (via IRC support) I found out that her iPhone is obviously sending lots of data, i.e. several hundred kbyte/s, as soon as she connects it to her home network. The iPhone itself seems to work fine.

To find the culprit responsible for these huge amounts of data I would probably need to find a way to measure how much data all connected applications are sending within a specific interval.

As I do not use an Apple mobile device myself I am not familiar with iOS. Are there any possibilities to get information about the network usage of specific apps, either natively or with the help of a third-party application that is for free or at least offers a free trial version?
You can do this with Onavo Count

Onavo Count monitors and analyzes all types of mobile data and phone use. This includes background, foreground, and Wi-Fi use.