Every release of a major iOS release creates problems for ISP administrators, and the chart above PROVE how big is a problem like this in reality. The graph above represents the internet traffic recorded at multiple internet service providers in the US and you notice that at some point after the launch iOS 7.1 the traffic volume increased from a few tens of GB per second to almost 1 TB per second and then during the following hours to over 1 TB per second.
The updates made by users for iOS generate extremely high data traffic, and Apple tries to make life easier for internet providers with the OTA Updates system, but things are not as simple as they seem.
