Summary of specific methods
1 The reason for the mobile phone network is relatively large, we to the mobile phone into restore network settings
In the 5s main screen click "Settings" to find "universal" entry and click "Restore" here to find "Restore network Settings" and then click on it, you can restore the network.
2) Reset Access Restrictions
Also go to the iphone desktop, and then we click "Set" to go to "universal" and then find "Access restrictions" to open it, and then close it later.
3) Reset the current WiFi
Click the "Settings" icon on the phone's desktop, and then click "WiFi" when you enter it and then click –> "Ignore this network" to reset the current WiFi
4) Check your time, as well as the timezone
There is another because of the internal and external time zone problem, we can try to set up, in the phone's "set" –> "General" –> "date and Time" –> turn off "Automatic settings" and then we repeat the more times to connect itunes.
5) Setting up a DNS server
In the Apple mobile theme "Settings"-"Wireless LAN"-"exclamation point"-dns-dns server address, I usually manually set two DNS server addresses, 8.8.8.8.