The iPhone software update server could not be contacted. Update software failed

Hi Experts,
Have a look at the error message below. What does it mean?
I tried several times to check for update software of iTunes but failed to get this error message. I think there is no problem with my network connection and settings.
How can I get a remedy of this issue?
Please help.
Thanks in advance.

The iPhone software update server could not be contacted.
Make sure your network settings are correct and your network connection is active, or try again latter.
