How to check a Server is available or not during installing process?

[shawnsang]

We want to download some R package from http://cran.r-project.org during installing process.
Now, we want to check the server (http://cran.r-project.org) is available or not before we start R downloading process.

Any one have any idea to implement the requirement?
We hope to use internal function or method in Installshield, such as script, but not add a new third party.

Thanks!

[TsungH]

Duplicate post. Interested parties please follow up here.