How to ping a webserver with php?

Hi there, I do have a webserver (that also runns php 4.x) running which I would like to ping from an intranet server. In case that the webserver is down and therefore my webapp the php script which does the ping should send an e-mail which results in a message on my mobile. Are there any commands for PHP which you can recommend for doing that? The plan was to write a php file which does the ping and e-mail thing and execute it via cron every few minutes. Can somebody give me a hint on the commands I could use for the ping? Thanx, merlin