Open Cdrom, from command prompt

Hi.
I have redhat 7.0
How do you open the cdrom tray from the command prompt.
Say I am in root. I have mounted the cdrom, and used it. When I press the button on the computer frame it does not open. So how can I open it from the command prompt???
Also, what command would you use to close it.
Thanks,,,,,,,,,,,Pat