The Communication Manager is the Private Branch Exchange [PBX] branded by Avaya. You'll find lot more details whenever you do search on Google. So, you do not need me in explaining the same stuff here. But, I am here to explain MY WAY of understanding about Avaya CM. Lets talk about each component of the image in detail. Here you go! Summary: * CM is running as an application inside the Linux OS (Red Hat Enterprise Linux) * There are other applications in the Linux help for CM not running within CM * CM is different than Server. CM means the call processing software with Linux where as Server means Platform+CM+other applications * Shell prompt: You can not administer CM features etc * Autosat prompt: You can not perform Linux stuff such as busy-out a server, reboot etc Thanks, Raj