NewB Q regarding Overview

[Janna]

Could someone possibly, briefly explain (or point me to an architectural
overview) of the following and their interrelationships of:

Java Application Server
Glassfish
JMS
Tomcat

Do I still need tomcat if I have Java Application Server?

Isn't Websphere, say, the IBM Brand of Java Application Server and JBoss the
Redhat version of the same?

If I have Java Application Server, Websphere or JBoss installed, don;t I
have all I need for JMS as well?

If I have Glassfish -- doesn't that replace Java Application Server?

Thanks guys, Janna