I got a rough overview of J2EE in my software architecture class and it
is described as a tiered structure. The web tier houses the web
server, Java servlets and JSPs and it sits between the client's web
browser and the application  server. Therefore, the web tier provides
HTTP capability to the system and houses any dynamic web content in the
form of JSPs. The application server  houses the EJBs and what not and
uses the web server found in the web tier to communicate with client
web browsers. The web tier can be completely bypassed however by
writing a stand-alone client application as oppose to an applet. The
client app then communicates with the application server via maybe raw
TCP or UDP without a dependency on HTTP thereby bypassing the web tier.
Does that answer your question?