Since the N-Tier world is a brave new world, we have been asked
to provide background on N-Tier concepts in general and will
continue to enhance these documents.
For General N-Tier Theory and a great description of the thread
and session pooling abilities of ASTAServer's check out COM+ and
the Battle for the Middle Tier by Roger Sessions
(Wiley Books). Although Sessions describes MTS it is very similar
to the way ASTA operates.
Support 
by Richard Gaskin