the node concept is the same in all environments ...
mainframe, server, workstation
complicated a bit by the conundrum physical VS logical
let' s keep it simple ...
ONE MAINFRAME ONE LPAR ONE NETWORK ADAPTER ONE IP Address, one Communication Controller for pre TCP network architecture
what do You want consider as a node
the MF the LPAR the NA the IP address, the CC
in the LPAR You have JES2, a ftp server, some CICS regions, NFS ... add as many applications as You want
what do You want consider as a node ...
in any environment something that is a terminal or a connecting point of the flow of information could be considered as a NODE
as per my first reply
and think before complaining about the answers You get.