If one browses the web for mathematical definition of a two port network
ones gets all kinds pf constraints depending on the V,I relationships one
is trying to enforce with their specific mathematical relationships. So yes one can
define a two port to require current in one port lead to equal that coming
out. Or one can define two port to also have energy sources/sinks in it and the
defining equations have to be changed to meet the constraint imposed. Hence
currents can differ.
Its not just one specific implementation with one set of constraints. It can be
anything the author decides, with defining equations solving all possibilities
the author imposed on his two port internals. The two port can be non linear
as well. So one solves with a different equation approach. IEEE papers on this.
Unless the FDA has issued some new definition that we all must obey.....
Regards, Dana.