There is never an absolute need to use a CPU but it usually makes life much simpler to process data using software than a purely hardware solution.
The answer you want depends on the format of the data, a transceiver alone generally handles the electrical requirements of data transfer but not the content of the data itself. If you have to deal with encoded data or data packaged in some kind of protocol, a CPU is the sensible solution.
I'm not sure what you mean by 'a stack' in this context and in what way you think Windows uses it. Can you be more specific please. A stack is just a list of data or addresses, I can't see why it is OS specific at all.
Brian.