oversampling

What possible methods of oversamping can be done between a dte and a
dce? I am aware that if the dte is async (such as it uses a serial
port) and the modem is working synchronously, that the sample rate at
the modem has to be quadruple that of the dte's sampling rate. For
example in hyperterminal i would work with 4800bps and the modem would
be set to work with 19200. Is it possible to oversample when the DTE
works synchronously and so does the DCE? would it at all be necessary?
Right now I have a lab but I can't check this over long distances.
Also, is it possible to oversample if the DTE is synchronous and the
DCE only works asynchronously? if not then what would be the necessary
procedure for these components to operate in a basic network, meaning
DTE (sync) -> DCE (async) ~~~ DCE (async) <- DTE (sync)

Happy holidays guys and gals