Differential Signalling on a 4 ports channel

Hi all,
I'm working on the development of a Matlab model for an High Speed serial interface.

Let's suppose to have a differential signalling scheme (NRZ) and that the medium is a 4ports network described with a TouchStone Sparameter file .s4p .

Let's consider this schematic structure and naming conventions:

-----HHHHHHHHHHHHHHHH -----
VS1, ZS1^^^^^^^^^^ ZL2
port1__________________ port2
-----HHHHHHHHHHHHHHHH -----


-----HHHHHHHHHHHHHHHH -----
VS3, ZS3^^^^^^^^^^^ ZL4
port3__________________ port4
-----HHHHHHHHHHHHHHHH -----

Let's assume that, because of mismatches, all the Zi are not equal to 50Ohms, the nominal reference voltage of the channel.

My question is: how is possible to compute THE VOLTAGE LEVELs at each of the two input ports of the channel and at each output port?
I would like to consider the contribution of the reflection and coupling effect among the lines (included in the Sparameter description).


For a two ports network I can calculate the input channel voltage using the Tin=f(sparams,ZS,ZL), but how can I calculate the equivalent with a 4 port network and an .s4p file?

Thank you very much for the attention!

Regards,
Gianni S.