Application with modem connection to a PC for transfer file

I have to develop an application under Windows CE.NET that make a call by
modem to a PC, than the application have to receive file and transfer file
from and to the PC and also communicate other data. The problem is what kind
of method of communication and what protocol is better to use.
1) Use TAPI for the connection and then use a self made protocol via serial
(or implement protocol as ZModem, etc)?
2) Use RAS to connect to the PC and than use TCP/IP (PPP)? But also in this
case I have to send the file or receive the file writing code with socket
functions?

Thanks in advance
--
RL