ppp over emulated comm port

We are trying to run TCP/IP using ppp over an emulated comm port in Windows
NT. we are using ‘dial-up networking serial cable between 2 PCs’ to install
ppp. we are able to get our driver loaded and the ppp is recognizing our
device. the transport layer of our device doesn’t support timeouts. for the
Ioctls which request for timeout settings, we simply return success and
ignore the handling. apart from that, our data transfer is well tested.
Is it O.K. if we return failure to timeout settings?
How will ppp handle such a case?
If we return failure, what should we say we support?
We are using very low baud-rate setting currently, 1200 bps. We are handling
immediate byte request and infinite waits sufficiently, but finite waits are
turning out to be tough.
Our stack looks somewhat like this

TCP

IP

PPP

Our driver emulating COMM port

Our driver handling transport layer

Serial port driver of NT

Any suggestions?
TIA,
Rakesh