High-speed serial interfaces?

[Rich Braun]

I'm in the midst of planning a product which will include a SLIP (or PPP)
interface over a serial port.  We don't want to require CTS/RTS or XON/XOFF
flow control; it would be nice to just be able to handle thousand-byte
bursts of input, flow-controlled at the packet level via ACK/NAK rather
than at the character level.

In my experience, I've yet to run across a Unix system capable of doing
that.  And to make my job more difficult, we'd like to have a "portable"
way of doing this inexpensively on a variety of platforms.

Has anyone else had to deal with this, specifically under SCO Unix or on
any other system?  Am I naive to think that packet-level flow control can
ever work at 9.6K or 19.2K over on a 386 box running Unix?

-rich