SCO PPP can also support third-party
PPP STREAMS
stacks for use with smart asynchronous
serial port devices that are
capable of performing packetization
and framing in hardware.
Using smart serial port devices has two performance benefits:
It relieves the kernel of these functions and
makes more CPU cycles available to the system.
Smart serial port devices handle
packetization and framing more efficiently
than the kernel.
To support on-card framing,
a third-party PPP STREAMS stack
can be defined in the file /etc/pppstack (see
pppstack(SFF)).
Such a stack consists of:
one or more STREAMS modules including an
asynchronous HDLC protocol module
a device driver for the smart serial port device
If /etc/pppstack specifies the driver and one or more
asynchronous modules for a third-party smart serial port device,
pppd opens the driver and pushes the specified modules
on top of it.
If /etc/pppstack does not exist,
the PPP daemon configures the default
SCO-supplied PPP stack.
Figure 9-2
shows how the SCO and third-party PPP stacks are configured
below the PPP driver.