> 
> On occasion, when I have a PPP connection up, I get the following message
> on the console (often repeatedly):
> 
> /netbsd: zstty0: ring overrun

What version of NetBSD are you using?

> Due to a variety of tests that are not all worth describing, I suspect
> that the cause of this is that the port speed on tty0 doesn't match the
> modem's speed.  I have a 33.6 modem, but I couldn't get pppd to start with
> the baud rate set at 33600.  Setting it at 38400 worked, so I've been
> going with that.

That's because the mac's serial ports can't handle 33600. They can
do 38400 and 57600, but not 33600.

> I'm curious as to what "ring overrun" means, and what its consequences
> are.  Does it mean that the OS has overflowed the modem's buffer, or
> something like that?  And is there anything I can change so that this
> error won't be reported? 

No. That means that you have something slow in your system. The ring
buffer is a buffer which holds characters which arrive from the
serial port, but have not yet been processed by the kernel. Basically
when we receive characters, we stick them in the ring buffer and read
them back out when the kernel is ready; when it's not in the middle of
something else.

Take care,

Bill