SUMMARY: Sunlink X.25 on Ultra serial ports

From: Peter Polasek (
Date: Tue Apr 14 1998 - 18:06:38 CDT

I did not get a lot of feedback on running a 64Kb X.25 interface over the
serial ports of an Ultra-10, so I assume there is not a lot of interest
in the subject. Nonetheless, I'll share the info I did collect. The
Ultra-5/10 ports are rated for 460Kb async, 64Kb sync so the 64K X.25 should
work. However, the buffer size of the serial ports is very small, so the
interface could be a CPU hog because of the frequent interrupts that will be
required to service the buffer. The Sun HSI card (and Aurora sync cards)
provide much higher performance because they buffer large amounts of data.
The HSI card is inconvenient to use because it requires an active RS-449 to
232 converter. The Aurora card is a far more convenient, space, and cost
efficient and one respondent has used it with Sunlink. Because we will be
building aoubt 100 of these machines, we will initially investigate using
the serial ports to see if performance is acceptable (I will summarize in
a few months when we receive the test results). Thanks to those who

Peter Polasek

Original Posting:
> I have an application that requires a single 64Kbps X.25 interface
> on every machine. The server will be either an Ultra-1 or Ultra-10.
> I would like to use Sunlink X.25 WITHOUT the Sun 'HSI' card. Because
> we will have more than 200 of these machines, the cost (and space) of
> the HSI card and the active RS449-RS232 converter is prohibitive.
> Does anyone have any experience running 64Kbps X.25 on the serial
> ports of an Ultra box? If so, I would appreciate a brief summary
> of your experiences. The specs say it will work, but the official
> response from Sun has been mixed. Some say it will work without an
> issue while others state that performance may be slow because the
> small buffer sizes in the 'zs' interface will cause excessive
> interrupts. Another possible option is to use the Aurora 400+
> board with the Sunlink X.25 (this approach costs less and is far
> more space efficient because the RS449 converter is not required).

From: Stephen Harris <>:
I used SunLink X25 in 1990->1995 on a Sun Sparc 1+ with the inbuilt serial
ports. This was only a 19.2 channel. Performance was really poor, but
this could easily have been the exchange (it was in Greece where telecomms
was very very very bad! We got X25 because normal international phone lines
couldn't handle a 2400 baud modem!!!!)

Builtin zs ports have trouble going over 38400 baud in async mode. I don't
know how well they work in sync mode.

It was Sunlink X25 8.0.2 on Solaris 2.4 at 19.2K. It was important to
have all the Sunlink X25 patches from Sun. Aurora provides a driver which
more or less takes over the zs devices. I think there was a small problem
with the links in /devices getting reset to the built in zs devices
after you do a "boot -r".

We used the X25 socket library and in-house C code to communicate to the

I don't know how well this would work with Solaris 2.6.

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