🚀 go-pugleaf

Paul Womar wrote:

> Stephen Maudsley <Stephen.Maudsley@esgem.com> wrote:
>
> [attributions lost]
> > > > > > > > > Nearly, but not quite in that although the maximum speed might
> > > > > > > > > be the same, the latency of a TA will be slightly higher.
> > > > > > > >
> > > > > > > > Why?
>
> > It's not clear what the question is but anyway....
>
> It's the one above, why is the latency greater on a TA than via a PCI
> card?

There's two contributory factors: the physical connection between the application
code and the ISDN device is far faster for PCI than for an external TA. If you
have a  connection with 1kbyte packets they will take at least (1024x8x26)uS for a
384kBaud link - 21 mS before its transferred into the TA or (1024/4x15)nS for a
66MHz PCI bus - 4uS. (I'm assuming PCI transfers at 32bits and an assumed bus
speed). The numbers may not be very accurate but they're of the right sort of
order and show that the TA has latencies comparable with network transfer times
and the PCI bus has latencies which are insignificant.

The second contributory factor is that the transfers to the TA will probably be
through the operating system and so may well have mS delays because of that,
although they will probably be second order effects in most cases.
--
Stephen Maudsley  mailto:Stephen.Maudsley@esgem.com
Esgem Limited for electronic product design
http://www.esgem.com
Tel: +44-1453-521626 Mobile: +44-370-810991