Wed, 20 Sep 2000 David Schleef wrote:
> On Wed, Sep 20, 2000 at 12:06:47PM +0200, Joachim Herb wrote:
> > Hello Karim,
> >
> > after reading your mail about the use of the LTT together with the RTNET
> > module, I would like to ask you some questions:
> >
> > - You wrote that the response time is <=65 microseconds. What is the
> > maximal throughput over the ethernet connection? What is the maximal packet size?
> > Is this the MTU value and is this value fixed or can it be changed?
>
> 65 usec is for small packets, add about 0.1 usec per byte for large packets
> because of the time it takes on the wire. The MTU value is 1500, and
> although some hardware supports larger packets, I wouldn't try.
>
> The maximum throughput is theoretically 100 Mbit/sec. This can
> actually be achieved on a full-duplex line. If you intend
> to use a non-full-duplex line, you need to have some kind of
> time-division protocol on top of rtnet, which will decrease
> throughput significantly.
BTW, has anyone measured this over networks with hubs or switches, rather than
crossover cables? Or; are there any hubs or switches that would be usable in low
latency RT networks? (Yeah, I'm thinking Beowulf clusters for audio/video
processing. :-)
David Olofson
Programmer
Reologica Instruments AB
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