Re: [rtl] IP useage from rtlinux

[Paul Koning <pkoning@xedia.com>]

>>>>> "Michael" == Michael Kaufmann <root@mucosa.franken.de> writes:

 Michael> On Tue, 9 Jun 1998, Richard Teltz wrote:
 >> I understand that the rtlinx system runs the LINUX "OS" portion as
 >> a low priority task under the rtlinux kernel.  Does this include
 >> the IP support (UDP in particular)?  Has anyone ported IP support
 >> to the rtlinux kernel level?

 Michael> Use IP with the linux kernel. IP is not able to transfer
 Michael> data in realtime, so we don't need IP in the rtlinux kernel
 Michael> (realtime level).

 Michael> I think it is very important to have the possibility to
 Michael> transfer realtime data with rtlinux over a network to other
 Michael> rtlinux systems, or what is much more important to other
 Michael> network nodes like sensor, ionodes ...

 Michael> To do this you need: - a realtime network hardware
 Michael> (e.g. ARCNET, ...)  - a realtime software protocol (not IP)
 Michael> or simply raw access.  - a rtlinux network driver for this
 Michael> network hardware.

No network can guarantee delivery of traffic to a destination with a
realtime bound.  On the other hand, many networks offer delivery of
traffic with probability P very close to 1 with a realtime bound.

You don't need ARCnet for this, nor "realtime protocols" (whatever
that means).  Ethernet will do fine, as many people have shown.  If
you're just transferring data within a LAN (no routers, no bridges
either), no layer 3 protocol is needed, but also no harm is done by
using IP (since it merely adds a few bytes of header). 

 If you do go through some sort of switch, you have to analyze the
congestion properties of the resulting setup.  If your loads are
reasonable, you should be able to maintain the "delivery of traffic
with probability P very close to 1 with a realtime bound" property.
This applies independent of network layer protocol used; they are all
essentially equivalent as far as this issue is concerned.

	paul
--- [rtl] ---
For more information on Real-Time Linux see:
http://www.rtlinux.org/