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[rtl] realtime network
On Mon, 15 Jun 1998, Paul Koning wrote:
> No network can guarantee delivery of traffic to a destination with a
> realtime bound. On the other hand, many networks offer delivery of
Sorry, i can't agree with you.
> traffic with probability P very close to 1 with a realtime bound.
Sure, when you cut the cable in the middle of a packet transfer or something
like this, all your calculations are useless. Also when you use a reduntant
network you will never have a absolute delivery of probability (with this
sort of view).
> You don't need ARCnet for this, nor "realtime protocols" (whatever
> that means). Ethernet will do fine, as many people have shown. If
For "soft-realtime" - no problem. There are some higher level protocols for
ethernet available to make ethernet realtime able. So your ethernet can do
"hard-realtime", this means you can calculate the exact time a packet needs
for transfer to another node, but your network is very slow.
Let us say you have a network where you can be sure that the packet needs
max. 2 seconds for transmission. This is also "hard-realtime", because you can
be SURE it never takes longer than 2 seconds. But the quality of this
"hard-realtime network" is not very good, when you don't need more - be happy.
But there are applications where you must be able to transfer realtime data
over a network in a shorter time. Let us say your application has a state
where it must be able to transfer every 50usec 10 Bytes to another station
over the network. The quality of such a hard-realtime must be a little bit
higher...
A so called realtime network (e.g. ARCNET) has some mechanisms with makes it
possible to transfer data in a very short time, and you can be sure that it
never takes longer!
When you want, i can give you a few examples for the fieldbus ARCNET, because
i know a lot about this type of network.
Bye
Michael
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--- [rtl] ---
For more information on Real-Time Linux see:
http://www.rtlinux.org/