[foxboro] Another mesh question

I don't know...I'm kinda old-school when it comes to DCS networks, and I 
believe in as much separation between the redundant halves of the control 
network as possible (lack of this separation is to me the classic 
nodebus's biggest problem).  So this whole mesh thing leaves me a little 
uncomfortable.  I can envision a failure mode in one of the switches 
causing problems on the entire control network, just as some failures on 
classic nodebus stations can cause problems on both sides of the nodebus 
(we've seen these happen).  I've never experienced this issue on systems 
where the redundanty control networks were more completely separated.

I just wonder what safeguards are present to prevent that sort of thing 
from happening?  Can you run the mesh separated (i.e., no 
cross-connections between switches) if you want, potentially giving up the 
ability to route around multiple endpoint connection failures in exchange 
for protection from rare, but potentially catastrophic, complete network 
failure?


Corey Clingo
BASF Corp.





"Boulay, Russ" <russ.boulay@xxxxxxxxxxxxxxxx> 
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Re: [foxboro] A mesh question






Stan..

In the Mesh world there are only a few restrictions when connecting the
switched network.

Multiple connections between switches are acceptable.

You could have 15 connections between two switches if you like.

RSTP Rapid Spanning Tree Protocol determines the connectivity and will 
block
and open ports between two switches at any given time.

Ports to use are determined by:
First)  Path "costs" as deemed by RSTP
Second) The actual Port #  1 vs 2 vs 3 if their path costs are equal.
Port 1 open, 2 & 3 blocked. If then connection to Port1 fails, Port 2 
would
then open.

Most important rule is:
No more than 7 switches between stations.
So if an AW is to communicate with a particular CP the interconnection
between switches to get from AW to CP must be less than 7 switches.
So all possible paths from one station to another station must be 
considered
when designing the layout.





 
 
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