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Lt. Commander

[import] what is the difference between direct outstation with dual network and shared outstation

>>Message imported from previous forum - Category:ClearSCADA Software<<
User: ZeeKH, originally posted: 2019-05-27 03:46:36 Id:437
Hi There,
I am using Optus and Telstra link from ClearSCADA to a 4G modem and from there to single port of a GE PLC over DNP3 protocol.
I can use a direct outstation with dual network using shared outstation set or I can use a shared outstation connected to a shared outstation set.
What is the difference between Direct outstation with dual network and SHARED outstation dual network? When do we use either of them?

Reply User: hardin4019, posted: 2019-06-17 14:24:01
There is some useful info in the help file on this, and to be honest, its all a little confusing. But you are getting into the area of Direct Set, Shared Set, Switched Set, and then Direct Outstation, and Shared Outstation.

A Direct Outstation will use a Direct Set or a Switched Set. Under what circumstances you would use a Direct Outstation with a Switched Set, I'm not entirely sure, but with a little reading of the help files, I'm guessing you would mostly use it when you have Dual Network, and do NOT use both networks at the same time (see my example below of using both at the same time).

A Shared Outstation will have a "Shared" tab in the properties and can only use the Shared Set. The shared tab gives you options like when to Switch Type, the Preferred Line, Inbound Connection, and Heartbeat.

For instance I use Shared Outstation and Set on sites where I have 2 networks, one Satellite and the other Cellular. Each has a completely different IP scheme. The preferred Line is set to Line A (first network connection, Satellite), and the heartbeat is enabled. With the heartbeat enabled, Line A Satellite gets all of the traffic, and Line B Cellular gets a heartbeat poll of a single point every few seconds to check the health of the second network connection. On site, both connections are permanently on and ClearSCADA determines which network is used. If the Line B Cellular connection is healthy, and the Line A Satellite comms go out, ClearSCADA automatically switches to Line B and polls data via the Cellular, and a that point begins doing a Heartbeat check on Line A. If the Satellite comes back and stays in good comms for the "Use Preferred Line After X Seconds" found on the shared tab under Heartbeat, then comms switch back to the Satellite since it is Preferred Line A.

In my example above, if the Cellular comms drop out, but the Satellite comms are good, then ClearSCADA stays in comms and no switch occurs, but instead of "Healthy Multidrop", you see "Health, B Failed". If only the Satellite is out, you get "Healthy, A Failed", but are still in comms after the switch. It isn't until both fail that any alarms show on the banner.



Reply User: BevanWeiss, posted: 2019-06-18 12:01:41
If you are talking about DNP3 Shared Outstations, then the Heartbeat option does not poll any 'data'. It merely issues a Get Link Status request to the DNP3 outstation. If the DNP3 outstation responds to this (on the channel the request was sent on) then this pathway remains 'Healthy' otherwise it will indicate 'Failed'.

Shared is used for if both channels can be used at the same time for multiple devices.
Switched is for where either channel (but not both) can be used at the same time. Instead of individual devices failing over, once a certain number of devices fail, then the whole set changes (switches) channel, so no devices will communicate on the old channel, only the new one, until forced back.
Direct is just a single channel so no switching at all.

In your situation I'm surprised that the Satellite is the preferred line. I've always found them to be incredibly long latency, and very expensive per kB of data. So I'd expect that 3G would have been preferred, but with Satellite as a backup.

Often our customers have an inhouse radio network as primary, since data across it costs nothing. But with 3G as the backup. Normally on a shared outstation set, since single sites can transition from radio to 3G. Often we will deliberately switch to the 3G for a site when doing config downloads etc as it's just so much faster and more reliable.

Reply User: hardin4019, posted: 2019-06-18 12:51:23
I'm using Modbus, and the sites I'm communicating with are often in poor cell reception areas. But its worth mentioning to my clients. Thanks Bevan.

Reply User: ZeeKH, posted: 2019-07-24 05:31:29
Thank you all for useful responses