I'm looking for information regarding the configuration of a redundant SMS-based alarm notification system.
From the information I've found online and in the manuals I must use the licensed "Pager" driver in conjunction with a compatible modem.
Has there been any recent progress in SMS Channel Redundancy as discussed in this thread?: SMS Channel Redundancy
Is it still recommended to use ST script to execute fail-overs? This seems a bit clumsy?
Are there any other tips/tricks others have used when designing SMS alarm notification in a Geo SCADA multi-server Primary/Standby architecture? I was hoping we would install a modem on the Primary server and a second modem on the Standby server. Only the "Active" server would send alarm notifications via their own modem.
Thanks in advance,
The Pager driver is 'licenced', but it's an out of the box licence. So if you have a licence to run your Geo SCADA Expert servers, then you also have the licence for the SMS Pager driver (unless you have a 'special' licence.. which is unlikely).
You're correct that even the latest March 2021 Update of Geo SCADA Expert 2020 does not have native support for redundant SMS Paging Modems.
The best solution that I've found still is to use something like a Robustel R2000 / R3000 modem which supports AT commands over TCP. This means that it can be installed anywhere on the SCADA network, and hence I would install several (one for every geographically diverse server that could go Main seems legit). Then I would use the ST logic to select the correct Paging modem based on some kind of health.
I have logic that does a periodic self test heartbeat to each modem, and flags it as failed if it doesn't receive this heartbeat SMS.
The basic concept is to always have an SMS Paging Modem attached to an SMS Paging Service, which ensures that it gets the AT heartbeats (so if the channel fails you get an alarm). And then wrapped over the top of that is the SMS heartbeat to ensure that the modem to SMS gateway link hasn't failed, or the SIM card has been cancelled etc etc.
My issue with having two modems, each connected to a physical server is that this doesn't provide you with much diversity. And your latent failure time drastically increases (the SMS paging modem may have failed anytime since you last tested your failover).
Thanks for your input and suggestion on the Robustel gear - will check them out. The modems haven't been selected yet, but we were already expecting some sort of Virtual COM/TCP/Serial server due to Virtualised nature of the installation (and lack of physical serial ports on the server.)
I don't quite follow your health-check mechanisms and how the ST interacts with the DB components, so I have some homework ahead! I might come back to this thread with a few more questions, once I'm a bit more informed.
The way that I have it structured is (kind of):
Each SMS Paging Modem is responsible for determining their own Pager Healthy status. This is done through a combination of the SMS Pager Channel status (if the modem is unplugged and SMS Pager Channel is unhealthy, then no point relying on the SMS Paging Modem), and the SMS self-test heartbeat which sends itself an SMS every so often, and does some stuff to say if it succeeded or not.
The Pager Channel => Service Mapping really only needs to care about the Active SMS Pager Service. This should be assigned to a healthy SMS Paging Channel. If the current channel isn't healthy, then assign it to the next healthy channel in accordance with some priority scheme.
Then all of the other SMS Paging Channels are assigned to dummy SMS Paging Services.
All the Active and Dummy SMS Paging Services are InService, as are all of the SMS Paging Channels.
In this way if someone unplugs or powers off a modem, then it can be detected (since the SMS Paging Channel sending its AT.. stuff every so often will not get an OK response).
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