by PCSC
A strong, dark stormy night ensued. The main controller of access control and security system, located on the fifth floor of a tall building, has just presented a total failure. It is totally out of operation for the eight door interface modules to which it must provide intelligence and monitoring.
What are they and why do we need them?
In a world where security is a concern and where the survival of the system is really important, this could be a critical situation. A situation that many building managers have experienced and with which they very commonly lose sleep early; however, in this situation things are different.
In fact, even in the mornings, when a call is made to the security system service provider, they do not promptly send the maintenance technician to replace the bad processor. The dispatcher calmly tells the building manager that he will replace the controller on his next scheduled maintenance visit in a few weeks and according to the pace of work they handle. The building manager looks calm and calm. What's going on here?
Is this a story about the indifference of a security systems service provider or something else? In this case, it's a story about how the latest innovation in the access control industry is changing the way we view critical equipment failures.
In the scenario described above, the main controller is part of a fault-tolerant system. As the name describes, this system tolerates equipment failures and, in fact, does not affect the performance of the system, whether such a main controller works or not. These new systems use a redundancy methodology that allows any primary controller in the system to double its capacity and take the place of any primary controller in the system. All but one of the main controllers could be lost, and the system would operate with little or no deterioration in performance.
Distributed vs servile
There are mainly two hardware architectures that are employed in the access control industry today. One is the "distributed" architecture, so called because the intelligence of the system is distributed to each and every control panel in the system.
With a distributed architecture, each card reader and its associated input and output points connect directly to an intelligent controller.
The other common architecture is the main controller/door controller style (or what we commonly call the main and slave). With this configuration the main controllers are the only intelligent component of the system and each door is connected to a "dumb", or at least "dumb" door interface module.
The advantage of the first type of system described above is that because intelligence (database storage capacity and decision making) is distributed to each panel and the number of doors connected to each panel is limited (usually only between 12 and 16 doors maximum), the risk of losing more than a few doors from the system due to a hardware failure is very low. Even a catastrophic failure of a controller would result in the loss of only 12 to 16 gates connected to the panel.
None of the other doors in the system would present problems. Conversely, the configuration of the main controller/door controller could possibly affect up to 128 doors in the event of a single main controller failing.
The advantage of main controller/door controller schemes is the low cost associated with having less intelligent (and therefore more expensive) controllers in the system.
Every service provider in our industry has had to evaluate the advantages and disadvantages of these two architectures in order to come up with the best solution that satisfies any specific access control application.
Both are valid designs and, depending on how critical it is that the system stops and continues to operate or the size of the end users' budget, either design may be the most appropriate. In large part, manufacturers of access control hardware subscribe to one or the other of these two architectural philosophies and will defend them vehemently.
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