Communication interfaces for access control systems.

Communication interfaces for access control systems.

Let me make a reservation right away: I am not writing these notes at all to compare the most frequently used communication interfaces for access control systems (ACS) today and to name the best ones. For a normal specialist, there are no «best» ones. There are those that are optimal for use in a specific project at a specific facility. At the same time, I will not consider today unique interfaces that some manufacturers develop only for their systems. For example, the English company PAC International uses a six-wire bus of its own design to communicate controllers.

So, if we talk about the most frequently used interfaces in ACS today, providing physical data transfer (it is clear that each manufacturer has its own protocol for exchanging devices included in the communication line), then the following can be highlighted.
Firstly, it is RS-485. Good old, proven.
Secondly, it is the connection of system components via existing local networks (ETHERNET).
Thirdly, industrial interfaces. Here we can name the CAN, LonWorks, PROFIBUS and other protocols.
And finally, fourthly, wireless technologies. Wi-Fi, WiMAX, GPRS interfaces (data transmission via GSM networks), in which the communication of system components is carried out via wireless channels.
Now I will briefly tell you about the advantages and disadvantages of each of the named protocols, focusing the readers' attention on the areas of their application. That is, on what types of objects it is more appropriate to use one or another interface.

RS-485
With a relatively low cost and simplicity, the interface has fairly good characteristics, in most cases sufficient for solving the problems of exchanging information between ACS components.
RS-485 has existed and has been used for a long time, but it is probably still too early to say that it is morally obsolete. On the contrary, the protocol's solid «age», in my opinion, is its obvious advantage. There are no problems with the supply of hardware drivers. The interface is familiar to a huge number of developers, it is clear how to work with it. The most significant disadvantage of RS 485 is its low throughput and large limitations when organizing master-leader networks for mutual inter-controller exchange. It is quite problematic to design powerful modern systems with a large volume of transmitted information and developed logic of inter-component «communication» based on this interface.Another limitation is the need to lay dedicated communication lines and a range of just over a kilometer (not all systems operate stably when using additional intermediate signal amplifiers). If, for example, the object on which a certain segment of the system is installed is located at a greater distance or there is no possibility of laying an additional cable, it can be very difficult to combine the system components via this interface.

ETHERNET
Having appeared in ACS relatively recently, this interface has become widespread, and this expansion continues. Which, in general, is not surprising, because according to experts, approximately 80 percent of the facilities that need to be equipped with access control and management systems are modern office, industrial and other buildings. Today, all such facilities already have a local network infrastructure. And using it at such facilities is logical, convenient and very profitable in terms of material costs. Indeed, why lay additional cables if you can connect the system to an existing network.
This is one of the main advantages of the interface. Also, its high bandwidth cannot be ignored. Today, 100 Mbit speeds are commonplace, so the need to exchange large amounts of information does not cause problems, compared to the same RS 485. In addition, there are no restrictions or obstacles to organizing the exchange of information between system components (for example, between controllers). Of course, there are disadvantages, how can we do without them? The first is that the standard range of Ethernet is 100-150 m. To ensure a greater communication range, you need to use fiber optics with converters, or install signal amplifiers every 150 meters.
An even more important point is the protection of data transmitted over the network. Connecting equipment to a common local enterprise network requires additional measures to ensure information security. I mean encryption of data transmitted from controllers to the server and back, as well as competent traffic administration. It is clear that if the controller is connected to a regular corporate network, and one of the employees is “downloading” a full-length film, then this network segment will be physically overloaded for some time, and information from the controller to the server may be delayed.
Today, there are many specialized programs that allow you to intercept information transmitted over a local network. In this case, to ensure the security of transmitted data within the ACS, it is necessary to either use data encryption (for example, use data transmission over secure VPN connections), or allocate the channels used for the security system to separate subnets.
In general, it should be noted that statistics on the use of ACS at facilities where there are no increased security requirements confirm that information circulating through the access control and management system is of little interest to intruders. Indeed, why would anyone in an ordinary office block the entrance to the premises of their neighbors on the floor? Or know who of them came to work and at what time. If we are talking about facilities with an increased secrecy regime, then there are many proven technologies for protecting information.

Industrial interfaces
Their main advantage is the ability to build multi-rank networks with exchange between system controllers. The protocols are very reliable in terms of information delivery, and provide high speed data exchange between system components. The main disadvantage is that Russian developers still lack experience in developing devices for these interfaces. The developer will encounter many more nuances than when using the same RS 485.
Industrial protocols are open. They have clear standardization. A manufacturer, having developed an output interface in this standard, can easily connect to this bus. It is enough to have a driver that will program this device and control it. By the way, just like Ethernet. You need a driver library for the computer that will communicate with this device, and that's it. Because the interface is standardized.
Industrial network standards are actively used in intelligent buildings, automation systems of some technological processes, that is, wherever there are increased requirements for speed and guaranteed data transfer. The same CAN is widely used in the automotive industry — all electrical equipment, from light bulbs to ABS systems, in modern cars is connected via this protocol.

Wireless network interfaces
In some cases they are irreplaceable. Here is an example. It is necessary to provide access control to the station of the short-range guidance system, which is located in the forest, 5 kilometers from the airfield. There is no communication with it. Naturally, no one will dig a trench 5 kilometers long to lay a cable. The only possibility of communication is a radio channel.
There are two ways to implement it. The first is to install a radio modem. The second is to use existing networks, the same GSM, which today covers most of the civilization in our country.
About the disadvantages of wireless technologies. First of all, it is necessary to talk about such an important criterion as the reliability of data transmission. Interference, temporary absence of coverage area are in principle tolerable, if we are talking, for example, about mobile telephony. In security systems, this is unacceptable, because the on-line mode is disrupted. If some event occurs, it simply will not come from the controller to the server, because there is no connection.
Another problem is bandwidth (this is especially true for data transfer over existing GSM networks). This imposes serious restrictions on the speed of loading controllers, the speed of transferring system events to the server, etc. That is, exchanging large amounts of information in the ACS via GSM is very difficult.
Using a radio modem requires additional equipment, in some cases — licensing, and the range is still limited.
If we are talking about a cottage, when there are two or three users in the system, and three events occur per day, radio channel interfaces work fine. If the ACS with a radio channel is installed, for example, at a remote checkpoint of an industrial enterprise, then it is clear that in the morning events will «pour in» several per second, and the communication channel simply will not have time to transmit this information.
For serious facilities, where the ACS has a fairly large event traffic, where guaranteed online mode is required, a wireless connection is not always suitable. Sometimes it turns out that the only solution is to dig a trench and lay a cable.