Network model
Let's make it clear right away that we are considering network professional ACS, i.e. distributed systems in which it is necessary to ensure interactions between components — computers and controllers, regardless of the exchange principles («each with each», a system with a dedicated server or some other topology).
If we are talking about simpler systems, this will be discussed separately.
Given the accepted premise, it is appropriate to recall that all exchange between applications in such systems, in accordance with the OSI network model, is divided into a maximum of seven levels, where the lowest level is the physical transmission of data over a transmission medium (wires, radio channel, or other medium), and the highest is the user application level, which performs the system-specific functionality.
The subject of our discussion is one or two lower levels that ensure the packaging of working data into protocol packets and their transmission through one or another physical medium.
So, we are interested in the applicability of wireless technologies for ACS, their advantages (if any) and disadvantages, from which we can draw a conclusion about the feasibility of using a radio channel in network access systems.
Radio channel options
There is a fairly large variety of wireless networks developed for certain purposes with specific characteristics that follow from this. Let's consider those of them that are suitable in one way or another for ACS.
Wi-Fi
In my opinion, this communication channel is the only one that can be used in professional ACS.
From the point of view of ACS components (controllers, computers), this is a complete analogue of wired Ethernet, and devices connected to wireless switches will not even distinguish one transmission medium from another.
Just as it is perfectly normal to use an Ethernet network to connect controllers to the system, it is also natural to use wireless communication channels based on Wi-Fi. This eliminates the need to lay parallel communications to connect components when using traditional RS-485.
The only difference is how the local network is built at a given enterprise or part of its territory: on twisted pair, fiber optics, or using a radio channel.
Thus, if we talk about Wi-Fi, then this is a pure replacement of only the transmission medium without any other changes. The transmission speeds are almost the same, as are the internal protocols. But you still have to reach the access point with a cable.
The implementation may be different — equip the access controller itself with a radio channel and the corresponding software stack, but I, for example, have not even heard of such developments yet.
The main reason, apparently, is that they will be quite expensive to produce, especially considering the initially low circulation of the equipment.
It is clear that ACS controllers will probably never be produced in millions of copies. At the same time, a ready-made Wi-Fi access point today costs two or three dozen dollars.
Bluetooth
This communication channel has a slightly different purpose.
In addition, Bluetooth has a small range, its own protocols. It must be used on both sides: on the computer side and on the controller side.
The transmission speeds would be sufficient, but with a short range, the point of using Bluetooth in professional systems is lost.
The main purpose of this interface is to connect something within at least one room. It is unrealistic to reliably connect the controller to the server, which is located 5 doors away, such a system simply will not work.
ZigBee
This is one of the fastest growing wireless technologies. But it is also not very suitable for use in access control and management systems, primarily because it was originally developed as a low-speed communication channel for combining various sensors into a network.
In terms of security, these could be security and fire alarm sensors.
Perhaps, and in the near future, ZigBee will displace many of the existing radio channel fire alarm systems.
After all, almost all of them are developed outside of any standards. Each manufacturer has its own exchange protocols, and it is impossible to replace the wireless sensors available at the facility with equipment from another manufacturer.
If the ZigBee standard becomes widespread, which is quite likely, the customer will be able to use almost any sensors of their choice in the fire alarm systems.
Moreover, standard profiles (specifications of command sets and exchange protocols) for specific applications in the field of building automation and security systems have been developed, published, and all this taken together guarantees compatibility of equipment from different manufacturers.
This standard, I will not be afraid to repeat myself, is good for connecting the central node with the periphery, which is located geographically distributed, and due to the inclusion of repeaters in the system, the coverage area can be quite large.
Theoretically, ZigBee can also be used in ACS. But this channel has a low data transfer rate and a short range.
Agree, it is irrational to build a long chain of repeaters for the sake of connecting the controller to the computer.
There are many simpler, and most importantly, cheaper and more reliable methods. The same Wi-Fi, for example.
GSM
Historically, this wireless network was the first to be used in security systems. GSM channels have a very big advantage: the network provides almost complete coverage. All the space where a person lives is within the network coverage area. It is tempting to use these channels to transmit information in security systems.
But let's ask ourselves: why? For what purposes? And most importantly — how?
To answer it, we must remember that the main methods of transmitting information in the GSM network are the SMS service, the voice channel, and the GPRS data transmission technology.
SMS service allows you to send short text messages. If there is a need to send non-text information, it must be recoded, then the permissible volume of this message will be reduced.
The main disadvantage in relation to security systems is that it is not an online service. And for professional ACS, online monitoring is simply necessary. That is, in real time, information must be sent to the response service, and in the same online mode, commands from the operator or computer must be sent to the controller. The service does not guarantee delivery time; the message may be lost altogether.
Of course, losses can occur in any extended communication channels – due to interference, noise, interference, etc.
Distorted information is lost information. This problem can be dealt with. In order to ensure guaranteed delivery, confirmation is used, which, as is known, is the basis of the TCP protocol.
A similar mechanism could be used in SMS. But the service does not guarantee prompt delivery of messages, and this fundamentally does not allow it to be used for real-time work.
Using SMS as a backup communication channel is quite normal and acceptable. As the main one — only in non-professional systems.
The voice channel is most often used to control, for example, home automation and security systems through voice menus, and this is probably the extent of its application.
GPRS
It is possible to use GPRS or EDGE in GSM channels – specialized services that are designed for exchanging information at relatively high speeds.
Using these services, it is possible to remotely connect IP equipment.
But the question arises again: how rational is this approach for professional systems?
Distributed remote offices are almost always connected to the Internet, and connected via ready-made communication channels with a minimum fee for traffic.
Using a parallel wireless channel for these purposes is not very interesting and quite expensive.
If the user has a communicator with a decent display, he can dial the number of his server on the way to work and see, for example, a report on working hours. A pleasant and for some useful function, but, you must agree, it cannot have a decisive meaning.
Security systems with a GSM channel have been developed and are being sold for a long time.
But we do not see the development of such systems, and this is the first sign of little prospects for the development.
They do not fully provide the required functionality, but perform only minor auxiliary functions, which can rather perform advertising functions than the basic functions of the system.
After all, systems of the same class are quite equivalent and equally functional.
For the sake of distinction, you can do something special.
As the hero of a popular comedy said, «the same, but with mother-of-pearl buttons.»
Conclusion
To summarize, the following conclusions can be made.
Only those wireless technologies that are equivalent in functionality, purpose and cost to a standard wired enterprise computer network can be used as the main communication channel in professional ACS — these are Wi-Fi, Wi-Max and similar wireless networks.
Sensor network technologies such as ZigBee, Z-Wawe and many similar ones should be used for their intended purpose — to receive information from various sensors without laying wires in a limited (local) area.
Such an attractive network as GSM can be used either in home systems or as an additional channel remote access to the ACS server to receive reports and similar actions.