Ethernet interface in fire alarm systems.
A few years ago, Ethernet was not considered the most suitable interface for data transmission in real-time systems, which, with some stretch, include fire alarm systems.
The fact is that the main disadvantage of this interface is the method of equipment access to the CSMA/CD data transmission medium (carrier sense multiple access with collision detection).
All devices in the network have equal rights to transmit, access time is regulated by a random delay, and collision control in Ethernet is destructive, i.e. when several transmitters go online at the same time, the transmitted data is distorted, all transmitters stop working for a random amount of time, and then the transmission is repeated.
All this can lead to unpredictable delays in data transmission, which is unacceptable in many applications.
Therefore, at one time it was believed that for time-critical transmission tasks, polling systems should be used, where the data delivery time is defined and guaranteed.
Basically, the so-called field buses Profibus, Modbus work on this principle.
As well as protocols with non-destructive collision testing based on message priorities, such as CAN.
However, over time, Ethernet, due to its widespread use and, as a result, low cost, was able to penetrate into the field of industrial automation.
The Industrial Ethernet standard has emerged, which provides regular and frequent transmission of small amounts of information over the network, which is typical for data exchange between controllers.
In addition, with the help of special switches, it is possible to organize a ring topology of the communication line, which, if broken, restores the connection, which allows to significantly increase the survivability of the system.
Today, there is probably not a single branch of instrument-making or mechanical engineering left, where IP technologies have not penetrated.
They have also become widespread in security systems. They are most in demand in security television due to the huge volume of transmitted video data. General IP-ization has not bypassed fire alarm systems either.
Currently, a significant number of manufactured control and monitoring devices have a built-in Ethernet interface.
The IP connection is used to communicate with a higher-level PC, as well as to combine individual devices into a network.
A number of devices have a built-in web server, which allows you to connect to it without special software, using only a standard browser.
If the control panel does not have a built-in interface, then in most cases you can connect the device to the network using an interface converter, for example RS-232 Ethernet. Connecting to a PC via Ethernet has a number of advantages over the traditional method of connecting via serial RS-232 or RS-485 interfaces.
Most facilities already have a developed network infrastructure, so there is no need to lay a separate cable line from the devices to the PC.
The devices can be placed anywhere in the security facility, within the coverage of the local network.
In the event of a PC failure, it becomes possible to automatically transfer the connection of the devices to the backup computer.
Unlike CCTV systems, the volume of data transmitted in the OPS is extremely small and has virtually no effect on network load, which allows the use of a common enterprise network without the risk of conflicts with other network applications.
At the same time, questions about data transmission security remain open if a general-purpose network is used.
To protect transmitted data, it is highly desirable to use encryption or organize a virtual private network (VPN) for the security system. Ideally, this is the organization of your own physically dedicated network. This will solve, if not all, then many issues with both security and reliability.
After all, if the fire alarm system does not have a significant impact on other equipment connected to the same network, then the opposite is quite possible.
And in case of any malfunctions in the network due to the fault of third-party equipment, there is a high risk of failure in the operation of the security or fire alarm system, which, you must agree, is extremely undesirable.
Network connection provides ample opportunities for organizing joint work directly between fire alarm devices.
For example, exchanging alarm events or controlling arming from a remote control connected to one device by loops on another device.
Ethernet is an ideal solution for building distributed security systems. As a rule, a distributed system of objects is already connected by a corporate data transmission network.
In this case, we get a ready-made transport network for centralized administration, system management, and the creation of a single corporate response center.
Global networks can be used to organize centralized security for commercial and private objects. The Internet is already used to connect a security facility with a centralized security point.
Moreover, the owner can receive information about the state of his object via the Internet and even manage it. Of course, if the security system has access to the Internet, the tasks of protection against distortion of transmitted data or unauthorized access to control come to the forefront.
As already mentioned above, at present, Ethernet is mainly used to connect control and monitoring devices to each other or to the upper level.
Sometimes addressable extenders are connected to the central panel via IP.
A new stage in the development of IP technologies in fire alarm systems may be the appearance of detectors with a built-in Ethernet interface on the market.
This is facilitated by the increasing spread of Power over Ethernet technology (or PoE – IEEE 802.3af standard).
PoE is a technology that allows the transmission of electrical power along with data to a remote device via a standard twisted pair in an Ethernet network.
This technology is intended primarily for IP telephony, wireless access points, web cameras, network hubs and other devices to which it is undesirable or impossible to run a separate electrical cable. This solution is quite suitable for connecting security and fire alarms.
In this case, the fire alarm system will be a control panel, an Ethernet transport system through which power and detectors are transmitted along with data, each of which is connected to a network patch cord from the nearest hub.
This will significantly simplify the installation and commissioning of the system, and the cost of work will decrease.
During operation, the system can be easily upgraded.
If there is a structured cabling system (SCS) at the facility, adding a new detector or moving a previously installed one to another location will not be difficult.
Of course, the presence of a built-in Ethernet interface in each sensor, and in the case of using PoE also a splitter (a separator that separates digital data from power supply and supplies them to two different outputs) makes the product more expensive.
But everything related to IP technologies is rapidly becomes cheaper.
And of course, we must not forget that the cable system is shared with other applications and building systems, which significantly reduces the cost of the project as a whole.