Multi-channel notification transmission subsystem.
Multi-channel notification transmission subsystem
To understand the fundamental differences between notification transmission systems, we offer a brief historical excursion. For a long time, up until the 2000s, monitoring systems based on low-speed communication channels dominated in the world, mainly using dial-up telephone lines and radio channels, and in Russian reality — non-departmental security equipment. The technological revolution in centralized security occurred at the time of the rapid development of 2.5G/3G cellular networks, with the introduction of packet data transmission based on IP protocols. But most manufacturers of monitoring systems, burdened with an old fleet of equipment, were forced to use outdated protocols and operating principles of the systems, not using the full potential of new technologies. Some manufacturers offer notification transmission devices not as full-fledged monitoring systems, but as an option to existing local integrated systems, with all the ensuing consequences. The fundamental difference of the Mirage system is that it was created «from scratch» to solve a specific problem — professional security of facilities in an open competitive market. The nature of the task and external factors determine the technical solutions that will be discussed below.
The channels and methods of transmitting information can be divided into two groups:
Off-line— based on the principle of channel switching and special services (CSD, SMS, DTMF, CALL ID), typical methods for second-generation communication networks and telephone networks. The main disadvantages are related to low speed, limited data transfer rate and information content;
On-line — based on packet data transfer (GPRS, CDMA, UMTS, ETHERNET) using IP. Progressive methods implemented in modern telecommunication networks, which include 2.5G/3G/4G cellular networks.
In the Mirage system, on-line channels of various physical nature are used as a priority, off-line channels are mainly used as backup. But taking into account all the advantages and disadvantages inherent in individual channels, the optimal result in terms of speed, reliability and cost is achieved by their comprehensive use. Maintaining the stable operation of several communication channels in real time, achieving a reasonable compromise between the speed of notification delivery, monitoring the serviceability of channels and operating costs is not a trivial task. Multichannel SPIinevitably leads to more complex operating algorithms and increases the requirements for the performance of both the monitoring station and the facility equipment. Operating algorithms of the Mirage-Professional series of equipment allow two on-line channels to be supported simultaneously with strict control of serviceability, as well as various combinations of on-line/off-line channels. This achieves extremely important
technical characteristics:
— notification delivery time — 1 … 2 seconds;
— communication channel control — 2 minutes.
We draw attention to one subtle point — in the Mirage system, the time is counted from the moment the sensor is triggered — the occurrence of an event, and not from the moment the information is received from the control panel. The loss of time and information is eliminated by using multiple access technology on the RS-485 interface, while the interface is a virtual continuation of the notification transmission system.
Control of communication channels in security monitoring systems is the most important parameter determining the system's ability to resist «intelligent hacking». The Mirage ISM implements an selective control algorithm for communication channels, which allows you to promptly and accurately assess the degree of technical problems and threats to the protected facility. The dispatcher is provided with operational information about short-term outages of on-line channels, failures of individual communication networks and suppression of communication channels. Detailed statistics allows the system administrator to make decisions about equipment settings, the choice of communication operators, cost optimization, etc. Selective control in multi-channel systems is a very effective tool that has virtually no alternative when using exclusively wireless communication channels.
Each on-line channel, depending on the physical environment, has its own specifics, which must be taken into account in the equipment operation algorithms. The Mirage system implements mechanisms for aggressive maintenance of on-line channels in standby mode, especially with regard to GPRS technology. The monitoring station supports two IP addresses and multiple TCP ports, which significantly increases the reliability of notification delivery in conditions of dynamic changes in the capacity of GPRS channels. The initiative to maintain the activity of on-line channels belongs to the facility equipment. Using its own TCP/IP protocol stack allows solving this problem without losing time and control over the exchange process. Practice has shown that the TCP/IP stacks built into modems do not cope with tasks in real time. In addition, using your own protocol stack ensures full continuity of debugged algorithms when transferring firmware to new hardware platforms.
The connecting logical link of any monitoring system is the exchange protocols between the monitoring station and the facility equipment. When the Mirage system was created, principles and technical requirements were incorporated into it, which led to the need to develop its own universal MSRV protocol, since the widespread protocols (Ademco Contact ID, etc.) were developed for one-way low-speed systems and are obviously outdated.
MSRV Protocol:
1. Does not limit the gradual expansion of the system's functionality and scale, and due to its versatility is used not only in security systems. The protocol has an automatic version detection mechanism, so new versions can be implemented without losing equipment compatibility;
2. Allows you to implement remote firmware configuration and update functions via communication channels, without disrupting the facility's operating mode;
3. Provides the ability to remotely configure and manage network equipment connected to base controllers via the RS-485 interface. This creates an “end-to-end channel” — the monitoring station gains direct access to network devices;
4. Provides two-way dynamic encryption of notifications when transmitting them via open communication channels;
5. The information table contains a significantly larger number of events and is easily expanded, which is extremely important when integrating facility equipment;
6. Allows the transmission of analog values, which significantly increases the information content and expands the scope of application.
The MSRV protocol allows you to encapsulate Contact ID, thereby ensuring integration with third-party monitoring stations. When integrating, please note that a significant portion of the functionality of the Mirage system will not be used due to limitations of legacy protocols.
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The diagram of the notification transmission system operation is shown in the figure. On-line channels are marked in blue, off-line — in black. Channels in working condition are marked with solid lines, backup — with dotted lines. The server receives packets from two Internet access points with static IP addresses, physically formed by fiber-optic communication lines (FTTx) and copper communication lines (xDSL). As a rule, all elements of the CMS are interconnected by a local area network (LAN). Three TCP ports are allocated for servicing each IP address. In the process of on-line exchange between the object and the server, several access points from different providers are involved, packets are automatically redirected by different routes to different IP addresses and ports, thus creating a continuous data flow, which is aggressively supported and controlled by the system. For full use of all algorithms of the system operation, three GSM modems are connected to the server, two of which receive information by the data transfer method (CSD) and SMS. The third modem is required to control the off-line communication channel and implement the algorithm for selective control of on-line communication channels. The STM-02 modem receives information via public switched telephone networks (PSTN), can be used as a remote control element in a geographically remote settlement and can be used as a gateway between communication networks. On the object side, either Ethernet (EM-01) or telephone lines (TM-01) can be used together with GSM/GPRS channels.