Comparison of rs 485 and ethernet. Such a different ip-scar

26.09.2020

We say IP, we mean Ethernet. We say Ethernet, we mean ... what?

Starting a conversation about IP-ACS, the question immediately arises - why exactly IP? What is it about this IP, and do we need it? What's wrong with traditional RS-485 systems? From the point of view of the logic of the system operation, is there any difference between these transmission methods? Let's try to answer these questions.

Don't compare green and solid

First of all, we note that it is incorrect to compare RS-485 and IP. RS-485 is a data transmission medium (wires, electronic components, currents, voltages, etc.). IP is a protocol (a set of rules that must be followed by participants in an exchange).

When comparing the concepts of IP and RS-485 and under IP, we usually mean the use of the IP protocol based on data transmission in an Ethernet environment (less often other data transmission media, but we will not consider them here). We propose to begin with comparing entities of the same order - RS-485 and Ethernet.

Comparison of RS-485 and Ethernet

Exchange environment parameters		Ethernet 1 Gbps
Maximum section length
Speed // transfer type	Depends on the length and quality of the cable. Up to 10 Mbps in sections up to 10 m; 62.5 kbps at sections from 1 km // simplex	Over copper cable 1 Gbps // duplex
Extending segments
Number of nodes in the network	256 including trunk amplifiers
Topology	Bus (serially from device to device)	Star, ring

When comparing the parameters of RS-485 and Ethernet, several conclusions can be drawn:

1. A good cable is needed everywhere, and de facto it will be UTP (FTP) of the 5th category.

2. Ethernet is more convenient in laying, since you can branch off from any hub.

3. Ethernet has a clear speed advantage. However, a modern access control system has low traffic, so a high exchange rate is not in great demand.

4. The advantage of RS-485 is also obvious - the considerable length of the cable line between devices. Together with the "bus" topology, this is very convenient, for example, when installing equipment on extended linear objects and perimeters.

5. Compared to a kilometer line RS-485, 100 meters "over copper" for Ethernet seem scanty. However, for most modern urban, office and industrial facilities, this distance is quite enough, especially when it comes to connecting to an existing network.

The Clear Benefits of Ethernet

Do not forget about mass-produced, and therefore inexpensive and familiar to a wide range of specialists, equipment for Ethernet transmission over fiber and radio.

In addition, you can use existing local networks, and this allows in most cases to save several times the cable and work on its laying. Moreover, the data streams generated by ACS devices are insignificant (unlike, for example, video devices), and the use of the existing network infrastructure does not cause any technical difficulties.

Ethernet topologies "star" and especially "ring" increase the reliability of the system, because in this case, if there is a problem with wires on one controllers, the rest of the controllers will work normally (in contrast to the "bus" for RS-485).

Ethernet assumes the absence of additional cables and devices (all sorts of converters) plugged into the USB or COM ports of the system unit. Thus, in principle, there is no assembly work at the "receiving end"

Rice. 1. Modern IP controller with RJ-45 connector

IP qualitatively changes the access control system

The use of the IP-protocol allows you to qualitatively change the access control system, the implementation of this system and its maintenance.

Massive and understandable technology

The level of service personnel is changing. The most important advantage of Ethernet is the massive use of the already proven technology and, as a result, the availability of inexpensive proven network equipment, software and an army of thousands of qualified specialists and advanced users.

For any system administrator in an enterprise, accepting several "IP-pieces" for service is a common task. Controlling a device comes down to a set of generally accepted actions: pinging, distributing IP addresses, checking the network settings via the Web-panel - everything is like any network product. It is necessary to transfer the controller - no problem either: I pulled out the patch cord from one RJ-45 and stuck it into another. I need to move my workplace - I just installed the software on another machine without any installation work. Another thing is specific controllers with ancient protocols and cable routing topologies that are tricky for modern IT specialists, which must be rebuilt with any changes.

What should be a real IP controller

The increase in the volume of transmitted data and the exchange rate make it possible to:

issue an event message to other network devices;

abandon the serial polling of devices - allows you to make the transmission of events almost instantaneous;

use ready-made routing methods to build geographically distributed systems.

However, to get the obvious benefit, the IP device must fully use the IP protocol stack with the ability to execute the ping commands dear to the heart of the advanced user, as well as configure the IP address via the local network, either manually or using DHCP.

The main advantage of a local area network - access to network devices from the administrator's workstation - must be realized. We cannot accept as satisfactory the option of changing the IP address in some "pseudo-IP" systems using a computer connected directly to the controller via USB. Imagine this procedure on a large facility with dozens of controllers installed in not the most convenient places.

Was it worth it for the sake of such torment to leave the good old RS-485? A real IP-ACS is simply obliged to provide a change of the controller's IP-address via Ethernet without jumping up ladders with a laptop.

Web panel: convenience and reliability

It is most reasonable to configure the device over the local network through the Web-panel, which becomes an integral part of "advanced" IP controllers. IP cameras have traveled a similar path in their time. If earlier for some the need for an embedded Web server of IP cameras was not obvious, now de facto almost all serious models have it, providing viewing and administration from a browser.

In addition to the undeniable ease of commissioning, the Web-panel is the basis for the stability of the system. So, the computer with the installed program may fail, and the distribution kit of the program is lost. Then the control and viewing of images from IP cameras, and in our case with parameters of access points, can be carried out from any computer in the network through the Web panel (of course, with the necessary protection against unauthorized access).

The presence of a WEB panel quite clearly separates full-fledged IP controllers and ancient low-power systems on RS-485, hastily converted into "almost IP" with the help of various kinds of adapters. The developers would be happy to squeeze a panel into it, but old people from the last millennium (meaning controllers) simply "don't have enough brains" on it. The presence of the panel guarantees a significant level of computing power and long-term operation of the product without obsolescence, with the possibility of implementing a variety of network solutions and protocols not only today, but also in the future.

Rice. 2. Web-control panel of the controller

Immediate prospects

Today, IP, being the most widely used protocol, has united the world, erased differences in distances and spawned systems of a new level. A network device becomes available anywhere, and different applications can access it at the same time. Configuring the device via the Web-panel "unloads" the program from the unusual "mundane" parameters (opening / delay time, lock type, IP-address, etc.).

ACS without software

It is possible that with the growth of the computing power of controllers, access control systems will begin to appear without any special software, designed exclusively for work through a browser. Thanks to a unified exchange environment and an increase in computing power, devices will be able to interact with each other, bypassing the coordination centers (all kinds of servers), which will greatly increase the reliability of systems. A similar trend can be traced in related areas - video surveillance and OPS. Thus, the basis for integration solutions based on hardware with onboard software is created, without the participation (or with minimal participation) of server software. For example, it is possible to synchronize databases across all networked devices without any single center.

Full compatibility

The development of ideas for the integration of network devices will be the development of uniform standards for the presentation of information. These standards already exist, it remains only to meaningfully implement them within the framework of devices of a new type. The result will be the compatibility of equipment and programs from different manufacturers with each other, similar to ONVIF in video surveillance. Standardization will require a certain amount of computing power on network devices, and the implementation of IP protocols is the first step in this direction.

The modern market offers a variety of options for access control, and all of them, to one degree or another, cope with the classic tasks of access control. In our opinion, already now, when building a promising distributed system, it is worth paying attention to "smart" IP controllers. If the system is not too large, fits well with the bus topology, and there is no local network at the site, then the proven controllers with RS-485 will still solve all the traditional tasks of access control. The era of IP-ACS is just beginning, and everyone chooses the time to enter it himself.

The best prospects have the introduction of IP access control equipment at facilities with a developed network infrastructure, such as energy, oil and gas, transport facilities, where there are already reliable communication channels.

For such objects, reliability and the ability to remotely control and administer are traditionally important. And here the equipment based on IP protocols manifests itself in all its glory; such equipment can be integrated into existing infrastructure with little or no change in communications. With "little money" it is possible to create a unified access control system for objects with a huge length.

As part of a developed network infrastructure, ACS controllers can show themselves from the other side: as a source of collection and transmission of information. Instead of conventional buttons and reed switches, data sources from technological (or any other) equipment can be connected to the inputs of the ACS controller. The experience gained over decades of working with data in the field of ACS can be effectively used to monitor the state and control of a variety of systems and complexes.

Hello dear reader! This article will help you understand access control systems and think about about increasing control in your enterprise. At the moment, there are two main architectures for building network access control systems - based on the RS-485 protocol and Ethernet. In this article, let's try to figure out which one is more convenient.

History of RS-485 and Ethernet

RS-485 is a half-duplex multi-drop serial data interface. Data transmission is carried out over one pair of conductors using differential signals. The voltage difference between conductors of the same polarity means a logical unit, the difference of the other polarity means zero.
There are several technology options depending on the data transfer rate and the transmission medium. Let's consider several options:
- 100BASE-T is a general term for standards that use twisted pair as a data transmission medium. Segment length up to 150 m. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2 standards.
- 100BASE-LX WDM is a standard using single mode fiber. The maximum segment length is 15 km in full duplex mode at 1310 nm and 1550 nm.
- 1000BASE-T, IEEE 802.3ab - a standard using a twisted pair of categories 5e or 6. All 4 pairs are involved in data transmission. The data transfer rate is 250 Mbps over one pair.

The RS-485 interface was the first to enter the security systems market and firmly established itself there. This happened due to its wide distribution in the industrial microcontroller market, at a time when Ethernet was just beginning to appear in the high-tech field. At the current time, the lion's share of the market for access control systems, as well as security and fire alarm systems, is unconditionally owned by RS-485.
ACS controllers that transmit data via the RS-485 protocol are often inexpensive.

What to choose RS-485 or Ethernet?

It would seem that if everything works, why invent something new? But the development of technology does not stop, the tasks of ensuring security are becoming more difficult every day, the development of software for control and access control systems is beginning to outstrip the hardware component.
And immediately problems begin to arise. Let's say we need to manage one or more checkpoints in real time using complex non-standard rules.

For example, using several identification methods at the same time (for example, by card, fingerprint and face), practicing the rules of two or three cards, using different identification devices for different groups of people. Usually, the controller cannot solve this problem on its own in offline mode. Such complex solutions are usually implemented by controlling the controller directly from a computer, using the controller simply as an interface module through which readers and access restriction devices are connected.

Simultaneous data exchange with 15 controllers via the RS-485 bus causes unacceptable delays in the system operation - the turnstile has to be opened for several seconds when the card is presented. It is practically impossible to speed up this process with technical tricks due to the “ideology” of organizing the RS-485 bus. All devices connected to this bus are interrogated sequentially, one after the other, and if we take into account the small data transfer rates of the RS-485 bus, it is easy to conclude that a large access control and management system using complex identification methods on the RS-485 bus, it is almost impossible to build.

The disadvantages listed above in a number of access control systems are manifested even at the level of simple solutions. For example, if, while adding users to the pass office, you try to open the turnstile from the security guard's workstation manually from the software, then the command to open the turnstile will be received with a significant delay.

This problem can be solved by replacing the data transfer protocol. The new protocol should provide parallel data transfer so that commands and data are not transmitted to all devices in turn, but to the required device at once. It is also necessary to increase the data transfer rate. Finally, the new protocol should be as widespread as possible to ensure compatibility with existing network devices and future developments. Using a widespread protocol, you can be sure that the access control and management system under construction will be able to evolve in the future. Ideally, if the protocol can organize a single data transfer bus for all elements of the complex security system of the facility.

Summarizing all the above theses, one can easily conclude that the only data transmission technology at the moment that meets all the above requirements is the Ethernet network.
Ethernet is the most widely used data network in the world. The equipment and data transfer protocols using this network are continually evolving. Due to the widespread prevalence, microcontrollers that support Ethernet have become significantly cheaper and, accordingly, the price of ACS controllers can be low. Also, Ethernet networks are already available in every office and enterprise, respectively, when using this network, additional costs for wiring will not be required.

Pros of IP solutions

Let's summarize the main advantages of using Ethernet for organizing access control systems:
the likely presence of an Ethernet network in the enterprise and, as a result, the absence of costs for laying the network;
parallel operation of all controllers makes it possible to organize direct control of devices from a computer and, as a result, extreme flexibility in building identification rules and the operation of the system as a whole;
high data transfer rate and parallel operation of all controllers allow building huge ACS systems, in fact, without limitation on the number of controllers;
the principle of building an Ethernet network assumes the most simple scaling of the system - just connect another controller;
parallel operation of all controllers increases the reliability of the system as a whole; if one device fails, all the others continue to work in normal mode;
the use of a standard data bus allows you to use a large number of different ways of organizing a network, including a radio channel;
ease of integration of controllers using the Ethernet bus into existing access control and management systems or automated enterprise management systems;
the use of a standard data transmission network makes it possible to build a single network for the transmission of information from all devices organizing the security system - video surveillance systems, fire alarm systems, access control, warning systems.

IP turnstiles

IP turnstiles are a complete, ready-to-install device that allows you to organize an automatic checkpoint and identify people passing by using contactless cards. You can not only prevent the penetration of strangers, but also set up different access modes for employees, receive reports on passages, organize the work of several users of the system, and much more.
Implementation of the IP-turnstile is as simple as possible - the work on connecting the controller and readers has already been done in production, which, in addition to saving time, also solves the issue of compatibility of the entire complex of equipment.
The main functions of the software in the IP turnstile complex:
Establishment of employee cards.
Automatic import of employee information from Excel spreadsheet.
Access control in friend / foe mode.
Control of repeated passes ("antipassback").
Photo identification (pop-up photo of people passing through the turnstile).
Organization of any number of remote workplaces (places for receiving reports, viewing events in real time). Including remote locations can connect to the server via the Internet.
Managing the rights of system operators (users of remote workplaces).
Multilingual (currently the software works in Russian and English, other languages will be added in cooperation with partners in the respective countries).
Receiving reports and uploading them to Excel:
–About employees
-According to the passes made "by card", "by button" (authorized from the remote control), on the facts of access denial.
-According to the location of employees at the current moment and for any historical date.
–According to the actions of the system operators.

Conclusion

Currently, the advantages of network access control and management systems are no longer in doubt - the ability to centrally maintain a database of passes, time tracking, remote control of access restriction devices have long become a de facto standard for projected systems. Also, in a separate category, it is necessary to make the customer's desire to have a distributed integrated security system, which includes, in addition to the ACS system, video surveillance systems, security and fire alarms, alerts, and perimeter protection.

While Ethernet is the most commonly used communication protocol among multiple types of devices, ranging from consumer gadgets to industrial devices, TIA / EIA-485 commonly known as RS-485 is still broadly used in industrial devices even if it is older than Ethernet. Let "s see why it is still in use and why, at Robotiq, we decided to use it as the standard communication protocol for our devices.

RS-485 You Said?

Many people are often confused when dealing with communication standards. Often, terms like "" RS-485 "", "" USB "" and "" Ethernet "" are interchanged as if they could be switched and do the same job. But in fact, the RS-485 standard is only a physical layer standard. It defines the electrical characteristics of the transmitter and the receiver. On top of that, an application layer must be used to handle stuff like device addresses, checksum, packet collision, master / slave topology, frame construction, etc. In the case of Ethernet and USB, these protocols define both the physical and application layer in their communication standard.

If you "re lost at this point, let" s make an analogy with human communications. As humans, we use our voice as a transmitter and our ears as receivers. This is our physical layer, the way we transmit information. Another example of a physical layer in our digital era could also be SMS that transmits our messages. It is still a physical layer from our perspective. The application layer in the case of humans is language. This is how we organize information. There are hundreds of them and even if they use the same physical layer, they are not necessarily compatible.

Why RS-485 Survived Ethernet

Ethernet (IEEE 802.3) is the most broadly used network protocol these days. It is also a serial communication standard. Since it is used in so many modern networks, the question is why hasn "t it replaced RS-485 and its other variations (RS-232, RS-422).

When comparing RS-485 with Ethernet both of them have advantages and disadvantages. The major drawback of RS-485 is its limited communication speed which is maxed out at 10 Mbaud. RS-485 is designed for a master / slave topology. In this system, the master polls each slave, waits for the response, and then polls the next slave. This allows a deterministic behavior by avoiding collisions of data packets. Ethernet however has no built-in methods to avoid data packet collisions. In applications like process control or robot control, for us, the deterministic behavior is mandatory while the speed of the communication is usually more than high enough. Communicating at lower speeds also has the advantage of being more resilient to the noise present in industrial environments.

RS-485 Standard

Forewarning: In standard applications where a Robotiq device is connected directly to a robot controller through the cable provided (normally 5 or 10 m) and where the Gripper is the only device on the communication bus, no special care is generally required to make the communication bus work. But for people who intend to attach our product to a custom bus or use a longer cable than provided by Robotiq, you should pay attention to the following concept.

RS-485 is capable of up to 32 drivers and up to 32 receivers in a half-duplex multi drop configuration. Receiver input sensitivity is ± 200mV, which means that to recognize a 1 or a 0 bit, the receiver must see signal levels between + 200mV and -200mV... Minimum receiver input impedance is 12kΩ, and the driver output voltage is ± 1.5V minimum, ± 5V maximum. Here "s an example of a multi drop RS-485 bus.

Cable length

RS-485 can be transmitted at a distance of up to 1200m (4000 feet) when the data rate is below 100k bps. At higher data rates, the cable length must be reduced as shown in the chart below.

A long cable can act like a transmission line, in which case, care should be taken to properly connect the network. Let "s look at the most important characteristics of the network that need to be accurately controlled.

Network topology

The network topology determines the way devices are connected together. The image below shows some common topologies. Among these possibilities, the best network topology for RS-485 is a daisy chain (or line), because this topology has the lowest impact on signal integrity. A bus topology (backbone using stubs) is okay, but as the length of each stub increases, the maximum data rate that can be transmitted will decrease due to signal distortion on the communication line.

Twisted pair cable

Using a twisted pair cable for RS-485 helps to reduce electromagnetic interference. The twisted pair allows the noise that is on the line to be equivalent on both wires. The noise is still there, but because the receiver looks at the difference between the two signals, this difference is not affected by the noise and thus the receiver can accurately reestablish the original signal at the end.

Termination resistor

Terminating a cable is the action of adding a resistor across the differential lines at both ends of the cable. The purpose of doing this is to reduce or eliminate the reflection coefficient on the line caused by an impedance mismatch. The resistance in the case of the RS-485 standard is define as 120 ohms. This reflection can lead to interference at the receiver input and then effect the signal integrity. This phenomenon is strongly correlated to the data rate and the length of the cable. So in some circumstance where low data rates and short cables are used, a RS-485 can work without a termination resistor. But as a precaution and to avoid any problems, resistors should always be used.

RS-485 at Robotiq

We decided to standardize our products by using RS-485 back in 2013 for many reasons, but mostly because it is resistant to noise, simple and effective. It is also a broadly used protocol among industrial devices which means that resources can be easily found on the web. Robotiq devices like the 2-Finger 85 and the FT 150 come with RS-485. Modbus RTU is used as our communication protocol. These devices have a termination resistor that can be activated easily through the User Interface Software that we provide. In addition, we support many other industrial protocols with the Robotiq Universal Controller, such as: Ethernet / IP, TCP / IP, DeviceNet, CANopen and EtherCAT.

Hope that you have found this blog post informative and that it helped you out with understanding just what a RS-485 is. If you want to learn more about the different communication protocols, we have complied a "" Communication Protocol Cheat Sheet "" that can be downloaded by using the link below.

S. Solodyankin
Steelsoft CJSC

Currently, the advantages of network access control and management systems are no longer in doubt - the ability to centrally maintain a database of passes, time tracking, remote control of access restriction devices have long become the de facto standard for projected systems. Also, in a separate category, it is necessary to make the customer's desire to have a distributed integrated security system, which includes, in addition to the ACS system, video surveillance systems, security and fire alarms, alerts, and perimeter protection. At the moment, there are two main architectures for building network access control systems - based on the RS-485 protocol and based on the Ethernet protocol. Let's try to figure out which one is more convenient.

A bit of history

RS-485 is a half-duplex multi-drop serial data interface. Data transmission is carried out over one pair of conductors using differential signals. The voltage difference between conductors of the same polarity means a logical unit, the difference of the other polarity means zero.
The RS-485 standard was jointly developed by two associations: the Electronics Industries Association (EIA) and the Telecommunications Industry Association (TIA). The EIA previously labeled all of its standards with the RS prefix (Recommended Standard). Many engineers continue to use this designation, but the EIA / TIA has officially replaced RS with EIA / TIA in order to make it easier to identify the origin of their standards. Today, various extensions to the RS-485 standard cover a wide variety of applications, this standard has become the basis for the creation of a whole family of fieldbuses widely used in industrial automation.
The RS-485 standard often uses a single twisted pair of wires to transmit and receive data. Link sharing procedures require a specific method to control the direction of the data flow. The most widely used method is to use RTS (Request To Send) and CTS (Clear To Send) signals.
Electrical and timing characteristics of the RS-485 interface:

32 transceivers for multi-point network configuration (on one segment, the maximum line length within one network segment is 1200 m).
Only one transmitter is active.
The maximum number of nodes in a network is 250, including backbone amplifiers.
Characteristic "exchange rate / communication line length" (exponential dependence):
- 62.5 Kbps 1200 m (one twisted pair);
- 375 Kbps 300 m (one twisted pair);
- 500 Kbps;
- 1000 Kbps;
- 2400 Kbps 100 m (two twisted pairs);
- 10,000 Kbps 10 m.

Ethernet (ezernet, from Lat. Aether - ether) is a packet technology of computer networks, mainly local.
Ethernet standards define wiring and electrical signals at the physical layer, packet format and media access control protocols at the link layer of the OSI model. Ethernet is mainly described by the IEEE 802.3 standards. Ethernet became the most widespread LAN technology in the mid-1990s.
Ethernet technology was developed in conjunction with many of Xerox PARC's early projects. It is generally accepted that Ethernet was invented on May 22, 1973, when Robert Metcalfe wrote a memo for the head of PARC on the potential of Ethernet technology. But Metcalfe received the legal right to the technology only a few years later. In 1976, he and his assistant David Boggs published a brochure titled Ethernet: Distributed Packet-Switching For Local Computer Networks.
Metcalfe left Xerox in 1979 and founded 3Com to promote computers and local area networks (LANs). He managed to convince DEC, Intel and Xerox to work together and develop the Ethernet standard (DIX). This standard was first published on September 30, 1980. He began a rivalry with two major patented technologies, token ring and ARCNET, which were soon buried under the rolling waves of Ethernet products.
There are several technology options depending on the data transfer rate and the transmission medium. Regardless of the method of transmission, the network protocol stack and programs work the same in almost all variants. Due to the huge number of various Ethernet protocol standards, many of which are outdated before they even appeared, we will consider only a few of the main ones:
100BASE-T is a general term for standards that use twisted-pair cable as the transmission medium. Segment length up to 150 m. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2 standards.
100BASE-LX WDM is a standard using single-mode fiber. The maximum segment length is 15 km in full duplex mode at 1310 nm and 1550 nm. Interfaces are of two types, differ in the transmitter wavelength and are marked with either numbers (wavelength) or one Latin letter A (1310) or B (1550). Only paired interfaces can work in pairs, on the one hand the transmitter is at 1310 nm, and on the other - at 1550 nm.
1000BASE-T, IEEE 802.3ab is a standard that uses a twisted pair of categories 5e or 6. All 4 pairs are involved in data transmission. The data transfer rate is 250 Mbps over one pair.

Considered interfaces in access control and management systems

The RS-485 interface was the first to enter the security systems market and firmly established itself there, as it happened due to its wide distribution on the industrial microcontroller market, at a time when Ethernet had just begun to appear in the high-tech field. At the current time, the lion's share of the market for access control systems, as well as security and fire alarm systems, is unconditionally owned by RS-485.
ACS controllers that transmit data via the RS-485 protocol are often inexpensive. The microcircuits that organize the bus are very cheap, the circuitry of the finished device is extremely simple - all these factors certainly speak in favor of RS-485.
Let's consider the process of data transmission via the RS-485 bus. The central controller (Master controller) or a computer provides loading of data on passes, access time schedules into the controller's memory. The controller's logic independently makes decisions about the admission of this or that person. After completing the passage, the controller provides uploading of events about the passage to the computer database (Master controller). The bus bandwidth and, as a consequence, the number of controllers on one bus are usually not of fundamental importance, due to the fact that the work on adding new passes and transferring events can occur in the background, simultaneously with the operation of the checkpoint.
It would seem that if everything works, why invent something new, but the development of technology does not stop, the tasks of ensuring security are becoming more difficult every day, the development of software for access control and management systems is beginning to outstrip the hardware component.
And immediately problems begin to arise. Let's say we need to manage one or more checkpoints in real time using complex non-standard rules. For example, using several identification methods at the same time (for example, by card, fingerprint and face), practicing the rules of two or three cards, using different identification devices for different groups of people. Usually, the controller cannot solve this problem on its own in offline mode. Such complex solutions are usually implemented by controlling the controller directly from a computer, using the controller simply as an interface module through which readers and access restriction devices are connected. Simultaneous data exchange with 15 controllers via the RS-485 bus causes unacceptable delays in the system operation - the turnstile has to be opened for several seconds when the card is presented. It is practically impossible to speed up this process with technical tricks due to the “ideology” of organizing the RS-485 bus. All devices connected to this bus are interrogated sequentially, one after the other, and if we take into account the small data transfer rates of the RS-485 bus, it is easy to conclude that a large access control and management system using complex identification methods on the RS-485 bus, it is almost impossible to build.
The disadvantages listed above in a number of access control systems are manifested even at the level of simple solutions. For example, if, while adding users to the pass office, you try to open the turnstile from the security guard's workstation manually from the software, then the command to open the turnstile will be received with a significant delay.
This problem can be solved by replacing the data transfer protocol. The new protocol should provide parallel data transfer so that commands and data are not transmitted to all devices in turn, but to the required device at once. It is also necessary to increase the data transfer rate. Finally, the new protocol should be as widespread as possible to ensure compatibility with existing network devices and future developments. Using a widespread protocol, you can be sure that the access control and management system under construction will be able to evolve in the future. Ideally, if the protocol can organize a single data transfer bus for all elements of the complex security system of the facility.
Summarizing all the above theses, one can easily conclude that the only data transmission technology at the moment that meets all the above requirements is the Ethernet network.
Ethernet is the most widely used data network in the world. The equipment and data transfer protocols using this network are continually evolving. Due to the widespread prevalence, microcontrollers that support Ethernet have become significantly cheaper and, accordingly, the price of ACS controllers can be low. Also, Ethernet networks are already available in every office and enterprise, respectively, when using this network, additional costs for wiring will not be required.
Let's summarize the main advantages of using Ethernet for organizing access control systems:

the likely presence of an Ethernet network in the enterprise and, as a result, the absence of costs for laying the network;
parallel operation of all controllers makes it possible to organize direct control of devices from a computer and, as a result, extreme flexibility in building identification rules and the operation of the system as a whole;
high data transfer rate and parallel operation of all controllers allow building huge ACS systems, in fact, without limitation on the number of controllers;
the principle of building an Ethernet network assumes the most simple scaling of the system - just connect another controller;
parallel operation of all controllers increases the reliability of the system as a whole; if one device fails, all the others continue to work in normal mode;
the use of a standard data bus allows you to use a large number of different ways of organizing a network, including a radio channel;
ease of integration of controllers using the Ethernet bus into existing access control and management systems or automated enterprise management systems;
the use of a standard data transmission network makes it possible to build a single network for the transmission of information from all devices organizing the security system - video surveillance systems, fire alarm systems, access control, warning systems.

But, as you know, any, even the most perfect, system has drawbacks. Let's consider the disadvantages of ACS controllers using the Ethernet bus.

somewhat higher, in comparison with controllers on the RS-485 bus, cost;
shorter maximum distance between controllers when using standard solutions: in the RS-485 bus - 1200 m, in the Ethernet bus - up to 300 m (switch between controllers). This disadvantage is more than compensated for by a large number of alternative ways of organizing an Ethernet network: fiber optic, SHDSL and PLC technologies operating over long distances;
higher qualifications of the system installer, basic knowledge of Ethernet networking is required.

The disadvantages of the Ethernet bus listed above cannot be compared with the ultimately obtained capabilities.
To fully appreciate the difference in technologies, let's consider the functional characteristics of the STS-407 ACS controller using the Ethernet bus, and the summary characteristics of the ACS controllers of a number of leading Russian and foreign manufacturers using the RS-485 bus (Table 1):

Practical check

In order to fully see the picture of the ACS market today, it was decided to do a little research. Two technical assignments were developed and sent to 36 randomly selected security systems installers on the Russian market. The companies were completely different: small and large, well-known and proven in the market and just starting their way.
The first technical task is a small office with one turnstile at the entrance. The following requirements were put forward: photo-identification, two video surveillance cameras, time tracking, the total number of employees is 120 people. The results were, in principle, predictable in advance, I would like to immediately warn that the average price of solutions turned out to be conditional, this is explained by the different policies of the companies (somewhere, for example, the price for installation work is clearly overstated and greatly lowered for equipment), as well as by different regions of the location of the installer companies ... The resulting results look something like this:
1. 25 companies offered a simple solution with controllers from different manufacturers based on the RS-485 bus, video surveillance was proposed as a separate system not related to the ACS system; the average price of equipment for this solution was 73,000 rubles.
2. 8 companies offered a complex (ACS integrated with video surveillance) solution based on a controller operating via RS-485; the average price did not differ much from the previous result, we will consider it equal to 73,000 rubles.
3. 3 companies offered a complex solution (ACS is integrated with video surveillance) based on a controller with an Ethernet bus. This solution turned out to be slightly more expensive than all the others and, on average, will cost the client 78,000 rubles.
The second technical task was not easy. One of the large objects of the oil and gas industry: 12 checkpoints, spread across the territory, 8 of them are connected to the server (located in the administrative building) local computer network, 2 have telephone communication and free twisted pair, but there is no possibility of installing a computer, the distance to the administrative building 1100 and 3300 m, 2 checkpoints without communication lines, distance 1600 and 2000 m line of sight to the office building. Overhead communication lines are not allowed, cable ducts exist, but access to them is not allowed. Requirements: the number of employees is 17,000 people, the global AntiPassBack prohibition mode, time tracking, the ability to use biometric scanners, etc. With). The results were very interesting:
1. It was not possible to get a clear answer from 7 companies in two days.
2. 1 company in 3 hours sent the TOR to the authors of this article with a request to propose a solution.
3. 16 companies offered solutions of the same type, which looked something like this: a computer is installed at each checkpoint, to which ACS controllers and video cameras are connected via RS-485. All computers organize a local network among themselves in different ways. Where it is not possible to install computers, RS-485 to Ethernet converters are used. The average price of such a solution turned out to be: equipment - 2,530,000 rubles, work and consumables - 1,980,000 rubles.
4. 12 companies suggested using Ethernet controllers, which form a local network in different ways (xDSL, WiFi technologies). For the organization of video surveillance, IP technologies were used. The average price of such a solution: equipment - 2,150,000 rubles, work and consumables - 1,550,000 rubles.
From our practical test, the following conclusions can be drawn:

The most common technology is RS-485.
The Ethernet protocol in ACS controllers has taken its niche in the Russian security systems market.
On small objects, RS-485 wins due to the cost.
In large facilities, due to the simplicity of the solution and the cost, Ethernet wins.
It should be noted that the average price of an object turned out to be very conditional for a number of reasons:
Incomplete and allowing for ambiguous understanding of the terms of reference.
Obvious errors in the estimates provided.
There is a big difference in the price of equipment not related to our research (turnstiles, server equipment, equipment for organizing communications).
The difference is in the functional characteristics of the solutions.

But within the framework of our study, the trend indicated above was traced quite clearly.

conclusions

Progress does not stand still, the last decade in the world with the naked eye is visible a tendency for the rapid growth of computer technology, computing power and huge data transfer rates. Many experts believe that in the not too distant future we will have "global network integration" based on the Internet. Considering the above, sooner or later all, or almost all, systems that use data transmission will happily switch to the Ethernet protocol. A striking example of this is CCTV systems: a few years ago, IP-video surveillance had a huge number of opponents, but time has put everything in its place, and now we see that IP-video is slowly but inevitably replacing the classic schemes of building video surveillance systems from the market. Although many experts in the field of access control consider that the Ethernet protocol is "redundant" for access control systems, that it is too "wide" and "fast", we can confidently say that there is no "too fast" in IT technologies. No one knows what requirements for the access control systems will be presented tomorrow, and the speed margin will definitely not be superfluous, but today it is possible to significantly simplify and reduce the cost of the complex security system of the facility by using a single data bus for all its elements (access control system, video surveillance, fire protection system) and by laying one data cable instead of a thick wiring harness. Considering all of the above, I think that I will not be too much mistaken, assuming that it will not take two or three years before the principle of building ACS on Ethernet will be considered a classic one.

S. Solodyankin
Steelsoft CJSC

Currently, the advantages of network access control and management systems are no longer in doubt - the ability to centrally maintain a database of passes, time tracking, remote control of access restriction devices have long become the de facto standard for projected systems. Also, in a separate category, it is necessary to make the customer's desire to have a distributed integrated security system, which includes, in addition to the ACS system, video surveillance systems, security and fire alarms, alerts, and perimeter protection. At the moment, there are two main architectures for building network access control systems - based on the RS-485 protocol and based on the Ethernet protocol. Let's try to figure out which one is more convenient.

A bit of history

RS-485 is a half-duplex multi-drop serial data interface. Data transmission is carried out over one pair of conductors using differential signals. The voltage difference between conductors of the same polarity means a logical unit, the difference of the other polarity means zero.
The RS-485 standard was jointly developed by two associations: the Electronics Industries Association (EIA) and the Telecommunications Industry Association (TIA). The EIA previously labeled all of its standards with the RS prefix (Recommended Standard). Many engineers continue to use this designation, but the EIA / TIA has officially replaced RS with EIA / TIA in order to make it easier to identify the origin of their standards. Today, various extensions to the RS-485 standard cover a wide variety of applications, this standard has become the basis for the creation of a whole family of fieldbuses widely used in industrial automation.
The RS-485 standard often uses a single twisted pair of wires to transmit and receive data. Link sharing procedures require a specific method to control the direction of the data flow. The most widely used method is to use RTS (Request To Send) and CTS (Clear To Send) signals.
Electrical and timing characteristics of the RS-485 interface:

32 transceivers for multi-point network configuration (on one segment, the maximum line length within one network segment is 1200 m).
Only one transmitter is active.
The maximum number of nodes in a network is 250, including backbone amplifiers.
Characteristic "exchange rate / communication line length" (exponential dependence):
- 62.5 Kbps 1200 m (one twisted pair);
- 375 Kbps 300 m (one twisted pair);
- 500 Kbps;
- 1000 Kbps;
- 2400 Kbps 100 m (two twisted pairs);
- 10,000 Kbps 10 m.

Considered interfaces in access control and management systems

the likely presence of an Ethernet network in the enterprise and, as a result, the absence of costs for laying the network;
parallel operation of all controllers makes it possible to organize direct control of devices from a computer and, as a result, extreme flexibility in building identification rules and the operation of the system as a whole;
high data transfer rate and parallel operation of all controllers allow building huge ACS systems, in fact, without limitation on the number of controllers;
the principle of building an Ethernet network assumes the most simple scaling of the system - just connect another controller;
parallel operation of all controllers increases the reliability of the system as a whole; if one device fails, all the others continue to work in normal mode;
the use of a standard data bus allows you to use a large number of different ways of organizing a network, including a radio channel;
ease of integration of controllers using the Ethernet bus into existing access control and management systems or automated enterprise management systems;
the use of a standard data transmission network makes it possible to build a single network for the transmission of information from all devices organizing the security system - video surveillance systems, fire alarm systems, access control, warning systems.

But, as you know, any, even the most perfect, system has drawbacks. Let's consider the disadvantages of ACS controllers using the Ethernet bus.

somewhat higher, in comparison with controllers on the RS-485 bus, cost;
shorter maximum distance between controllers when using standard solutions: in the RS-485 bus - 1200 m, in the Ethernet bus - up to 300 m (switch between controllers). This disadvantage is more than compensated for by a large number of alternative ways of organizing an Ethernet network: fiber optic, SHDSL and PLC technologies operating over long distances;
higher qualifications of the system installer, basic knowledge of Ethernet networking is required.

Practical check

The most common technology is RS-485.
The Ethernet protocol in ACS controllers has taken its niche in the Russian security systems market.
On small objects, RS-485 wins due to the cost.
In large facilities, due to the simplicity of the solution and the cost, Ethernet wins.
It should be noted that the average price of an object turned out to be very conditional for a number of reasons:
Incomplete and allowing for ambiguous understanding of the terms of reference.
Obvious errors in the estimates provided.
There is a big difference in the price of equipment not related to our research (turnstiles, server equipment, equipment for organizing communications).
The difference is in the functional characteristics of the solutions.

But within the framework of our study, the trend indicated above was traced quite clearly.