Using wired communications for IP-based security systems.

The article's author, Alastair MacLeod, managing director of Veracity, notes that while the use of wired communications for data transmission in security systems may seem like a broad topic, when you consider the useful distance and acceptable data transfer speeds, as well as the ability to supply power, it can actually be reduced to a few technologies.

Many standard wired communication formats can be ignored due to their very small coverage (e.g. USB, SCSI, Firewire, etc.). While simple serial interfaces such as RS232 are still popular and reliable security solutions, their data rates are too low to be considered anything more than interfaces for slow connections to simple devices. For this reason, they are also not covered in this article.
We are looking at mid-range systems that can be used at a specific site where security is required. This means excluding long-range technologies such as DSL. While fiber optic cable can be used within a large site, we are also not including it in this review because it is a separate topic for discussion and, in addition, is not capable of transmitting power.
So, let's focus on wired communication systems that can deliver power, video, audio, and other high-speed data to security systems. The unifying factor here is Ethernet, which has become the dominant networking and high-speed data technology over the past 10 years, so there's little point in talking about other options. Even small, inexpensive devices are equipped with Ethernet ports, and access control systems are rapidly moving to IP-based technologies, as are surveillance systems. The main driver of this change is the desire for simplicity: if all devices have the same Ethernet characteristics, the integration problem will no longer be a hardware problem but a software problem, and the problem of incompatible and proprietary hard connectors and data protocols will disappear altogether.
We have established that Ethernet is a nearly universal standard. Now we will look at the options for data transmission media. These include power transmission cables, unshielded twisted pair cables (such as standard CAT5e/6 network cable), single twisted pair cables (such as telephone cable), and coaxial cables (such as the cables used for analog video in closed-circuit television systems).
Power Line Communications
Power line communications systems were developed by the companies that owned the electric utility systems. Deregulation forced them to look for new commercial opportunities. Seeing their installed power cables as potential data transmission systems, the companies funded the development of power line communications technology. Although high-speed data transmission over long distances over power lines poses significant challenges due to interference, local power line communications systems are now widely used in residential environments. The most commonly used standard is the HomePlug Powerline Alliance standard. Many manufacturers produce these systems. However, as convenient as the system may be for home use, it is unlikely that power line communications can be successfully used for security purposes, especially in industrial or corporate environments where other devices connected to the network may weaken signals or cause interference.
Power line communications systems are inherently capable of transmitting power, so this is clearly not the problem. But data transfer speed is directly proportional to distance, and again, while a trade-off between data transfer speed and distance might be enough for a home, it doesn't sound so tempting for a large office building or warehouse. And it's practically unusable, for example, in a hospital, university, city center, prison or airport.

CAT5e/6 ETHERNET
Standard network cable is the ideal transmission medium for wired communication systems, as it is specifically designed for high-speed network signal transmission (up to 1 gigabit per second). An additional benefit is that most systems are designed for CAT5e cable with universal RJ45 connectors. This standard “network cable” is familiar to almost everyone.
However, when it comes to security applications, especially CCTV, there is one major drawback: distance. After about 100 meters, the Ethernet signal begins to drop out and the connection is broken. For a well-designed and wired office, where there are multiple switches and routers on each floor and where any network device is within a few dozen meters of such a connection, this is not a major issue. However, network cameras often need to be used at the edges of a facility (fence lines, parking lots, entrances and exits, corridors, driveways, etc.). They are typically more than 100 meters away from the nearest switch. This also applies, although to a lesser extent, to access control devices, Voice over IP (VoIP) phones, and help desks.
The distance problem can be easily solved by using LAN extenders and Power over Ethernet (PoE), which have appeared in recent years. These are small network repeaters that receive power through the Ethernet network patch cable and are placed at or just before the 100-meter edge of the Ethernet network. They regenerate and resend Ethernet network packets (like a switch), thereby doubling the effective transmission distance of data over the network cable to 200 meters. Several of these devices can be used to provide transmission over distances of 300, 400 meters, etc. Depending on the input power and the required distance (and the power consumption of the repeater), effective power levels can be transmitted over some distance using Power over Ethernet. Such devices are becoming an important part of the IP video system designer's toolkit.
Almost all Ethernet equipment today operates at or above 100 megabits per second (Mbps). Gigabit Ethernet is popular, but it requires high-quality cable and is generally not supported by LAN and Power over Ethernet extenders. However, this is rarely a problem, even when it comes to IP video using megapixel camera systems, because long runs of cable typically carry one, two, or four video streams at any one point. Closer to the center of the network (such as the main building), where the streams are combined at the network switches, the switches and other network devices can operate at gigabit speeds, and cable runs become shorter from that point on.
Thus, the organization of the Ethernet network via CAT5e/6 cable is a virtually universal solution, and with the use of modern LAN extenders and Power over Ethernet, it is ideal for all types of security systems. Although this article is devoted to wired communication, it should be noted that wireless network segments can be effectively integrated into standard networks, which will significantly increase the flexibility of system design. However, to ensure maximum coverage, wireless access points should not be located more than 100 meters from the nearest wired network point (switch). Again, the use of LAN extenders and Power over Ethernet is allowed.
Comparison of Ethernet Data Transmission Media

Shielded twisted pair
Shielded twisted pair cable is generally used (for high-speed data transmission) only when there are no other options, or when such cable is already available and cannot be replaced (for example, a telephone line). There are devices for transmitting Ethernet over shielded twisted pair cable. Using DSL (Digital Subscriber Line) technology, designed for high-speed connections, it is possible to transmit data over long distances. However, as a rule, the data transfer rate drops sharply with increasing distance.
Ethernet over Coaxial Cable
There are vast quantities of coaxial cables installed around the world that were originally intended for analog closed-circuit television cameras. Indeed, despite the explosion in network camera sales, many surveillance cameras are still analog, most of them connected via 75-ohm coaxial cables of varying types and qualities. As these cameras are replaced by network ones, that old coaxial cable can be reused for high-speed Ethernet (100 Mbps) connections using powered Ethernet over Coax (EoC) adapters.
There are many Ethernet over coaxial solutions on the market. Most of these solutions are designed for home use (using TV cable infrastructure), but they are generally not suitable for professional security systems (they are too big, have different types of connectors, are less robust, have specific/standard power requirements, often lack proper support and diagnostics, and have limited features). However, some companies have focused on solutions for the video surveillance market, which is actively used by various consultants, specifiers and system integrators.
There are a number of significant advantages to reusing existing coaxial cable: There is no need to pull new cables; Installation time is reduced; Customer business interruption is minimized; Reusing existing cable is an environmental benefit; Even long cable runs of 200 or 300 meters transmit data at 100 Mbps without the need for repeaters. In addition, using EoC multiport camera adapters, data streams from multiple network cameras can be transmitted over a single coaxial cable. This is a cost-effective way to increase the number of cameras while requiring minimal additional cabling. It is also worth noting that these Ethernet over coaxial cable connections can be used for any network connection, such as IP access control, VoIP, IP alarm systems, building management systems, or several similar systems with or without simultaneous IP video transmission.

There are no simple solutions
PLC is not the best solution for professional security systems, but is more suitable for home use, including home automation. When organizing an Ethernet network using PLC, there is signal interference and unpredictable reactions. As a rule, twisted pair cable is used only when more acceptable options are not feasible for some reason.
With CAT5e/6 cable, Ethernet becomes a virtually universal solution, and the security-related distance issues are solved by LAN extenders and Power over Ethernet. Existing coaxial cables that were originally installed for analog video can also be reused for «fast» Ethernet segments, which will eliminate serious market limitations regarding the conversion of analog video to IP-based video.

Source: asmag