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Demystifying Wired Communications for IP-Based Security Applications
Submitted by Veracity 2011/2/16

Demystifying wired data communications for security applications initially sounds like a very broad topic, but if we assume a useful distance and reasonable data rates, plus the ability to deliver power, then in fact it can be narrowed down to just a few technologies. Many common wired communications formats can be discounted due to their very short range (such as USB, SCSI, Firewire and others). Simple serial data connections such as RS232, while still a stalwart of the security industry, have data rates which are far too low to be considered for anything other than very slow-speed connections for simple devices and therefore lie outside the scope of this article.

Demystifying wired data communications for security applications initially sounds like a very broad topic, but if we assume a useful distance and reasonable data rates, plus the ability to deliver power, then in fact it can be narrowed down to just a few technologies.

Many common wired communications formats can be discounted due to their very short range (such as USB, SCSI, Firewire and others). Simple serial data connections such as RS232, while still a stalwart of the security industry, have data rates which are far too low to be considered for anything other than very slow-speed connections for simple devices and therefore lie outside the scope of this article.

We are discussing mediumrange systems, such as those which would be useful on a particular security site. This means long-range technologies such as DSL are excluded. Although fiber-optic cabling might be used within a large site, this, too, is excluded from our review as it is a specialist subject in itself and also because it cannot transmit power. As this is still a large topic in a short article, for t he re ade r who would like to know more detail, we have suggested some keywords for Internet searches in square brackets.

Thus, our focus is wired communications which can carry power, video, audio and other high-speed data for security systems. The common factor here is Ethernet, which in the last 10 years has become the dominant networking and high-speed data communications technology, so much so that it is hardly worth considering anything else. Even small, low-cost devices are being fitted with Ethernet connections, and access control systems are rapidly switching over to IP-based technology, as is surveillance. The main driving force behind all this is simplification: If all devices share a common Ethernet capability, the problem of integration becomes one of software, and the problem of incompatible and proprietary hardwired connectors and communication protocols disappears.

Having established that Ethernet is the almost universal standard, let us consider the transmission medium options. These include electrical power delivery cables, unshielded twisted-pair (UTP) cabling (such as common CAT5e/6 network cabling), single twisted-pair (STP) cable (such as telephone cable) and coaxial cabling (such as that used for analog video in CCTV systems).

PLC
Power-line communications (PLC) systems have been developed by power utility companies with deregulation driving them to seek new business opportunities. Viewing their installed power cables as potential data communications systems, they funded or inspired the development of PLC technology. While long-distance, high data rate communications over power lines has

considerable challenges due to noise generation, local PLC systems are now quite common within domestic environments. The most common standard employed is that of the HomePlug Powerline Alliance, and there are a multitude of manufacturers of these systems [search “HomePlug AV”]. However useful for domestic applications, it is doubtful whether PLC is particularly useful for security applications, especially in industrial or corporate settings, where other devices on the “network” are very likely to attenuate the signals and/or cause interference.

By definition, PLC systems are able to carry power, so that is hardly an issue. However, data rates are directly proportional to distance and again, while that data rate versus distance trade-off may be acceptable for a house, it becomes far less attractive in a larger office building or warehouse and completely impractical in a hospital, university, city center, prison or airport, to name a few [search “Power line communications”].

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CAT5e/6 ETHERNET
Standard networking cable is an ideal medium for wired data communications as it has been specially developed for the purpose of transmitting Ethernet network signals at high speed (up to 1 gigabit per second). It has the added advantage that so many systems are designed for CAT5e cabling with the ubiquitous RJ45 connectors. Almost everyone is familiar with this standard “network cable.”

However, for security applications and for video surveillance in particular, it does have a serious limitation: distance. After approximately 100 meters, the Ethernet signal is liable to dropouts and failed connections [search “Ethernet distance limit”]. This is never much of a problem in a structured, cabled office, where multiple switches and routers are on every floor and each network device is rarely more than dozens of meters away from such a connection. However, network cameras often need to be deployed at the peripheries of a site (fence lines, parking lots, entrances and exits, walkways, access roads and so on). These are usually more than 100 meters from the nearest switch. This also holds true, although slightly less so, for access control devices, VoIP phones and help points.

There is an easy solution to this distance problem, thanks to LAN and PoE extenders which have become available in the last couple of years. These are small network repeaters powered through the network connecting cable by PoE and are placed at or before the 100-meter Ethernet limit. They reconstruct and resend the Ethernet network packets (just like a switch) and so double the effective network cable transmission to 200 meters. Multiple devices can be deployed to reach 300 meters, 400 meters and so on. Depending on the power injected and the distance required (and indeed the power consumption of the repeater device), useful levels of PoE power can still be delivered at some distance [search “LAN and PoE extender”]. Such devices are becoming an essential part of an IP video system designer's toolbox.

These days, almost all Ethernet equipment runs at 100 megabits per second (Mbps) at least. Gigabit Ethernet is common, but requires high-quality cabling and is typically not supported by LAN and PoE extenders. However, this is rarely a problem, even for IP video using megapixel camera systems, as the long cable run sections usually carry only one, two, maybe four video streams at any point. In toward the center of the network (such as a main building) where the streams are aggregated at network switches, the switches and the rest of the network can run at Gigabit speeds, and the cable runs tend to be shorter from that point onward.

Thus, Ethernet over CAT5e/6 cabling is an almost universal solution and, with modern LAN and PoE extenders, is ideal for all types of security applications. Although this article is about wired communications, it is important to note that wireless network segments can seamlessly integrate with standard networks and greatly increase system design flexibility. However, the optimum siting of wireless access points for greatest signal coverage is often inconveniently more than 100 meters away from the nearest wired network point (switch). Again, LAN and PoE extenders can be exploited.

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STP
Typically, STP cable is only used (for high-speed data) when there is no other option available or where such cable is already in place and cannot be replaced (such as a telephone line). There are devices available to run Ethernet over STP [search “Ethernet over single twisted pair”]. Quite long distances can be achieved with DSL technology developed for broadband connections, but typically the data rates fall off quite sharply with increasing distance.

EoC
There are vast lengths of coaxial cabling installed all over the world, originally installed for analog CCTV cameras. Indeed, despite the dramatic surge in network camera sales, the vast majority of surveillance cameras are still analog, and most of them are connected with 75-ohm coaxial cable of varying types and quality. As these cameras are replaced with network ones, this legacy coaxial cable can be reused as a full-speed, 100-Mbps Ethernet link by using powered Ethernet-over-coax (EoC) adaptors.

There are a number of EoC solutions available on the market [search “Ethernet over coax“]. Many are designed for domestic applications (using TV cabling infrastructure), and these are generally unsuited to professional security applications (the units are too big, have wrong connector types, exhibit lower robustness, have specific/custom power supply requirements, and offer poor support and limited performance and diagnostics). However, a number of companies have focused on solutions for the surveillance market in particular, and many consultants, specifiers and integrators are taking full advantage of these.

Reusing installed coaxial cabling has a number of significant advantages: no new cabling needs to be pulled; installation time is reduced; business disruption for the customer is minimised; environmentally, it is good to “recycle” the existing cabling; even long cable runs of 200 meters or even 300 meters will still run at 100 Mbps without repeaters. Further, by using multiport EoC adaptors at the camera end, multiple network cameras can be streamed over a single coaxial cable, thus providing a very cost-effective way of increasing camera count with minimal extra cabling. Note also that these EoC connections can be used for any networking connection, such as IP access control, VoIP, IP alarm systems, building management or multiples of those, with or without concurrent IP video.

[Side note: In discussing coax as a medium which can be reused for digital video transmission, we should not ignore the technological approach of the HDcctv Alliance. However, to compare the very product-specific technology of HDcctv with the much more general solution of EoC requires more space than is available here and will be the subject of a future article].

NO SILVER BULLET
PLC is not a great solution for professional security applications and is more suited to domestic applications including home automation. Ethernet over PLC suffers from signal interference and can have unpredictable performance. Twisted-pair cabling is normally only relevant when better options are not possible for whatever reason.

Ethernet is an almost universal solution on CAT5e/6 cabling, with security-specific distance problems overcome by PoE-powered LAN extenders. Existing coaxial cables which were originally installed for analog video can also reused for fast Ethernet segments and removes a significant market restraint on the conversion from analog to IP-based video.

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