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).
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”].