Powerful stuff!

Picture the scene … you've toiled long and hard working out how best to install networked CCTV cameras and secure access terminals in some hard-to-reach location, only to discover that the need for a separate power supply makes the whole installation either prohibitively expensive or too time consuming.

How many times must that have happened? Well, it need be a problem no longer, because with Power over Ethernet (PoE), the same wires that carry the data to and from the connected systems can also carry the power.

The emergence of PoE means both suppliers and users of Ethernet-based network security products have a beneficial new technology. Concentrating for a moment on the “power” aspect of PoE, this technology represents the only truly universal power standard. Whilst there are differences in the mains plugs in the UK to that of Europe and again to the USA, the RJ45 connection and -48V voltage of PoE are standard the world over.

Indeed, when you think about the multitude of electronic devices that require a DC input but consume less than 15W of power, it is not difficult to foresee a time when PoE is the world's most popular source of power. The potential for PoE, then, is enormous, and in the security and surveillance markets the applications encompass wireless access points, VoIP entry phones, sensors, lighting controllers, and security cameras.

Today, there are already more than 200 different types of device which are PoE-enabled. And over the next few years it is likely that PoE will rise to become the power source of choice for devices such as smoke/fire detectors, RFID scanners, and many others.

Good ideas, practical applications

Thus, Power over Ethernet has become one of the hottest topics in twenty first century technology.

As trends in VoIP, Wi-Fi (802.1) wireless networks, and security accelerate, the numerous benefits provided by PoE can help turn good ideas into practical applications. These benefits include:

l Easier deployment – Access to hard-to-reach locations or places with a lack of space for power deployment becomes much simpler and easier to maintain.

l Lower cost – Costs can quickly escalate when the installation of separate power outlets are factored into a project. PoE switches save both time and money by avoiding the need for separate installation of Power outlets.

l Multi-location – Wherever there is an Ethernet connection, a powered device can be used.

l Increased uptime – If a UPS is used in the power supply for the PoE switch, reliability rises towards the optimum “five nines” due to reliance not being placed on the mains AC voltage supply.

l Improved Safety – 48 Volt Direct Current levels are much safer than AC mains voltage.

l Plug and Play – Equipping applications with PoE switches is simple and enables interoperability with a growing variety of devices.

PoE technology

The numerous benefits provided by PoE can help turn good ideas into into practical applications

The PoE standardisation project began in 1999, and in 2003 the Institute of Electrical and Electronics Engineers (IEEE) task force ratified the technology into the Ethernet standard 802.3af.

The IEEE 802.3af standard – also referred to as Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI) – is the first international standard to define the transmission of Power over Ethernet infrastructure.

The mechanism for delivering power via PoE is similar to the way in which the PSTN (Public Switched Telephone Network) carries enough power to every public telephone handset.

PoE delivers DC power of up to a theoretical maximum of about 15W per cable. In practice, however, a maximum power of 12.95W is available, limited by degradation of power over the cable – typically standard Ethernet cabling of CAT5 or better.

A CAT5 cable has four twisted pairs, but only two of the pairs are used for data. The IEEE 802.3af specification allows either the spare pairs to be used (pins 4 and 5, or 7 and 8) or the data pairs (pins 1 and 2, or 3 and 6) to carry the power. Typically, a PoE system consists of both Power Sourcing Equipment (PSE) and a Powered Device (PD). The PSE may either be an Endspan (L2 Ethernet switch supporting PoE) or a Midspan (PoE hub).

The PD is a PoE-enabled terminal such as an IP phone. PoE systems are deployed in a “star topology”, so each PD is connected to a separate channel of the central PSE. Users need to be cautious when using Midspan products because they are not 802.3af compliant and therefore do not verify that the end device they are powering is a PD. The 802.3af standard requires that a PSE probes the end device to determine whether or not it is a PD and, if so, what its capability is. The 802.3af standard ensures the safety of PDs by making a 25k Ohm resistor in the PD mandatory.

Power is applied only when the “discovery process” running from the PSE detects the resister. This prevents damage from occurring to non-PD devices. In addition, the PoE standard calls for over-current protection, under-current detection, and fault protection of PDs from shorts, power fluctuation or failure.

In-depth application

GarrettCom has built the first hardened PoE switch specifically targeted at industrial-grade applications, including outdoor CCTV cameras, for example.

By integrating Ethernet switching, PoE power sourcing and industrial-hardened components, the company has delivered single a unit that is ready and able to support industrial strength PDs.

The arrival of PoE power sourcing Ethernet switches for industrial Ethernet applications changes the network design possibilities. The 4-port PS14P PoE Convenient Switch will save money and space, as well as increase reliability for a wide spectrum of applications. In the past, it has taken 10 years or longer for Enterprise-based Ethernet technologies to be adapted for use in industrial applications. But with its introduction of the first industrial PoE switch less than two years after the IEEE 802.3af standard was solidified, GarrettCom has made a major contribution to speeding the adoption of PoE technology.

Conclusion

Not only can PoE allow a whole host of networked security devices to be powered in remote locations where access to power is unavailable, but it opens the door to a whole new world of exciting possibilities for innovative security installations.

It is almost certain that PoE will herald major changes for security applications. Despite the available power in a PoE connected device being limited to about 13 watts, the advantages of blending signal and power in one Ethernet cable connection will contribute to the already-rapid transition to Ethernet based industrial control systems.