Extending Power-over–Ethernet technology for security

Aug. 6, 2012
PoE solutions reduce power consumption, simplify installation of security devices

Security professionals worldwide are increasingly turning to Power-over-Ethernet (PoE) solutions as demand for enhanced security monitoring technology continues to rise. Advancements of the technology have made it more convenient to deploy network devices by enabling both power and data to be delivered over the existing Ethernet cabling in a unified infrastructure that is easier to expand, upgrade and maintain. PoE, which delivers safe, uninterrupted power over the existing local area network (LAN) infrastructure, has become an important tool for simplifying network deployment while improving remote-management capabilities, security benefits and overall energy efficiency.

Today’s security systems demand consistent, 24/7 operation. PoE provides power and data to a system’s power devices (PDs) over a single RJ45 connector, eliminating the need for a local alternating current (AC) outlet and enabling wireless access points, video surveillance cameras, access control systems and other PDs to be installed wherever they are needed. This can include difficult-to-reach locations, regardless of whether or not there is an electrical outlet nearby. Not only does PoE power ensure installed cameras operate reliably day and night, it also features a centralized architecture that provides the ability to back up the security system. In contrast, if AC power is used, which cannot be backed up, cameras will not operate if there is a power interruption. Given these significant advantages, in addition to those addressed further below, it’s no surprise that the majority of today’s IP cameras are PoE-compatable.

The original, low-power IEEE 802.3af PoE standard used two of the four pairs of wires in the Category 5 (Cat 5) cable to deliver up to 15.4 watts (W), while the latest PoE standard can deliver 30W over two pairs and even 60W when using all four pairs. The four-pair powering also helps maintain high levels of power efficiency thanks to the lower current levels used compared to two pairs. But perhaps one of the most exciting advancements in PoE for security professionals is the ability to expand the distance PDs can be placed from the data and power source with PoE extension technology.

The appeal of extending PoE

PoE extension is particularly important for security applications like access control and video surveillance where power is needed in hard-to-reach places. With Ethernet, each device must be installed 100 meters (m) between the switch (typically located in the communication room) and any device connected to it, such as an IP camera. Data integrity cannot be guaranteed beyond this distance. If an additional camera is needed to monitor a company’s parking lot, for example, the company would need to build another communication room or install a switch in every 100-meter segment, generating potentially expensive additional costs. But PoE extenders can help solve the distance dilemma.

PoE extender devices enable network administrators to deliver both data and power to network devices such as WLAN (wireless local area network) access points (AP) and network cameras at baseline distances of 200m, which is an additional 100m to the original Ethernet segment as defined by IEEE specifications (Fig. 1).

Extenders can also be cascaded to span even longer distances. If a daisy chain is used, in which multiple devices are wired together in sequence, power can be distributed even further, up to 500m. These flexible solutions can be installed wherever they’re needed—even difficult-to-reach walls and ceilings—to ensure they’re in the best place for their usage despite the presence of a nearby power outlet.

The most important advantage of a PoE extender over a PoE switch is that the PoE extender does not need local powering; it gets the power from the original PoE source (PoE switch or midspan). The extender will use small portion of the power and forward the remaining power to the PD. This feature enables the PoE extender to be small, as no internal AC-to-DC or DC-to-DC conversion is needed.

The extender output power is dependent upon the input power. If using the original PoE source of 802.3af (15.4) then the guaranteed power after 200m will be 802.3af class 2. If using the original PoE source of 802.3at (30W) then full 802.3af (15.4W) of power can be guaranteed after 200m. There are some new PoE extenders in the market that can accept 60W of power as input power, allowing full 802.3at power levels (30W) to be guaranteed after 200m. This solution is optimal to power 802.3at IP cameras or WLAN access points at a 200-meter distance from the Ethernet switch. An example of an end-to-end solution could be any Ethernet switch at the communication room connected to a single port 60W PoE midspan, with a PoE extender installed after 100m and the 802.3at IP camera/WLAN AP installed 100m further from the extender.

When four-pair powering is used with a PoE-powered extender that has the lowest possible power dissipation, less power is wasted regenerating data, which means more power reaches the other side of the connection. Additionally, the combination of PoE extenders with four-pair powering ensures that power can be transmitted at the higher, 60W IEEE802.3at levels across these same 200m distances, while supporting gigabit speeds that are necessary for HD network cameras, 802.11n WLAN access points and other PDs. This extends PoE’s benefits to devices such as outdoor IP cameras with motors and/or heaters, or access control systems (which, with a controller, reader and multiple door locks, can consume as much as 45W of power).

Four-pair powering with PoE extenders is also easier and less expensive to deploy than alternative approaches. It only takes one extender to reach 200m distances, compared to the two required with many solutions based on xDSL and optical technologies. In addition, there is no need for expensive, specialty optical and high-gauge copper cables.

The two major benefits of four-pair PoE are the ability to provide higher power while maintaining low current levels (60W of power in 600mA) and the improved energy efficiency over any two-pair PoE source. Four-pair PoE actually saves 50 percent of the power losses over the Ethernet cable regardless of the type of cable used.

Other benefits of PoE

Security personnel seeking the most cost-effective method of deploying PoE utilize midspans (a device used to combine power and data into a single cable) that are installed between an existing non-PoE switch and the network PDs. Midspans can significantly reduce power consumption and simplify maintenance with their unique capabilities such as remote PD monitoring and configuration. They also enable a more scalable network than is possible with switches that incorporate embedded PoE functionality. In addition, midspans enable network administrators to monitor per-port and total power consumption, and configure PDs for instant and scheduled port ON/OFF functions, as well as UPS (uninterruptible power supply) status port On/Off functions.

Midspans also play an important role in providing power backup. With PoE, all devices are supported using a centralized power architecture, and all are backed up. For example, a single UPS can be used to back up a PoE midspan serving 20 IP cameras on a network. Without the PoE midspan, 20 UPS systems would be necessary.

Security professionals can also use midspans to prioritize power to specific devices on the network. If a managed PoE midspan is used concurrently with a managed UPS, those PDs can communicate and enable security personnel to predefine the highest priority devices that should continue to operate when power fails. For example, security personnel can define that if the UPS battery level drops below 60 percent, the PoE midspan will turn off power to the WLAN APs while continuing to deliver power to the more crucial IP cameras.

Easy maintenance is another benefit of PoE. If a wireless LAN location must be in a high location and needs to be restarted, PoE eliminates the need for professionals to physically climb to the location to shutoff/restart it. With PoE, the access point can be reset remotely.

PoE technology also offers safer work environments than other power systems. Unlike AC outlets, which can potentially electrocute personnel working on the system, PoE provides very safe power. Power is only delivered when a valid device is identified as being PoE-enabled. Power is disengaged when the device is disconnected or a short circuit takes place, reducing the risk of any accidental harm to personnel.

Also of note is PoE’s recognition as the first international power standard. Electrical plugs and sockets differ by country in voltage and current rating, shape, size and type of connectors—with each country setting its own national standards. However, the PoE international standard allows manufacturers to avoid supplying different power supply for different countries and removes the need for PoE installers to worry about differing equipment and power cords. A PoE power source will provide the same power in any country or region, catering to the needs of today’s growing global market.

What’s next for PoE?

Experts have hailed PoE as the power technology of the future, with product designers and manufacturers expected to create broader product portfolios that can be powered by PoE. However, PoE’s future depends heavily on its ability to continue delivering increased levels of power. The next generation of PoE technology, expected to become available later this year, further boosts powering capabilities, with the ability to deliver 95W of power and extend PoE’s benefits to an even broader range of PDs and applications. As greater powering capabilities will undoubtedly increase the popularity of PoE by supporting new types of devices, as well as its eco-friendly benefits, it will continue to thrive as a viable technology for security professionals.

About the Author: Sani Ronen is director of marketing in Microsemi Corporation’s Analog Mixed Signal Group.