Extending Power-over–Ethernet technology for security

PoE solutions reduce power consumption, simplify installation of security devices


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.