Eye on Video: Power over Ethernet for network video surveillance

Plus a look at the newly proposed 802.3at PoE standard

While the 802.3af standard has provided numerous benefits, after more than five years on the market, its limitations are becoming evident. Foremost of these is its limited power per port because the wattage is insufficient for some surveillance equipment. For the network video market that means that most outdoor cameras - which require additional power to run the built-in heaters and fans - as well as pan/tilt/zoom (PTZ) cameras - which draw additional power to control camera movement - have not been able to capitalize on the advantages of PoE.

802.3at: the proposed new standard for PoE

The IEEE has been listening to concerns expressed by the PoE user community and is currently working to define a new standard - often referred to as HiPoE, PoE+, or PoE Plus - that will support the needs of more advanced technologies.

The foremost difference from the current standard is the proposed near-doubling of power that can be distributed over the network to enable devices that require more current to benefit from PoE. In particular, the new 802.3at specifications call for delivering 30 watts of power via two twisted pairs - a significant boost from the previous standard. Even going beyond 30 watts using all four twisted pairs has been discussed as a potential future revision on the new standard.

Some of the other proposed improvements include backwards compatibility with 802.3af devices. 802.3at also proposes embedding intelligence via a newly defined data link layer (layer 2) protocol. This Link Layer Discovery Protocol (LLDP) will allow the power source equipment to discover devices on the network and communicate with those powered devices to enable dynamic allocation of power levels and even putting a device in sleep mode.

Interim solutions for high-power devices

If you cannot wait for next year's ratification of a new standard, several vendors currently offer a few options that can provide an interim solution to your power needs. Many of these solutions consist of midspan and splitter technology added onto the existing network switches and cameras respectively.

The midspan, which adds power to an Ethernet cable, is placed between a network switch and powered devices. Midspans often have 1, 6, 12, 24 or 48 ports. The splitter splits the power and data in an Ethernet cable into two separate cables, which can then be connected to a device that has no built-in support for PoE.

Projected impact of 802.3at

With ratification expected in 2009, analysts believe that the new 802.3at standard, like its predecessor, will further accelerate the adoption of network video by including substantial savings for PTZ and outdoor camera installations.

802.3af Powered Device Classifications


Power range

Typical device

Class 0

0.44 W to 12.95 W

Any device that does not advertise its class

Class 1

0.44W to 3.84 W

Network cameras

Class 2

3.84 W to 6.49 W

Network cameras, encoders, VoIP phones, access control readers, RFID, small wireless access points

Class 3

6.49 W to 12.95 W

Network cameras, VoIP phones, access control readers, RFID, wireless access points,
video phones

Class 4

Reserved for future use

About the author: Fredrik Nilsson is general manager of Axis Communications, a provider of IP-based network video solutions that include network cameras and video encoders for remote monitoring and security surveillance.

This article also appears in the January 2009 issue of Security Technology Executive magazine