|
Ask the Expert: What should I know about the new PoE standard? |
 |
 |
 |
|
Networking -
Editorials
|
|
Written by Robert Moore
|
|
Wednesday, 03 December 2008 11:50 |
 Indeed a new proposed standard, 802.3at, is expected to come out in 2009 and will be backward compatible with the 802.3af standard, which is about five years old. Essentially, both standards enable organizations to avoid using separate power cables in IP-based surveillance systems, but differ in the maximum power they permit.
Using PoE, organizations have the option of using their data
communication cable to supply power to network video components instead
of running a second cable to those devices.
The adoption of the PoE 802.3af standard has been very helpful in
accelerating market acceptance of IP-based solutions because it offers
two primary advantages for surveillance users.
First, PoE cuts installation cost, because by eliminating the necessity
of installing power cables, organizations can save up to several
hundred dollars per camera, depending on where the camera is deployed.
A PoE configuration also makes it easier to move a camera to a new
location, or add cameras to a video surveillance system, since only a
network drop is needed, which is normally available in buildings today.
Also, many heritage buildings are not easily wired to include
additional power so using PoE in older buildings is often necessary
when deploying security cameras.
In addition, PoE can power a device during a power outage, which
increases security protection. A video surveillance system installed
with PoE can be powered from the server room, and when using best IP
practices, it is always backed up with an uninterrupted power supply
(UPS). This ensures that the video surveillance system remains
operational even during a power outage when facility security is often
most vulnerable.Most power interruptions are of short duration so you
are likely to get closer to 100 per cent up time with this strategy.
If PoE is so beneficial, you might wonder why the new standard is
needed. Using the current standard, organizations can only power
devices at a maximum power of 13 watts (at the powered device after
factoring in normal power loss that occurs on a twisted pair cable). Of
the four pairs of twisted cables in typical CAT wiring, PoE can use
either the two dormant twisted pairs or overlay the current on the two
twisted pairs used for data transmission. As a rule, switches with
built-in PoE supply electricity via the same twisted pairs used for
data transmission, while midspans normally use the dormant twisted
pairs. A powered device such as a network camera supports both options.
Unfortunately, pan/tilt/zoom (PTZ) cameras exceed 13 watts, because
they draw additional power to control camera movement. And outdoor PTZ
cameras in Canada must also use built-in heater and blower units,
because of Canada’s cold winter temperatures. This means that up to
now, many organizations have been unable to take advantage of PoE
unless they are using fixed, indoor network cameras.
The IEEE is currently working to define a new standard — often referred
to as HiPoE, PoE+, or PoE Plus — that will support the needs of more
advance technologies.
The biggest 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 cables– a significant boost from the previous
standard. The IEEE has even discussed allowing more than 30 watts using
all four twisted pairs in a potential future revision of 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 will allow power source equipment to discover devices on the
network and communicate with those powered devices to enable dynamic
allocation of power levels and even place devices in sleep mode.
If you can’t 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 proprietary solutions consist of midspan and active
splitter technology added onto the existing network switches and
cameras, respectively. You will need to make sure to buy the midspan
and active splitter from the same manufacturer to ensure reliability.
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.
Using this approach, the data passes through without interruption and
the separate cable can power PTZ network cameras and associated
heater/blower units.
Some organizations have expressed confusion regarding when they may
need equipment supporting the current or future standard or an interim
solution. Consider the following:
If you have an existing interior installation of fixed network cameras
and wish to add only fixed cameras in the future, you need do nothing.
If you are using or will soon add interior PTZ network cameras or any
type of exterior camera — and you wish to take advantage of PoE
benefits — then you should consider one of the interim solutions on the
market.
Finally, for those that can wait until the new 802.at standard is
released next year, they’ll obtain good cost and time savings by
implementing PoE-compatible PTZ and outdoor surveillance equipment.
Robert Moore is the Canadian Country Manager for Axis Communications.
|
