Simplifying the Complexity of IP Video
Every part of an IP system interacts with all system components, affecting its quality and performance. Understanding bandwidth restrictions and shared power requirements is critical when deploying a successful IP video security system.
VideoIQ's video analytics are configurable to define the regions and select the rules. Alarms are sent when the perimeter is crossed, along with a video clip of the event.
Power Between Ports
IP cameras are typically connected to network switches. In addition to switching signals to a common network source, more of these switches have the added ability to provide power in the form of PoE. The ability to provide camera power in the same cable that carries signals results in significant installation cost savings and eliminates the need for local power sources. A total system price can potentially be reduced by as much as 60 percent in labor costs.[IMAGE]Ss12ip2.jpg[/IMAGE]
As a standard, PoE is defined under the Institute of Electrical and Electronics Engineers (IEEE) 802.3af. This standard breaks down power provided at Ethernet ports into four different power device classifications. These classifications define the power that is available at the device. As PoE operates over an Ethernet connection, it is defined by the Ethernet cable limitations of 328 feet. This means the power at the power source is higher, usually around 15.4 watts.
What the 802.3af specification doesn’t tell you is just as important as what it does. The specification has no requirements regarding how many ports must provide power or how many can provide power shared between ports. Therefore, if one port complies with the 802.3af specification and shares power with another port, thus reducing the power to each port, it could be considered as a PoE switch. Therefore, one port at 15.4 watts can result in 7.5 watts in two shared ports, with further reductions as additional ports are powered. This power sharing can be critical to your operation.
Maximizing Your Power
Most security operations, and specifically video surveillance, require the maximum power ratings under 802.3af. Even access control systems using power devices at the door require close to the maximum power rating when taken at complete system (see chart).
|
PoE 802.3f Power Rating Specifications |
|
|
Power Device at the Door |
Required Power |
|
Door Interface Module (DIM) |
2.4 watts |
|
Reader |
3 watts |
|
Lock |
6 watts |
|
Request to Exit (REX) |
1 watts |
|
Total required power |
12.4 watts |
Stationary cameras used in outdoor applications can comply with PoE 802.3af even under sharing conditions when power requirements are kept under 7 watts. However, if you add a heater, which is required for outdoor operations in most parts of the United States, the power requirement can easily rise to more than 20 watts, thus exceeding that provided under 802.3af.
The same is true of IP-based pan/tilt/zoom (p/t/z) domes. There are two factors to consider, with the first being outdoor use that requires powering fans and heaters. The second is dome speed that is based on the power provided. Standard 802.3af can provide enough power to rotate a dome, providing that the distributed power is restricted to powering the camera and rotating the dome at slow to medium speeds. Combine rotation with fans, heaters and high-speed rotation, and you easily will require 20-plus watts – once again greater than that provided by 802.3af.
Higher Standards in PoE Plus
For the growing demands of network users in general, network manufacturers are developing a PoE standard commonly referred to as PoE Plus. Many chip manufacturers have already released their PoE Plus versions. This specification adds a fifth Class Signature raising the available power to 25.5 watts to meet most video and access control requirements. There is still discussion about raising this figure; however, at higher power levels there are additional environmental concerns.
Like its 802.3af counterpart, the new PoE Plus standard does not account for how many ports in a switch are actually powered or what happens under power sharing conditions. Another consideration of using PoE Plus is the requirement for Cat-5 wiring instead of Cat-3 as the additional power requires two four-wire cables.
A simple Google search will display hundreds of network switches in a low price range; however, dig deeper and you will find these types of switches do not meet system requirements. The first thing to look for is how many ports actually provide full power with no power sharing. In likelihood, it will be less than the total number of ports available on the switch.
Next, consider your real power requirements. With PoE limited to only powering the camera and not the heater or full speed dome rotation, you still need a local power supply. The need to fully power current video and access control equipment requires PoE Plus.
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