How fiber optic cabling combined with PoE converters allows long-distance IP camera placement

Power over Ethernet (PoE) technology enables powering IP surveillance cameras through the transfer of DC electrical power along with data over standard unshielded twisted pair (UTP) cabling. This cabling connects to a network device through an RJ-45 port that injects the power from power sourcing equipment such as a PoE switch or midspan PoE injector. PoE provides a flexible and convenient means of powering devices that are located in out-of-the-way locations, and saves money by eliminating the expense and difficulty of direct electrical wiring. A challenge with PoE is reaching remote locations outside the distance limitation of UTP cabling. According to the TIA/EIA 568-5-A standard for category 5e cable, the maximum length for a cable segment is 100 meters (328 ft), and PoE power injectors or midspans do not increase the distance of the data link.

So, how do you get beyond that 100-meter limit? Once answer is through fiber optics. Fiber optic cabling is an effective method to overcome the distance and bandwidth limitations of UTP, and media converters are a commonly used to integrate copper network equipment and fiber. Since DC power cannot be conducted over fiber, PoE media converters are the solution to extend network distances via fiber to remote IP cameras. A PoE media converter converts the fiber to copper, and sends DC power to the camera over the UTP cabling.

How PoE Media Converters Work
On the main article image/PoE schematic that appears at right, an Ethernet switch with RJ-45 ports resides in a control room or data closet. The copper UTP cabling is converted to fiber with a standard media converter. The fiber is run a long distance to the PoE media converter located near a convenient AC or DC power source, where it converts the fiber back to copper UTP. The PoE media converter also functions as a power-sourcing mini switch, and injects PoE (DC power) over the UTP cable. At the other end of the UTP cable is the IP camera, located up to 100 meters away from the PoE media converter.
PoE media converters are available with Gigabit Ethernet and Fast Ethernet data rates and can support PoE (15.4 watts) or PoE+ (25.5 watts). PoE media converters function like PoE mini-switches, and are available in a variety of multi-port configurations, including dual RJ-45 and dual fiber ports. They can support fixed fiber connectors or small form pluggable transceivers.
To understand those power specifications, it’s worth knowing that in 2003, the IEEE ratified the 802.3af PoE Standard. That standard provides up to 15.4 watts of power per port. Late in 2009, the IEEE ratified the 802.3at PoE Standard known as PoE+ that provides up to 25.5 watts of power for each port. PoE+ can be required to power IP cameras with Pan-Tilt-Zoom (PTZ) / Speed Dome Camera capabilities, and weather-hardened cameras used in cold environments that feature blowers and de-icers.

Leverage the Benefits of Fiber
There are several solutions available to extend the distances of PoE network links, including LAN extenders that convert Ethernet to DSL, UTP to coax converters and wireless technology. When you’re going long distance, however, fiber optic cabling provides several advantages over these technologies.
Unlike copper, fiber extends network distances up to 87 miles (140 kilometers) per link with no data deterioration over distance (signal deterioration is to be expected in copper cabling). LAN extenders can only extend network distances about 3,300 feet, but a data rate of 100 Mbps can drop by 70 percent at longer distances.
Fiber cabling provides security benefits as well. It is a secure medium that generates no electro-magnetic emission and is very difficult to tap. Fiber is also very reliable because it is not susceptible to electrical interference, or data loss due to temperature or atmospheric conditions.

Understanding Power over Ethernet for video surveillance

PoE was, and is, supposed to make the powering of devices easy. You take your camera or other device that accepts power via the Ethernet port, you plug in the RJ45 jack to the port, and you walk away. Inside the head end, you plug the other end of the same Ethernet cable into a PoE switch or PoE injector and voila, power is magically delivered to the device along with the data connection. In theory, all of the normal worries are gone. AC power or DC power is irrelevant, and you don't even have to worry about over-powering a camera that, were you to fry it, could potentially set you back a few thousand dollars in equipment costs and man hours!

PoE was supposed to be this way, but practical reality has diverged from the perfect world concept in such a way that the actual installation is almost never that easy. So set aside the “perfect world” notions you have, and let’s start with the basics, so you can understand how PoE works.

There are four classes of PoE: Class 1, 2, 3 and 0. Each PoE classification denotes a range of power that is available to the end device as well as the power that must be available on the port of the power sourcing equipment (PSE):

PoE Classifications

• Class 1 --  4.5 watts at PoE port; 3.84 watts at device
• Class 2 --  7.5 watts at PoE port; 6.49 watts at device
• Class 3 --  15.4 watts at PoE port; 12.95 watts at device
• Class 0 --  15.4 watts at PoE port; .44 to 12.95 watts at device

In the world of PoE there are two kinds of switches that can provide PoE; the kind that operates with a “guarantee per port” and the kind that operates with a “total power budget”. Both kinds of switching are useful but there is a significant difference between them. If you happen to have a switch nearby, look at it and see if you can tell into which one of the above two categories your switch falls.

A switch that guarantees a certain wattage per port -- 15.4 watts per port, for example -- means that you can be sure that no matter how many Class 3 or Class 0 devices are plugged in, the switch will be able to power them. Of course, these switches tend to be bigger, more expensive and ill-suited for use outside of a nice climate controlled room, but they do prevent errors in power planning.

The second type of switch mentioned above -- the kind with a total power budget -- can only power as many PoE devices as it has power to spare. Imagine that you are working with a 4-port switch that carries a total power budget of 30 watts. This kind of switch could power four Class 2 cameras (4 devices x 7.5 watts = 30 watts needed). It could also easily power four Class 1 devices (4 devices x 4.5 watts = 18 watts needed). Continuing with that math, it would be able to power Class 3 or Class 0 devices, but it could only power two of those types of devices.

Power planning is where the rubber meets the road, and it brings up a challenge in our industry.

What happens if a chosen device (i.e., a PoE powered camera) does not clearly specify the PoE class and instead simply gives an operating wattage? You might think that this is OK since a camera which says “6.01 watts” is within the Class 2 specifications and therefore must be Class 2. But that’s where reality often diverges from common sense. In theory, what is supposed to happen is that a device is clearly labeled with a PoE classification so that when said device is plugged into a PSE device, the power budget has been worked out such that each device will receive its required PoE.

What I believe the security industry needs – right now, since PoE is happening today -- is clear labeling of the correct classification of PoE on each and every device that uses PoE. It is all well and good to place the operating or maximum wattage on the device, but industry manufacturers need to take the next step!

Manufacturers should label the device, print it on in large type and with bold colors, CLASS 1, CLASS 2, CLASS 3, CLASS 0, or whatever PoE Plus will hold as a classification. It's OK if your device actually only draws 3 watts during normal operation but for some reason is Class 0. Just tell your integrator channel partners and end users by labeling the device in the manner in which it was intended to be used. This lets system designers know the classification so that they might properly create a power plan and buy the correct devices. No one wants to be in the field trying to get a project done on time and only then realize that their switches don’t have enough power for the devices they’ve purchased.

While I am solidly standing on my PoE soapbox, let me also make a plea for PoE classification to be a priority on data sheets and marketing slicks. Some camera manufacturers make wonderful versions of these spec sheets. You’ll find photos, technical illustrations, cross reference charts, and more -- and often not a hint of PoE classification to be found anywhere. As someone who works with PoE, it sometimes seems as though PoE has become the crazy uncle that everyone has and who no one wants to invite to the party. Unfortunately for all of us, the crazy uncle could actually be the life of the party -- he makes it easy to entertain the guests and always has enough cash to pay for pizza -- but we haven't managed to take advantage of him yet!

PoE is supposed to make things easy, and between the standards bodies, the independent PoE offerings, the lack of classification usage, the errors in PoE chip usage within devices, and the propensity of some manufacturers to create Class 0 signatures in devices that draw minimal wattage, PoE's original purpose has been obfuscated in a way only rivaled by the current explanation of the financial bailout.

Why has it become so complex? Who knows! Unfortunately it has, and confusion has also shared a taxi with a lack of education on the road to PoE's widespread acceptance. People see a label on a device that says “802.af” or “IEEE Compliant” and then automatically assume that they can plug it into a PoE switch or midpsan and have it work with no problem. What makes the education problem worse is that often it does work with no problem, and this leads people to the assumption that PoE is really nothing more than Windows “plug and play” for power. Unlike Windows, however, there is no “blue screen of death” when using PoE. Instead there is a device that does not power on, or (in rare cases) a device that does power on followed by smoke, the smell of singed chip boards and fried capacitors, and then what was a very expensive security device becomes an equally expensive paperweight.