IP surveillance with Power over Ethernet

An increasing number of businesses, school districts and healthcare facilities are delving into Smart Ethernet switches with Power-over-Ethernet (PoE) technology—and reaping big benefits for their IP Surveillance networks. Power over Ethernet technology describes a system to pass electrical power over Ethernet cabling, along with data. This means that a network device can be powered and operated using the same cable as for network connection, eliminating the need for power outlets close to an IP camera, for example. However, in order to save money on installation and increase the security level by using PoE, it's important to keep certain key points in mind when dealing with the technology. This article will guide you through equipment and standards within PoE that will help you succeed in the field.

Power over Ethernet, or PoE, is not a new technology and it's already widely utilised in networking, for example in IP phones, wireless AP's and IP cameras. The first successful design and implementation of a proprietary PoE system was accomplished by Cisco in the year 2000. Their technique of putting 48V DC power on the LAN data cable along with the data traffic helped them overcome their customer's objections to wall adapter powering – and in the end also helped them to sell a lot of VoIP phone systems.

The PoE scheme

In a PoE scheme, two different types of devices are involved: power sourcing equipment (PSE) and powered devices (PD). A PD is a PoE enabled network end device, such as an IP security camera, equipped to accept low voltage power transmitted over Ethernet cabling.

A PSE on the other hand, is a device that provides ("sources") power to the Ethernet cable. Power is supplied in common mode over two or more of the differential pairs of wires found in Ethernet cables and comes from a power supply such as an Ethernet switch. There are two types of PSEs which can add PoE to your network: endspans and midspans. Endspans are Ethernet switches that include the power over Ethernet transmission circuitry and are commonly called PoE switches. Midspans are power injectors that stand between a regular Ethernet switch and the powered device, injecting power without affecting the data.

IEEE standards In June 2003, the IEEE working group released the ratified IEEE 802.3af PoE standard. It provides up to 15.4W of DC power (minimum 44V DC and 350mA) to each powered device. The maximum current of IEEE 802.3af is 360mA. The output voltage range of IEEE 802.3af is from 44V DC to 57V DC.

In 2010, IEEE ratified a new PoE standard, 802.3at, which provides 30W of DC power to the PD. The maximum current of IEEE802.3at is 600mA. The output voltage range varies from 50V DC to 57V DC. The IEEE 802.3at standard is also known as PoE+ or PoE plus.

The four PoE phases Every PSE is responsible for managing four basic aspects (or phases) of PoE:

1. PD detection
2. PD classification
3. Power-up
4. Power-removal

PD detection and PD classification are carried out through complex signaling protocols which make sure that power is delivered to the PD according to the classification. It prevents powering when no PD is connected and assures prompt power removal when a PD is disconnected. The protocols also maintain a stable DC current flow at all voltage levels. A PoE enabled PSE provides a low power signaling mechanism that constantly monitors for a 802.3 powered device (PD) to appear at the end of the LAN cable. If a non-powered network device is connected, the PSE can function just as a non-PoE and perform an "ordinary" link to the networked device. However, if an 802.3 PD is connected, the PSE will quickly recognise this and begin the process of powering it up.

Cables The IEEE standard for PoE requires Category 5 cable (CAT-5) or higher for high power levels, but can operate with Category 3 cable for low power levels. But still, even high quality outdoor Category 5 cable (CAT-5) is much cheaper than USB repeaters or AC wire.

Fault protection To minimize the possibility of damage to equipment in the event of a malfunction, the more sophisticated PoE systems employ fault protection. This feature is good to have and shuts off the power supply if excessive current or a short circuit is detected.

UPS PoE can increase your security level through a so called central UPS (Uninterrupted Power Supply) in the monitor room or central control room where the PoE Ethernet switch is located.

In case of a power outage, critical networking devices will become inoperable unless they are protected by a UPS with battery backup. Having the networked equipment distributed throughout your building or campus requires the distribution of several UPS systems. With PoE, a single, centrally managed UPS can be used to supply backup power to your PSE equipment. All the distributed PD networking devices can then receive battery-backed power even in power outages.

Centrally managed power also enables remote shutdown or remote reset capabilities. Through managing a PoE-enabled LAN switch via a web browser or by SNMP, remote networking devices can be easily reset or shut down saving the time and expense of dispatching a technician.

PSE Conformance Test is important despite the various requirements described for PD detection signaling in the 802.3 specification, there is considerable room for design variation. In practice, detection pulses and detection measurement schemes do vary significantly across PSE interface technologies. The 802.3at specification leaves considerable room for implementation dependent behaviours. Additionally, many vendors of PSE will choose to go outside the 802.3 specification in ways that will affect the ability to power and maintain pure 802.3at PDs. This high degree of variation adds a number of PoE compatibility issues, such as problems with voltage levels.

PoE challenges design and test engineers a great deal. Evaluating the quality of a PSE comes down to having to work with "smart" multi-channel DC power sources that are activated and deactivated through signalling protocols operating over several power delivery and polarity configurations. The application and management of DC power over multiple local area network connections must be completely transparent, safe, non-destructive, and non-disruptive to the traditional data transmission behaviours of those network connections and associated network equipment.

for example, has over ten years of PoE Ethernet switches design experience, and in the quality assurance lab every PSE needs to pass the PSE Conformance Test Suite offered by Sifos Technologies. The test suite for 802.3at produces up to 115 test parameters depending upon PSE capabilities. These parameters are measured in 23 distinct tests that cover over 95 percent of the PSE PICS (conformance check list items) in the IEEE 802.3at specification. The test is widely used throughout the networking community as the industry "norm" for PSE specification compliance.

Due to the fast pace of this sector, with most equipment having a realistic lifespan of around five years, it is most important to buy a fully qualified system. If you buy equipment which is not fully conformant to IEEE 802.3at or IEEE 802.3af, you might end up having to deal with a real nightmare in the future.

A few of the advantages with PoE

• Equipment can be placed in the most optimal location instead of choosing one where power is available.
• Network installations can be accomplished cheaper, easier and faster.
• Network changes, such as adding, removing or moving something, can be made much easier.
• Using a PoE infrastructure enables centralised power management capabilities for critical network devices.
• PoE can be used in security applications where USB or AC power is unsuitable, inconvenient or too expensive to use.

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.