One Cable Does it All

The new Power over Ethernet (PoE) technology lets networked devices like surveillance cameras and other security equipment receive power and communication over the same cable. How does it work? What are the benefits?

The ongoing development towards an all-IP world of communications has seen networked devices increasingly communicating via Ethernet. This trend is further fuelled by the arrival of the new Internet Protocol (IPv6) and the new Power over Ethernet (PoE) solution for sourcing electrical power over existing LAN infrastructure.
Networks and surveillance systems need fixed IP addresses in order to be “always connected, always on-line”. The number of available 32-bit addresses under the “old” protocol (IPv4) is, however, limited to 4 billion, whereas the 128-bit addressing field of IPv6 offers up to 35 trillion unique IP addresses – or 2,000 individual IP addresses for every man, woman and child on Earth. In other words,  quite a few surveillance cameras…

Digital revolution
In addition, IP-surveillance systems based on streaming digital video over Ethernet are rapidly replacing analog systems, since the technical development is constantly boosting the quality of digital media, while equipment prices are dropping. But networked devices need more than IP-based communication signals to do their job – they need electrical power as well. One solution that uses the same transportation channel to fulfill both needs is PoE, a technology for integrating data, voice and power over standard LAN infrastructure. Using PoE removes the requirement for a local power source at the location of a device, and it does not interfere with the overall network performance.
“PoE is a means to supply reliable, uninterrupted power to IP telephones, wireless LAN access points, network cameras and other Ethernet devices,” says Ron Vidano of ASSA ABLOY.

Cost-saving solution
Vidano points out that PoE is a potentially cost-saving solution, since it uses existing LAN cable infrastructure. “There is no rational basis for running any wires except power and CAT5 in a new building. PoE sources power from the same location as the Ethernet switch/hub.”Other benefits associated with the use of PoE, besides the reduced need for cabling (since only one cable is required), is that it facilitates installations of surveillance cameras and other security equipment in locations that might be hard to reach when you have to consider the need for AC power outlets.Getting rid of the need for power outlets may also bring more flexibility into designing a security system. When you don’t need to install a new power outlet to alter a camera’s position, it becomes easier to experiment with different angles for the most  coverage.

Injects power into cables
How does PoE work? The system contains two basic components: Power Supply Equipment (PSE) is the unit that injects power into the network cable, while the device being powered via the network is called Powered Device (PD). The latter can either have built-in functionality for PoE – like some network cameras already have – or use an external splitter to split network and power into two separate functions/cables and provide PoE functionality to products without built-in support. 

There are two types of PSE, depending on whether you’re adding PoE functionality to an existing network or constructing new premises or LANs. The unit used in the former case is often referred to as a Midspan, and is a standalone injector that adds power to a network cable. It is a patch-panel like device located between an ordinary Ethernet switch and the terminals. Power is added on the spare wires, without any data interruptions.

When starting fresh, you would install a so-called Endspan, which is a network switch with built-in PoE functionality in addition to switching functionality. Power is supplied directly from the data ports.

From access control to Gibson guitars
Vidano says there are many examples of security products that already utilize PoE: “Besides network cameras, it is used in devices for biometric access control, card access control and electronic keys.”
By allowing the convergence of video, data and power in any IP-based security application, PoE may be capable of revolutionizing the entire security area.
Biometric Identification, for example, is becoming widely used, since it offers the benefits of not having to carry keys or cards and helps prevent identity fraud. The most popular biometric method today is fingerprint identification.
Visitor Management means temporary visitors are tracked by issuing a temporary visitor badge (ID card), which grants specific access rights according to particular visitors. All visit information including the visitor, host and recorded access events are collected via a PoE-enabled network.While today, PoE is most frequently associated with two applications – IP telephony and 802.11 wireless networking –.tomorrow’s applications of PoE are only limited by the imagination of vendors and users, and new PoE-enabled devices are pouring onto the market daily. One of the more entertaining applications was announced recently, when the Gibson Guitar Corporation introduced a PoE-enabled electric guitar.

More power coming up
But how much power can you expect from a regular LAN cable? And is PoE really safe? Obviously, PoE does not grant you the opportunity to chuck all your power cords out the window. The IEEE802.3af PoE standardized solution (which was approved by the IEEE Standards Board in 2003) allows up to 15.4W of power to a device. That’s equal to telephony level power (48VDC).There are non-standard PoE-systems capable of providing higher power, but these are manufacturer specific.
Given the significant market demand for applications such as multiband wireless access points and controllable security cameras, however, the IEEE Standards Board has launched a project aimed at providing a new standard for powering devices up to 40W, called PoE Plus.This would allow PoE options for cell phones, laptops and a host of other devices. The project is scheduled for completion by 2008.

Damage prevention
What if you hook up a device that is not ready for PoE? Connecting a 48V supply to network devices such as laptops would most likely harm the unit (or, worse, the user). To counter this, there is a built-in check to prevent damage to any non-PoE devices that may be attached to the power sourcing equipment. The PSE does not apply power to a port until the connected device has been detected and verified as a PoE-enabled device. This is done automatically whenever a cable is connected to the port.The PSE does this with a technology called Resistive Power Discovery, in which the unit sends out two different short low voltage discovery signals (between 2.7V and 10.1V), with at least 2 ms in-between, to the PD. Once the device has been verified and classified, the unit will provide full power to the port.

Are there any limitations to PoE? Some network cameras come with extras that require more power than the solution can provide. A dome camera or a camera that is able to pan, tilt or zoom, for example, requires additional power for the motors. And wireless cameras obviously need to be powered locally.Moreover, cameras installed outdoors are frequently weather-protected by a housing, which is equipped with either a heater to remove condensation from the front glass or a fan to circulate air inside to avoid overheating. Both these devices require power beyond what the PSE may provide – at the moment. Upping the power capabilities of PoE is, however, on the technology roadmap. Finally, is PoE expensive? “The typical cost,” says Vidano, “is between US$ 60 and US$ 100 per installed port.”It looks as if a “cordless Nirvana” has just moved a little closer…

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