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 (view a larger version here), 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.
Representative examples of PoE media converters (image courtesy Omnitron)
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) 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.