Overcoming network distance limitations to PoE cameras

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.

PoE Media Converters

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.

Network Architecture Options with PoE Media Converters
Multi-port PoE media converters enable a variety of flexible network designs. Typically, they feature single or dual RJ-45 ports to power one or two IP cameras per converter, and single or dual fiber ports.

PoE media converters with a single fiber port are deployed in a point-to-point, network star topology (see following image). In the following application example, IP cameras are installed throughout a facility. Fiber is distributed from a fiber switch (this can also be a copper switch and media converters). The fiber links connect to distant locations where PoE media converters are installed near AC or DC power sources. The PoE media converters convert the fiber to copper and inject PoE over the UTP cabling to the IP cameras.

Dedicated fiber links to PoE media converters

PoE media converters with dual fiber ports support three types of network architectures: linear daisy chain, ring, and redundant.

The first architecture supports linking multiple PoE media converters in a linear daisy chain configuration (also known as a bus architecture) with a fiber uplink port and a fiber downlink port. This architecture can be used in a variety of applications where IP cameras are installed along railroad or subway lines, highways, perimeter fences, pipelines, etc. The advantage of daisy chaining is that it conserves fiber strands, but multiple devices can add potential points of failure, so daisy chains may not be the best design for mission-critical security applications. This is what a daisy chain design might look like:

Daisy chain network architecture using fiber optic and PoE

The second architecture enables linking multiple PoE media converters in a ring (see image below). The fiber switch shown in this diagram supports Spanning Tree Protocol, which enables a resilient ring architecture. The advantage of a ring architecture is that in the event of a link failure, the fiber switch reroutes the traffic in the opposite direction on the ring.

Ring type architecture using fiber optic to connect to IP video surveillance cameras

The third architecture enabled by dual fiber ports is redundant fiber links for applications requiring fiber facility protection. There is an active fiber port, and a protection fiber port that can support a fiber failure switchover of less than 50 milliseconds.

Redundant fiber connections with fail-over

In this application, redundant fiber is used for a mission-critical link to a PTZ IP camera that requires PoE+. The PoE+ media converter has one fiber port for the active fiber link, and one port for the protection fiber link, with fiber failure switchover of less than 50 milliseconds. The PoE+ media converter supplies power to the camera, and has power protection from an uninterruptible power supply (UPS) battery back-up. In the event of a fiber cut and a loss of power, the camera continues to send data on the protection link.

PoE media converters provide a flexible and cost-effective solution to power PoE-driven IP cameras, and overcome the distance limitations of copper UTP network cabling. They combine the benefits of PoE and fiber in a compact and reliable device that supports PoE+ for the higher power requirements of today’s sophisticated security and surveillance cameras.

About the author: Ty Estes is the marketing communications director for Omnitron Systems. Omnitron is based in Irvine, California, and is a leading manufacturer of fiber connectivity solutions, including PoE and PoE+ media converters.

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