The Continuing Evolution of PoE

Most equipment manufacturers’ offerings now include models that offer PoE capability, which has essentially become the primary means of powering video systems today. This is largely due to the ability to provide power and transmission for any IP device over a single cable and eliminating the need to install separate power cables, which significantly reduces costs.

As new IP-powered devices are developed, network power and transmission manufacturers continue to design and develop products that supply the increased power requirements and meet some of the challenges these devices pose, says Skip Haight of ComNet.

“The challenge now is the ever-increasing requirement for more delivered power. The first standard, IEE 802.3af was for 15 watts, IEEE802.3at or PoE+ was for 30 watts and now IEEE802.3bt 4PPoE or UPOE is for 60 watts,” Haight says. “As these PDs require more power for the use of PTZ and heaters, more power must be supplied.”

The 8 Most Common Causes of Video Loss & How To Avoid Them

According to John Nave, design center engineer for Danbury, Conn.-based Communication Networks (ComNet), there are eight general categories into which nearly every reason for video loss can be grouped: user error, intentional or malicious actions, equipment failure, cabling issues, power and grounding issues, electromagnetic interference (EMI), compatibility issues and improper system design.

To help integrators avoid these common causes and ensure the most reliable video systems for their customers, Nave offers the following solutions.

User error: While it may not eliminate the issue, a well-designed system along with well-written user instructions and good training can minimize user error. Instructions should include easy-to-understand parameters including system limitations, capacities and capabilities.

Intentional or malicious actions: Video systems are mainly used for security and surveillance or for automation and process control. While use of video systems for automation and process control is generally welcomed, electronic security and surveillance may not always be viewed in the same way. Because these systems are almost always performing functions that had been or that could have been performed by people, they may not always be as welcomed by labor unions or workers whose jobs may be impacted. Tamper switches and enclosures or areas with access control and secondary monitoring systems may need to be considered depending on the level of concern.

Equipment failure: Any device — whether active or passive — can and likely will fail at some time in its useful lifetime. This can be caused by a component failure, influences in the environment (such as temperature extremes, excessive moisture, dirty power, accidental contact with high voltage including lightning, etc.) or due to malicious activity.

Selecting high-quality, well-designed product is the best defense against premature component failure. Whenever possible, specify products from a recognized company with a strong track record of service, support and reliability. Proper system design, discussed below, can help minimize losses from environmental influences.

Cabling issues: At least in part, every electronic communications system uses copper-based and/or optical fiber-based cabling. Even wireless systems use cables, if only to connect short distances between supporting devices. All cabling should be strictly specified as to pinout, composition, number of strands or conductors, shielding or lack of a metallic shield, maximum allowable lengths, etc. Defining the proper environmental rating of the jacket warrants the most attention.

Copper cabling or optical fiber cabling can be purchased as factory terminated and tested or it can be self-terminated and tested. Whether factory terminated or self-terminated, it is highly recommended that installers carry the proper cable test equipment to confirm cable parameters or to rule out cable issues.

Each and every optical fiber should be tested. Optical loss testing should be performed end-to-end and as optical loss is directional, should be performed in each direction at the wavelength(s) that will be used. For example, a good report would show the following four results when testing at 1310 nm and at 1550 nm. The losses in dB shown in the example below are for illustration only as they will vary depending on the actual fiber path. To cross-check results, use the following conservative parameters:

• Loss per 1,000 ft. of multimode fiber @ 850 nm = 1 dB
• Loss per 1,000 ft. of multimode fiber @ 1,300 nm = 0.5 dB
• Loss per 1,000 ft. of single-mode fiber @ 1,310 nm = 0.2 dB
• Loss per 1,000 ft. of single-mode fiber @ 1,550 nm = 0.1 dB
• Loss per mated connector pair = 0.75 dB

For example, testing a single-mode fiber at 4,000 ft. in length with one connector-to-connector coupling in the fiber path:

Cable 1, fiber 1:

• Calculated end-to-end loss @ 1,310 nm reading should be 0.2 dB x 4 + 0.75 dB = 1.6 dB, max.
• Calculated end-to-end loss @ 1,550 nm reading should be 0.1 dB x 4 + 0.75 dB = 1.2 dB, max.

Testing at 1,310 nm:

• Cable 1, fiber 1. From Point “A” to Point “B”. End-to-end optical loss = 1.4 dB @ 1310 nm.
• Cable 1, fiber 1. From Point “B” to Point “A”. End-to-end optical loss = 1.5 dB @ 1310 nm.

Testing the same fiber at 1,550 nm:

• Cable 1, fiber 1. From Point “A” to Point “B”. End-to-end optical loss = 1.0 dB @ 1550 nm.
• Cable 1, fiber 1. From Point “B” to Point “A”. End-to-end optical loss = 1.2 dB @ 1550 nm.

Continue on to Cable 1, fiber 2, etc.

Similar testing can be performed on copper-based cables to measure simple continuity, frequency response or to detect ground faults, for example.

Type and number of connection points should be specified, as well. Too many connection points can yield a system that is unreliable, intermittent or unusable. For example, an optical fiber path should not contain more than two connector-to-connector couplings. The air gaps introduced by such couplings become the issue. Mechanical splices or fusion splices eliminate the air gap and should be used as alternatives. Similar parameters exist for copper-based systems as well.

Power and grounding issues: Frequently overlooked, possibly because of perceived simplicity, providing proper power and proper grounding to an electronic communication system deserves much attention during system design or troubleshooting. Power problems can result from improper power (the wrong type or level of power), dirty power (spikes, noise, etc.) or unreliable access to a constant source of power. Grounding issues can result in potentially damaging ground loops; lack of a proper signal ground can prevent operation altogether.

Any electronic device wants to consume a constant amount of power. If the proper amount of voltage is not available for a device, it will respond by altering the amount of current that it will draw in an attempt to maintain constant power consumption. It goes without saying that providing too much voltage to a device will damage it. Similarly, and usually not quite as dramatically, providing too little voltage can damage an electronic device as well.

A device receiving too little voltage will respond by attempting to draw more current if it is available. Depending on the severity of the deficiency, this could result in damage to the electronic device over the long term. Use of an uninterruptable power supply (UPS) often misleads users to believe that their electronic devices are being properly powered and protected. Not infrequently, the opposite can be true. A well-designed UPS will provide the proper amount of voltage in the form of a smooth AC sinusoid. A UPS that allows an under-voltage condition and/or AC sinusoids that are not clean can actually allow damage to the connected electronic device(s) to occur in the long term.

Grounding issues are simple to design on paper but can be quite complex to implement or troubleshoot. Electronic devices use a ground reference for power as well as for signal. The ground also serves as a means of protecting these devices by draining noise or potentially damaging current away from the devices. Protective grounds should ideally have a zero Ohm short to a solid earth ground achieved by a proper copper cable. Power and signal ground connections could be more complicated because they can be needed in more than one location in an electronic communications system. The danger is that ground references at physically diverse locations may differ and whenever the ground potential is different between any two locations, current will flow. This current is called a ground loop and depending on the severity, can cause communications problems, prevent communications altogether or damage the equipment. Follow grounding code and best practices and use ground loop isolators as needed.

Electromagnetic interference (EMI): Sources of EMI may be difficult to control, especially if the source is from a neighboring location not directly controlled or owned by the video system user. For example, an adjacent property may contain a microwave communication system, a RADAR system or some other source of high-level EMI. A business can use a microwave system as a back up to their primary Internet link, and a nearby airport or shipping port will use RADAR. Hospitals and schools could have equipment that generates high levels of EMI. Physical separation, shielding and use of ferrite rings in power and signal cabling are the best defenses from EMI.

Compatibility issues: When electronic communications systems are designed, it is typical for system components to be sourced from multiple manufacturers. When mixing devices from different sources that must communicate with each other, proper selection and integration of components warrants attention to detail. In addition to making sure that signal types, levels and impedances match, compliance with standards must be considered.

For example, PoE is almost ubiquitous and while standards do exist, not all PoE devices comply with the standards. For PoE, the IEEE has created the 802.3af (prior to 2009) and the newer 802.3at standard (since 2009) that defines power levels and signaling between PoE devices. The device that produces the PoE — the Power Sourcing Equipment (PSE) — and the device that requests and ultimately will use the PoE — the Powered Device (PD) — must both comply with the same IEEE PoE standards.

Improper system design: Probably the single greatest impact on system function and long-term reliability is proper system design. Failures, errors or omissions during system design — unless caught before being implemented — can have consequences that range from mild inconvenience to system failure and economic losses. Most issues have been covered in the items previously discussed but should be addressed during system design. In summary, they include controlling access to sensitive system components to minimize the chance of malicious activity; selecting good quality, reliable sources for equipment and cabling; specifying proper testing for cables and equipment; considering power, grounding, and potential EMI issues; confirming compatibility and proper integration between system components; confirming compliance with industry standards; and always specifying best practices.