Power when you need it

It's a little black box packed with the power to run technology over Ethernet cabling. With multiple ports to support future needs, the midspan has the capability to power an array of devices from VoIP to motorized PTZ cameras. Powering devices over networks is experiencing tremendous growth due to the midspan's efficiency to deliver power and the industry's insatiable need to run it more effectively. Midspan manufacturers are eager to meet the industry demand for increased power often staying ahead of current standards with power supplied exceeding what is called for.

Power detection

With the introduction of VoIP the race was on to add and power additional technologies. Ethernet technology is where the capacity to safely power devices continues to change. The challenge of course was how to deliver this power without overloading the circuits.

"Before there were standards for power, the need for PoE dated back to 2000 for powered devices," explained Sani Ronen, senior product marketing manager for Microsemi PowerDsine Midspans, Irvine, Calif. Providing power safely according to the standards is done without it being live all the time. "The midspan detects if the device on the other side needs to get power-if the midspan notices the signature of a device then it delivers the power-the power is only delivered when needed," continued Ronen. If power is always being sent out over the lines there would be too much of it carried over the Internet cable, resulting in possible damage. Thus, the midspan device was developed to power up technology only when needed. This makes it safe and energy-efficient.

One of the greatest advantages of the midspan is the ability to take it out of the box, plug it in and begin using it. But there are other benefits as well.

"The most obvious is the midspan allows you to add power over Ethernet to a variety of applications: VoIP, wireless access points, security cameras, biometric devices-anything that can handle PoE without replacing switch infrastructure," said Jeff Snowden, sales manager, SEI Power, Frederick, Md. "As a result, there is a faster turnaround time, a faster install and it certainly is less expensive than doing a turnkey forklift replacement of your switches," he continued. The company offers a midspan product that allows users to add a battery pack without having to upgrade their UPS (uninterruptible power supply) systems.

Powering the midspan can also be accomplished through AC or DC power sources and this depends on the location of the peripherals and the cabling required. "The midspan is typically an AC powered device," Snowden added. However, SEI also makes a DC powered version which is helpful for data centers or other locations that have a DC plant or a DC UPS. "You can plug our DC version in and that DC power directly-at this point the midspan becomes an intelligent PoE compliant patch panel," said Snowden.

Select your cable wisely

Choosing the right cables is also important and based on the power standards, Category 5 is recommended, however, Category 3 can be used.

"Cat 5 is used because of the gauge of the wire-it delivers better quality and the high level of power being sent through it is best handled with Cat 5," Snowden explained. The recommended use, Snowden added, "Cat 5 is for data use while Cat 3 will handle telephony applications-traditional analog signals. The connection is not as clean or standardized and the gauge of the wire is different." Honeywell, Morris Township, N.J., recently announced the introduction of its Cat 6 line, further evidence that the industry is future-proofing for increased power delivery which will be necessary as products continue to evolve.

"The issue is, there are more devices that need more power," Ronen added. As part of the next working group to work on standards for increasing power, Ronen noted, "when you move to higher power, the current level on the cable is getting higher. The new standard will take up all four cable lines out of eight in order to keep the current low. Some vendors have already designed a four-pair PoE," he said. Many of these products will hit the market before the next standard is written, which is expected to be out within three years.

PoE Refresher Course

Power over Ethernet (PoE) technology is used to pass electrical power, along with data, over Ethernet networks. PoE requires Category 5 cable or higher for high power levels, but can operate with Category 3 cable for low power levels. Power can come from a supply within a PoE-enabled networking device such as an Ethernet switch or from a device built for "injecting" power into the Ethernet cabling called a midspan. The high power market is experiencing the highest growth in the PoE market, the total solution is in need of this power and beyond. Future PoE standards can be expected within three years. Ahead of these new standards, some vendors have already introduced higher power midspans to deliver more power to meet the future energy needs of new technology; while keeping power current levels low.

802.3af and 802.3at Standards

The IEEE 802.3af PoE standard ratified in June 2003 provides up to 15.4 W of DC power to each device. Only 12.95 W is assured to be available at the powered device as some of the power is dissipated in the cable. The IEEE 802.3at PoE standard, known also as PoE+ or PoE Plus, ratified September 2009, provides up to 25.5W of power up to 100 meters. Some manufacturers can supply up to 51W of power over a single cable by using all four pair of Cat 5 cable. Current and power are the differences between the two standards.

Technology Match Up
Midspan and endpoint devices are part of the new techno-jargon landscape but what is their practical relevance?

By Jonathan Sohnis

Some clarification is in order here. PoE power supplies come in two basic flavors, midspan and endspan (also known as endpoint). Both will inject managed power onto the Cat 5. In a typical IP surveillance network a camera communicates with a video IP server through a network switch. A midspan is placed between the switch and the camera, passing through its video data and injecting power, whereas an endspan incorporates the switch in the same enclosure.

A common question is: why not just use an endspan device? It is not quite as simple as it may seem and there are benefits to applying each. Both midspan and endpoint devices enable PoE capabilities using IP camera infrastructure, but most video systems incorporate IP cameras that are not PoE-compliant and require separate power sources. The combination of a midspan device and a switch provide optimum flexibility to support PoE cameras using products like Altronix's NetWay midspan solutions, while also managing non-compliant PoE IP cameras directly from the switch. The NetWay midspan solution also includes provisions for PTZ and IR cameras that require more power than conventional IP cameras and provide security professionals with the flexibility to specify different cameras for specific surveillance applications within the same system.

Another advantage of this configuration is that network switches are low-cost commodities that can be replaced or upgraded separately without affecting the midspan device, making the use of a midspan and switch combination more economical. Finally, an endpoint switch's aggregate power may not be sufficient to provide the power required for maximum usage on all ports simultaneously.

This is not an issue using a midspan device like Altronix's NetWay which has been designed to deliver maximum output power on all of its ports.

- Jonathan Sohnis is the chief technology officer for Altronix Corporation, based in Brooklyn, N.Y.