The Power of Power Over Ethernet

April 02, 2020

The Power of Power Over Ethernet

Published in Military Embedded Systems

For integrators of deployed aerospace and military platforms, size, weight, and power (SWaP) is always at a premium. The use of smaller and lighter equipment enables more electronics payloads to be integrated, while the use of SWaP-optimized subsystems enables platforms to be more energy-efficient, to go farther and/or faster. While this is true for virtually all military vehicles, it’s especially true for unmanned air, surface, ground, and undersea drones, for which every additional ounce can potentially limit mission distance or duration. One enabler for SWaP optimization is Power Over Ethernet (PoE), which simplifies cabling and power needs for networked cameras, phones, and other IP [Internet Protocol] devices.

When introduced by the IEEE 802.3 Working Group in 1999, PoE enabled power sourcing equipment (PSE) such as a network switch to provide DC current to a powered device (PD), using the unused twisted pairs in traditional Ethernet cable that were not being used for 10BASE-T or 100BASE-TX operation. The PoE standard sought to address safety considerations and eliminate the risk of power injection unintentionally damaging a device.

By 2003, the IEEE 802.3 Working Group had ratified IEEE 802.3af for what it called Type 1 PoE devices. Under this standard, power is transported on the same wire pairs, or spare wire pairs, as the data for 10 and 100 Mbit/s Ethernet variants. Because twisted-pair Ethernet uses differential signaling, this configuration does not interfere with data transmission.

The original PoE standard allowed for PSE to source up to 15.4 watts and deliver as much as 12.95 watts per port to PDs. While 12.95 watts may not seem like a lot of power, it was sufficient for many popular PDs, including Voice over IP (VoIP) phones, stationary cameras, and door access-control units. However, it wasn’t long before some industries demanded even more power per port.

More power needed

The IEEE 802.3 Working Group responded in 2009 by adopting a new standard, which nearly doubled the available power output. The IEEE 802.3a standard for Type 2 devices was called PoE-Plus (or PoE+) and enabled PDs to source up to 30 watts and deliver at least 25.5 watts per port. This standard enabled expanded device usage with wireless access points (WAPs) and motorized security cameras with pan-tilt-zoom (PTZ) capabilities.

Not surprisingly, it wasn’t long before even more PoE power was desired to support even more applications. In 2018, the new IEEE 802.3bt standard, known as 4-Pair Power Over Ethernet (4PPoE), rolled out to support Type 3 (60 watt) and Type 4 (90 watt) devices for applications such as industrial lighting, door access systems, video phones, and thin-client computers. 4PPoE uses all four twisted pairs of an Ethernet cable to transmit power for GbE or faster, with support for 2.5GBASE-T, 5GBASE-T and 10GBASE-T also included.

The beauty of PoE is that it eliminates the need for separate power supplies and cabling for each end device. PoE can also provide some additional device-management capabilities, since device power can be monitored and controlled over the network. PoE is also seen to reduce wiring costs, since the same traditional CAT5/5E/6 cabling that may already be installed for network use can now also be used to power IP endpoint devices, reducing the cost of infrastructure or installation labor.

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