Understanding PoE: power over Ethernet
Power over Ethernet has become one of those checklist items many enterprises rely on to bring electricity over existing data cables to Wi-Fi access points, firewalls, IP phones and other infrastructure throughout their networks.
PoE’s use has grown substantially since the IEEE standardised it in 2003, and its use will only increase in the coming years as new applications develop. In fact, the Dell’Oro group says that PoE port shipments will total over 624 million over the next five years.
“There are a number of drivers for the current PoE technology. For example, if you look at WLAN [wireless LAN] access points, you have increased number of [wireless-spectrum] bands and higher speeds which require higher power,” said Sameh Boujelbene, senior research director for Ethernet Switch market research at Dell’Oro. “The new generation of IP phones is adding telepresence features. If you look at surveillance cameras, you have zooming features, you have added analytics. All these new features require higher power.”
What is Power over Ethernet?
PoE is the delivery of electrical power to networked devices over the same data cabling that connects them to the LAN. This simplifies the devices themselves by eliminating the need for an electric plug and power converter, and makes it unnecessary to have separate AC electric wiring and sockets installed near each device.
In the case replacing legacy phone systems with of IP phones, the need for separate dedicated DC power cables is eliminated. When networks are expanded or reconfigured, so long as data cable is pulled to the devices, they will have power.
The original IEEE PoE standard (802.3af-2003) specifies how to deliver up to 15.4W of DC power per switch port to each device at up to 33 feet over Category 3, 5, 5e and 6 Ethernet cables. The standard sets 15.4W as the maximum but provides for only 12.95W to reach the devices because power is dissipated within the cable over distance. That loss doesn’t affect network performance of 10/100/1000Mbps Ethernet links to the devices.
Over time newer devices required more power, so a new standard, PoE+ (IEEE 802.3at), was created in 2009, bumping the maximum power to 30W with 25.5W reaching devices.
The latest standard, 802.3bt, pushes the maximum power from the source switch to 90W, with 71.3W available to devices. It is expected to be the last PoE standard, according to David Tremblay, Ethernet Alliance PoE Subcommittee chair and system architect, at Aruba Networks an HPE company.
Benefits
The driving ideas behind PoE were to eliminate the need for electrical outlet installation, especially in remote or hard to reach locations. PoE also promised to:
- Reduce deployment costs up to $1,000 per device.
- Reduce the need for AC power adaptors.
- Simplify installation by letting customers employ a single Cat5/5e/6 cable for both data and power.
- Offer customers centralised power backup and management.
- Make it possible to repurpose copper from legacy phone networks.
- Enable moving PoE devices without the network seeing any down time.
“Energy saving is a big part of PoE in particular, but the standard is really focused on energy efficiency as it uses all 4 pairs of [wires in] Ethernet Cat 5 cabling whereas previous versions of the standard used two,” Tremblay said.
The latest standard maintains a power-signature level that supports lighting or IoT applications to be powered with PoE and have acceptable standby performance when needed.
Another benefit, Tremblay said, is that PoE in combination with analytics software can let facilities-management teams determine what areas of buildings are unoccupied and save electricity by remotely turning off lights and HVAC devices.
An important and growing benefit of PoE is in deploying Wi-Fi access points. These devices are often placed in locations where it would be difficult to extend traditional electric lines, such as behind ceiling panels, Boujelbene said.
The growth of wireless in buildings, offices and places like sports arenas fuels the need for PoE, Tremblay said. “PoE makes wireless rollouts so much more tangible.”
PoE and IoT
Using PoE in wireless rollouts may be the technology’s primary application but many think it will find a home in the internet of things where wired IoT devices can receive power from their network connection.
Versa technology wrote a blog about the use of PoE and IoT by the city of San Diego, which is using Ethernet cabling to deliver power to thousands of interconnected LED streetlights, which are integrated into the city’s IoT network. Power to the smart lamps can be turned up and down to optimise illumination for each space.
Such lighting systems have low power requirements, making them cheaper to use. The PoE streetlights are integrated with the city’s IoT network, which makes it possible to monitor and control them remotely. The smart lamps are fitted with motion sensors to conserve energy by optimising lighting based on the needs of each space. The system saves the city $250,000 (€229,550) or more per year, Versa stated.
IP security cameras, which are often placed in difficult-to-access locations, are another key PoE application target.
The big challenge: interoperability
The single greatest challenge for PoE is assuring interoperability.
The Ethernet Alliance’s Power over Ethernet (PoE) Certification Program can help enable faster PoE installations and avoid interoperability issues, Tremblay said. Ethernet vendors including Analog Devices, Cisco, HPE, Huawei, Microsemi, and Texas Instruments are part of the certification programme.
But as new classes of devices are developed, industry players need to forge new partnerships with companies offering certified equipment, the Dell’Oro group said. “With the diversity of application, come interoperability problems which dictate the need for testing and certification,” Boujelbene said.
Certified products range from component-level evaluation boards, to power-sourcing enterprise switches, to midspan PoE power sources. Details of certified products are available via the programme’s public registry.
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