Next-generation 5G technology offering advanced mobile internet connectivity with faster speeds creates new business opportunities by enabling a variety of IoT and Big Data applications. These applications are driving unprecedented demand for connecting additional types of powered devices (PDs) to Ethernet networks including IP surveillance cameras, 802.11ac and 802.11ax access points, LED luminaires, 5G small cells, and other IoT appliances. Power-over-Ethernet (PoE) technology offers numerous advantages for powering these devices in 5G deployments and the latest IEEE® 802.3bt standard makes this possible by pushing the power limit of Power Sourcing Equipment (PSE) and Powered Devices (PDs) to 90W and 71.3W respectively.
The challenge is how to deploy PDs that support this latest generation of PoE technology so they can work alongside existing pre-IEEE® 802.3bt 2-pair and 4-pair PDs that support earlier pre-standard Universal PoE (UPOE) and Power-over-HDBaseT (POH) specifications. The industry has now bridged this interoperability gap, ensuring that both pre-standard and new IEEE® 802.3bt-2018-compliant PDs can share the same Ethernet infrastructure without requiring changes to existing switches or cabling.
The Road to IEEE 802.3bt
Since the ratification of the first PoE standard in 2003, PoE use has increased dramatically and made headway into new applications. PoE provides huge benefits in relation to ease of installation, saving CAPEX and OPEX costs and providing a unified and safe power standard for worldwide use.
The main limiting factor affecting the use of PoE in new applications is the amount of available power. While 15.4W at the power source is sufficient for most IP phones and 802.11a/b/g access points, it is not enough for IP video phones, 802.11n, and pan-tilt-zoom (PTZ) IP cameras. For this reason, the Institute of Electrical and Electronic Engineers (IEEE) released IEEE 802.3at-in 2009, specifying 30W at the PoE source.
Today there is a demand for even higher power to support additional devices connected to the Ethernet network, such as PTZ security cameras, kiosks, POS terminals, thin client, 802.11ac and 802.11ax access points, small cells, and connected LED lighting, all of which can benefit from PoE. To meet this demand, the new IEEE 802.3bt standard increases the maximum PoE power available mainly by utilizing all four pairs of the structured wiring. IEEE 802.3bt extends the power classification information exchanged during initial negotiation to allow meaningful power management capability, enabling support of multiple PoE classes, while also being backward-compatible. These enhancements solve the challenge of higher power and more efficient PoE delivery systems.
IEEE 802.3bt Call for Interest (CFI) activity started in early 2013, and the ratification of the standard took place in September 2018. The new standard addresses the existing market needs and is considered a major catalyst to PoE market growth as it facilitates the expansion of PoE use cases by pushing the power limit of PSEs and PDs to 90W and 71.3W respectively.
Prior to this IEEE 802.3bt initiative, however, there were parallel efforts to increase power delivery to PDs. It started with the IEEE 802.3af-2003 PoE standard that provided up to 15.4W of output power to each device over two pairs of Category 5e (Cat5e) cables. The IEEE 802.3at-2009 standard, also known as PoE+, introduced the “Type 2” PSE/PD capable of supporting 30W output power and 25.5W load power. The latter is mainly an extension of the first standard. Next, the HDBaseT Alliance standardized the HDBaseT protocol, which allows extending HDMI links up to 100m over Cat5e or better cables. In 2011, the HDBaseT Alliance created the Power over HDBaseT (PoH) standard that extends the maximum power deliverable to 95W over four pairs.
The following table 1 summarizes the pre-IEEE 802.3bt standards:
Table 1: Extended power capability allows PD input power to reach up to 95W if channel length is known.
IEEE 802.3bt adds a number of capabilities. In addition to introducing Type 3 and Type 4 PSEs/PDs and working over four pairs, it also supports both the single- and dual-signature PD constructions and adds class 5 to 8 as part of an improved mutual identification process. Automatic class functionality is added, and power capability has been extended as long as channel length is known. Finally, it includes low standby power support and supports 10G-BASE-T with PoE. The table 2 below shows the PoE capabilities that were available upon ratification of the IEEE 802.3bt standard.
Table 2: Extended power capability allows PD input power to reach up to 60W for Type 3 and up to 90W for Type 4 if channel length is known.
One of the objectives of the IEEE 802.3bt standard is to comply with the limited power source and Safety Extra Low Voltage (SELV) requirements as defined in ISO/IEC 60950. However, this compliance means that power cannot exceed 100W per port. Despite this power ceiling, 100W per port is still sufficient for applications previously unsupportable under the prior IEEE standards, expanding the potential number of PoE ports deployments.
The IEEE 802.3bt specifications ensure that the IEEE 802.3bt system will work automatically with legacy Type 1 and Type 2 devices, as long as the PSE is capable (in terms of power) of supporting the PD and both are standard-compliant. Should the PD require higher power (IEEE 802.3bt PD) and the PSE cannot support it (IEEE 802.3af/at PSE), the PD will either remain off or it will turn on and consume only the power available from the PSE.
One of the first examples of solutions that deliver this interoperability is a PSE chipset from Microchip that enables pre-standard switches to interoperate with new IEEE 802.3bt-2018-compliant products. The chipset followed an earlier PSE chipset from Microchip for implementing the widely adopted PoH four-pair power standard for 95 W PDs and is also at the heart of an offering of IEEE 802.3bt-2018-compliant PoE injectors and midspans that bridge the interoperability gap for users.
IEEE 802.3bt-2018-compliant PoE injectors and midspans are installed between PDs and an existing switch, enabling users to power any combination of pre-standard and IEEE 802.3bt-2018-compliant PDs. The availability of single- and multi-port options enables new IEEE 802.3bt-compliant switches to power pre-standard PDs.
For system developers, IEEE 802.3af/at/bt PoE chipsets provide the scalability to incorporate, into a single board design, the two- and four-pair systems that are required for supporting pre-standard and IEEE 802.3bt-2018-compliant PoE. These chipsets must be able to balance thermal dissipation evenly across the system, and should include all required manager and controller functionality for building PSE equipment that can source 90 to 99.9 watts of power per port while supporting up to 48 ports for IEEE 802.3bt Type 3 (Classes 1-6) and Type 4 (Classes 7-8) applications. An additional consideration is the ability for systems based on these chipsets to be upgraded from earlier standards to IEEE 802.3bt via software update with no hardware changes.
One last concern for developers is whether they can protect PDs against reverse-polarity connections and cut power space and the costs of delivering IEEE 802.3bt Type 4 Class 8 power. This, too, has been solved with the latest IEEE 802.3bt solutions, through the availability of full-bridge rectifier devices that are used on the powered side of the PoE connection.
The new IEEE 802.3bt standard enables delivery of 90W over four pairs of Cat5e cables and above. This PoE level is expected to be the maximum level defined, as higher levels may not be safe for the existing cabling and connectors deployed in today’s infrastructures. The standard will replace all existing pre-standard solutions that deliver 60W/75W/95W today, such as UPOE or 4PPoE. PoE system and device suppliers are providing a roadmap forward to implement these new standards while also supporting earlier pre-standard implementations including those supporting UPOE and POH specifications. Implemented properly, pre-standard and new IEEE® 802.3bt-2018-compliant PDs can share the same Ethernet infrastructure without requiring changes to existing switches or cabling.
Galit Mendelson is Senior Manager of PoE Marketing and Business Development at Microchip Technology.
>> This article was originally published on our sister site, Power Electronics News.
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