——Address the interoperability challenge of providing up to 90W of power over Ethernet in existing switch infrastructure

Microchip Technology

Senior manager of Poe marketing and business development

Galit Mendelson

The new generation of 5g technology can provide advanced mobile Internet connection with higher speed, help to realize various IOT and big data applications, and create new business opportunities. These applications are driving the need to connect more types of power receiving devices (PD) to the Ethernet network at an unprecedented speed, including IP surveillance cameras, 802.11ac and 802.11ax access points, LED lamps, 5g small base stations and other IOT appliances. Power over Ethernet (POE) technology has brought many advantages to power these devices in 5g deployment. By setting the power limits of power supply equipment (PSE) and power receiving equipment (PD) to 90W and 71.3w respectively, the latest IEEE ® The 802.3bt standard makes this possible.

The challenge is how to deploy PD supporting this latest generation of Poe technology, so that they can work with 2 pairs and 4 pairs of PD before the existing IEEE 802.3bt standard, that is, PD supporting the earlier general POE (upoe) and hdbaset power supply (POH) specifications. Today, the industry has closed this interoperability gap to ensure that PDS that comply with previous standards and the new IEEE 802.3bt-2018 standard can share the same Ethernet infrastructure without replacing existing switches or cabling.

The road to IEEE 802.3bt

Since the first Poe standard was approved in 2003, the application scope of Poe has increased greatly, and new applications have made continuous progress. Poe has great advantages in simplifying installation, saving CAPEX and OPEX costs, and providing a unified and safe power standard for global use.

In new applications, the main limiting factor of Poe usage is the available power. Although 15.4W power supply is enough to meet the needs of most IP phones and 802.11a/b/g access points, it is not enough to power IP video phones, 802.11n and PTZ IP cameras. Therefore, the Institute of electrical and Electronic Engineers (IEEE) issued the IEEE 802.3at standard in 2009, which specifies the POE power supply with 30W power.

Today, higher power is needed to support other devices connected to Ethernet, such as PTZ surveillance cameras, self-service terminals, POS terminals, thin clients, 802.11ac and 802.11ax access points, small base stations, and networked LED lighting, and these devices can benefit from Poe. In order to meet this demand, the new IEEE 802.3bt standard mainly uses all four pairs of structured cabling to improve the maximum available power of Poe. IEEE 802.3bt extends the power classification information exchanged during the initial negotiation to achieve efficient power management, support multiple Poe levels, and backward compatibility. These enhancements address the challenges of higher power and more efficient Poe power supply systems.

The IEEE 802.3bt standard solicitation of interest (CFI) campaign started in early 2013 and was officially approved in September 2018. As the new standard expands the use scenarios of Poe by setting the power limits of PSE and PD to 90W and 71.3w respectively, it can not only meet the existing market demand, but also is generally considered as the main driving factor for the growth of Poe market.

However, before the implementation of IEEE 802.3bt, there are some synchronous work to improve the power supply performance of PD. Starting from IEEE 802.3af-2003 Poe standard, it can provide up to 15.4W output power for each device through two pairs of CAT5e cables. IEEE 802.3at-2009 standard (also known as Poe +) introduces “type 2” PSE / PD which supports 30W output power and 25.5w load power. The latter is mainly an extension of the first standard. Subsequently, the hdbaset alliance standardized the hdbaset protocol, allowing the HDMI link to be extended to a maximum length of 100m through CAT5e or higher standard cables. In 2011, the hdbaset alliance created the hdbaset power supply (POH) standard, which extends the maximum power supply of four pairs of cables to 95w.

The following table summarizes the pre IEEE 802.3bt standards:

Note 1: if the channel length is known, the expanded power capacity can achieve a maximum PD input power of 95w.

IEEE 802.3bt adds many functions. In addition to introducing type 3 and type 4 PSE / PD and working through four pairs of cables, this standard also supports single signature and double signature PD structures, and adds level 5 to level 8 to the improved two-way authentication process. As long as the channel length is known, automatic classification function will be added and power capacity will be expanded. Finally, the standard also includes low-power standby function and supports 10g-base-t with Poe. The following table shows the POE functions provided after IEEE 802.3bt standard approval.

Note 1: if the channel length is known, the expanded power capacity can achieve the maximum PD input power of 60W (type 3) and 90W (type 4).

One of the goals of IEEE 802.3bt standard is to meet the limited power supply and safe extra low voltage (SELV) requirements defined in ISO / IEC 60950. However, this compliance means that the power of each port can not exceed 100W. Despite this power cap, the power of 100W per port is still enough to meet the requirements of applications that were not supported under the original IEEE standard, which can expand the potential number of Poe port deployment.

Ensure interoperability

Only PSE can support PD (in terms of power) and both meet the standard, IEEE 802.3bt specification can ensure that IEEE 802.3bt system can automatically work with traditional type 1 and type 2 devices. If the PD requires higher power (IEEE 802.3bt PD) and the PSE cannot support the PD (IEEE 802.3af / at PSE), the PD will remain off or enter the on state and consume only the available power from the PSE.

One of the earliest solutions to provide such interoperability is microchip’s PSE chipset, which implements the interoperability between switches conforming to the previous standard and products conforming to the new IEEE 802.3bt-2018 standard. The chipset is based on microchip’s early PSE chipset and is used to implement the widely adopted poh four pair power supply standard (for 95w PD). In addition, it is also the core of Poe power supply and mid span products conforming to IEEE 802.3bt-2018 standard, which can bridge the interoperability gap for users.

By installing Poe injector and mid span conforming to IEEE 802.3bt-2018 standard between PD and existing switch, users can supply power for any combination of PD conforming to previous standard and PD conforming to IEEE 802.3bt-2018 standard. By using the single port and multi port options, switches that meet the new IEEE 802.3bt standard can also power PDS that meet the previous standard.

For system developers, IEEE 802.3af/at/bt Poe chipset provides scalability, and can integrate two and four pairs of systems needed to support Poe conforming to the previous standard and IEEE 802.3bt-2018 standard into the board design. These chipsets must be able to balance the heat dissipation of the whole system, and should include all the manager and controller functions needed to build PSE devices. These devices can provide 90W to 99.9w power for each port, and provide up to 48 ports for IEEE 802.3bt type 3 (level 1-6) and type 4 (level 7-8) applications. In addition, the system based on these chipsets should have the ability to upgrade the early standard to IEEE 802.3bt by software update without changing the hardware.

The last concern of developers is whether they can protect Pd from reverse polarity connection and reduce the power space and cost required to provide IEEE 802.3bt type 48 power supply. With the full bridge rectifier used in the power supply side of Poe connection, the latest IEEE 802.3bt solution also solves this problem.

The new IEEE 802.3bt standard can provide 90W power through four pairs of CAT5e cables and higher standard cables. This Poe level is expected to be the highest level defined, as higher levels may not be safe for existing cables and connectors deployed in today’s infrastructure. This standard will replace all existing 60W / 75W / 95w solutions, such as upoe or 4ppoe. Poe system and equipment suppliers provide a roadmap for the implementation of these new standards, as well as support for early implementation solutions that conform to previous standards, including those that support upoe and poh specifications. PD conforming to the previous standard and PD conforming to the new IEEE 802.3bt-2018 standard can share the same Ethernet infrastructure without replacing the existing switches or cables.

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