White Paper I PoEPower over Ethernet

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Content
1. Introducing the PoE technology .................................................................................................... 3
2. PoE Nomenclature ........................................................................................................................... 4
3. The Standards .................................................................................................................................. 5
3.1
PoE Type 1................................................................................................................................. 5
3.2
PoE Type 2................................................................................................................................. 5
3.3
PoE Type 3................................................................................................................................. 6
3.4
PoE Type 4................................................................................................................................. 6
3.5
Maximum Power per Port........................................................................................................ 8
4. Source (PSE) configurations............................................................................................................ 8
4.1
PSE endspan configuration...................................................................................................... 84.2
PSE midspan configuration...................................................................................................... 84.3
PoE injector configuration....................................................................................................... 95. Active and passive Poe.................................................................................................................. 10
5.1
Active PoE............................................................................................................................... 105.2Power negotiation (handshake)............................................................................................ 105.3
Passive PoE.............................................................................................................................. 115.4
Power disconnect................................................................................................................... 126. Power Delivery Method ............................................................................................................... 13
7. IEEE Standard Pin Assignments ................................................................................................... 16
8. Bibliography................................................................................................................................... 17

Document Identification
White Paer - PoE Power over Ethernet
Document No: NWP11
Version: 2021/11 V1Autor:
Language:

Wolfgang Hasler
English© NEUTRIK AG. All rights reserved.

This white paper is a publication of NEUTRIK AG.
This white paper represents the technical status at the time ofprinting. The product information, specifications, and all technical datacontained within this white paper are not contractually binding.
NEUTRIK AG reserves the right to make changes at any time to thetechnology and / or configuration without announcement.

2Manufacturer
Neutrik® AG
Im alten Riet 143
9494 Schaan
Liechtenstein
Phone: +423 2372424
Fax: +423 2325393
E: neutrik@neutrikgroup.com
www.neutrik.com

NEUTRIK AG is not to be held liable for statements and declarations
given in this white paper.

NEUTRIK AG explicitly exonerates itself from all liability for mistakes inthis white paper.

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1. INTRODUCING THE POE TECHNOLOGY

PoE = Power over Ethernet
A definition of power and data on the same cabling which has been standardized by theIEEE 802.3 working group started in 2003.
PoE technology is used to power remotely connected devices and simultaneously transmit
information using an Ethernet cable support consisting of 4 pairs of twisted copper wire.

Power over Ethernet (PoE) does exactly what its name suggests: it delivers usable power over Ethernet(twisted pair) cabling. Providing both the power and data required by an attached device provides
significant benefits such as• quick installation and flexibility:ease of installation and relocation of the powered device without the need to consider the location of
the power source• safety:
PoE uses relatively low voltages, so there is low risk of electrical hazard• reliability:
Since data and the power supply pass in the same Ethernet cable, there is only one cable to be pulled
per connected device. Compared to an external power supply, the number of connectors and adaptersis reduced.
• scalability:
easy to add new equipment to a network (PoE devices are plug-and-play)
Even though there are some obvious benefits to PoE, there are some things to know and others to beconsidered.

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2. POE NOMENCLATURE
PoE systems consist of three main elements:• PSE: Power Sourcing Equipment• PD: Powered Device• infrastructure Cabling

figure 1: PoE nomenclature

The principle of PoE power supply is based on the use of twisted copper pairs of the Ethernet cable topower from the source called PSE (Power Sourcing Equipment), the remote equipment called PD (PowerDevice).
An Ethernet cable can carry information (voice, data, images, etc.) at a rate up to 40 Gbit/s depending on
the type of cable and the active devices (router, switch) used and is made up of four pairs of wires. Whenthe connection is 10 or 100 Mbit/s, the data travels on only two pairs, namely wires 1, 2, 3 and 6; theother two spare parts, namely the wires 4, 5, 7 and 8, can be used to convey the electric current (type A).
It is however possible to use the wires 1, 2, 3 and 6 to convey the data and the power (type B), leaving
the free pairs unused. When the connection is above 100 Mbit/s, the four pairs are used to carry thedata. In this case, the power can be transmitted on the pairs 1/2 and 3/6 or 4/5 and 7/8. The IEEE 802.3af(15 W), 802.3at (30 W) and 802.3.bt (90 W) PoE standards describe these two scenarios. According to thestandard, PDs must support power transmission capabilities in both types A and B. On powerup, the PSE
needs to determine how much power it needs to supply the PD to avoid damaging it. For this there are two
methods: either by a HW protocol (Physical Layer Classification) or by using the LLDP protocol (Link Layer
Discovery Protocol) for data exchange between the two devices PSE and PD.

Category 5e cable should be the minimum to use in AV projects for any version of PoE and to support data up to 10Gbps.
A minimum of AWG 26 is required.

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3. THE STANDARDSPoE has been in use in different forms for over 20 years. The IEEE has standardized four versions. The firstPoE standard IEEE 802.3af-2003 allowed for the powering of devices up to 15.4 W. The second standard
IEEE 802.3at 2009, so called PoE plus or PoE+, was specified a maximum powering of 30 W. The lateststandard (as of May 2021) IEEE 802.3bt-2018 specifies PoE type 3 and type 4 (sometimes referred to asPoE++) to deliver a maximum of 60 W and 90 W respectively.
The voltage at the PSE is defined in all standards (IEEE 803.2 af/at/bt) between 44 V and 57 V.
Due to the worst-case scenario (a voltage drop of 7 V), the PD must also accept 37 V.

3.1 PoE Type 1• Name: PoE, 2-pair PoE• Standard: IEEE 802.3af• Maximum port power: 15.4 W
PoE was originally designed to power low-power devices such as IP telephones. The IEEE 802.3af wasstandardized in 2003 to use two of the four twisted pairs of wires in standard (at the time) Cat3 Ethernet
wire runs.
Examples of devices that PoE Type 1 can support include static surveillance cameras, wireless access points
and VoIP phones.

3.2

PoE Type 2• Name: PoE, 2-pair PoE• Standard: IEEE 802.3af• Maximum port power: 15.4 W
PoE Type 2 also utilizes 2-pair PoE, like PoE Type 1. Its basis is the PoE+ or IEEE 802.3at Ethernet standard.
It delivers up to 30 W of power at the port level over an Ethernet twisted pair cable.
Because it is backward compatible, it can support the types of devices typically supported by PoE Type 1 as
well as devices supported by PoE Type 2.
It connects higher-powered devices to a network such as PTZ cameras, RFID readers, video IP phones, andalarm systems.

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3.3

PoE Type 3• Name: 4-pair PoE, 4P PoE, PoE++, UPOE
• Standard: IEEE 802.3bt• Maximum port power: 60 W
Also known as 4-pair PoE, 4PPoE, PoE++, or UPoE, PoE Type 3 uses all four pairs in a twisted-pair copper
cable to deliver power to the PD - unlike Type 1 and 2 which only use two pairs. This higher level of PoE
adheres to the IEEE 802.3bt standard which came out in 2011.
It delivers 60 W of power to each PoE port.
Examples of devices that these higher levels of power support include multi-radio wireless access points,PTZ cameras, building management devices, and video conferencing equipment.

3.4PoE Type 4• Name: Higher-Power PoE• Standard: IEEE 802.3bt• Maximum port power: 100 W
Type 4 PoE, commonly known as Higher Power PoE, offers the highest capabilities of any currently existing
PoE type (May 2021) . This PoE type helps to meet the growing power requirements of network devices.
Conforming to the newest IEEE 802.3bt standard, Type 4 PoE de-livers 90 W of power from the PSE.
It has the potential to supply a maximum of 100 W of power per port if necessary.
Type 4 PoE can support extremely power-hungry devices such as laptops and flat screens.

3.5 Maximum Power per PortOne of the objectives of the 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 90 W per port. Despite this power ceiling, 100 W per port is still sufficient for applications
previously unsupportable under the prior IEEE standards, expanding the potential number of PoE ports
deployments.

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The table below summarizes the different types of IEEE 802.3 standards:Standard(IEEE)

Type

Max. number ofenergized pairs

Max. Data rate

Max. current
per device

Class143.84

802.3af

121000 BASE-T

350 mA

276.49

3

15.4

12.95

430

25.5

545

40

660

51

775

62

890

71.3

802.3at2321000 BASE-T

4802.3bt

600 mA
600 mA

1000 BASE-T
44960 mA

Sourced Powerat PSE (W)

Requested Powerat PD (W)figure 2: IEEE 802.3 PoE standards

While these values are the reported maximum powers that can be provided by the power source equipment(PSE), it is not the actual power that is ultimately delivered to the powered device (PD). The small conductor
cross-sections, the long cable lengths and the low system voltage as well as the losses in the power supply
units of PSE and PD contribute to a noteworthy power loss.
Efficiencies of less than 70 % are not uncommon in such applications. The power delivered by the PSE(sourced power) and the power received by the PD (requested power) therefore differ.

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4. SOURCE (PSE) CONFIGURATIONS
4.1

PSE endspan configurationThe endspan configuration is used to connect a PoE power supply, usually a switch, to a PoE compatible
PD device. Endspans have internal or external power supplies and provide data and power to connected PD
devices via RJ45 ports. Endspans provide policy management and enforce PoE budgets through negotiation
as well as perform PD scheduling, and PD maintenancefigure 3: PSE endspan4.2

PSE midspan configuration

Midspans have internal or external power supplies and combine Ethernet data with power typically on
a one-to-one relationship. Midspans typically do not have the same kinds of management options as
endspans do, but they do still negotiate with PD devices for power needs.

figure 4: PSE midspan8

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4.3

PoE injector configuration

PoE injectors (also known as Passive PoE - see 5.3 for details about passive PoE) typically have an internal
power supply. They also usually have data in, and data/power out connections to allow Ethernet passthrough.
They do not negotiate (see 5.2 power negotiation) with the PD for power class and they do not have anyway to scale power back from the PD for PoE budgeting purposes.

figure 5: PoE injector

Since PoE injectors do not negotiate with the PD, care must be used when specifying this kind of power
supply. (see 5.3 passive PoE)

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5. ACTIVE AND PASSIVE POE
5.1

Active PoE

Active PoE is also known as standard PoE, which refers to any type of PoE that negotiates the power
requirements between the PSE and the PD device. Active PoE switch is a device that complies with standard
PoE, so it is also named standard PoE switch. This type of switch is rated to be IEEE 802.3af, IEEE 802.3at
or IEEE 802.3bt compliant.
Before powering up, the active PoE switch will test and check to ensure the electrical power is compatible
between the switch and the remote device. If it isn’t, the active PoE switch will not deliver power,
preventing any potential damage to the non-PoE device.

5.2

Power negotiation (handshake)

The low voltage PoE is not always on. If no device is detected, then the power is off. Only when a PD is
attached to a PoE enabled source the power is made available to the PD. This addresses any concerns overpeople receiving electric shocks from Ethernet sockets or patch cords if they are left accessible.
There is a handshake that occurs between the PSE and the PD prior to the power being enabled. This only
takes a fraction of a second and during the handshake the PD communicates its powering requirementsback to the PSE so that the correct mode can be set in the PSE.
Typical voltage waveform at the Ethernet port when the PD is powered by a PSE(Type 4 - Class 8)

figure 6: power up - active10settingstandards

5.3

Passive PoE

Passive PoE is a non-standard PoE. It can also deliver power over Ethernet, but without the negotiation
process. Passive PoE switch/injector does not conform to any IEEE standard. When using passive PoE
switches or injectors, the power supply is “alwayson”. This means that it always sends current with acertain voltage via the Ethernet cable, regardless of whether the PD supports PoE or not.
When connecting a non-PoE device to a passive PoE supply, the supply is short circuited due to the low
resistance of the magnetics used in the non-PoE device.
For example, the NPS-30W detects this low resistance as a short circuit and stops delivering power. In mostcases this avoids damage to the non-PoE device.
The PSE (NPS-30W) then tries cyclically to supply the device and remains in supply mode when the shortcircuit is removed (hick-up mode).
In any case, damage cannot be ruled out 100 %, as this short impulse can be sufficient to damage thedevice. It may be possible to destroy a device that is not PoE compatible by supplying it with passive PoE.
Typical Voltage Waveform at the Ethernet Port when PD is Powered by a passive, PoE injector

figure 7: power up - passive

Since the internal surge protection is designed for high-voltage, low-energy surge events, it cannot handle
the massive amount of power delivered by the passive PoE injector, which can lead to a malfunction ofthe device.

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5.4

Power disconnect

It may happen that a user swaps a connection from a powered to a non-powered device. When theconnection is established to the nonpowered device, the 48 V power source could damage it. The 802.3af
standard specifies the PSE to disconnect power to a device when it stops receiving a power signature fromthe PD. When the connection is terminated, power will be cut around 250 ms later.
Although the power is off when there is no PD connected to the link and the handshake between the two
activates the power, the removal of the PD doesn’t benefit from the same degree of control.
In other words, the PSE cannot anticipate the removal of the PD through the unplugging of a patch cord
and as such the voltage and current are still present when this action occurs. The net result of unplugging
the cord is a small arc discharge between the removed plug and socket on one or more of the contacts.

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6. POWER DELIVERY METHOD
In addition to the four present power levels that are deliverable using PoE, there are numerous power
delivery methods. However, only two power delivery methods have been standardized by the IEEE; they
are referred to as Alternative A and Alternative B and describe the methods employed to deliver the powerfrom the PSE to the PD.
The references to Alternative A and B only apply to the PSE since the PDs are normally designed to support
both power delivery techniques as shown in figure 8 to figure 13.
It is generally understood that the two alternatives simply define whether the power is transmitted via usedor unused pairs. This is the case for 10BASE-T and 100BASE-T Ethernet where only the orange and green
pairs are used. However, this is not so for 1000BASE-T and 10GBASE-T where all four pairs are used fordata transmission.
Figure 8 shows the endpoint PSE location of Alternative A for 10BASE-T/100BASE-TX using the data pairsand Figure 9 shows the endpoint PSE location of Alternative B for 10BASE-T/100BASE-TX using the unused(blue and brown) pairs.

figure 8figure 9White Paper – PoE Power over Ethernet

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For the four-pair signalling of 1000/2.5G/5G/10GBASE-T, the two alternatives simply determine which
two pairs deliver the power. Figure 10 and Figure 11 show the endpoint PSE location of Alternative A andAlternative B respectively, with Figure 10 using the orange and green pairs, and Figure 11 using blue andbrown.

figure 10

figure 1114

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PoE type 3 and type 4 allow all four pairs to carry a certain amount of current. Figure 12 and Figure 13
show the endpoint PSE locations for 4-pair PoE for 10BASE-T/ 100BASE-TX and 1G/2.5G/5G/10GBASE-T
respectively.

figure 12

figure 13

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7. IEEE STANDARD PIN ASSIGNMENTS

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8. BIBLIOGRAPHY• Braithwaite, Michael (2019), “How the latest version of PoE Can Will Impact your AV Designs”,
presentation at infocomm conference 2019• DIGISOL SYSTEMS LTD, “The Power of Ethernet - PoE & PoE+ Solutions”• Eisen, Morty (2009), “Introduction to PoE and the IEEE802.3af and 802.3at Standards”, MarcumTechnology• Feldman, Shahar, Ohana, Eli (2019), “Next-Generation PoE: IEEE® 802.3bt”, White Paper, Microchip
Technology Inc.
• James, Jasen (2019), “Power over Ethernet – The Story So Far”
• Netgear (2019), “NETGEAR Ultra60 PoE++”, white Paper, Netgear Business• Netscout, Phoenix Datascom, “Power Over Ethernet”, 802.3af/at Standards A and B - Power Sourcing
Equipment (PSE)• Sage, Jean-Jacques (2019), “PoE technology - Part 1: Introduction”, White Paper• Sage, Jean-Jacques (2020), “PoE technology - Part 2: Market and applications”, White Paper• Schnabel, Patrick (2016), “Netzwerktechnik‑Fibel: Grundlagen, Übertragungstechnik “• Schnabel, Patrick (2015), “Kommunikationstechnik-Fibel“• Silicon Labs, “Protecting PoE PD Designs against Non-Standard PoE Injectors”,

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PoE White Paper 2021/11 V1 - NWP11 - Data subject to change without prior notice. © 2021 NEUTRIK . NEUTRIK , etherCON are registered trademarks of NEUTRIK AG. ALL RIGHTS RESERVED.

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