4ppoe parameters for network planning 150717

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White Paper

More Power over Ethernet: 4PPoE –parameters for network planning



White Paper | More Power over Ethernet: 4PPoE | v1.0 | en | Matthias Gerber 2

More Power over Ethernet: 4PPoE – parameters for network planning

Contents

More Power over Ethernet: 4PPoE – parameters for network planning 1

1. Improving performance with remote powering 3

2. The increase in cable temperature 5

3. The temperature increase inside the cable bundle 6

4. The temperature increase of the cable bundle relative to the environment 7

5.

Choosing the correct dimensions for patch cords 7

6. Considering the quality of plug connectors 8

7. Consequences for planning and installation 9

8. New tool: the R&M PoE Calculator 9

9. Annex 11

© Copyright 2015 Reichle & De-Massari AG (R&M). All rights reserved.

It is not permitted to pass on and replicate this publication or parts of it for whatever reason and in whatever form without expresswritten permission from Reichle & De Massari AG. Information contained in this publication may be altered without prior notice. Thisdocument was produced with the greatest possible care; it presents the state of the art at the time of preparation.




Remote power supply according to IEEE802.3bt is placing new demands on installationprocesses

IEEE 802.3bt is a leap forward for Power over Ethernet(PoE): instead of 13 or 22 watts, end devices will be ableto be supplied with up to 100 watts of power. In order toachieve this, PoE will use all four wire pairs to transmitpower in future. This will allow powerful devices such aswireless access points and multimedia devices to bepowered via the data cables within the office’s orbuilding’s structured cabling system. Intelligent devices,

sensors, etc. for the Internet of Things or IP telephonescan be plugged in like conventional appliances. But what

requirements must the installation meet? How does theLAN cable behave? What must planners and installerstake note of today to ensure that their customers canfully enjoy the opportunities presented by Power overEthernet tomorrow?

This white paper lists the most important parameters, provides tips for successful installation, and

presents a calculation tool developed by R&M that makes it easy to determine the range of links

based on the starting conditions.

1. Improving performance with remote powering

Power over Ethernet (PoE) has established itself on the market over the past 15 years. The idea iscaptivating. If there is already a data cable leading to a device, it can also be used to transmit power. With 10or 100 Megabit Ethernet, PoE can use both unoccupied wire pairs, or – by means of phantom power – thedata-carrying pairs themselves, in order to transmit power. The applications of PoE and its usable power

range have been increased in stages over the past years (figure 1).

IEEE is now aiming to provide end devices with between 55 and 100 watts of power, which is only possible if

all four wire pairs are used to transmit this power. This is the origin of the new abbreviation, 4PPoE: 4-PairPower over Ethernet. The aim is to make it possible to transmit 1 to 10 Gigabit Ethernet at the same time. AsGigabit Ethernet requires all four pairs for data transmission, four phantom power supplies must be created(figure 2). Two pairs form the supply line and the other two form the return line for the power supply.

In order to do this, each wire pair must carry a current of 650 to 1100 mA – quite literally a hot topic, as anylosses on the way to the consumer are converted to heat. Similarly high demands are placed on theconnectivity, as on the cables and on the way these are laid.

Application: Remote powering of data devicessuch as IP telephones, wireless

(WLAN) access points, sensors,surveillance cameras, andcomponents for the Internet ofThings (IoT), as well as forbuilding automation.

Technology: Power over Ethernet (PoE) and4 Pair PoE (4PPoE)

Subjects: The current development of PoE,future standard IEEE 802.3bt,important parameters and theirsignificance for planning andimplementation, cable heating,shortening links

Objective: To demonstrate the technicalpossibilities and challenges, tointroduce the R&M calculator forcalculating link lengths

Target group: Network planners, installers, R&MQPP partners

Author: Matthias Gerber

Published: June 2015




Figure 1: the evolution of Power over Ethernet since 2000. Graphic, photos: R&M

Figure 2: 4PPoE will require a phantom power supply over all four wire pairs.Graphic: R&M

End Device

Evolution of Remote Powering

2000 2003 009 2011 2015 and onward

Inline Power IEEE 802.3 af IEEE 802.3 at Cisco (proprietary) IEEE 802.3 bt (Draft)Power over Ethernet (PoE) PoE Plus (PoEP or PoE+) Unuversal PoE (UPoE) 4-Pair PoE (4PPoE)

7W 15W / 13W 26W / 22W 60W / 54W > 55W / 49W up to 100W300mA / pair 00mA / pair 700mA / pair 650mA up to 1100mA / pair




2. The increase in cable temperature

The physical consequences of using PoE are clear: the higher the current in a copper wire and the lower itscross section, the hotter it gets. Nowadays, however, younever find one wire on its own. The overall heating of thecable depends on several other factors:

• The type of cable

• The number of cables in the bundle

• The way the cable has been laid – open or closedinstallation ducts

• Air convection and forced ventilation

These effects must be looked at separately. Draft standards

such as ISO/IEC TR 29125 (see attachment) use calculation

models that divide the temperature increase into two stages:

• Temperature increase inside the cable bundle

• Temperature increase of the cable bundle relative tothe environment

This model can be used to calculate the expected heating of the hottest cable in a bundle. However, thestandardization process is still in a state of flux (as of July 2015). It is not the model itself that is being

debated; rather, there are questions concerning the weighting of the effects through the choice ofcoefficients. These coefficients will continue to be changed until the simulation values correspond to themeasurements taken in reality.

In connection with this, R&M has conducted its own tests at its laboratory in Wetzikon (Figure 3).

It is not just fire and health and safety regulations that make it necessary to limit the temperature increase.Even if the temperature remains well under the combustion point, permanent heating by as little as 10 ºC canhalve the cable’s expected service life.

Higher temperatures also increase the copper resistivity and therefore the attenuation of the transmittedsignal, which reduces the possible length of the links. The heating that results from power transmission canincrease the attenuation of a cable to such an extent that data transmission becomes impossible.

Figure 3: infrared photo of a cable bundle duringpower transmission. Photo: R&M




3. The temperature increase inside the cable bundle

The temperature increase inside the cable bundle is primarily determined by the cable properties. Thetemperature in the cable bundle increases exponentially with the electric current. The smaller the cross-section of the conductor, the more the temperature increases (figure 4).

Shielded cables are advantageous here, as they are better at transporting the heat to the outside of the

bundle. The cable shielding serves as a thermal bridge that can guide the heat around the cable core fromthe inside to the outside.

The number of cables in the bundle also plays a crucial role, as the outer cables “insulate” the inner ones.The more layers of cables there are lying on top of one another, the hotter the cable in the center of thebundle will be. Therefore, it is better to arrange the cables alongside one another than in a concentricbundle.

Figure 4: temperature increase for a bundle of 100 cables with different conductor cross-sections, laid open (AWG 24,23 and 22 correspond to conductor diameters of approx. 0.5, 0.56 and 0.64 mm). Graphic: R&M




4. The temperature increase of the cable bundle relative to the environment

The way the cables have been laid is the sole factor that determines the temperature increase of the cablebundle relative to the environment, for example in the conduit. If the bundle cannot be cooled by airconvection, the temperature increases rapidly (figure 5).

However, short, insulated pieces – e.g. for passing through fire barriers in walls – do not present a problem.Copper wires are good at transporting and distributing locally produced heat.

Figure 5: temperature increase for a bundle of 100 cables with different conductor cross-sections, laid in open and ininsulated environment. Graphic: R&M

4PPoE therefore represents a challenge for the cabling industry in that not only is the temperature increasein a cable defined by the cable properties, but the way the cable is laid can also influence the functionality of

the installation.

Planners and installers will play a key role in ensuring the functionality of 4PPoE.

5. Choosing the correct dimensions for patch cords

The change in the attenuation of patch cords due to temperature increases usually has normally little impact,as these cords are very short. However, depending on the cable management scheme, large bundles ofpatch cords may be present in racks. In these bundles, too, there is a maximum temperature (usually 60 ºC)that must not be exceeded. Calculations show that the introduction of 4PPoE will necessitate the use of apatch cable with a conductor cross-section of at least AWG26.




6. Considering the quality of the connectivity

The same principle applies to the connectivity: the greater the contact resistance, the higher the losses andthe hotter the contacts. Therefore, the connector/cable contacts are of increased significance for 4PPoE. Aninsulation displacement contact (IDC) is far superior to an insulation piercing connector (IPC) in terms ofcontact reliability, with IDC technology offering higher long-term stability. IDCs use insulation displacementtechnology to create a connection similar to a solder joint, while IPCs merely pierce the insulation and createa loose contact. Over time, the stability of an IPC contact will diminish (see the R&M white paper: “IDCConnection Technology”).

A serious problem can arise if contacts are damaged by fine arcs when being disconnected under load. Thiscan lead to permanent impairment of the transmission properties. The contact design is also an issue in thiscontext.

During disconnection, the current ultimately flows over a small remaining contact area. When the contact ispulled out, sparks are generated. This creates a plasma with extremely high temperatures that can causelocal damage to the contact. Craters have been known to form on the contact surfaces (see the R&M whitepaper: “Power over Ethernet Plus – Update and Cabling Considerations”).

High-quality plug connections are therefore constructed in such a way as to create sufficient distancebetween the pull-out point and the nominal contact area (figure 6).

Figure 6: The contact on an RJ45 plug with the spring tab of a connection module. In a well-constructed connection,the nominal contact area is far away from the first/last contact point. Graphic: R&M

Nominal areaof contact

Pull out pointwith contactdamage dueto sparks




7. Consequences for planning and installation

The loss budget on the link is the main factor influencing the performance of the network and the ability totransmit data without interruptions. In the case of remote power supply over the data lines, the attenuation isdirectly influenced by the heating of the cable. Following a few rules makes it possible to minimize thisimpact:

• Avoid thick cable bundles. Multiple, smaller bundles are better than fewer, larger ones.

• Arrange the cables in stacks with as few layers as possible.

• Avoid heat accumulation in the conduits. Leave space for air convection or forced ventilation.

• Cables with a larger conductor cross-section make longer cabling links possible. For example, ifCat.6 cables (AWG23) are used instead of Cat.5e for class D (1000Base-T), the full cabling lengthcan almost always be used. The same applies to using Cat.7A cables (AWG22) instead of Cat.6A forclass EA (10GBase-T).

• Avoid cable temperatures over 60 ºC, even if the loss budget permits them.

• Chose connectivity, e.g. patch cords with IDC connections whose service life corresponds to the

expected overall service life of the installation even for power transfer.

8. New tool: the R&M PoE Calculator

Active planning of the loss budget is necessary before installation in order to ensure 4PPoE functionality.The expected heating and the resulting maximum possible permanent link length are parameters that requireseveral calculations when planning the influencing factors and conducting product evaluation. R&M hasdevised an easy-to-use tool to help network planners and installers. All relevant standards and physicalvariables have been stored in the Excel spredsheet and linked to one another (figure 7). The “PoE

Calculator” also has a special feature that lets you choose parameters for multiple segments, as exist inpractice on most data links. The parameters that can be entered include:

• The PoE application (PoE, PoEP, UPoE, POH, 4PPoE 55W, 4PPoE 100W)

• The class (D, E, EA, F, FA)

• The number of plug connectors in the channel

• The total length of the patch cord

• The maximum cable temperature

And the following can be grouped according to segments:

• Cable types (according to categories and conductor cross-sections)• Environmental temperatures

• Bundle thicknesses

•

Planned segment lengths, etc.

This allows users to consider environmental temperature, link length, bundle thickness, conductor cross-section, etc. in relation to each other during the planning stage and to avoid surprises after the installation.The PoE Calculator is an Excel file that R&M provides to its customers and partners free of charge. You candownload the tool from www.rdm.com.




Figure 7: the R&M PoE Calculator for determining the optimum link lengths when using Power over Ethernet. Graphic:R&M




9. Annex

Standards and committees

IEEE 802.3bt

DTE Power via MDI over 4-Pair Task Force

IEC PAS 61156-1-4:2010

Multicore and symmetrical pair/quad cables for digital communications – Part 1-4: Symmetrical pair/quadcables with transmission characteristics up to 1000 MHz – Conductor heating of bundled data grade cablesfor limited power transmission based on IEEE 802.3

ISO/IEC TR 29125:2010

Information technology – Telecommunications cabling requirements for remote powering of terminalequipment

CENELEC TR 50174-99-1

Information technology – Cabling installation – Remote powering

Model calculation according to draft standard ISO/IEC TR 29125 and EN TR 50174-

99-1The model (figure 8) divides the heating in a cable into two components:

• ∆Tth = temperature increase inside a cable bundle

• ∆Tu = temperature increase of the cable bundle relative to the environment

Figure 8: model for calculating the temperature increase.




The following formulas are used for the calculation:

cth: coefficient that describes the thermal properties of the cable(U/UTP: 5.0; F/UTP: 3.0; S/FTP: 2.5; etc.)

cu: coefficient that describes the thermal properties of the environment surrounding the bundle(open/ventilated laying: 0.2; closed conduits: 0.4; insulated: 1.0; etc.)

N: number of cables in the bundlenc: number of current-carrying wires in the cable (4 or 8)ic: current per wire (in A)

R: resistance of 1 m of cable (ohm/m)d: cable diameter (in m)

Empirical methods (measurements) are being used to adapt the coefficients cth and cu to real conditions.While cth has largely been determined, the value for cu still varies considerably across the individual draftstandards. R&M has chosen average values for cu for the “PoE Calculator” that appear to be realistic at thistime.

You can find more information about R&M’s products and solutions at www.rdm.com.

4ppoe parameters for network planning 150717

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