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Design Guidelines for PoE Based Security Systems

Carlos Carle, P.E.SignaMax Systems, Inc.

What is PoE?

Power Over Ethernet or PoE Technologydescribes a system to safely transferelectrical power, along with data, toremote devices over standard data cables(Cat3, Cat5, Cat5e, Cat6) in an Ethernetnetwork.

PoE Standard Development

Technology first Developed by CISCO in 2000to support IP Telephony deployments.

The IEEE Standard was developed on 2003(IEEE 802.3af).

IEEE Revised Standard (IEEE 802.3at) releasedon 2009.

Energy Efficient Ethernet Standard (EEE) waspublished in November 2010 (IEEE 802.3az).

PoE (Power Over Ethernet)

There are 3 types of devices used in a PoEenvironment:

PSE (Power Sourcing Equipment) ‐EndspanPI (Power Injector) ‐MidspanPD (Powered Device)

PoE Components Definition

Power Sourcing Equipment (PSE) – speciallyconfigured power supply designed to provide powersafely to a valid PD.Powered Device (PD) – End Device that accepts anduses power from the Ethernet cable for its operation.Midspan (PI) ‐ type of PSE and in simple terms istypically a pass through RJ45 box which adds PoEpower, also known as a Power Injector.

TIA 568 A/B Wiring Diagrams

IEEE 802.3 Ethernet Over Twisted Pair Cables 

10 BASE‐T (Ethernet 10 MB/S) and 100BASE‐TX (Fast Ethernet 100 MB/S) usesonly two pairs for data transmission.Conductors 1‐2, 3‐6 (Pairs 2 and 3)

1000 BASE‐T (Gigabit Ethernet 1000MB/S) uses all four pairs for datatransmission.

10/100 BASE‐T Layout

1000 BASE‐TX Layout

PoE (PSE/PD) Block Diagram

PoE Midspan Block Diagram

PSE Equipment

PD Equipment

PoE Midspan Equipment

PoE System

PoE Security System

PoE (CISCO)

CISCO original PoE delivers 15.4W ofpower from the Power SourcingEquipment (PSE) to the Powered Devices(PD).Cisco PoE Switches uses the CiscoDiscovery Protocol (CDS) to detect Ciscopre‐standard or IEEE 802.3af devices.

CISCO Discovery Protocol

IEEE 802.3af Standard (PoE)

Requires CAT3 Cable or Higher.Standardized on 48 VDC as the InjectedPoE voltage.

Maximum Power Transmitted by PSE is15.4W.

Maximum Power Received by PD is12.95W (2.45W Power wasted perPort).

IEEE 802.3af Standard (PoE)

Only two pairs are needed for 10 BASE‐T (10MB/S) and 100 BASE‐TX (100 MB/S) totransmit Power.Mode A – Power is transmitted on the DataConductors 1‐2, 3‐6 (Pairs 2 and 3).Mode B – Power is transmitted on theunused Conductors 4‐5, 7‐8 (Pairs 1 and 4).

IEEE 802.3 af (Mode A)

IEEE 802.3af (Mode B)

IEEE 802.3at Standard (PoE+)Known as PoE+, PoE Plus or Full PowerPoE.

802.3at defines two types of PSE: Type 1 (Over 2 Pairs) – The PSE delivers amaximum of 15.4W over a voltage range of44 to 57 VDC, using CAT3 cable or higher.

Type 2 – The PSE can supply 30.8W (Over 2Pairs), or 60W (Over 4 Pairs) using a voltagerange of 50 to 57 VDC, using CAT5 cable orhigher.

IEEE 802.3 af/at PSEPower Requirements

IEEE 802.3at Standard (PoE+)

Powered Devices – Has differentclassifications: Class 1 – Power is limited to 3.84W (overtwo pairs). Very Low Power Device.

Class 2 – Power is limited to 6.49W (overtwo pairs). Low Power Device

IEEE 802.3at Standard (PoE+)

Powered Devices

Class 3 – Power is limited to 13W (over twopairs). Mid Power Device.

Class 4 – Power is limited to 25.5W (overfour pairs). High Power Device.

PoE Powering Schemes 802.3at

There are four basic power schemes,each with two alternative powerinsertion method: Alternative A – Power is supplied via centertaps of the coupling transformers on dataconductors 1‐2, 3‐6 (Pairs 2 and 3).

Alternative B – Power is transmitted overunused conductors 4‐5, 7‐8 (Pairs 1 and 4)

IEEE 802.3 af/at PSEPower Requirements

IEEE 802.3 af/at PSEPower Requirements

IEEE 802.3 af/at MidspanPower Requirements

IEEE 802.3 af/at MidspanPower Requirements

IEEE 802.3az Standard (EEE)

Energy Efficient Ethernet (EEE) –Released on 2010. Enhancements toEthernet over Twisted‐Pair , that allowsless power consumption during periodsof low data activity.

Projected Power savings of 45 to 80percent (Switches, Routers, AP).

IEEE 802.3az Standard (EEE)

Allows each port on a Switch (PSE) topower down into a standby or “sleep”mode when there’s no activity.

Switch detects cable length of each linkand adjusts the power accordingly.

Approximately 4.5W/port is wasted on aCAT5/CAT5e/CAT6/CAT6A cable after100meters.

IEEE 802.3az Standard (EEE)

Energy Efficient PoE (EEPoE) – Increaseefficiency by 94% transmitting over thesame cable, powering IEEE802.3atcompliant devices in synchronous fourpairs.

Projected Power savings of 45 to 80percent (Switches, Routers, AP).

IEEE 802.3 az (EEPoE) Example

Design Considerations for PoE1) DO NOT assume your device is 802.3af

compliant because it is listed as PoE‐capable.

2) Because there is no requirement for PSEsto perform BOTH Mode A and Mode B,verify with the vendor documentationwhich mode their device utilizes.

3) Confirm specific model numbers andoperation of the equipment required.

Design Considerations for PoE4) Determine the Total Load of you PSE

equipment by adding the powerrequirements of all the PD’s plus a 25%buffer for future growth.

5) The application requires PoE+ or PoEdevices?. This will determine if yourswitch will be PoE or Full PoE.

(PoE) Examples

(PoE) Examples

(PoE) Examples

(PoE) Examples

THANKS…….

Carlos E. Carle, PEccarle@prtc.net

SignaMax Connectivity Systemswww.signamax.com