Power Over Ethernet: Implementatión Simplified

Deliver power and data over one connection to simplify network installation and reduce costs; eliminating the need for additional power supply.


What is Power over Ethernet?

A PoE system consists of two elements, the Power Sourcing Equipment (PSE) and one or more Powered Devices (PD). A Powered Device, once connected to a Power Sourcing Equipment, does not need a dedicated PSU because the PSE supplies the power via the Ethernet cable.

Usually, the PSE is an Ethernet access switch at the edge of the network. But it can also be a dedicated device, like a power injector, that adds the PoE to a non-powered Ethernet cable or media converter equipped with a PoE port.

The Powered Device could be a range of equipment: wireless Access Point, VoIP phone, IP camera, lighting system, or any other IoT device or sensor.

Aplicación PoE
Aplicación PoE

 

What are the advantages of PoE Technology?

Cost

Installing PoE devices lowers costs because separate power supplies and cables are not required—only a connection to an Ethernet port on the PSE. Upgrading a standard Ethernet network to support PoE only requires replacing the access switch, the other physical infrastructure can stay the same.

Reliability

Power failures are a leading cause of reliability problems in any network. Battery backup units reduce dependency on continuous power and increase the reliability of active devices. However, this approach can be expensive in a large network, requiring that all active devices connect to a battery backup unit. By delivering PoE instead, the cost is minimized by connecting only the access switch to the battery backup. During a power outage, the switch and all the connected PoE devices stay powered.

Flexibility

PoE switch interfaces can connect to PoE or non-PoE devices without any restriction. Once a PoE switch is in place, it is possible to connect a PoE or non-PoE device to the Ethernet port. The only limitation is that the total PoE power requirements are within the power budget of the switch.

How much power can PoE supply?

The amount of PoE power that a switch can supply is dependent on two things:

  • The maximum PoE power a single port can supply
  • The total PoE power available (the power budget)

The first value determines if a powered device is compatible with the port of a specific switch. The second value indicates how many powered devices can connect to the same switch.

 

PoE Power Classes

The maximum power supplied by a single port depends on the switch's capabilities, as defined by international standards (such as IEEE 802.3at and IEEE 802.3bt). These rules dictate that a switch or injector can't supply more power than the standard allows. The standards define four power level types for individual PoE ports:

Type 1 (called PoE)
Maximum power per port is 15W. (Allowing for losses through the cable, the max power available at the PD is 12.95W)

Type 2 (known as PoE+)
Maximum power available for each port is 30W (or up to 25.50W at the PD)

Type 3 (called 4PPoE, Ultra PoE, UPOE)
Maximum per port power is 60W (which equates to 51W at the PD)

Type 4 (called Ultra PoE, UPOE)
Maximum power available for each port is 100W (with up to 71W available at the PD)

For a reliable PoE solution, the PD's power requirements must match the capabilities of the PSE's port.

 

PoE Power Budget

The power budget is the maximum PoE power a PSE can supply to all of its PoE ports. Therefore, a switch can power all the connected PDs provided the total power consumption of the devices does not exceed the power budget of the switch. If the PDs draw too much power from the PSE, it may cause an error condition that restricts power to some PDs.

It is important to note that most PSEs use the PoE Type to calculate the power consumption, not the actual PD consumption. This means that even if a PD is consuming only 20W, the PSE assumes that it is a Type 2 device and allocates it 30W.

 

Smart Power Budget Features

Allied Telesis has been developing PoE products ever since the first standards were published. We've used this experience to create some useful features that make using PoE more flexible and reliable:

PoE Power Budget Override

Instead of allowing the switch to determine the PD power consumption using PoE Type, our switches enable you to specify the maximum power a port can supply. This optimizes the amount of power for each device to support more PDs per switch.

Dynamic Power Allocation

Some Allied Telesis switches can calculate their power budgets based on the actual power consumption of the attached PDs. So, the budget reflects the real-time power requirements of the connected PDs, and no manual configuration is required.

PD Priority

If the PDs exceed the PSE power budget, the PSE will remove power from some PDs to protect itself from damage. Our switches allow you to allocate a priority to each of the PDs so you can choose those to sacrifice first to protect your most critical services.

 

Continuous PoE

Usually, when the switch is rebooted (for a firmware upgrade, for example), the PoE power is interrupted until the switch is back online. Continuous PoE maintains power throughout the reboot to minimize disruption and keep PDs operational.

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