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FAQ

  • IEEE 802.3 is the standard that defines the physical layer of Ethernet cabling. It includes wire type, signal level and bandwidth in 2003, the standard was updated to include PoE IEEE 802.3af defines the voltage and power availability of devices on a network. The specification provides PoE with up to 15.4 watts of power. The specification was updated again in 2009. The IEEE 802.3 at provides higher power (25.5 watts), called PoE +.

    The IEEE-compliant PoE injector provides 44 to 57 volts. The effective distance of the cable is the same as the standard ethernet distance of 100 meters (328 feet). There are two modes, A and B, for powering devices. These modes define the polarity of the wire pair and the voltage used for the power supply. The new PoE injector can provide more than 50 watts of power to a network-connected device. These higher power Ethernet devices use two pairs of wires to transmit power to the device.

    802.3af (2003)
    • Power Sourcing Equipment (PSE) transmitted a maximum of 15.4W which assured delivery of 12.95W (350mA) to the Powered Device (PD).
    • Total throughput was limited to 100Mbps and allowed power to be distributed over only two pairs, and in two different modes (Mode A and Mode B) as seen in Figure 1 below.

    Figure 1

    IEEE 802.3at (2009)
    • Power Sourcing Equipment (PSE) transmitted a maximum of 30W which assured delivery of 25.5W (600mA) to the Powered Device (PD).
    • Total throughput was limited to 1000 Mpbs or 1Gbps.
    • The same Mode A and Mode B were used again, and the same pairs are used to transmit power. The difference with 802.3at is that all four pairs are used to transmit data packets to achieve 1Gbps throughput (Figure 2).

    Figure 2
    IEEE 802.3bt (2018)
    • Two power levels emerging: Version 1 - 60W from Power Sourcing Equipment (PSE) and 50W assured at Powered Device (PD) side. Version 2 - about 100W from PSE and about 80W assured at PD side.
    • All four pairs will transmit data packets and power.
    • Total throughput will be 10Gbps, a 10x increase over previous generations.
    • Backwards compatible with previous generations of PoE; 802.3af and 802.3at.
    • Figure 3 illustrates a proposed 4-pair power delivery solution.

    Figure 3
  • A POE injector, which is also called as a “midspan,” injects power onto an Ethernet cable. Thus it combines power with data which is from a non-PoE switch or “endspan.” It has an external power supply.

    PoE Injector
    The POE injector is well suited for low-power installations where power outlets are not available. As a result, greater flexibility can be achieved by providing access to equipment installed in hard-to-reach areas with minimal impact on existing structures and budgets.


  • Power over Ethernet (PoE) is also called PoE power supply. It is a technology that can transmit power and data to devices through Ethernet over twisted pair.

    Through this technology, devices such as VoIP, wireless base stations, cameras, hubs, and computers can be powered by PoE technology.

    Products using PoE


    IP Camera

    VoIP Phones


    Wireless Access Points


    Since electronic devices powered by Ethernet can be used without an additional power outlet, the time and money for configuring the power cord can be eliminated, and the cost of the entire equipment system is relatively reduced. RJ-45 sockets are widely used all over the world, that makes so all PoE devices are compatible. This technique is often compared to the traditional telephone network (POTS), which also receives power and data (although analog data) on the same cable. PoE does not need to change the Ethernet cable layout to operate, thus the PoE system not only saves cost, but also has the ability to control the power on and off remotely.

    PoE power supply terminal is divided into Power Sourcing Equipment (referred PSE) and the receiving end (Powered Device, referred to as PD).

    PSE

    Power sourcing equipment (PSE) refers to devices such as a network switch that provides (sources) power on the Ethernet cable. When the device is a switch, it is commonly called an endspan. Otherwise, if it's an intermediary device between a non PoE capable switch and a PoE device, it's called a midspan. An external PoE injector is a midspan device.

    PD

    Powered device (PD) refers to devices powered by a PSE and thus consuming energy. Examples include wireless access points, VoIP phones, and IP cameras.
    Many powered devices have an auxiliary power connector for an optional, external, power supply. Depending on the PD design, some, none, or all power can be supplied from the auxiliary port, with the auxiliary port sometimes acting as backup power in case PoE-supplied power fails.
  • Specifying Power over Ethernet brings many advantages to an installation:

    • Save Time and cost-by reducing the time and cost of installing power cables. Network cables do not require a qualified electrician to install them, and can be located anywhere.
    • Flexibility-no need to connect the power outlet, IP camera and wireless access point devices can be placed in the most needed place, if needed, can easily reposition.
    • Secure-PoE delivery is intelligent and designed to protect network devices from overload, strong or incorrect installation.
    • Reliability-the PoE power comes from a central and universally compatible source, rather than a collection of distributed wall adapters. It can be backed up via uninterruptible power supply, or it can be easily disabled or reset by control.
    • Scalability-having power available on the network means the installation and distribution of network connections is simple and efficient.
  • Many Internet connected devices, such as IP cameras, VoIP phones, WIFI radios, and Ip access card readers, use Power over Ethernet. A single network cable transmits data and power to the device, making installation simple. Data uses one set of wires, and power uses another set of wires in a network cable.
    Devices that plug power into certain wire pairs in an Ethernet cable are called injectors or MIDSPAN. Use a separate power supply (injector) or use an Exchanger containing built-in PoE to inject power to an Ethernet cable. Many devices using PoE comply with the IEEE standard. But be careful. Some devices don't meet this standard. Before using PoE, it is important to know exactly what voltage and current is required for the device. Here's a review of the technology.

    PoE Injector

    In all cases, electricity is sent over a network line. In diagram A, power is supplied on the same wire as the signal. In Mode B configuration, power is provided through two sets of optional wires in the network cable.
    The following figure shows the pattern a configuration. The power supply is provided by a Exchanger, which Exchanger includes a PoE on a port or an injector connected between the switch and the device.


    PoE Mode A Diagram

    The following figure shows the Mode B configuration. In this case, power from the switch or ejector is supplied on a separate network line. Many devices are designed to receive power using either mode a or mode B.


    PoE Mode B Diagram

    There are some passive PoE sources and there are “active” or “smart” type sources.  The “active” type communicates with the device. This provides device protection that can prevent damage caused by short circuits, as well as providing overcurrent and overvoltage protection. The passive PoE sources are less expensive and provide power without any verification from the device.
    Power sources that conform to the IEEE standard include network switches individual or multiport PoE injectors (or midspans).

  • A splitter is a device that is the opposite direction of the Injector. It has two output cables: one supplies data and the other power. It is used to deploy remote non-PoE devices with no nearby AC outlets.

    A PoE splitter allows a non-compliant device to upgrade to PoE. By plugging into the network connection, it can pull power, and convert it into low-voltage ranges as required.





    The difference between the injector and separator is that the PoE injector delivers power to a PoE device receiving data through an existing non-PoE switch. The splitter also provides power, but it does so by separating the power from the data and feeding it into separate inputs that can be used by non-PoE compatible devices.
  • Both the POE injector and splitter deliver power according to each of the four power sources. The newer the device is, the higher the power level most likely to be required for the PoE Product List Type-3 is the current mainstream The Type 4 product is rising rapidly.

    Levels of Power

    IEEE Standard

    Watts Supplied

    Type 1

    IEEE 802.3af

    Up to 15.4W

    Type 2

    IEEE 802.3at

    Up to 30.8W

    Type 3

    Ultra PoE/802.3bf

    Up to 60W

    Type 4

    IEEE 802.3bt

    Up to 960W


  • Passive PoE: also known as "always on”. Power is delivered immediately without negotiation.
    Active PoE: IEEE 802.3 af / at (active PoE) , standardized solution to provide power from a power supply device after negotiation with the receiving device.


    PoE 802.3af/at

    Passive PoE

    Related cost*

    Medium

    Low cost*

    Max.cable distance

    100m

    100m

    Power Injection

    After Negotiation

    Immediately

    Ethernet Support

    10/100/1000 Mbit/s

    10/100 Mbit/s(injected pairs +4,5 and -7,8)

    Standard

    802.3af/at

    N/A, use by some vendors such as Mikro Tik or Ubiquity

    Robust Against Wrong Cabling

    Yes

    No. Only anchor device can be connected into PoE socket!

    Never connect to PC or another network device.