Power over Ethernet
Power over Ethernet ( PoE) is a procedure that can be powered via an 8-wire Ethernet cable with power to the network devices.
General
In a narrower sense today with PoE mostly the IEEE 802.3af - 2003 ( " DTE Power over MDI") is meant, which was adopted in June 2003, in its final version. Before there were already some vendor-specific implementations, which were also sold under the name Power over Ethernet. There is a newer standard IEEE 802.3at - 2009 - before remediation as PoE or PoE plus known - which increases the maximum power output of 15.4 W to 25.5 W.
Main advantage of Power over Ethernet is that you can save a power cable and so even in hard to reach areas or in areas where many cables would interfere, can install Ethernet connected devices. This product allows on the one hand, sometimes drastically reduce installation costs, on the other hand so easy to implement using a central uninterruptible power supply (UPS ) can increase the reliability of the connected devices.
PoE is used by network devices that require little power. It is typically used in IP phones, small hubs, cameras, small servers or wireless transmission devices ( wireless access points, Bluetooth access points ).
802.3af divides the devices involved in energy source (Power Sourcing Equipment PSE) and consumer (Powered Devices PD). The supply voltage is 48 V, the maximum current consumption of the devices 350 mA ( 802.3at Type 2: 600 mA) in continuous operation ( briefly when you turn 400 mA allowed). The maximum output power is 15.4 watts. The standard assumes that after line losses 12.95 watts usable power remain or may be taken so as not to exceed the maximum power output. For energy transfer normally be the ( Ethernet and Fast Ethernet) free pairs in the Ethernet cable. If this is not possible (because, for example, ISDN is fed via line or Gigabit Ethernet), the signal carrying conductors can be used. Consumers need to support both modes of operation, consumer support only one mode are not permitted. The power supply via the signal lines affects (10 Mbit / s) and 100BASE -TX (100 Mbit / s ) is not disturbing to the Ethernet signal for 10BASE -T. Also on 1000BASE -T ( Gigabit Ethernet) PoE is possible. Since 1000BASE- T has all 8 wires in the cable, the DC voltage for the power supply is hereby given to any case " under the signal".
The challenge for manufacturers of proprietary PoE solutions existed earlier is to avoid damage to non-PoE devices where possible. Although the veins are 4, 5, 7 and 8 actually not used for 10BASE -T and 100BASE- TX, that does not mean that it is not yet NICs are, etc., in which the corresponding pins are looped after somewhere. If there accidentally Power over Ethernet should lie, this can lead to irreparable damage to the device. 802.3af solves this problem by a process called Resistive Power Discovery process. Here, the utility shall initially multiply a minimal tension on the wires, the damage can no device in the normal case. He recognizes whether and where the energy consumer has a 25 k-ohm terminating resistor and thus is PoE capable. Then the load is powered with low power, and now needs to signal to which of four defined in the standard output classes it belongs to. Only then the PD gets the full power and can resume operation.
The power to the powered devices can be carried out by so-called end-span devices (eg switches ) or midspan devices ( units between switch and end device ).
As Midspan Devices Hubs or so-called PoE injectors are usually used to supply the power to the respective wires. Due to the additional space requirements and the additional necessary patch cables in wiring closets and patch panels ( patch panels, PoE patch panels ) are now available, which provide the power. These replace the conventional patch panels and therefore do not take up extra space in the wiring closets. Through appropriate management software on each port can be defined without current or energized with these patch panels.
Available power classes
Classification signature
General features
- Twisted-pair cable CAT -5 ( UTP cable with possible)
- RJ45 connector
- Remote power supply called (power over unused pairs of data ), also known as phantom power or Mode A
- Designated power over unused pairs of data, even as spare -pair power or mode B
- Midspan (power supply through intermediary sources, example: PoE Injector )