Mike's PBX Cookbook

Power over Ethernet

802.3af is the original PoE standard, 48VDC at up to 350mA - not to exceed 15W - originally designed to power IP telephones.
802.3at (also known as PoE+) provides up to 25.5 W of power, and prohibits Inline Power, enabling 1000 Base-T support.

Power is carried over the (Category 3, 5, 5e and 6) cabling by one of the following techniques:

The power source (not the device) decides whether Mode A or B is used. Compliant devices must support both Modes.
Avaya IP Phones support Mode A (2 pairs) with a PoE data switch, and/or Mode B (4 pairs) with a midspan power injector.

Pin #
T568A T568B 10/100 Base-T 1000 Base-T
Pair Colour Pair Colour  A-MDI  A-MDIX Mode B Mode A Mode B
1 3 2 Rx+ Rx+ Rx+ TxRx A+ TxRx A+
2 Rx- Rx- Rx- TxRx A- TxRx A-
3 2 3 Tx+ Tx+ Tx+ TxRx B+ TxRx B+
4 1 1 unused unused DC+ TxRx C+ TxRx C+
5 DC+ TxRx C- TxRx C-
6 2 3 Tx- Tx- Tx- TxRx B- TxRx B-
7 4 4 unused unused DC- TxRx D+ TxRx D+
8 DC- TxRx D- TxRx D-

DC 48V (+)DC Return (-)

T568A and T568B are the two wiring standards for 4-pair data cable. The only difference is the position of the orange and green wire pairs. T568B is preferred, and should be used wherever possible. A "crossover" cable has A at one end, and B at the other.

Home » Other » Rj45poe