True Knowledge
10Base-T, 100Base-TX, 1000Base-T and 1000Base-TX. The differences and commonalities.
10Base-T: 10 Mbps (megabits per second), over 100 meters of standard Ethernet cable, consisting of four twisted pairs. Only two are used for data pairs. Two are unused (spare pair). One wire pair is dedicated to sending signals in one direction while ...
Why is PoE+ power output 30W?
When the IEEE 802.3at standard was written, it became clear that lead-acid batteries were obsolete. Most applications had turned to the AC-DC power supply. The minimum voltage can be target at 50 V. The current was fixed at 600 mA to keep the ...
Why is PoE power output 15.4W?
When IEEE 802.3af was written, the committee had CAT3 cable in their mind. They assume it’s the worst case. And 350 mA is the maximum continuous current considered to be safe for CAT3 cabling. The typical PoE voltage is 48Vdc but may drop to 44V, ...
Why does PoE use 48V?
First, 48V is just symbolic. In reality, the actual voltage range might not even include 48 volts. By nature, PoE is DC power. And historically, DC power source equals batteries. A typical lead-acid battery has a nominal voltage of "12V", but they ...