3.4.7 - Power Over Ethernet Issues

Flashcards about Power Over Ethernet (PoE)

What pairs does Alternative A use to deliver power and data?

Pairs 1/2 and 3/6

With what link speeds is Alternative A compatible?

10/100 and 10/100/1000

What pairs does Alternative B use to deliver power?

Spare pairs 4/5 and 7/8

Is Alternative B compatible with Gigabit Ethernet?

No

What is required by PoE++ Type 3 and Type 4 PDs?

Four-pair power delivery over all pairs

With what link speeds is four-pair power delivery compatible?

10/100/1000 and 10G

What cabling is required for PoE+?

Cat 5e or better, but Cat 6A is typically recommended

Why does drawing power down the cable generate more heat?

Due to resistance

How can thermal performance be improved?

Using pure copper cabling with thicker conductors and shielded cabling

How is conductor thickness measured?

American Wire Gauge (AWG)

What does a smaller AWG number mean?

A thicker wire

What can happen if a PD only supports the first PoE standard?

The negotiation process with the switch may fail, especially with high power PoE++ Type 4 PDs

What must the switch and PD negotiate?

A compatible mode

What is a typical total power budget for a switch?

Around 300–400 watts (30,000–40,000 milliwatts)

What can happen if the power requirements exceed the budget?

Some devices will not be activated, or there might be intermittent resets

What command reports the power budget and consumption?

show power inline

What can be done if the power budget is exceeded?

Provision another switch or use power injector devices