Passive PoE?

[TommyPedersen69598]

We would like to use passive PoE for Cisco CP-7821 IP phones in a special application.

Edit: By passive PoE I mean applying voltage without the standardized protocol that determines device class etc before the application of 48V.

1. Does the phone support passive PoE?

2. What voltage should we use? Is 48V ok? What is the preferable voltage?

3. If we would like to support other Cisco phone models, e.g. 8811, do these support passive PoE?

Thanks in advance for answers!

[TommyPedersen69598]

Thanks, I am referring to providing power directly - without IEEE 802.3af negotiation, - with the pinout of 802.3af mode B which in the final state provides 48V on the two unused pairs in 100Base-TX.

No questions that the Cisco phones supports 802.3af and at. The question is if also direct power is possible (either that it actually is designed so in the phone, and/or it is allowed in the standard).

I know the standard implementation has a number of advantages regarding shutting down power if not needed and not providing more power than the device has asked for, but none of those advantages are really applicable in our case as the PoE PSE will be integrated in the box we build on the back of the IP phone. The PSE and the PD in essence becomes the same device in our case.

Just because the phone supports standard 1 and 2 does not mean that is does not support standard 3. A traffic light may have a yellow light and not only green and red to make an overly obvious analogy.

[Nithin Eluvathingal]

Better you involve local Cisco. The hardware team could be able to confirm it.