[TriLUG] OT: Ethernet hot-pluggability

[Rick DeNatale]

On 8/8/05, Aaron Joyner <aaron at joyner.ws> wrote:
> There is a protocol
> (802.3af) designed to allow the device end to request power, and allow
> the transmitting end to define how much power the port is allowed to
> consume.  

As I understand it, it's not a protocol as we normally use the term,
it's all done using electrical properties. The power sourcing device
uses a small limited current to pulse to determine the impedance
presented by the device.  This impedance in turn determines the power
requirement.

For more here's an engineering note on a design for the power sensing:
http://www.powerint.com/PDFFiles/di88.pdf

It would be hard to use any kind of network protocol with a device
which needed power before you gave it any power.