[cisco-voip] Power over ethernet question

[Gary Roberton]

Hello

We are running a 3750 PoE switch and are attaching 3rd party phones to
it.  I understand that IOS 12.2(25) introduces power budgeting but I
want to understand what is happening with the phones before
introducing an enforced power budget.

My inline power status is;

Module   Available     Used     Remaining
          (Watts)     (Watts)    (Watts)
------   ---------   --------   ---------
1           370.0      369.6         0.4

Interface  Admin    Oper     Power        Device           Class
                            (Watts)
---------- ----- ---------- ------- -------------------  ----------
Fa1/0/1    auto  off           0.0  n/a                  n/a
Fa1/0/2    auto  on           15.4  Ieee PD              Class 0
Fa1/0/3    auto  on           15.4  Ieee PD              Class 0
Fa1/0/4    auto  on           15.4  Ieee PD              Class 0
Fa1/0/5    auto  on           15.4  Ieee PD              Class 0
Fa1/0/6    auto  on           15.4  Ieee PD              Class 0
Fa1/0/7    auto  on           15.4  Ieee PD              Class 0
Fa1/0/8    auto  on           15.4  Ieee PD              Class 0
<REMOVED>


On debugging the port I get the following output;

1d16h: ILP uses AC Disconnect(Fa1/0/7): state= ILP_DETECTING_S, event= TWTI_CLAS
S_DONE_EV
1d16h: %ILPOWER-7-DETECT: Interface Fa1/0/7: Power Device detected: IEEE PD
1d16h: ilpower_powerchange( Fa1/0/7 ) power: 15400
1d16h: ILP Power apply to ( Fa1/0/7 ) Okay
1d16h: ILP Start PHY Cisco IP phone detection ( Fa1/0/7 ) Okay
1d16h: %ILPOWER-5-POWER_GRANTED: Interface Fa1/0/7: Power granted
1d16h: ILP Power Accounting REQ_PWR ( Fa1/0/7 ) Okay sys_used=369600
1d16h: ilpower_pd_statechange( Fa1/0/7 ) pd_class: 3
1d16h: ILP State_Machine ( Fa1/0/7 ): State= ILP_IEEE_PD_DETECTED_S, Event= TWTI
_PWR_GOOD_EV
1d16h: ****Power controller address 0x42****
1d16h: Reg 0x0  = 0
1d16h: Reg 0x1  = F6
1d16h: Reg 0x2  = 0
1d16h: Reg 0x4  = 0
1d16h: Reg 0x10 = FF
1d16h: Reg 0x12 = AA
1d16h: Reg 0x13 = F0
1d16h: Reg 0x14 = FF
1d16h: Reg 0x17 = A0
1d16h: *************************************

It would seem that each device is given a class of 0 (IEEE Optional)
meaning that 15.4w is budgeted.  However on closer inspection of the
debug I can see this line - ilpower_pd_statechange( Fa1/0/7 )
pd_class: 3

Does this mean that the phone has requested class 3?  I know my phone
requires 6.8w, which is within class 3, however I want to know if it
is the phone that has requested class 3 .
One final question, if the phone has asked for class 3 and I limit the
port to 7.5w using power management does this mean that the switch
will refuse power?  Does the switch make its decision based on the
class that the device asks for or the amount of power consumed?

If anyone can respond quickly I would really appreciate it.

Best regards

Gary