06-01-2011 04:30 AM - edited 03-16-2019 05:14 AM
Good day!
We purchase 20 new Ip Phones 9971 (CP-9971-W-CAM-K9) with CAM and extension module (CP-CKEM-W=), i we already have PoE+ switch HP E2910-24G-PoE+ (J9146A).
Is there any compatibility problems between 9971 and third party PoE+ HP switces?
Solved! Go to Solution.
06-02-2011 07:53 AM
You are correct on your power assumptions then, but you are cutting it very very close. I had a rollout going on and the customer purhcased 3750 POE switches. We started loading up the switches and got down to the last couple phones and found out there was not enough power for the last few phones. The person who spec'd out the switch, forgot to figure out the POE requirements for 7975 color phones. When all 48 POE ports are full, there is not enough power for all 7975 phones.
Also, Im not quite sure, but I think the power sequence may draw more power initially. The only way to check is to monitor the power as the phone is plugged in. If you reboot your phones all at once, you may see a power spike and a few phones not come on, until possible the switchport is reset. Im not sure how it would work in the HPs to reset the POE when power is "full".
It boils down to doing some tests. Theory is one thing, testing is another.
06-01-2011 11:22 AM
Just remember, the 9971 sucks a ton of power.
IEEE 802.3af Power over Ethernet (PoE): provides up to 15.4 W per port to IEEE 802.3af-comp is what your switch will handle.
The side car is using the power cube, but that only powers the side car alone, not the phone. (reduces the phone down to a 802.3af.
If you want the 9971, with camera and side car, it is now a class 4 802.3at requirement. Your HP switch will not power the device properly because in will require more than 15.4ws.
And remember, the switch can only provide so much POE power. I was trying to dig around the specs, but they dont say (or couldnt find) what HP recommends. Just because it has a 20 port switch, does not mean you can power 20 POE devices at 15.4w. (or maybe you can?)
If you buy the power cube for the side car, then the phone will work on your switch. Because it will now be a 802.3af compliant.
06-02-2011 04:59 AM
Good day, Tommer Catlin!
As i can find on cisco.com:
Power Requirements
- Cisco Unified IP Phone 8961, 9951, and 9971 support IEEE 802.3af Class 3 power on signal pairs and spare pairs.
- Cisco Unified IP Phone 8961, 9951, and 9971 support IEEE 802.3at for external add-on devices.
As far as I remember to get Watts you need: 48VDC * 0.2A = 9.6 W |
PoE |
---|
The updated IEEE 802.3at-2009[7] PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power.[8] Some vendors have announced products that claim to comply with the 802.3at standard and offer up to 51 W of power over a single cable by utilizing all four pairs in the Cat.5 cable.[9] |
06-02-2011 07:53 AM
You are correct on your power assumptions then, but you are cutting it very very close. I had a rollout going on and the customer purhcased 3750 POE switches. We started loading up the switches and got down to the last couple phones and found out there was not enough power for the last few phones. The person who spec'd out the switch, forgot to figure out the POE requirements for 7975 color phones. When all 48 POE ports are full, there is not enough power for all 7975 phones.
Also, Im not quite sure, but I think the power sequence may draw more power initially. The only way to check is to monitor the power as the phone is plugged in. If you reboot your phones all at once, you may see a power spike and a few phones not come on, until possible the switchport is reset. Im not sure how it would work in the HPs to reset the POE when power is "full".
It boils down to doing some tests. Theory is one thing, testing is another.
06-02-2011 11:35 AM
Tommer Catlin, thank you for your advice!
We will test this schema! =) hope, all will work correctly!
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