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Cisco 9971+CKEM and third party PoE+ switch

incomf_lankey
Level 1
Level 1

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?

1 Accepted Solution

Accepted Solutions

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.

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4 Replies 4

Tommer Catlin
VIP Alumni
VIP Alumni

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.

Good day, Tommer Catlin!

As i can find on cisco.com:

Power Requirements

If the Cisco Unified IP Color Key Expansion Module is connected to a Cisco Unified IP Phone that uses 802.3AT power, a local power supply is not required. If the phone uses 802.3AF power, you must connect a power cube to it for it to supply power for all connected key expansion modules. If the phone is already locally powered by a power cube, no additional power cube is required when installing the key expansion module to it.

-    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.


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]
Аnd switch HP E2910-24G-PoE+ has 490 W (maximum) power consumption (http://h10010.www1.hp.com/wwpc/uk/en/sm/WF06b/12883-12883-4172267-4172278-4172278-3901671-3901677.html).
In my case we have ten phones CP-9971-W-CAM-K9 (now we don't need to power up CAMERA!) and ten CP-9971-W-CAM-K9 with ten extension modules CP-CKEM-W=. It requires ten PoE 802.3af ports (for 9971 without CKEM and CAMERA) and ten PoE+ 802.3at ports (for 9971 with CKEM, without CAMERA):
10*30,8W per phone = 308W
10*15,4 per phone = 154W
308W + 154W = 462W
HP E2910-24G-PoE+ has 490 W (maximum) power consumption!
No power cube required for this scheme. Correct me if I'm wrong!

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.

Tommer Catlin, thank you for your advice!

We will test this schema! =) hope, all will work correctly!

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