Solved: 7970 and PoE

donjohnson911 · ‎06-05-2007

Hello,

I have a number of questions regarding using the 7970 IP Phone with PoE. Firstly, I have an IEEE 802.3af power injector that isn't a Cisco brand. It is 48v and I'm wondering if I can use that with the phone, though I understand this is probably not the most recommended resolution because it isn't a Cisco product. I'm just wondering if it has the right specifications to meet the need of the phone (being the 802.3af IEEE 48v interface).

Secondly, I've read that for full screen brightness it is recommended that you get a PWR-CUBE adapter for the phone. What I'd like to know is what the difference is exactly? Is it possible to run the phone, fully featured, without having to get a PWR-CUBE for each of the 7970's we have here. If the screen is just a little bit dark I think we can live with that.

Thanks a lot for all the great assistance you guys have given me. This tool really is indispensable.

Rob Huffman · ‎06-05-2007

Hi Don,

You are most correct using the 48v model. I also found a note indicating 3rd party IEEE 802.3af switches are supported with the 7970;

IEEE 802.3af, also known as PoE, defines a way to build Ethernet power-sourcing equipment and powered terminals. The specification involves delivering **48V of AC power over unshielded twisted-pair wiring. It works with existing Ethernet cable plan, including Category 3, 5, 5e, or 6; horizontal and patch cables; patch panels; outlets; and connecting hardware, without requiring modification. The IEEE 802.3af standard specifies support for two power levels, low-power powered devices at 7W per port and

high-power powered devices at 15W per port.

7970 Power Consumption and Display Brightness for Power Configurations

IEEE 802.3af Class 3 power from a third-party switch

Max. Power Consumed from a Switch 6.3 W

Phone Screen Brightness Approx. 1/2

http://www.cisco.com/en/US/products/hw/phones/ps379/products_administration_guide_chapter09186a008066b8d0.html#wp1079121

Hope this helps!

Rob

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Tommer Catlin · ‎06-05-2007

Ok, that made me laugh.

Nah, the POE will not burn out the phone at all. It will either power up the phone, or no power will be available for it.

Customer of mine had 4006 CAT switches with POE blades in, but not using the POE function. (no power shelf) So, we got new 4506 switches, pulled the blades out and put them into the new switches, worked like champ. But later, realized that the POE used in the older blades is not the same as the new blades. We could supply power to our AP's in the office, which was odd. Check on some tech specs and turns out, there IS a differene in the newer and older blades. I dont have it in front of me, but that was the issue.

So no, it would burn out a phone, never. It's still standard POE, but the newer version supplies just a tad more into the line.

I'm more of a Reno 911 junkie. So Lt. Dangle is the man. haha

View solution in original post

Rob Huffman · ‎06-05-2007

Hi Don,

Be careful with this one :)I don't see why the 3rd party power injector wouldn't work although I do agree with your assessment on the recommended resolution. IEEE 802.3af is certainly supported on the 7970. My vote would be to go Cisco but it may be worth a try!

For your second question, we run our 7970's without any power cube and the screen brightness is really good. I have never had any user ask for it to be "brighter".

Hope this helps!

Rob

donjohnson911 · ‎06-05-2007

Am I correct in needing the 48v model? I assume if all the specifications are correct then it will work, also. I assume there has to be people out there running cisco phone networks, with maybe another brand of router with PoE.

Rob Huffman · ‎06-05-2007

Hi Don,

You are most correct using the 48v model. I also found a note indicating 3rd party IEEE 802.3af switches are supported with the 7970;

IEEE 802.3af, also known as PoE, defines a way to build Ethernet power-sourcing equipment and powered terminals. The specification involves delivering **48V of AC power over unshielded twisted-pair wiring. It works with existing Ethernet cable plan, including Category 3, 5, 5e, or 6; horizontal and patch cables; patch panels; outlets; and connecting hardware, without requiring modification. The IEEE 802.3af standard specifies support for two power levels, low-power powered devices at 7W per port and

high-power powered devices at 15W per port.

7970 Power Consumption and Display Brightness for Power Configurations

IEEE 802.3af Class 3 power from a third-party switch

Max. Power Consumed from a Switch 6.3 W

Phone Screen Brightness Approx. 1/2

http://www.cisco.com/en/US/products/hw/phones/ps379/products_administration_guide_chapter09186a008066b8d0.html#wp1079121

Hope this helps!

Rob

donjohnson911 · ‎06-05-2007

Thank you very much. This was extremely helpful information!

Rob Huffman · ‎06-05-2007

Hi Don,

You are most welcome :) The 7970's are a fantastic phone. Very "Top of the Line". You should have some really happy users when you roll these out.

Thanks for the nice comments and rating,

Rob

Tommer Catlin · ‎06-05-2007

I have also found in the field older 48 port line cards in the CAT switches to have the older version of POE. They do not spit out enough power to bring a 7970 or an access point online. It was the first version of POE, forgot what it was now, but just beaware, all POE cards in the CATs are not the same. POE has (2) different flavors of output power. (I was suprised to find as well!)

looks like Rob got your answer for you, but just thought I would add my 2 cents.

Nice name too, not sure if I should ask what it means?? donjohnson911? ha

cheers!

donjohnson911 · ‎06-05-2007

Hello,

Thanks for the added information. If it is not the correct flavor of PoE do you suspect it may burn out the phone? I would be quite upset if this was the case. Seems to be a somewhat new injector though.

To answer your question donjohnson911 is 2 things conjoined. :p Firstly, Nash Bridges is pretty much the man. Second, I work for a sherrifs department, thus the 911. :)

Thanks!

Tommer Catlin · ‎06-05-2007

Ok, that made me laugh.

Nah, the POE will not burn out the phone at all. It will either power up the phone, or no power will be available for it.

Customer of mine had 4006 CAT switches with POE blades in, but not using the POE function. (no power shelf) So, we got new 4506 switches, pulled the blades out and put them into the new switches, worked like champ. But later, realized that the POE used in the older blades is not the same as the new blades. We could supply power to our AP's in the office, which was odd. Check on some tech specs and turns out, there IS a differene in the newer and older blades. I dont have it in front of me, but that was the issue.

So no, it would burn out a phone, never. It's still standard POE, but the newer version supplies just a tad more into the line.

I'm more of a Reno 911 junkie. So Lt. Dangle is the man. haha

donjohnson911 · ‎06-05-2007

Awesome great information.

Thanks!

p.s. I am also a Reno 911 fan, absolutely hilarious show. :)