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Author Topic: 3524GT-PWR+ POE - 30W???  (Read 5669 times)

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Offline mega8220

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3524GT-PWR+ POE - 30W???
« on: August 02, 2013, 01:14:32 AM »
hi all,

I have a little problem with ERS 3524GT-PWR +.
What happens is when I connect an IP phone Cisco (has webCam and additional panel) to a Cisco Switch POE turns on as normal, but when I connect it to ERS 3524GT-PWR + only turn on the phone but do not turn on the webcam and the additional panel .
When revice power consumption in the SW 18w cisco was about as revice in the ERS 3524GT-PWR + was only 6.7w, set several things in the ERS to improve but always consumes the same, according to the datasheet supports up to 30W per port but I can not increase it.
My question is if there is any way to make the switch to emit more power per port.
In reviewing the datasheet says team provides 370W but if that value is divided into the 24 port that has 15W per port would come about then, I wonder Where will get the 30w?.

Greetings.


Offline Telair

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Re: 3524GT-PWR+ POE - 30W???
« Reply #1 on: August 02, 2013, 01:52:58 PM »
The 3524GT-PWR+ switch can output up to 32 watts per port, so you should be fine to fully power up the Cisco phone.  Unfortunately I don't have a 3500 switch to try it out, but on the larger PoE switches when you manage them, under the port there is a PoE tab.  Take a look in there as to what the port is set to output.  Yes, if the switch is fully loaded with PoE devices, it only has the power to give 15.4 watts to each port if they all wanted power.  If you have less than a fully loaded switch, that's when the switch can push 32 watts to a port.  Just not all of them at the same time.

Offline Michael McNamara

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Re: 3524GT-PWR+ POE - 30W???
« Reply #2 on: August 13, 2013, 09:14:23 AM »
I'm wondering if Cisco is utilizing CDP to help the IP phone determine that POE+ is available. If that's the case then you'll most likely never get it to work properly. Is there a mechanism for an edge device (phone, camera, etc) to detect whether a port supports PoE (802.3af) or PoE+ (802.3at)? I personally don't know.
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Offline roncassette

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Re: 3524GT-PWR+ POE - 30W???
« Reply #3 on: October 01, 2013, 05:56:13 PM »
Did you find an answer for this? I am currently running into the same issue with some new 802.11AC wi-fi AP's. They are only pulling AF power and will not draw AT (they need about 18w).

Offline Telair

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Re: 3524GT-PWR+ POE - 30W???
« Reply #4 on: October 01, 2013, 07:38:10 PM »
This is a decent article on Wikipedia about how PoE vs. PoE+ is detected.  Typically when a device is plugged in to the switch port of a PoE switch, the switch checks the resistance value between the pins on the cable to see if there is a 1926.5 kΩ resistor present.  If there is, then it know it is a PoE device and depending on the resistance, it will deliver the appropriate amount of power.  For PoE+ there is some extra negotiation that occurs via voltage pulses between the switch and the PoE+ device and then the switch should deliver the requested power amount.  Apparently LLDP can also be used to negotiate the power amount.  You should be able to see what class of power your AP's are requesting on the switch in the GUI.  Class 0-3 is PoE, class 4 is PoE+.

http://en.wikipedia.org/wiki/Power_over_Ethernet#Powering_devices

Offline roncassette

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Re: 3524GT-PWR+ POE - 30W???
« Reply #5 on: October 04, 2013, 02:37:36 PM »
Just an update on our progress, we ended up sending one of the AP's to Avaya for them to test out. It sounds like the AP is requesting POE+ voltage on Layer 1 but the 3524GT-PWR+ is looking for it in Layer 2 (LLDP). This could be a problem if we can not make the AP send a LLDP request. I thought LLDP was optional???

Offline Telair

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Re: 3524GT-PWR+ POE - 30W???
« Reply #6 on: October 04, 2013, 04:53:15 PM »
OK when dealing with 802.3at, the end devices that are using the PoE+ power must be able to negotiate the power requirement sequence using the 802.3af resistor method AND using the LLDP method.  The switches that provide the PoE+ power must use the resistor method OR LLDP, but it is not a requirement to be able to use both.  So if the 3524GT-PWR just uses LLDP for PoE+, it is in spec it would seem.