7945 - PoE Class 3

Unanswered Question

Hello,


We are designing a 520 Ip Phones UCC solution for a client, the LAN Switches we are proposing are 3750G-48PS and the 520 IP Phones we are proposing are 7945G.


On the 7945G Product Overview page:

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps379/ps8534/product_data_sheet0900aecd8069bb80.html


we see that the phone Power supports IEEE 802.3af PoE (Class 3).


and for the 3750G-48PS POE Switch:

http://www.cisco.com/en/US/products/hw/switches/ps5023/prod_models_comparison.html


we see under the 'PoE Class 2/PoE Class 3 Devices Supported' column that only 24 PoE Class 3 devices are supported.


Does that mean that the 7945G being PoE Class 3, the 48 port PoE LAN Switch will only support 24 7945 phones?


And, if yes, is there a way to 'tweak' the LAN Switch Power settings, or feed in more power to the LAN switch, to make it support all 48 ports for Class 3 PoE devices.


Thanks & Regards,

Kartik Bhatia

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paolo bevilacqua Wed, 10/07/2009 - 03:53
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Correct, you could use the 7942 that are poe class 2, or 2x 2960PS 24 ports instead of the 3750.

Thanks ...



1. Using the 2x 2960PS 24 ports will allow me to PoE 48 7945 phones? I mean, does a 2960PS supports all 24 ports for Class 3 PoE?


2. ALso, is there a way to 'tweak' the 37xx LAN Switch Power settings, or feed in more power to the LAN switch, to make it support all 48 ports for Class 3 PoE devices?

Rob Huffman Wed, 10/07/2009 - 04:44
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Hi Kartik,


It's excellent that you picked up on this before moving ahead :) Just to add a note to the great tips from my good friend Paolo (+5 ponts here buddy!)


WS-C3750E-48PD1150W = 48x 7945/7965


WS-C3750G-48PS = 30x 7945/7965



When making these decisions, this is a very valuable tool;


PoE calculator


Use http://tools.cisco.com/cpc/launch.jsp


Cheers!

Rob

Rob Huffman Wed, 10/07/2009 - 05:20
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Hi Kartik,


The bottom line here is that the 7945 is not a "true" Class 3 device in that it actually uses 12w vs 15.4w for Class 3 devices.


If you are looking at putting in 48 (7945) phones you can either uses 2x24 port 2960's as paolo nicely noted or 1x WS-C3750E-48PD1150W = 48x 7945/7965



Hope this helps!

Rob

Rob Huffman Wed, 10/07/2009 - 06:09
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Hi Kartik,


No worries :)


1. From the doc you linked;


Cisco Catalyst 2960-24PC-L can support 24 simultaneous full-powered PoE port at 15.4W.


2. Sorry my friend, no "magic" tweaks.



Cheers!

Rob

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