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7945 - PoE Class 3

kartik.bhatia
Level 1
Level 1

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

12 Replies 12

paolo bevilacqua
Hall of Fame
Hall of Fame

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?

1 last thing:

I do not see 2960PS or any 29xx switch which supports all ports for Class 3 PoE:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/product_data_sheet0900aecd80322c0c.html

Kindly Assist

Rob Huffman
Hall of Fame
Hall of Fame

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

Hmmmm...

Me confused now, even though it says 48 Ethernet 10/100/1000 ports with PoE BUT the link:

http://www.cisco.com/en/US/products/ps7077/prod_models_comparison.html

clearly says under 'PoE Class 2/PoE Class 3 Devices Supported' as 48/24

???

And the same links talks about 3750E-48PD-F to supprt 48 ports

:-)

How can I miss that.

Got it now, thanks Rob and p.bevilacque

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

Got ir... one last thing though:

1. I do nto see any 2960 switch which supports all ports on Class 3 PoE:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/product_data_sheet0900aecd80322c0c.html

2. No tweaking possible to make a 3750 G switch support all ports on CLass 3 PoE - coz E series are Class 3 switches - much expensive.

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

Ya I saw that before but sorry I forgot to tell this - only GIG LAN Switches

Requirement is GIG LAN ata each node - so can not go for 10/100 Phone like 7941/7942 or 10/100 LAN Switches

:-)

Right. Want much = spend much.

lol... got it

thanks

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