CISCO POE

[Sivanesan Rathinam]

Hi All - Is that possible to make use of unused power in cisco Switches?

Lets say a switch Which has 5 Port POE with 15.4 watts out of which 4 device requires only 5.4 Watts and the 5th device requires more than 15.4 W at this time swich can support the power to device, Since it has 40 Watts which is unused?

Please share any document which expalins how this power management works on cisco POE switches.

SIVANESAN R       

[dominic.caron]

Hi,

First, your switch must support 802.3at to deliver more then 15.4 on a port. Power is negociated using LLDP or CDP. (DC load detection will only allow you 15.4 W)

You can use power that is not reserved for another port. the device need to be classified as a class 1-3.  A class 0 (the default) will be allocated 15.4w of power.

[Leo Laohoo]

Yes, this is very much possible.

This is evident when the switch can support PoE and PoE+ particularly when you are deploying VoIP phones, wireless access points and PTZ cameras.

The proviso, however, is that you do NOT hardcode the PoE settings on a per-interface-level.

[Sivanesan Rathinam]

Thaks Leo, Is there any document to understand how this Power Management works on Cisco Switches?

I believe there should be some intelligent built on cisco switches where it allocates power to each port thats why devices which requires more power able to use unused power when we not hardcode on per interface level?

SIVANESAN R

[Leo Laohoo · Accepted solution]

Thaks Leo, Is there any document to understand how this Power Management works on Cisco Switches?

Pffft.  Maybe.   The concept of PoE is already so "old" that Cisco no longer updates the documentation.

Get a Cisco PoE switch and observe.  This is the only way I learnt.

I believe there should be some intelligent built on cisco switches where it allocates power to each port thats why devices which requires more power able to use unused power when we not hardcode on per interface level?

It's not just Cisco.  Apparently, all the big player's products do the same thing.  If each port can push up to 20.0w PoE, for example, and your PD uses only 5.5w PoE, then the excess go into the "pool".  Here's another proviso:  The excess power can be pushed to other ports that require more but not too much.

For example, you have a switch which allows up to 20.0w per port and you've got 120w available.  You can't channel 120w PoE to a single port. 

[Sivanesan Rathinam]

Thank you so much Leo, Please let me know if you come across any good documentiaon to understand POE working Priunciple and Power allocation pool on cisco switches....

SIVANESAN R

[Leo Laohoo]

Thank you so much Leo, Please let me know if you come across any good documentiaon to understand POE working Priunciple and Power allocation pool on cisco switches....

If I find one, I'll post it here.

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