power inline consumption" command usefulness

[ima imtiger]

Hi all,

Please waht'is the usefulness of "power inline consumption" command if poe requirement can be set with command 'power inline {auto [max milli-watts] | never | static [max milli-watts]}' ?

thanks a lot

ima

[Somasundaram Jayaraman]

Hi,

There are two scenarios in which the  Consumption Command Line Interface (CLI) can be used to manually  configure the PoE allocation much more efficiently than the automatic  algorithms:

++ Currently, the Cisco Catalyst  3750 Series budgets 15.4 W for Class 0 PDs. However, some of these PDs  require a maximum of much less than 15.4 W (for example, the Siemens IP  phone requires 5 W).

++ Without the Power Inline Consumption feature,  customers could only deploy 24 of these devices. Customers can deploy up  to 48 of these devices with the power inline consumption command for configuration of switchport power requirements.

++ Class  3 PDs are allocated 15.4W normally. Some IEEE Class 3 PDs (8-15 W  range) use considerably less than 15.4 W maximum.

++ An example is the  Avaya 2620SW, which uses 8W in the worst case scenario. If the  Consumption CLI configured ports that support this phone to 8 W, a  3750-48PS could safely power 46 phones instead of 24.

++ Any misconfiguration on the switch (an over-subscription of the power  supply) can reduce its reliability or damage the switch. If the power  supply is over-subscribed by up to about 20 percent, the switch  continues to operate but its reliability can be reduced. Above about 20  percent, the short-circuit protection circuitry triggers and shuts the  switch down.

++ Issue the power inline consumption global or interface configuration command on the switch stack or on a  standalone switch to override the amount of power specified by the IEEE  classification for the device. Then, specify the wattage used by each  powered device.

Hope this answers your question.

Cheers

Somu

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[ima imtiger]

Hi Jayaraman,

thank u for your reply.

++ Without the Power Inline Consumption feature,  customers could only deploy 24 of these devices. Customers can deploy up  to 48 of these devices with the power inline consumption command for configuration of switchport power requirements.

this is the problem : we can limit the consumption by issuing ' power inline auto max milli-watts' without appling the power inline consumption command !! is it true ????

thx

ima

[Somasundaram Jayaraman]

Hi,

By default, when the switch detects a powered device on an interface, it  assumes the powered device consumes the maximum the port can provide (7  W on a legacy Power over Ethernet (PoE) module and 15.4W on the IEEE  PoE modules introduced in Release 12.2(18)EW).

Then, when the switch  receives a CDP packet from the powered device, the wattage automatically  adjusts downward to the specific amount required by that device.  Normally, this automatic adjustment works well, and no further  configuration is required or recommended.

However, you can specify the  powered device's consumption for the entire switch (or for a particular  interface) to provide extra functionality from your switch. This is  useful when CDP is disabled or not available.

When  manually configuring the consumption for powered devices, you need to  account for the power loss over the cable between the switch and the  powered device

This link might interest you

-http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/25ew/configuration/guide/PoE.html

Cheers

Somu

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