[cisco-voip] Maximum number of 7970's on a 3750-48ps-s

[Anthony H]

Perhaps this information could be of some use.  Though Robert did give some
great detailed information on the subject.

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_qanda_item09186a00801b0971.shtml

*Q.* How does Power Management work in the Cisco Catalyst 3750 PoE switches?
*A.* The Cisco Catalyst 3750-24PS switch supports a maximum of 15.4W per
port of -48V DC power on all 24 ports over standard Category 3 and 5
unshielded twisted-pair (UTP) cable up to 100 meters, however all 48 10/100
ports in Cisco Catalyst 3750-48PS switch will be able to deliver
7.7Wsimultaneouslyand any given port can be configurable to support up
to the maximum of
15.4 watts as long as the switch's - 48V power capacity is not exceeded. The
Cisco Catalyst 3750 PoE switches monitor and track the requests for power,
and only grants power when it is available. If the connected PD draws more
power, which results in exceeding the system power budget that is available
on the switch, then power will be denied to that port and the PD will not
power up. If power is denied, the switch re-checks the power budget
periodically (every 15 seconds), and continues to attempt to grant the
request for power. If power is granted, the switch updates the power budget.
Additional power management features are described later in this section.

Anthony

On 8/24/07, Pennington, Craig <cpennington at ncaa.org> wrote:
>
>  I noticed we have reached our maximum power output for the 3750 (540
> watts).  I then noticed it is set to the default settings of auto with
> 15.4 watts max on a port with the switch reporting each 7970 as using 10.3watts.  I tried to do the power inline auto max XXXXX (where XXXXX is the
> number of milli-watts between 4000 and 15400) to lower the max setting in
> hopes of increasing the number of ports that would give power. 540/15.4
> gives you a max of 35 powered ports.  And that is what I have, 35 phones, on
> each switch and I need to add more.  When I tried to lower the milli-watts
> below 15400 the port would say deny power and the phone would not boot.  has
> anyone had any luck trying to lower the power on a 3750 to service more
> 7970's?
>
>  Craig Pennington
> Network Engineer
> *N*ational *C*ollegiate *A*thletic *A*ssociation
> Fax: 317-917-6888
> cpennington at ncaa.org
> www.ncaa.org
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-- 
Anthony
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