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Using class 3 power (switch limit) with class 4 wifi device.

Chris McCann
Level 1
Level 1

I have a switch that will supply max class 3 power but my wifi devices are class 4 power. Will this have an impact on wifi performance, if so why? Just getting more complaints recently with more usage of the wifi.

thanks,

 

Chris.

 

1 Accepted Solution

Accepted Solutions

Since you're running the APs less than 2/3 of full power they are probably running below full capacity - only the AP vendor can tell you what the AP disables when it doesn't have full power.  Cisco APs vary in behaviour - some disable WiFI altogether although many disable some of their antennae so operate below full capacity.  Some just disable the USB port like 1832.  So check the vendor's data sheet and if that doesn't answer your question ask the vendor.  But as Scott says the problem could be something else altogether so check it all.

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7 Replies 7

marce1000
VIP
VIP

 

 - The why in such questions usually defies itself..., anyway sometimes not all radios or antennas will get enabled, if this concerns AP's , for instance issue show logging just after reboot. Or follow boot process , watch for errors or defuncts if reported.

 M.



-- ' 'Good body every evening' ' this sentence was once spotted on a logo at the entrance of a Weight Watchers Club !

Leo Laohoo
Hall of Fame
Hall of Fame

How much power does the port support?

How much power does the AP require? 

NOTE:  Please do not respond the "class" because manufacturing vendors like to "skew" this figure.  

Hi Leo,

The switch in question is a WS-C3560G-48PS-S which supplies POE range from 4 to 15.4w per port. The device I am plugging in (non cisco AP) powers up fine and runs but is class 4 PD2, so usually demands upto 24w.

Gi0/2     auto   on         15.4    Ieee PD             4     15.4
Gi0/3     auto   on         15.4    Ieee PD             4     15.4
Gi0/4     auto   on         15.4    Ieee PD             4     15.4
Gi0/5     auto   on         15.4    Ieee PD             4     15.4
Gi0/6     auto   off        0.0     n/a                 n/a   15.4

 

We have some of the same APs plugged into a new switch and the output for show power inline is as below.


Gi1/0/1   auto   on         24.5    Ieee PD             4     30.0
Gi1/0/2   auto   on         24.5    Ieee PD             4     30.0
Gi1/0/3   auto   on         24.5    Ieee PD             4     30.0

 

Doing a show LLDP neig command on the older switch gives the below

Physical media capabilities:
    1000baseT(FD)
    100base-TX(FD)
    100base-TX(HD)
    10base-T(FD)
    10base-T(HD)
Media Attachment Unit type: 30
Vlan ID: - not advertised


Where the newer switch gives.

Vlan ID: - not advertised
PoE+ Power-via-MDI TLV:
 Power Pair: Signal
 Power Class: Class 4
 Power Device Type: Type 2 PD
 Power Source: PSE
 Power Priority: unknown
 Power Requested: 20800 mW
 Power Allocated: 20800 mW

 

The devices have worked fine until now where demand has gone up, now we have users complaining of constant network dropping.

 

Instead of looking at the power, have you looked at the infrastructure? Do you have a good high density deployment? What are the number of devices connecting to each ap? When a user complains, what ap is he/she on and how many clients? What band are they connected to and what is their rssi and snr? Was a site survey done?
-Scott
*** Please rate helpful posts ***

Since you're running the APs less than 2/3 of full power they are probably running below full capacity - only the AP vendor can tell you what the AP disables when it doesn't have full power.  Cisco APs vary in behaviour - some disable WiFI altogether although many disable some of their antennae so operate below full capacity.  Some just disable the USB port like 1832.  So check the vendor's data sheet and if that doesn't answer your question ask the vendor.  But as Scott says the problem could be something else altogether so check it all.

Hi,

I think we have found the issue, the devices we are using (Aruba 315) may be reducing output by 3bd on the 2.4Ghz channel, no effect on the 5Ghz. Also switching off the USB port (which is irrelervent).

Got this from the datasheet for the Aruba.

- When using IPM, the AP may enter power-save mode with reduced functionality when powered by an 802.3af PoE source (see details on Intelligent Power Monitoring elsewhere in this datasheet) - Without IPM, the USB port is disabled and transmit power of the 2.4 GHz radio chains are reduced by 3dB to 15dBm max when the AP is powered by an 802.3af PoE source

 

Thanks for your replies.

Chris.

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