How do you check current power level on 7921?

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Jul 12th, 2009
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Is there any way to check what power level a 7921 is using at a given moment?

Correct Answer by migilles about 7 years 8 months ago

Yes, either locally in the UI (Settings > Device Information > WLAN) or via the phone webpage under Information > Wireless LAN.


The 7921G phone will use what's advertised by DTPC by default. Otherwise it will use the highest tx power available based on the regulatory domain or 802.11d info provided by the AP.


See the 7921G Deployment Guide for more info @ http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7921g/6_0/english/deployment/guide/7921dply.pdf.

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Correct Answer
migilles Tue, 07/14/2009 - 14:46
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Yes, either locally in the UI (Settings > Device Information > WLAN) or via the phone webpage under Information > Wireless LAN.


The 7921G phone will use what's advertised by DTPC by default. Otherwise it will use the highest tx power available based on the regulatory domain or 802.11d info provided by the AP.


See the 7921G Deployment Guide for more info @ http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7921g/6_0/english/deployment/guide/7921dply.pdf.

Roman Rodichev Tue, 07/14/2009 - 21:13
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Ok, I see it now, thanks!

Does AP advertise different DTPC for each client based on client's RSSI? I assume that AP sends traffic to all clients using the same power (manually set or TPC determined), and clients will send traffic using whatever power setting AP advertised to that specific client.


On another topic, I remember a thread where you discussed how 7921 CCKM fast roaming is only supported with WPA, and not WPA2. Does it work with both WPA+TKIP and WPA+AES?

migilles Fri, 07/17/2009 - 16:06
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No DTPC is a static value. With the WLAN controller, it will send the max tx power that the AP is using.


CCKM is only supported with WPA(TKIP) at this time.

Roman Rodichev Sat, 07/18/2009 - 17:27
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You know, this is what I'm confused about.


I start with DTPC disabled for 802.11b/g network in WLC 4.2. Cisco 7921 phone associates. Device information on the phone shows Tx Power set to 17 dBm (50 mW). I believe that's the max power the phone supports.


So far so good.


I enable DTPC for 802.1b/g network. Reboot the phone just in case. Device information on the phone shows Tx Power set to 5dBm (power setting 6 on AP), but the AP it's associated with is set to TX power 1 (manually).


The phone is very close to the AP. To me this almost seems as the AP tells the phone via DTPC to use the lowest power because the phone's RSSI is very good. Am I wrong?

Roman Rodichev Sat, 07/18/2009 - 23:20
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Nevermind, I remember you mentioned that when 7921 is very close to the AP it's designed to throttle down power. I just tested with 7921 further away from AP and it behaves as expected. With DTPS on, I change AP's TX power setting and the phone automatically changes its TX power to match AP's setting. Thanks!

j.metzger Tue, 07/21/2009 - 12:03
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Is there any way to adjust the DTPC power setting that the phone will use?

I can't see how a phone with 0 gain antenna against someone's head, would match an AP on the ceiling with a 4.5 dB gain antenna.

Wouldn't this create the very situation we're trying to avoid? Would it be better to do AP power +1 setting higher (if possible)?

migilles Fri, 07/24/2009 - 11:53
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It uses the value provided by the AP.

If DTPC is enabled on the WLC, then it sends the same local configured setting for the AP radio. In autonomous, you can configure the client power separately as necessary.

If you don't want to use DTPC, then if diasbled, the phone will use the max tx power available (i.e. 16 dBm for 5 GHz).

pratik.rb Tue, 07/28/2009 - 05:54
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I cant get the 7921 to get connected to Aruba AP. Are there any special settings to be done on the 7921. The 7921 I have are ETSI (Europe) for reference.


"Connection Failed" is error I get. The SSID is hidden but open with authentication disabled. I am able to connect to this SSID with my laptop.

migilles Wed, 07/29/2009 - 14:15
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If you are getting connection failed, then is either a security mode mismath or is an unsupported country code.

Obviously the SSID is correct as it is finding it.

You can put the phone into site survey mode and see what the AP config is.


See page 30 of the 7921G Deployment Guide for more on the site survey mode @ http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7921g/6_0/english/deployment/guide/7921dply.pdf.

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