VoIP over WLAN - Client Roaming Settings

[Frank Wagner]

Hello,

what would you suggest, are the best settings in the "Client Roaming Section" of the WLC Configuration for the following requirements:

VoIP over WLAN deployment, 802.11a, WLC 4402, 25 - 30 access points (mainly 1252, a few 1130), 7925G phones.

In the moment the settings are set to default, that means: Min. Rssi = -85; Hysteresis = 3; Scan Tresh. = -72; Trans. Time = 5

Unfortunately we are not completely satisfied with the roaming behavior of our phones, so there is the question,

if the roaming behavior of the phones can be improved. Sometimes it looks like the phone takes too much time to make a roaming decision.

Thanks,

Greeting Frank

[peter_bruckner]

Many thanx for the detailed answer.

Best greetings from Bavaria.

Peter

[peter_bruckner]

Hello Aaron,

would like to ask another question.

Configuration:

AP

- AIR-LAP1242AG-E-K9,

- rubber duck

- radio A Power Level 2

7925G

- 1.4(1)

WLC

- Model: WS-C3750G-24WS-S50

- Version:7.0.98.0

AP sees the phone      with -71bm, Power level 3

phone sees AP           with -59 dbm with power of 14

! there is a huge difference!

Well, these values are generated about every 30 sec. Based on these values I suppose it is vey difficult to make sure that roaming can work quite well, esp. what´s the roaming of the 7925G is concerned.

So among other things

- how to calculate the limits of my cells, based on phone site survey or entries of the AP

- how is the content of the IE in the Beacons created or on what it is based on as far as the power level are concerned

-> how can the AP, configured with Power level 3, advise the phone to 14?

Or do I not see the wood for the trees?

Any hints&tips are highly appreciated.

Rg

Peter

[mlieber]

Hello Peter,

yerstady I saw similar results.

I had a 7925 and a 7921 phone and I opened the site survey tool on both phones.

The signal strenght on the 7921 was very much better than the 7925, partly up 10dBm!!!!

About the roaming events: The 7925 tried a roaming to an AP on another floor (debug client) although on the same floor there was another AP and that AP was better seen by the phone (I had another phone 7925 at the same time and opened the site survey tool)

So we had a roaming issuewith the 7925 in this area but not with the 7921 phones

I think there is a huge difference between the 7925 and the 7921 phone.

Additional I have looked on the client details on the WLC.

Like you I saw the 7925 phone with -75dBm and the 7921 with -60dBm.

I had put both phones side by side.

cheers martin

[uvaldememorialhospital]

We are experiencing the same issue. The 7921 phones perform much better than the new 7925s. Both run the latest firmware 1.4.1SR1.

In our case all of the APs are from Meraki and when you take into account that the roaming decisions are made by the phone it pretty much points the finger at the new design of the 7925 and not into misconfiguration of the CUCM (which is used only to establish the initial connection), WLC, QoS, etc...

7921 & 7925 - same firmware, same wireless environment, same QoS, same settings in CUCM (continuous scanning for APs, enabled restricted data rates, etc.), same settings in the wireless profiles on the phones, different hardware = 7921 works fine while 7925 experiences audio gaps that last 2-6 seconds.

From reading previous posts it seems like even people that have Cisco gear throughout and have had engineers on site are still having the issue...which is very discouraging...

[Terri Carstenson]

Did anyone resolve their issues?

We are experiencing the same problems with roaming.  7925 Phones and 70+ WoWs on 5ghz A.

5508 controller on firmware 7.0.220.0 (no intra-controller roaming)

170 1142n APs

7925 phones on 1.4.1SR1 or 1.4.2

8 channels on 5ghz (uni2 and uni3)

Linksys AE1000 with latest drivers in WoWs

Cisco 3750-X switches or 3750-V2-PS firmware 12.2.58SE2

-Calls get dropped, are full of static

-Some calls only one party can hear (caller is on 7925 calling a 7945 desk phone).  Desk phone user cannot hear 7925 caller.

-WoWs will freeze for 5+ seconds when roaming to another AP

Message was edited by: Terri Carstenson to add AP model and switches

[uvaldememorialhospital]

Terri,

You may wanna try opening a TAC case and request 1.4.2ES.1 firmware release. There is a bug (CSCtk58591)

which affects the phones on the a band only. The workaround is to pin them to use b/g but that firmware release supposedly fixes the problem. I am yet to try it though.

Regards,

Ted

[Terri Carstenson]

Thank you.   I do have an open TAC case.  I will ask for that release.

[migilles]

Suggest to use 1.4(2) as it has an enhanced scanning algorithm, so the neighbor list will be real-time to ensure roam success.

There are no known issues with using the 7925s on UNII-2 or UNII-3.

But since you are having issues with Linksys adapters as well, seems your issue is related to the infrastructure/network or WLC/AP.

Suggest that you open a TAC case.

[Terri Carstenson]

I have seen my laptop drop a network connection and it is on the b/g radio and is using an Intel card.

The issue seems to be roaming in general.  WoWs with Proxim cards also experience 'freezing' for at least 5 seconds when roaming to a new AP.

[migilles]

In response to UvaldeMemorialHospital's post on 7/20/11.

Suggest to try 1.4(2), which has the enhanced scanning mechanism.

Would also see if the issues are specific to a certain area or channel.

There is a current issue that is being investigated, which has to do with the AP1140/AP33500 (any Cisco 11n AP) has trouble receiving ACKs from the 792x phone intermittently when UNII-1 channels (36,40,44,48) are used.

CSCtx43105      11n AP on UNII-1 doesn't demodulate ACKs from 7925G

CSCtt67979       11n AP on UNII-1 doesn't demodulate ACKs from 7925G

In response to UvaldeMemorialHospital's post about CSCtk58591, this issue is very rare.

Only a handful of customers have experienced this issue, where  when going outside or in range of a WLAN that is advertising  non-supported channels and country code (e.g. channel 50 and country  code ZY), the 792x phone will need to power cycled in order to reconnect  to the WLAN.

If you are hitting this issue, you should see that the MAC address in the phone UI (Settings > Model Info) is blank.

Yes we have an ES available called 1.4.2ES.1 which is 1.4(2) + the fix for CSCtk58591.

If you are encountering this issue, the open a TAC case and request the load.

This will be resolved in the 1.4(3) release, which is scheduled for mid 2012.

In response to the RSSI difference inquiries between 7921 and 7925, these do have different chipsets and antennas, so they will not be 1 for 1, plus there is RSSI averaging in place.

Also there was an issue in the past, where the 7921 was displaying an RSSI a bit hotter than actual.

Ensure you are using 1.4(2) firmware.

But still may see up to 3 dB difference variance between phones.

[Terri Carstenson]

Thank you.

We are using these channels: 52, 56, 60, 64, 149, 153, 157, 161

[Terri Carstenson]

Jan 25, 2012 12:34 PM (in response to migilles)

Re: VoIP over WLAN - Client Roaming Settings

In response to UvaldeMemorialHospital's post on 7/20/11.

Suggest to try 1.4(2), which has the enhanced scanning mechanism.

Would also see if the issues are specific to a certain area or channel.

There is a current issue that is being investigated, which has to do with the AP1140/AP33500 (any Cisco 11n AP) has trouble receiving ACKs from the 792x phone intermittently when UNII-1 channels (36,40,44,48) are used.

-> we are not using channels 36, 40, 44, 48

CSCtx43105 11n AP on UNII-1 doesn't demodulate ACKs from 7925G

CSCtt67979 11n AP on UNII-1 doesn't demodulate ACKs from 7925G

In response to UvaldeMemorialHospital's post about CSCtk58591, this issue is very rare.

Only a handful of customers have experienced this issue, where when going outside or in range of a WLAN that is advertising non-supported channels and country code (e.g. channel 50 and country code ZY), the 792x phone will need to power cycled in order to reconnect to the WLAN.

-> we are not using non supported channels or country code

If you are hitting this issue, you should see that the MAC address in the phone UI (Settings > Model Info) is blank.

Yes we have an ES available called 1.4.2ES.1 which is 1.4(2) + the fix for CSCtk58591.

If you are encountering this issue, the open a TAC case and request the load.

This will be resolved in the 1.4(3) release, which is scheduled for mid 2012.

In response to the RSSI difference inquiries between 7921 and 7925, these do have different chipsets and antennas, so they will not be 1 for 1, plus there is RSSI averaging in place.

Also there was an issue in the past, where the 7921 was displaying an RSSI a bit hotter than actual.

Ensure you are using 1.4(2) firmware.

But still may see up to 3 dB difference variance between phones.

[migilles]

Terri,

My response immediately above was not intended for you, but instead for

UvaldeMemorialHospital.

For you, looks like your issues are not restricted to the 792x phones.

Suggest to work with the Cisco WLAN TAC folks.

[jonas]

We are having the same critical problems as described throughout this thread: choppy audio and or lost audio on the Cisco CP-7925G handset. I currently have a Cisco TAC case open (SR 620443387) but after a few days back and forth and me referring to this thread I have actually been recommended by TAC to continue my efforts within this thread. So here goes.

Our wireless infrastructure consists of a Cisco WiSM with software version 7.0.220.0 and 76 AIR-LAP1142N-E-K9. We have 290 Cisco CP-7925G with software version 1.4(2) and 9 Cisco CP-7921G software version 1.4(2). Worldwide we have approx. 600 7925's devices and 300 7921's. All access switches are Cisco WS-C6513 with WS-SUP32-GE-3B and WS-X6148-GE-45AF modules. I believe I have as others in this thread followed the Cisco 7925G Deployment Guide recommendations to the letter. Also Voice over the Wireless LAN 4.1 Design Guide has been read thoroughly. Finally all specific recommendations in this thread regarding channel settings, power settings, speed (partially) and beacon settings have been implemented and tested.

We have only one SSID on all A radios (5GHz) using channels 52, 56, 60, 64, 100, 104, 108, 112. This SSID is dedicated to only the Cisco 7925 and 7921 devices. We use WPA/TKIP, 802.1x+CCKM, EAP-FAST and Cisco ACS server 5.2 with 1 internal user account for all phones on this site. Speed settings are 6mbit and 9mbit supported, 12mbit Mandatory, 18mbit and 24mbit supported. Setting Beacon to 6mbit as suggested in bug workaround CSCtx43105 and CSCtt67979 will require manually reconfiguring all phones as currently they are set to 12mbit as minimum rate. Please advise how effective this part of the workaround actually is so I can dedicate resources to performing this change if needed.

Before I fill this entire page up with technical information I will cut to the chase. Our Cisco 7921 phones work perfectly. No choppy voice, dropped calls or voice gaps. The Cisco 7925 has all of these "features". Using AirMagnet VoFi Analyser and 2 network adapters it is extremely clear that the Cisco 7921 remains associated to one access point for the entire duration of a call (30min call duration) while totally stationary in a vertical position on a desk. The Cisco 7925 however standing vertically 10cm away from the Cisco 7921 roams very often for no good reason. Often the roam is to an access point offering worse conditions. The two phones, 7921 and 7925 have identical profiles apart from the fact that antenna configurations are not available in the 7925. The 7921 is set to "diversity" on the A radio.

I am certain that the choppy voice and or lost audio is directly related to this excessive roaming behavior. This problem has detrimental consequences to our organization. We have been fighting with voice quality issues ever since we began issuing the Cisco 7925 model to our employees. We need a solution now! Personally I think there is a flaw in the 7925 hardware platform perhaps on the antenna/s or wireless chipset. Either way I sincerely hope a solution presents itself in the near future. Please advise. We will perform any debug, trace, capture or logging you require. It just needs to happen fast.

I have just requested the software version 1.4.2ES.1 from TAC but I dont believe this will solve the excessive roaming issue.

Best regards,

Jonas A. H. Nielsen

WDH Network and Communications Team

http://www.demant.com/

Message was edited by: Jonas Nielsen The roaming reason has been identified.  My scan defer setting was set to 3, 4, 5.  this is wrong!  The WLC is not deferring scanning when servicing 802.1p packets tagged with 6.  Not good.  After changing to 4, 5, 6 the Cisco 7925 with software version 1.4(2) stopped roaming wildly and remained stable on one access point.  I appologize if I stirred up a storm.  I have had a multitude of TAC engineers look at my WLC config and none picked up on the configuration error.  I was getting desperate :(

[uvaldememorialhospital]

A very thorough post! I've also been through the implementation guides many times and have tried a multitude of settings to no avail. The situation you describe with roaming on the a band and the difference in behavior of the 7921 and 7925 is exactly what we are experiencing. I used the camera on my phone and captured it on video. The 7925 will roam randomly (while stationary and regardless if on a call or not) to a distant AP with a much weaker signal.

I have also tried 1.4.2ES.1 and it didn't resolve the issue (granted it contains a fix for a different bug but as you can tell I am grasping at straws at this point).

Our deployment is much, much smaller than yours and our financial resources are limited but we are also looking at investing in Airmagnet VoFI to see where the problem lies. Right now at my disposal is AirPcap Nx & Wireshark...

We use channels 36, 44, 149 and 157, dedicated vlan and SSID for wifi voice, QoS on the Cisco switches, etc…

I’ll capture fresh trace logs (and this time instead of “info” I’ll turn it up all the way to “debug”) and e-mail the person at Cisco handling our ticket along with a link to this thread.