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Contributor I

Max Transmit Attempts

What is the purpose of the Max Transmit Attempts under the SSID advance tab?  I'm having issues with an VoIP app running on iPhones and the app vendor is telling me that the Max Transmit Attempts should set to 0.  He says he got this recommendation from Aruba.  Currently is set to 2 on the VoIP SSID and 4 on my data SSID.

 

What does setting it 0 do?  How could it possibly affect my non-iPhone VoIP traffic or would it affect them at all?

 

The app is Voalte btw.  Has anyone come in contact  with this app in the wild?  Just curious.

 

 

Community Administrator

Re: Max Transmit Attempts

That is the maximum number of attempts a frame can be transmitted. I would think 0 would mean no allowed retries to prevent clogging up airtime.

CWNA, ACMP, Security +
Guru Elite

Re: Max Transmit Attempts

wcummings,

 

The person you are communicating with might be referring to the  Roaming VRD here:  http://www.arubanetworks.com/wp-content/uploads/DG_Roaming.pdf

 

Quite frankly this is general advice and usually for well known handsets we have recommended settings in the Roaming VRD.  There are none for Voalte, but the settings that Aruba recommends normally originate from the manufacturers recommendations.  Does Voalte have general RF recommendations for the environment?

 

Below is the general recommendations from the Roaming VRD:

voip-vrd.png



Colin Joseph
Aruba Customer Engineering

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Aruba Employee

Re: Max Transmit Attempts

 

If the only impact is the Voalte application, we need better understand the issue before we make a change that is SSID specific.   I need to understand the problem that we are attempting to fix:  roaming performance or voice quality issue or call setup issue.

 

We need to understand the application before I can give you a firm recommendation.

 

1)   Is this a hospital issued client or a personal client?

 

2)  Does the application control the WiFi interface?

 

3)   Does the application support WMM?

 

Thanks,

--Kevin.

 

Contributor I

Re: Max Transmit Attempts

Kevin,

 

The only impact is the with the Voalte app.  All our other VoIP cleints are not having issues.  Roaming seems to be fine but may be a minor issue.  The Voalte RF engineer wants to the change the Max retries but I'm not convinced that will help.  I would test in the lab before changing it in production anyway.

 

Voice quality is good.  There haven't been any complaints for voice quiality.  Only dropped or missed calls.

 

The uses SIP to build and tear down the call.  I've been using the voice commands from the cli to monitor the calls logs and counters. 

 

1)   Is this a hospital issued client or a personal client?  It is a hospital issued client being used by all the nurses.

 

2)  Does the application control the WiFi interface?  The app does not control the WiFi interface.

 

3)   Does the application support WMM?  I don't think it does but I will need to confirm.

 

Voalte's RF Engineer says the wireless network is fine and that roaming with the iPhone could be the major issue.  He did the wireless site survey before implementation and we remediated areas where he saw possible coverage issues.

 

I'm trying to schedule a call with Voalte's PBX/App Engineers for later this week in order to understand a little more about Voalte app.  It has a lot of moving parts where something could be broken.  But the wireless network is always the first thing that gets blamed.

 

Thanks,

William

 

 

Contributor I

Re: Max Transmit Attempts

Thanks  Colin freshing my memory.  I remember working VoIP issues a few years ago and verifiying that we were running the recommended settings.  We still are.

 

I have asked Voalte for any RF recommendations.  I'm waiting on a reply.  I'm pretty sure their response is going to be what ever is used for the iPhone.

 

Aruba Employee

Re: Max Transmit Attempts

Hi William,

 

Please confirm that that all the clients are on the voice SSID.     If this  is the case, the requirements will be different for the two clients, and we need to find a common set of configurations.

 

Based on the response, your application vendor needs to provide more evidence before I will agree to a change.

 

The symptom sounds like a call setup issue.     I would look for an ACL and or a power-save issue.

 

Thanks,

--Kevin

Contributor I

Re: Max Transmit Attempts

Kevin,

 

All the clients are on the voice SSID.  Currently we are running Spectralink 2211's, 6140's and the Voalte app running on the iPhone.  The 2211's are b only radio's with about 225 in production (hopefully replaced soon so I can make the voice SSID a only).  The 6140's are a/b/g but are hardcoded to a only with 300 or more in production.  The iPhones are a/b/g with 300 or so in production and have connected on both 2.4gHz and 5gHz.  We have no control over what the iPhone does with power or radio settings.

 

Are there any best practices when it comes to iPhone voice mobility?

 

Thanks,

William

Aruba Employee

Re: Max Transmit Attempts

Hi William,

 

The challenge is that the application does not have control of the WiFi on the iPhone.  

 

We can try to make this work on voice SSID, but this maybe a challenge that may not work well.    Mixing SVP and WMM on the same SSID will have mixed results.    At some point, the iPhone tuning will break the Spectralink phones.

 

I will need more engineering specific details on the application and logging data from the client before we can move forward.

 

I do have one request to move the iPhone to the data SSID for a test.

 

Thanks,

--Kevin.

 

 

 

 

Contributor I

Re: Max Transmit Attempts

Thanks Kevin,

 

I think we are at the point that the iPhones are the best they are going to get without breaking the Spectralink phones.  Right now on one controller there have been 84175 voice calls made since July 22nd.  170 have dropped or been aborted.

 

Here's a little more background on what has gone on in the last couple weeks.

 

I did a code upgrade to 6.3.1.8 on July 22nd and that seemed to break the Voalte iPhones in one particular building.  I fixed those issues  last Thursday July 31th.  I had to tweak the power settings since there is a dense deployment of AP's and power was too high.

 

The Voalte app does have bugs that our customers misinterpret as missed or dropped calls so I started getting more calls about wireless Voalte issues after the upgrade.  It took a while to wade through what the issues really were but the Voalte issues seemed to snowball after the code upgrade.  There were no other issues from any other clients on any of our other SSID's after the code upgrade.

 

I think everything is stable for now but wanted to start some dialogue on the issues we are seeing with the Voalte app and the iPhones.  The Voalte bug fixes won't be pushed out until the first week of Septembe time frame.  So, I want to be prepared if I start getting more calls.

 

I'll update the post once I have the call with the PBX/App Engineer from Voalte. It does things in the background that are not voice related that could affect the voice.

 

Thanks,

WIlliam

 

 

 

 

 

 

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