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Max Number of Voice Clients on an AP

David Rosener
Level 1
Level 1

I have a high school wireless environment that was installed approximately 5 years ago with 1242AG APs. The install was done based on 2.4GHz coverage everywhere, not for 5GHz or for good density. The high school uses wireless cisco 7921G phones for all the staff and teachers. The issue we're running into is over the last couple years more and more students are bringing in iPhones and android phones that can connect to the public wireless ssid. And with the increase of these wireless devices in the classroom, we've been experiencing more and more call dropped on the wireless phones. I have collected information on number of clients on specific APs that are in the area of most of the dropped calls. At times some of these APs have a total of 40 clients associated to them, over half of which are on the public ssid. I have thought about putting all the phones on to the 5GHz radios, but the implementation of the wireless was only for 2.4GHz coverage, so we have coverage gaps on the 5GHz network. We're thinking about adding more APs but the budget isn't available yet for that, so we're looking at what we can do to make this better for the time being.

Main questions are:

Is there a best practices number of max clients per AP in a wireless voice network?

Are there any other options for preventing dropped calls on the wireless?

I should mention I have already looked over the VoWLAN Troubleshooting Checklist at the link below and made the necessary changes to assure we are following the items on the checklist as close as possible.

http://www.cisco.com/en/US/docs/wireless/technology/vowlan/troubleshooting/VoWLAN_Troubleshooting_Checklist.html

Any advise is helpful!

David

1 Accepted Solution

Accepted Solutions
9 Replies 9

Shawn Purdy
Level 1
Level 1

I've researched this and have found that you should have no more than 15 calls per AP. Also I would look at forcing those phones to use the 5ghz channel if they can. Also with all those other mobile devices, more density may be needed but an updated survey may help to see if that is really needed.

Sent from Cisco Technical Support iPad App

Leo Laohoo
Hall of Fame
Hall of Fame

I think Leo has the best answer here. I stumbled across the 7921 Cisco Unified Wireless IP Phone 7921G Deployment Guide over the weekend. And the section for Call Capacity was the key to figuring out what I was trying to understand.

http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7921g/6_0/english/deployment/guide/7921dply.pdf

Page 36 has a table for # of Call Streams based on Data Rates. But the key statement in this section is:

"To achieve this capacity, there must be minimal wireless LAN background traffic and radio frequency (RF) utilization."

In this environment, there is a lot of background traffic.

In this environment, there is a lot of background traffic.

Thanks for the rating David.

Which background traffic?  LAN or RF?

David Rosener
Level 1
Level 1

LAN traffic. We have two other SSIDs, one for internal users, and one for publicwireless users. When I look at a specific AP that is near a problem area, over two thirds of the associations are either in the internal or public SSIDs.

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When I attended the recent Cisco Live 2012 in Melbourne, one of the sessions I attended was in the regards to implementation of wireless VoIP.  The speaker stated that the new recommendation is to use 802.11a radio for wireless VoIP for several reasons:

1.  802.11a has numerous channels and minimizes the possibility of channel interferrence; and

2.  802.11a can push higher traffic rates.

Set your 7921G to use 802.11a instead.  If you can prove to the school that service improves then you could be able to justify adding more WAPs to plug coverage holes.

David Rosener
Level 1
Level 1

We already looked into that option. But we did a wireless site survey first and determined there were a lot of coverage holes in the 5GHz range. Once they get more APs installed in the future, the plan is put all the phones on A radio then.

Lucky you got to go to Cisco Live!

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Lucky you got to go to Cisco Live!

Not lucky.  I had to pay for my own.

My employer refused to pay for me to LEARN SOMETHING NEW. 

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