A VoWLAN Design Guide Rulebook - The Rules (Potentially)

Unanswered Question
Aug 1st, 2008

Hi all,

I have just been doing some reading from the Cisco web site and would like to summarise what I saw as the important factors in the documentation in reference to some basic guidelines to providing a successful VoWLAN deployment. This is the first time I have looked at the VoWLAN deployment and there are some points I don't fully understand, and maybe some points I have completely missed out. I will need to translate all of these summary points at a later stage to a design document to start looking at a potential VoWLAN design so just thought I'd get a couple of notes down on paper. It may help some other people also, in summarising (I sure hope so, as its nice to share this stuff with you guys - if correct).

Anyway, if you kind people would take time to read this and maybe comment on it, that would be fantastic. The points started out in order but as I write this and few points at the bottom should be near the top, but I think I need a beer and cant think about re-numbering them at the mo :))


Opps, the post is above the 4000 chars (I can't have written that much can I) so now have attached it to a word file.

Pls see attached word doco.


Guys and girls, would you mind looking at points 5, and points 18. And if anyone could add anything else to this, or correct any of this information (all gleaned from the white-papers) if I have got it wrong, which is quite likely :))

Many kind regards as always and hope all is well :)


I have this problem too.
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rob.huffman Sat, 08/02/2008 - 08:13

Hi Ken,

Looks like a great doc so far! I wanted to send you these links to address Point #5;

VoWLAN Call Capacity

An important parameter in VoWLAN planning is call capacity-the number of simultaneous VoWLAN calls that can be supported in an area. This value can vary depending upon the RF environment, the VoWLAN handset features, and the WLAN system features. For example, the VoWLAN maximum capacity for a Cisco Unified IP Phone 7921G using a WLAN that provides optimized WLAN services (such as the Cisco Unified Wireless Network), the capacity is expected to be 14 simultaneous VoWLAN calls per 2.4 GHz channel and 20 simultaneous VoWLAN calls per 5 GHz channel. These capacity values are based on assuming no competing high priority WLAN traffic and normal background noise. Note that because the 5 GHz spectrum generally features less noise and interference, there can be greater capacity with the higher carrier frequency implementation. The additional non-overlapping channels available in the 5 GHz spectrum also provides a great deal more call capacity for a given area.


Note The call capacities are quoted per non-overlapping channel because the channel capacity is the limiting factor-not the number of access points (AP). This is explained in more detail in the following section. The purpose of providing these maximum call capacity figures is general planning purposes. The call capacity specified by the actual VoWLAN handset should be used for deployment since this is the supported capacity of that handset.

From this excellent VoWLAN SRND doc;


Choosing Between IEEE 802.11b/g and IEEE 802.11a


Design Principles for Voice Over WLAN

The 802.11 wireless networking protocol uses a contention-based access algorithm. Based on this access methodology, protocol overhead, bandwidth calculations, and wireless voice network testing, Cisco has determined that with the IEEE's 11-Mbps throughput limitation on 802.11b, a single 802.11b wireless access point can support up approximately to seven active voice streams using the G.711 codec or eight active voice streams using G.729 codec and also handle a reasonable level of data traffic. An active phone session is one carrying on a conversation. A voice client that is associated with an access point and not carrying on a VoIP session (that is, conversation) is not considered active.


For Point# 18, I didn't think Cisco Wireless deployments supported 802.11f and actually use a proprietary IAPP Protocol?

Hope this helps and keep up the great work here!



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