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Voice over WLAN Mobile IP Touch Design Guide R2.0
3.7.1. Converged Wireless Environments (Voice & Data Combinations)
One of the most significant reasons that businesses look to use wireless LAN technology to support voice is
the desire to have a single infrastructure for both voice and data services. While this may at first sound
like a very simple thing to implement, it often is far more complex to design than most customers
originally anticipate. Alone, a VoWLAN environment has some challenges that must be overcome.
Combined with a need to coexist with data client service, VoWLAN environments can face a tremendous
amount of competition that requires special planning to minimize.
One of the major complexity factors faced during the design stage is the varied nature of the standards
that can be used to support a data WLAN, and the affects each method has on voice quality and
performance.
3.7.1.1. Voice alone on 802.11b
Under ideal conditions, VoWLAN networks can be constructed so that the voice traffic is not subject to
competition from any non-voice related wireless traffic. This results in the availability of the full 11Mbps
of bandwidth (less signaling and overhead) on all Access Points. A customer that does not possess a Wi-Fi
environment for data clients, and does not wish to implement one is a perfect example of this most ideal
of scenarios.
3.7.1.2. Voice on 802.11b, Data on 802.11g (Shared AP & Bandwidth)
A very common environment to encounter is that of an existing IEEE 802.11b/g network. Wi-Fi is widely
acknowledged as being one of the most quickly proliferating technologies in networking history. The vast
majority of customer environments responsible for this explosive growth utilize 2.4 GHz versions of the
IEEE 802.11 standard. This environment can prove to be a daunting one for the insertion of VoWLAN
technology.
Because the "b" and "g" variants of Wi-Fi use the same three available non-overlapping channels within
the 2.4 GHz spectrum, the addition of VoWLAN specific Access Points to a network is often not an option.
This leaves us with a few things to consider before proceeding further.
Bandwidth advantages presented by 802.11g are significantly reduced when 802.11b
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clients share the wireless environment. This may be unacceptable to some customers.
Due to quality concerns and sensitivity differences between voice and data Wi-Fi clients,
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the mandatory VoWLAN Radio Coverage Audit may mandate that nearly all existing
Access Points be relocated in order to better service voice clients without large coverage
holes. This network disruption may introduce more cost than switching data elements to
IEEE 802.11a.
The limited number of non-overlapping IEEE 802.11b/g radio channels may make it nearly
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impossible to offer both voice and data services in the same location with multiple (and
application dedicated) Access Points due to radio spectrum competition. This means that
common Access Points must be used, impacting bandwidth availability to the data
network, and the number of simultaneous calls to the voice environment.
ESD/ Central Pre Sales / DF/ PH
35/45
January 2007 – Ed 01
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