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May 2008 | Volume 11/ Number 5
Integrator’s Corner

A Winning Recipe for Successful VoWiFi Deployment and Operation

After a rather slow start, voice over wireless LAN services (VoWLAN or VoWiFi) are finally starting to become more mainstream, particularly in industries like healthcare and retail sales where much of the workforce is mobile within a building or campus throughout the work day, but still needs to be able to communicate at any time. However, horror stories of VoWiFi implementations fraught with problems still abound. So how do VoWiFi adopters avoid the pitfalls and maximize their potential for success? Here are some ingredients that will help:

Ingredient No. 1: Know expected call volumes and call patterns and design accordingly. Unlike traditional data traffic, which can tolerate retransmission and delay, voice traffic is time-sensitive and subject to critical end user perceptions and expectations. This means issues like accidental disassociation, bandwidth constraints due to AP oversubscription, and delays in roaming between APs cannot be tolerated. When designing for VoWiFi, plan on no more than 8 to 10 simultaneous active calls per AP at any time. This is significantly less than the 20 or more simultaneous data users typically supported by an AP.

Ingredient No. 2: Turn down the signal power. Given the above-mentioned constraint, an architecture with more APs deployed more closely together will be required. To accomplish this, the power of each AP must be lowered to minimize interference between cells. This will diminish signal propagation at the periphery of an individual AP’s coverage area, without appreciably shrinking the coverage area where the signal is above the desired signal strength and desired bandwidth. Minimum signal strength for reliable voice operation should be in the range of -65dBM and minimum speed or bandwidth per voice user should be at least 6Mbps.

Ingredient No. 3: Invest in proper tools and training on how to use them. Because of the nature of wireless (no physical connection to the end device and susceptibility to RF interference), and the nature of voice traffic (sensitivity to delay and jitter), it is critical that VoWiFi adopters invest in appropriate tools and the training needed to facilitate their proper use. In addition to wireless spectrum analysis tools required to identify RF propagation and interference patterns, and WiFi (News - Alert) traffic analysis tools needed to decode and analyze wireless data traffic, specialized tools that can decode and analyze the VoWiFi protocols and traffic will also be needed. This is not a place to cut corners!

Additional Ingredients: This is certainly not an exhaustive list of what should be done to maximize the potential for success. Securing the wireless realm is clearly also very critical. Remember also that the wired infrastructure, the QoS configuration, the call processing platform, and the end devices all affect the VoWiFi service. Nonetheless, by following the above guidelines, at least the wireless infrastructure should be properly designed to accommodate voice traffic. IT

Darrell L. Epps, Director of Network Solutions (News - Alert) for Forsythe Solutions Group, has more than 20 of experience in networking and IT and numerous manufacturer certifications. His broad experience includes network and IP infrastructure project management, implementation engineering and operations support.

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