Analysis of the radio frequency environment in VoWLAN deployments

Meeting call quality goals requires maintaining a consistently strong signal throughout your facility. The first step is a comprehensive analysis of your facility's radio frequency (RF) environment, which requires:

• Tools designed specifically for the task.
• Personnel with the expertise to understand the results.

Any wireless deployment should include an RF analysis, but a VoWLAN deployment also requires the analysis to cover areas of the building that may not have been considered in an earlier wireless deployment (e.g., stairwells or even restrooms), because voice users expect to be able to make or continue calls from anywhere in the building.

"Implementing Wi-Fi for VoIP today demands a level of engineering expertise that goes well beyond what's needed for email and Web surfing," said Joe Bardwell, chief scientist at Connect802 Corp. of San Ramon, Calif. "The characteristics of a voice call make it necessary to focus on a careful RF analysis of the entire facility and on manufacturers' key specifications for call quality, rather than simply focusing on 802.11 data rates the way one would for simple Internet connectivity."

RF analysis for any wireless deployment requires use of a spectrum analyzer to measure signal strength. Analysis for VoWLAN should also include measurement of R-value, a measure of call quality developed by the International Telecommunications Union (ITU). Specialized tools to measure and display R-value are available from vendors such as AirMagnet and Veriwave.

The R-value measurement includes:

• Factors resulting from signal quality -- for example, signal-to-noise ratio and single and burst packet loss.
• End-to-end delay, jitter and codec characteristics that are the result of overall network design and the choice of wireless equipment and phone handsets.

VoWLAN: Preparing your network for a voice over wireless LAN deployment

  Introduction
  Analysis of the radio frequency environment
  Review of network security
  Investigation of the wireless vendor's voice experience and product features

About the author
David B. Jacobs has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies as well as software startups.