Jul 06 2011

Strategies for Optimizing Vo-Fi

Follow these five tips to get the most out of Voice over IP over Wireless technology.

Because wireless LANs provide primary or default network access for many organizations, IT professionals have begun to use their established WLANs for phone services. One way to use these services is through Voice over Wireless, or Vo-Fi. As with VoIP, making Vo-Fi work requires smart management that reduces endpoint delays and prioritizes and monitors all network activity to ensure the needs of both voice and data traffic are being adequately met. Are you prepared to manage your new Vo-Fi environment? Consider the following five tips to get the most out of an investment in this mission-critical service.

Tip 1: Understand the traffic requirements of Vo-Fi. Many organizations make the mistake of assuming that the low throughput requirements of Vo-Fi mean that voice won't put much of a strain on their network. This is a bad assumption because voice and other isochronous (time-bound) traffic have a very low tolerance for latency. This means the provisioning of voice requires sufficient headroom, not just throughput. Networks that are already heavily loaded aren't good candidates for voice, although adding another radio channel often works if sufficient capacity is available in the rest of the network.

Photo: Jorg Greuel

Tip 2: Consult with your WLAN supplier. Each WLAN systems manufacturer has its own approach to (and set of services for) supporting Vo-Fi. While the protocols involved are standardized, the mechanisms are not. Most manufacturers will be able to provide detailed advice, usually in the form of application notes, on how to optimize their particular products for voice. This information can have a profound impact on basic features such as the number and configuration of radio channels, SSIDs and VLANs. So don't try to reinvent the wheel — take advantage of what your supplier already knows.

Tip 3: Understand what your WLAN is doing before and after Vo-Fi installation. Network management consoles and logs provide a wealth of information about loads on the network, so it's a good idea to review the status of the network before adding voice. Because factors such as user location and call volume can't always be accurately estimated, a similar exercise for the first few weeks after installation is in order as well. The quality of radio channels is of particular importance and inexpensive spectrum analyzers can be used to monitor for interference. Roaming performance is also critical, but again, this is manufacturer-dependent (particularly with clients) because there is no standard for the actual roaming process itself. If you really want to see what's happening, voice-centric analytical tools can produce mean opinion scores and r-values, measures that will remove all doubt as to actual performance.

Tip 4: Remember the rest of the Vo-Fi value chain. As is always the case in networking, the weakest link in the value chain will determine performance. While there's a tendency to blame the airlink (the wireless connection between a station and the access point) when something goes wrong, bottlenecks elsewhere are often the problem. Make sure that interconnect and backhaul links are up to snuff (Gigabit Ethernet is cheap and getting cheaper, and is required for 802.11n), and that gateways and IP PBXs are appropriately provisioned and configured. Also, check the network management logs, including on the wired side, to be sure.

Tip 5: When in doubt, overprovision. The bottom line here is really quite simple: Don't skimp on infrastructure. A general strategy that works well is to install much more capacity than required. WLAN equipment is very affordable today, and the market for gear is highly competitive. Adding additional APs is an inexpensive solution, especially when the required backhaul cable is already in place (or easily installed). It makes little sense to try to squeeze that last bit of capacity out of existing infrastructure. Just use the latest technology, in sufficient quantities, and you can maximize user (and operations staff) productivity at minimal cost.


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