Raised hands at trade shows, and informal chats with enterprise network managers, indicate a healthy interest in running voice over 802.11-based wireless LANs.

Many organisations figure that if they are bothering to install WLANs for data, and are also amenable to migrating to VoIP, they might as well go the distance. Converging the whole network, regardless of physical medium, satisfies both data and voice demands for local mobility.

However, simply tossing VoIP onto your WLAN may not be as simple as it sounds. Most IP PBXs, for example, were not designed with wireless networking in mind. So you'll need to quiz suppliers on what it takes to integrate your WLAN with your IP PBX.

For example, if you are using different vendors for IP PBXs and 802.11 voice handsets, you'll need to check on what codec(s) must be supported in your phones to meet your IP PBX's requirements.

Speaking of codecs, there is some debate over whether voice compression is desirable in WLANs. You get better quality without compression. But the most widely implemented 802.11 flavor today is 802.11b, with actual throughput rates of about 5 to 7 Mbit/s. Currently, most WLANs run uncompressed voice at 64 kbit/s speeds.

Lumping large volumes of uncompressed voice calls onto this network, particularly now that 802.11 WLANs require data to wait while voice transmits, can take a big bite out of your available data throughput. Don't misunderstand: data's deference to real-time voice is necessary for good-quality voice. But depending on how much voice traffic joins the WLAN, data could eventually suffer.

On the upside, most vendors of enterprise-class access points have built load-balancing capabilities into their devices - among them Airespace, Aruba, Cisco, Enterasys, Proxim, Symbol and Trapeze. So if a client device faces congestion, it will automatically attempt to associate with another access point. Among these, most will mention voice as a possible application and Airespace is actively promoting its networks for voice duty.

Of course, Wi-Fi is not the only game in town for wireless voice in the office. It faces competition from both Bluetooth and the established cordless phone standard, DECT, both of which have profiles designed specifically for voice. Users' decisions between these will depend on their other equipment and plans, but Wi-Fi will close the standards gap to some extent when the IEEE finalises the 802.11e standard for quality of service, which is designed very much for voice.

Relative newcomer Meru Networks says it has voice-optimised its WLAN system by making contention for the wireless medium a round robin-type process, whereby each client "speaks" in turn. This way, data doesn't get preempted indefinitely.

In an 802.11b-only network with a mere three non-overlapping channels, though, you can only put so many access points in a given area without interference seeping in.

So adding 802.11a networks to the mix for the extra channels will likely be an eventual requirement for converged nets. If that sounds complex, see our guide to migrating between the two standards.

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