VOIP on WLANs

By C.J. Mathias, Farpoint Group |  Mobile & Wireless

There's been a lot of talk about voice over IP (VOIP) on wireless LANs (WLANs), but it seems that the term "Wi-Fi" is really taking over lately, despite the fact that it's someone's trademark. For those of you unfamiliar with the term, VOIP involves implementing digital voice telephony over an Internet Protocol (IP) connection, typically a LAN (sometimes with Internet connectivity as well, such as the services offered by Vonage and Net2Phone), or the interconnection of LANs carrying voice traffic via WANs. Connections can be point-to-point and all-IP through a network, or gateways can be used to convert between VOIP signals and traditional telephone connections. Many believe that VOIP will eventually constitute all telephony, but if it happens, it is many years away. There are a lot of copper loops in the world, and these are by no means obsolete just because we can do voice over IP.

But with so much WLAN capacity going into the enterprise and public spaces, why not use WLANs for VOIP? And, indeed, the designers of 802.11 included in the original standard a couple of mechanisms designed to support the time-bounded traffic typical of voice (and, for that matter, video); these are known as the "Point Coordination Function" and "RTS/CTS". The Point Coordination Function, or PCF, is now being improved by the IEEE 802.11e Working Group to further enhance the performance of time-bounded packets within a wireless LAN. And there are already a number of VIOP WLAN products available, for example from Cisco, Spectralink, and Telesym. One would expect that VOIP on WLANs is really going to take off over the next couple of years; some analysts and investors believe that voice is going to be the major driver of future enterprise WLAN installations. I've pointed out that VOIP on WLANs will be a major incentive for cellular operators to make investments in public-access WLANs. It should even be possible to hand off a call, in real time, between a cellular network and a VOIPOWi-Fi network. Home cordless phones? Sure, another good application, facilitated by the upcoming availability of combined cellular/Wi-Fi handsets. And using your cell phone as your office phone, with cordless service as a bonus, has undeniable appeal - one handset, anytime, anywhere.

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