Voice over WLAN: Gearing up for primetime

VoIP is an established and rapidly maturing technology. It is less expensive to install and maintain than traditional telephony, and the core equipment is comparable in cost and offers many integration options. Wireless LAN technology is also rapidly maturing, so the next step is to deploy a converged technology that delivers IP voice on a wireless LAN.

VoWLAN is growing in certain vertical industries like healthcare, hospitality, retail, and manufacturing. These are industries where the combined benefits of mobility and flexibility for voice and data are so compelling that organizations are willing to forgo the current lack of handset choice, the enforced deployment of proprietary equipment, the lack of scalable network management tools and poorly addressed security, standards and QoS issues. For other industries, the usual view is that VoWLAN is not quite ready. So how might the remaining challenges be resolved?

Part of the problem is that wireless is a contention media--users share the available bandwidth, so wireless will always have overhead issues and complex management requirements. When rolling out enterprise-wide wireless, especially VoIP, the need for prioritized data streams, transparent access point handoffs and seamless security are essential, so sophisticated wireless network management tools are critical to the success of VoWLAN.

In terms of quality, companies are willing to trade mobility and reduced costs for reliability for data packet delivery, but voice packets are more sensitive to service degradation. You really need to have a max of 150ms to make sure users are not bothered by QoS issues when you are using a VoIP system.

The Wireless Multimedia Extensions 802.11e QoS standard will not be ratified until late 2004 or early 2005. Most wireless equipment has not yet incorporated any QoS because they are waiting for this emerging standard, although some companies are implementing a subset of 802.11e. Additionally, while 802.11b officially delivers 11MB with QoS, the actual useable bandwidth is closer to 6MB. That 6MB is shared by anyone on the access point. With 10 to 15 VoIP users, you are quickly down to unacceptable data rates. The reality: With most wireless equipment, planners should expect six to seven voice calls maximum per channel.

Security is essential for VoWLAN, and wireless security is finally improving with the newly ratified 802.11i standard, but these have not been fully adopted into the VoWLAN equipment. 802.11r is a brand new IEEE taskforce created specifically to address VoWLAN security issues. Expect to see handsets incorporating the improved security standards in six to eight months, and new standards in this area in a year or so.

The need to re-authenticate every time users move between access points is a problem. Session switching can cause unacceptably high delays (up to 500ms) or dropped calls. Obviously, the re-authentication process is in direct conflict with the QoS requirements of maintaining the call data stream. To overcome this, the call session needs to be transparently switched to a new access point to minimize signal delay as the user roams the network.

So where is the innovation coming from to address these inherent challenges? Currently there are two main companies in the VoWLAN handset market, Vocera and SpectraLink. Because they were first to market, neither of these are standards-based systems. As power over Ethernet standards and cell phone technology are incorporated, better handsets will emerge, from these and other vendors, including Cisco and Motorola.

However, WLAN switch vendors have the best opportunity to get in on the action here. The market is already highly competitive, with numerous start-up vendors and well-established LAN switch and enterprise networking players. So far, these companies have differentiated themselves with solutions for managing spectrum, security, users, rogue access points, etc. Now they're starting to position themselves as VoWLAN platforms.

For VoWLAN handsets, wireless LAN switches can actively improve performance. If the switch sees that a client is getting a weaker signal, it can see which access points are gaining in signal strength, and then it can pre-authenticate the handoff. It can save time by starting the handoff process earlier so it can switch over to the next access point faster, more easily, and with less latency. This is compelling, and could be the real raison d'etre for the WLAN switch vendors and propel them more firmly into the enterprise markets they covet.

Finally, a single standard is emerging as well: VoWLAN in the enterprise market will specifically require the use of 802.11a, not 802.11b or 802.11g. With 802.11a, the range is shorter, which is generally viewed as a bad thing, but it turns out that having a shorter range has benefits: less interference and the ability to more densely pack APs and VoIP users.

However, this could be a significant problem, as companies will be required to install 802.11a networks if they wish to support VoWLAN, as the more-prevalent 802.11g/b standard cannot provide the level of service needed by VoIP. 802.11g/b, with only three channels that do not overlap, is able to support between six and eight calls at a time. In comparison, 802.11a boasts 21 non-overlapping channels able to handle 25 VoIP calls from a single WLAN access point. For converged networks, voice should be deployed over 802.11a while data is deployed over 802.11g.

With the maturing of both VoIP and wireless technologies, converging the two seems a terrific idea, but for most, VoWLAN is still too immature to deploy. In the next 12 months there will be products that address these issues as WLAN switch vendors look to the potential of VoWLAN for future differentiation. Once the technical issues have been properly addressed and the standards settle down, VoWLAN-with its potential to merge data, voice, and mobility into one neat package-promises to be something that could seriously transform how companies do business.

Richard Webb is the directing analyst, Wireless LANs at Infonetics Research, Inc. He can be reached at richard@infonetics.com. 

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