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VoWLAN: Two degrees of separation

Jun 07, 20043 mins
Network SecurityVoIP

Commentary on last month’s NetWorld+Interop show seemed to cite the buzz as either VoIP or wireless. From my perspective, the real buzz was the combination of the two technologies – VoIP over wireless LANs.

Commentary on last month’s NetWorld+Interop show seemed to cite the buzz as either VoIP or wireless. From my perspective, the real buzz was the combination of the two technologies – VoIP over wireless LANs.

With VoWLAN, there are now two degrees of separation between “native” analog voice and the current state-of-the-art offerings. First, the voice was digitized and packetized to run over the LAN. Now the LAN is, at least for part of the trip – a wireless one.

There’s no doubt that the Wi-Fi based mobility that VoWLAN delivers is essential to driving and justifying corporate deployment of both technologies. Yet, the pace of change is such that network managers are faced, potentially, with complex decisions about VoWLAN when they might not feel comfortable with “plain old” VoIP.

When VoIP was first proposed as a replacement for PBX systems, we worried about a lot of things. Was there sufficient bandwidth? Could we guarantee voice quality? Were the conversations secure?

As it turned out, we had little reason for concern. Even a toll-quality VoIP call wouldn’t even consume 100K bit/sec – or about 0.1% of a Fast Ethernet connection. Congestion on the campus LAN was rare and even basic two-queue switches typically could provide the headroom needed for VoIP. While most sessions were unencrypted, the nature of LAN switches make snooping into non-broadcast traffic difficult (though possible).

When voice is carried over today’s Wi-Fi networks, though, these issues arise again. And new issues emerge.

The networks are slower (than Fast Ethernet), and they are shared. Thus, degradation is possible and quality of service becomes more than a theoretical consideration. The broadcast nature of wireless makes session security a big item and Wired Equivalent Privacy, Wi-Fi Protected Access and other initiatives have been put in place to address this.

Ultimately, the key technical issue is roaming. By definition, someone on a Wi-Fi phone is likely to roam from access point to access point while circulating through a building. Roaming “gaps” measured in seconds, which might be acceptable to data applications, will negate any benefit of using Wi-Fi voice because users simply will hang up.

All this takes place against a backdrop of very active 802.11 sub-committees no doubt diligently working on vendor-neutral solutions to these and other challenges.

Even where standards committees haven’t finished their work, a variety of pre-standard methods exist to overlay VoIP on wireless. In our testing practice, we’ve seen informal and formal partnerships between the voice providers and the WLAN infrastructure providers to illustrate these capabilities.

Yet, given the leading-edge nature of technologies and the narrow nature of most partnerships, it is not surprising that most enterprise architects aren’t quite sure what works with what.

To remedy this situation, at least in part, we plan to host a VoWLAN Interoperability event this August in Boca Raton, Fla.

We’ll look to work with the vendors of both the switch and the voice infrastructure to craft a series of interoperability scenarios that will help illustrate what type of functionality is available in heterogeneous VoWLAN.

Tell me what’s uppermost on your mind. I’ll be sure to feed back what readers tell me – and keep you posted on what we find in the lab.