Voice-over-WLAN (VoWLAN) technology is supposed to help end-users stay in touch with customers and colleagues even when they’re not at their desks. But it won’t come to fruition before network gear makers create quality-of-service (QoS) standards, according to one industry observer.
Ted Stevenson, executive editor of Wireless Internet Channel, an online wireless technology resource, said VoWLAN equipment, which transmits phone calls over Wi-Fi networks, is “taking hold very slowly,” and the turtle-paced adoption rate might stem from a protocol void.
VoWLAN lacks QoS techniques to ensure voice traffic gets enough bandwidth for jitter-free transmissions. Without QoS, voice must compete against data traffic. If data gets in the way of voice, users could experience garbled conversations.
Standards bodies like the IEEE are devising ways to make peace between data and voice on wireless nets. Stevenson moderated a panel about this very thing at Wi-Fi Planet, a wireless technology conference in Toronto from March 16 to 18.
Chris Thurson was one of the panelists. He’s a senior product manager at SpectraLink Corp., a wireless phone system provider. He outlined the IEEE’s 802.11e (“11e”) protocol, which aims to bring QoS to WLANs.
Thurson said there are two flavours of 11e. The first one, dubbed “mandatory,” is also known as Wi-Fi Multimedia Extensions (WME). Thurson said data equipment makers designed this version, which simply lets Wi-Fi access points discern between data traffic and voice calls, so the network can give priority to the vocal track.
The second 11e iteration is called Wi-Fi Scheduled Multimedia (WSM). It’s a more sophisticated prioritization scheme that checks network capacity before letting voice transmissions onto the WLAN. Voice technology companies came up with WSM, Thurson said, adding that 11e should reach ratification by mid-2004.
Thurson said 11e has been slow in coming because it’s difficult to reconcile voice and data on the same network, especially when voice and data experts come up with different notions of prioritization (WSM and WME respectively).
“It’s not so much a fight as they (data experts) don’t think about it,” Thurson said, explaining that perhaps people in the data camp didn’t appreciate just how sensitive voice transmissions are to network traffic congestion.
Joel Vincent, director of product marketing at Wi-Fi system provider Meru Networks Inc., said the debate over what to do about prioritization swung between different schemes like WSM and WME, and creating a whole new wireless substructure, something designed from the ground up to support voice traffic.
He also pointed out that once equipment makers adopt 11e, there’s no going back. If 11e-enabled devices compete for bandwidth against non-11e devices, the 11e equipment will lose. “The guys without 11e will dominate the conversation,” he told the Wi-Fi Planet audience.
Another problem for VoWLAN implementations is the speed at which voice transmissions hop from one access point to another. When users go out of one access point’s range and into the purview of another access point, the handoff between the two wireless nodes must be below 50 milliseconds, otherwise users would notice a dip in transmission quality. But right now WLAN handoffs take closer to 500 milliseconds.
Thurson said the IEEE is investigating a “fast roaming” protocol to address this problem, but Alain Mouttham, CEO of SIPQuest Inc., said his company already has a solution. SIPQuest’s collaboration agent provides handoffs in the 10-millisecond range.
“It’s handled at the application layer, which gives much more flexibility,” Mouttham said during his part of the seminar.
However, SIPQuest won’t compete for the roaming spotlight against the IEEE. “It’s proprietary,” Mouttham said of the collaboration agent. “You always prefer a standards-based solution.”
Asked if VoWLAN QoS is more a matter of traffic prioritization or quick handoffs, Stevenson, the panel moderator, sided with prioritization, pointing out that fast roaming means nothing if users can’t get a dial tone in the first place.
